INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

    ENVIRONMENTAL HEALTH CRITERIA 152

    POLYBROMINATED BIPHENYLS

    This report contains the collective views of an international group of
    experts and does not necessarily represent the decisions or the stated
    policy of the United Nations Environment Programme, the International
    Labour Organisation, or the World Health Organization.

    First draft prepared by Dr. W. Gross, Dr. J. Kielhorn
    and Dr. C. Melber, Fraunhofer Institute for
    Toxicology and Aerosol Research, Hanover, Germany

    Published under the joint sponsorship of
    the United Nations Environment Programme,
    the International Labour Organisation,
    and the World Health Organization

    World Health Orgnization
    Geneva, 1994

          The International Programme on Chemical Safety (IPCS) is a joint
    venture of the United Nations Environment Programme, the International
    Labour Organisation, and the World Health Organization.  The main
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    the effects of chemicals on human health and the quality of the
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    with chemical accidents, coordination of laboratory testing and
    epidemiological studies, and promotion of research on the mechanisms
    of the biological action of chemicals.

    WHO Library Cataloguing in Publication Data

    Hexachlorobutadiene.

          (Environmental health criteria: 152)
          1. Polybromobiphenyl compounds - adverse effects
          2. Polybromobiphenyl compounds - toxicity
          3. Environmental exposure
          4. Environmental pollutants   I.Series
          ISBN 92 4 157152 7         (NLM Classification QV 633)
          ISSN 0250-863X

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    CONTENTS

    ENVIRONMENTAL HEALTH CRITERIA FOR POLYBROMINATED BIPHENYLS (PBBs)

    1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS

         1.1. Summary and evaluation
              1.1.1. Identity, physical and chemical properties,
                        analytical methods
              1.1.2. Sources of human and environmental exposure
              1.1.3. Environmental transport, distribution, and
                        transformation
              1.1.4. Environmental levels and human exposure
              1.1.5. Kinetics and metabolism
              1.1.6. Effects on organisms in the environment
              1.1.7. Effects on experimental animals and
                        in vitro test systems
              1.1.8. Effects on humans
              1.1.9. Overall evaluation of toxicity and
                        carcinogenicity
         1.2. Conclusions
         1.3. Recommendations
              1.3.1. General
              1.3.2. Future research

    2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

         2.1. Identity
              2.1.1. Primary constituents
              2.1.2. Technical products
                        2.1.2.1   Major trade names
                        2.1.2.2   Composition of the technical products
         2.2. Physical and chemical properties
              2.2.1. Physical and chemical properties of individual
                        congeners
         2.3. Conversion factors for PBB in air
         2.4. Analytical methods

    3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

         3.1. Natural occurrence
         3.2. Man-made sources
              3.2.1. Production levels and processes
                        3.2.1.1   World production figures
                        3.2.1.2   Manufacturing processes
                        3.2.1.3   Loss into the environment during
                                  normal production

                        3.2.1.4   Methods of transport, accidental
                                  release, and disposal of production
                                  wastes
              3.2.2. Uses

    4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION

         4.1. Transport and distribution between media
              4.1.1. Air
              4.1.2. Water
              4.1.3. Soil
              4.1.4. Biota
                        4.1.4.1   Terrestrial ecosystems
                        4.1.4.2   Aquatic ecosystems
                        4.1.4.3   Accidental contamination of the
                                  food chain
         4.2. Degradation
              4.2.1. Photolytic degradation
              4.2.2. Microbial degradation
              4.2.3. Degradation by plants and animals
              4.2.4. Bioaccumulation
                        4.2.4.1   Aquatic organisms
                        4.2.4.2   Terrestrial organisms
         4.3. Ultimate fate following use
              4.3.1. Disposal of PBB-contaminated animals
                        and wastes from the Michigan disaster
              4.3.2. Thermal decomposition of PBBs

    5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

         5.1. Environmental levels
              5.1.1. Air
              5.1.2. Water and sediments
                        5.1.2.1   Surface waters
                        5.1.2.2   Sediments
                        5.1.2.3   Groundwater
              5.1.3. Soil
              5.1.4. Feed and food
                        5.1.4.1   Feed
                        5.1.4.2   Food
              5.1.5. Other products
              5.1.6. Terrestrial and aquatic organisms
                        5.1.6.1   Aquatic and terrestrial plants
                        5.1.6.2   Animals
         5.2. General population exposure
              5.2.1. Quantified data on human exposure
                        5.2.1.1   Worldwide
                        5.2.1.2   The Michigan accident
              5.2.2. Human monitoring methods for PBBs
              5.2.3. Human monitoring data
              5.2.4. Subpopulations at special risk

         5.3. Occupational exposure during manufacture, formulation, or
              use

    6. KINETICS AND METABOLISM

         6.1. Absorption
              6.1.1. Animal studies
                        6.1.1.1   Gastrointestinal absorption
                        6.1.1.2   Dermal and inhalation absorption
              6.1.2. Human studies
         6.2. Distribution
              6.2.1. Animal studies
                        6.2.1.1   Levels in organs and blood
                        6.2.1.2   Transfer to offspring
              6.2.2. Human studies
         6.3. Metabolic transformation
              6.3.1. In vitro studies
              6.3.2. In vivo studies
              6.3.3. Metabolic pathway
         6.4. Elimination and excretion in expired air, faeces,
              urine
              6.4.1. Animal studies
              6.4.2. Human studies
         6.5. Retention and turnover
              6.5.1. Animal studies
                        6.5.1.1   Time trends, retention:
                        2,2',4,4',5,5'-hexabromobiphenyl
                        (BB 153)
                        6.5.1.2   Biological half-lives
                        6.5.1.3   Differences between individual
                                  congeners
                        6.5.1.4   Octabromobiphenyl
              6.5.2. Human studies
         6.6. Reaction with body components
              6.6.1. Animal studies
              6.6.2. Human studies

    7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT

         7.1. Microorganisms
         7.2. Aquatic organisms
         7.3. Terrestrial organisms
              7.3.1. Wildlife
              7.3.2. Farm animals
                        7.3.2.1   Cattle
                        7.3.2.2   Other farm animals
         7.4. Population and ecosystem effects
         7.5. Effects on the abiotic environment

    8. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS

         8.1. Lethality
         8.2. Single and short-term exposures: general signs of
              toxicity
              8.2.1. PBB mixtures
                        8.2.1.1   Overt clinical signs, food intake,
                                  and body weight changes
                        8.2.1.2   Haematology and clinical chemistry
                        8.2.1.3   Morphological and histopathological
                                  changes
              8.2.2. Individual PBB congeners and comparative
                        studies
                        8.2.2.1   Food intake, overt clinical signs,
                                  body weight changes
                        8.2.2.2   Haematology and clinical chemistry
                        8.2.2.3   Morphological and histopathological
                                  changes
         8.3. Skin and eye irritation, sensitization, dermal
              lesions, and acne
         8.4. Long-term toxicity
              8.4.1. Rat
                        8.4.1.1   Overt clinical signs, body weight
                                  changes, food intake
                        8.4.1.2   Haematology and clinical chemistry
                        8.4.1.3   Morphological changes
                        8.4.1.4   Histopathological changes
              8.4.2. Mouse
              8.4.3. Cattle
              8.4.4. Mink
              8.4.5. Rhesus monkey
              8.4.6. Pre- and perinatal exposure
         8.5. Reproduction, embryotoxicity, and teratogenicity
              8.5.1. PBB mixtures
                        8.5.1.1   Mammals
                        8.5.1.2   Avian species
              8.5.2. Individual PBB congeners
         8.6. Mutagenicity and related end-points
         8.7. Carcinogenicity
              8.7.1. Carcinogenicity in long-term toxicity studies
              8.7.2. Mechanisms of carcinogenicity
                        8.7.2.1   Tumour initiation
                        8.7.2.2   Tumour promotion
                        8.7.2.3   PBBs acting as complete carcinogens
         8.8. Biochemical toxicity
              8.8.1. Induction of microsomal enzymes
                        8.8.1.1   Commercial PBB mixtures
                        8.8.1.2   Individual PBB congeners

              8.8.2. Endocrine interactions
                        8.8.2.1   Thyroid hormones
                        8.8.2.2   Sex hormones
                        8.8.2.3   Prostaglandins
              8.8.3. Interaction with drugs and toxicants
              8.8.4. Effect on vitamin A storage
              8.8.5. Porphyria
              8.8.6. Miscellaneous effects
         8.9. Effects on intercellular communication
         8.10. Immunotoxicity
         8.11. Neurotoxicity
              8.11.1. Exposure of adult animals
              8.11.2. Perinatal exposure
         8.12. Factors modifying toxicity, toxicity of metabolites
              8.12.1. Contaminants affecting toxicity
                        8.12.1.1  Polybrominated naphthalenes (PBNs)
                        8.12.1.2  Mixed polybromo-chlorobiphenyls
              8.12.2. Toxicity of metabolites
              8.12.3. Toxicity of photolysis and pyrolysis products
                        8.12.3.1  Photolysis products
                        8.12.3.2  Pyrolysis products
         8.13. Mechanism of toxicity including carcinogenicity

    9. EFFECTS ON HUMANS

         9.1. General population exposure
              9.1.1. Acute toxicity-poisoning incidents
              9.1.2. Epidemiological studies
                        9.1.2.1   Studies conducted by the Michigan
                                  Department of Public Health
                                  (MDPH studies)
                        9.1.2.2   Studies conducted by the
                                  Environmental Science Laboratory,
                                  Mount Sinai School of Medicine,
                                  New York (ESL studies)
              9.1.3. Special studies
                        9.1.3.1   Examination of subjects with
                                  complaints
                        9.1.3.2   Cutaneous effects
                        9.1.3.3   Effects on liver function
                        9.1.3.4   Porphyria
                        9.1.3.5   Effects on spermatogenesis
                        9.1.3.6   Paediatric aspects
                        9.1.3.7   Neurological and neuropsychiatric
                                  aspects
                        9.1.3.8   Lymphocyte and immune function
                        9.1.3.9   Carcinogenic embryonic antigen
                                  plasma levels
                        9.1.3.10  Biochemical effects

         9.2. Occupational exposure
              9.2.1. Epidemiological studies
              9.2.2. Clinical studies
              9.2.3. Special studies
                        9.2.3.1   Cutaneous effects
                        9.2.3.2   Memory performance
                        9.2.3.3   Thyroid effects
                        9.2.3.4   Reproductive effects
                        9.2.3.5   Lymphocyte function
                        9.2.3.6   Mortality

    10. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

    REFERENCES

    ANNEX 1

    RESUME ET EVALUATION, CONCLUSIONS ET RECOMMANDATIONS

    RESUMEN Y EVALUACION, CONCLUSIONES Y RECOMENDACIONES

    WHO TASK GROUP ON ENVIRONMENTAL HEALTH

    CRITERIA FOR POLYBROMINATED BIPHENYLS

     Members

    Dr   L. Albert, Consultores Ambientales Asociados, S.C., Xalapa,
         Veracruz, Mexico

    Dr   J. Alexander, Department of Toxicology, National Institute of
         Public Health, Oslo, Norway

    Dr   W. Gross, Fraunhofer Institute for Toxicology and Aerosol  
         Research, Hanover, Germany

    Dr   R.F. Hertel, Federal Health Department CV 2.1, Berlin,  
         Germany  (Co-Rapporteur)

    Dr   B. Jansson, Swedish Environmental Protection Agency,
         Environmental Impact Assessment Department, Solna, Sweden

    Dr   J. Kielhorn, Fraunhofer Institute for Toxicology and Aerosol
         Research, Hanover, Germany

    Dr   R.D. Kimbrough, Institute for Evaluating Health Risks (IEHR),
         Washington, DC, USA (Chairman)

    Dr   C. Melber, Fraunhofer Institute for Toxicology and Aerosol
         Research, Hanover, Germany (Co-Rapporteur)

    Dr   K. Mitsumori, Division of Pathology, Biological Safety
         Research Center, National Institute of Hygienic Sciences,
         Tokyo, Japan

    Dr   S. Sleight, Department of Pathology, Michigan State
         University, East Lansing, Michigan, USA

    Professor P. Yao, Institute of Occupational Medicine, Chinese
         Academy of Preventive Medicine, Beijing, People's Republic of
         China  (Vice-Chairman)

     Observers

    Dr   B. Savanne, ELF ATOCHEM, Paris La Défense, France

    Mr   S. Tsuda, Environmental Health and Safety Division,  
         Environment Directorate, Organisation for Economic
         Co-operation and Development, Paris, France

     Secretariat

    Dr   H. Galal-Gorchev, International Programme on Chemical  
         Safety, World Health Organization, Geneva, Switzerland  
          (Secretary)

    Dr   K.W. Jager, International Programme on Chemical Safety,  
         World Health Organization, Geneva, Switzerland

    NOTE TO READERS OF THE CRITERIA MONOGRAPHS

         Every effort has been made to present information in the
    criteria monographs as accurately as possible without unduly
    delaying their publication. In the interest of all users of the
    Environmental Health Criteria monographs, readers are kindly
    requested to communicate any errors that may have occurred to the
    Director of the International Programme on Chemical Safety, World
    Health Organization, Geneva, Switzerland, in order that they may be
    included in corrigenda.

                               *   *   *  

         A detailed data profile and a legal file can be obtained from
    the International Register of Potentially Toxic Chemicals, Case
    postale 356, 1219 Châtelaine, Geneva, Switzerland (Telephone
    No. 9799111).

                               *   *   *  

         This publication was made possible by grant number 5 U01
    ES02617-14 from the National Institute of Environmental Health
    Sciences, National Institutes of Health, USA.

    ENVIRONMENTAL HEALTH CRITERIA FOR POLYBROMINATED BIPHENYLS

         A WHO Task Group on Environmental Health Criteria for
    Polybrominated biphenyls (PBBs) met at the Fraunhofer Institute for
    Toxicology and Aerosol Research, Hanover, Germany, from 22 to 26
    June 1992. Dr H. Galal-Gorchev, IPCS, welcomed the participants on
    behalf of Dr M. Mercier, Director of the IPCS, and the three IPCS
    cooperating organizations (UNEP/ILO/WHO). The Group reviewed and
    revised the draft and made an evaluation of the risks for human
    health and the environment from exposure to PBBs.

         The first draft was prepared by Dr W. Gross, Dr J. Kielhorn 
    and Dr C. Melber of the Fraunhofer Institute for Toxicology and 
    Aerosol Research, Hanover, Germany, who also prepared the second
    draft, incorporating comments received following circulation of the
    first drafts to the IPCS Contact Points for Environmental Health
    Criteria monographs.

         Dr H. Galal-Gorchev and Dr K.W. Jager of the IPCS Central Unit
    were responsible for the scientific content of the monograph, and
    Mrs M.O. Head of Oxford for the technical editing.

         The efforts of all who helped in the preparation and
    finalization of the monograph are gratefully acknowledged.

    1.  SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS

    1.1  Summary and evaluation

    1.1.1  Identity, physical and chemical properties, analytical
           methods

         The term polybrominated biphenyls or polybromobiphenyls (PBBs)
    refers to a group of halogenated hydrocarbons, formed by
    substituting hydrogen by bromine in biphenyl. PBBs are not known to
    occur as natural products. They have a molecular formula of C12
    H(10-x-y)Br(x+y) where both x and y = 1 to 5. Theoretically 209
    congeners are possible. Only a few have been synthesized
    individually and characterized. PBBs, manufactured for commercial
    use, consist mainly of hexa-, octa-, nona-, and decabromobiphenyls,
    but also contain other homologues. They are additive type flame
    retardants, and when blended with the dry solid or liquid polymeric
    material, provide filter-type, flame retardant action with the
    chemical release of hydrogen bromide if ignited.

         PBBs are manufactured using a Friedel-Crafts type reaction in 
    which biphenyl is reacted with bromine with, or without, an 
    organic solvent, using, e.g., aluminium chloride, aluminium 
    bromide, or iron as catalyst.

         Most research has been carried out on FireMaster BP-6 and
    FF-1, which were involved in the Michigan disaster when this
    compound was inadvertently added to animal feed instead of
    magnesium oxide. The ensuing contamination of farm animals resulted
    in the destruction of thousands of cattle, pigs, and sheep, and
    millions of chickens.

         The composition of FireMaster(R) changes from batch to
    batch,  but its main constituents are
    2,2',4,4',5,5'-hexabromobiphenyl (60-80%), and
    2,2',3,4,4',5,5'-heptabromobiphenyl (12-25%) together with lower
    brominated compounds because of incomplete bromination reaction.
    Mixed bromochlorobiphenyls and polybrominated naphthalenes have
    also been observed as minor components of FireMaster(R).
    FireMaster FF-1 (white powder) is FireMaster BP-6 (brown flakes) to
    which 2% calcium silicate has been added as an anti-caking agent.

         PBBs are solids with a low volatility that decreases with
    increasing bromine number. PBBs are virtually insoluble in water,
    soluble in fat, and slightly to highly soluble in various organic
    solvents; solubility also decreases with increasing bromine number.
    These compounds are relatively stable and chemically unreactive,
    though highly brominated PBB mixtures are photodegraded with
    reductive debromination upon exposure to ultraviolet radiation
    (UVR).

         The products of the experimental thermal decomposition of PBBs
    depend on the temperature, the amount of oxygen present, and a
    number of other factors. Investigations into the pyrolysis of
    FireMaster BP-6 in the absence of oxygen (600-900 °C) have shown
    that bromobenzenes and lower brominated biphenyls are formed, but
    no polybrominated furans. In contrast, pyrolysis in the presence of
    oxygen (700-900 °C) yielded some di- to heptabromodibenzofurans. In
    the presence of polystyrene and polyethylene, higher levels were
    found. Pyrolysis of FireMaster BP-6 with PVC at 800 °C yielded
    mixed bromochlorobiphenyls. There is no information on the nature
    of the products of incineration of PBB-containing material. Little
    is known about the toxicities of brominated and
    brominated/chlorinated dioxins and furans, but they are estimated
    to be of about the same order as those of chlorinated dioxins and
    furans.

         The primary analytical technique used for the biological
    monitoring of PBBs in environmental samples and biological tissues
    and fluids, after the Michigan disaster, was gas chromatography
    with electron capture detection. Individual congeners can be
    determined by capillary gas chromatography and more specific
    detection can be obtained with selected ion monitoring mass
    spectrometry. Because of the large numbers of congeners possible,
    investigations are hampered by lack of suitable synthetic
    standards. Methods for extracting PBBs from biological samples have
    been based on those for pesticides. PBBs are extracted with the
    fat, and then purified.

         The recent finding of PBB congeners in background biological
    samples does not necessarily mean that concentrations are
    increasing in the environment. The development of more sensitive
    analytical techniques, such as negative ion chemical ionization
    mass spectrometry, may be the explanation. Thus, the need for
    retrospective studies is urgent. With improved clean-up methods, it
    is possible to carry out specific analyses of the toxic co-planar
    PBB congeners and such data are also needed.

    1.1.2  Sources of human and environmental exposure

         The commercial production of FireMaster(R) was started in
    the USA in 1970. After the Michigan disaster, production was 
    discontinued (November 1974). The estimated production of PBBs in
    the USA between 1970 and 1976 was 6000 tonnes (commercial
    quantities). Octabromobiphenyl and decabromobiphenyl were produced
    in the USA until 1979. A mixture of highly brominated PBBs called
    Bromkal 80-9 D was produced in Germany until mid- 1985. Technical
    grade decabromobiphenyl (Adine 0102) is currently produced in
    France. As far as is known, this is the only current production of
    PBBs.

         PBBs were introduced as flame retardants in the early 1970s. 
    Prior to November 1974, hexabromobiphenyl was the most commercially
    significant PBB in the USA and was incorporated into
    acrylonitrile-butadiene-styrene (ABS) plastics (PBB content 10%),
    used mainly in small appliance and automotive applications,
    coatings, lacquers, and polyurethane foam. The other PBB flame
    retardants have similar uses.

         Losses of PBBs into the environment during normal production
    can occur through emission into the air, waste waters, losses into
    the soil, and to landfills, and have been found to be generally
    low.

         These chemicals can also enter the environment during 
    shipping and handling, and accidentally, as occurred in Michigan. 

         There is also the possibility of their entrance into the 
    environment as a result of the incineration of materials containing 
    PBBs as well as during accidental fires with the formation of other 
    toxic chemicals, such as polybromodibenzofurans or mixed 
    bromochloro derivatives.

         The major part of the total volume of these compounds produced
    will ultimately enter into the environment, as such, or as
    breakdown products.

    1.1.3  Environmental transport, distribution, and transformation

         Long-range transport of PBBs in the atmosphere has not been
    proven, but the presence of these compounds in Arctic seal samples
    indicates a wide geographical distribution.

         The principal known routes of PBBs into the aquatic
    environment are from industrial waste discharge and leachates from
    industrial dumping sites into receiving waters and from erosion of
    polluted soils. PBBs are almost insoluble in water and are
    primarily found in sediments of polluted lakes and rivers.

         Pollution of soils can originate from point sources, such as
    PBB plant areas and waste dumps. Once introduced into the soil,
    PBBs do not appear to be translocated readily. PBBs have been found
    to be 200 times more soluble in a landfill leachate than in
    distilled water; this may result in a wider distribution in the
    environment. The hydrophobic properties of PBBs make them easily
    adsorbed from aqueous solutions onto soils. Preferential adsorption
    of PBB congeners was noted, depending on the characteristics of the
    soil (e.g., organic content) and the degree and position of bromine
    substitution.

         PBBs are stable and persistent, lipophilic, and only slightly
    soluble in water; some of the congeners are poorly metabolized and
    therefore accumulate in lipid compartments of biota. Once they have
    been released into the environment, they can reach the food chain,
    where they are concentrated.

         PBBs have been detected in fish from several regions.
    Ingestion of fish is a source of PBB transfer to mammals and birds.

         Degradation of PBBs by purely abiotic chemical reactions 
    (excluding photochemical reactions) is considered unlikely. The 
    persistence of PBBs under field conditions has been reported. Soil 
    samples from a former PBB manufacturing site, analysed several 
    years after the Michigan incident, still contained PBBs though the 
    PBB congener composition was different, indicating a partial 
    degradation of the PBB residues in the soil sample.

         Under laboratory conditions, PBBs are easily degraded by UVR.
    Photodegradation of the commercial FireMaster(R) mixture led to
    diminished concentrations of the more highly substituted PBB
    congeners. The rates and extent of photolytic reactions of PBBs in
    the environment have not been determined in detail, though field
    observations indicate a high persistence of the original PBBs, or
    a partial degradation to the less brominated congeners.

         In laboratory investigations, mixtures of PBBs appear to be 
    fairly resistant to microbial degradation.

         Neither uptake nor degradation of PBBs by plants has been
    recorded. In contrast, PBBs are easily absorbed by animals and
    though they have been found to be very persistent in animals, small
    amounts of PBB metabolites have been detected. The main metabolic
    products were hydroxy-derivatives, and, in some cases, there was
    evidence of partially debrominated PBBs. No investigation of
    sulfur-containing metabolites analogous to those of PCBs have been
    reported.

         The bioaccumulation of PBBs in fish has been investigated.
    Bioaccumulation of PBBs in terrestrial animals has been
    investigated in avian and mammalian species. Data were obtained
    through field observations, evaluation of the Michigan disaster and
    through controlled feeding studies. Generally, the accumulation of
    PBBs in body fat depended on the dosage and duration of exposure.

         Bioaccumulation of individual PBB congeners has been found to
    increase with degree of bromination up to at least tetrabromo
    biphenyls. Higher brominated congeners can be expected to
    accumulate to an even greater extent. However, no information is
    available for decabromobiphenyl; it is possible that it is poorly
    absorbed.

         Brominated dibenzofurans or partially debrominated PBBs have
    been reported as products of the thermal decomposition of PBBs.
    Their formation depends on several variables (e.g., temperature,
    oxygen).

    1.1.4  Environmental levels and human exposure

         Only one report is available on PBB levels in air. In this
    study, concentrations in the vicinity of three PBB-manufacturing or 
    PBB-processing plants in the USA were measured.

         Levels in surface waters in the same vicinity and in the
    Gratiot County landfill (Michigan, USA), which received over a
    hundred thousand kg of waste containing 60-70% PBBs between 1971
    and 1973, were monitored.

         Groundwater monitoring data from the Gratiot County landfill
    showed trace levels of PBBs even outside the landfill area,
    however, PBBs were not detected in drinking-water wells in the
    area.

         Data on soil pollution by PBBs are available for areas of
    manufacture, use, or disposal of PBBs, and for soils from fields of
    the PBB-contaminated Michigan farms.

         In the Michigan disaster, FireMaster(R) was inadvertently
    added to animal feed. It was almost a year later that the mixing
    error was discovered and the analyses indicated that PBBs were
    responsible. During this time (summer 1973 - May 1974),
    contaminated animals and their produce entered the human food
    supply and the environment of the state of Michigan. Hundreds of
    farms were affected, thousands of animals had to be slaughtered and
    buried, as well as thousands of tons of farm produce.

         Most data available on the PBB-contamination of wildlife refer
    to fish and birds in the USA and Europe, primarily waterfowl, in
    the vicinity of industrial sites, and marine mammals.

         Recent reports on the PBB-contamination of fish, terrestrial
    and marine mammals, and birds in the USA and Europe indicate a wide
    distribution of these compounds. The congener pattern found in fish
    samples is quite different from that found in commercial products.
    Many of the major peaks could well be the result of the
    photochemical debromination of decabromobiphenyl (BB 209), but this
    has not been confirmed.

         Occupational exposure was found in employees in chemical
    plants in the USA, and in farm workers, as a result of the Michigan
    PBB incident. Median serum and adipose tissue PBB levels were
    higher among chemical workers. Information from other
    countries/companies on occupational exposure associated with
    manufacturing, formulation, and commercial uses is not available.

         For most human populations, direct data on exposure to PBBs
    from various sources have not been documented. Widespread human
    exposure resulting from direct contact with contaminated feed and,
    primarily, from the consumption of PBBs in meat, eggs, and dairy
    products has been reported from Michigan, USA. At least 2000
    families (primarily farmers and their neighbours) received heavy
    exposure. Recently, PBBs have been detected in cows' milk and human
    milk in Germany.

         The congener patterns in these samples are different from that
    in fish. The relative concentration of BB 153 is higher in human
    milk than in fish.

         The routes of exposure of the general population to PBBs are
    not well known. Present knowledge indicates that ambient air and
    water do not contain high levels. Lipid-rich food, especially from
    contaminated waters, is probably of great importance. There is no
    information on levels of exposure in indoor air and dermal exposure
    levels from materials containing PBB flame retardants.

         The PBB congener pattern found in human milk, collected in
    Germany, resembled that found in cows' milk from the same region,
    but levels in the human samples were substantially higher.

         An estimate of the daily intake of PBB via food by the general
    population has to be based on very few data. If it is assumed that
    fish contains 20 µg PBB/kg lipid and 5% lipid and that a 60-kg
    person eats 100 g fish/day, the intake will be 0.002 µg/kg body
    weight per day. A PBB concentration of 0.05 µg/kg lipid in milk
    (4% lipid) and a milk consumption of 500 ml/day will give the same
    person a PBB intake of about 0.00002 µg/kg body weight per day.

         An infant of 6 kg body weight consuming 800 ml human milk
    (3.5% lipid) per day will have an intake of 0.01 µg PBB/kg body
    weight per day, if the milk contains 2 µg PBB/kg lipid.

    1.1.5  Kinetics and metabolism

         Gastrointestinal absorption of PBBs varies according to the
    degree of bromination, the lower brominated compounds being more
    easily absorbed.

         There is inadequate information on the absorption of DeBB and
    OcBB/NoBB.

         PBBs are distributed throughout the animal species and human
    beings, the highest equilibrium concentrations being in adipose
    tissues. Relatively high levels have also been found in the liver,
    particularly of the more toxic congeners, which appear to be
    concentrated in the liver. The partitioning ratios of the various
    PBB congeners appear to differ between several tissues. Generally,
    there is a marked tendency for bioaccumulation. In mammals,
    transfer of PBBs to offspring occurs through transplacental and
    milk routes. Human milk was found to contain levels of
    2,2',4,4',5,5'-hexabromobiphenyl that were more than 100 times the
    maternal serum levels. During a multigeneration study on rats,
    administration of PBBs to a single generation resulted in
    detectable residues in more than two subsequent generations. Eggs
    of avian species were also affected by maternal PBB body burden.

         Many PBB congeners are persistent in biological systems. There
    was no evidence for significant metabolism or excretion of the more
    abundant components of the FireMaster(R) mixture or for octa- and
    decabromobiphenyl.  In vitro-metabolism studies showed that
    structure-activity relationships exist for the metabolism of PBBs.
    PBBs could be metabolized by PB (phenobarbital)-induced microsomes
    only if they possessed adjacent non-brominated carbons,  meta and
     para to the biphenyl bridge on at least one ring. Metabolism by
    MC (3-methylcholanthrene)-induced microsomes required adjacent
    non-brominated  ortho and  meta positions on at least one ring of
    lower substituted congeners and higher bromination appeared to
    prevent metabolism. Hydroxylated derivatives as major  in vitro-
    and  in vivo-metabolism products of lower brominated biphenyls
    have been identified in vertebrates. The metabolic yield was
    relatively low. The hydroxylation reaction probably proceeds via
    both arene oxide intermediates and by direct hydroxylation.

         Humans, rats, rhesus monkeys, pigs, cows, and chickens
    eliminate PBBs mainly in the faeces. In most cases, excretion rates
    seem to be slow. Concentrations of 2,2',4,4',5,5'-hexabromobiphenyl
    observed in the bile and faeces of humans were about 1/2 to 7/10 of
    the serum levels and approximately 0.5% of the adipose levels.
    Treatment to enhance elimination of PBBs in animals or humans had
    no, or little, success. Another pathway of elimination is excretion
    through milk.

         Complex and varied relationships were found in PBB tissue
    concentrations with time after PBB administration to rats and other
    animals. They are described by several compartmental models. A
    half-life of approximately 69 weeks was calculated for the
    elimination of 2,2',4,4',5,5'-hexabromobiphenyl from the body fat
    of rats. A half-life of more than 4 years was found in rhesus
    monkeys. Average half-lives in humans have been estimated to be
    between 8 and 12 years for 2,2',4,4',5,5'-hexabromobiphenyl. Ranges

    of 5-95 years have been suggested in the literature. There are some
    differences in retention and turnover between individual PBB
    congeners. Results of analyses of serum from farmers and chemical
    workers for 2,3',4,4',5-pentabromobiphenyl were inconsistent. This
    inconsistency was probably because of the different sources of
    exposure. The workers were exposed to all compounds of
    FireMaster(R), while the Michigan population was exposed to
    contaminated meat and milk containing a different PBB mixture as a
    result of metabolic processes in farm animals. Bromine levels did
    not decrease in the adipose tissue of rats, when technical
    octabromobiphenyl was given. No information is available on the
    retention of decabromobiphenyl.

         Humans may have a greater tendency to retain certain PBB
    congeners than experimental animals. This factor should be taken
    into consideration in evaluating the human health hazards from
    these chemicals.

         In conclusion, all available data indicate that PBBs have a
    marked tendency to bioaccumulate and persist. Metabolism is poor
    and half-lives in humans are of the order of 8-12 years or longer.

    1.1.6  Effects on organisms in the environment

         Only few data are available on the effects of PBBs on
    organisms in the environment. They refer to microorganisms, water
    fleas, waterbirds, and farm animals.

         Waterbirds nesting on islands in northwestern Lake Michigan
    were studied to see if environmental contaminants were producing
    effects on reproduction. Seventeen contaminants, including PBBs,
    were measured, but none seemed to have a pronounced effect on
    reproduction.

         Farm animals that ingested feed inadvertently containing
    Firemaster(R) FF-1 instead of magnesium oxide became sick. The
    estimated average exposure of cows on the first identified highly
    contaminated farm was 250 mg/kg body weight. The clinical signs of
    toxicity were a 50% reduction in feed consumption (anorexia) and a
    40% decrease in milk production, a few weeks after ingestion of the
    contaminated feed. Although the supplemented feed was discontinued
    within 16 days, milk production was not restored. Some cows showed
    an increased frequency of urination, and lacrimation, and developed
    haematomas, abscesses, abnormal hoof growth, lameness, alopecia,
    hyperkeratosis, and cachexia; several died within 6 months of
    exposure. Altogether, the death rate on this farm was 24/400. The
    death rate of 6- to 18-month- old calves was much higher. About 50%
    died within 6 weeks, only 2 out of 12 surviving after 5 months.
    They developed hyper keratosis over their entire bodies. There were
    also a variety of reproductive problems.

         Necropsy findings have been reported for some of the mature
    cows that died in the 6 months following exposure.
    Histopathological studies revealed variable liver and kidney
    changes.

         Several clinical signs and pathological changes noted above
    were later confirmed in controlled feeding studies (anorexia,
    dehydration, excessive lacrimation, emaciation, hyperkeratosis,
    reproductive difficulties, some clinical chemistry changes, and
    renal damage).

         A drop in production and sterility were reported in herds with
    low-level contamination. This contrasts with results of controlled
    studies, which did not show any significant differences between
    herds with low-level contamination and control herds.

         Although it was cattle feed that was originally involved in
    the accidental substitution, other animal feeds became involved by
    cross contamination, e.g., in the mixing machinery of feed
    companies. It is likely that the exposure was not as high as that
    of cattle. Although other animals (poultry, swine, horses, rabbits,
    goats, and sheep) were reported as being contaminated and were
    killed, details of ill effects were not recorded.

         No information is available on the effects of PBBs on the
    ecosystem.

    1.1.7  Effects on experimental animals and in vitro test systems

         The LD50 values of commercial mixtures show a relatively low
    order of acute toxicity (LD50 > 1 g/kg body weight) in rats,
    rabbits, and quails, following oral or dermal administration. 
    Deaths and acute manifestations of toxicity were delayed after
    administration of PBB. The total dose administered determined the
    extent of toxicity, whether given as a single dose or as repeated
    doses over short periods (up to 50 days). The toxicity of PBBs was
    higher with multiple-dose rather than single-dose administration.
    Deaths after exposure to PBBs are delayed.

         The few studies performed with commercial octa- and deca
    bromobiphenyl mixtures did not result in mortality in rats and
    fish. Of the individual PBB congeners, only three hexa isomers have
    been tested, 3,3',4,4',5,5'-HxBB; and 2,3',4,4',5,5'-HxBB being
    more toxic for rats than 2,2',4,4',5,5'-HxBB. On the basis of
    limited, available data, OcBB and DeBB appear to be less toxic than
    the PBB mixtures and less well absorbed.

         In many acute and short-term studies, signs of PBB (mostly
    FireMaster) toxicity have included reductions in feed consump tion.
    At lethal doses, the cause of death cannot be ascribed to pathology
    in a particular organ but rather to a "wasting syndrome" that the
    animals develop as a first indication of toxicity. At death, the
    loss in body weight can be as great as 30-40%. The few studies with
    technical OcBB and DeBB did not show any such effects.

         Morphological and histopathological changes, caused by PBB
    exposure, are most prominent in the liver. Enlargement of the liver
    frequently occurred at doses lower than those required to produce
    body weight changes. The principal histopathological alterations in
    rodent species may consist of extensive swelling and vacuolation of
    hepatocytes, proliferation of smooth endoplasmatic reticulum, and
    single-cell necrosis. The severity of the lesions depends on the
    dose and the composition of the PBB material given.

         Decreases in thymus weights were observed in rats, mice, and
    cattle after doses of FireMaster(R), but not OcBB or DeBB.

         There are some reports of increase in thyroid weight and
    histological changes in the thyroid of rats, which have been
    observed at low concentrations.

         It is evident that individual PBB congeners differ in their
    pattern of toxicity. The more toxic isomers and congeners cause a
    decrease in thymus and/or body weight and produce pronounced
    histological changes in the liver and thymus. Categorization of
    halogenated biphenyls has been made on a structural basis. 
    Category 1 comprises isomers and congeners lacking ortho-
    substituents (coplanar PBBs). Mono-ortho-substituted derivatives
    constitute the second category. Other PBBs (mainly those with two
    or more ortho-bromines) have been organized into the third
    category. Congeners of Category 1 tend to elicit the most severe
    effects, while the congeners of the second and third categories
    show decreasing toxicological changes. Within the category, the
    degree of bromination may also influence toxicity. 

         In all combinations tested, 3,3',4,4',5,5'-HxBB was found to
    be the most toxic PBB. This congener is present in low
    concentrations as a constituent of FireMaster(R). Of the major
    FireMaster(R) constituents, 2,3,3',4,4',5-HxBB appeared to be the
    most toxic one followed by 2,3',4,4',5,5'-HxBB and
    2,3',4,4',5-PeBB. The main component of the FireMaster(R)
    mixture, 2,2',4,4',5,5'-HxBB was relatively non-toxic as was
    2,2',3,4,4',5,5'-HpBB, the second most abundant constituent.

         The toxicity of technical OcBB and DeBB mixtures in relation
    to their contents of various PBB congeners (and other possible
    contaminants) is not so well elucidated.

         Common skin and eye irritation tests and sensitization tests
    resulted in no, or only mild, reactions to the technical PBB
    mixtures tested (OcBB and DeBB). However, hyperkeratosis and hair
    loss were seen in cattle, and lesions resembling chloracne were
    seen in Rhesus monkeys, following the ingestion of a
    FireMaster(R) mixture. Hyperkeratosis of the inner surface of the
    rabbit ear was produced by FireMaster, but not by its main
    components (2,2',4,4',5,5'-HxBB and 2,2',3,4,4'5,5'-HpBB).
    Fractionation of FireMaster(R) revealed that most activity was
    associated with the more polar fractions containing minor
    components. Treatment with sunlight-irradiated HxBB caused severe
    hyperkeratosis in rabbit ears.

         Low dose, long-term feeding of technical OcBB to rats did not
    affect food consumption and body weight, but an increase in the
    relative liver weights of exposed rats was found at 2.5 mg/kg body
    weight for 7 months. Long-term feeding of FireMaster(R) to rats
    at doses of 10 mg/kg body weight for 6 months did not affect food
    consumption. Doses of 1 mg/kg body weight over a 6-month period
    affected liver weight. The thymus weight was decreased in female
    rats administered 0.3 mg/kg body weight. Histopathological changes
    were also noted. Controlled, long-term feeding studies on cattle
    exposed to low doses of FireMaster(R) did not reveal any adverse
    effects as indicated by food intake, clinical signs,
    clinicopathological changes, or performance. Minks, guinea-pigs,
    and monkeys appeared to be more susceptible to PBB toxicity.

         Long-term effects related to the retention of administered
    PBBs following pre- or perinatal exposure to high doses of
    FireMaster(R) have been recorded in rats.

         The most common adverse effects on reproduction were fetal
    wastage and decrease in viability of offspring. Some effects were
    still noted in mink at concentrations of 1 mg/kg diet. Decreases in
    the viability of the offspring were observed in Rhesus monkeys
    following a 12.5 month exposure to FireMaster(R) (0.3 mg/diet). 
    The monkeys received a daily dose of 0.01 mg/kg body weight and a
    total dose of 3.8 mg/kg body weight. Reproduction and
    neurobehavioural studies on monkeys and rats with low-level
    exposure could not be evaluated since insufficient information was
    given in the published papers on the experimental design of the
    studies. A weak teratogenic potential was seen in rodents at high
    doses that may have caused some maternal toxicity.

         PBBs interact with the endocrine system. Rats and pigs showed
    dose-related decreases in serum thyroxine and triiodo-thyronine.
    PBBs have also been reported to affect the levels of steroid
    hormones in most cases. The extent depends on the species as well
    as the dose and time administered.

         PBBs produced porphyria in rats and male mice at doses as low
    as 0.3 mg/kg body weight per day. The no-effect level was 0.1 mg/kg
    body weight per day. There was a pronounced influence of PBBs on
    vitamin A storage as well as effects on the intermediary
    metabolism.

         Atrophy of the thymus was a frequent observation following PBB
    exposure, and other lymphoid tissues have been shown to be
    affected. Further indicators of a suppressed immune function have
    also been demonstrated for FireMaster(R). Data on OcBB, NoBB,
    DeBB, or individual PBB congeners are lacking.

         One of the most intensively studied effects of PBBs is their
    induction of mixed function oxidase (MFO) enzymes. Consistently,
    FireMaster(R) was found to be a mixed-type inducer of hepatic
    microsomal enzymes in rats and all other animal species tested.
    Induction was also found to a lesser extent in other tissues. The
    ability to induce hepatic microsomal enzymes differed for
    individual PBB congeners. Correlations between structure and
    microsomal enzyme inducing activity have been demonstrated.

         Several studies have revealed that PBBs are able to alter the
    biological activity of a variety of drugs and toxic substances.
    This may partly be because of the ability of PBBs to induce
    microsomal enzymes involved in the activation or deactivation of
    xenobiotics.

         The FireMaster(R) mixture, and some of its major components,
    were found to be capable of inhibiting intercellular communication
     in vitro. This inhibition occurs at non-cytotoxic concentrations.
    Both the cytotoxicity and metabolic cooperation-inhibiting
    properties of PBB congeners seem to be related to their structure,
    i.e., presence or lack of ortho-substitution. 

          In vitro and  in vivo assays (microbial and mammalian cell
    mutagenesis, mammalian cell chromosomal damage, mammalian cell
    transformation, and DNA damage and repair) have failed to indicate
    any mutagenicity or genotoxicity of individual PBB congeners or
    commercial mixtures.

         Long-term toxicity studies have shown the liver to be the
    principal site of the carcinogenic effects of PBB. The incidences
    of hepatocellular carcinoma were significantly increased in both
    male and female mice and rats receiving oral doses of the
    FireMaster(R) mixture. Carcinogenic effects in the liver have
    been reported in mice receiving diets containing Bromkal 80-9D
    (technical nonabromobiphenyl) at 100 mg/kg (5 mg/kg body weight per

    day) or more for 18 months. The lowest dose of PBB that produced
    tumours (mostly adenomas) in rodents was 0.5 mg/kg body weight per
    day for 2 years. The rats receiving 0.15 mg/kg body weight per day
    in addition to pre- and perinatal exposure did not suffer any
    adverse effects. The carcinogenicity of technical octabromobiphenyl
    and decabromobiphenyl has not been studied.

         Neither Firemaster BP-6 nor 2,2',4,4',5,5'-hexabromobiphenyl
    showed tumour-initiating (using TPA as promotor) or
    tumour-promoting (using DMBA as initiator) activity in a mouse skin
    bioassay. However, in other mouse skin models (using DMBA or MNNG
    as initiators), FM FF-1, 3,3',4,4',5,5'-hexabromobiphenyl, but not
    2,2',4,4',5,5'-hexabromobiphenyl, showed tumour promoting activity.
    In a two-stage rat liver bioassay using phenobarbital as promotor,
    3,3',4,4'-tetrabromobiphenyl showed a weak initiating activity. In
    the two-stage rat liver model using diethylnitrosamine and partial
    hepatectomy, FM, 3,3',4,4'-tetra bromobiphenyl, and
    2,2',4,4',5,5'-hexabromobiphenyl, but not
    3,3,',4,4',5,5'-hexabromobiphenyl, showed tumour promoting
    activity.

         The results of the studies on cell communication, the negative
    results of studies on genotoxicity and mutagenicity, and the
    results of tumour promotion assays indicate that the mixtures and
    congeners studied cause cancer by epigenetic mechanisms. No
    information is available on technical octa-, nona-, or decabromo
    biphenyl.

         The mechanisms of action underlying the many manifestations of
    the toxicity of PBBs and related compounds are not known. However,
    some of the effects, such as the wasting syndrome, thymus atrophy,
    hepatotoxicity, skin disorders, and reproductive toxicity may be
    related to interaction with the so-called Ah- or TCDD-receptor
    causing alteration in the expression of a number of genes.
    Different PBB congeners vary in their interaction with the
    receptor, the coplanar congeners being more active.

         Many of the effects of PBB are seen after long-term exposure. 
    The reason for this may be the pronounced accumulation of some PBB
    congeners and the poor ability of the body to metabolize and
    eliminate them. This results in a build-up of the chemical in the
    body overcoming compensatory mechanisms leading to adverse effects.

         Some polybrominated naphthalenes (PBNs), known contaminants of
    the FireMaster(R) mixture, are potent toxic substances and
    teratogens. Although PBNs are only present at low levels in the
    FireMaster(R) mixture, it is possible that they may contribute to
    its toxicity.

         Studies on the FireMaster(R) mixture and its main component,
    2,2',4,4',5,5'-HxBB showed that the photolysis products were more
    toxic than the original PBB. The pyrolysis products of FM caused
    MFO enzyme induction, body weight loss, and thymic atrophy. Liver
    enlargement was observed with pyrolysis products of technical OcBB.

    1.1.8  Effects on humans

         There was no example of acute PBB toxicosis in humans with
    which to compare the potential effects at lower exposures following
    the poisoning incident in Michigan, USA, 1973. The main
    epidemiological studies were conducted by the Michigan Department
    of Public Health (MDPH) and the Environmental Science Laboratory,
    Mount Sinai School of Medicine, New York (ESL).

         It was estimated that the most highly exposed people consumed
    5-15 g PBB over a 230-day period through milk. Some additional
    exposure may have occurred through meat. The exposure levels among
    some of the farmers and most of the general population in Michigan
    were much lower, i.e., the total exposure was 9-10 mg. However,
    some people in this group may have received a total exposure of
    about 800-900 mg. (A total dose of 9 mg corresponds to 0.15 mg/kg
    body weight, and 900 mg-15 mg/kg body weight for a 60-kg average
    adult; the dose/kg body weight would be higher for children).

         In 1974, the first MDPH study compared the health status of
    people on quarantined farms with people on non-quarantined farms in
    the same area. Although a variety of symptoms were reported by both
    groups, there was no pattern of differences between the groups. No
    unusual abnormalities of the heart, liver, spleen, nervous system,
    urinanalysis, blood counts, or any other medical conditions
    examined could be found. In a later comprehensive MDPH study
    including groups with different levels of exposure, there was no
    positive association between serum concentrations of PBB and
    reported symptom or disease frequencies. The ESL studies involved
    about 990 farm residents, 55 chemical workers, and a group of
    Wisconsin dairy farmers who were used as a control. The incidence
    of symptoms in Michigan farmers was greater than the incidence in
    Wisconsin farmers. The greatest differences were in the broad
    classification of neurologi cal and musculoskeletal symptoms.
    Elevated serum concentrations of some liver enzymes and
    carcinoembryonic antigen were more prevalent in Michigan farmers
    than in Wisconsin farmers. Chemical workers had a higher prevalence
    of chest and skin symptoms and a lower prevalence of
    musculoskeletal symptoms than farmers.

         Although results of ESL studies were at times interpreted
    differently from results of comparable studies, there was one area
    of consistent agreement. Neither sets of studies demonstrated a
    positive dose-response relationship between PBB levels in serum or
    adipose tissue and the prevalence of symptoms or abnormal clinical

    measurements. Several clinical areas were investigated using more
    intensive special studies. Examination of neurological aspects by
    means of objective performance tests revealed in one study a
    negative correlation of serum PBB levels with performance test
    scores, particularly in males in older age groups. The other
    studies showed no association between serum or fat concentrations
    of PBBs and performance in a battery of tests measuring memory,
    motor strength, coordination, cortical-sensory perception,
    personality, higher cognitive functioning, and other functions.

         Paediatric aspects of PBB exposure were examined in families
    of the ESL studies. Although many symptoms were reported, physical
    examination failed to reveal any objective alteration that could be
    attributed to PBB. There were different views about the more subtle
    neuropsychological effects in the offspring and the results of
    investigations of developmental abilities remain controversial,
    too. The same is true for the investigation of lymphocyte and
    immune function. One set of authors found no differences in
    lymphocyte count or functions between groups with high and low
    serum PBB levels, the other found a significant decrease in T- and
    B-lymphocyte subpopulations in about 40% of an exposed Michigan
    group, compared with unexposed groups, and impaired lymphocyte
    function, i.e., decreased response to mitogens.

         In the epidemiological studies reviewed, efforts have been
    made to evaluate the relationship between PBB exposure and a large
    number of adverse effects including behavioural effects and
    subjective complaints. However, most studies suffer from major
    failures in design introducing confounders that make it difficult,
    or impossible, to draw conclusions about the relationship between
    PBB exposure and possible health effects. The follow-up time has
    not been long enough to evaluate possible carcinogenic effects.

         Two small groups of workers with occupational exposure to a
    mixture of PBBs or to DeBB and DBBO were identified. Lesions
    resembling chloracne were found in 13% of the workers exposed to
    the PBB mixture, such lesions were not seen in the DeBB- exposed
    workers. However, a significantly higher prevalence of
    hypothyroidism was seen in the latter group.

    1.1.9  Overall evaluation of toxicity and carcinogenicity

         The only lifetime study with a PBB mixture was conducted on
    rats and mice in a recent NTP bioassay. The lowest dose tested that
    still produced carcinogenic effects was 0.5 mg/kg body weight per
    day (liver tumours in rodents). In other carcinogenicity studies,
    3 mg/kg body weight per day given for 6 months resulted in a
    carcinogenic response. The 6-month study demonstrates that less
    than lifetime exposure at similar doses will also result in similar
    adverse effects. Effects on reproduction in subhuman primates and
    mink may occur at lower doses.

         In addition, in the 2-year NTP rat study, a daily dose of
    0.15 mg/kg body weight per day and prenatal and perinatal exposure
    of the dam to 0.05 mg/kg body weight per day did not result in any
    adverse effects. Thus, the total daily intake from food, water,
    air, and soil should be less than 0.15 µg/kg body weight per day,
    extrapolating from a NOAEL (no-observed- adverse-effect level) of
    a positive carcinogenicity study, using an uncertainty (safety)
    factor of 1000, since these compounds probably produce cancer by an
    epigenetic mechanism.

         The total dose received by the subpopulation in Michigan was
    estimated to have ranged from 0.15 to 15 mg/kg body weight over a
    230-day period. For this population, dividing the doses over a
    lifetime for the average human being would be equivalent to a daily
    dose ranging from 6 ng to 0.6 µg/kg body weight per day.

         A total intake of 2 ng PBB/kg body weight per day, from known
    sources, has been estimated for adults in the general population
    and 10 ng/kg body weight per day for infants receiving human milk.
    It should be kept in mind that these estimates are based on a very
    limited and regional data base.

         These calculations assume that a steady state for PBBs would
    not be reached over a lifetime and that short-term higher exposure
    can be substituted for long-term lower exposures, since these
    compounds are extremely poorly metabolized and excreted.

         Insufficient information is available for OcBB, NoBB, and DeBB
    to calculate a total daily intake that would not result in adverse
    effects.

    1.2  Conclusions

         Most of the PBB congeners found in commercial flame retardants
    are lipophilic, persistent, and bioaccumulating. These compounds
    are biomagnified in environmental food webs and pose a threat,
    especially to organisms in the higher levels of these webs. 
    Furthermore, some PBB products are precursors to toxic
    polybrominated dibenzofurans in combustion processes.

         In addition to emissions during manufacture and use, PBB will
    enter the environment from the widespread use of flame retardant
    products. A considerable part of the PBB produced will ultimately
    reach the environment because of the high stability of these
    compounds.

         PBBs are also found in environmental and human samples from
    places far from known point sources. The congener pattern in the
    environmental samples does not match those found in the technical
    products, which indicates an environmental alteration, possibly a
    photochemical debromination.

         Very little information is available at present on the extent
    of the exposure of the general population to PBBs. However, in the
    few instances where measurements were made, trace amounts of PBBs
    were identified. At present, this exposure does not give rise to
    concern, but further build-up should be avoided. Human data from
    the Michigan episode suggest that exposures in Michigan were
    several order of magnitude higher than the exposure of the general
    population. No definitive health effects that could be correlated
    with PBB exposure in the Michigan population have been identified,
    though the follow-up period has not been long enough for the
    development of cancer. Since PBB levels in adipose tissue and serum
    remain high in the Michigan population, their internal exposure
    continues. In contrast, toxicity was observed in cattle in
    Michigan. This discrepancy is explained by differences in the
    extent of the exposure of the cattle.

         Occupational exposure has only been examined in two plants in
    the USA. It appears that chloracne-like lesions may develop in
    workers producing PBB, and hypothyroidism in workers exposed to
    DeBB. No studies have been conducted on workers incorporating deca-
    or octa-/nona-bromobiphenyl into commercial products.

         PBBs are extremely persistent in living organisms and have
    been shown to produce chronic toxicity and cancer in animals. 
    Although the acute toxicity was low, cancer was induced at a dose
    of 0.5 mg/kg body weight per day and the no-observed-effect level
    was 0.15 mg/kg body weight per day. A number of chronic toxic
    effects have been observed in experimental animals at doses of
    around 1 mg/kg body weight per day following long-term exposure.

    1.3  Recommendations

    1.3.1  General

         The Task Group is of the opinion that human beings and the
    environment should not be exposed to PBBs in view of their high
    persistence and bioaccumulation and potential adverse effects at
    very low levels after long-term exposure. Therefore, PBBs should no
    longer be used commercially.

         Because of the limited toxicity data on DeBB and OcBB, their
    extreme persistence and their potential break-down in the
    environment, and the more toxic persistent compounds formed through
    combustion, they should not be used commercially, unless their
    safety has been demonstrated.

         It is known that observations on the Michigan cohort are still
    continuing. Publication of these data is required.

    1.3.2  Future research

         Future human and environmental PBB monitoring, including
    workplace monitoring in the manufacture and user industries, should
    be expanded, should be congener specific, and should include
    OcBB/NoBB and DeBB. These compounds should be included in
    monitoring programmes in progress for other halogenated compounds.
    The time trends and geographical distribution of PBB levels in the
    environment should continue to be monitored. Release of PBBs into
    the environment from waste disposal sites should be surveyed.

         Thermolysis experiments simulating conditions of accidental
    fires and municipal incineration should be conducted. Additional
    research should be continued on the mechanisms of toxicity and
    carcinogenicity of PBBs and related compounds. PBBs may serve as
    model compounds for such mechanistic research. Purified congeners
    should be used in these studies.

         The effects of PBBs on reproduction are not well elucidated.
    Therefore, well-designed, long-term, reproductive studies at low
    doses, using a sensitive species, should be performed.

         There is also a need for more information on the
    bioavailability and toxicokinetics of OcBB/NoBB, DeBB, and selected
    congeners.

    2.  IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

    2.1  Identity

    2.1.1  Primary constituents

         The term "polybrominated biphenyls" or "polybromobiphe nyls"
    (PBBs) refers to a group of halogenated hydrocarbons, formed by
    substituting hydrogen by bromine in biphenyl (Fig. 1).

         Molecular formula C12H(10-x-y)Brx+y
         (x and y = 1 to 5)

         Molecular (empirical) formulae for PBB components of different
    degrees of substitution and their relative molecular masses are
    given in Table 1.

         Theoretically, there can be 209 different forms (congeners) of
    a brominated biphenyl, depending on the number and position of the
    bromine (see Table 2).

         At present, 101 individual PBB congeners are listed in the
    Chemical Abstracts Service (CAS) registry. Because bromobiphe nyls
    are produced commercially by the bromination of biphenyl, the
    existence of any of the 209 congeners is possible in any commercial
    mixture (Aust et al., 1983). Some PBBs exist primarily as
    metabolites or accumulation or degradation products of the original
    mixture. With increasing advance in analysis techniques, the number
    of actually identified PBB compounds is growing.

    Table 1.  PBBs: molecular formula and relative molecular mass

        PBB                        Formula               Relative
                                                         molecular mass

    Monobromobiphenyl              C12H9Br               232.9

    Dibromobiphenyl                C12H8Br2              311.8

    Tribromobiphenyl               C12H7Br3              390.7

    Tetrabromobiphenyl             C12H6Br4              469.6

    Pentabromobiphenyl             C12H5Br5              548.5

    Hexabromobiphenyl              C12H4Br6              627.4

    Heptabromobiphenyl             C12H3Br7              706.3

    Octabromobiphenyl              C12H2Br8              785.2

    Nonabromobiphenyl              C12HBr9               864.1

    Decabromobiphenyl              C12Br10               943.0

    Table 2. Multiplicity of PBB isomers and congenersa

    Number of
    Br Substituent      1     2     3     4     5     6     7     8     9     10

    Number of
    Isomers             3     12    24    42    46    42    24    12    3     1

    a    Modified from: Safe (1984).
    
         The synthesis of pure congeners for use as standards is a
    prerequisite for advances in chemical analysis, as well as research
    into the toxicological and biological effects of PBBs. Some routes
    for the synthesis of PBB congeners have been described by Sundström
    et al. (1976b), Robertson et al. (1980, 1982a, 1984a), Höfler et al.
    (1988), and Kubiczak et al. (1989).

         Table 3 gives a list of all 209 possible congeners and their
    CAS numbers, if already designated. The CAS names are designated as
    follows:

         1,1'-Biphenyl, .......... bromo-
         e.g., 1,1'-Biphenyl, 2,2',4,4',5,5'-hexabromo- or
              2,2',4,4',5,5'-hexabromo-1,1'-biphenyl (BB-153).

    2.1.2  Technical products

    2.1.2.1  Major trade names

         The PBBs produced for commercial use include mixtures mainly
    containing hexa-, octa-/nona-, and decabromobiphenyls. Data on past
    and present trade names and manufacturers are summarized in Table 4
    (for further details see section 3.2.1).

    2.1.2.2  Composition of the technical products

         Commercial PBB products are mixtures of various brominated
    biphenyls. Several structural isomers of each of these brominated
    compounds are possible and may be present in the product. All
    mixtures are relatively highly brominated, with bromine contents
    ranging from about 76% for hexabromobiphenyls to 81-85% for octa- to
    decabromobiphenyl mixtures (Brinkman & de Kok, 1980).

         Data on the composition of PBB mixtures are given in Table 5.
    As shown in Table 5, the analytical results concerning the various
    products are rather divergent. It indicates that the exact
    composition of the mixtures varies between batches, and also within
    each batch according to the sampling and analytical method. It can
    be seen that samples of "octabromobiphenyl" often contained a larger
    proportion of nona- than of octa-substituted PBBs. In this
    monograph, these compounds are also referred to as "octa/nona"
    bromobiphenyls.

         Information on the isomeric composition of the octa- to deca-
    mixtures is scarce. In an analysis of Bromkal 80, three isomers of
    octabromobiphenyl were found to be present at 14, 16, and 42%
    (Norström et al., 1976). A comparison of the isomeric composition of
    an "octabromobiphenyl"-mixture with the FireMaster(R)- mixture has
    been given by Moore & Aust (1978). De Kok et al. (1977) analysed
    various "octabromobiphenyl"-mixtures and Bromkal 80-9D and discussed
    the structures of isomers.  Furthermore, two isomeric octa- and
    three hexa-bromobiphenyls of a commercial decabromobiphenyl mixture
    (RFR) have been reported (de Kok et al., 1977).

    
    Table 3.  Systematic numbering of PBB compounds and their CAS numbers

      BB-No.a       Structure              CAS No.                 BB-No.a         Structure                      CAS No.

         Monobromobiphenyls                (26264-10-8)            17              2,2',4
                                                                   18              2,2',5                         59080-34-1
         1          2                      2052-07-7               19              2,2',6
         2          3                      2113-57-7               20              2,3,3'
         3          4                      92-66-0                 21              2,3,4
                                                                   22              2,3,4'
         Dibromobiphenyls                  (27479-65-8)            23              2,3,5
                                                                   24              2,3,6
         4          2,2'                   13029-09-9              25              2,3',4
         5          2,3                    115245-06-2             26              2,3',5                         59080-35-2
         6          2,3'                   49602-90-6              27              2,3',6
         7          2,4                    53592-10-2              28              2,4,4'                         6430-90-6
         8          2,4                    49602-91-7              29              2,4,5                          115245-07-3
         9          2,5                    57422-77-2              30              2,4,6                          59080-33-0
         10         2,6                    59080-32-9              31              2,4',5                         59080-36-3
         11         3,3'                   16400-51-4              32              2,4',6                         64258-03-3
         12         3,4                    60108-72-7              33              2',3,4
         13         3,4'                   57186-90-0              34              2',3,5
         14         3,5                    16372-96-6              35              3,3',4
         15         4,4'                   92-86-4                 36              3,3',5
                                                                   37              3,4,4'                         6683-35-8
         Tribromobiphenyls                 (51202-79-0)            38              3,4,5                          115245-08-4
                                                                   39              3,4',5                         72416-87-6
         16         2,2',3

         Tetrabromobiphenyls               40088-45-7              65              2,3,5,6
                                                                   66              2,3',4,4'                      84303-45-7
         40         2,2',3,3'                                      67              2,3',4,5
         41         2,2',3,4                                       68              2,3',4,5'
         43         2,2',3,5                                       69              2,3',4,6

    Table 3.  cont'd

      BB-No.a       Structure              CAS No.                 BB-No.a         Structure                      CAS No.

         44         2,2',3,5'                                      70              2,3',4',5                      59080-38-5
         45         2,2',3,6                                       71              2,3',4',6
         46         2,2',3,6'                                      72              2,3',5,5'
         47         2,2',4,4'              66115-57-9              73              2,3',5',6
         48         2,2',4,5                                       74              2,4,4',5
         49         2,2',4,5'              60044-24-8              75              2,4,4',6                       64258-02-2
         50         2,2',4,6                                       76              2',3,4,5
         51         2,2',4,6'              97038-95-4              77              3,3',4,4'                      77102-82-0
         52         2,2',5,5'              59080-37-4              78              3,3',4,5
         53         2,2',5,6'              60044-25-9              79              3,3',4,5'                      97038-98-7
         54         2,2',6,6'              97038-96-5              80              3,3',5,5'                      16400-50-3
         55         2,3,3',4               97038-99-8              81              3,4,4',5                       59589-92-3
         56         2,3,3',4'
         57         2,3,3',5                                       Pentabromobiphenyls                            (56307-79-0)
         58         2,3,3',5'
         59         2,3,3',6                                       82              2,2',3,3',4
         60         2,3,4,4'                                       83              2,2',3,3',5
         61         2,3,4,5                115245-09-5             84              2,2',3,3',6
         62         2,3,4,6                115245-10-8             85              2,2',3,4,4'
         63         2,3,4',5                                       86              2,2',3,4,5
         64         2,3,4',6                                       87              2,2',3,4,5'
         88         2,2',3,4,6             77910-04-4              111             2,3,3',5,5'
         89         2,2',3,4,6'                                    112             2,3,3',5,6
         90         2,2',3,4',5                                    113             2,3,3',5',6
         91         2,2',3,4',6                                    114             2,3,4,4',5                     96551-70-1
         92         2,2',3,5,5'                                    115             2,3,4,4',6
         93         2,2',3,5,6                                     116             2,3,4,5,6                      38421-62-4
         94         2,2',3,5,6'                                    117             2,3,4',5,6
         95         2,2',3,5',6            88700-05-4              118             2,3',4,4',5                    67888-97-5
         96         2,2',3,6,6'                                    119             2,3',4,4',6                    86029-64-3
         97         2,2',3',4,5                                    120             2,3',4,5,5'                    80407-70-1
         98         2,2',3',4,6                                    121             2,3',4,5',6

    Table 3.  cont'd

      BB-No.a       Structure              CAS No.                 BB-No.a         Structure                      CAS No.

         99         2,2',4,4',5            81397-99-1              122             2',3,3',4,5
         100        2,2',4,4',6            97038-97-6              123             2',3,4,4',5                    74114-77-5
         101        2,2',4,5,5'            67888-96-4              124             2',3,4,5,5'
         102        2,2',4,5,6'            80274-92-6              125             2',3,4,5,6'
         103        2,2',4,5',6            59080-39-6              126             3,3',4,4',5                    84303-46-8
         104        2,2',4,6,6'            97063-75-7              127             3,3',4,5,5'                    81902-33-2
         105        2,3,3',4,4'                                    
         106        2,3,3',4,5                                     Hexabromobiphenyls                             (36355-01-8)
         107        2,3,3',4',5                                    
         108        2,3,3',4,5'                                    128             2,2',3,3',4,4'                 82865-89-2
         109        2,3,3',4,6                                     129             2,2',3,3',4,5
         110        2,3,3',4',6                                    130             2,2',3,3',4,5'                 82865-90-5
         131        2,2',3,3',4,6                                  155             2,2',4,4',6,6'                 59261-08-4
         132        2,2',3,3',4,6'         119264-50-5             156             2,3,3',4,4',5                  77607-09-1
         133        2,2',3,3',5,5'         55066-76-7              157             2,3,3',4,4',5'                 84303-47-9
         134        2,2',3,3',5,6                                  158             2,3,3',4,4',6
         135        2,2',3,3',5,6'         119264-51-6             159             2,3,3',4,5,5'                  120991-48-2
         136        2,2',3,3',6,6'                                 160             2,3,3',4,5,6
         137        2,2',3,4,4',5          81381-52-4              161             2,3,3',4,5',6
         138        2,2',3,4,4',5'         67888-98-6              162             2,3,3',4',5,5'
         139        2,2'3,4,4',6                                   163             2,3,3',4',5,6
         140        2,2',3,4,4',6                                  164             2,3,3',4',5',6                 82865-91-6
         141        2,2',3,4,5,5'          120991-47-1             165             2,3,3',5,5',6
         142        2,2',3,4,5,6                                   166             2,3,4,4',5,6
         143        2,2',3,4,5,6'                                  167             2,3',4,4',5,5'                 67888-99-7
         144        2,2',3,4,5',6          119264-52-7             168             2,3',4,4',5',6                 84303-48-0
         145        2,2',3,4,6,6'                                  169             3,3',4,4',5,5'                 60044-26-0
         146        2,2',3,4',5,5'                                 
         147        2,2',3,4',5,6                                  Heptabromobiphenyl                             (35194-78-6)
         148        2,2',3,4',5,6'                                 

    Table 3.  cont'd

      BB-No.a       Structure              CAS No.                 BB-No.a         Structure                      CAS No.

         149        2,2',3,4',5',6         69278-59-7              170             2,2',3,3',4,4',5               69278-60-0
         150        2,2',3,4',6,6'         93261-83-7              171             2,2',3,3',4,4',6
         151        2,2',3,5,5',6          119264-53-8             172             2,2',3,3',4,5,5'               82865-92-7
         152        2,2',3,5,6,6'                                  173             2,2',3,3',4,5,6
         153        2,2',4,4',5,5'         59080-40-9              174             2,2',3,3',4,5,6'               88700-04-3
         154        2,2',4,4',5,6'         36402-15-0              175             2,2',3,3',4,5',6
         176        2,2',3,3',4,6,6'                               195             2,2',3,3',4,4',5,6
         177        2,2',3,3',4,5,6'                               196             2,2',3,3',4,4',5',6
         178        2,2',3,3',5,5',6       119264-54-9             197             2,2',3,3',4,4',6,6'            119264-59-4
         179        2,2',3,3',5,6,6'                               198             2,2',3,3',4,5,5',6
         180        2,2',3,4,4',5,5'       67733-52-2              199             2,2',3,3',4,5,6,6'
         181        2,2',3,4,4',5,6                                200             2,2',3,3'4,5',6,6'             119264-60-7
         182        2,2',3,4,4',5,6'       119264-55-0             201             2,2',3,3',4',5,5',6            69887-11-2
         183        2,2',3,4,4',5',6                               202             2,2',3,3',5,5',6,6'            59080-41-0
         184        2,2',3,4,4',6,6'       119264-56-1             203             2,2',3,4,4',5,5',6
         185        2,2',3,4,5,5',6                                204             2,2',3,4,4',5,6,6'             119264-61-8
         186        2,2',3,4,5,6,6'        119264-57-2             205             2,3,3',4,4',5,5',6
         187        2,2',3,4',5,5',6       84303-49-1
         188        2,3',3,4',5,6,6'       119264-58-3             Nonabromobiphenyls                             (27753-52-2)
         189        2,3,3',4,4',5,5'       88700-06-5
         190        2,3,3',4,4',5,6        79682-25-0              206             2,2',3,3',4,4',5,5',6          69278-62-2
         191        2,3,3',4,4',5',6                               207             2,2',3,3',4,4',5,6,6'          119264-62-9
         192        2,3,3',4,5,5',6                                208             2,2',3,3',4,5,5',6,6'          119264-63-0
         193        2,3,3',4',5,5',6                               
                                                                   Decabromobiphenyl
         Octabromobiphenyls                (27858-07-7)            
                                                                   209             2,2',3,3',4,4',5,5',6,6'       13654-09-6
         194        2,2',3,3',4,4',5,5'    67889-00-3              

    a    The Nos 1-209 correspond to those used by Ballschmiter & Zell (1980) for PCBs (January 1990).

    
    Table 4.  Major trade names and manufacturers of technical-grade PBBs and
              commercial PBB mixturesa

    PBB mixture            Manufacturer                                     CAS No.

    Hexa-PBBs
    FireMaster(R) BP-6     Michigan Chemical Corp. (St. Louis, Mich.)       59536-65-1
    FireMaster(R) FF-1b    Michigan Chemical Corp. (St. Louis, Mich.)       67774-32-7

    Octa/nona-PBBs
    Bromkal 80-9D          Chemische Fabrik Kalk (Cologne, Germany)         61288-13-9
    Technical
    octabromobiphenyl      White Chemical Corp. (Bayonne, New Jersey)
    Octabromobiphenyl
    FR 250 13A             Dow Chemical Co. (Midland, Mich.)

    Deca-PBB
    Adine 0102             Ugine Kuhlmann now Atochem (Paris, France)       13654-09-6
    Berkflam B 10          Berk (London, United Kingdom)
    Flammex B-10           Berk (London, United Kingdom)
    Technical
    decabromobiphenyl      White Chemical Corp. (Bayonne, New Jersey)
    HFO 101                Hexcel (Basildon, United Kingdom)

    a    Adapted from: Brinkman & de Kok (1980).
    b    A pulverized form of FireMaster BP-6 containing 2% calcium polysilicate
         to prevent caking. It was produced in limited quantities as a
         development-product in 1971 and 1972.
    
         Most research has been conducted with the hexabromobiphenyl
    mixture FireMaster(R), which accounts for most of the manu
    factured products and most of the environmental contamination
    (Di Carlo et al., 1978). The main constituent of FireMaster(R) is
    2,2',4,4',5,5'-hexabromobiphenyl. Its identification was reported by
    Andersson et al. (1975), Jacobs et al. (1976), and Sundström et al.
    (1976a). The second major component is heptabromobiphenyl containing
    bromine at positions 2,2',3,4,4',5,5' (Hass et al., 1978; Moore
    et al., 1978c). Accordingly, these two congeners account for about
    75% of the mixture (e.g., Dannan et al., 1982d). Data on the
    isomeric composition of FireMaster(R) found in the literature are
    given in Table 6. The ranges of relative abundances of some
    FireMaster(R) constituents are compiled in Table 7. Altogether at
    least sixty compounds have been detected in FireMaster(R) (Orti
    et al., 1983). About twelve of them are major PBB-components (Aust
    et al., 1981), the others belong to the minor components (< 1%).

    
    Table 5.  Survey of literature on the composition of PBB mixturesa

    PBB mixture (manufacturer)     Weight of                     Weight of different homologus groups                     Reference
                                 bromine (%)
                                                                                                                 
                                                 Br10       Br9       Br8       Br7       Br6       Br5       Br4

    "Hexabromobiphenyl"

    FM BP-6 (Michigan Chemical)      75                                        13.8      62.8      10.6        2          de Kok et al.
                                                                                                                          (1977)c

    "   [Lot RP-158 (1971)]                                                    12.5      72.5        9         4          Willett & Irving
                                                                                                                          (1976)
    "   [Lot 6244A (1974)]                                                      13       77.5        5        4.5         Willett & Irving
                                                                                                                          (1976)
    "                                                                                     90        10                    Norström et al.
                                                                                                                          (1976)
    "                                                                  1        18        73         8                    de Kok et al.
                                                                                                                          (1977)
    "                                                                           33        63         4                    Hass et al.
                                                                                                                          (1978)
    "                                                                           7.7      74.5       5.6                   Robertson et al.
                                                                                                                          (1984b)
    "                                                                          24.5       79         6                    Krüger (1988)
    2,2',4,4',6,6' (RFR)                                                        12        84         1                    de Kok et al.
                                                                                                                          (1977)
    2,2',4,4',6,6' (Aldrich)                                           2        24        70         4                    de Kok et al.
                                                                                                                          (1977)
    "Hexabromobiphenyl" (RFR)                                                   25        67         4
                                                                              (12-25)   (60-80)   (1-11)    (2-5)b        de Kok et al.
                                                                                                                          (1977)

    Table 5 (contd).

    PBB mixture (manufacturer)     Weight of                   Weight of different homologus groups                       Reference
                                 bromine (%)
                                                                                                                 
                                                 Br10       Br9       Br8       Br7       Br6       Br5       Br4

    Octanonabromobiphenyl

    Bromkal 80-9D (Kalk)           81-82.5         9        65         1                                                  de Kok et al.
                                                                                                                          (1977)

    Bromkal 80                                                        72        27         1                              Norström et al.
                                                                                                                          (1976)
    XN-1902 (Dow Chemical)c          82            6        47        45         2                                        Norris et al. (1973)
    XN-1902 (Dow Chemical)c                        2        34        57         7                                        de Kok et al. (1977)
    Lot 102-7-72 (Dow Chemical)c                   6        60        33         1                                        Waritz et al. (1977)
    "Octabromobiphenyl" (RFR)                      4        54        38         2                                        de Kok et al. (1977)
    2,2',3,3',5,5',6,6' (RFR)                      1        28        46        23         2                              de Kok et al. (1977)
    FR 250 13A (Dow Chemical)                      8        49        31         1                                        Krüger (1988)

    Decabromobiphenyl

    HFO 101 (Hexcel)                 84           96         2                                                            de Kok et al. (1977)
    Adine 0102 (Ugine Kuhlmann)     83-85         96         4                                                            de Kok et al. (1977)
    Adine 0102 (Ugine Kuhlmann)                  96.8       2.9       0.3                                                 Millischer et al.
                                                                                                                          (1979)
    "Decabromobiphenyl" (RFR)                     71        11         7         4         4                              de Kok et al. (1977)
    "DBB": Flammex B 10 (Berk)c                  96.8       2.9       0.3                                                 Di Carlo et al
                                                                                                                          (1978)

    a    Adapted from: Brinkman & de Kok (1980).
    b    Range of above readings with the exception of that of Norström et al. (1976), which differs greatly from the others.
    c    According to de Kok et al. (1977), these have never been marked.

    
    Table 6.  Identified PBB congeners in FireMaster(R)

    BB No.a       Structure              % Composition of         References
                                       FM BP-6       FF-1

    Dibromobiphenyls

        4         2,2'-                 0.02                      Moore et al. (1979a)

    Tribromobiphenyls

        18        2,2'5-                0.050                     Robertson et al. (1984b)
        26        2,2',5-               0.024
        31        2,4',5-               0.015
        37        3,4,4'-               0.021

    Tetrabromobiphenyls

        49        2,2',4,5'-            0.025
        52        2,2',5,5'-            0.052
        66        2,3',4,4'-            0.028
        70        2,3',4',5-            0.017
        77b       3,3',4,4'-                        < 0.08        Orti et al. (1983)
                                        0.159                     Robertson et al. (1984b)

    Pentabromobiphenyls

        95        2,2',3,5',6-          0.02                      Orti et al. (1983)
        99        2,2'4,4',5-                       < 0.08
        101       2,2',4,5,5'-          2.69                      Robertson et al. (1984b)
                                        4.5           3.7         Aust et al. (1981)
                                                     1.54         Orti et al. (1983)
                                        2.6                       Krüger (1988)
        118       2,3',4,4',5-          2.94                      Robertson et al. (1984b)
                                                      0.7         Aust et al. (1981)
                                        3.2                       Krüger (1988)
                                                      0.8         Orti et al. (1983)
        126b      3,3',4,4',5-                      < 0.01
                                        0.079                     Robertson et al. (1984b)

    Hexabromobiphenyls

        132       2,2'.3.3',4,6'-       1                         Krüger (1988)
        138       2,2',3,4,4',5'-      12.3                       Robertson et al. (1984b)

    Table 6. cont'd

    BB No.a       Structure              % Composition of         References
                                       FM BP-6       FF-1

                                       12             8.6         Aust et al. (1981)
                                                     5.23         Orti et al. (1983)
                                       10.6                       Krüger (1988)
        149       2,2',3,4',5',6-       2.24                      Robertson et al. (1984b)
                                        1.4           1.3         Aust et al. (1981)
                                                     0.78         Orti et al. (1983)
        153       2,2'4,4',5,5'-       53.9                       Robertson et al. (1984b)
                                       47.8          47.1         Aust et al. (1981)
                                       55.2                       Orti et al. (1983)
                                       58.5                       Krüger (1988)
        155       2,2',4,4',6,6'-       0.5
        156       2,3,3',4,4',5-        0.980                     Robertson et al. (1984b)
                                        5.0                       Aust et al. (1981)
                                        0.37                      Orti et al. (1983)
                                        1.0                       Krüger (1988)
        157       2,3,3',4,4',5'-       0.05                      Orti et al. (1983)
                                        0.526                     Robertson et al. (1984b)
                                        0.5                       Krüger (1988)
        167       2,3',4,4',5,5'-       5.5           3.3         Aust et al. (1981)
                                        3.37                      Orti et al. (1983)
                                      < 0.3
                                        7.95                      Robertson et al. (1984b)
                                        5.5                       Krüger (1988)
        169b      3,3',4,4',5,5'-       0.294                     Robertson et al. (1984b)

    Heptabromobiphenyls

        170       2,2',3,3',4,4',5-     0.256
                                        1.1           1.5         Aust et al. (1981)
                                        1.66                      Orti et al. (1983)
                                        2.4                       Krüger (1988)
        180       2,2',3,4,4',5,5'-     6.97                      Robertson et al. (1984b)
                                                     24.7         Aust et al. (1981)
                                                     23.5         Orti et al. (1983)   20.8  Krüger (1988)
        172       2,2',3,3',4,5,5'-   < 0.30                      Orti et al. (1983)
        174       2,2',3,3',4,5,6'-     0.24
        178       2,2',3,3',5,5',6-     0.3                       Krüger (1988)
        187       2,2',3,4',5,5',6-     0.392                     Robertson et al. (1984b)
                                                      1.0         Krüger (1988)
        189       2,3,3',4,4',5,5'-                  0.51         Orti et al. (1983)

    Table 6. cont'd

    BB No.a       Structure              % Composition of         References
                                       FM BP-6       FF-1

    Octabromobiphenyls

        194       2,2',3,3',4,4',       0.9           2.4         Aust et al. (1981)
                  5,5'-
                                                     1.65         Orti et al. (1983)

        possible structures for two
        minor Br8 peaks:

        196       2,2',3,3',4,4',                                 Moore et al. (1980);
                  5,6'-
        201       2,2',3,3',4,5,                                  Orti et al. (1983)
                  5',6'-
        203       2,2',3,4,4',5,
                  5'6-

    a    From: Ballschmiter & Zell (1980).
    b    These coplanar congeners are the most toxic congeners identified in
         FireMaster BP-6 (Robertson et al., 1984b).

    Table 7.  Range of relative abundance of some PBB constituents
              of Firemaster(R) FF-1 and BP-6a

    Structure           No.b            BB No.c        Abundance (%)

    2,2',4',5,5'-         1             101              1.5-4.5
    2,3',4,4',5,-         2             118              0.7-4.2
    2,2',3,4',5',6-       3             149              0.8-2.2
    2,2',4,4',5,5'-       4             153              47.1-59
    2,2',3,4,4',5'-       5             138              5.2-12.3
    2,3',4,4',5,5'-       6             167              3.3-8.0
    2,3,3',4,4',5-        7             168              0.4-5.0
    2,2',3,4,4',5,5'-     8             180              7.0-24.7
    2,2',3,3',4,4',5-     9             170              0.3-2.4
    2,2',3,3',4,4',5,5'- 12             194              0.9-2.4

    a    For references, see Table 6.
    b    Congener designation made on the basis of the gas chromatographic
         elution sequence of the FireMaster(R) mixture.
    c    Congener designation according to Ballschmiter & Zall (1980).

         Variations are due to differences in batches and analytical
    techniques. In many cases, the differing electron capture responses
    of the various congeners within the mixture were not taken into
    account. Thus, values in Table 7 only give an approximate range of
    composition and it is not possible to provide a precise composition
    for the material that was introduced into the Michigan environment
    (Fries, 1985b).

         Both formulations of FireMaster(R) mixture, BP-6 and FF-1
    have a similar isomeric composition. However, FireMaster BP-6
    contains roughly 10% more of the relatively minor congeners (Dannan
    et al., 1982b).

         As can be concluded from the composition of the commercial
    mixtures (Table 5), the major source of impurity that occurs in PBBs
    results from the spread in the degree of bromination. For example,
    FireMaster(R) BP-6 has been marketed as a hexabromin ated
    biphenyl, but more than one quarter of the product consists of lower
    brominated biphenyls because of incomplete bromination reaction
    (Neufeld et al., 1977).

         However, a producer of decabromobiphenyl has reported that
    their material has a degree of purity of more than 98%, the
    remaining 2% being nonabromobiphenyl. It is manufactured by a
    special proprietary process rendering no brominated by-products
    (Neufeld et al., 1977).

         It is noteworthy that mixed polybromochlorobiphenyls (PCBs)
    have been observed as minor contaminants in FireMaster(R). For
    example, monochloropentabromobiphenyl (CAS No. 88703-30-4) was added
    to the list of detected impurities (Domino & Domino, 1980; Tondeur
    et al., 1984). Such compounds probably result from contamination of
    commercial bromine by chlorine (Domino & Domino, 1980).

         Polybrominated naphthalenes (PBNs) (Fig. 2) have been
    identified as minor components in commercial PBB mixtures (see
    Table 8). The isomeric composition of PBNs in FireMaster(R) is
    unknown, but studies on this subject have been started (Robertson
    et al., 1984a). It is assumed that naphthalene, present as an
    impurity in industrial-grade biphenyl, is brominated during the
    production of FireMaster(R), and that the presence of numerous
    isomers and congeners of PBNs in FireMaster(R) is possible
    (Robertson et al., 1984b).

    Table 8.  Occurrence of polybrominated naphthalenes (PBNs) in FireMaster(R)-mixtures

    PBN                       CAS-Registry   FireMaster(R)      Concentration     Reference
                              Number         mixture

    Tetrabromonaphthalene     88703-31-5     BP-6 or FF-1    no information    Tondeur et al.
                                                             available         (1984)

    Pentabromonaphthalene     56448-55-6     BP-6 or FF-1    no information    Tondeur et al.
                                                             available         (1984)
                                             FF-1            1 mg/kg           O'Keefe (1979)
                                             BP-6            150 mg/kg         Hass et al.
                                                                               (1978)

    Hexabromonaphthalene      56480-06-9     BP-6 or FF-1    no information    Tondeur et al.
                                                             available         (1984)
                                             FF-1            25 mg/kg          O'Keefe (1979)
                                             BP-6            70 mg/kg          Hass et al.
                                                                               (1978)

         It has been shown that synthesis of hexa-bromonaphthalenes by
    direct bromination results in a mixture of two isomers (Birnbaum
    et al., 1983; Birnbaum & McKinney, 1985). The major isomer,
    1,2,3,4,6,7-HBN, can be metabolized and excreted, while the minor
    isomer, 2,3,4,5,6,7-HBN, is extremely persistent (Birnbaum &
    McKinney, 1985).

         Polybrominated benzenes and a possible methylbrominated furan
    have also been reported to occur in FireMaster(R) (Brinkman & de
    Kok, 1980).

         Approximately 20 compounds, other than PBBs, were either
    tentatively identified in FireMaster(R) or partially characterized
    by Hass et al. (1978).

         Polybromodibenzo- p-dioxins and polybromodibenzofurans were
    searched for, because of their extreme toxicity and because
    chlorinated dibenzofurans had been detected in commercial PCBs
    (Nagayama et al., 1976). If present, their concentrations did not
    exceed 0.5 mg/kg (Hass et al., 1978, O'Keefe, 1979). Polybromo
    dibenzodioxins and polybromodibenzofurans were determined in a
    sample of Adine 0102 (decabromobiphenyl). Monobromobenzo difurans
    were present at a level of 1 mg/kg (1 ppm), otherwise all other
    polybromodibenzodioxins and polybromodibenzofurans were present only
    at less than 0.01 mg/kg (Atochem, 1990).

         So far, phenoxyphenols and hydroxybiphenyls, which might be
    intermediates in the formation of brominated dibenzo- p-dioxins and
    brominated dibenzofurans, respectively, have not been identified
    (O'Keefe, 1979).

         Some impurities in PBBs result from impurities in the original
    biphenyl material. According to two major manufacturers, their
    biphenyl grade used for bromination contained less than 5 mg/kg and
    5000 mg/kg, respectively, of impurities, e.g., toluene, naphthalene,
    methylene biphenyl (fluorene), and various methyl biphenyls (Neufeld
    et al., 1977).

    2.2  Physical and chemical properties

         In general, PBBs show an unusual chemical stability and
    resistance to breakdown by acids, bases, heat, and reducing and
    oxidizing agents (Safe, 1984).

         PBBs can be compared chemically to the PCBs. Bromine, however,
    is a better leaving group in chemical reactions than chlorine.
    Unlike PCBs, the reactivity of PBBs has not been well studied and
    documented in the literature (Pomerantz et al., 1978).  Like PCBs
    their chemical stability is dependent, in part, on the degree of
    bromination and the specific substitution patterns (Safe, 1984). All
    highly brominated PBB-mixtures are known to degrade rather rapidly
    with UV irradiation (Brinkman & de Kok, 1980).

         The technical mixtures typically are white, off-white, or beige
    powdered solids. Some physical data on commercial PBB mixtures are
    given in Table 9. It can be seen that there are discrepancies in the
    values for the solubility of commercial PBBs in water (given in

    Table 9) as well as those calculated for various PBB congeners
    (Table 10). The source and quality of the water is important. 
    Determinations of water solubility of these very hydrophobic
    compounds are also difficult to perform. Adsorption effects on
    particles and glass surfaces may influence the results. PBBs were
    found to be 200 times more soluble in landfill leachate than in
    distilled water (Griffin & Chou, 1981a). In general, it can be said
    that PBBs are only slightly soluble in water and that the solubility
    decreases with increasing bromination.

         For details of thermal decomposition, see section 4.3.2.

    2.2.1  Physical and chemical properties of individual congeners

         PBBs show a wide range of volatility (Farrell, 1980). Partition
    coefficients between water/ n-hexane and water/1-octanol, as well
    as aqueous solubilities for some individual PBB congeners are given
    in Table 10. Correlations for predicting aqueous solubility and
    partition coefficients for PBBs based on molecular structure have
    been proposed (Patil, 1991). The solubility of PBBs in  n-hexane
    decreases rapidly with increasing bromine content (de Kok et al.,
    1977).

         Data on the melting points and UV absorption of individual PBB
    congeners are summarized in Table 11. The main band in these spectra
    is caused by pi -> pi* electron transitions, while the k band is
    generally attributed to the conjugated biphenyl system with the
    contribution of both biphenyl rings. With the k band, the
    introduction of bromine atoms in positions meta or para to the
    phenyl-phenyl bond induces a shift in kmax towards the visible
    region, as is illustrated by 3,3',5,5'-tetra- and 3,3',4,4',5,5'-
    hexabromobiphenyl. On the other hand, ortho substitution, which
    causes a considerable hindrance for free rotation of the rings and,
    thus, a loss in coplanarity, effects a sharp decrease in the
    extinction coefficient of the k band (de Kok et al., 1977).

         Data on NMR spectra are given by Orti et al. (1983), Robertson
    et al. (1984b), and Kubiczak et al. (1989), and on mass spectrometry
    (MS) by Erickson et al. (1980), Roboz et al. (1980), Buser (1986),
    and Sovocool et al. (1987a,b). The "ortho" effect, observed for PBBs
    and PCBs having 2,2'-; 2,2',6- or 2,2',6,6'- halogens can be
    combined with GC retention index for isomer specific identifications
    by gas chromatography and mass spectrometry (GC/MS) (Sovocool
    et al., 1987a).

    
    Table 9.  Some physical data on commercial PBB mixturesa

                                        "Hexabromobiphenyl"            "Octabromobiphenyl"      "Nonabromobiphenyl"      "Decabromobiphenyl"
                                         (Firemaster BP-6)                (Dow XN 1902)          (Bromkal 80-9D)c           (Adine 0102)d

    Melting point (°C)                          72                           200-250                  220-290                 380-386b
                                                                                                                               360-380
                                                                                                                                 385

    Lambda max (nm)                            219e                           225e                     224e                     227e

    Density (g/cm3) at                          2.6                             -                       3.2                      3.2
    room temperature

    Solubility in water                         11f                           20-30                    < 30
    (µg/litre) at 25 °C            30f (pure 2,2', 4,4', 5,5'-)
                                               610f
                                         0.06g (deionized)
                                         0.32g (distilled)                                           insoluble

    Solubility in organic
    solvents (g/kg
    solvent) at 28 °C
    petroleum ether                             20                             18               insoluble in common
    acetone                                     60                                               organic solvents
    carbon tetrachloride                        300                                                                              10e
    chloroform                                  400
    benzene                                     750                            81
    toluene                                     970
    dioxane                                    1150
    copra oil (37 °C)                                                                                                            0.8

    Table 9 (contd).

                                        "Hexabromobiphenyl"            "Octabromobiphenyl"      "Nonabromobiphenyl"      "Decabromobiphenyl"
                                         (Firemaster BP-6)                (Dow XN 1902)          (Bromkal 80-9D)c           (Adine 0102)d

    Vapour pressure (Pa)
    25 °C                                    0.000007h                                                                       < 0.000006
    90 °C                                      0.01                                                                    (temperature not given)
    140 °C                                       1
    220 °C                                      100

    Volatility (% weight loss)                                           < 1% at 250 °C           1-2% at 300 °C           < 5% at 341 °C
                                                                         < 10% at 330 °C                                   < 10% at 363 °C
                                                                         < 50% at 350 °C          < 25% at 388 °C

    log Pow                              < 7 (calculated)d                                                                8.6 (calculated)

    Decomposition temperature               300-400 °C                       435 °C                   435 °C                   395 °C
                                                                                                                              > 400° C

    a    Mumma & Wallace 1975).
    b    Norris et al. (1973).
    c    Kerscher (1979); CFK (1982).
    d    Atochem (1990).
    e    Brinkman & de Kok (1980).
    f    Filonow et al. (1976).
    g    Griffin & Chou (1981a,b).
    h    Jacobs et al. (1976).

    
    Table 10. Partition coefficients between water and n-hexane (KHW) and 1-octanol
    (Kow) and aqueous solubilities (Sw) for some individual PBB congeners (all
    aqueous solubility measurements were carried out by the generator method)

                                       Log KHW      Log KOW         Sw mol per     Sw µg/litred
                                                                   litre x 10-9       (25 °C)
                                                                     (25 °C)

    2-bromobiphenyl                                  4.59a

    3-bromobiphenyl                                  4.85a

    4-bromobiphenyl                                  4.96a            2800            650

    3,5-dibromobiphenyl                              5.78c

    4,4'-dibromobiphneyl                5.61         5.72             18.4            5.7

    2,4,6-tribromobiphenyl              6.21         6.03             41.1            16

    3,4',5-tribromobiphenyl                          6.42c

    2,2',5,5',tetrabromobiphenyl        6.72         6.50             8.6             4

    3,3',5,5'-tetrabromobiphenyl                     7.42c

    2,2',4,5,5'-pentabromobiphenyl                   7.10a            0.8b            0.4

    2,2',4,4',6,6'-hexabromobiphenyl    7.52         7.20             0.9             0.56

    decabromobiphenyl                                8.58a

    Values from Gobas et al. (1988) with the exception of:

    a    From: Doucette & Andren (1987).

    b    From: Doucette & Andren (1988).

    c    From: Sugiura et al. (1978).

    d    calculated.

    
    Table 11.  Melting points and UV spectral data for some PBB congenersa
    UV conditions: solutions in n-hexane; Beckman Acta CIII spectrometer

    No.c        PBB-isomer                   Melting point           Main band                              k band
                                               (°C)d           lambda            Log                lambda            Log
                                                               maximum         epsilon              maximum         epsilon
                                                                (nm)       (1.mol-1.cm-1)            (nm)       (1.mol-1.cm-1)

                Biphenyl                        71               201            4.66                  246            4.26
    1           2-                               e               201            4.51                  240            3.90
    2           3-                               e               205            4.60                  248            4.21
    3           4-                               e               200            4.67                  254            4.38
    4           2,2'-                           81               198            4.64                220-230            e
    9           2,5-                             e               203            4.49                  226            4.38
    15          4,4'-                           164              201            4.64                  261            4.43
    20          2,4,6-                         65-66             213            4.70                220-230            e
    21          2,2',5-                         78               200            4.66                235-245            e
    26          2,3',5-                          e               213            4.57                   e               e
    31          2,4',5-                         78               205            4.60                245-255            e
    49          2,2',4,5'-                      84               207            4.66                235-245            e
    52          2,2',5,5'-                      143              204            4.67                235-240            e
    80          3,3',5,5'-                      188              220            4.76                  255            4.18
    114b        2,3,4,4',5-                     128             222.6          (54.8)                 258              e
    137b        2,2',3,4,4',5-                  124             223.1          (35.4)                  e               e
    141b        2,2',3,4,5,5'-                  127             223.4           (191)                  e               e
    153         2,2',4,4',5,5'-             (159-160)f           216            4.66                   e               e
    156b        2,3,3',4,4',5-                  178             224.9           (229)                 259              e
    159b        2,3,3',4,5,5'-                  195             226.1          (61.4)                 258              e
    167         2,3',4,4',5,5'-             (165-166)f            e               e                    e               e

    Table 11 (contd).

    No.c        PBB-isomer                   Melting point           Main band                              k band
                                               (°C)d           lambda            Log                lambda            Log
                                                               maximum         epsilon              maximum         epsilon
                                                                (nm)       (1.mol-1.cm-1)            (nm)       (1.mol-1.cm-1)

    169         3,3',4,4',5,5'-                 248              227            4.76                  272            4.34
    180b        2,2',3,4,4',5,5'-          166(165-166)f        224.1          (62.4)                  e               e
    189b        2,3,3',4,4',5,5'-               219             230.7           (102)                 265              e
    194b        2,2',3,3',4,4',5,5'-       235(232-233)f        223.7          (51.6)                  e               e
    202         2,2',3,3',5,5',6,6'-             e               224            4.85                   e               e
    206b        2,2',3,3',4,4',5,5',6-    262(263-264)f,g       225.2           (131)                  e               e
                Nona-(unidentified)              e               225            5.18                   e               e
                Deca-                           378              227            5.11                   e               e

    a    Adapted from: de Kok et al. (1977), with the exception of the congeners marked with b.
    b    Congener data, including melting points are taken from Kubiczak et al. (1989).  UV measurements: in n-heptane.
    c    No. according to Ballschmiter & Zell (1980).
    d    Melting points from Sundström et al. (1976b) but confirmed by de Kok et al. (1977), unless otherwise stated.
    e    No data available.
    f    From: Moore & Aust (1978).

    2.3  Conversion factors for PBB in air

         1 ppm =   26.1 mg/m3 for hexabromobiphenyl at 20 °C and
                   101.3 kPa.

         1 mg/m3 = 0.038 ppm.

    2.4  Analytical methods

         Analytical methods for the determination of PBBs, which have
    been reviewed by de Kok et al. (1977), Pomerantz et al. (1978), and
    Fries (1985b), were adapted from established methods for chlorinated
    hydrocarbon insecticides and PCBs (AOAC, 1975). The chronological
    development of analytical methods for the detection and
    quantification of PBB mixtures and congeners is summarized in
    Table 12. In the wake of the Michigan disaster, methods were
    described for the analysis of: contaminated feed, milk, and milk
    products (Fehringer, 1975a,b); animal blood plasma, faeces, milk,
    and bile (Willett et al., 1978) and liver and fat (Fawkes et al.,
    1982). The methods were developed using tissue from animals fed with
    PBBs of known composition. Needham and coworkers developed a method
    to determine PBBs in human blood serum (Burse et al., 1980; Needham
    et al., 1981) which was thoroughly tested in several laboratories,
    but, even here, only the main components of FireMaster(R) were
    determined. Similarly, the investigation by Eyster et al. (1983)
    into the levels of PBBs in fat, serum, faeces, milk, and placenta
    were not isomer specific. Thus, reported values may not reflect the
    hazard of the residue because, for example, some congeners are more
    toxic than the prominent 2,2',4,4',5,5'-HBB. Most samples of
    biological origin have congener distributions that differ from those
    of the original material (Fries, 1985b).

         Concentrations of PBBs as low as 10 µg/kg in fatty foods
    (Fehringer, 1975a), 3 µg/kg in dry feeds (Fehringer, 1975b) and
    1 µg/litre in blood serum (Needham et al., 1981) can be detected and
    quantified using routine methods. Coefficients of variation become
    large as concentrations approach the limits of sensitivity of the
    method; thus, values near the limit must be treated with caution
    (Fries, 1985b). PBBs adsorb to glass more tenaciously than other
    halogenated hydrocarbons, and are not easy to remove by the usual
    cleaning methods (Willett et al., 1978). This can lead to erroneous
    values, particularly when concentrations in samples are low and
    there is a carry over from samples of high concentration. This
    problem can be solved by using disposable glassware (Willett et al.,
    1978).

    
    Table 12.  Analysis of commercial mixtures and individual PBB congeners: A chronological surveya

    Sample                Solvent                     Analytical method    Detection   Detection           Comment                  Reference
                                                                                       limit

    FireMaster(R)         recrystallization           GC                   FID         no data        identification of             Sundström
    BP-6                  from ethanol/                                                given          BB 153 and a HpBB as          et al.
                          isopropanol                                                                 major components              (1976a)

    PBB congeners         no data given               GC                   ECD         no data        routes of synthesis,          Sundström
                                                                                       given          melting points, relative      et al.
                                                                                                      retention times, electron     (1976b)
                                                                                                      capture responses for
                                                                                                      some PBB congeners

    Commercial -          solubility of               HPLC, TLC,           MS          no data        survey of analysis for        de Kok
    mixtures FR 250 13A   PBBs in n-hexane            UV, GC                           given          PBBs                          et al.
    (octabromobipheyl)    decreases rapidly with      1H- & 13C-NMR                                                                 (1977)
    FireMaster(R) BP-6    increasing bromine
    and PBB congeners     content; PBBs dissolved
                          in warm CCl4

    Commercial sample     hexane                      GC, 13C-NMR,         ECD         no data        identification of             Moore
    of                                                1H-NMR, IR                       given          BB 180                        et al.
    octabromobiphenyl                                                                                 heptabromobiphenyl            (1978)

    FireMaster(R)         methylene chloride;         GC, NMR,             MS          0.5 mg/kg      contains at least 13          Hass
    BP-6                  hexane                      HPLC                 SIM                        different PBBs and            et al.
                                                                                                      bromonaphthalene (no          (1978)
                                                                                                      bromodibenzofurans or
                                                                                                      bromodibenzo-p-dioxins
                                                                                                      found)

    Table 12 (contd).

    Sample                Solvent                Analytical method        Detection    Detection          Comment                     Reference
                                                                                       limit

    FireMaster(R)         hexane                 GC, NMR                  MS           no data       purification and                 Moore &
    FF-1 or BP-6 and                                                                   given         structural characterization      Aust
    octabromobiphenyl                                                                                of 6  further PBB congeners      (1978)

    FireMaster(R)         hexane                 GC                       ECD          0.03 ng       absolute and relative            Domino
    FF-1                                                                                             retention times of the 8         et al.
                                                                                                     major constituents using         (1980a)
                                                                                                     tetrabromobiphenyl
                                                                                                     as an internal standard

    FireMaster(R)         hexane                 GC                       MS           no data       mass spectra of major            Domino &
    FF-1                                                                               given         PBBs in FireMaster; mixed        Domino
                                                                                                     poly-bromo and                   (1980)
                                                                                                     chlorobiphenyls detected

    FireMaster(R)                                 GC                       ECD          no data       comparison of packed and         Farrel
    BP-6                                                                               given         capillary columns; solves        (1980)
                                                                                                     some problems with lower
                                                                                                     brominated biphenyls, but
                                                                                                     has no great advantages
                                                                                                     over packed columns for
                                                                                                     more highly substituted
                                                                                                     biphenyls

    FireMaster(R)         no data given          GC                       PED          2.8 mg        comparison with ECD; not         Mulligan
    BP-6                                                                               (cf 1.5 ng    quite so sensitive, but          et al.
                                                                                       ECD)          is selective                     (1980)

    Individual PBB        toluene                GC                       MS, SIM      < 1 ng        mono-deca PBB congeners          Erickson
    congeners                                                                                                                         et al.
                                                                                                                                      (1980)

    Table 12 (contd).

    Sample             Solvent               Analytical method       Detection         Detection          Comment                    Reference
                                                                                       limit

    22 individual      hexane                GC                      ECD, micro-       40 pg         retention times given           Sweetman &
    PBBs FireMaster(R)                       (preceeded              coulometric                     for 23 congeners response       Boettner
    FF-1                                     by HPLC)                GC-detector                     increases with degree of        (1982)
                                                                     MS                              bromination, increased
                                                                                                     detection temperature gives
                                                                                                     improved sensitivity

    FireMaster(R)      carbon                preparative             FID, MS                         polar and unpolar hexane        Needham
    FF-1               tetrachloride;        HPLC and                                                fractions were also             et al.
                       hexane                GC 1H-NMR                                               tested for hyperkeratotic       (1982)
                                                                                                     activity

    FireMaster(R)      hexane                GC                      NCI, SIM          0.6 ng        evaluation of halogen anion     Greaves
    BP-6                                                                                             formation by polybrominated     et al.
                                                                                                     compounds in NCI-MS; SIM of     (1982)
                                                                                                     bromine anions has greater
                                                                                                     specificity than ECD

    FireMaster(R)      fractionation by      GC                      ECD, MS           no data       seven congeners were            Dannan
    BP-6               preferential                                                    given         purified                        et al.
                       acetone                                                                                                       (1982d)
                       solubilization,
                       repeated
                       crystallization,
                       alumina
                       adsorption
                       column
                       chromatography,
                       reversed phase
                       Lipidex-500

    Table 12 (contd).

    Sample             Solvent               Analytical method       Detection         Detection          Comment                    Reference
                                                                                       limit

    FireMaster(R)      see Needham et al.    preparative             FID, MS                         at least 60 components          Orti
    FF-1               (1982)                HPLC, GC,                                               observed; isolated/             et al.
    lot FH 7042                              GC 1H-NMR                                               determined structure of         (1983)
                                                                                                     10 minor components of
                                                                                                     FireMaster (most are very
                                                                                                     polar, later eluting
                                                                                                     fractions)

    PBB                hexane                GC                      helium            230 pg        simultaneous monitoring         Eckhoff
    (unspecified)                                                    plasma                          of 4 atomic emission            et al.
                                                                     atomic                          wave-lengths; PBB mentioned     (1983)
                                                                     emission
                                                                     spectrometric
                                                                     detection

    FireMaster(R)      no data given         GC                      MS, ECD                         identity of over 91% of         Robertson
    BP-6                                     1H-NMR                                                  PBB components in               et al.
                                                                                                     FireMaster using 22             (1984b)
                                                                                                     individual PBB congeners
                                                                                                     as standards; identification
                                                                                                     of 7 additional PBBs
                                                                                                     including 3 very toxic
                                                                                                     coplanar PBBs

    FireMaster(R)      hexane                GC                      PED, rapid                      multi-element quantification    Zerezghi
    BP-6                                                             scanning                                                        et al.
                                                                     plasma                                                          (1984)
                                                                     emission

    Table 12 (contd).

    Sample             Solvent                 Analytical method    Detection        Detection           Comment                     Reference
                                                                                     limit

    FireMaster(R)      hexane                  GC                   SIM, MS                         determination of suspected       Tondeur
    FF-1                                                                                            toxic impurities                 et al.
                                                                                                                                     (1984)

    PBB photolysis     hexane                  GC                   FID, ECD,                       purification of PBB congener     Barnhart
    mixture                                                         MS                              2 using charcoal pretreatment    et al.
                                                                                                    and RPLC                         (1984)

    Benzenes,          hexane                  GC                   NCI-MS           0.1 pg         especially valuable for          Buser
    biphenyls                                                                                       measuring trace levels in        (1986)
    dibenzodioxins,                                                                                 biological and environmental
    dibenzofurans,                                                                                  samples; must be two Br;
    diphenylethers,                                                                                 structural information is
    benzofurans,                                                                                    partly lost
    phenols

    PBB congeners      no data given           GC                   MS               no data        use of 'ortho' effect for        Sovocool
                                                                                     given          PBB and isomer                   & Wilson
                                                                                                    identification; accurate         (1982);
                                                                                                    structure assignments            Sovocool
                                                                                                    without use of multiple GC       (1987a)
                                                                                                    determinations

    Various PBB        hexane                  GC, HPLC             FID              no data        relationship between             Höfler
    congeners                                                                        given          recorded retention data          et al.
                                                                                                    from HPLC and GC and             (1988)
                                                                                                    molecular surface area

    Table 12 (contd).

    Sample             Solvent               Analytical method       Detection       Detection            Comment                    Reference
                                                                                     limit

    Nine synthetic     products purified     GC                      MS              1 ng           synthesis of 2,3,4,5-            Kubiczak
    PBBs;              by alumina/Florisil;                                                         substituted PBBs and             et al.
    FireMaster(R)      recrystallization                                                            characterization                 (1989)
    FF-1 and BP-6      from methanol or
                       methylene chloride

    Mono- and          no data given         1H-NMR,                 no data         no data                                         Anklam
    poly-brominated                          13C-NMR                 given           given                                           (1989)
    biphenyls

    a    Abbreviations used:

    ECD  = Pulsed 63Ni electron capture detector.          NMR       = Nuclear magnetic resonance.
    FID  = Flame ionization detector.                      PED       = Microwave-induced plasma emission detector.
    GC   = Gas chromatography.                             PPINICI   = Pulsed positive ion-negative ion chemical ionization.
    GPC  = Gel permeation chromatography.                  RPLC      = Reverse-phase liquid chromatography.
    HPLC = High pressure liquid chromatography.            SIM       = Selected ion monitoring.
    IR   = Infrared radiation.                             TLC       = Thin layer chromatograpy.
    MS   = Mass spectrometry.                              Unitrex   = Universal Trace Residue Extractor.
    NAA  = Neutron activation analysis.                    UV        = Ultraviolet.
    NCI  = Negative ion chemical ionization mass
           spectrometry.

         Recovery of PBBs using established methods is in the range of
    80-90% (Fries, 1985b). The solvent system that is used for sample
    extraction can affect recovery. Poor recoveries were often found
    with hexane but the optimal solvent conditions depend on the source
    of the medium sample.

         For extraction conditions see Table 13 (environmental samples),
    Table 14 (food/feed), Table 15 (biological tissues and fluids (a)
    serum/blood (b) adipose and other tissues).

         In soil, Griffin & Chou (1981a) found that a polar organic
    solvent was important and obtained the best results with
    hexane/acetone (9:1).

         For serum and blood, the standard extraction method given by
    Burse et al. (1980) has been used by most workers.

         Extraction of PBBs from adipose and other tissues presents
    greater problems. PBBs are readily soluble in fat. They can
    therefore be extracted with the fat out of the tissue/sample but,
    afterwards, an intensive clean-up procedure for PBBs is necessary. 
    Various methods, such as adsorption chromatography with Florisil,
    gel permeation chromatography, Florisil cartridges (Chiang et al.,
    1987), and Unitrex (Head & Burse, 1987) have been proposed.

         The sample extraction and clean-up techniques for the
    determination of PBBs are similar to those used for PCBs (Krüger
    et al., 1988; Jansson et al., 1991). The lipids can be removed from
    the extract by gel permeation (Krüger, 1988) or by hydrolysis
    (Jansson et al., 1991). Usually PBBs and PCBs are separated from
    more polar compounds by adsorption chromatography on silica gel or
    Florisil. If the coplanar compounds are to be determined, they have
    to be isolated from the major compounds in the extract. This can be
    done using activated charcoal, which adsorbs the planar molecules
    more strongly than the non-planar. Brominated naphthalenes, dioxins,
    and furans will also be separated from the major PBB components in
    this step. HPLC methods are now being adopted for these separations
    and both charcoal and modified silica gel columns are available for
    HPLC separations of coplanar compounds.

    
    Table 13.  Determination of PBBs in environmental samplesa

    Matrix             Extraction     Clean up     Analytical    Detection      Detection limit         Comment                    References
                                                   method

    Soil, grass,       benzene/       Florisil     GC            ECD, FID       0.1 µg/kg               BB 153, two PeBB           Jacobs
    carrots            2-propanol                                MS             dry weight (soil)       isomers, three             et al.
                                                                 13C-NMR        10 µg/kg                additional HxBB            (1976)
                                                                                wet weight (plant)      isomers, two HpBB
                                                                                                        isomers detected

    Soil leachate      benzene/                    GC            ECD            0.1 µg/kg               laboratory experiments     Filonow
                       2-propanol                                               dry weight                                         et al.
                                                                                                                                   (1976)

    Soil, plant        hexane/        Florisil     GC            ECD            0.1 µg/kg               field and laboratory       Jacobs
    samples            acetone                                                  dry weight (soil)       experiments; no            et al.
                                                   TLC           ECD            0.3 µg/kg               significant                (1978)
                                                                                wet weight (plant)      degradation of PBBs
                                                                                                        after 1 year

    Effluent river     hexane/        no data      GC            ECD            0.1 µg/litre            environmental              Hesse (1975)
    water              diethyl        given                                     (later 0.01 µg/         samples                    Hesse &
                       ether                                                    litre)                                             Powers
                                                                                                                                   (1978)

    Sediment           hexane/        no data      GC            ECD            100 µg/kg               environmental              Hesse &
                       acetone        given                                                             samples                    Powers
                                                                                                                                   (1978)

    Soil               hexane/        no data      GC            ECD, FID,                              separation of 30 PBB       Stratton &
                       acetone 9:1    given                      MS                                     congeners tested           Whitlock
                                                                                                        optimum conditions         (1979)

    Table 13 (contd).

    Matrix             Extraction     Clean up     Analytical    Detection      Detection limit         Comment                    References
                                                   method

                                                                                                        for extraction of
                                                                                                        PBBs from soil;
                                                                                                        polar organic solvent
                                                                                                        important

    98 environmental   hexane,        Florisil     GC            MS             0.2 µg/kg               analysed for hexa-,        Stratton
    samples            Soxhlet                                                                          hepta-, octa-, nona-,      et al.
    (fish, sediment,                                                                                    decabromobiphenyls;        (1979)
    soils,                                                                                              HxBB in 84% of samples
    vegetation)

    Soil, sediment,    hexane         Florisil     GC            MS (SIM)       0.2 µg/kg               congeners detected         Griffin &
    sludge,                                                                                                                        Chou (1981a)
    vegetation

    Soil               hexane/        Florisil     GC            FID, ECD                               degradation of PBBs        Hill et al.
                       acetone 1:1                                                                      in soil                    (1982)

    Sewage sludge      hexane/                     TLC           IR, NMR, MS    10 ng/kg                no PBBs found              Strachan
                       methanol                    GC                                                                              et al.
                       Soxhlet                                                                                                     (1983)
                       extraction

    Plants             cut,           Florisil     GC            ECD            0.3 µg/kg               no translocation           Chou et al.
                       extracted                                                wet basis               in plants                  (1978)
                       with hexane/
                       acetone

    Table 13 (contd).

    a      Abbreviations used:

    ECD    = Pulsed 63Ni electron capture detector.   MS     = Mass spectrometry.
    FID    = Flame ionization detector.               NMR    = Nuclear magnetic resonance.
    GC     = Gas chromatography.                      SIM    = Selected ion monitoring.
    IR     = Infrared radiation.                      TLC    = Thin layer chromatography.

    Table 14.  Determination of PBBs in food/feeda

    Matrix         Extraction                 Clean up              Analytical            Detection    Detection     Comment        References
                   method                     limit

    Dairy          fat extracted by AOAC      GPC, 25% toluene      GC                    ECD          7 µg/kg       comparison     Fehringer
    products       (1975) methods             in ethyl acetate                                                       of methods     (1975a)
                   (methanol/ether)

                                              Florisil/pet ether    TLC                                0.2 mg/kg

    Dry animal     finely ground feed         Florisil/pet ether    GC, TLC               ECD          8 µg/kg       hexabromo      Fehringer
    feeds          packed into a column                                                                30 µg/kg      isomer         (1975b)
                   containing celite,                                                                                measured
                   elution with methylene
                   chloride

    Feeds and      see Fehringer                                    GC before and         ECD          5 µg/kg       confirmation   Erney
    dairy          (1975a,b)                                        after UV irradi-                                 of PBB         (1975)
    products                                                        ation to determine                               residues
                                                                    background                                       using UV
                                                                                                                     irradiation

    a    Abbreviations used:

    ECD    = Pulsed 63Ni electron capture detector.    TLC   = Thin layer chromatography.
    GC     = Gas chromatography.                       UV    = Ultraviolet.
    GPC    = Gel permeation chromatography.

    Table 15.  Determination of PBBs in biological tissues and fluidsa

    Matrix             Extraction                  Clean up        Detection    Detection limit    Comment                       References

    a) Serum/blood

    Human serum        methanol-treated serum,     Florisil        ECD          5 pg               analysis based on HxBB        Bekesi et al.
                       extraction with hexane                                                      peak                          (1978)

    Human serum        methanol-treated serum,     Florisil        ECD          0.2 µg/litre                                     Wolff et al.
                       extraction with hexane/                                                                                   (1978)
                       ether

    Human/rat serum    methanol-treated serum,     Florisil        ECD          0.2 µg/litre       PBB homologues as % HxBB      Wolff &
                       extraction with hexane/                                                     peak                          Aubrey
                       ether                                                                                                     (1978)

                       methanol-treated serum,     Florisil        ECD, MS      < 1 mg/ml                                        Wolff et al.
                       extraction with hexane/                                                                                   (1979a)
                       ether

    Plasma from        multiple extraction with    Florisil        ECD          0.001 µg/litre     recovery 96%                  Willett
    PBB-fed cows       mixture of diethyl and pet.                                                                               et al.
                       ethers                                                                                                    (1978)

    Human serum        methanol-treated serum;     Florisil        ECD          0.1 µg/litre       interlaboratory comparison    Burse et al.
                       extraction with hexane/                                                                                   (1980)
                       ether

    Table 15 (contd).

    Matrix             Extraction                  Clean up        Detection    Detection limit    Comment                       References

    Plasma, white      methanol; precipitated      Florisil        MS-SIM       0.1 µg/mg          very exact details with       Roboz et al.
    cell fraction      protein removed;            NCI             protein      review             spectra                       (1980)
    erythrocytes       extraction with hexane/
    ß-lipoprotein      ether (1:1)

    Human serum        methanol; hexane/           silica gel      ECD          1 µg/litre                                       Needham
                       diethylether (1:1)                                                                                        et al.
                                                                                                                                 (1981)

    Human serum        + methanol precipitated     Florisil        ECD          < 1 µg/litre       serum protein precipitated    Roboz et al.
                       protein not removed +                       MS-NCI                          with methanol should not      (1982)
                       hexane/diethylether (1:1)                                                   be removed from sample

    Human serum        see Burse et al. (1980)                     ECD          1 µg/litre                                       Eyster
                                                                                                                                 et al.
                                                                                                                                 (1983)

    Blood (in vitro    see Roboz et al. (1982)                     MS-                             in vitro                      Roboz et al.
    experimental)                                                  (PPINCI)                                                      (1985a)

    Human blood        see Roboz et al. (1982)                     ECD, SIM,    10-35 ng           distribution of PBBs          Roboz et al.
    (model and                                                     NCI          individual         among blood components        (1985b)
    environmentally                                                             serum              congener/litre
    exposed)

    b) Adipose and other tissues

    Adipose tissue     toluene/ethyl acetate       GPC (Bio        ECD          0.5 µg/kg          major HxBB peak determined    Wolff et al.
    from exposed       (1+3)                       Beads                                                                         (1979a)
    workers                                        toluene/ethyl
                                                   acetate (1+3)

    Table 15 (contd).

    Matrix             Extraction                  Clean up        Detection    Detection limit    Comment                       References

    Various rat        Burse et al. (1980)                         ECD          10 µg/kg           comparison of                 Miceli &
    tissues and                                                                                    concentrations of PBBs        Marks
    serum                                                                                          in various tissues with       (1981)
                                                                                                   time

    Liver and          1) hexane (liver and        1) Florisil     ECD, NAA                        comparison of extraction      Fawkes et al.
    perirenal          adipose)                                                                    methods (showed PBB           (1982)
    adipose tissue                                                                                 extraction with hexane
    from dosed rats                                                                                leads to erratic recoveries
                                                                                                   and results) increase in
                                                                                                   detection limits over
                                                                                                   ECD ( 2 pg FireMaster);
                       2) chloroform:              2) acidic                                       1 µg/litre or less of
                       methanol (liver)            alumina                                         hexa congener)

                       3) methylene chloride
                       chloroform (adipose)

    Human adipose      15% diethyl ether           Florisil/GPC    ECD                             GPC clean-up tested (85%      MacLeod
    tissue             in hexane                                   MS                              recovery); MS free of         et al.
                                                                                                   serious interference          (1982)
                                                                                                   from 46 to 500 m/z

    Adipose tissue     6% diethyl ether            Florisil/GPC    MS           1-2 µg/kg          HxBB peak                     Lewis &
    from general       in hexane                                                                                                 Sovocool
    population                                                                                                                   (1982)

    Human adipose      hexane/diethylether         silica gel      ECD          1 µg/kg                                          Eyster
    tissue, placenta,                                                                                                            et al.
    cord blood,                                                                                                                  (1983)
    biliary fluid,
    faeces

    Table 15 (contd).

    Matrix             Extraction                  Clean up        Detection    Detection limit    Comment                       References

    Human postmortem                               Chromaflex      ECD          0.5 µg/kg          HxBB peak                     Miceli
    tissue                                         adsorption                                                                    et al.
                                                   column with                                                                   (1985)
                                                   5% silica
                                                   gel + sodium
                                                   sulfate/
                                                   hexane

    Adipose tissue     hexane                      solid phase     ECD                             1-14 ng/kg Florisil           Chiang et al.
    (bovine), spiked   Florisil cartridges                                                         cartridges to separate        (1987)
    for model system                                                                               fat; 116% recovery

    c)  Milk

    Human milk         potassium oxalate,                          ECD          1 µg/kg                                          Eyster et al.
                       ethanol/diethyl ether;                                                                                    (1983)
                       hexane

    Human milk         potassium oxalate,          Bio Beads/      MS (NCI,     1 ng/kg            separation of coplanar        Krüger (1988)
                       ethanol/diethyl ether       Florisil/       SIM)                            and planar isomers with
                                                   activated                                       charcoal
                                                   charcoal

    d)  Biological samples from the environment

    Fish, seal         freeze, pulverize,          Bio Beads/      MS (NCI,     10 ng/kg                                         Krüger (1988)
                       pet. ether                  Florisil/       SIM)
                                                   activated
                                                   charcoal

    Table 15 (contd).

    Matrix             Extraction                  Clean up        Detection    Detection limit    Comment                       References

    Dolphin fat/       Soxhlet; hexane,            GPC; silica     MS           no data given      lowest value given:           Kuehl et al.
    organ tissue       methylene chloride          gel                                             40 µg/kg                      (1991)

    Terrestrial,       diethyl ether/hexane        hydrolysis      MS (NCI)     no data given      lowest value given:           Jansson
    freshwater and                                 with 98%                                        40 ng/kg                      et al.
    marine samples                                 H2SO4/Bio                                                                     (1991, 1992)
                                                   Beads/ silica
                                                   gel/activated
                                                   charcoal

    a    Analytical method used was gas chromatography.
         Abbreviations used:

         ECD    = Pulsed 63Ni electron capture detector.     NCI        = Negative ion chemical ionization mass spectrometry.
         GPC    = Gel permeation chromatography.             PPINICI    = Pulsed positive ion-negative ion chemical ionization.
         MS     = Mass spectrometry.                         SIM        = Selected ion monitoring.
         NAA    = Neutron activation analysis.

         Using negative ion chemical ionization mass spectrometry
    (MS-NCI), the bromide ions can be used to detect brominated
    compounds with high sensitivity and selectivity. However, using this
    detection method (or ECD), interference between congeners of PBB and
    polybrominated diphenyl ethers is possible.

         The 209 possible PBB congeners have a wide range of volatility,
    which causes very difficult separation problems (Farrell, 1980). In
    earlier studies, gas chromatography (GC) with packed columns, e.g.,
    3% OV-1 on 80/100 mesh Chromosorb W(HP) was used (Fehringer,
    1975a,b). Capillary columns enable a good separation with lower
    brominated biphenyls but do not have any great advantages over
    packed columns for more highly substituted biphenyls (Farrell, 1980;
    Orti et al., 1983; Robertson et al., 1984b).

         The detection method most frequently used is that of pulsed
    63Ni electron capture detection (ECD). In general, retention times
    and electron capture responses increase with increasing bromination.
    This is a sensitive method, but has some shortcomings. ECD is a
    group selective detector that responds to halogens and other
    electronegative groups. This places stringent requirements on
    chromatographic separation. Moreover, ECD responds differently to
    different compounds, depending on the molecular structure. The
    response or sensitivity of the ECD depends on the position of the
    halogen on the biphenyl nucleus as well as the number of halogens.
    This necessitates running a standard for each compound to be
    determined (Zerezghi et al., 1984). Sweetman & Boettner (1982)
    analysed the structure-sensitivity of PBBs using ECD (see Table 12).

         Flame ionisation detection (FID) can only be used for the
    analysis of standard substances because of its low specificity
    (Krüger, 1988).

         A microwave-induced plasma emission detector has been used as a
    specific method of detection for bromine (Mulligan et al., 1980;
    Zerezghi et al., 1984). However, the method is not sensitive enough
    for environmental samples.

         Some authors have confirmed their results by GC/ECD
    determination before, and after, exposure to UVR. The PBBs present
    are photolyzed and, in this way, the background values can be
    eliminated (Erney, 1975; Trotter, 1977).

         Very often, the presence of PBBs is confirmed using mass
    spectrometry (MS) together with gas chromatography. The purity of
    the sample can be verified by comparison with known standards.
    Negative chemical ionization (NCI) mass spectrometry has a

    sensitivity comparable with, and somewhat better than, GC/ECD
    analysis. The detection level for hexabromobiphenyl standards is
    lower by a factor of 20 to 10-35 ng/ml in comparison with GC/ECD
    analyses (Roboz et al., 1982). This relatively new method has also
    been used to detect polychlorinated and polybrominated dioxins and
    furans (see section 4.3).

    3.  SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

    3.1  Natural occurrence

         PBBs are not known to occur naturally.

    3.2  Man-made sources

    3.2.1  Production levels and processes

    3.2.1.1  World production figures

    1) United States of America

         The commercial production of PBBs in the USA commenced in 1970
    (Neufeld et al., 1977). Several US producers of commercial
    quantities have been identified (Mumma & Wallace, 1975; Neufeld
    et al., 1977; Di Carlo et al., 1978; Brinkman & de Kok, 1980).

         In 1976, a US firm had a combined production of about 0.45
    million kg of PBBs for export to Europe (Anon., 1977).

         A list of suppliers of laboratory quantities (with a maximum
    production or importation of about 2 kg/year) is presented by Mumma
    & Wallace (1975) and Neufeld et al. (1977).

         As a result of the Michigan catastrophe of mid-1973, the sole
    US manufacturer of hexabromobiphenyl ceased production in November
    1974. It is not clear, whether the production of bromine-based fire
    retardants was resumed by another US company in 1978 (Brinkman & de
    Kok, 1980). Two other companies continued their production of octa-
    and deca-PBB until 1977 (Di Carlo et al., 1978). According to the
    German "Umweltbundesamt" (UBA, 1989), decabromobiphenyl was produced
    in the USA until 1979.

         There are repeated statements that all PBBs manufactured in the
    USA since 1975-76 have been exported, mainly to Europe, and that
    there is no importation of any PBB mixtures into the USA (Brinkman &
    de Kok, 1980).

         Relevant production data for the period 1970-76 are presented
    in Table 16.

    
    Table 16.  Commercial production of polybrominated biphenyls in the USA, 1970-76a

                                                      Estimated production in thousand kg
                                                                                                                
    Product                     1970       1971       1972      1973      1974       1975      1976      1970-76

    Hexabromobiphenyl            9.5       84.2      1011       1770      2221        0          0        5369

    Octabromobiphenyl           14.1       14.1        14.6      163        48       77.3      366         702
    and decabromobiphenylb

    Total PBBs                  23.6       98.3      1025       1933      2269       77.3      366        6071

    a    From: Di Carlo et al. (1978).
    b    Manufacture was continued in 1977, but production figures are not available.

         Hexabrominated biphenyl forms the major part (about
    5.4 million kg FireMaster(R) BP-6 plus some 68 300 kg
    FireMaster(R) FF-1) of the estimated total production of
    6.1 million kg (Neufeld et al., 1977). The remaining 0.7 million kg
    are accounted for by the higher brominated biphenyls. In 1976, for
    example, 0.35 million kg of decabromobiphenyl and 13 600 kg of
    octabromobiphenyl were manufactured (Neufeld et al., 1977). No
    production figures are available for 1977 (Di Carlo et al., 1978).

    2) Japan

         According to IARC (1978), PBBs have never been produced in
    Japan, but, up to 1978, some were imported.

    3) Europe

         a) Germany

         A German firm produced a mixture of highly brominated PBBs,
    called Bromkal 80-9D until mid-1985, when the activities concerning
    bromine-based fire retardants were shifted to the USA. No production
    figures are available.

         b) France

         A French firm manufactures a technical-grade decabromobiphenyl,
    sold as Adine 0102, production being a few hundred thousand kg/year
    (Atochem, 1988). It is marketed in France, Great Britain, Spain and
    the Netherlands (Atochem, 1988; UBA, 1989). More than 200 tonnes
    decabromobiphenyl/year were used in the Netherlands for
    incorporation into polybutylenterephthalate plastics (UBA, 1989).

         c) United Kingdom

         Two companies are reported to have marketed or produced
    technical-grade decabromobiphenyl in the United Kingdom (Brinkman &
    de Kok, 1980). In 1977, the production of PBBs was discontinued
    (Neufeld et al., 1977).

         No production or sales data are available.

         d) Netherlands

         No domestic producer has been identified. An Israeli company
    with two bromine plants in Holland denied the production of PBBs
    (Neufeld et al., 1977). However, the amount of decabromobi phenyl
    sold annually in the Netherlands was estimated to be of the order of
    91 000 kg (Brinkman & de Kok, 1980).

         No information is available on production in other parts of the
    world.

    3.2.1.2  Manufacturing processes

         The process of manufacturing PBBs consists of a Friedel-Crafts
    type reaction in which biphenyl is reacted with bromine in the
    presence of chloride in an organic solvent, using aluminium
    chloride, aluminium bromide, or iron as catalyst (Brinkman & de Kok,
    1980). In the Atochem decabromobiphenyl manufacturing process,
    biphenyl is directly brominated in a large excess of bromine, used
    as reactant and solvent in the presence of a Lewis acid catalyst
    (aluminium type). Decabromobiphenyl is further purified by
    distillation of the excess bromine in the presence of a brominated
    solvent (Atochem, 1992).

    3.2.1.3  Loss into the environment during normal production

         Data are published only for the USA. The following information
    refers to reviews by Neufeld et al. (1977) and Di Carlo et al.
    (1978).

         Losses of PBBs to the environment at sites of its manufacture
    can total 51 kg/1000 kg of product. These losses occur through:

         1)  Emission into the air

         In 1977, the maximum air losses as particulate matter at
    production sites were estimated to total 1.1 kg of PBBs/1000 kg
    manufactured.

    (a)  Emission to the air from the vents of the hydrogen bromide 
         recovery system:

         Total emission of FireMaster(R) PB-6 was estimated to amount 
         to 70 mg/1000 kg produced.

    (b)  Loss of particulate PBB to the atmosphere during centrifugation
         (which was carried out to separate the solid reaction products
         from the organic solvent).

         A New Jersey permit application by Hexcel Corp. plant (1976)
         indicated a loss of less than 0.05% of the product.

    (c)  Loss of dust from drying and pulverizing PBBs to a fine powder
         (dust from this operation was removed by a bag type filter).

         In 1974, atmospheric levels of PB-6 in the Michigan Chemical
    Corp. bagger area were 16-32 mg/m3 during the bagging operation
    and 3 mg/m3 after bagging was completed. Lower levels were
    detected in other areas of the plant.

    (d)  Emission of hexabromobiphenyl as a vapour contaminant in 
         vapour streams leaving scrubbers or equivalent equipment was 
         calculated to be less than 25 µg/m3 (1 ppb) at ambient 
         temperature (Neufeld et al., 1977).

         2)  Losses in waste waters resulting from the quenching and
    washing of the PBBs as they are recovered from the reaction mass:

         The losses of PBBs to sewers at manufacturing sites were
    estimated, in 1977, to be 4.6 µg/kg of product.

    -    In 1972, samples of the Michigan Chemical Corp. effluent 
         discharges were found to contain PBB levels of 98-503 µg/litre 
         (Hesse, 1975);

    -    The total quantity of PBBs being discharged to the Pine River 
         was estimated as 0.11 kg daily.

    -    Unfiltered water from an industrial storm sewer at the Hexcel
         Corp. plant contained 92 µg/litre, mainly as decabromobiphenyl
         (hexa-, octa-, and nonabromobiphenyls levels were also 
         measurable).

    -    Liquid effluents, diluted by canal water, from the White 
         Chemical Co. plant showed values of up to 31 µg PBBs/litre.

         3)  Solid losses to landfills resulting from drying, handling,
    shipping and transportation.

         An estimate of PBB losses as solid waste to landfills was
    50 g/kg of product.

         According to a report of the Michigan Chemical Corp., their
    solid waste included approximately 5% of the BP-6 produced.

         4)  Losses to the soil

         Soil samples from the bagging and loading areas of the Michigan
    Chemical corp. contained PBBs at concentrations of 3500 and
    2500 mg/kg, respectively.

         Losses of other compounds:

         The following typical air contaminants released during PBB-
    manufacture were reported: hydrogen chloride, bromine, ethylene
    dichloride, aluminium chloride, and biphenyls. The total quantity
    emitted was stated to be less than 5.5 kg/day.

    3.2.1.4  Methods of transport, accidental release, and disposal of
             production wastes

         Details of present-day labelling and transport regulations are
    given in the Health and Safety Guide for PBBs (WHO, 1993).

         In 1973, an accidental release of PBBs occurred in Michigan
    ("Michigan disaster"), when two products manufactured by the
    Michigan Chemical Company were inadvertently confused, i.e., 
    250-500 kg (Di Carlo et al., 1978) of FireMaster(R), instead of
    NutriMaster(R), a magnesium oxide-based cattle feed supplement,
    were added to animal feed and distributed to farms within the state.
    The compound is believed to have been FireMaster(R) FF-1
    (e.g., Fries, 1985b), even if in some publications the name
    FireMaster(R) BP-6 is used (e.g., Neufeld et al., 1977; Di Carlo
    et al., 1978). This accidental mix up resulted in widespread
    contamination by PBBs (see section 5). As a result of this incident,
    the production of FireMaster(R) BP-6 by Michigan Chemical Corp.
    was stopped in 1974 (Di Carlo et al., 1978).  Chronological reports
    or reviews of the PBB disaster are given by Carter (1976), Getty
    et al. (1977), Kay (1977), Di Carlo et al. (1978), Damstra et al.
    (1982), Zabik (1982), and Fries (1985b).

         Details of the disposal of manufacturing waste during present
    production are not available. In a report by Neufeld et al. (1977),
    solids from manufacturing operations were disposed of in landfills. 
    Waste waters containing small amounts of PBBs were discharged into
    the chemical sewer.

    3.2.2  Uses

         Commercially manufactured PBBs are processed by industrial
    users, primarily as flame retardants in polymeric materials. PBBs
    were developed for this major application, because: they are able to
    meet the flame-resistance performance requirements, they are
    economically feasible, and they have little effect on the
    flexibility of the base compounds (Mumma & Wallace, 1975).

         The process of application is basically one of physical
    blending: the PBBs are not functional additives, and on blending
    with the dry solid or liquid polymeric material, provide filter-type
    flame retardant action with the chemical release of hydrogen bromide
    if ignited (Neufeld et al., 1977).

         Neufeld et al. (1977) list 34 applications of PBBs found in
    patent and technical literature. The majority are related to the use
    of the PBBs as flame retardants in polymeric materials, other claims
    include self-extinguishing properties and improved wearability and
    machinability. Further potential uses of PBBs are: in the synthesis
    of biphenyl esters or in a modified Wurtz-Fittig-synthesis; in

    light sensitive compositions to act as colour activators; as
    relative molecular mass control agents for polybutadiene; as wood
    preservatives; as voltage stabilizing agents in electrical
    insulation; as functional fluids, such as dielectric media (Neufeld
    et al., 1977). In the USA and Canada, hexabromobiphenyl
    (FireMaster(R)) was the principal PBB product. It was used as a
    fire retardant in three main commercial products:
    acrylonitrile-butadiene-styrene (ABS) plastics; coatings and
    lacquers; and polyurethane foam (Neufeld et al., 1977).

         The types of ABS plastic products in which FireMaster(R) BP-6
    was used are compiled in Table 17.

         According to Neufeld et al. (1977), the use of FireMaster(R)
    BP-6 as a flame retardant in thermoplastic resins was confined to
    products that do not come into contact with food or feed and are not
    used in fabrics to which humans are exposed.

         Although more than 130 companies in the USA used PBBs prior to
    1976 (Di Carlo et al., 1978), only a limited number seems to have
    been the major users of PBBs. For example, in 1974, the final year
    of US production, Borg Warner Corp. (Parkersburg, W.Va.; using
    FireMaster(R) in ABS plastics) and Standard T Chemical Co. (Staten
    Island, New York; using FireMaster(R) in fire retardant coatings
    for industry) consumed over 50% of the total US yearly production
    (Mumma & Wallace, 1975; Jamieson, 1977; Neufeld et al., 1977;
    Brinkman & de Kok, 1980).

         Of the estimated 2200 tonnes hexabromobiphenyl produced in 1974
    (IARC, 1978), about 900 tonnes (Mumma & Wallace, 1975; Neufeld
    et al., 1977; IARC, 1978) were used in ABS plastic products and
    about 34 000 tonnes (Mumma & Wallace, 1975; Neufeld et al., 1977;
    IARC, 1978) in cable coatings.

         The exact quantity of FireMaster(R) used in polyurethane foam
    for automobile upholstery was not published. The two larger
    consumers ceased using hexabromobiphenyl (one of these in 1972)
    because PBBs did not decompose in the ultimate incineration of
    scrapped automobiles (Neufeld et al., 1977).

         No current users of hexabromobiphenyl have been identified
    (Neufeld et al., 1977; Di Carlo et al., 1978; Brinkman & de Kok,
    1980). As regards octa- and decabromobiphenyl, no commercial use was
    reported in the USA during 1970-74 (Neufeld et al., 1977). In
    Western Europe, the use of higher brominated PBBs seems to be
    dominant. The decabromobiphenyl Adine 0102(R) (in the past
    manufactured by Ugine Kuhlmann, at present by Atochem) is used as a
    flame retardant for thermoplastics and thermosets (e.g., in
    polyesters, epoxy resins, polystyrene, ABS, polyolefines, and PVC),

    for elastomers (e.g., in PU-elastomers and india rubber) and for
    cellulosics (e.g., chip-board). It is applied frequently in
    association with antimony trioxide (Sb2O3) (Atochem, 1984a). Its use
    in paints and varnishes has also been reported (Brinkman & de Kok,
    1980).

    Table 17.  Uses of FireMaster(R) BP-6 in ABS plastics in the USAa

    Industry                    Approximate %      Examples
                                of total use

    Business machines and           48             Typewriter, calculator and microfilm-reader
    industrial equipment                           housings; business machine housings

    Electrical                      35             Radio and TV parts, thermostats, shaver and
                                                   hand-tool housings

    Fabricated products             12             Projector housings, movie equipment cases

    Transportation                   1             Miscellaneous small automotive parts;
                                                   electrical-wire connectors, switch
                                                   connectors, speaker grills

    Miscellaneous                    4             Small parts for electrical applications,
                                                   motor housings; components for industrial
                                                   equipment

    a    From: Brinkman & de Kok (1980).
    
         Losses of PBBs to the environment from processing plants are
    possible, but little information is available about this.

         Although decabromobiphenyl and, possibly, other PBBs are still
    produced commercially, alternative chemicals have been introduced to
    replace them as flame retardants, in particular polybrominated
    biphenyl ethers (oxides) (PBBO), e.g., decabromobiphenyl ether
    (Adine 505; Bromkal 82-0 DE; Great Lakes DE-83TM and DE 83RTM),
    octabromobiphenyl ether (Bromkal 79-8 DE; Great Lakes DE 79), and
    pentabromobiphenyl ether (Bromkal 70-5 DE; Great Lakes DE-71TM:
    Atochem, 1984b; Great Lakes Chemical Corp., 1986).

         Decabromobiphenyl ether (DBBO) for example, appears to be a
    much less toxic material than PBBs. However, DBBO is said to have a
    tendency to degrade to lower brominated biphenyl oxides. It is
    possible that these lower order compounds may pose environmental
    problems similar to those of the lower brominated PBBs (Mumma &
    Wallace, 1975). In addition, on pyrolysis, PBBOs produce larger
    amounts of dioxins and furans than PBBs and so may themselves have
    to be replaced by other compounds.

    4.  ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION

    4.1  Transport and distribution between media

    4.1.1  Air

         The commercial PBB-mixtures are solids at room temperature. 
    Despite their low vapour pressure, air pollution by PBBs can occur
    as follows:

         PBBs may be released into the atmosphere as vapour or dust 
    from production and processing plants. Stratton & Whitlock (1979)
    found indirect evidence of airborne discharges of PBBs near two out
    of three chosen industrial sites in north-eastern New Jersey and
    Staten Island, New York, where these materials had been manufactured
    or used in product formulations.

         Further air contamination may occur during the incineration of
    industrial and municipal wastes. Most municipal incinerators are not
    very effective in destroying halogenated biphenyls. Like PCBs, PBBs
    do not burn readily and incinerating conditions must be carefully
    controlled, otherwise these compounds will reenter the environment
    in the stack gases (Griffin & Chou, 1981a) or may be transformed to
    polybro minated dibenzofurans.

         Flameless combustion of the consumer products causes
    volatilization of intact PBBs (Benbow & Cullis, 1975).

         An appreciable loss of PBBs during the lifetime of PBB-
    containing products is unlikely.

         Secondary ways of entrance of PBBs into the atmosphere, e.g.,
    through evaporation from contaminated soils, are thought to be
    negligible, though small losses of PBBs from soil during long-term
    (6 months) incubation studies were observed, which were associated
    with volatilization rather than sorption or masking (Griffin & Chou,
    1981a).

         The ability of PBBs to co-distil from landfills or from the
    surface layer of water bodies, as reported for PCBs (Kalmaz &
    Kalmaz, 1979), has not yet been examined.

         By analogy with PCBs, it might be expected that PBBs entering
    the atmosphere in the vapour phase would be adsorbed rapidly onto
    particles, which would then be deposited by particle sedimentation,
    depending on micro- and macrometeorological conditions.

         According to Eisenreich et al. (1981) organic compounds having
    a vapour pressure > 10-5 kPa should exist almost entirely in
    the vapour phase, and those having a vapour pressure > 10-9 kPa
    should exist almost entirely in the particulate phase.

         PBBs, e.g., hexabromobiphenyl or FireMaster with a vapour
    pressure of 6.9 x 10-9 kPa (Jacobs et al., 1976), belong to the
    latter. In reality, distribution and atmospheric lifetimes of
    organic compounds with a high relative molecular mass depend largely
    on the particle concentration and composition in the atmosphere
    (Eisenreich et al., 1981). Gas-phase reactions with hydroxyl (OH)
    radicals also influence the lifetimes of organic compounds emitted
    into the atmosphere. Atkinson et al. (1984) determined rate
    constants for the gas-phase reaction of OH radicals with biphenyl
    and predicted, from their findings, that the chlorine - and
    bromine-substituted biphenyls would have OH radical rate constants
    of < 8 x 10-12 cm3/molecule per second at room temperature.

    4.1.2  Water

         The principal route of entrance of PBBs into aquatic
    environments is from industrial waste streams into receiving waters.
    Further potential routes (of minor relevance) are atmospheric
    deposition and erosion of polluted soils. Groundwater contamination
    is possible, if these compounds are leached from landfills (Shah,
    1978).

         Because compounds like PBB are very poorly soluble, they are
    primarily found in sediments of polluted lakes and rivers
    (Kimbrough, 1980a). In laboratory experiments, Simmons & Kotz (1982)
    determined the "percent adsorption" of PBBs in sediments from sites
    at Lake Michigan and the Huron River and concluded from values
    ranging from 9 to 32% that the capacity of the sediments for PBB was
    small to moderate.

         PBBs in water are mainly adsorbed on particulate matter
    followed by sedimentation at a rate that depends on several factors,
    such as the size and type of the sediment and/or the organic
    contents of both the sediment and the overlying water mass. The
    relative importance of these parameters is controversial (Simmons &
    Kotz, 1982). Laboratory results concerning PCBs (Jensen et al.,
    1973) led to the assumption that the kinetics of the sorption
    reaction may vary inversely with particle size (because smaller
    particles have a larger surface area for surface adsorption). 
    Leland et al. (1973), Choi & Chen (1976), and Simmons et al. (1980)
    have shown that the organic content of the sediment is directly
    related to its adsorptive capacity for a specific contaminant.
    According to Schwarzenbach & Westall (1981), adsorption of non-polar
    compounds is highly correlated with the organic carbon content of
    sorbents containing more than 0.1% organic carbon. Simmons & Kotz
    (1982) found strong correlations between the adsorptive capacity of
    the sediments for PBBs and TOC (total organic carbon) and the %
    silt/clay fraction.

         Sediments are potential sources as well as sinks for most
    chemicals (Simmons & Kotz, 1982). Desorption of a contaminant from
    the sediments is favoured where a high concentration of organic
    matter exists in the water column (Huang, 1971). The presence of
    organic matter may also enhance the partitioning of the contaminant
    in the water phase and, thus, facilitate further movement with the
    water mass (Hassett & Anderson, 1979). Laboratory studies on the
    mode of action that PBBs may take in their movement through the
    water column have verified that the total organic content of the
    natural water will decrease the adsorption of PBB onto sediment and
    therefore keep the PBB in the water phase. For example, comparing
    the distilled water versus natural water systems, in river water
    with an organic content of 11-12 mg C/litre, the % PBB-adsorption
    was decreased by 33-43%; for lake water with an organic content of
    3.8 mg/litre, the % PBB-adsorption was reduced by about 12% (Simmons
    & Kotz, 1982). Another investigation indicated that the solubilities
    of PBBs were directly correlated with the levels of dissolved
    organics in the water (Griffin & Chou, 1981a) (see also section
    4.1.3).

         However, in the natural environment, upon settling out, the
    association of the contaminant with the sediment may become the
    dominant process in the water/sediment system (Simmons & Kotz,
    1982). Transport of PBBs is thought to take place, when mixing or
    bioturbation of sediments causes redistribution of the contaminant
    in the water column (Simmons & Kotz, 1982), and through transport of
    the sediment itself.

    4.1.3  Soil

         Pollution of soils can originate from point sources such as PBB
    plant areas and waste dumps. Very few data are available on the
    deposition of PBBs on soil via the atmosphere, sewage sludge from
    municipal sewage treatment systems, and the dredging of sludge from
    contaminated waters.

         Other possible sources are illicit, or improper, disposal of
    such chemicals (Kimbrough, 1980a) and incidents. For example, as a
    consequence of an incident in 1973, Michigan soils have been
    contaminated by manure from PBB-fed animals and by the disposal of
    contaminated feed, milk, carcasses, etc. (Getty et al., 1977; Chou
    et al., 1978; Damstra et al., 1982; Fries, 1985b). Once PBBs have
    been introduced into the soil, they appear to have little tendency
    to translocate (Damstra et al., 1982).

         The ability of rainfall to carry PBBs through the soil was
    tested in a laboratory simulation. Filonow et al. (1976) percolated
    water through columns of 4 Michigan soils containing 100 mg
    2,2',4,4',5,5'-hexabromobiphenyl/kg. They found a loss of less than
    0.6% of the hexabromobiphenyl congener from each soil, even with
    leachate quantities equivalent to 20 times the average annual
    rainfall in Michigan.

         Field investigations also indicated that PBBs were retained in
    the top soil. Results of subsequent studies on highly contaminated
    farm soils showed that PBBs did not move below the 15 cm level,
    except where there was a history of physical mixing of the soil
    (Fries, 1985b).

         The mobility in soils of a chemical like PBBs will largely be
    governed by its solubility in water and its adsorption, or
    interaction, with soil particles (Jacobs et al., 1978).

         As already mentioned, PBBs have a very low solubility in water.
    However, studies with distilled, tap, river, and soil waters showed
    that their solubility was markedly influenced by water purity
    (Jacobs et al., 1978). Griffin & Chou (1981a) ascertained, under
    well defined conditions, the following average solubilities of PBBs:
    0.06 µg/litre in distilled water, 0.3 µg/litre in deionized water,
    0.5 µg/litre in creek water, 8.9 µg/litre in Du Page leachate, and
    16.9 µg/litre in Blackwell leachate.

         Hence, PBBs were more than 200 times more soluble in landfill
    leachate than in distilled water; the solubilities of PBBs were also
    higher in creek water than in distilled water. As shown by the TOC
    (total organic carbon) values for the waters, the higher
    solubilities of PBBs were directly correlated with the level of
    dissolved organic compounds in the waters. The type of dissolved
    organic matter may also influence the solubility (Griffin & Chou,
    1981a).

         PBBs are quite soluble in organic solvents, such as dioxane,
    carbon tetrachloride, acetone, and methanol. This could play a major
    role in soil environments where leachates from chemical waste
    disposal sites are percolating.

         The other important factor affecting the migration of PBBs,
    i.e., their adsorption by soils, was also studied under laboratory
    conditions. The hydrophobic properties of PBBs make them easily
    adsorbed from aqueous solutions onto soils. Filonow et al. (1976)
    examined the adsorption of purified 2,2',4,4',5,5'-hexabromobi
    phenyl (BB153) on four soil types. They found that the adsorption of

    2,2',4,4',5,5'-hexabromobiphenyl conformed well to Freundlich
    adsorption isotherms, and that 2-19% of the available HBB was
    adsorbed. Adsorption of HBB was influenced primarily by the organic
    content of the soils. An increase in the organic matter content of
    soils enhanced their adsorption capacity.

         Neither percentage clay nor pH correlated well with BB153
    adsorption. Any effect that the clay contents may have had, was
    apparently masked by the effect of the organic contents on
    adsorption (Filonow et al., 1976).

         Griffin & Chou (1981a,b), using the PBB-mixture FireMaster(R)
    BP-6 or 14C-labelled-PBB, also confirmed the strong adsorption of
    PBBs on soils and indicated a very high direct correlation between
    the total organic carbon content (TOC) of three different soils and
    the amounts of PBBs adsorbed. However, they pointed out that, in
    soils with a low TOC, the mineral fraction may contribute markedly
    to the adsorption capacity.

         Furthermore, preferential adsorption of PBB congeners and
    isomers was noted, depending on the characteristics of the
    adsorbent, e.g., organic content (Griffin & Chou, 1981a), as well as
    on the degree and position of bromine substitution (Griffin & Chou,
    1980, 1981b).

         No measurable adsorption on soils occurred of PBBs from organic
    solvents (Griffin & Chou, 1981a).

         The results of migration studies were in agreement with the
    findings discussed above. The mobility of PBBs in five soils was
    measured with several leaching solvents, using a thin-layer
    chromatography technique and column leaching studies (Griffin &
    Chou, 1981a,b). PBBs remained immobile in the soils when leached
    with water or landfill leachate, but were highly mobile when leached
    with organic solvents. Mobility was directly proportional to the
    solubility in the leaching solvents and inversely proportional to
    the soil total organic content.

         On the other hand, because PBBs are bound to soil, wherever
    contaminated soil moves, whether through wind or water erosion or
    animal ingestion and migration, traces of PBBs (if present) can be
    expected to be found (Jacobs et al., 1978).

    4.1.4  Biota

         PBBs are stable and persistent, lipophilic, and only very
    slightly soluble in water; they are poorly metabolized, and
    therefore accumulate in lipid compartments of biota. Once they have
    been released into the environment they will reach the food chain,

    where they are concentrated. Fish and wildlife are the most
    consistent targets for such contamination, but livestock and humans
    may also become contaminated (Kimbrough, 1980a). The precise routes
    and transport mechanisms of PBBs travelling through biota have not
    been thoroughly investigated as pointed out below.

    4.1.4.1  Terrestrial ecosystems

         Several studies have been concerned with whether plants in
    terrestrial ecosystems would take up, translocate, and introduce
    PBBs into the food chain. Jacobs et al. (1976) selected orchard
    grass  (Dactylus glomerata) as test plants in their greenhouse
    studies because of its extensive root mass, and carrots  (Daucus
     carota), which, according to Iwata et al. (1974), have an
    outstanding ability to absorb pesticide residues from the soil. They
    did not detect any PBBs in the tops of either species grown in soils
    supplied with high levels of PBBs (10 or 100 mg/kg of
    FireMaster(R) BP-6).  However, they did find traces of PBBs
    (20-40 µg/kg) associated with carrot roots. 14C-uptake studies
    (autoradiography and GC-analysis) on corn and soybean seedlings
    grown in hydroponic solutions and on three root crops (radishes,
    carrots, and onions) grown in two different soils, also showed no
    translocation of PBBs into plant tops (Chou et al., 1978). In
    addition, these authors found that the amount of PBBs associated
    with roots depended on plant species and the clay and organic matter
    contents of the soil.  Roots of carrots contained more PBBs than
    those of radish or onion bulbs; all roots had higher levels of PBBs
    (50-500 µg/kg tissue) when grown in a high-PBB treatment soil
    (100 mg/kg) with lower clay and organic content, than they did
    (30-120 ng/g plant tissue) in a soil containing more clay and
    organic matter. Furthermore, PBBs seem to be localized on the
    surfaces of roots, because a significant portion of 14C-PBBs was
    removed, when the roots were dipped in acetone.

         Analyses of field samples from plant tissues of corn, alfalfa,
    and sudax, grown on Michigan fields with soil PBB levels ranging
    from 9 to 371 µg/kg, resulted in no detectable (detection limit:
    0.3 µg/kg) PBB (Jacobs et al., 1978). The same was true for washed
    radishes from a garden with an estimated PBB concen tration of
    500-1000 µg/kg and for corn leaf whorls containing dust from a PBB
    contaminated soil (102 µg/kg) (Chou et al., 1978).

         However, Stratton & Whitlock (1979), who conducted a field
    screening survey near sites of manufacture and use of PBBs, found
    high surface contamination of lichens and reeds.

         The salt marsh cordgrass  (Spartina alterniflora) is reported
    to take up, accumulate, and transfer effectively PCB from
    contaminated sediments to food chains (Mrozek et al., 1982). No data
    are available with regard to PBBs.

         So far, except for the surface contamination of roots from
    contaminated soils and of foliage via air deposition processes,
    plants are generally free of significant amounts of residue. Thus,
    vegetation on PBB-contaminated soils is a less likely source of
    contamination of animals (Damstra et al., 1982; Fries, 1985a,b).

         In contrast, a major route of residue transmission from soils
    to animals is the direct ingestion of soil (Fries 1982; 1985a). The
    degree of contamination depends on the amount of soil ingested and
    the bioavailability of the residues.

         Quantitative data on soil ingestion by farm animals are given
    by several authors (Healy et al., 1967; Healy, 1968; Fries, 1982;
    Fries et al., 1982a,b) and range from 2 to 15% of the intake of dry
    matter.

         Fries (1985a) determined the bioavailability of soil-borne PBBs
    in sheep, under controlled feeding conditions, using diets
    containing 5% PBB-contaminated soil, and found 65% PBB absorption
    from this diet, which contained 9 µg PBB/kg. Addition of activated
    carbon to soil had only little effect on bioavailability of PBB.

         The same author recorded PBBs in the fat of beef cows, beef
    calves, ewes, and pigs from several farms on which soil-borne PBBs
    in confinement areas was the only source of PBBs. It can also be
    concluded from these results that the animals consumed soil, and
    that soil-borne PBB was bioavailable. As might be expected, pigs
    accumulated higher PBB concentrations from a soil environment than
    ruminants (Fries, 1985a). Recontamination of soil by animal excreta
    (Getty et al., 1977; Fries, 1985a) or carcasses (Shah, 1978) also
    occurred.

         Recently, PBBs have been detected in European herbivorous
    mammals (Swedish reindeers: Jansson et al., 1992; German cows
    (milk): Krüger, 1988) (see also sections 5.1.4 and 5.1.6).

         Despite the affinity of PBBs for soil, there are no
    investigations on the role of the soil fauna in the transfer of
    PBBs. Earthworms are of great ecological importance and might be
    expected to take up and accumulate PBBs as has been ascertained for
    PCBs (Diercxsens et al., 1985) and, thus, introduce them into the
    food chain.

    4.1.4.2  Aquatic ecosystems

         PBBs enter the aquatic food chains via water and food. Bacteria
    and plankton play an important role in the accumulation and
    translocation of PCBs to higher trophic levels (Kalmaz & Kalmaz,
    1979; Lorenz & Neumeier, 1983). According to Falkner & Simonis
    (1982), sorption processes probably control uptake and accumulation

    of PCBs by phytoplankton, because of its high surface-volume ratio.
    These mechanisms could also be valid for PBBs. However, Stratton &
    Whitlock (1979) did not find PBBs in algae collected in the vicinity
    of industrial sites, where PBB concentrations of sediments ranged
    from 20 to 60 µg/kg and where captured fish contained 220-230 µg
    PBB/kg (detection limit: not given).

         No information on the uptake of PBBs from sediment through
    bottom living organisms (e.g., mollusca or oligochaete worms) is
    available.

         In contrast, several laboratory (Norris et al., 1973; Zitko &
    Hutzinger, 1976; Zitko, 1977; Sugiura et al., 1978) and field (Hesse
    & Powers, 1978; Stratton & Whitlock, 1979; Jaffe et al., 1985)
    studies on fish have been conducted. They confirm PBB uptake from
    water and food, with the exception of hepta- and octabromobiphenyl
    (Norris et al., 1973; Zitko, 1977), which were not taken up from
    water.

         Consequently, ingestion of fish is a source of PBB transfer to
    mammals and birds. Because of the possible selective accumulation
    and metabolism of PBB congeners in prey, it can be expected that
    predators will be subjected to a somewhat different PBB congener
    composition than that found in the surrounding media (sediment,
    water, etc.).

         In natural situations, food chains become linked together in
    complex food webs, and PBBs are distributed in the corresponding
    manner.

         PBBs have been detected in other species of wildlife besides
    fish, e.g., in ducks living near contaminated waters (Hesse &
    Powers, 1978), in a turtle (Stratton & Whitlock, 1979), in the eggs
    of waterbirds (Haseltine et al., 1981; Heinz et al., 1983, 1985), in
    eagles (Kaiser et al., 1980), and in marine mammals (Jansson et al.,
    1987, 1992; Krüger, 1988; Kuehl et al., 1991) (see also section
    5.1.6).

    4.1.4.3  Accidental contamination of the food chain

         A special case of entrance of PBBs into the food chain occurred
    accidentally in 1973 in Michigan, when FireMaster(R) FF-1 was
    inadvertently substituted for magnesium oxide as a supplement in the
    formulation of cattle feed (Damstra et al., 1982). Ten to twenty
    bags, 22.8 kg each, of PBBs (Carter, 1976) were mixed into feeds,
    that were widely distributed to Michigan farmers.

         In addition, feeds not formulated to contain magnesium oxide
    also became contaminated (with relatively low concentrations)
    because of carryover of PBBs from batch to batch in the mixing
    equipment (Dunckel, 1975) and, on farms, through the recycling of
    contaminated products (Kay, 1977). Distribution of contaminated
    antibiotics, e.g., aureomycin, also contributed to the introduction
    of PBBs into farm animals (Di Carlo et al., 1978).

         The mixing error was not discovered immediately, and it was
    almost a year before analyses indicated that a compound of PBB was
    involved in the illness or death of farm animals (Getty et al.,
    1977). During this time (IARC, 1978; Zabik, 1982), contaminated
    animals and their produce entered the human food supply and the
    environment of the state of Michigan. Hundreds of farms were
    affected. Altogether, at least 29 800 cattle, 5920 pigs, 1470 sheep,
    and 1.5 million chickens had been killed and buried by the end of
    1975 (Robertson & Chynoweth, 1975; Carter, 1976), in order to
    minimize further human exposure. In addition, at least
    785 thousand kg of feed, 8185 kg of cheese, 1197 kg of butter,
    15 500 kg of dried milk products, and nearly 5 million eggs were
    destroyed (Carter, 1976). The number of animals quarantined or
    contaminated below quarantine level was estimated to be several
    thousands (Isleib & Whitehead, 1975). Although the Michigan PBB
    episode was primarily an incident of feed contamination, it also
    resulted in secondary contamination of animals from contaminated
    soil (Fries, 1985a).

    4.2  Degradation

         Compounds like PBBs are very stable to hydrolysis, chemical
    oxidation, and thermal decomposition. Degradation by purely abiotic
    chemical reactions (excluding photochemical reactions) is therefore
    considered an unlikely environmental sink (Pomerantz et al., 1978;
    Pearson, 1982).

         The persistence of PBBs under actual field conditions is
    reported in some publications. Jacobs et al. (1976) detected PBBs in
    soils from a field that had received manure from a
    FireMaster(R)-contaminated dairy herd 10 months earlier.

         Follow-up surveys over a three-year period following the
    termination of PBB production showed no significant decline in PBB
    levels in sediments from the Pine River (Hesse & Powers, 1978). Soil
    samples from the former PBB-manufacturing site in St. Louis,
    Michigan, analysed several years (nearly ten years?) after
    contamination (during the early 1970s) still contained PBBs.
    However, the PBB congener composition differed from that of the
    original FireMaster(R) mixture, indicating a partial degradation
    of the PBB residue in the soil sample (Hill et al., 1982).

         The chemical Inspection and Testing Institute, Japan (1987) has
    listed decabromobiphenyl as non-biodegradable.

         The most probable degradation mechanisms of PBBs in the
    environment, if there is any degradation at all, are
    photodecomposition and microbial degradation.

    4.2.1  Photolytic degradation

         Under laboratory conditions, PBBs were easily degraded by UVR.
    The photoreactivity of PBBs has been used to confirm PBB residues
    (Erney, 1975; Trotter, 1977). The predominant photochemical reaction
    of PBBs in organic solvents was a reductive debromination.
    Irradiation of 4-monobromobiphenyl at 300 nm in various polar and
    nonpolar solvents led to the formation of biphenyl as the sole
    product (Freeman et al., 1991). Earlier studies using lower
    brominated PBB congeners (i.e., tetra and lower) reported a
    preferential loss of ortho bromines (Bunce et al., 1975; Ruzo
    et al., 1976). Irradiation of higher brominated congeners yielded a
    series of photoproducts (Table 18), but a stepwise cleavage of
    orthobromines did not appear to be preferred to meta or para
    debromination (Patterson et al., 1980; Millis & Aust, 1985).

         The photoreactivity of 2,2',4,4',5,5'-hexabromobiphenyl, the
    main component of FireMaster(R), was consistently found to be
    relatively high (Andersson et al., 1975; Ruzo et al., 1976;
    Robertson et al., 1983a; Millis & Aust, 1985), and degradation
    occurred more rapid than with the hexachloro analogue (Andersson
    et al., 1975; Ruzo & Zabik, 1975).

         Consistent with the dehalogenation pathway, photodegradation of
    the commercial FireMaster(R) mixture led to reduced concentrations
    of the more highly substituted PBB congeners (De Kok et al., 1977;
    Robertson et al., 1981b, 1983; Epling et al., 1987). Robertson
    et al. (1983a) examined changes in the composition of
    FireMaster(R) BP-6 during photolysis (300 nm for 2-12 h; solvent:
    cyclohexane) by monitoring 25 individual PBB congeners; they also
    did not find a preferential loss of ortho bromines. Nevertheless,
    the photoproducts of FireMaster(R) did contain increased
    concentrations of congeners possessing no ortho bromines (e.g.,
    3,4,4'-tri-, 3,3',4,4'-tetra-, 3,3',4,4',5-penta bromobiphenyl).
    Moreover, other congeners, known as relatively toxic (e.g.,
    2,3',4,4',5-pentabromobiphenyl), were enriched (Robertson et al.,
    1983). Biphenyl, the ultimate product of the debromination pathway,
    was found only to a small extent after the photolysis of
    FireMaster(R) BP-6 (Epling et al., 1987).

    
    Table 18.  Photodegradation of higher brominated PBB congeners under laboratory conditions

    PBB                 Irradiation     Solvent       Initial rate     Primary products          Remarks                      References
                        (duration)                    of photolysis    of photolysis
                                                      (nmol/min)       identified

    2,2',4,5,5'-        254 nm          hexane           43.4a         2,3',4',5-tetra           ortho-debromination          Millis & Aust
    penta               (up to 100                                     (minor product)                                        (1985)
                        min)                                           2,2',4,5'-tetra           meta-debromination
                                                                       2,2',5,5'-tetra           para-debromination
                                                                       (major product)
                                                                                                 (additional production
                                                                                                 of a yellow gum)

    2,3',4,4',5-        254 nm          hexane           50a           2,3',4',5-tetra           para-debromination           Millis & Aust
    penta               (up to 90                                      3,3',4',4'-tetra          ortho-debromination          (1985)
                        min)

    2,2',4,4',5,5'-     366 nm          methanol      not specified    lower brominated PBBs     degradation (90% after 9     Andersson et al.
    hexa                                                               (main products)           min) more rapid than with    (1975)
    BB 153                                                             methoxy- PBBs (minor      the hexachloro analogue
                                                                       products)

                        > 300 nm        hexane        not specified    lower brominated PBBs     BB 153 was 24.4 times        Ruzo et al.
                        (0.5-2 h)                                      quaterphenyls (< 5%)      more reactive than           (1976)
                                                                                                 4,4'-dibromobiphenyl

    2,2',4,4',5,5'-     254 nm          hexane            53a          2,2',4,5,5'-penta         para-debromination           Millis & Aust
    hexa                (up to 100                                     (major product)                                        (1985)
                        min)                                           2,3',4,4',5-penta         ortho-debromination
                                                                       2,2',4,4',5-penta         meta-debromination

    Table 18 (contd).

    PBB                 Irradiation     Solvent       Initial rate     Primary products          Remarks                      References
                        (duration)                    of photolysis    of photolysis
                                                      (nmol/min)       identified

    2,2',4,4',5,5'-     254 nm          hexane           53a           2,2',4,5.5'-penta         para-debromination           Millis & Aust
    hexa                (up to 100                                     (major product)                                        (1985)
                        min)                                           2,3',4,4',5-penta         ortho-debromination
                                                                       2,2',4,4',5-penta         meta-debromination

                                                                       secondary photoproduct:
                                                                       3,3',4,4'-tetra

                                                                       formation of yellow
                                                                       gum at 25 min

    2,2',3,4,4',5,5'-   sunlight           not          not            2,2',4,4',5,5'-hexa       meta-debromination           Patterson
    hepta               (390 min)       specified     specified        (major product)                                        et al. (1980)
                                                                       2,3',4,4',5,5'-hexa       ortho-debromination

    2,2',3,3',4,4',     sunlight           not          not            unidentified hexa-                                     Patterson
    5,5'-octa           (300 min)       specified     specified        PBB (major product)       ortho- and meta-             et al. (1980)
                                                                       2,3',4,4',5,5'-hexa       debromination

    2,2',3,3',5,5',     300 nm          hexane        not specified    di- to                                                 Ruzo et al.
    6,6'-octa           (0.5-2 h)                                      heptabromobiphenyls,      ortho debromination          (1976)
                                                                       e.g., 3,3',5,5'-tetra

    a    Original PBB concentration = 1.59 mmol/litre.

         Technical octabromobiphenyl has been reported to photo degrade
    in xylene by reductive debromination with a half-life of 40 h
    (Norris et al., 1973).

         There were investigations to enhance the photochemical process
    aiming at a potential technique for the breakdown and removal of
    PBBs from the environment. In laboratory testing, photodegra dation
    of PBBs was accelerated in the presence of ethylenediamine and
    tertbutylamine (Christensen & Weimer, 1979) and in the presence of
    sodium borohydride (Epling et al., 1987).

         Epling et al. (1987) obtained high yields of biphenyl during
    borohydride enhanced photolysis of FireMaster(R) BP-6 (irradiation
    under nitrogen at 254 nm; solvent: 90% acetonitrile/water).

         The rates and extent of photolytic reactions of PBBs in the
    environment have not been determined in detail. However, the few
    field observations available indicate a high persistence of the
    original PBBs (Jacobs et al., 1978) or a partial degradation to less
    brominated (and often more toxic) photoproducts (Hill et al., 1982).
    Jacobs et al. (1978) examined field soil that had received manure
    from FireMaster(R)-contaminated cattle, for the first time, 2-3
    years earlier. They did not detect any significant changes in the
    relative concentrations of the major PBB peaks (Br5, Br6, Br7)
    compared with the FireMaster(R) standard. In contrast, soil
    samples, obtained from the former FireMaster(R) manufacturing site
    in Michigan and analysed several years (approximately 10 years?)
    after contamination, contained enhanced concentrations of possible
    photodegradation products including 2,3',4,4',5-pentabromobiphenyl,
    2,2',4,4',5-pentabromobiphenyl, and two unidentified
    tetrabromobiphenyls (Hill et al., 1982).

         Considering the diversity of microenvironments, both laboratory
    and field data on photo alteration of PBBs are incomplete; there is
    a lack of studies on the photochemistry of PBBs in water, or in the
    vapour or solid states.

    4.2.2  Microbial degradation

         In laboratory investigations, mixtures of PBBs appear to be
    fairly resistant to microbial degradation. Soil incubation studies
    using FireMaster(R) BP-6 (lot no. 6244A) and 14C-PBB
    (lot 872-244) showed a little, but not significant, degradation of
    the major hexa- and heptabromobiphenyl congeners after 6 months or
    1 year; only pentabromobiphenyl was assumed to degrade slowly
    (Jacobs et al., 1976, 1978). These results were deduced from
    recovery rates of PBBs from soil, 14CO2 production, and the lack of
    14C-PBB intermediates.

         Soils incubated with photodecomposition products of 14C-hexa
    and heptabromobiphenyl caused enhanced, but still minor, degradation
    (ca. 3%) as measured by 14CO2 production (Jacobs et al., 1978).
    These findings are consistent with observations according to which
    degradation of PCBs by bacteria increases with decreasing
    chlorination (Kalmaz & Kalmaz, 1979; Fries, 1982).

         In further incubation experiments with FireMaster(R) BP-6
    (lot no. 6244A) in sterilized and nonsterilized Catlin-soil, Griffin
    & Chou (1981a) measured the recoveries of penta-, hexa-, and
    heptabromobiphenyls and found that all PBBs persisted for 6 months
    with no significant microbial degradation. They observed the same
    kind of persistence over a period of 4 weeks in PBB incubations with
    mixed cultures of microorganisms (predominantly  Alkaligenes
     odorans, A. denitrificans, and an unidentified bacterium). This
    culture had been isolated previously and was known to degrade
    water-soluble PCBs (Clark et al., 1979). No PBB metabolites were
    found in the PBB-saturated mineral solution after 4 weeks of
    incubation (Griffin & Chou, 1981a).

         As with PCBs, the high degree (penta or greater) of halogen
    substitution of its major components probably accounts for the lack
    of degradation of the FireMaster(R)-mixture (Griffin & Chou,
    1981a). Congruently, biodegradation of monobrominated biphenyls has
    recently been reported.

         A soil isolate, strain S93B1, identified as  Pseudomonas
     cruciviae, could grow on more than ten biphenyl-related compounds
    including  o-bromobiphenyl (Takase et al., 1986).  O-bromobiphenyl
    was converted to  o-bromobenzoic acid (Fig. 3) (identified by
    IR-spectrum). This is analogous with some PCBs showing chlorinated
    benzoates as metabolites (Ballschmiter et al., 1977). In these
    experiments, biphenyl-related compounds 0.2-0.5% (w/v) were added as
    the sole sources of carbon to the liquid artificial medium.

         However, this pathway is also realized under simulated natural
    conditions (aquatic environments), as reported by Kong & Sayler
    (1983). They used river water as supportive culture medium and
    "mixed bacterial cultures" (not identified), which were obtained
    from PCB-contaminated river sediments. This mixed bacterial culture
    was capable of degrading monohalogenated biphenyls.

         The degradation rates of 2-, 3-, and 4-bromobiphenyl, at
    30 µg/ml, were 2.3, 4.2, and 1.4 µg/ml per day, respectively, and
    were comparable with those of monochlorinated biphenyls. Degradation
    occurred when the substrates were supplied as the sole carbon source
    or when added in combination with glucose. The major metabolite of
    4-bromobiphenyl  (para) was 4-bromobenzoate, identified by means of
    cochromatography with an authentic compound in HPLC. Two bacterial
    strains of the genus  Pseudomonas, isolated from a lake sediment by
    using  p-chlorobiphenyl as a sole carbon source, were capable of
    degrading 2-, and 4-bromobiphenyl, but they did not degrade
    4,4'-dibromobiphenyl (Sugiura, 1992).

         In contrast to several reports indicating that chlorobenzoates
    are the principal stable metabolites of PCBs (Furukawa & Matsumara,
    1976; Furukawa et al., 1979; Yagi & Sudo, 1980; Reichardt et al.,
    1981), 4-bromobenzoate as well as 4-chlorobenzoate appeared
    transient. For, when tested with the same bacterial consortium,
    4-bromobenzoate at 30 mg/kg was readily degraded at the rate of
    4 µg/ml per day (Kong & Sayler, 1983). The terminal decomposition
    product is assumed to be CO2 (Kong & Sayler, 1983), i.e.,
    4-bromobiphenyl can most likely be completely mineralized by this
    bacterial culture. Suflita et al. (1982) also observed degradation
    of bromobenzoates. They reported the reductive dehalogenation of
    halobenzoates, including 2-, 3-, or 4- bromobenzoate by
    microorganisms of lake sediment and sewage sludge. Dehalogenation
    required strict anaerobic conditions. The primary degradative event
    was loss of the aryl halide without the alteration of the aromatic
    ring, the end products were CH4 and CO2. The stable bacterial
    consortium enriched from sludge consisted of both chemolithotrophic
    and heterotrophic methanogens as well as three, unidentified,
    non-motile Gram- negative rods.

         Recently, there was a brief report on the reductive
    debromination of the FireMaster(R) mixture (rate and extent of
    debromination reaction not given) by anaerobic microorganisms eluted
    from PCB-contaminated river sediments (Quensen et al., 1990;
    abstract only).

    4.2.3  Degradation by plants and animals

         No degradation of PBBs by plants has been recorded. In contrast
    to plants, animals can easily absorb PBBs and, though they have been
    found to be very persistent in animals, small amounts of PBB
    metabolites have been detected. The main metabolic products were
    hydroxy-derivatives and, in some cases, there was evidence of
    partially debrominated PBBs (cf. also section 6.3).

         The metabolism of crude FireMaster(R) BP-6 by a pig gave a
    monohydroxypentabromobiphenyl (Kohli & Safe, 1976). The faeces of
    dogs fed FireMaster BP-6 contained a metabolite identified as
    6-hydroxy-2,2',4,4',5,5'-hexabromobiphenyl (Gardner et al., 1979).
    However, the authors do not exclude microbial metabolism of PBB in
    the dog's gut followed by excretion into the faeces. Doses of
    2,2',4,4',5,5'-[14C]-hexabromobiphenyl given intravenously or
    orally to male rats were not subject to appreciable metabolism
    (Matthews et al., 1977). Metabolites were not detected in tissue
    extracts. A trace of radioactivity, which may have represented a
    PBB-metabolite, was found in bile and faeces, but the quantity was
    too small to be isolated and identified.

         Some investigations imply that fish may debrominate the more
    highly brominated components of PBB-mixtures. Fish (juvenile  Salmo
     salar), exposed in laboratory studies to FireMaster(R) BP-6 in
    water, contained several mono to pentabromobiphenyls that were not
    present in BP-6. Several additional pentabromobiphenyls were
    detected in fish fed FireMaster(R) BP-6-contaminated food. Fish
    fed octabromobiphenyl contaminated food contained unidentified
    penta-, hexa-, and heptabromobiphenyls in addition to the
    octabromobiphenyls (Zitko, 1977). It was not known whether the
    partially debrominated biphenyls were generated by the fish, or by
    the associated microflora.

         Because the carbon-bromine bond is less stable than the
    carbon-chlorine bond, reductive debromination may be a degradative
    pathway of bromobiphenyls, and this reaction may have toxicological
    consequences not encountered with PCBs (Zitko & Hutzinger, 1976;
    Zitko, 1977).

    4.2.4  Bioaccumulation

         As expected from their high lipophilicity, PBBs show a marked
    tendency to accumulate in animals. However, data are available only
    on single links of food chains. It has been reported that similar
    compounds, e.g., PCBs, which are more widely spread in the
    environment, may have bioconcentration factors of 3-4 orders of
    magnitude between water and fish, with a further 1-2 orders of
    magnitude between whole fish and the fat storage tissues of fish
    predators, such as cormorant, heron, and seal (Pearson, 1982).

    4.2.4.1  Aquatic organisms

         Fish are the only aquatic organisms for which the bioaccumu
    lation of PBBs has been investigated intensively. They serve as an
    example for the efficiency of such bioaccumulation (Damstra et al.,
    1982).

         Fathead minnows  (Pimephales promelas) caged in a river, where
    water levels of PBB (Firemaster(R) BP-6; probably measured as
    concentration of the main peak, 2,2',4,4',5,5'-hexabromobiphenyl)
    remained consistently at less than 0.1 µg/litre, concentrated these
    contaminants in their bodies more than 10 000 fold in two weeks of
    exposure (Hesse & Powers, 1978). In laboratory studies, accumulation
    coefficients of FireMaster(R) BP-6 and technical octabromobiphenyl
    from water (A = concentration in fish, µg/g wet weight/concentration
    in water, µg/ml) and from food (B = concentration in fish, µg/g wet
    weight/concentration in fish-food, µg/g) were determined.
    FireMaster(R) BP-6 reached values of A = 48 (after an exposure of
    48 h) and B = 1.0 (in equilibrium) in juvenile Atlantic salmon
     (Salmo salar). The main component accumulated was
    2,2'4,4',5,5'-hexabromobiphenyl (Zitko, 1977). In contrast,
    octabromobiphenyl, as such, was not concentrated from water by
    Atlantic salmon (Zitko, 1977) and by rainbow trout (Norris et al.,
    1973), but a little uptake (B = 0.023) was observed from suspended
    food (Zitko, 1977). Instead of octabromobiphenyl, an unidentified
    hexabromobiphenyl was mainly accumulated (A = 1.73; B = 0.114;
    Zitko, 1977). In comparison with Aroclor 1254, the accumulation of
    FireMaster(R) BP-6 from water was less, but accumulation from food
    was a little higher than that of the corresponding PCB mixture (A =
    282; B = 0.358; Zitko, 1977).

         There are some differences in the accumulation of different
    congeners. Zitko & Hutzinger (1976) determined accumulation
    coefficients of di-, tri-, and tetrabromobiphenyls in  Salmo salar. 
    The coefficients were calculated on the basis of accumulation from
    water after a 48-h exposure, and of the extrapolated equilibrium
    levels in fish fed contaminated food. The accumulation coefficients
    generally decreased with increasing degree of substitution during

    the uptake from water, and increased, when taken up from food. Of
    the dibromobiphenyls, the 3,4-isomer accumulated from water much
    less than the 2,6- and 2,4-isomer, and did not accumulate from food
    (Zitko & Hutzinger, 1976). Sugiura et al. (1978) dealing with the
    accumulation of lower substituted halobiphenyls (di-, tri- and
    tetra-) in killifish  (Oryzias latipes) found that equilibrium
    accumulation from water was not reached during a period of 20 days.
    Their data, derived from a flow through test using PBB
    concentrations of 0.5-50 µg/litre, resulted in bioaccumulation
    factors (equilibrium extrapolated) ranging from 340 to 7340. They
    also found that accumulation factors were proportional to partition
    coefficients  (n-octanol/water), when the coefficients were below
    106, but not when the coefficients were above 106.

         It is obviously important to note the lipid contents of test
    animals in bioaccumulation studies. For example, the bioconcen
    tration factors of PCB congeners for whole fish tissue were
    proportional to the lipid content of the different species, which
    can range from 3 to nearly 20% (Sugiura et al., 1979). Gobas et al.
    (1989) reported lipid weight-based bioconcentration factors, log
    KL ranging from 5.06 to 6.16, for some PBBs (di- to hexa-) in the
    guppy  (Poecilia reticulata).

    4.2.4.2  Terrestrial organisms

         Bioaccumulation of PBBs in terrestrial organisms has been
    considered only for avian and mammalian species of farm and
    laboratory animals. Data were obtained through field observations
    (accumulation from soil), evaluation of an accident, and through
    controlled feeding studies.

         Accumulation of soilborne PBBs has been studied in Michigan
    farms that were contaminated accidentally by FireMaster(R) FF-1
    (Fries, 1985a). Ratios of PBB concentrations between the fat of farm
    animals (cows, sheep, pigs) and soil ranged from 0.10 to 1.86. 
    Multiparous dairy cows had lower ratios, because of the excretion of
    PBB in milk during long-term lactation, and swine had higher ratios,
    because they ingest greater amounts of soil than other species
    (Fries, 1985a). In another study, PBB (FireMaster(R) FF-1) was
    applied to the soil surface for experimental purposes. Sheep grazing
    for 180 days on these plots containing 33 mg PBB/m2 (plot 1) and
    48 mg/m2 (plot 2) reached average residue levels in body fat of
    0.30 and 0.79 µg PBB/g fat (quantified as concen trations of
    2,2',4,4',5,5'-hexabromobiphenyl), respectively. Average residue
    concentrations in ewes that grazed for 60 days were nearly as great
    (Fries & Marrow, 1982). A second trial, conducted 3 years later
    after ploughing and reseeding the plots, showed that PBBs were
    distributed throughout the top 16 cm of soil with an average
    concentration of 0.14 µg 2,2',4,4',5,5'- hexabromobiphenyl/g soil in
    plot 2. Sheep grazing here for 136 days had average concentrations
    of 0.032 µg PBB/g body fat (Fries & Marrow, 1982).

         The accidental ingestion of FireMaster(R) FF-1 by cattle on
    Michigan farms, first described by Jackson & Halbert (1974),
    resulted in high body burdens of PBBs. There were tissue levels of
    2,2',4,4',5,5'-hexabromobiphenyl in the fat of cows of up to
    approximately 4000 mg/kg, nearly one year after high exposure
    (estimated total dose: 150-400 g of FireMaster(R) FF-1/cow over
    14 days). Low exposure from cross contamination produced PBB
    concentrations in fat of less than 0.3 µg/g (Fries et al., 1978a,b;
    Fries, 1983).

         Laboratory data for the accumulation of PBBs from known diets
    are given in Table 19 (diets supplemented with FireMaster(R)) and
    in Table 20 (diets supplemented with single PBB congeners). PBB
    levels in tissues of FireMaster(R)-exposed animals were expressed
    as the concentration of the most abundant constituent of the
    mixture, namely 2,2',4,4',5,5'-hexabromobiphenyl. Fries et al.
    (1976) additionally reported the concentration of a heptabromobi
    phenyl component (not the pure isomer). They found 31.4 mg/kg of
    this component in the body fat of hens fed diets containing 20 mg
    FireMaster(R)/kg feed for 63 days. The fate of minor constituents
    of the FireMaster(R) mixture is not evident from the studies
    compiled in Table 19.

         Generally, accumulation of PBBs in body fat depended on dosage
    and duration of exposure. The highest accumulation coefficients
    (mg PBB/kg of tissue divided by mg PBB/kg feed) were found in minks
    (Table 19). PBB residue levels in the adipose tissue of treated
    minks were 60 times the amount in the diet (Aulerich & Ringer,
    1979). According to the authors, the high diet-to-fat residue
    accumulations in the minks may be due, in part, to the relatively
    small subcutaneous fat deposits of the test animals, most of which
    were extremely emaciated at the time of death. Technical
    octabromobiphenyl was also accumulated from the diet, as shown by
    analyses of the bromine contents of the tissues (Norris et al.,
    1973; Lee et al., 1975a; Waritz et al., 1977). There was a
    dose-related build-up of bromine, predominantly in the fat, as well
    as in the liver, of rats fed octabromobiphenyl. For example, after 4
    weeks of feeding 1, 10, 100, or 1000 mg octabromobiphenyl/kg feed,
    the bromine concentrations in adipose tissue were 2, 12, 120, and
    600 times, respectively, greater than those of the controls (Lee
    et al., 1975a).

    
    Table 19.  Accumulation of PBBs in feeding studies on mammals and birds
    a)  Feeding of FireMaster(R)

    Species      FireMaster(R)   Dietary         Feed intake     Feeding        Residue level (mg/kg)a         Weight    References
                              concentration        (g/day)       period                                        basis
                              (mg/kg)
                                                                          Adipose      Liver     Others
                                                                                       tissue

    Rat (male)   BP-6         0.1             20.9c           9 days      0.3          1.5       brain: 0.5    lipid     Render et al. (1982)
    Rat (male)   BP-6         1               23.3b           9 days      1.7          8.3       brain: 1.8    lipid
    Rat (male)   BP-6         1               not specified   2-3 weeks    -           2.7           -         dry       Babish & Stoewsand
                                                                                                                         (1977)
    Rat (male)   BP-6         1               not specified   30 days     7.8          22.3      thymus: 21    lipid     Akoso et al. (1982a)
    Rat (male)   BP-6         10              22.9b           9 days      27           135       brain: 12.3   lipid     Render et al. (1982)
    Rat (male)   BP-6         10              not specified   30 days     61.6         310       kidney: 147   lipid     Akoso et al. (1982a)
    Rat (male)   BP-6         50              not specified   2-3 week    -            341          -          dry       Babish & Stoewsand
                                                                                                                         (1977)
    Rat (male)   BP-6         50              26b             10 weeks    864          55           -          wet       Harris et al. (1978b)
    Rat (male)   BP-6         100             22b             9 days      251          1213      brain: 103    lipid     Render et al. (1982)
    Rat (male)   BP-6         100             not specified   30 days     1535         2507      thymus:1044   lipid     Akoso et al. (1982a)
    Rat (male)   BP-6         100             27b             10 weeks    3460         107          -          wet       Harris et al. (1978b)
    Rat (male)   BP-6         150             26b             10 weeks    3574         295          -          wet
    Rat (male)   BP-6         200             26b             10 weeks    3242         245          -          wet
    Mouse        BP-6         100             not specified   14 days     223          33.2      thymus: 391   wet       Corbett et al. (1978a)
    (male)
    Mouse        BP-6         1000            not specified   11 days     39.5         2.5          -          wet       Corbett et al. (1975)
    (male)
    Mouse        FF-1         5               not specified   3 weeks      -           7         thymus: 20    wet       Loose et al. (1981)
    (male)
    Mouse        FF-1         5               not specified   6 weeks      -           15        thymus: 37.8  wet
    (male)

    Table 19 (contd).

    Species      FireMaster(R)   Dietary         Feed intake     Feeding        Residue level (mg/kg)a        Weight    References
                              concentration        (g/day)       period                                       basis
                              (mg/kg)
                                                                          Adipose      Liver     Others
                                                                                       tissue

    Mouse        FF-1         167             not specified   3 weeks       -          154       thymus: 109   wet
    (male)
    Mouse        FF-1         167             not specified   6 weeks       -          623       thymus:       wet
    (male)                                                                                       3088
    Sheep        BP-6         50              1000            30 days     25           12        heart: 4.3    wet       Gutenmann & Lisk
    (male)                                                                (omental                                       (1975)
                                                                          fat)
                                                                          42 (renal
                                                                          fat)
                                                                          17
                                                                          (brisket
                                                                          fat)

    Pig          BP-6         20              1880c           4 weeks     0.33          -         -            wet       Ku et al. (1978)
                                                                          (back fat)
    Pig          BP-6         20              1880c           16 weeks    64           8.5       muscle: 6.6   wet
                                                                          (back fat)
                                                                          42.9
                                                                          (leaf fat)

    Pig          BP-6         200             1230c           4 weeks     6.7            -         -           wet       Ku et al. (1978)
                                                                          (back fat)
    Pig          BP-6         200             1230c           16 weeks    503          17.2      muscle:       wet
                                                                                                 18.4
                                                                          (back fat)
                                                                          459
                                                                          (leaf fat)

    Table 19 (contd).

    Species      FireMaster(R)   Dietary         Feed intake     Feeding        Residue level (mg/kg)a         Weight    References
                              concentration        (g/day)       period                                        basis
                              (mg/kg)
                                                                          Adipose      Liver     Others
                                                                                       tissue

    Mink         FF-1         2.5             not specified   136 days    149            -       muscle: 7.3   wet       Aulerich & Ringer
                              6.25                            172 days     -             -       brain: 66     wet       (1979)
                              15.6                            72-93       986            -       muscle: 70    wet
                                                              days

    Japanese     not          10               -b             9 weeks       -           48       heart: 78     dry       Babish et al. (1975a)
    quail        specified
    (male)                    20               -b             9 weeks       -          374       kidney: 105   dry
                              100              -b             9 weeks       -          642       kidney: 725   dry
    Japanese     not          10               -b             9 weeks       -           99       heart: 48     dry
    quail        specified
    (female)                  20               -b             9 weeks       -          225       heart: 50     dry
                              100              -b             9 weeks       -          503       kidney: 428   dry

    Chicken      BP-6         20              not specified   63 days     79.8           -       egg: 20       wet       Fries et al. (1976)
    (White
    leghorn
    hens)
                 BP-6         20               -b             4-8 weeks    -             -       egg: 30       wet       Cecil & Bitman (1978)
                 BP-6         64               -b             4-8 weeks    -             -       egg: 100      wet
                 not          1               106b            5 weeks                  0.6       egg: 1.5      wet       Ringer & Polin (1977)
                 specified

                 not          125             94c             5 weeks      -            -        egg: 209      wet       Ringer & Polin (1977)
                 specified

                 not          625             28.4c           5 weeks      -           80         -            wet
                 specified

    Table 19 (contd).

    Species      FireMaster(R)   Dietary         Feed intake     Feeding        Residue level (mg/kg)a         Weight    References
                              concentration        (g/day)       period                                        basis
                              (mg/kg)
                                                                          Adipose      Liver     Others
                                                                                       tissue

    Chicken      FF-1         0.2             99b             5 weeks     (-)d         (-)d      egg: 0.3      wet       Polin & Ringer
    (White                                                                                                               (1978a,b)
    leghorn      FF-1         1               106b            5 weeks     (-)d         (-)d      egg: 1.5      wet       Polin & Ringer
    hens)                                                                                                                (1978a,b)
                 FF-1         5               100b            5 weeks     (-)d         (-)d      egg: 7.4      wet       Polin & Ringer
                                                                                                                         (1978a,b)
                 FF-1         25              99b             5 weeks     (-)d         (-)d      egg: 43.4     wet       Polin & Ringer
                                                                                                                         (1978a,b)
                 FF-1         125             94c             5 weeks     (-)d         (-)d      egg: 215      wet       Polin & Ringer
                                                                                                                         (1978a,b)
    Chicken      FF-1         0.1             35              2 weeks       -            -       carcass:      wet       Polin & Leavitt (1984)
    (White                                                                                       0.11
    leghorn      FF-1         1               35              2 weeks       -            -       carcass:      wet       Polin & Leavitt (1984)
    cockerels)                                                                                   0.87
                 FF-1         10               -b             28 days       -          83.8       -            lipid     Dharma et al. (1982)
                 FF-1         100              -b             28 days       -          752        -            lipid     Dharma et al. (1982)

    a    Measured as the concentration of 2,2',4,4',5,5'-hexabromobiphenyl.
    b    Values not significantly different from control values.
    c    Values significantly different from control values.
    d    Diagrams only, generally, the ratios of tissue PBB: diet PBB averaged 3:1 for adipose tissue, 0.8:1 for liver,
         and 1.5:1 for whole egg.

    Table 20.  Accumulation of PBBs in feeding studies on mammals and birds
    b) Feeding of individual PBB congeners

    Species              Species    Dietary         Feed intake    Feeding    Residue level (mg/kg lipid)               References
                         (sex)      concentration   (g/day)        period                                     
                                    (mg/kg)                                   Adipose      Liver        Others
                                                                              tissue

    2,2',4,4',5,5'-      rat           0.1          23.8a          9 days       0.2         1.7         brain: 0.3      Render et al. (1982)
    Hexabromobiphenyl    (male)

                                        1           26.2b          9 days       3.1        11.4         brain: 1.1

                         rat            1           not            30 days      16         68.6         kidney: 38.7    Akoso et al. (1982a)
                         (male)                     specified

                         rat           10           25.5b          9 days      31.2         181         brain: 11.5     Render et al. (1982)
                         (male)

                         rat           10           not            30 days      149         693         kidney: 373     Akoso et al. (1982a)
                         (male)                     specified

                         rat           100          23.2a          9 days       436        2558         brain: 143      Render et al. (1982)
                         (male)

                         rat           100          not            30 days      992        6062         thymus: 3841    Akoso et al. (1982a)
                         (male)                     specified

                         chicken       10              -a          28 days        -         105            -            Dharma et al. (1982)
                         (male)

                                       62              -a          28 days       -          751            -

    Table 20 (contd).

    Species              Species    Dietary         Feed intake    Feeding    Residue level (mg/kg lipid)               References
                         (sex)      concentration   (g/day)        period                                     
                                    (mg/kg)                                   Adipose      Liver        Others
                                                                              tissue

    2,3',4,4',5,5'-      rat            1           not            30 days      9.1        23.5         kidney: 13.9    Akoso et al. (1982a)
    Hexabromobiphenyl    (male)                     specified

                         rat           10           not            30 days     69.1         242         thymus: 211     Akoso et al. (1982a)
                         (male)                     specified      (1982a)

                         rat           100          not            30 days      648        4340         thymus: 1639    Akoso et al. (1982a)
                         (male)                     specified

                         chicken        4           -a             28 days       -         32.5             -           Dharma et al. (1982)
                         (male)

                         chicken       10           -a             28 days       -          132             -           Dharma et al. (1982)
                         (male)

    3,3',4,4',5,5'-      rat           0.1          23.6a          9 days        0          3.3         brain: 0        Render et al. (1982)
    Hexabromobiphenyl    (male)

                                        1           24.7a          9 days       0.4         101         brain: 0

                         rat            1           24.7b          30 days      0.6         125         thymus: 0       Akoso et al. (1982a)
                         (male)

                         rat           10           20.2b          9 days       1.9          -          brain: 0        Render et al. (1982)
                         (male)

                         rat           10           21.3b          30 days      6.9         448         thymus: 20.4    Akoso et al. (1982a)
                         (male)

    Table 20 (contd).

    Species              Species    Dietary         Feed intake    Feeding    Residue level (mg/kg lipid)               References
                         (sex)      concentration   (g/day)        period                                     
                                    (mg/kg)                                   Adipose      Liver        Others
                                                                              tissue

                         rat           100          13.7b          9 days      22.5        1098         brain: 0        Render et al. (1982)
                         (male)

    a    Values not significantly different from control values.
    b    Values significantly different from control values.

         Data on accumulation of technical decabromobiphenyl have not
    been found in the literature.

         Isomer specific accumulation has been studied for three
    hexabromobiphenyl congeners. The residue levels in rats and chickens
    fed with 2,2'4,4',5,5'-; 2,3',4,4',5,5'- or 3,3',4,4',5,5'-
    hexabromobiphenyl are listed in Table 20. In many cases, the lowest
    concentrations in tissues were found with 3,3',4,4',5,5'-
    hexabromobiphenyl and the highest, with
    2,2',4,4',5,5'-hexabromobiphenyl.

    4.3  Ultimate fate following use

    4.3.1  Disposal of PBB-contaminated animals and wastes from the
           Michigan disaster

         Accidental contamination of livestock feed in 1973 by PBBs led
    to the destruction of over 30 000 animals in Michigan. As the
    toxicity and other physical and chemical properties of PBBs were at
    that time not so well known, the State of Michigan decided to locate
    an environmentally safe site for the burial of contaminated
    carcasses (Shah, 1978). A site in Kalkaska County was chosen and
    test drilled in order to determine the long-range protection for
    groundwaters in the area. The Kalkaska disposal site received over
    10 000 animal carcasses most of which contained PBB levels above
    1 mg/kg fat, and close to 20 000 carcasses with PBB levels ranging
    from 0.3 to 1 mg/kg. This animal disposal site contains
    approximately 45 kg of PBBs in all buried carcasses (Shah, 1978; see
    section 5.1.2.3. for groundwater studies).

         The Gratiot County landfill near St. Louis became operational
    in late 1970, and it was designed only for general municipal solid
    waste disposal. According to the Michigan Chemical Corporation
    report to the Environmental Protection Agency, PBB wastes were
    disposed of in the landfill between 1971 and 1973. Wastes containing
    large amounts of PBBs (60-70%) were received in the landfill before
    any information about the toxic effects of PBBs on animals was
    publicly known (Shah, 1978).

         The Forest Waste Disposal site consists of an 11-acre,
    abandoned, municipal and industrial waste landfill and 9 surface
    impoundments. It is located in Genesee County, Michigan, and is
    surrounded by agricultural land and undeveloped woodlands and
    wetlands. Forest Waste Disposal conducted landfill operations from
    1972 to 1978. PBB-contaminated feed has recently been found in the
    landfill. A decontamination programme has been recommended (Anon.,
    1988).

         The Michigan Chemical Corporation stated that, in their
    opinion, PBBs would eventually undergo oxidative/biological
    degradation forming carbon dioxide, water, and bromide ion (Cordle
    et al., 1978). However, studies on PBBs in soil indicate that they
    may remain in soils for many years, because of their resistance to
    degradation (Jacobs et al., 1976).

    4.3.2  Thermal decomposition of PBBs

         There is little information on the pyrolysis of PBBs. The
    products of the thermal decomposition of PBBs depend on the
    temperature as well as on the amount of oxygen present.

         Norris et al. (1973) constructed a special apparatus to measure
    the relative amounts of bromine from octabromobiphenyl converted
    during combustion, when these materials were used as additives in
    thermoplastic resins. An exact temperature is not given. Hydrogen
    bromide and bromine were not detected.

         Waritz et al. (1977) carried out experiments to determine the
    approximate lethal temperature of hexa- and octobromobiphenyl. The
    dense clouds of fumes obtained at 350 °C were lethal to rats whereas
    those produced at 290 °C were not. The fumes were not analysed.

         Earlier experiments by Benbow & Cullis (1975) on the pyrolysis
    of decabromobiphenyl pressed together at 160 °C with polystyrene and
    polypropylene, respectively, showed that, during flameless
    combustion, decabromobiphenyl appeared to be volatilized virtually
    unchanged from the polymer, whereas when the polymer burned, the
    decabromobiphenyl was converted quantitatively to hydrogen bromide.

         In these early experiments, the analytical methods were not so
    refined that it was possible to detect furans and dioxins. O'Keefe
    (1978) pyrolyzed samples of FireMaster FF-1 at 380-400 °C in open
    glass tubes and in tubes sealed after nitrogen flushing. Analysis by
    low resolution direct probe mass spectrometry showed the presence of
    tetra- and pentabrominated dibenzofurans in extracts of the open
    tube pyrolyzed material and trace levels of tetrabromodibenzofuran
    in those from PBB pyrolyzed under nitrogen.

         Buser et al. (1978) studied the pyrolysis of FireMaster BP-6
    with oxygen in sealed tubes. The flame retardant was completely
    destroyed at 700 °C, but, at 600 °C, new compounds were formed, one
    of which was probably tetrabromodibenzofuran.

         The diversity of possible brominated and mixed brominated
    furans and their toxicological implications led to further
    refinements in analytical methods (Buser, 1986) and to the demand
    for, and synthesis of, suitable standard isomers (Mason et al.,
    1987a; Sovocool et al., 1987a; Munslow et al., 1989). There are over

    5000 halogenated dibenzodioxins and dibenzofurans containing
    chlorine and/or bromine, over 400 of which are 2,3,7,8-substituted
    tetra-, penta- and hexahalo congeners suspected to be of high
    toxicity (Buser 1987). These mixed congeners are of particular
    importance with regard to chemical waste burning (Schäfer &
    Ballschmiter, 1986).

         Investigations into the pyrolysis of FireMaster BP-6 in the
    absence of oxygen have shown that small amounts of bromobenzenes and
    lower brominated biphenyls are formed (600-900 °C), but no furans
    (Thoma et al., 1987a; Thoma & Hutzinger, 1989).

         In contrast, the pyrolysis of FireMaster BP-6 in an open quartz
    tube (700-900 °C) in the presence of oxygen yielded over 3 mg/kg
    (ppm) of di- to heptabrominated dibenzofurans, though the pyrolysis
    of pentabromodiphenyl ethers yielded brominated dibenzofurans at
    over 300 times this level (Thoma et al., 1987a). In the presence of
    polystyrene and polyethylene, higher levels of brominated
    (mona-tetra) dibenzofurans (over 8 and 51 mg/kg (ppm), respectively)
    were found (Thoma et al., 1987a). Pyrolysis of FireMaster BP-6 with
    PVC at 800 °C yielded mixed bromide/chloride biphenyls, the bromine
    atoms being substituted by the chlorine. No ring closure to dioxins
    and furans occurred (Thoma et al., 1987b).

         Decabromobiphenyl was pyrolyzed for 10 min at 800 °C in a
    loosely plugged quartz tube. The pyrolysates were extracted with
    toluene and after clean-up, analysed using GC/MS. No brominated
    dioxins or dibenzofurans were detected (detection limits
    0.2-0.8 µg/g). The clean-up was said to be very difficult because of
    the formation of a large number of brominated compounds that were
    not dioxins or furans. Debromination of decabromobiphenyl appeared
    to be the main reaction, but no details were given (Atochem, 1987).

         Zacharewski et al. (1988) pyrolyzed samples of FireMaster(R)
    BP-6 in open quartz tubes at 800 °C for 10 min. The resulting
    products, mainly tetrabromodibenzofurans (1183 µg/g) but also
    tribromo-, pentabromo-, hexabromo-, and heptabromodibenzofurans
    (187, 584, 107, and 11 µg/g, respectively), were tested for toxicity
    (see section 8.12.3.2). Very little is known about the toxicities of
    brominated and brominated/chlorinated dioxins and furans, but they
    are estimated to be of the same order as those of PCDD and PCDF
    (Mason et al., 1987a; Safe, 1987).

         Analysis of actual environmental samples has also been carried
    out. Monobromo-polychloro substituted benzenes, biphenyls,
    dibenzodioxins, and dibenzofurans have been detected in solid
    material collected from a chimney of an industrial waste incinerator
    (Schäfer & Ballschmiter, 1986). Brominated dibenzo furans with a
    very small amount of mixed brominated/chlorinated compounds were
    detected in soot from an accidental fire at a bowling alley (Buser,

    1986). Schwind et al. (1988; 1989) analysed samples from a municipal
    waste incinerator and detected for the first time a complete series
    of tetrahalogenated dibenzofurans (Cl4DF, Br1Cl3DF,
    Br2Cl2DF, Br3Cl1DF and Br4DF). It is possible that PBCDD/F
    could occur during the incineration of flame retardant-treated
    plastic material, which produces PBDD and PBDF. These could react
    with PVC via the mixed brominated/chlorinated dioxins and furans to
    PCDD and PCDF (Schwind et al., 1988).

         As with PCB disposal, the destruction of PCB-contaminated waste
    should be carefully controlled. For PCBs, a burning temperature
    above 1000 °C for 2 seconds is recommended (WHO/EURO, 1987).

    5.  ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

    5.1  Environmental levels

    5.1.1  Air

         Only one report is available on PBB levels in air. It refers to
    air samples taken in the vicinity of three PBB-manufacturing or -
    processing plants in the USA (Stratton & Whitlock, 1979). Traces of
    hexabromobiphenyl (0.06-0.10 ng/m3) were found at two of the three
    industrial sites examined.

         Further information on PBB levels in ambient air, e.g., near
    municipal incinerators, is lacking.

    5.1.2  Water and sediments

    5.1.2.1  Surface waters

         Surface waters have been monitored in the vicinity of PBB-
    producing or -processing industrial sites in the USA and in the
    vicinity of the Gratiot County landfill (Michigan, USA), which had
    received 122 000 kg of wastes containing 60-70% PBBs between 1971
    and 1973. The results are summarized in Table 21.

         Depending on the sources, the predominant PBB compounds
    detected in surface waters were hexabromobiphenyl and
    decabromobiphenyl. However, only Stratton & Whitlock (1979)
    determined all PBB homologues from Br1 to Br10, the percentage
    composition of some of which is given in Table 22.

    5.1.2.2  Sediments

         Generally, PBBs reach higher concentrations in sediments (Table
    23) than in the associated waters (Table 21).

         PBB concentrations in sediments of the Pine River were as high
    as 77 mg/kg near the Michigan Chemical Corp. plant. The assays
    conducted from July 1974 to April 1975, upstream and downstream of
    the plant, showed a decline in sediment PBB content to 6.2 mg/kg,
    half a mile downstream, and to 0.1 mg/kg, 24 miles or 29 miles
    downstream (Hesse & Powers, 1978).

    
    Table 21.  PBB levels in surface waters near sites of manufacture, use, or disposal in the USA

    Site                        Date of sampling    No. of         PBB compound       PBB concentration      References
                                                    samples        examined           (µg/litre)

    Pine River                 1974                 8              HxBB               0.01-3.2               Hesse (1975)
    (downstream from
    the Michigan
    Chemical Co.,
    St. Louis)

    Tittabawassee              1974                 2              HxBB               < 0.01
    Rivera

    Canal (called              1977                 3              total PBB          not detected-46        Stratton & Whitlock (1979);
    Platti Kill) in the                                            (MoBB-DeBB)                               DeCarlo (1979)
    vicinity of White
    Chemical Co., Bayonne,
    New Jersey

    Canal (discharging         1977                 1              total PBB          < 0.2                  Stratton & Whitlock (1979)
    into Kill van Kull                                             (HxBB-DeBB)
    River) in the vicinity
    of Standard T Chemical
    Co., Staten Island,
    New York

    Storm sewer,               1977                 5              total PBB          < 0.2-210              Stratton & Whitlock (1979);
    receiving swamp, etc.                                          (HxBB-DeBB)                               DeCarlo (1979)
    in the vicinity of
    Hexcel Fine Organics
    Sayreville, New Jersey

    Table 21 (contd).

    Site                       Date of sampling     No. of         PBB compound       PBB concentration      References
                                                    samples        examined           (µg/litre)

    Drain waters at            1977                 not            HxBB               0.1-14                 Shah (1978);
    or near the margin                              specified                                                Rosenblatt et al. (1982)
    of the Gratiot County
    landfill, Michigan

    a    Note that PBBs were not detected in fish from the Tittabawassee River in 1974 but were detected in 1983 (see Table 30).

    
    Table 22. Percentage of different PBB homologues detected in surface water
    samples taken in the vicinity of PBB-producing plantsa

    PBB homologues            Bayonne, New Jersey             Sayreville, New Jersey
                              (White Chemical Corp.)b         (Hexcel Corp.)c

                              Sample 1        Sample 2        Sample 1       Sample 2

    PeBB                         1               0               -              -

    HxBB                         4               2               5              < 1

    HpBB                         2               2               1.6            < 1

    OcBB                         2               17              1              1

    NoBB                         15              20              1              2.6

    DeBB                         76              58              91             96

    a    From: Stratton & Whitlock (1979).
    b    Producer of octa- and decabromobiphenyl along with bromobiphenyl ethers.
    c    Producer of laboratory quantities of various PBBs.
    
         Concentrations measured upstream were all less than the
    sensitivity limit of 30 µg/kg with the exception of one sample
    collected a quarter of a mile upstream of the plant, which contained
    60 µg/kg (Hesse, 1975). This latter analysis was repeated in 1977
    (Hesse & Powers, 1978) giving 350 µg/kg (detection limit 100 µg/kg).

         Hesse & Powers (1978) compared the PBB levels of Pine River
    sediments from the same locations over a period of time after the
    termination of FireMaster(R) BP-6 production. The results of the
    1976 and 1977 analyses showed that PBB distributions and
    concentrations in the sediments had not changed significantly in the
    three years after PBB manufacture stopped.

         Various PBB homologues were identified again only by Stratton &
    Whitlock (1979) who examined aquatic sediments, sludge deposits, and
    marsh soils near the sites of manufacture and use of PBBs in New
    Jersey and New York (see Table 24).

         More recently, sewage sludge has been analysed for PBBs
    (Strachan et al., 1983). The authors did not detect any PBBs, PCBs,
    or chlorinated hydrocarbon pesticides in the three sludge samples
    obtained from sewage treatment plants in three Indiana cities (USA).
    However, the detection limit for PCBs and PBBs with the GC-MS system
    used was about 10 µg/g, and this apparently is not sensitive enough,
    even for PCBs. For example, the amounts of PCBs found in sewage
    sludge of German (Lorenz, 1983) and Canadian (Webber et al., 1983)
    cities ranged from 1.8 to 2.5 µg/g (dry weight) and from 0.13 to
    1.61 µg/g (dry weight), respectively. Values for PBBs have not been
    reported in these investigations.

    
    Table 23.  PBB levels in sediments and sludge from surface waters near sites of manufacture, use, or disposal in the USA

    Site                             Date of sampling    No. of       PBB compound     PBB concentration     References
                                                         samples      examined         (µg/kg dry weight)

    Near Michigan                         1974/75         19              HxBB            < 30-77 000        Hesse (1975)
    Chemical Co.                           1974            9                              < 100-9200         Hesse & Powers (1978)
    Pine River                             1976            9                              < 100-1200
                                           1977            8                               < 100-500

    Tittibawassee River                    1974            2                                 tr-16           Hesse (1975)

    Near White Chemical                    1977            3            total PBB           < 10-20          Stratton & Whitlock (1979)
    Co., Bayonne, New Jersey:                                          (MoBB-DeBB)
    Sediments from Platti
    Kill Canal and Kill
    van Kall River

    Sludge from Platti                                     1                                431 000
    Kill Canal

    Near Standard T Chemical               1977            1                                  60
    Co., Staten Island, New
    York Sediment from Kill
    van Kull River (at
    discharge site)

    Near Hexcel Fine                       1977            1            total PBB            4600            Stratton & Whitlock (1979)
    Organics, Sayreville,                                              (MoBB-DeBB)                           DeCarlo (1979)
    New Jersey
    Marsh Soil

    Table 23 (contd).

    Site                             Date of sampling   No. of        PBB compound     PBB concentration     References
                                                        samples         examined      (µg/kg dry weight)

    Gratiot County                         1977           not             HxBB            up to 17 000       Shah (1978)
    landfill, Michigan                                 specified                                             Rosenblatt et al. (1982)

    Associated sediments
    of surface drain waters

    

        Table 24. Concentration of PBB-homologues in aquatic sediment, sludge deposit,
    or marsh soil samples taken in the vicinity of PBB-producing or -processing
    plantsa (µg/kg dry weight)

    PBB                Bayonne, New Jersey                  Staten Island,    Sayreville,
                      (White Chem. Corp.)b                  New Jersey        New Jersey
                                                            (Standard T       (Hexcel
                                                            Chem Corp.)c      Corp.)d
                                                                                            
                Sediment                      Sludge        Sedimente         Marsh soile
                samples:e
                1 + 2         3

    MoBB           -         n.d.               540            n.d.              n.d.
    DiBB           -         n.d.              2200            n.d.              n.d.
    TrBB           -         n.d.              4300            n.d.              n.d.
    TeBB           -         n.d.              n.d.            n.d.              n.d.
    PeBB           -         n.d.               590            n.d.              n.d.
    HxBB         n.d.          10              3800              40                30
    HpBB         n.d.          10              3300              20              n.d.
    OcBB         n.d.        n.d.              3600            n.d.              n.d.
    NoBB         n.d.        n.d.            22 500            n.d.                80
    DeBB         n.d.        n.d.           390 000            n.d.              4500

    a    From: Stratton & Whitlock (1979).
    b    Producer of octa- and decabromobiphenyl along with bromobiphenyl ethers.
    c    Major user of FireMasterR BP-6.
    d    Producer of laboratory quantities of various PBBs.
    e    n.d. = Not detected (detection limit = < 10 µg/kg).
    
         Surficial sediments from the St. Lawrence River (USA/Canada)
    were analysed for HxBB, but the compound was not detected (estimated
    detection limit: 1 ng/g) at the ten stations surveyed (Sloterdijk,
    1991).

    5.1.2.3  Groundwater

         Groundwater monitoring data from the Gratiot County landfill
    (Michigan, USA) mentioned above, have shown trace levels of PBBs,
    even outside the landfill area (see Table 25). However, so far,
    domestic drinking-water wells have not shown any traces of PBBs
    (Shah, 1978). Groundwater near the disposal site of PBB-
    contaminated animals and other products (see section 4.3.1) in
    Kalkaska County (Michigan, USA) is reported not to be contaminated
    by PBBs (Shah, 1978).

    Table 25. PBB levels in groundwater from Gratiot County landfill, 1977a

    Site                       No. of              PBB compound           PBB
                               samples             examined               concentration
                                                   range (µg/litre)

    Test wells within          4                   HxBB                   0.5-26
    the landfill site

    Observation wells          11                                         0.1-4.4
    outside the landfill
    area

    Domestic                   not specified                              not detected
    drinkingwater wells
    near the landfill

    a    From: Shah (1978).

    5.1.3  Soil

         Data on soil pollution by PBBs are available for areas of
    manufacture, use, or disposal of PBBs (Table 26), and for soils from
    fields, etc. of the PBB-contaminated Michigan farms (Tables 27 and
    28).

         Concentrations of PBBs in soils from industrial sites were
    highest (more than 2000 mg/kg) in areas around the Michigan Chemical
    Company (see Table 26). Although such highly  contaminated soils
    were removed (Hesse & Powers, 1978), Hill et al. (1982) still found,
    some years later, PBB levels up to 2130 mg/kg in soils of the former
    manufacturing site. Various PBB homologues from Br4 to Br10 were
    present in the industrial soil samples (see Table 27).

    
    Table 26.  PBB levels in soils near sites of manufacture, use, or disposal in the USA

    Site                        Date of sampling    No. of         PBB compound           PBB concentration      References
                                                    samples        examined               (range) dry weight

    Michigan Chemical Co.,
    St. Louis, Michigan

    bagging area                not specified       1              HxBB                   3500 mg/kg             Hesse (1975);
                                                                                                                 Hess & Powers (1978)
    loading area of             not specified       1              HxBB                   2500 mg/kg
    the plant

    "former manufacturing       not specified       3              PBB                    16-2130 mg/kg          Hill et al. (1982)
    site"                                                          (C12H6Br4-C12H3Br7)

    Vicinity of White
    Chemical Co.,
    Bayonne, New Jersey

    150 m east                  1977                1              total PBB              4.250 mg/kg            Stratton & Whitlock (1979)

    150 m west of the           1977                1              (C12H9Br1-C12Br10)     1.135 mg/kg            DeCarlo (1979)
    plant

    not specified               not specified                      PBB                    0.75-2.8 mg/kg         Di Carlo et al. (1978)

    Vicinity of Standard        1977                4              total PBB              10-100 µg/kg           Stratton & Whitlock (1979)
    T Chemical Co., Staten                                         (MoBB-DeBB)
    Island, New York

    75 m south west                                                                       30

    900 m west                                                                            10

    Table 26 (contd).

    Site                        Date of sampling    No. of         PBB compound           PBB concentration      References
                                                    samples        examined               (range) dry weight

    1500 m south                                                                          10

    700 m east (prevailing                                                                100
    down-wind direction)

    Vicinity of Hexcel          1977                               total PBB                                     Stratton & Whitlock (1979);
    Fine Organics,                                                 (MoBB-DeBB)                                   DeCarlo (1979)
    Sayreville, New Jersey

    75 m southeast                                  1                                     40 µg/kg

    Soil in roadside                                1                                     3400 µg/kg
    ditch

    Gratiot County landfill,
    St. Louis, Michigan

    Samples inside of the       not                 not            "PBB"                  12 (16) mg/kg          Rosenblatt et al. (1982)
    landfill from the           specified           specified      HxBB
    uppermost 2.5 cm
    (after capping of
    the landfill)

    Sample somewhat distant                                        "PBB"                  61 µg/kg
    from the landfill, in                                          (HxBB)
    the area of the Michigan
    Chemical plant

    Table 27.  Concentration of PBB homologues detected in soil samples taken in the vicinity of PBB-producing or processing plants
    (µg/kg dry weight)

    PBB         Bayonne, New Jerseya        Staten Island, New Yorka         Sayreville, New Yorka     Michiganb
                (White Chemical Corp.)c     (Standard T-Chemical Corp.)d     (Hexcel Corp.)e           (Michigan Chemical Corp.)f

    MoBB              n.d.g                            n.d.g                          n.d.g                      -
    DiBB              n.d.g                            n.d.g                          n.d.g                      -
    TrBB              n.d.g                            n.d.g                          n.d.g                      -
    TeBB              n.d.g                            n.d.g                          n.d.g               < 1000-510 000
    PeBB              n.d.g                          n.d.-100                         n.d.g                 4000-60 000
    HxBB              15-30                           n.d.-10                         40-90               12 000-670 000
    HpBB             30-110                           n.d.-10                        n.d.-90              < 1000-190 000
    OcBB             90-150                            n.d.                         n.d.-170                     -
    NoBB            330-2200                           n.d.                         n.d.-440                     -
    DeBB            530-2100                          n.d.-10                       n.d.-2600                    -

    a    Data from: Stratton & Whitlock (1979); No. of samples = 2, 4, 2 respectively.
    b    Data from: Hill et al. (1982); No. of samples = 3.
    c    Producer of octa- and decabromobiphenyl along with bromobiphenyl ethers.
    d    Major user of FireMaster(R) BP-6.
    e    Producer of laboratory quantities of various PBBs.
    f    Producer of FireMaster(R) BP-6.
    g    n.d. =  Not detected (detection limit = < 10 µg/kg).

    
    Table 28.  Composition and concentration of PBBs in soil samples from former
    FireMaster(R) manufacturing plant site (St. Louis, Michigan)a

                                     % Composition (concentration in mg/kg)
                              FireMaster(R)
    Compound                  Lot #5143       Soil 1          Soil 2        Soil 3

    Tetrabromobiphenyls        < 0.1        23.9 (510)       11.3 (6)        (< 1)

    Pentabromobiphenyls

    2,2',4,5,5'-                3.9          2.8 (60)         9.4 (5)      12.5 (2)
    2,2',4,4',5-               < 0.1         5.2 (110)         (< 1)         (< 1)
    2,3',4,4',5-                5.7         27.7 (590)        9.4 (5)      12.5 (2)

    Hexabromobiphenyls

    2,2',4,4',5,5'-            54.9         24.4 (520)       56.6 (30)     62.5 (10)
    2,2',3',4,4',5-            10.3          4.7 (100)        7.5 (4)       6.2 (1)
    2,3',4,4',5,5'-             5.0          1.9 (40)         5.7 (3)       6.2 (1)
    2,3,3',4,4',5-              2.1          0.5 (10)          (< 1)         (< 1)

    Heptabromobiphenyls

    2,2',3,4,4',5,5'-          12.8          5.2 (110)         (< 1)         (< 1)
    2,2',3,3',4,4',5-           1.7          3.8 (80)          (< 1)         (< 1)

    (Total PBBs)              (2130)           (53)            (16)

    a    Adapted from: Hill et al. (1982).

         Hill et al. (1982) identified not only PBB homologues, but also
    the isomeric composition of PBBs in the soil samples from the
    Michigan Chemical Corp. plant (Table 28). Thus, they provided more
    exact analytical data and were able to make an interesting
    comparison with the original FireMaster(R) mixture; conclusions
    could then be drawn on the environmental fate of PBBs (section 4.2).
    According to Shah (1978), test samples of the Gratiot County
    landfill showed that, in general, the concentrations of PBBs in the
    fill increased with depth and were highest at a depth of 3 to 7.6 m
    below the top of the refuse.

         As a consequence of the Michigan cattle food mixing error, the
    soils of the farms involved have been contaminated by PBBs, mainly
    through the faeces of the exposed animals. Fries (1985b) calculated
    that about 145 kg of PBBs were distributed in this way, and that
    most of this was located on 20-25 farms. (The total number of
    quarantined farms was over 500; Robertson & Chynoweth, 1975).

         Concentrations of PBBs in soil samples from fields that had
    received PBB-contaminated manure were as high as 371 µg/kg (dry
    weight), whereas levels in samples from manure piles and from dirt
    exercise lots were as high as 2000 µg/kg (Jacobs et al., 1978;
    Fries, 1985b).

         Soil contamination by PBBs can result in PBB accumulation in
    animals, when they have direct access to the contaminated soil. 
    This is most likely to occur when animals are confined to dirt lots
    on which manure-containing PBB has been deposited. Crops grown on
    PBB-contaminated soils are not considered an important source of PBB
    contamination in animals (Fries & Jacobs, 1986).

         Soils from industrial sites have, in general, been more heavily
    contaminated than Michigan soils.

    5.1.4  Feed and food

    5.1.4.1  Feed

         Contamination of feed by PBBs has been reported only in
    connection with the Michigan PBB incident.

         In 1973, about 290 kg (Fries, 1985b) - 1000 kg (IARC, 1978) of
    FireMaster(R) FF-1 was inadvertently mixed in cattle feeds and
    delivered to Michigan farms.

         Three feed preparations appeared initially to be involved in
    the Michigan episode with PBB levels as follows:

         Feed No. 405, 2.4 mg PBB/kg,
         Feed No. 410, 1790 mg PBB/kg,
         Feed No. 407, 4300 mg PBB/kg
         (Cordle et al., 1978).

         A concentration as high as 13 500 mg PBB/kg was also cited
    (Kay, 1977; Di Carlo et al., 1978; Damstra et al., 1982). Feed of
    one highly contaminated farm (Halbert farm) is reported to have
    contained 2900 mg PBB/kg (Fries, 1985b).

         In 1974, 68% of 1770 feed samples collected in Michigan
    contained PBB residues: 60% in the range of trace to 0.99 mg/kg, and
    8% over 1 mg/kg. Resampling in 1975 revealed that 6% of 1208 feed
    samples were contaminated and that fewer than 0.16% contained more
    than 1 mg PBB/kg. In 1976, only 0.3% of 663 samples analysed were
    contaminated: no samples contained more than 0.1 mg/kg (Di Carlo
    et al., 1978).

         PBB residues were not detected in harvested forages grown on
    soils with residue levels as high as 0.3 mg/kg (Fries & Jacobs,
    1980).

         In 1974 and 1975, low-level feed contamination with PBBs was
    detected in Indiana and Illinois, which are neighbours of Michigan
    (Di Carlo et al., 1978).

    5.1.4.2  Food

         Again, almost all the data available on PBB residues in food
    are derived from the Michigan cattle food contamination incident in
    1973.

         The extent to which the general population was exposed depended
    on where they obtained their milk, dairy products, and eggs, i.e.,
    direct from the contaminated farms or from sources where
    contaminated products had been mixed with non-contaminated samples.
    Table 29 shows examples of some PBB levels in Michigan foods.
    Whereas in 1974 milk from some highly contaminated cows contained
    PBB concentrations of up to 900 mg/kg fat (Robertson & Chynoweth,
    1975), canned milk samples contained concentrations of up to
    1.6 mg/kg fat (Cordle et al., 1978). The most highly contaminated
    milk (1 to > 100 mg PBB/kg milk fat) originated from a total of 40
    herds with different levels of PBBs at the time of detection (Fries,
    1985b). In 1975, PBBs were still detected in milk from some herds
    (Kay, 1977).

         Data on meat can be derived from Table 33, which shows PBB
    levels in Michigan farm animals.

         Milk contains far less fat than meat (about 4% versus 30%), and
    butterfat contains only 40% of the PBB concentration found in the
    animal from which it comes (Fries et al., 1978b; Rosenblatt et al.,
    1982). Among the dairy products, PBBs are again concentrated in the
    high-fat products (Murata et al., 1977; Zabik et al., 1978).

    Table 29. Some examples of PBB levels in food (contaminated as a consequence of
    the Michigan PBB incident in 1973)

    Product                  Year of       PBB concentration      References
                             sampling      (mg/kg)

    Milka                    1974           2.8-270.5h            Cordle et al. (1978)
    Milkb                    1974             44-900h             Robertson & Chynoweth (1975)
    Milkc                    1974             43-56h              Jackson & Halbert (1974)
    Milkd                    1974            up to 595            Kay (1977); IARC (1978)
    Milke                    1974            1-> 100h             Fries (1985b)
    Canned milk              1974           1.15-1.62h            Cordle et al. (1978)
    Dry skimmed milkf        1974            0.75-1.5             Isleib & Whitehead (1975)
    Fluid milk               1974           < 0.02-1.15
    processors' products
    Butter                   1974              1-2h               Cordle et al. (1978)
    Cheese                   1974            1.4-15.0h
    Milkg                    1975              1-13h              Kay (1977); IARC (1978)
    Eggs                     1974           up to 59.7

    a    = Collected from individual farms.
    b    = Collected from 21 cows.
    c    = Collected from 2 cows (having 174 and 200 mg PBBs/kg in body fat,
           respectively).
    d    = Collected from 22 farms.
    e    = Collected from 28 herds.
    f    = From one dairy plant.
    g    = Collected from 16 herds.
    h    = On a fat basis.
    
         In May 1974, the US Food and Drug Administration (FDA)
    established the following enforcement limits for unavoidable
    residues of PBBs in foods: 1 mg/kg in the fat of meat, milk, and
    dairy products, 0.3 mg/kg in animal feeds, 0.1 mg/kg in eggs. These
    enforcement guidelines were reduced in November 1974 to 0.3 mg/kg in
    the fat of meat, milk, and dairy products, and 0.5 mg/kg in eggs and
    animal feeds. In February 1977, the FDA rejected a petition to lower
    the enforcement guideline level to 0.02 mg/kg for all food products
    (IARC, 1978). However, according to Fries (1985b), final
    legislation, Act 77, lowered the tolerance to 0.02 mg/kg in the body
    fat of all cull dairy cows offered for slaughter. (Unlike the
    situation under the previous regulations, the finding of a single
    animal with a higher than legal body fat level did not lead to
    quarantine and the disposal of the whole herd.) As a result of the

    rigid quarantine policy, the food levels of PBBs decreased in
    Michigan. In 1975, none of 18 milk samples, 3 out of 14 butter
    samples, and none of 13 cheese samples exceeded FDA guidelines
    (0.3 mg/kg). Also in 1975, 245 of 2040 meat samples were
    contaminated with PBBs: 24 contained more than 0.3 mg/kg. None of
    the meat specimens collected in 1976 exceeded FDA guidelines: 96% of
    1430 samples were contaminated, but only 1 sample contained more
    than 0.6 mg/kg of PBBs. A market basket survey of meat in 1976
    revealed detectable PBBs in only 1 out of 102 samples in Michigan
    (Di Carlo et al., 1978).

         Additional information on PBB findings is presented in several
    government reports, which are cited by Di Carlo et al. (1978).
    According to these reports 29 170 products had been assayed. In
    1974, 14 out of 16 milk samples, 4 out of 34 butter samples and 11
    out of 23 cheese samples, collected in Michigan, were found to
    exceed FDA guidelines for PBBs. Another survey showed that 24.9% of
    272 finished product samples, collected from May to October 1974,
    were contaminated with PBBs and that 15.8% contained more than
    0.3 mg/kg (Di Carlo et al., 1978).

         PBBs were also detected in other states in the USA, for example
    in beef in Iowa, duck in Wisconsin, chicken in Alabama, Mississippi,
    New York, and Texas, and turkey in Indiana: the levels were
    extremely low. During 1975 and 1976, PBBs were found in 9 out of 597
    food samples outside of Michigan (Di Carlo et al., 1978).

         Food contamination, not derived from the Michigan PBB-
    incident, becomes evident, when looking at PBB levels in fish (see
    Table 30) some of which are used for human consumption. For example,
    skinless fillets of carp from the Pine River, captured in the
    vicinity of Michigan Chemical Company, contained 1.33 mg PBBs/kg
    (wet weight basis) which is approximately equivalent to 30 mg/kg on
    a fat weight basis (Hesse & Powers, 1978). This was obviously
    greatly in excess of the US FDA tolerance limit for beef, a
    tolerance limit for fish has not been established (Hesse & Powers,
    1978).

         More recent information on "background" PBB levels in food may
    be expected in future via a USA data collection programme
    (Foodcontam) initiated by the US Food and Drug Administration which
    includes PBBs besides other chemicals (Minyard et al., 1989).

    
    Table 30.  PBB levels in fish

    Year        Region                         Species             Type of          PBB concentration     Weight     PBB           References
                                                                   sample           (µg/kg)               basis      examined

    1974        Pine River, downstream         Carp                skinless         not detected-1330     wet          HxBB        Hesse &
                from St. Louis (vicinity       (Cyprimus carpio)   fillets                                                         Powers
                of Michigan Chemical Co.)                                                                                          (1978)

                                               White sucker                                670
                                               Northern pike                               540
                                               Bullhead                                  450-780

    1974        Tittabawassee                  Carp                                   not detected
                River                          (Cyprimus carpio)

                                               Freshwater drum                        not detected
                                               (Aplodinotus
                                               grunniens

    1976        Pine River, downstream         Carp                                      60-750
                from St. Louis (vicinity       (Cyprimus carpio)
                of Michigan Chemical Co.)

                                               Northern pike                             180-230

    1976        Pine River, downstream         Largemouth          skinless         not detected-740      wet          HxBB        Hesse &
                from St. Louis (vicinity       bass                fillets                                                         Powers
                of Michigan Chemical Co.)                                                                                          (1978)

                                               Smallmouth bass                             130
                                               Rockbass                                  320-700

    Table 30 (contd).

    Year        Region                         Species             Type of          PBB concentration     Weight     PBB           References
                                                                   sample           (µg/kg)               basis      examined

    1977        Kill van Kull River            Killifish           whole                   220            dry        total PBB     Stratton &
                (vicinity of White Chemical                        HxBB-DeBB                                                       Whitlock
                Co., Bayonne, New Jersey);                                                                                         (1979)
                Port Johnson

    1977        Kill van Kull River            Killifish           whole                   230            dry        total PBB
                (vicinity of Standarad T                           HxBB-DeBB
                Chemical, Staten Island,
                New York); canal at
                discharge site

    Not         Lake Huron                     Yellow perch                              0.3-0.8                                   Kreis & Rice
    specified   (Saginaw Bay)                                                                                                      (1985)
                Saginaw Bay                    Catfish                                    21.0

    1983        Pine River                     Hogsucker           whole                  6000            fat          most        Jaffe et al.
                                                                                                                     abundant      (1985)
                                                                                                                     congeners

    1983        Chippewa River                 Carp                                    5300-15 000

    1983        Tittabawassee                                                            140-160
                River

    1983        Shiawassee River                                                           120

    Table 30 (contd).

    Year        Region                         Species             Type of          PBB concentration     Weight     PBB           References
                                                                   sample           (µg/kg)               basis      examined

    1983        Flint River                                                               15-32

    1983        Saginaw River                                                            80-200

    1983        Saginaw Bay                                                             110-1100

    

         Four samples of cow's milk from Germany have been analysed for
    PBBs (Krüger, 1988). Three congeners were detected; BB 153
    (0.025-0.053 µg/kg milk fat), BB 180 (0.001-0.007 µg/kg) and BB 187
    (0.005-0.014 µg/kg). The other 30 congeners covered by the method
    were not detected with detection limits ranging from 0.001 to
    0.003 µg/kg milk fat (see Table 33).

         The processing and cooking of contaminated food have been found
    to have some potential for reducing PBB levels. Spray-drying
    appeared to reduce the contents of PBBs in whole milk and skim milk
    by 30-36% and 61-69%, respectively (Murata et al., 1977; Zabik
    et al., 1978). Pressure cooking of chicken pieces also resulted in a
    loss of PBBs, however, part of the PBBs lost were found in the drip
    (Zabik et al., 1978).

    5.1.5  Other products

         Antibiotics used for attending farm animals were also found to
    be contaminated: Levels of PBBs in aureomycin, which was distributed
    by the Michigan Farm Bureau, were as high as 70 mg/kg (Di Carlo
    et al., 1978).

    5.1.6  Terrestrial and aquatic organisms

    5.1.6.1  Aquatic and terrestrial plants

         Only few data on PBB contamination of aquatic and terrestrial
    plants are available. Stratton & Whitlock (1979) analysed algae
    (e.g., filamentous green algae) from surface waters in the vicinity
    of White Chemical (Bayonne, New Jersey) and near Standard T Chemical
    Company (Staten Island, New York) for PBBs (MoBB through DeBB). The
    two samples did not contain detectable levels of PBBs (detection
    limit: 10 µg/kg, dry weight). However, bottom sediments taken in the
    same location contained hexa- and heptabromobiphenyl.

         Surface contamination was observed on terrestrial vegetation in
    the vicinity of PBB facilities (up to 92 mg/kg dry weight; Stratton
    & Whitlock, 1979). As Chou et al. (1978) reported, the PBB
    contamination of field soils in Michigan (USA) did not result in any
    detectable surface contamination of field crops.

    5.1.6.2  Animals

    a) Wildlife

         Most earlier data available on PBB contamination of wildlife
    refer to freshwater fish (Table 30) and birds (Tables 31 and 32),
    primarily waterfowl in the USA. Recent reports refer to PBB
    contamination of fish-eating mammals and birds from marine

    environments in the USA (Kuehl et al., 1991) and in Europe (Jansson
    et al., 1987, 1992; Krüger, 1988). Residues were found also in
    terrestrial mammals (Jansson et al., 1992) and in freshwater and
    marine fish in Europe (Krüger, 1988; Jansson et al., 1992).

         Table 30 gives PBB levels in fish captured for analysis in
    industrialized areas of the USA, at various distances from PBB-
    containing or -using facilities. PBBs were detected in several fish
    species from all rivers or bays examined. The PBB levels ranged up
    to a maximum of 1.33 mg/kg wet weight (approximately equivalent to
    30 mg/kg on a fat basis) found in carp from the Pine River near
    Michigan Chemical Company (Hesse & Powers, 1978).

         No apparent change in PBB concentrations was observed in Pine
    River fish between 1974 and 1976 (Hesse & Powers, 1978; see also
    Table 30). Although Michigan Chemical Co. had terminated PBB
    production in 1974, even in 1983, Jaffe et al. (1985) detected PBB
    in fish from the Saginaw River system, with highest concentrations
    in fish from Pine and Chippewa Rivers (Table 30). While carp from
    Tittabawassee River, to which Pine River joins, did not contain any
    detectable PBBs in 1974, PBB-residues were detected (approximately
    150 µg/kg on a fat basis) in 1983 (Table 30).

         Various PBB homologues were examined in killifish  (Oryzias
     latipes) from Kill van Kull River near White Chemical Co.
    (Bayonne, New Jersey). The main component found was NoBB. In the
    vicinity of a FireMaster(R)-using facility (Staten Island, New
    York), killifish samples contained only HxBB (Stratton & Whitlock,
    1979).

         PBB contamination has been reported in wild ducks collected
    within two miles of the Michigan Chemical Corporation plant (Table
    31), in eggs of waterfowl nesting around Green Bay and other areas
    of Lake Michigan and on Lake Michigan island (Table 32), and, in
    bald eagles found moribund or dead in 13 US states (Table 31).

         Approximately one third of bald eagles examined contained PBB
    residues (see Table 31).

         Concentrations of PBBs in duck samples with skin left on were
    considerably higher than those in skinless samples (see Table 31)
    indicating that much of the PBBs is associated with the skin or fat
    layer between the skin and muscle (Hesse & Powers, 1978).

    
    Table 31.  PBB residues in birds (ducks and bald eagles)

    Year     Region             Species            Type of sample       No. of     PBB concentrationb (mg/kg wet weight)    References
                                                                       samplesa    mean            range       median

    1974     Pine River         Mallard            breast tissue          3        0.25                                     Hesse & Powers
             within two miles                      (skinless)                                                               (1978)
             downstream from
             St. Louis

                                Wood duck                                          0.29

                                Teal                                               1.8

    1976                        Mallard            breast tissue:
                                                   skinless              3c        0.24
                                                   with skin             3c        2.00

                                Wood duck
                                                                         4c        0.17
                                                                         4c        2.70

    1977                        Wood duck          breast tissue:
                                                   skinless              4c        0.08
                                                   with skin             4c        0.23

    1977                        Teal               breast tissue:
                                                   skinless            0c (1)      not detected

                                                   with skin           0c (1)      not detected

    Table 31 (contd).

    Year     Region             Species            Type of sample       No. of     PBB concentrationb (mg/kg wet weight)    References
                                                                       samplesa    mean            range       median

             13 US states       Bald eagle         found moribund                                                           Kaiser et al.
                                (Haliaeetus        or dead;                                                                 (1980)
                                leucocephalus)
                                                   carcass               10                        0.03-0.27   0.07
                                                                        (32)d

                                                   brain                  7                        0.03-0.17   0.05

    a    Number of samples containing residues; median is based on this number. Total number of samples in parentheses.
    b    PBB values were based on the major hexabromobiphenyl peak (BB 153).
    c    Paired samples.
    d    Detection limit: 0.02 mg PBBs/kg.

    Table 32.  PBB residues in eggs of fish-eating and non-fish-eating waterbirds from Green Bay and Lake Michigan (USA)

                                                                                            PBB concentrationb
    Year     Collection site                 Species                      No. of            (mg/kg wet weight)              References
                                                                          eggsa        geometric mean    range

                                             Fish eater

    1975     Green Bay                       Little gull                    1             n.d.                              Heinz et al.
             (Sensila Wildlife Area)         (Larus minutus)                                                                (1985)

    1977     three Lake Michigan islands     Red-breasted merganser        114            0.06           n.d.-0.13          Haseltine et al.
             off the tip of Door County,     (Mergus serrator)            (109)                                             (1981)
             Wisconsin

    1977     islands in north-western        Red-breasted merganser                                                         Heinz et al.
             Lake Michigan                   (Mergus serrator):                                                             (1983)
                                             eggs from the same nests
                                             randomly selected             49             0.05
                                             unhatched                     49             0.04

    1977     Lake Michigan                   Herring gull                   9             0.18           0.11-0.25          Heinz et
             (Gravel Island)                 (Larus argentatus)            (9)                          al. (1985)

    1977     Green Bay                       Common tern                   10             0.06           0.02-0.22          Heinz et al.
             (Lone Tree Island)              (Sterna hirundo)             (10)                                              (1985)

             Green Bay (St. Vital Island)    Common tern                  2 (2)           0.03           0.03-0.04
                                             (Sterna hirundo)

             Green Bay (Portage Point)                                    2 (2)           0.03           0.02-0.06

             Green Bay (Cat Island)          Double-crested               4 (3)           0.01           n.d.-0.02
                                             cormorant
                                             (Phalocrocorax
                                             auritus)

    Table 32 (contd).

                                                                                            PBB concentrationb
    Year     Collection site                 Species                      No. of            (mg/kg wet weight)              References
                                                                          eggsa        geometric mean    range

             Lake Michigan (Fish Island)                                  6 (3)           0.02           n.d.-0.05

             Green Bay (Oconto Marsh)        Black-crowned night-heron    1 (1)           0.02
                                             (Nycticorax nycticorax)

             Green Bay (Oconto Marsh)        Green-backed heron             1             n.d.
                                             (Butorides striatus)

                                             Non-fish eater

    1977     Three Lake Michigan             Mallard                       22             n.d.                              Haseltine
             islands off the tip of          (Anas platyrhynchos)                                                           et al. (1981)
             Door County, Wisconsin

    1977     Lake Michigan (three            Gadwall                        4             n.d.
             islands off the tip of          (Anas strepera)
             Door County, Wisconsin)

                                             Black duck (Anas rubripes)     3             n.d.

    a    Number of collected eggs (in parentheses: number of eggs with quantifiable levels of PBBs).
    b    PBB values were based on hexabromobiphenyl;
         n.d. = No residue of quantifiable level. Level over which quantification was possible: 0.02 mg/kg.
         Samples with no detectable residues were calculated in the means as one-half the quantification level.

         While the majority of ducks analysed from the Pine River
    contained measurable concentrations of PBBs (Table 31), the eggs of
    ducks from Lake Michigan islands did not contain detectable PBB
    residues (Table 32). In contrast, most eggs of fish-eating
    waterbirds from Green Bay and Lake Michigan showed PBB residues
    (Table 32). Highest concentrations were detected in herring gull
    eggs (0.18 mg/kg wet weight), perhaps reflecting their year round
    residence on the Great Lakes (Heinz et al., 1985).

         Stratton & Whitlock (1979) analysed a snapping turtle captured
    in the vicinity of Hexcel Fine Organics Division (Sayreville, New
    Jersey) for hexa- to decabromobiphenyls and found a tissue
    concentration of 20 µg hexabromobiphenyl/kg (dry weight).

         Di Carlo et al. (1978) reported on PBB contamination of
    miscellaneous wildlife, such as deer, rabbits, coyotes, and ravens,
    without, however, specifying the sampling locations and the levels
    of contamination.

         In Europe, 2,2',4,4',5,5'-hexabromobiphenyl (BB 153) was found
    in fish from German and Swedish rivers at concentrations ranging
    from 0.3 to 0.6 µg/kg lipid (Krüger, 1988; Jansson et al., 1992; see
    also Tables 33 and 34). A trout sample from a breeding farm
    contained much lower levels of PBBs than the fish samples from the
    rivers (Krüger, 1988).

         A residue of 22 µg BB 153/kg lipid was observed in pooled
    samples of osprey specimens found dead in various parts of Sweden
    (Jansson et al., 1992; Table 34).

         Swedish reindeers (pooled samples) showed BB 153 levels as low
    as 0.04 µg/kg lipid (Jansson et al., 1992; Table 34).

         PBBs (as a group) were not found in otters  (Lutra canadensis)
    from a region relatively remote from industrial sites in north
    eastern Alberta (Canada) (Somers et al., 1987).

         Fish samples (freshwater and marine species) collected in 1983
    from an industrial area of Japan (Osaka) did not contain "PBBs" (not
    specified) (Watanabe & Tatsukawa, 1990).

         Recently, PBBs have been identified in bottlenose dolphins
     (Tursiops truncatus) collected during the 1987/88 mass mortality
    event along the Atlantic Coast of the USA. All three animals
    (females), analysed for PBBs (tetrabromo- to hexabromobiphenyl
    congeners) within a subset of the screening programme for
    anthropogenic contaminants, contained PBBs at concentrations ranging
    from 14 to 20 ng/g lipid (Kuehl et al., 1991).

    
    Table 33.  Average concentrations (µg/kg lipid) of PBB congeners in fish, seals, cows, and human milk samples

    Congener               River fish     Baltic fish     North Sea      Spitbergen      Cow's milk     Human milk
                           (Germany)                      fish           seal            (Germany)      (Germany)
                           (No. = 17)     (No. = 6)       (No. = 11)     (No. = 5)       (No. = 4)      (No. = 25)

    BB 103                  0.02            0.12            0.10         < 0.02          < 0.02        not analysed
    BB 131 + 142/146        0.30            0.62            0.25           0.03          < 0.02          < 0.01
    BB 132                  0.33            1.25            0.62           0.15          < 0.02            0.05
    BB 135 + 144/151        0.69            4.10            1.48           0.46          < 0.02            0.12
    BB 147/135 + 144        0.21            0.31            0.25         < 0.02          < 0.02          < 0.01
    BB 148/136              0.10            0.13            0.11         < 0.02          < 0.02          < 0.01
    BB 149                  0.26            0.45            0.53         < 0.02          < 0.02          < 0.01
    BB 153                  0.60            2.39            1.31           0.81            0.04            1.03
    BB 154/151              0.22            0.54            0.37         < 0.02          < 0.02            0.01
    BB 155                  0.66            2.64            1.11           0.40          < 0.03            0.05
    BB 169                < 0.01           15.16          < 0.01         < 0.01          < 0.01            0.05
    BB 176                  0.03          < 0.01            0.02         < 0.01          < 0.01          < 0.05
    BB 178                  0.18            0.87            0.36           0.03          < 0.01            0.09
    BB 179                  0.08            0.04            0.04         < 0.01          < 0.01          < 0.05
    BB 180                  0.02          < 0.01            0.02         < 0.01          < 0.04            0.02
    BB 181 + 174            0.01            0.01            0.01         < 0.01          < 0.01          < 0.05
    BB 184                  0.05            0.09            0.03         < 0.01          < 0.01            0.01
    BB 185                  0.03          < 0.01          < 0.01         < 0.01          < 0.01          < 0.05
    BB 186                  0.30            0.40            0.16           0.01          < 0.01            0.02
    BB 187 + 182            0.03            0.05            0.04           0.03            0.01            0.33
    BB 188                  0.11            0.28            0.11         < 0.01          < 0.01            0.01
    BB 192                  0.01          < 0.01          < 0.01         < 0.01          < 0.01         n< 0.05
    BB 194                  0.07          < 0.02            0.04         < 0.02          < 0.02          < 0.05
    BB 197                  0.11            0.11            0.08         < 0.02          < 0.02            0.04
    BB 198                  0.27            0.14            0.12         < 0.02          < 0.02          < 0.05
    BB 200 + 204            0.41            0.36            0.24         < 0.02          < 0.02            0.02
    BB 201                  0.09          < 0.02            0.03         < 0.02          < 0.02          < 0.05

    Table 33 (contd).

    Congener               River fish     Baltic fish     North Sea      Spitbergen      Cow's milk     Human milk
                           (Germany)                      fish           seal            (Germany)      (Germany)
                           (No. = 17)     (No. = 6)       (No. = 11)     (No. = 5)       (No. = 4)      (No. = 25)

    BB 202                  0.87            0.42            0.36          < 0.02          < 0.02            0.01
    BB 206                  0.05          < 0.03            0.04          < 0.03          < 0.03          < 0.01
    BB 207                  0.06          < 0.03            0.02          < 0.03          < 0.03          < 0.01
    BB 208                  0.16            0.04            0.04          < 0.03          < 0.03          < 0.01

    PBB                      6.3            30.5             7.9            1.9             0.05            2.0

    From: Krüger (1988).

        Table 34.  Concentrations (µg/kg lipid) of 2,2',4,4',5,5'-HxBB (BB 153)
    in pooled biological samplesa

    Species                               Number of           Sampling         Concentration
                                          specimens in        site             of BB 153
                                          the homogenate

    Rabbit (Oryctlagus cuniculus)              15             S. Sweden         not detected
    Moose (Alces alces)                        13                               not detected
    Reindeer (Rangifer tarandus)               31             N. Sweden             0.037
    White fish (Coregonus sp.)                 35                                   0.29
    Arctic char (Salvelinus alpinus)           15             S. Sweden             0.42
    Herring (Clupea harengus)                 100             Bothnian Bay          0.092
    Herring (Clupea harengus)                  60             Baltic Proper         0.16
    Herring (Clupea harengus)                 100             Skagerrak             0.27
    Ringed seal (Pusa hispida)                  7             Svalbard              0.42
    Grey seal (Halichoerus grypus)              8             Baltic Sea             26
    Osprey (Pandion haliaetus)                 35             S. Sweden              22

    a    From: Jansson et al. (1992).
    
         In Europe, PBBs have been detected in seals  (Phoca vitulina;
     Pusa hispida), guillemots  (Uria aalge; U. lomvi), and
    white-tailed sea eagles  (Haliaeetus albicilla). The concentrations
    (estimated by comparison with the technical product FM BP-6) ranged
    from 3 to 280 µg/kg lipid (Jansson et al., 1987). The concentrations
    of PBBs in comparable samples from the Baltic Ocean were all higher
    than concentrations in samples from the Arctic Ocean. The same was
    true for polybrominated biphenyl ethers and PCBs (Jansson et al.,
    1987).

         Concentrations of BB 153 determined in marine fish ranged from
    0.2 to 2.4 µg/kg lipid (Krüger, 1988; Jansson et al., 1992; see also
    Tables 33 and 34). BB 153 levels of 0.4-26 µg/kg lipid were found in
    seals (Krüger, 1988; Jansson et al., 1992; see also Tables 33 and
    34).

         Detailed isomer-specific PBB analyses were carried out by
    Krüger (1988) in fish (several species) from the Baltic and North
    Seas and from sections of the Lippe and Rur rivers in North
    Rhine-Westphalia, Germany. Seal samples from Spitsbergen (Norway)
    were also included in this investigation (Table 33). All samples
    contained PBBs. The smallest number of PBB congeners was found in
    seals (n = 5) from an area remote from industrial sites. The main

    components were different hexabrominated isomers with
    2,2',4,4',5,5'-hexabromobiphenyl reaching a mean concentration of
    0.8 µg/kg fat. The mean concentrations of several PBB congeners and
    isomers (penta- to nonabrominated biphenyls) measured in fish
    (n = 35) ranged, mostly, between 0.01 and 2 µg/kg fat. The pattern
    of PBB congeners found in fish differed in a characteristic manner,
    depending on the different capture sites. While relatively high
    amounts of nona- and octabromobiphenyls (besides polybrominated
    biphenyl ethers) were present in fish from German rivers (n = 17;
    several species), hexabrominated biphenyls were predominant in fish
    from the North Sea and the Baltic Sea (n = 17; several species). In
    all samples from the Baltic Sea (n = 6),
    3,3',4,4',5,5'-hexabromobiphenyl was found in relatively high
    concentrations (maximum concentration: 36 µg/kg fat), but it was not
    detected in samples from the North Sea and from rivers. The
    concentrations of the other hexabrominated biphenyls were mostly
    higher in fish from the Baltic Sea than in fish from the North Sea.

    b) Farm animals

         Farm animals in Michigan were contaminated by PBBs, when
    FireMaster(R) FF-1 was accidentally mixed with animal feed in
    mid-1973 (see section 4.1). The PBB levels resulting from this event
    varied greatly with the extent of exposure. Data reported in the
    literature are compiled in Table 35. The extent of contami nation
    can be seen from the fact that, during the months following the
    event, 172 dairy and beef herds (18 000 animals), 32 swine herds
    (3500 animals), 16 sheep flocks (1200 animals), and 92 chicken
    flocks (1.5 million birds) were destroyed (Isleib & Whitehead, 1975;
    Robertson & Chynoweth, 1975; Mercer et al., 1976). In relation to
    these great numbers, the portion of highly contaminated animals was
    small (e.g., 40 herds of cattle, as can be derived from
    contamination values measured in milk (section 5.1.4.2).

    5.2  General population exposure

         Apart from data collected after the Michigan disaster, there is
    only limited information on exposure of the general public. PBBs
    have been detected in humans in the vicinity of manufacturing
    premises and in a few sites in the USA and Europe, not directly
    connected with PBB contamination.

    Table 35.  PBB levels in farm animals (derived from the Michigan
    cattle food contamination incident in 1973)

    Year             Animal                   PBB concentrationa     References
                     (Type of sample)         (mg/kg)

    1974             Poultryb (tissue)        4600                   Kay (1977); IARC (1978)
    Not specified    Cattle (fat)             up to 200              Pearson (1982)
    Not specified    Aborted calves           120-400                Kay (1977)
    1974             Cattlec (body fat)       110-2480               Robertson &
                                                                     Chynoweth (1975);
                                                                     Mercer et al. (1976)
    1974-75          Cattled (fat)            9-4100                 Fries et al. (1978b)
    1974             Cattleb (tissue)         up to 2700             Kay (1977); IARC (1978)
    1974             Cattlej (body fat)       174-200                Jackson & Halbert (1974)
    March (1975)     Dairy cattlee            1-12                   Kay (1977)
    1975             Cowsf (tissue-fat)       not detected-1.69      Isleib & Whitehead (1975)
    1975             Steers and heifersg      not detected-2.27
                     (tissue-fat)
    1975             Pigsh (tissue-fat)       not detected-0.58
    1975-76          Cattlei (male and        not detected-0.13      Cook et al. (1978a)
                     female) (eye fat)
    Not specified    Cattlek (body fat)       not detected-3.8       Mercer et al. (1976)

    a    PBB values were based on 2,2',4,4',5,5'-hexabromobiphenyl.
    b    From 22 farm premises.
    c    21 highly exposed cows.
    d    32 cows from one herd heavily contaminated during September/October
         1973, and 9 calves borne to these cows in 1974.
    e    16 herds of dairy cattle with a history of feed levels from 1 to 14 mg/kg PBB.
    f-h  Slaughter house survey during a 3-month period (January-April 1975).
    f    Number of samples: 216; mean-PBB: 0.018 mg/kg.
    g    Number of samples: 247; mean-PBB: 0.030 mg/kg.
    h    Number of samples: 213; mean-PBB: 0.017 mg/kg.
    i    Cattle of 5 affected herds.
    j    2 cows of the Halbert farm.
    k    Cattle of 12 affected herds.

    5.2.1  Quantified data on human exposure

    5.2.1.1  Worldwide

         For most human populations, direct data on exposure to PBBs
    from various sources have never been documented. This is true also
    for the possible exposure of the general population from the use of
    PBB-containing plastic products, and from fumes, generated in the
    combustion of these products inadvertently in fires, or from burning
    in dumps (Kay, 1977), and, additionally, from sources such as
    PBB-containing landfills or PBB-manufacturing and processing
    plants.

    5.2.1.2  The Michigan Accident

         Widespread human exposure resulting from direct contact with
    contaminated feed, and, primarily, from the consumption of PBBs in
    meat, eggs, and dairy products has been reported from the state of
    Michigan, USA (Kay, 1977; Landrigan, 1980; Fries, 1985b; Table 36).
    Many Michigan residents were exposed to PBBs between the onset of
    contamination in the autumn of 1973 and the establishment of the
    quarantine of affected farm animals in the spring of 1974. There was
    considerable variation in both lengths and levels of exposure. At
    least 2000 families (primarily farmers and their neighbours)
    received the heaviest exposure (Meester & McCoy, 1976; IARC, 1978).

         Brilliant et al. (1978) concluded from their results of human
    milk analyses, conducted in 1976, that about 8 million of the 9.1
    million residents of Michigan have detectable body burdens of PBBs.
    Further studies (see Table 37) confirmed this widespread
    distribution of PBBs.

         The amount of PBBs consumed or absorbed by the various groups
    in Michigan cannot be determined accurately (Safe, 1984). However,
    there have been some trials to estimate the possible exposure to
    PBBs of farm families and other people. The estimates were based on
    kinetic data and other observations, e.g., time and level of animal
    exposure, residue levels in herds at the time of the contamination,
    and serum levels of exposed people.

         In this way, Fries et al. (1978a) estimated (assumptions: see
    Fig. 4), that the total exposure of an individual in a farm family
    consuming its own milk was, for example, 9.8 g over the 230-day
    period, during which the contamination was undetected. The
    cumulative intake over time is shown in Fig. 4. In addition, the
    authors concluded that the most highly exposed people consumed from
    5 to 15 g PBBs over a 230-day period via milk. The projected intake
    of PBB via the meat of cows slaughtered for home consumption would
    have exceeded the projected intake from milk.

    Table 36.  Approximate distribution of PBBs in the Michigan episodea

    Item                                                Amount (kg)

    Total released                                         295

    Not fed to livestock                                    45

    Fed to livestock                                       250

    Eliminated in faeces                                   125

    Absorbed by animals                                    125

    In human foods before regulation                        94

    a    Modified from: Fries (1985b).

         Application of a pharmacokinetic model (Tuey & Matthews, 1980)
    to the mean serum concentrations for residents of quarantined farms
    resulted in similar values, e.g., about 170 mg mean total exposure
    per individual and 11.7 g highest exposure to PBBs (Fries, 1985b;
    Brown & Nixon, 1979) supposed a consump tion of 1-20 g of PBB by
    families on the most contaminated farms.

         The exposure of an individual in the general population would
    have a pattern over time as projected above for the farm family
    (Fries et al., 1978a). However, the exposure level would have been
    much less, because of dilution in the normal marketing channels (the
    mixing of milk from a large number of producers; the use of meat of
    cull dairy cattle for hamburger and processed meat products). The
    calculations of Fries (1985b) indicate that total exposure was about
    9-10 mg for an average male with an average adipose content.
    However, the individual with the highest PBB serum concentration was
    projected to have had a total exposure of about 800-900 mg.

    
    Table 37.  Distribution of serum levels of PBBs, Michigan, 1974a

                                 Quarantined farms                                       Non-quarantined farms

                         Adults                      Children                    Adults                        Children

    Serum PBBs       Number        (%)           Number         (%)          Number         %              Number          %
    (µg/litre)

    0                   3          3.7             -             -             21          28.4              -             -
    2-19               43         52.4             8            28.6           52          70.3             29            96.7
    20-90              19         23.2            10            35.7            1           1.4              1             3.3
    100-490            11         13.4             3            10.7            0           0                0             0
    500-2260            6          7.3             7            25.0            0           0                0             0

    Total              82        100.0            28           100.0           74         100.1             30           100.0

    a    From: Humphrey & Hayner (1975).

    

         People who bought food primarily from quarantined farms were
    thought to have been exposed 10 to 100 times more than the typical
    retail store customer (Schwartz & Rae, 1983): ca. 100 mg of PBBs
    versus 1-10 mg (Brown & Nixon, 1979).

         While many dust and cobweb samples found in the buildings of
    some PBB-contaminated farms had very high residue levels, the amount
    of PBB residue involved is said not to be sufficient to be an
    important contributor to animal residues (Fries & Jacobs, 1980) and,
    possibly to human exposure.

    5.2.2  Human monitoring methods for PBBs

         Usually, suitable human monitoring data, as such, are used to
    describe the real exposure to a toxic chemical. As an indicator of
    human exposure to PBBs, the presence of PBBs in adipose tissue,
    breast-milk, whole blood, serum, red and white blood cells (Bekesi
    et al., 1979a,b), and human hair oils (Stratton & Whitlock, 1979)
    has been assessed. The most commonly used specimens were serum,
    breast-milk, and adipose tissue (see Tables 38-40).

    
    Table 38.  Human monitoring data: PBB levels in the Michigan population (USA)

    Year      Number     Positive  Specimen                                            PBB-concentrationa           Detection     References
              of         findings  (tissue,   Group                 Range         Arithmetic   Geometric   Median   limit
              specimens  (%)       etc.)                                                       mean        mean

    1974      82         96.3      serum      adults from            not                                   14       not           Humphrey &
                                              quarantined farms    detected-                                        specified     Hayner (1975)
                                                                     2260

              28         100       serum      children from         2-2260                                 35       not
                                              quarantined farms                                                     specified

              5          100       serum      lactating females     3-1068
                                              from quarantined
                                              farms

    1976      524                  serum      Michigan farmers                    23.7                      2.6     0.2           Wolff et al.
                                                                                                                    µg/litre      (1978a);
                                                                                                                                  Lilis et al.
                                                                                                                                  (1978)
              283                  serum      residents on        0.2-> 1000      33.9          3.9
                                              quarantined farms

              153                  serum      residents of          0.2-50         2.9          1.4
                                              non-quarantined
                                              farms

              40                   serum      consumers of         0.3-1000       56.6          4.2
                                              products
                                              from quarantined
                                              farms

    Table 38 (contd).

    Year      Number     Positive  Specimen                                            PBB-concentrationa           Detection     References
              of         findings  (tissue,   Group                 Range         Arithmetic   Geometric   Median   limit
              specimens  (%)       etc.)                                                       mean        mean

              28                   serum      consumers of           0-50          3.4          2.2
                                              products from
                                              non-quarantined
                                              farms

                                              consumers and                                                                       Wolff et al. 
                                              residents:                                                                          (1978)
                                              quarantined farms:
              40                   serum      females < 18 years                  28.0                      2.3     0.2
                                                                                                                    µg/litre
              102                  serum      females > 18 years                  18.2                      2.5
              51                   serum      males < 18 years                    67.7                      7.3
              129                  serum      males > 18 years                    28.2                      4.4

                                              consumers and
                                              residents:
                                              non-quarantined
                                              farms:
              37                   serum      females < 18 years                   3.1                      1.3
              57                   serum      females > 18 years                   1.7                      0.9
              35                   serum      males < 18 years                     4.8                      1.7
              51                   serum      males > 18 years                     3.1                      2.2

    Table 38 (contd).

    Year      Number     Positive  Specimen                                            PBB-concentrationa           Detection     References
              of         findings  (tissue,   Group                 Range         Arithmetic   Geometric   Median   limit
              specimens  (%)       etc.)                                                       mean        mean

    1976      485                  serum      consumers and                                                                       Chanda et al.
                                              residents:                                                                          (1982)
                                              quarantined farms:
              27                   serum      0-5 years              0.2-64.2     10.15                             not
                                                                                                                    specified
              137                             6-18 years             0.0-962.4    27.22                             not
                                                                                                                    specified
              321                             > 18 years            0.2-1778.0    24.42

    1976      321                  serum      consumers and                                                                       Chanda et al.
                                              residents:                                                                          (1982)
                                              non-quarantined
                                              farms:
              18                              0-5 years              0.2-37.4      6.42                             not
                                                                                                                    specified
              104                             6-18 years             0.0-42.6      3.25                             not
                                                                                                                    specified
              177                             > 18 years             0.0-94.0      3.03                             not
                                                                                                                    specified

    1976                           serum      Michigan children                                 3.41                not           Barr (1980)
                                                                                                                    specified
              143                             females                                           2.72                not
                                                                                                                    specified
              149                             males                                             4.23                not
                                                                                                                    specified
              33                              0-4 years                                         2.75                not
                                                                                                                    specified

    Table 38 (contd).

    Year      Number     Positive  Specimen                                            PBB-concentrationa           Detection     References
              of         findings  (tissue,   Group                 Range         Arithmetic   Geometric   Median   limit
              specimens  (%)       etc.)                                                       mean        mean

              77                              5-8 years                                         5.59                not
                                                                                                                    specified
              81                              9-12 years                                        3.18                not
                                                                                                                    specified
              101                             13-16 years                                       2.65                not
                                                                                                                    specified

    1976-77   3639                 serum      Michigan residents     0-1900        21.2                     3.0     1 µg/litre    Landrigan
                                              with various                                                                        et al.
                                              degrees of exposure                                                                 (1979);
                                                                                                                                  Landrigan
                                                                                                                                  (1980)

    1976-77   1750                 serum      contaminated farm      0-1900        26.9                     4.0     1 µg/litre    Landrigan
              1114                            residents farm          0-659        17.1                     3.0                   et al.
                                                                                                                                  (1979);
              216                             product recipients     0-1240        43.0                     4.5                   Landrigan
                                                                                                                                  (1980)
              559                             chemical workers and    0-111         3.4                     2.0
                                              families volunteers

    1976-77   52                   serum      women at the time        not         26.2                     2.5     1             Landrigan
                                              of delivery           detected-                                       µg/litre      et al. (1979)
                                                                      1150

    1977      3683                 serum      Michigan PBB cohort   < 1-3150       23.2         4.1         3       not           Kreiss et al.
                                                                                                                    specified     (1982)
              1888                            males                                             5.8
              1795                            females                                           2.8

    Table 38 (contd).

    Year     Number     Positive  Specimen                                            PBB-concentrationa           Detection      References
             of         findings  (tissue,   Group                  Range        Arithmetic   Geometric   Median   limit
             specimens  (%)       etc.)                                                       mean        mean

    1978     1681                 serum      Michigan residents                                                                   Wolff et al.
                                                                                                                                  (1982)
                                             (randomly selected)
             1120       68.9                 adults                 0.2-120.5     1.3                      0.6     0.2
                                                                                                                   µg/litre
             461        72.7                 children               0.2-37.2      1.8                      0.8
             232                             Upper Peninsula                                               0.2
                                             Lower Peninsula:
             467                             Detroit Area                                                  0.5
             191                             Muskegon Area                                                 1.7
             791                             remainder of state                                            0.9

                                             Muskegon County:
             54                   serum      male adults                          4.0          2.6                 0.2            Wolff et al.
                                                                                                                   µg/litre       (1982)
             74                              female adults                        2.1          1.4
             36                              male children                        4.9          3.4
             27                              female children                      3.8          2.0

    1975-80                       serum      Michigan PBB cohort:                                                                 Eyster et al.
                                                                                                                                  (1983)
             61                              pregnant females          not                     3.5         3       1
                                                                    detected-                                      µg/litre
                                                                      1068
             56                              non-pregnant females      not                     3.1         2
                                                                    detected-
                                                                       873

    Table 38 (contd).

    Year     Number     Positive  Specimen                                            PBB-concentrationa           Detection      References
             of         findings  (tissue,   Group                  Range        Arithmetic   Geometric   Median   limit
             specimens  (%)       etc.)                                                       mean        mean

             29                              male chemical workers    1-1200                  25.4       20
             83                              male farm and other        not                    5.4        4
                                             workers                 detected-
                                                                       1515

    1974-75  5          100       milk       women from             0.21-92 660                                    not            Humphrey &
                                             quarantined farms                                                     specified      Hayner (1975)

    1976                          milk       lactating women                                                                      Brilliant
                                  (fat)      (randomly selected                                                                   et al. (1978)
             53         96                   from Michigan:             not                               0.068    0.1 mg/kg
                                             Lower Peninsula         detected-
                                                                        1.2
             42         43                   Upper Peninsula            not
                                                                     detected-
                                                                       0.320

    1976-77  32         100       milk       women at the time of    0.032-93      3.61b                  0.225b                  Landrigan
                                  (fat)      delivery (Michigan                                                                   et al. (1979)
                                             PBB cohort)

    1976-78  2986       88.5      milk       lactating women           not         0.097       0.1        0.06     < 0.05 mg/kg   Miller et al.
                        milk                 (self-selected)        detected-2                                                    (1984)

    1975-80                                  Michigan                                                                             Eyster et al.
                                             PBB cohort                                                                           (1983)

    Table 38 (contd).

    Year        Number     Positive  Specimen                                                   PBB-concentrationa         Detection  References
                of         findings  (tissue,         Group                  Range         Arithmetic  Geometric  Median   limit
                specimens  (%)       etc.)                                                             mean       mean

                47                   milk             pregnant females         not                     0.312b     0.250b   0.001
                                     (fat)                                   detected-                                     mg/kg
                                                                               92.7

    1974-75     15         100       adipose          persons from          0.104-175c                                                Humphrey
                                                      quarantined farms                                                               & Hayner
                                                                                                                                      (1975)

    1975-76     53                   adipose          quarantined farmers                   1.965                                     Meester &
                                                                                                                                      McCoy
                                                                                                                                      (1976)
                29         100                        non-quarantined                       0.516
                                                      farmers

                9          100                        city residents                        0.226

                116                  fat              members of farm       0.58-273.0
                                                      families

    1977        19                   subcutaneous     children with known                                                             Weil et al.
                                                      exposure to PBBs                                                                (1981);
                                     fat              in utero and/or                                                                 Schwartz &
                                                      through breast milk                                                             Rae (1983);
                                                                                                                                      Seagull
                                                                                                                                      (1983)

                10         100                        "high exposure"         0.116-                   4.218
                                                                              20.960

    Table 38 (contd).

    Year        Number     Positive  Specimen                                                   PBB-concentrationa        Detection  References
                of         findings  (tissue,         Group                  Range         Arithmetic  Geometric  Median  limit
                specimens  (%)       etc.)                                                             mean       mean

                9          100                        "low exposure"          0.010-                    0.050
                                                                               0.074

    1978        844        97.3      adipose          Michigan residents     < 0.002-        0.4                  0.199    0.002      Wolff et al.
                                                                               36.7                                        mg/kg      (1982)
                                                      (randomly selected)                                         0.015
                87                                    Upper Peninsula
                                                      Lower Peninsula:
                255                                   Detroit Area                                                0.16
                84                                    Muskegon Area                                               0.50
                418                                   remainder of state                     0.24       0.050

    1975-80     32                   adipose          Michigan PBB-cohort:      not                     0.330     0.540    0.001      Eyster et al.
                                     lipid            pregnant females       detected-                                     mg/kg      (1983)
                                                                                174

                56                                    non-pregnant females      not          0.00057    0.460
                                                                             detected-
                                                                               0.619

                29                                    male chemical           0.4-350        5.29       6.0
                                                      workers

                83                                    male farm and other     70-350         1.65       1.05
                                                      workers healthy male

    Not         7          100       adipose          volunteers, aged       0.01-2.72                                     0.001      Schnare
    specified                        lipid            20-30 years                                                          mg/kg      et al.
                                     (subcutaneous)                                                                                   (1984)

    Table 38 (contd).

    Year        Number     Positive  Specimen                                                   PBB-concentrationa        Detection  References
                of         findings  (tissue,         Group                  Range         Arithmetic  Geometric  Median  limit
                specimens  (%)       etc.)                                                             mean       mean

    1983        15         100       perirenal        autopsy cases from   0.032-1.65       0.475                 0.32     0.0005     Miceli
                                     post-            the "high" exposure                                                  mg/kg      et al.
                                     mortem           area of Michigan                                                                (1985)
                                     adipose          (Grand Rapids)
                                     tissue
                                     (wet wt)

    a    Expressed as the concentration of the major hexabromobiphenyl component (BB 153) in µg/litre serum or
         mg/kg milk, or adipose tissue, respectively.
    b    The sample measuring 93 mg/kg was excluded from statistical analysis.
    c    Most in the order of 1 mg/kg.

         The last one has been preferred for analysis, since depot fat
    is the predominant storage site of PBBs (and other persistent
    halogenated hydrocarbons), and, therefore, allows an increased
    detectability of body burden. For example, had serum PBBs been used
    alone as an indicator of exposure in the PBB survey of the general
    population of Michigan (Table 38), only 70% of the 839 individuals
    would have been considered exposed. When adipose tissue results are
    added, an additional 24% indicate exposure, raising the positive
    rate to 94%. Even though the limit of detection was an order of
    magnitude higher (2.0 µg/litre in adipose tissue vs. 0.2 µg/litre in
    serum), the partition ratio of approximately 300:1 made the adipose
    limit of detection a more sensitive indicator of exposure (Wolff
    et al., 1982; Anderson, 1985).

         On the other hand, collection of hair, blood, and breast-milk
    samples is simpler and less invasive than adipose tissue biopsy. 
    Moreover, with some exceptions, significant correlations between
    adipose tissue and blood serum or breast-milk PBB levels were found
    (section 6.2). Further advantages and limitations of these
    techniques are discussed in detail by Anderson (1985) and Fries
    (1985b).

         It should be noted that levels of PBBs in breast-milk may not
    be comparable between studies unless the concentration is adjusted
    for fat content, because the fat content of breast-milk varies
    widely from woman to woman, and the value increases during feeding
    (Rogan et al., 1980).

         Although the accurate relationship between observed body levels
    of PBBs and individual exposure to PBBs is not clear (Safe, 1984),
    PBB concentrations in human tissues can give some idea of the levels
    of exposure (Kimbrough, 1980a).

    5.2.3  Human monitoring data

         In the following subsection, human monitoring data are
    presented from contaminated farms in Michigan, from Michigan state,
    and from other countries.

         Most data available refer to the Michigan PBB incident in
    1973-74 (Tables 38 and 39). Because, in this case, the spilling of
    PBBs started from farms, the Michigan Department of Public Health
    (MDPH) undertook a series of studies on farm families as a high-risk
    group in the summer and autumn of 1974.

         Serum samples were obtained from 110 persons in the exposed
    group (had been working or living in the quarantined farms for six
    months or more since the accident) and for 104 persons from the
    control group (randomly selected from a list of dairy producers in

    the same geographical area, where farms had not been quarantined).
    As shown in Tables 37 and 38, serum levels of PBBs were
    significantly higher in the people from quarantined farms compared
    with those from non-quarantined farms, though low levels were also
    observed in the control group (Cordle et al., 1978). In 1976, the
    MDPH, together with the Centre for Disease Control, the FDA, NIH,
    and EPA, established a cohort of 4545 people in Michigan to be
    examined at regular intervals over several decades (Barlow &
    Sullivan, 1982) to evaluate the long-term effects of PBB exposure.
    Four groups were included (Landrigan, 1980): Quarantined farm
    residents, direct recipients of farm produce, chemical workers and
    their families, and persons who either volunteered for the study or
    who had participated as control subjects in an earlier pilot study
    (Humphrey & Hayner, 1975). The first report was published by
    Landrigan et al. (1979) followed by several reports on subgroups of
    this population (e.g., Kreiss et al., 1982; Eyster et al., 1983).

         Study groups of the Mount Sinai School of Medicine have also
    conducted comprehensive examinations on similarly categorized
    groups, e.g., residents of quarantined farms, residents of
    non-quarantined farms, consumers of products directly from
    quarantined or non-quarantined farms, and Michigan Chemical Company
    workers; residents of the state of Wisconsin were used as a control
    group.

         It can be seen from Table 38 that nearly 100% of the adipose
    samples randomly selected throughout the state had detectable PBB
    concentrations. Thus, statewide exposure of Michigan residents to
    PBBs can be demonstrated.

         Levels of PBBs in serum (Landrigan, 1980; Wolff et al., 1982),
    breast-milk (Brilliant et al., 1978; Miller et al., 1984), and
    adipose tissue (Wolff et al., 1982) were highest in the area of the
    accident (lower peninsula), and lowest in the upper peninsula,
    farthest from the source.

         Compared with residents of quarantined farms, direct consumers
    of products from quarantined farms, and PBB- production workers, the
    tissue burdens among the general population of Michigan were 1-3
    orders of magnitude lower. Moreover, for example, only 36% of the
    general population had serum PBB concentrations greater than
    1 µg/litre, compared with 78% among farmers (Anderson et al., 1979;
    Wolff et al., 1982).

         PBB levels appear to be higher in males than females (Meester &
    McCoy, 1976; Landrigan et al., 1979; Landrigan, 1980; Wolff et al.,
    1978; 1980; Kreiss et al., 1982; Eyster et al., 1983) and higher in
    children (below the age of 10 years) than in adults (Humphrey &
    Hayner, 1975; Landrigan et al., 1979; Landrigan, 1980; Barr, 1980;
    Wolff et al., 1982).

         A later study (Schnare et al., 1984) recorded not only the
    concentration of the most abundant congener of the FireMaster(R)-
    mixture (2,2',4,4',5,5'-hexabromobiphenyl) but also the concen
    trations of other PBB congeners detected in subcutaneous adipose
    tissue samples of 7 former participants of the Michigan PBB studies
    (Table 39).

    Table 39.  Range of adipose tissue concentrations of various PBBs in 7 personsa
               (mg/kg on a lipid weight basis)b

    PBB                                       Rangec (mg/kg)

    2,3',4,4',5-penta                          nd-0.16

    2,2',4,4',5,5'-hexa                       0.01-2.72

    2,2',3,4,4',5'-hexa                        nd-0.22

    2,3',4,4',5,5'-hexa                        nd-0.09

    2,2',3,3',4,4',5-hepta                     nd-0.26

    2,2',3,4,4',5,5'-hepta                     nd-0.01

    a    7 healthy male volunteers, aged 20-30 years, having been exposed to PBBs some
         years earlier, as a consequence of the Michigan PBB incident in 1973.
    b    From: Schnare et al. (1984).
    c    nd = Not detectable; detection limit = 0.001 mg/kg.
    
         In most cases, PBB concentrations did not appear to be
    decreasing significantly over time. Wolff et al. (1979b) did not
    find any significant variation in the serum PBB levels of nine dairy
    farm residents during 18 month of observation.

         Paired serum samples, one collected in 1974 and the other in
    1977, were also available for 148 members of the Michigan PBB
    cohort. The data indicate that levels were generally stable over the
    3-year period with a mean change of 16 µg/litre (Landrigan et al.,
    1979). In another study of the Michigan PBB-cohort, the decrements
    in median serum levels of PBBs between matched pairs over one -
    (1977-78) and two - (1977-79) year intervals were both only 1
    µg/litre (Kreiss et al., 1982). No significant change in blood
    plasma PBB levels was observed over a 5-month period in 41 residents
    of quarantined farms (Humphrey & Hayner, 1975). In contrast, Meester

    & McCoy (1976) reported a marked decline over 3 years (1974-76) in
    serum levels of PBBs. These authors also found that the average
    decrease in PBB concentrations in the fat of 16 individuals was
    about 40%, in a period of 6 months. No changes in PBB levels were
    seen over an 11-year period (1976-87) in fat samples from a patient
    with long-term exposure to PBBs from the early 1970s as a result of
    the Michigan PBBs accident.  The average fat level of PBBs was
    0.8 mg/kg (Sherman, 1991).

         In 1981, PBBs were found in 13-21% of serum samples from
    4-year-old Michigan children. Their mothers belonged to a group that
    was surveyed either with regard to the consumption of Lake Michigan
    sport fish (mean PBB level detected in children: 2.4 ng/ml) or with
    regard to former exposure to quarantined farm products (mean PBB
    level detected in children: 3.0 ng/ml) (Jacobson et al., 1989).

         Few human monitoring data are available for the US population
    outside of Michigan. They are summarized in Table 40. One study
    deals with the population in the vicinity of industrial areas
    involved in PBB production or use (Stratton & Whitlock, 1979), the
    other with farmers of the state of Wisconsin who were examined as
    control group in connection with the Michigan PBB studies (Wolff
    et al., 1978).

         PBBs were found in all studies, but, because of the limited
    data, the significance is unclear. The highest PBB levels were found
    in the hair of humans living near PBB industry. Of the nine samples
    analysed, five had detectable PBB levels. Both male and female hair
    samples contained PBBs (Stratton & Whitlock, 1979).

         In contrast to the other surveys, which had regard only to the
    major PBBs component (hexabromobiphenyl), Stratton & Whitlock (1979)
    identified the different PBB homologues in the extracted oils of the
    human hair, collected from barbershops and beauty parlours (Table
    41). There were identifiable differences in the composition of PBB
    congeners found in hair from the three locations.

         The samples with the highest concentrations contained
    relatively large amounts of decabromobiphenyl, while the samples
    with lower concentrations contained only hexabromobiphenyl (Stratton
    & Whitlock, 1979). One sample was different from the others because
    it contained dibromobiphenyl (see Table 41). As a result of the
    sampling method, it was impossible to ascertain whether the exposure
    was related to the workplace or to the ambient environment.

         In a report by Lewis & Sovocool (1982), pooled adipose tissue
    samples from 202 individuals from nine census regions in the USA
    were analysed for HxBB. Although the average concentration was 1-2
    µg/kg, it cannot be excluded that this was because of the inclusion
    of a few samples with high PBB concentrations.

    
    Table 40.  Human monitoring data: PBB levels in the US population (outside of Michigan)

    Year   No. of     % of             Specimen                     PBB               PBB           Detecion    Remarks         References
           specimens  positive  tissue       group/area             concentrationa    examined      limita
                      findings                                      range

    1977   56         3.6       serum        Wisconsin farmers          not           C12H4Br6                  examined as     Wolff
                                             a control              detected-1.1b                                               et al. (1978)
                                             population

    1977   3          33        hair (from   males and females,      < 100-8100       total PBBs    100         reported as     Stratton &
                                barber-      Bayonne New Jersey,                                                µg/kg in oil    Whitlock
                                shops)       Vicinity of White                                                                  (1979)
                                             Chemical

           3          100       hair (from   males and females,      440-26 600       total PBBs    100         reported as
                                barber-      Staten Island,                                                     µg/kg in oil
                                shops)       New York, Vicinity
                                             of Standard T
                                             Chemical Co.

           3          33        hair (from   males and females,     < 100-310 000     total PBBs    100         reported as&
                                barber-      Sayreville New                                                     µg/kg in oil
                                shops)       Jersey, Vicinity of
                                             Hexcel Fine
                                             Organics

    a    (µg/litre or µg/kg).
    b    PBBs not detected in 54/56 persons. PBBs observed at 1.1 µg/litre in one person, identified as recently
         moved from a Michigan farm, and at 0.5 µg/litre in another person.

        Table 41.  Concentration (range) of different PBB congeners in human hair samples
    taken in the vicinity of three industrial sites in the USA, reported as
    µg/kg in oila

    PBB-congeners      Bayonne, New         Staten Island, New     Sayreville,
                       Jersey (White        York (Standard T       New Jersey
                       Chemical Corp.)b     Chemical Comp.)c       (Hexcel Corp.)d

    MoBB                   nde                   nde                   nde

    DiBB                 nd-8100                 nd                    nd

    TrBB                   nd                    nd                    nd

    TeBB                   nd                    nd                    nd

    PeBB                   nd                    nd                    nd

    HxBB                   nd                  440-740               nd-480

    HpBB                   nd                  nd-890                  nd

    OcBB                   nd                  nd-1100                 nd

    NoBB                   nd                  nd-3600              nd-22 500

    DeBB                   nd                 nd-20 000            nd-285 000

    a    Data from: Stratton & Whitlock (1979).
    b    Having manufactured octa- and decabromobiphenyl along with bromobiphenyl
         ethers.
    c    Major user of FireMaster BP-6.
    d    Producer of laboratory quantities of various PBBs.
    e    nd = Not detected (detection limit = 100 µg/kg).
    
         There is very little human monitoring data on PBBs in the
    populations of countries other than the USA. Krüger et al. (1988)
    reported PBB contamination of breast-milk from European women in a
    survey from North Rhine-Westphalia, Germany (Table 33).  The milk
    samples (n=25) contained a typical pattern of certain PBB congeners.
    It included penta- to octabromobiphenyls in concentrations ranging
    from 0.002 to 28 µg/kg, based on milk fat. The most abundant
    component was 2,2'4,4',5,5'-hexabromobiphenyl (BB 153) followed by a

    peak consisting of two heptabromobiphenyl isomers (2,2',3,4',5,5',6-
    and 2,2',3,4,4',5,6'-heptabromobiphenyl BB 187 and 182). Differences
    in the pattern were only found in the milk given by a Chinese woman
    and in that given by a woman having been exposed to several fires in
    industry.

         Concentrations of BB 153 in human and cow's milk, both
    collected from the same region (North Rhine-Westphalia), were
    1 µg/kg and 0.03 µg/kg, respectively, measured on a fat basis
    (Krüger, 1988).

    5.2.4  Subpopulations at special risk

         Children are at risk from exposure to PBBs in different ways.

         Studies on the Michigan population indicated a significant PBB
    transfer to the fetus (Landrigan et al., 1979; Eyster et al., 1983;
    Jacobson et al., 1984) and to breast-milk (Brilliant et al., 1978;
    Landrigan et al., 1979; Eyster et al., 1983; Jacobson et al., 1984,
    1989; Miller et al., 1984). PBB levels to which fetuses and newborn
    infants were exposed in the Michigan accident are shown in Table 42.
    Because the placenta acts only as a partial barrier to PBBs, a
    newborn baby has a body burden, even before breast feeding.
    Placental and cord serum levels are much lower than levels in
    breast-milk. However, even at low concentrations, intrauterine
    exposure may be significant, for several reasons, as pointed out in
    detail by Jacobson et al. (1984).

         Infants are not only exposed to PBBs through their mothers and
    through consumption of contaminated food, but they also through
    contact with PBBs from the environment. Young crawling children are
    known to ingest accidentally soil or dust to an extent of up to
    0.1 g/day.

    5.3  Occupational exposure during manufacture, formulation, or use

         In general, occupational exposure is to be expected in PBB
    manufacturing and processing plants. In Michigan, as a result of the
    PBB incident, farmers, and possibly dairymen, elevator, mill
    personnel etc. were occupationally exposed (Kay, 1977).

    Table 42. PBBb concentrations in maternal serum, adipose lipid, and milk lipid, and in
    the cord serum and placenta of Michigan women (Michigan PBB-cohort) at the time of
    parturition (1975-80)a

    Paired specimen     No.         Rangec          Median        Geometric      Measure
                                                                    mean

    Maternal serum      61          nd-1068           3             3.5          µg/litre
    Placenta                        nd-370           < 1             -           µg/kg

    Maternal serum      60          nd-1068           3             3.2          µg/litre
    Cord serum                      nd-104           < 1             -           µg/litre

    Maternal serum      47          nd-1068           3             3.0          µg/litre
    Milk lipid                     nd-92 667         250            312          µg/kg

    Milk lipid          27         52-92 667         384            472          µg/kg
    Adipose lipid                 nd-174 000         522            82           µg/kg

    a    From: Eyster et al. (1983).
    b    Concentrations expressed as concentrations of hexabromobiphenyl.
    c    nd = Not detected (detection limit: 1 µg/litre or kg).
    
         Bialik (1982) reported the following contaminant levels of
    decabromobiphenyl measured in 1977 in the manufacturing area of
    Hexcel/Fine Organics and Saytech, Inc. (Sayreville; USA):

    -    Plant air samples: 0.18 and 0.23 mg/m3 8 h TWA (time-weighted
         average);

    -    Wipe tests, unspecified: up to 8 mg/100 cm2; -  Wipe tests,
         eating Table: 0.1 mg/100 cm2.

         At this time, 95% of the plant production consisted of
    decabromobiphenyl (18%) and decabromobiphenyl oxide (77%). About
    2000 tonnes of decabromobiphenyl were manufactured during 1973-77
    (Bialik, 1982).

         Employees of chemical plants may be exposed directly to PBBs
    (in most cases along with other chemicals) through contact,
    inhalation, or ingestion (Wolff et al., 1979a). As an index of
    individual exposure, PBB levels in the serum and adipose tissue of
    chemical workers have been recorded. The results of several authors
    are compiled in Table 43.

         Most data refer to the Michigan Chemical Corp., St. Louis
    (Michigan), which produced several brominated organic compounds and
    manufactured over 5000 tonnes of PBBs, predominantly
    hexabromobiphenyl, from 1970 to 1974. Some additional general
    exposure from contaminated food can also be included for the workers
    of Michigan Chemical.

         To summarize, median serum and adipose tissue PBB levels were
    higher among chemical workers than among male residents of
    quarantined farms.

         Non-production workers at the Michigan Chemical plant showed
    significantly lower levels than workers involved in PBB production;
    for example, median adipose tissue concentrations of PBBs were
    2.49 mg/kg and 46.94 mg/kg, respectively.

         In another study on workers at a PBB plant in New Jersey, Bahn
    et al. (1980b) presented a detailed comparison of serum PBB levels
    in various occupational groups. A significantly higher number of PBB
    workers had detectable levels of PBBs, compared with other workers
    in the study (35.9% compared with 12.2%). Among workers with
    detectable PBB levels, the PBB workers had significantly higher
    serum levels than workers from neighbourhood industries not using
    PBBs.

         Although this factory concentrated on manufacturing
    decabromobiphenyl and decabromobiphenyl oxide (ether), there was no
    positive identification of C12Br10 (Table 44) or C12Br14O
    (Bahn et al., 1980b).

         No data are available about occupationally exposed women.

         Family members of chemical workers have also been found to have
    a body burden of PBBs (Landrigan, 1980).

         Bekesi et al. (1979b) determined the distribution of PBBs in
    the blood compartments of 4 Michigan Chemical plant workers (Table
    45) and suggested that the PBB level of the white cell fraction may
    be a better indicator for risk potential than the total plasma PBB
    concentration.

    
    Table 43.  Occupational exposure: PBB levels in chemical workers (USA)

    Year     Plant            Group                 Sample PBB concentrationa                              PBB       Detection    References
                              (number)                        range                Mean       Median     examined     limita
                                                                                (geometric
                                                                                   mean)

    1975     Michigan         workers (8-36         serum         6-85                                   HxBB                     Kay (1977)
             Chemical Corp.   months exposure (7)
             (MCC)
             (St. Louis,
             Michigan)

    1976     MCC (St. Louis,  employees (55)        serum       1.1-1729           123          9.3      HxBB                     Wolff
             Michigan)                                                                                                            et al.
                                                                                                                                  (1978,
                                                                                                                                  1979a)

                              production workers    serum                         603.9        108.4     HxBB            1        Wolff
                              (10)                                                                                                et al.
                                                                                                                                  (1979a)

                              non-production        serum                         16.5          6.1      HxBB            1
                              workers (45)

                              workers (14)          serum        1-1530                                  HxBB          < 0.2      Wolff
                                                                                                                                  et al.
                                                                                                                                  (1979b)

    1978                      workers (14)                       1-1363                                  HxBB          < 0.2
                              (matched pairs)

    Table 43 (contd).

    Year     Plant            Group                 Sample PBB concentrationa                              PBB       Detection    References
                              (number)                        range                Mean       Median     examined     limita
                                                                                (geometric
                                                                                   mean)

    1976-77  MCC (St. Louis,  workers and           serum          not            43.0          4.5      C12H4Br6        1        Landrigan
             Michigan)        families (216)                  detected-1240                                                       et al.
                                                                                                                                  (1979)

    1975-80  MCC (St. Louis,  workers (male)        serum        1-2000          (25.4)         20       C12H4Br6        1        Eyster
             Michigan)        (29)                                                                                                et al.
                                                                                                                                  (1983)

    1978     Hexcel/Fine      PBB workers           serum          not                                   MoBB                     Bahn
             Organics and     (exposure to PBBs               detected-1340                              DeBB                     et al.
             Saytech, Inc.    (and PBBOs) for at                                                                                  (1980b)
             (Sayreville      least 6 weeks
             New Jersey)      between January
                              1973 and August
                              1978) (39)

    1976     Michigan         production workers    adipose   5000-581 000       196 490      46 940     HxBB           500       Wolff
                              (7)                   tissue                                                                        et al.
                                                                                                                                  (1979a)
                              non-production                   500-10 000         3880         2490
                              workers

    1975-80  Michigan         workers (male)        adipose    400-350 000        5290         6000      HxBB            1        Eyster
                              (29)                  tissue                                                                        et al.
                                                                                                                                  (1983)

    a    In µg/litre or µg/kg.

    
    Table 44.  Detectablea serum levels (µg/litre) of PBB homologues in workers
    at a plant producing decabromobiphenyl and decabromobiphenyl oxideb

    PBB homologue             Number of cases           Range

    C12H9Br                         14                 0.3-5.5

    C12H8Br2                         1                   6.9

    C12H7Br3                         1                   0.9

    C12H6Br4                         0                    -

    C12H5Br5                         2                1.6-13.0

    C12H4Br6                         2                 0.4-6.0

    C12H3Br7                         7                9.0-40.0

    C12H2Br8                         9               20.0-800.0

    C12H Br9                         1                   500

    C12Br10                          0                    -

    Total PBBs                      26                0.3-1340

    a    Excludes cases with "trace", "not confirmed" and "not detectable" levels.
    b    From: Bahn et al. (1980b).
    
         Despite its significance for toxicological assessment, the
    content of minor constituents of FireMaster(R) in the body burden
    was rarely investigated. For example, Wolff & Aubrey (1978) examined
    other PBB congeners, which are identifiable as peaks by GC/MS
    (2 pentabromobiphenyl peaks, and 2 heptabromobiphenyl peaks), in the
    serum of Michigan Chemical workers (n = 24) and Michigan dairy
    farmers (n = 37), besides the major component (2,2',4,4',5,5'-
    hexabromobiphenyl) of FireMaster(R). The relative concentrations,
    with respect to the major hexabromobiphenyl peak, of these PBB
    components were somewhat different for chemical workers and for
    farmers, i.e., the two pentabromobiphenyl values (peak area ratios)
    were significantly higher in the serum from chemical workers.

    Table 45. Distribution of PBBs in blood compartments of Michigan Chemical Workersa

                                                 Polybrominated biphenyls
                                         ng/mg Protein                        Ratiob
                                    RBC     plasma    WBC            RBC    plasma   WBC

    Michigan Chemical Workers;
    not directly involved in        0.07    0.13      3.9            1      : 2      : 56
    the production of PBB           0.03    0.23      1.8            1      : 8      : 60

    directly involved in            0.67    10.0      57.3           1      : 15     : 86
    the production of PBB           0.63    10.2      32.0           1      : 16     : 51

    a    From: Bekesi et al. (1979b).
    b    RBC = Red blood cells; WBC = white blood cells.
    
         This variation might be attributed to the different routes
    (skin contact, inhalation, direct ingestion versus, primarily,
    ingestion of animal foodstuff) and to the different composition
    (unchanged versus animal-mediated material) of exposure in chemical
    workers versus farmers. Further reasons might be the earlier initial
    onset of contamination in workers and slight variations in the
    composition (section 2.1.2) of several lots of FireMaster(R) BP-6
    (the main product of Michigan Chemical) and FireMaster(R) FF-1,
    which caused contamination of livestock feed (Anderson et al.,
    1978a; Wolff & Aubrey, 1978; Wolff et al., 1979a).

         The change in serum PBB levels over time was investigated in
    chemical workers at two facilities. Wolff et al. (1979b) reexamined
    serum PBB concentrations (determined as the major hexabromobiphenyl
    peak) in 1978 from 14 workers of the Michigan Chemical Corp., who
    had also been tested 18 months earlier. They found PBB levels of a
    comparable order. In contrast, no subject (n=109) in a study on
    chemical workers of Hexcel/Fine Organics and Saytech Inc.
    (manufacturing decabromobiphenyl and decabromobiphenyl oxide) showed
    any detectable serum level of PBBs (different congeners) in 1981
    (Bialik, 1982), which was true, even for the two persons who had
    shown high levels of serum PBBs in the previous study of 1978 (Bahn
    et al., 1980b; Table 43). However, the results of PBB determination
    in the fat of these two cases were positive in 1981. The negative
    results of the determination of PBBs in serum were not expected, and
    the authors suggested further studies.

    6.  KINETICS AND METABOLISM

    6.1  Absorption

    6.1.1  Animal studies

    6.1.1.1  Gastrointestinal absorption

         Studies have been performed only on the gastrointestinal
    absorption of PBBs. Some studies indicate that PBBs are rapidly and
    efficiently absorbed, other studies indicate a much lower efficiency
    of absorption (see Table 46). No information is available on the
    extent of absorption of decabromobiphenyl.

         Absorption can be strongly influenced by the vehicle in which
    the compound is administered (Birnbaum, 1985). Administration of
    hexabromobiphenyl in mineral oil or olive oil solution resulted in
    higher absorption than administration in a methyl cellulose
    suspension (see Table 46: Rozman et al., 1982). The degree of
    halogenation also appeared to influence the absorption of PBB. For
    example, less than 10% of 14C-labelled hexabromobiphenyl, but 62%
    of a dose of 14C-labelled octabromobiphenyl were eliminated in the
    faeces of rats in 24 h, though both compounds had been administered
    in corn oil (see Table 46).

         The conclusion that more brominated biphenyls are absorbed less
    efficiently than less brominated biphenyls can, possibly, be drawn
    from other findings. Willett & Durst (1978) observed that, during
    feeding of FireMaster(R) BP-6, the relative concentration of
    pentabromobiphenyl in the faeces of cows was decreased, and that of
    heptabromobiphenyl was elevated compared with the
    FireMaster(R)-standard. Similarly, faecal concentrations of
    heptabromobiphenyl were enhanced relative to concentrations of
    hexabromobiphenyl in the faeces of hens, when FireMaster(R) BP-6
    was fed (Fries et al., 1976). However, Polin & Leavitt (1984) found
    that the ratio of 3.5 for hexa- to heptabromobiphenyl in the
    chemical sample of FireMaster(R) FF-1 shifted to an average ratio
    value of 2.5 in the whole carcasses of chickens analysed on days 0,
    21, and 42 of withdrawal, inferring a better absorption of hepta-
    bromobiphenyl.

         Generally, it should be noted that faecal elimination during
    the first few days following dosing might be an indicator, but is
    not a measure, of lack of absorption, because some absorbed PBB is
    eliminated and recycled into the faeces in bile and by diffusion
    across intestinal membranes (Rozman et al., 1982; Fries, 1985b).

    
    Table 46.  Absorption of PBBs after oral administration

    PBB compound                Species       Vehicle                Absorption     Methods             Comments               References
                                (sex)                                parametera

    [14C-]2,2',4,4',5,5'-       rat           emulphor-EL 620:       90%, 24 h      faeces analysis     single dose            Matthews
    hexabromobiphenyl           (male)        ethanol: water                        gut content                                et al. (1977)
                                              (1 : 1 : 8)

                                              corn oil               90%                                multiple doses (4)

    [14C-] octabromobiphenyl    rat (male,    corn oil               38%, 24 h      faeces analysis     single dose            Norris et al.
    (technical mixture)         female)                                                                                        (1973)

    [14C-]2,2'4,4',5,5'-        rhesus        1% methyl cellulose    40%, 10 days   faeces analysis     two doses              Rozman et al.
    hexabromobiphenyl           monkey        mineral oil            62%,  5 days   faeces analysis     single dose            (1982)
                                (male)        olive oil              66%,  5 days   faeces analysis     repeated doses (4)

    FireMaster(R) BP-6          cow           crystalline PBB in     50%, 168 h     faeces analysis     single dose            Willett &
                                (female)      gelatin capsules       (7 days)                                                  Irving (1976)

                                calf          crystalline PBB in     95%, (9 days)  faeces analysis     daily feeding
                                (male)        gelatin capsules

    a    Values based on concentrations of 2,2',4,4',5,5'-hexabromobiphenyl (FireMaster(R) BP-6 sample) or on [14C-]activity.

    6.1.1.2  Dermal and inhalation absorption

         No quantitative information is available on skin absorption and
    intake through inhalation.

    6.1.2  Human studies

         It is plausible that inhalation and dermal contact are the main
    routes of exposure to PBBs for chemical plant workers (Wolff et al.,
    1979a), while the main route for Michigan people was the ingestion
    of PBBs dissolved in the fat of meat and milk (Di Carlo et al.,
    1978). An appropriate model for assessing the latter kind of
    absorption is thought to be the rat-corn oil model (Fries, 1985b).

         No quantitative data are available on PBB absorption in humans.

    6.2  Distribution

    6.2.1  Animal studies

    6.2.1.1  Levels in organs and blood

         As can be seen from Tables 47, 48, and 49, most studies on the
    distribution of PBBs have been conducted with the FireMaster(R)
    mixture. A few earlier publications refer to technical
    octabromobiphenyl. No experimental data are available on tissue
    distribution of decabromobiphenyl. When FireMaster(R) was
    administered, the distribution process was studied predominantly as
    the distribution of 2,2',4,4',5,5'-hexabromobiphenyl, and, with far
    less emphasis, on the distribution of the minor components of the
    mixture. Little information is available on the distribution of PBB
    congeners, when administered individually.

         Investigations on rats, mice, cows, sheep, pigs, and avian
    species demonstrated that PBBs were distributed widely throughout
    the body tissues in all species. Highest (equilibrium)
    concentrations on a wet tissue basis were found in adipose tissues,
    consistent with the solubility characteristics of PBBs. Adipose
    concentrations are usually an order of magnitude higher than those
    of most muscle and organ tissues (see Tables 47, 48, 49, and 50).

         Much of the variation in concentrations among tissues can be
    accounted for by variations in the fat concentrations in these
    tissues (Willett & Durst, 1978; Fries et al., 1978b; Fries, 1985b).

    
    Table 47.  Distribution of PBBs in mammals after the administration of a single dose of PBBs

    PBB                       Species   Administration    Time after    Tissues, organs, under study - ranked in           References
                              (sex)     (dose in mg/kg    dosing        order of decreasing PBB concentrationsa
                                        body weight)                    (mg/kg or mg/litre, unless otherwise specified)

    FireMaster(R) FF-1        rat       oral 1000         10 monthsb    adipose tissue (714) > liver (60) > blood          Kimbrough et al.
    (lot No. 7042)            (male)    in corn oil                     (0.94)                                             (1978)

                              rat                         10 monthsb    adipose tissue (1202) > liver (37) > blood
                              (female)                                  (2.9)

    FireMaster(R) FF-1        rat       oral 80           42 days       fat (295) > blood (0.38)                           Wolff &
                              (male)    in corn oil                                                                        Selikoff (1979)

    FireMaster(R) FF-1        rat       oral 500          4 months      adipose tissue (1008) > liver (50) > blood         Kimbrough et al.
    (lot No: 7042)            (male)    in corn oil                     (2.1)                                              (1980)

    FireMaster(R) FF-1        rat       oral 10           24 hb         sc fat I (61 500) > sc fat II (38 700) > liver     Domino et al.
    (lot No: FF-1312-FT)      (male)                                    (20 900) > lung (7650) > kidney (7310) > heart     (1980b)
                                                                        (6470) > jejunum (4860) > spleen (3530) >
                                                                        cerebellum (2990) > grey matter (2850) > white
                                                                        matter (2750) > testes (2380) > blood (945)

                                                          4 weeksb      sc fat (19 200) > jejunum (3170) > lung (1240)     Domino et al.
                                                                        > liver (690) > kidney (650) > spleen (520)        (1980b)
                                                                        > heart, testes (both 240) > grey matter
                                                                        (210) > cerebellum (200) > white matter (170)
                                                                        > blood (56.9)

    FireMaster(R) BP-6        rat       intraperitoneal   12 weeks      serum (46.80 ng/ml)                                Miceli &
                              (male)    10 in corn oil                                                                     Marks (1981)

    Table 47 (contd).

    PBB                       Species   Administration    Time after    Tissues, organs, under study - ranked in           References
                              (sex)     (dose in mg/kg    dosing        order of decreasing PBB concentrationsa
                                        body weight)                    (mg/kg or mg/litre, unless otherwise specified)

                                                                        fat (21.90) > adrenal (3.64) > lung (0.98)
                                                                        > liver (0.59) > pituitary (0.91) > gonad (0.33)
                                                                        > kidney (0.22) > heart (0.20) > spleen (0.17)
                                                                        > brain (0.13)

                                                          36 weeksb     serum (23 ng/ml)

                                                                        fat (16.62) > adrenal (2.67) > lung (0.51) >
                                                                        pituitary (0.29) > liver (0.20) > kidney (0.14)
                                                                        > gonad, brain (both 0.10) > heart (0.08)
                                                                        > spleen (0.05)

    2,2',4,4',5,5'-           rat       oral 1 in:        1 day         muscle (29.9) > adipose (25.5) > skin (17.9)       Matthews et al.
    [14C]-hexabromobiphenyl   (male)    Emulphor                        > liver (9.0) > blood (0.90)c                      (1977)
                                        EL 600: ethanol:
                                        water (1:1:8)

    14C-PBB                   rat       intraperitoneal   28 days       ovaries (130) > skin (15.1) > testicles (13.3)     McCormack et al.
                              (male     150 in: peanut                  > intestine (11.7) > lung (7.3) > liver (4.7)      (1979b)
                              and       oil                             > muscle, heart (1.9) > fat (1.8) > brain (0.9)d
                              female
                              pups)

    FireMaster(R) BP-6        cow       oral 5.95 in:     10 days       liver (1.35) > fat (sc: 1.15; perirenal: 1.09;     Willett &
    (lot No. RP-158)          (female)  gelatin capsule                 peri-cardiac: 0.97; intermuscular: 0.81; omental:  Irving (1976)
                                                                        0.78) > brain (pons: 0.27; cortex: 0.08) >
                                                                        mammary gland (0.25) > kidney (0.12) > heart
                                                                        (0.11) > lung, muscle (0.08) > ovaries, uterus
                                                                        (0.06) > plasma, rumen wall (0.04) > bile
                                                                        (0.02) > synovial fluid (0.01)

    Table 47 (contd).

    PBB                       Species   Administration    Time after    Tissues, organs, under study - ranked in           References
                              (sex)     (dose in mg/kg    dosing        order of decreasing PBB concentrationsa
                                        body weight)                    (mg/kg or mg/litre, unless otherwise specified)

    [14C-]octabromobiphenyl   rat       oral 1 in:        16 days       adrenal, adipose, heart, skin > liver,             Norris et al.
    (technical mixture)       (male)    corn oil                        pancreas, spleen                                   (1973)

    a    Measured as concentration of 2,2',4,4',5,5'-hexabromobiphenyl or [14C-]activity; (in parentheses: values measured - referring
         to various measures).
    b    For additional time points: see original reference.
    c    Values in average % total PBB dose.
    d    Values in µg-equivalents/g wet weight.
         sc.  = Subcutaneous.

    Table 48.  Studies on the distribution of PBBs in animals following dietary or repeated oral intake
    of the FireMaster(R) mixtures or 2,2',4,4',5,5'-[14C]-hexabromobiphenyl

    PBB                Species       Exposure                                               Tissues, organs, under study -       References
                                                                             Duration of    ranked in order of decreasing
                                                                             recovery       PBB concentrationsa (mg/kg or
                                     Dietary          Duration                              mg/litre wet weight, unless
                                     concentration                                          otherwise specified)
                                     or dose

    FireMaster(R)      rat           50 mg/kg         day 8 of gestation     0              fat (330) > mammary gland (318)      Rickert
    BP-6               (pregnant)    feed             until day 21 of                       > kidney (30) > skin (22) > liver,   et al. (1978)
                                                      gestation                             lung, brain, heart, small
                                                                                            intestine, placenta, uterus (all
                                                                                            < 5)

    FireMaster(R)      rat           50 mg/kg         day 8 of gestation     0              mammary gland (117) > liver (4)      Dent et al.
    BP-6               (maternal)    feed             to 14 days                                                                 (1977b)
                                                      postpartum

    FireMaster(R)      rat           25 mg/kg         day 8 of pregnancy     0              fat (74) > mammary > liver           McCormack
    BP-6               (maternal)    feed             to 14 days                            > kidney > lung (6)                  et al.
                                                      postpartum                                                                 (1979a)
                                     50 mg/kg                                0              fat (483) > mammary > kidney
                                     feed                                                   > lung (13)
                                     200 mg/kg                               0              fat (966) > mammary > kidney
                                     feed                                                   > lung (21)

    FireMaster(R)      rat           100 mg/kg        day 8 of pregnancy     0              fat (813) > liver (54) > mammary     McCormack &
    BP-6               (maternal)    feed             to 28 days                            (43)                                 Hook (1982)
                                                      postpartum             14 weeks       fat (459) > mammary (225) > liver
                                                                             (after first   (12)
                                                                             and only

    Table 48 (contd).

    PBB                Species       Exposure                                               Tissues, organs, under study -       References
                                                                             Duration of    ranked in order of decreasing
                                                                             recovery       PBB concentrationsa (mg/kg or
                                     Dietary          Duration                              mg/litre wet weight, unless
                                     concentration                                          otherwise specified)
                                     or dose

                                                                             litter was
                                                                             weaned)
                                                                             > 10 weeks     fat (77) > mammary (19) > liver (3)
                                                                             and after
                                                                             weaning
                                                                             their second
                                                                             litter

    2,2'4,4',5,5'-     rat           1 mg/kg          4 days                 3 days         adipose (41.1) > skin > muscle       Matthews
    hexabromobiphenyl  (male)        body weight                                            > liver > blood (0.32)b              et al. (1977)
                                     per day

    FireMaster(R)      rat           0.1 mg/kg        9 days                 0              liver (1.5) > brain (0.5),           Render et al.
    BP-6 (Lot 6224A)   (male)        feed                                                   adipose (0.3)c                       (1982)
                                     1 mg/kg          9 days                 0              liver (8.3) > brain (1.8),
                                     feed                                                   adipose (1.7)c
                                     10 mg/kg         9 days                 0              liver (135) > adipose (27)
                                     feed                                                   > brain (12)c
                                     100 mg/kg        9 days                 0              liver (1213) > adipose (251)
                                     feed                                                   > brain (103)c

    FireMaster(R)      rat           3 mg/kg          20 days                0              adrenal (93.7) > thyroid (> 20)      Allen-
    FF-1 (Lot No.      (male)        body weight                                            > testes (8.7)                       Rowlands et al.
    FF-1312-FT-3)                    per day (in                                                                                 1981);    
                                     lecithin                                                                                    Castracane   
                                     liposomes)                                                                                  et al. (1982)

    Table 48 (contd).

    PBB                Species       Exposure                                               Tissues, organs, under study -       References
                                                                             Duration of    ranked in order of decreasing
                                                                             recovery       PBB concentrationsa (mg/kg or
                                     Dietary          Duration                              mg/litre wet weight, unless
                                     concentration                                          otherwise specified)
                                     or dose

                                                      20 days                5 months       adrenal (481)                        Castracane
                                                                             (plus dietary                                       et al. (1982)
                                                                             restriction)

    FireMaster(R)      mouse         100 mg/kg        14 days                6 h            thymus (391) > fat > liver > brain   Corbett et al.
    BP-6                             feed                                                   > pancreas > testicles > spleen      (1978a)
                                                                                            (2.7)

                                                                             14 weeks       thymus (50) > adrenals = fat >
                                                                                            liver > testicles > spleen > brain
                                                                                            > pancreas (n.d.)

                                                                             12 weeks       perithymic fat (96) > perirenal
                                                                                            fat > adrenal glands > thymus
                                                                                            gland (5.5)

    FireMaster(R)      mouse         5 mg/kg          3 weeks                0              thymus (20) > lung, liver > spleen   Loose et al.
    FF-1                             feed                                                   > serum (< 0.002)                    (1981)
    (lot No. 7042)
                                                      8 weeks                0              thymus (24) > liver, lung > spleen
                                                                                            > serum (0.019)

    FireMaster(R)      mouse         167 mg/kg        3 weeks                0              thymus (109) > liver > lung >        Loose et al.
    (lot No. 7042)                   feed                                                   spleen > serum (1.22)                (1981)

                                                      6 weeks                0              thymus (3088) > liver > spleen
                                                                                            > lung > serum (4.75)

    Table 48 (contd).

    PBB                Species       Exposure                                               Tissues, organs, under study -       References
                                                                           Duration of    ranked in order of decreasing
                                                                             recovery       PBB concentrationsa (mg/kg or
                                     Dietary          Duration                              mg/litre wet weight, unless
                                     concentration                                          otherwise specified)
                                     or dose

                                                      8 weeks                0              thymus (2426) > liver > lung
                                                                                            > spleen > serum, (11)
                                                      8 weeks                0              thymus (2426) > liver > lung
                                                                                            > spleen > serum (11)

    FireMaster(R)      cow           50 mg/kg         15 days                15 days        renal fat (10) > omental fat         Gutenmann &
    BP-6               (lactating)   feed                                                   > brisket fat > liver = thyroid      Lisk (1975)
                                                                                            > mammary = chuck muscle > loin
                                                                                            muscle > heart > kidney = brain
                                                                                            > adrenal = spleen (0.4)

    FireMaster(R)      calf          25 g daily       9 days                 0              rumen contents (14257) > feces       Willett &
    BP-6                             (in gelatin                                            > rumen wall > bile > marrow         Irving (1976)
    (lot 6244 A)                     capsules)                                              > perirenal fat (441) > kidney
                                                                                            > testes > liver > thymus > heart
                                                                                            > brain, pons > lymph nodes >
                                                                                            tongue > spinal cord > brain,
                                                                                            cortex > plasma > small intestine
                                                                                            > lung > spleen > thyroid >
                                                                                            muscle (25)

    FireMaster(R)      cow           250 mg daily     60 days                0              fat (25) > liver > glands > nervous  Willett &
    BP-6               (heifer)      (in gelatin                                            > bile > contractiles > plasma       Durst (1978)
    (lot 6244 A)                     capsules)                                              > liquids (0.0198)

    Table 48 (contd).

    PBB                Species       Exposure                                               Tissues, organs, under study -       References
                                                                             Duration of    ranked in order of decreasing
                                                                             recovery       PBB concentrationsa (mg/kg or
                                     Dietary          Duration                              mg/litre wet weight, unless
                                     concentration                                          otherwise specified)
                                     or dose

    FireMaster(R)      cow           environmentally  ca. 14 days            9 months       perirenal fat (380*) > omental fat   Fries et al.
    FF-1                             contaminated                                           > subcutaneous fat > kidney > liver  (1978b)
                                     (Michigan PBB                                          > skeletal muscle > cardiac muscle
                                     incident)                                              > lung > brain (10.5*)

                                     ca. 200-400 g                           9-12 months    perirenal fat (1224*) > omental fat
                                                                             (killed in     >subcutaneous fat > skeletal muscle
                                                                             extremis)      > liver > cardiac muscle > kidney
                                                                                            > lung > brain (57*)

    FireMaster(R)      calf          10 mg/kg         4 weeks                0              fat (378) > kidney > liver > muscle  Robl et al.
    FF-1               (female)      body weight                                            (1.26)                               (1978)
                                     per day in
                                     gelatin
                                     capsules

                       calf          100 mg/kg        6 weeks                0              fat (6080) > kidney > liver
                       (male)        body weight                                            > muscle (34)
                                     per day

                       cow           1                158 days               182 days       brisket fat (4.5) > bone marrow
                                                                                            > stomach fat > tail fat (3.3)

    Table 48 (contd).

    PBB                 Species       Exposure                                              Tissues, organs, under study -       References
                                                                            Duration of     ranked in order of decreasing
                                                                            recovery        PBB concentrationsa (mg/kg or
                                      Dietary          Duration                             mg/litre wet weight, unless
                                      concentration                                         otherwise specified)
                                      or dose

    FireMaster(R)       sheep         50 mg/kg         30 days              0               renal fat (42) > omental fat         Gutenmann &
    BP-6                              feed per day                                          > brisket fat > liver > chuck        Lisk (1975)
                                      (complete                                             muscle > loin muscle > heart >
                                      ration)                                               thyroid > brain > adrenal > kidney
                                                                                            = spleen (0.9)

    FireMaster(R)       pig           20 mg/kg         16 weeks             0               back fat (64) > leaf fat > liver     Ku et al.
    BP-6                              feed                                                  > muscle > kidney (0.9)              (1978)

                                      200 mg/kg        16 weeks             0               back fat (503) > leaf fat > muscle
                                      feed                                                  > liver > kidney (13.5)

    FireMaster(R)       pig           100 mg/kg        during 2nd           0               adipose tissue > liver > kidney >    Werner &
    BP-6                (lactating    feed             half gestation                       > braind                             Sleight (1981)
                        sow)          200 mg/kg        and during
                                      feed             lactation

    "PBB"               Japanese      20 mg/kg         9 weeks              0               liver (374) > kidney > muscle        Babish et al.
    (ca 75%             quail         feed                                                  > heart > brain (40)e                (1975a)
    hexabromobiphenyl)  male

                        female                                              0               liver (225) > heart > kidney >
                                                                                            > muscle > brain (26)e

    FireMaster(R)       chicken       various          5 weeks              0               adipose tissue (3:1) > whole egg     Polin &
    FF-1                (White        concentrations                                        > liver > muscle (0.008:1)f          Ringer
                        Leghorn                                                                                                  (1978a)
                        hens)

    Table 48 (contd)
    a    Measured as concentrations of 2,2',4,4',5,5'-hexabromobiphenyl (in parentheses: values measured - referring to various measures).
    b    Values in average % total PBB dose.
    c    Values on a fat basis.
    d    Concentrations are listed in Table 53.
    e    Values in mg/kg dry weight.
    f    Values as ratios of tissue PBBs: diet PBBs.
         * = Geometric mean.

    Table 49.  Studies on distribution of the following continuous exposure to octabromobiphenyl

    Species              Exposure                              Duration of     Tissues and organs under study, ranked        References
              Route,                     Duration              recovery        in order of decreasing concentrations
              concentration                                                    (average bromine content; µg/g wet weight)

    Rat       in diet                                                                                                        Lee et al. (1975a)
    (male)    0 mg/kg feed (control)     2 weeks                               liver (3.4) > fat (1.7) > muscle (1.6)

              100 mg/kg feed             2 weeks                    -          liver (83) > fat (73) > muscle (14)

              1000 mg/kg feed            2 weeks                    -          fat (333) > liver (319) > muscle (77)

              100 mg/kg feed             4 weeks               0,2,6 weeks     fat > liver > muscle

              100 mg/kg feed             4 weeks               18 weeks        fat > muscle > liver

    Rat       inhalation                 23 h/day, 7 days                                                                    Waritz et al.
              (OcBB vapour)a             per week, 15 weeks                                                                  (1977)

              0 pg/litre air                                                   liver (3) > muscle (1.6) > fat (1.5)
              (control)

              3.5 pg/litre air                                      -          liver (4.2) > fat (3.0) > muscle (1.5)

    a    OcBB = Octabromobiphenyl, Dow, Lot 102-7-72.

    
    Table 50. Tissue: blood ratios of PBBs estimated in a standard 250-g rata

              Compartment                   Ratio

              Liver                         17:1

              Muscle                        5:1

              Skin                          56.5:1

              Adipose                       340:1

              Intestine tissue              1:1

    a    From: Tuey & Matthews (1980).
    
         However, even when concentrations are expressed on a fat basis
    rather than a wet tissue basis, there are some deviations from
    uniform concentrations among tissues (Fries, 1985b). PBB
    concentrations, for example, were low in nervous tissue, despite its
    high lipid content and often disproportionally high in liver,
    considering its relatively low lipid content (see Tables 47, 48, and
    49; additional information on fat content percentage, e.g., by
    Willett & Irving, 1976; Fries et al., 1978a,b; Kimbrough et al.,
    1978; Werner & Sleight, 1981).

         The ratios between the PBB concentrations of adipose tissue,
    blood, and vital organs are different when animals are not at
    equilibrium (see also section 6.5) with respect to dosing regimen or
    body condition. Usually, concentrations in liver are very high
    compared with those in other tissues, immediately after dosing, and
    decline relatively as equilibrium concentrations are established
    (e.g., Lee et al., 1975a; Matthews et al., 1977; Miceli & Marks,
    1981; Fries, 1985b). Generally, this phenomenon is most pronounced
    in tissues that have high blood flow rates relative to tissue mass
    (Tuey & Matthews, 1980). As an exception, livers of mice, tested in
    a small series, appeared to have relatively concentrated the PBB
    with passing time (Corbett et al., 1978a).

         On the other hand, body weight changes, pregnancy, parturition,
    and lactation can affect the concentration relationships until
    equilibrium is reestablished (e.g., Rickert et al., 1978; Willett &
    Durst, 1978; McCormack & Hook, 1982).

         The route of exposure (oral or intravenous administration) had
    no effect on the tissue distribution (blood, liver, muscle, adipose,
    skin) of 14C-labelled 2,2',4,4',5,5'-hexabromobiphenyl (dose =
    1 mg/kg body weight) in rats (Matthews et al., 1977).

         Kimbrough et al. (1980) studied the effects of different diets
    and of mineral oil on the HxBB concentration in rats that had
    received a single oral dose of FireMaster(R) FF-1 (500 mg/kg body
    weight, in corn oil). After 3 months of feeding, GC-analysis of
    blood, liver, and adipose tissue showed no statistically significant
    differences in PBB concentrations among the differently fed groups,
    when concentrations were calculated on a lipid weight basis. On a
    wet weight basis, however, the PBB concentrations were significantly
    increased in the livers of rats on the experimental diets (Teklad-4%
    and -20% fibre) and on mineral oil compared with those of rats on
    the basal diet (Purina Chow).

         In another study, McCormack et al. (1979a) examined the
    consequences of simultaneous exposure to PCBs and PBBs in
    (lactating) rats, because human populations that have been exposed
    to PBBs are also likely to have been exposed to PCBs. The
    extrahepatic tissue (kidney, mammary, lung, fat) concentrations of
    PCBs and PBBs were similar, regardless of whether the agents were
    administered together or alone. Liver, however, contained lower
    concentrations of PBBs after treatment with an equal mixture of PCBs
    and PBBs than when PBBs were administered alone. (None of the
    tissues had higher concentrations of PBBs than PCBs after
    concomitant administration. The reasons for this were not clear).

         The distribution of PBB (hexa) among blood compartments
    (plasma, red cells) has been studied in rats (Domino et al., 1980b). 
    It was found that plasma levels of 2,2',4,4',5,5'-hexabromobiphenyl
    were generally four times greater than red cell levels.

         Matthews et al. (1984) reported that 81% of plasma PBB (hexa)
    was associated with the total lipoprotein fraction. In another study
    (Kraus & Bernstein, 1986), approximately 65% of all radiolabelled
    HxBB incubated with human serum in vitro was recovered in the
    lipoprotein fraction. Of the HxBB in the lipoprotein fractions, 40%
    was recovered in low-density lipoproteins (LDL), 33% in
    very-low-density lipoproteins (VLDL), and 23% in high-density
    lipoproteins (HDL). Addition of human lipoprotein to a culture
    medium influenced the partition of HxBB between adipocytes and
    culture medium (Kraus & Bernstein, 1989).

         Some data are available on the tissue distribution of the minor
    components of FireMaster(R)-mixture (see also section 6.5). Domino
    et al. (1980b) analysed the relative percentages of various PBB
    congeners (two penta-, three hexa-, and three heptabromobiphenyls)
    in several tissues of rats given FireMaster(R) FF-1. From their

    list, it was evident that each of the PBB analogues was found in all
    tissues examined (liver, lung, testes, fat; blood, brain) but their
    partitioning ratios differed. Distribution has been recorded also
    after exposure to single PBB congeners, e.g., tetra-, penta-, and
    hexa-isomers (Akoso et al., 1982a; Dharma et al., 1982; Domino
    et al., 1982; Render et al., 1982; Millis et al., 1985a). In some
    cases, it was not clear whether the differences in partitioning
    between congeners were real or were caused by analytical problems
    (Render et al., 1982).

    6.2.1.2  Transfer to offspring

    1) Mammals

    Placental transfer

         PBBs are capable of passing through the placental barrier into
    the developing fetuses. This has been demonstrated in mice (Corbett
    et al., 1978a; Welsch & Morgan, 1985), rats (Beaudoin, 1977; Rickert
    et al., 1978), guinea-pigs (Ecobichon et al., 1983), minks and
    ferrets (Bleavins et al., 1981), cows (Detering et al., 1975; Fries
    et al., 1978a,b), and pigs (Werner & Sleight, 1981) by administering
    the Fire-Master(R)-mixture or individual PBBs, or by using
    technical octabromobiphenyl in rats (Aftosmis et al., 1972a; Waritz
    et al., 1977).

         The studies compiled in Table 51 are rarely intercomparable. 
    However, it is obvious that PBBs are readily transferred across
    placental membranes, the concentrations among fetal tissues being
    highest in the liver. The limited data on the distribution of PBBs
    in fetal tissues showed often, but not always (Ecobichon et al.,
    1983; Welsch & Morgan, 1985), lower PBB residues in fetal than in
    maternal tissues (see Table 51). In cows, the average ratio of PBB
    concentrations in fetal or calf tissue to PBB concentrations in dam
    tissue was 0.36 : 1 for fat and 0.37 : 1 for blood (Fries et al.,
    1978a,b). In contrast, the concentration ratio between the fetal and
    maternal liver of mice ranged from 3.5:1 to 10:1 (Welsch & Morgan,
    1985).

         Species-dependent differences in the amounts of PBBs
    transferred have been demonstrated for two mustelids, the mink and
    the European ferret. PBB levels in the ferret kit were significantly
    greater than those in the mink kit (see Table 51: Bleavins et al.,
    1981).

    
    Table 51.  Placental transfer: PBB concentrations in the fetus and the mother

                                           PBB concentrations

    Species     Dosing regimena                 Maternal               Whole              Fetalb                Concentration     References
                                      adipose    liver      others     fetus    adipose   liver    others       expressed as:c

    Mouse       FireMaster(R) BP-6;   39.52      2.51         -        0.53                                     [HxBB]            Corbett
                                                                                                                (mg/kg)           et al. (1975)
                1000 mg/kg diet
                on days 7-18 of
                pregnancy

                0 mg/kg (control)                0.04                  0.05

    Mouse       FireMaster(R) BP-6;   112.74     12.02        -        0.95       -       5.86       -          [HxBB]            Corbett
                                                                                                                (mg/kg)           et al.
                100 mg/kg diet                                                                                                    (1978a)
                on days 7-18 of
                pregnancy

    Mouse       2,2',4,4',5,5'-                                                                                 [HxBB]            Welsch &
                hexabromobiphenyl                                                                               (mg/kg)           Morgan (1985)
                (purity: > 99%)
                dietary intake
                from day 6-15 of
                pregnancy; sacrifice
                on day 17

                                                 placenta:
                100 mg/kg feed        9.08       17.26      3.79       3.06               182.88
                300 mg/kg feed        17.30      39.84      8.23       4.56               217.48
                500 mg/kg feed        69.13      89.47      24.58      17.64              316.79
                750 mg/kg feed        95.36      103.70     54.33      18.64              453.12

    Table 51 (contd).

                                           PBB concentrations

    Species     Dosing regimena                 Maternal               Whole              Fetalb                Concentration     References
                                      adipose    liver      others     fetus    adipose   liver    others       expressed as:c

    Rat         FireMaster(R) BP-6                                                                              [HxBB]            Beaudoin
                                                                                                                (mg/kg)           (1977)
                single oral dose of
                800 mg/kg body
                weight (in sesame                                                                               (pooled
                oil) at day 12 of                                                                               samples
                pregnancy; killing:   51         267                   13                                       from 4 rats)
                24 h later

                48 h later            250        248                   6

    Rat         FireMaster(R) BP-6;   330        4.2           -       1.6                0.2      GI tract:    [HxBB]            Rickert
                                                                                                   0.1          (mg/kg)           et al. (1978)
                50 mg/kg diet from
                day 8-21 of
                pregnancy

    Rat         Octabromobiphenyl                                                                                                 Waritz
                (technical);                                                                                                      et al. (1977)
                dietary intake
                from day 8-15 of
                pregnancy; sacrifice
                on day 20;

                0 mg/kg (control)     1.43       3.56                  4.38                                     [Br]
                100 mg/kg             70.4       16.1                  7.62                                     (mg/kg)
                1000 mg/kg            326        79.8                  21.2
                10 000 mg/kg          590        158                   30.1

    Table 51 (contd).

                                           PBB concentrations

    Species     Dosing regimena                 Maternal               Whole              Fetalb                Concentration     References
                                      adipose    liver      others     fetus    adipose   liver    others       expressed as:c

    Mink        [14C-]-PBBs (HxBB     0.031      1.622      plasma:    0.002    0         0.005    kidney:      % of the          Bleavins
                and HpBB); iv                               0.04                                   0.003;       initial dose      et al. (1981)
                injection (1 µCi)                                                                  brain: 0;    per g of tissue
                in the final                                                                       intestine:   or ml of fluid
                trimester of                                                                       0.001
                gestation; killed
                2 h later

    Ferret      see above             0.124      1.625      plasma:    0.005    0.004     0.013    kidney:      see above
                                                            0.07                                   0.010
                                                                                                   brain:
                                                                                                   0.003
                                                                                                   intestine:
                                                                                                   0.005

    Guinea-     FireMaster(R) FF-1;   45         7          kidney:             45        45       kidney: 1    [HxBB]            Ecobichon
    pig                                                     4.5;                                                (mg/kg)           et al. (1983)
                single oral dose of                         lung: 7
                50 mg/kg body weight                                                               lung: 1.5
                at approximately 65
                days of gestation;
                killed 2 days later

    Table 51 (contd).

                                           PBB concentrations

    Species     Dosing regimena                 Maternal               Whole              Fetalb                Concentration     References
                                      adipose    liver      others     fetus    adipose   liver    others       expressed as:c

    Pig         FireMaster(R) BP-6;                                                                                               Werner &
                                                                                                                                  Sleight (1981)
                dietary intake
                during 2nd half of
                gestation

                10 mg/kg feed                                                   0.4       1.0      kidney:      [HxBB]
                                                                                                   nd;          (mg/kg)
                                                                                                   brain: nd

                100 mg/kg feed                                                  4.9       11.5     kidney:
                                                                                                   nd;
                                                                                                   brain: nd

                200 mg/kg feed                                                  40.3      24.2     kidney: 1.5
                                                                                                   brain: 1.8

    a    HpBB  = 2,2',3,4,4',5,5'-heptabromobiphenyl.
    b    nd = Not detected.
    c    [HxBB] = Concentration of 2,2',4,4',5,5',-hexabromobiphenyl; [Br] = Concentration of bromide.

    Milk transfer

         In mammals, the second route of PBB transfer from the mother to
    the offspring is nursing. The efficiency of this way has been shown
    through determining the PBB content in milk in relation to the body
    burden or in relation to exposure levels of contaminated dams, and
    through measuring PBB levels in kits that have been exposed to PBBs
    only from suckling. The FireMaster(R) mixture was used in all
    studies. Mammary transfer of technical octa- or decabromobiphenyl
    has not (yet) been assayed.

         Most investigations on the PBB contents of milk from
    contaminated animals have been conducted on cows (Fries & Marrow,
    1975; Willett & Irving, 1976; Robl et al., 1978; Fries et al.,
    1978a,b; Willett & Durst, 1978). The ratios of concentrations in
    milk fat to body fat in cows no longer receiving PBBs averaged about
    0.4 :1 (Willett & Durst, 1978; Fries et al., 1978a,b; see also
    Fig. 5). This ratio is much lower than the ratio in humans (see
    section 6.2.2).

         For other species (guinea-pig, rat, mink, pig) only single data
    can be found in the literature. When (lactating) guinea-pigs
    received a single oral dose of FireMaster(R) FF-1 (50 mg/kg body
    weight) within 6-12 h of parturition, levels of HxBB in breast milk
    (and in perirenal adipose tissue) were of the order of 22 µg/g (and
    17 µg/g), respectively, 2 days after treatment (Ecobichon et al.,
    1983). Rats fed 50 mg FireMaster(R) BP-6/kg in their diet from day
    8 of pregnancy until 14 days after delivery showed, on day 14
    postpartum, HxBB concentrations of about 51 µg/ml in the milk and
    about 483 µg/g wet weight in their body fat (McCormack et al.,
    1979a). In the same study, milk transfer of PBBs and PCBs was
    compared. Milk usually contained higher concentrations of PCBs than
    of PBBs, after simultaneous or separate exposure.

         Contrary results were obtained with minks, intraperitoneally
    injected with either 3 µCi of 14C-labelled PCB or 3 µCi of 14C-
    labelled PBB on the approximate date at which the embryos would have
    been implanted (Bleavins et al., 1981). Two weeks postpartum, milk
    levels of PBBs were determined to be four times those of PCBs
    (0.105% versus 0.025% of the initial maternal dose per gram of
    tissue). Werner & Sleight (1981) determined PBB concentrations in
    the tissues and milk of sows fed various amounts of FireMaster(R)
    BP-6 (Table 53). At the end of lactation (4th week), the adipose
    tissue and milk of sows, fed daily with 200 mg PBB/kg feed, had HxBB
    concentrations of 194 µg/g tissue (wet weight) and of 22 µg/ml whole
    milk, respectively. The authors calculated that, on a body weight
    basis, nursing pigs consumed PBBs in concentrations similar to the
    concentration given to the sows. Tissue levels of young exposed to

    PBBs only via nursing have been determined for rats (Rickert et al.,
    1978) and for guinea-pigs (Ecobichon et al., 1983). When pups of
    non-treated female rats were nursed by dams fed FireMaster(R) BP-6
    (50 mg/kg body weight) on days 1-14 postpartum, hepatic HxBB-
    concentrations were on average approximately eight times higher than
    those in the dams on day 14 postpartum (Rickert et al., 1978).

         When dams of guinea-pigs received a dose of FireMaster(R)
    FF-1 on day 1 after delivery, the concentrations of 2,2',4,4',5,5'-
    HxBB in the lungs, livers, kidneys, and fat of the pups were similar
    to those of the dams for 4-60 days after treatment (Ecobichon
    et al., 1983).

    Combined placental and milk transfer

         Rickert et al. (1978), Bleavins et al. (1981), and Werner &
    Sleight (1981) concluded from their studies on rats, minks, and
    pigs, respectively, that milk transfer is far more important than
    placental transfer; studies on guinea-pigs (Ecobichon et al., 1983)
    did not confirm this observation. However, under less controlled
    conditions, perinatal exposure (both placental and milk transfer)
    occurs and results in a marked body burden in the offspring, as has
    been shown in studies on rats (Table 52 and McDaniel & Lucier, 1979)
    and pigs (Table 53). From minks, it has been reported that
    14-day-old kits of dams that had received a single intraperitoneal
    dose of 14C-PBB at an early stage of pregnancy, contained about 3%
    of the initial maternal dose (Bleavins et al., 1981). PBB body
    burdens in the offspring of rats were still measurable at 328 days
    of age and at the end of their life span (see Table 52).

         Moreover, a multigeneration study on rats (McCormack et al.,
    1981) demonstrated that administration of PBBs to a single
    generation resulted in detectable residues in two subsequent
    generations (Table 54). The concentrations of PBBs measured in the
    tissues of F1-animals were approximately 5-30 times higher than
    those in tissues from F2-animals and approximately 50-1000 times
    higher than those in tissues from F3-animals (see Table 54).

    2) Birds

         In birds, eggs are the medium of PBB transfer to the offspring. 
    The ratio of egg PBB contents to dietary level has been reported to
    be 1 : 1 (Fries et al., 1976) and 1.3 - 1.5 : 1 (Babish et al.,
    1975a; Ringer & Polin, 1977; Cecil & Bitman, 1978; Polin & Ringer,
    1978a) in chickens (White Leghorn hens) and Japanese quail,
    respectively. After 63 days of feeding FireMaster(R) BP-6 in the
    diet, the PBB level in body fat of White Leghorn hens was about 4
    times the level in eggs (Fries et al., 1976).

    6.2.2  Human studies

         Studies on the distribution of PBBs in humans refer only to
    people having been exposed in a direct or indirect way to the
    FireMaster(R)-mixture.

         As can be seen from a post-mortem study on people from a "high"
    exposure area of the State of Michigan (USA), PBBs are distributed
    throughout the entire human body (Table 55). Moreover, it was found
    that fat and fat-rich tissue had the highest HxBB concentrations.
    Perirenal fat had the highest mean concentration (475 ng/g).
    Adrenal, atheromatus aorta, and thymus had mean concentrations of
    about half that of perirenal fat; all other tissues had mean
    concentrations of only one-tenth or less of that of perirenal fat
    (Miceli et al., 1985).

    
    Table 52.  Tissue concentrations of PBBs in rats following perinatal exposure to PBBs (FireMaster(R)-mixture BP-6 or FF-1)

    Dosing regimen to dams           Age of            Tissue concentrations of PBBsa (mg/kg wet weight)                     References
                                     offspring
                                                                              Offspring                       Dams

    50 mg BP-6/kg diet: day 8 of     14 days      liver                                       carcass         liver          Rickert et al.
    gestation through day 14                      9.5                                         149.7           4.0            (1978)
    postpartum

    100 mg PB-6/kg diet: day 8 of                 liver                       kidney          fat             b              McCormack et al.
    pregnancy through 28 days        28 days      397                         96              1693                           (1980)
    postpartum                       328 days     17                          11              387

    BP-6 (lot 6244 A) in the diet:   28 days      lung          liver         kidney          fat             b              McCormack et al.
    day 8 of pregnancy through                                                                                               (1982a)
    28 days postpartum:
       10 mg/kg                                   5             18            8               162
      100 mg/kg                                   32            410           109             1693

    200 mg FF-1/kg body weight                    liver:        liver:                                        liver          Groce &
    (in corn oil; by stomach tube):               (female)      (male)                                                       Kimbrough (1984)
    day 7 and 14 of pregnancy        2 months     2.4 (218)c    3.0 (280)c                                    7.8 (542)c
    (weaning at day 21 of age)       2 years      0.8 (107)c    0.6 (58)c

    a    Concentration expressed as the concentrations of 2,2',4,4',5,5'-hexabromobiphenyl.
    b    See McCormack & Hook (1982) and Table 48.
    c    Values calculated on a lipid basis.

    Table 53.  Mean concentrations of PBBs (mg/kg of tissue, wet weight) in tissues of sows and
    4-week-old nursing pigs following perinatal exposure to PBBsa

    PBBsb                     Liver                  Adipose tissue                Kidney                    Brain
    (mg/kg feed)       Sows         Pigs            Sows       Pigs           Sows       Pigsc          Sows        Pigsc

    10                  1.0          2.4            15.2       14.8            0.6        nd             0.2         nd

    100                45.8         30.2            96.3       96.7            2.3        nd             1.7         nd

    200                92.6         41.3           194.2      222.5            3.7         4.1           2.7          4.2

    a    From: Werner & Sleight (1981).
    b    FireMaster(R) BP-6 fed to the sows during the second half of gestation and during lactation.
    c    nd = Not detected.

    Table 54.  Tissue concentrations of PBBs in several generations of rats following perinatal exposure to PBBsa,b,c

    Treatment       Liver             Kidney        Lung           Thyroid        Testis          Ovary            Fat

    Control          < 0.1            < 0.1         < 0.1          < 0.1          < 0.1           < 0.1           < 0.1

    F1-10         17.1 ± 3.6        7.5 ± 0.6     5.1 ± 0.8      4.4 ± 1.0      8.2 ± 5.3      24.0 ± 1.6     161.7 ± 24.2

    F2-10          0.4 ± 0.1        0.6 ± 0.2     0.9 ± 0.1      0.5 ± 0.1      0.2 ± 0.1       3.0 ± 0.5       6.7 ± 1.9

    F1-100       410.2 ± 40.6     108.6 ± 11.2   32.4 ± 2.0    162.6 ± 20.8        -d              -d        1693.2 ± 250.4

    F2-100        21.8 ± 3.2        7.2 ± 1.3     8.7 ± 1.0      2.7 ± 0.6     1.8 ± 0.11       6.5 ± 2.6     159.5 ± 16.9

    F3-100         0.4 ± 0.1        0.8 ± 0.4     0.6 ± 0.1      0.2 ± 0.1      0.3 ± 0.1       0.6 ± 0.1       4.9 ± 0.8

    a    From: McCormack et al. (1981).
    b    Rats were fed 0,10, or 100 mg PBBs (FireMaster(R) BP-6)/kg from day 8 of pregnancy until 28 days postpartum at which
         time all offspring (F1-10 and F1-100) were weaned on to a control diet, allowed to mature sexually, and bred with
         littermates to produce the F2-generation (F2-10 and F2-100). F2-100 littermates were bred to produce F3-100 animals.
    c    Values are means in mg 2,2',4,4',5,5'-hexabromobiphenyl/kg wet tissue ± SE for at least three animals at 28 days of age.
    d    Sample not available.

         Most of the distribution studies performed with living subjects
    used paired samples of serum, adipose tissue (fat biopsy technique,
    e.g., Daum et al., 1978), and breast-milk (see Tables 56, 57 and
    58). Other tissues or fluids have rarely been analysed for PBB
    content, e.g., there is one report on liver biopsy tissue (300 µg
    HxBB/kg), fat (1069 µg/kg), bone marrow (3.5 µg/kg) and synovial
    fluid (twice the amount present in serum) of a single person
    (Meester & McCoy, 1976).

         In some early investigations, serum (plasma, resp.) and adipose
    tissue levels (Table 56) or serum (plasma, resp.) and breast-milk
    levels (Table 57) did not seem to correlate well with each other. 
    Later studies, performed when continuing exposure had ceased
    (Anderson, 1985), did reveal good correlations between serum and
    adipose levels (Table 56) and between breast-milk and serum or
    adipose tissue levels (Tables 57 and 58). The PBB concentrations
    measured are compiled in section 5.2 and 5.3.

         Different groups of the population can differ in their ratios. 
    For example, lowest adipose to serum ratios were found in lactating
    and pregnant females (see Table 56). Eyster et al. (1983) found
    statistically different ratios for females and male chemical workers
    versus farm workers and other males. The adipose to serum ratio of
    340:1, theoretically predicted by Tuey & Matthews (1980) was between
    the values reported for the Michigan general population (see Table
    56). Factors that appear to affect the partitioning ratios are sex,
    pregnancy, occupational status, the total amount of PBBs present,
    and whether samples were collected during exposure or during the
    recovery phase (Eyster et al., 1983; Anderson, 1985). Generally, the
    stability of a ratio would depend on a person being at equilibrium
    with respect to PBB intake and fat mobilization (Fries, 1985b).

         Transfer of PBBs to offspring occurs via transplacental passage
    and via breast-milk (see also section 5.2.4). Breast-milk had levels
    of more than 100 times the maternal serum levels (Table 57). The
    ratios of 2,2',4,4',5,5'-HxBB concentrations in milk fat to maternal
    body fat were found to be in the range of 0.7-0.9 : 1 (Table 58). 
    Placental tissue and cord or fetal serum levels were 1/6 to 1/10 the
    maternal serum levels (see Tables 59 and 60).

         According to Jacobson et al. (1984), the higher maternal serum
    levels were, in part, reflecting the greater concentration of lipids
    found in maternal serum (Table 60). Nevertheless, even when
    calculated on a fat basis, PBB concentrations in maternal serum were
    still about three times higher than those in cord serum (Jacobson
    et al., 1984).

    
    Table 55.  PBB postmortem study: autopsied tissue samples from humans in the Grand Rapids area (Michigan, USA)a

    PBBsb in tissue (µg/kg wet weight)

    Subject                           Heart           Kidney                                    Renal      Skeletal
    No.      Adrenal  Aorta   Brain   I. vent.   Cortex   Medulla   Liver   Lung     Pancreas   fat        muscle    Spleen   Thymus   Thyroid

    1           40      -        2        6         2        4         9       2         4        80          8        3        -         3
    2          407     118       1       15         4       15        17       2        43       457         10        9       295        9
    3          242     247      16       21        18       61         0      63        51       320         42        2        -        80
    4          148     294     103       36        32       30       147      73       653       430         84      123        -         -
    5           43      18       3        4         3        6        39       4       135       134          7        1        -         5
    6           98      64      24      126        53       77       104      14       130       110         45       64        29       12
    7           35       6       1       52         5        6         5       2         9        32          2        2         0        5
    8          868    1011     142      233        61      100       259      93       188      1650         22       69        -         -
    9           -       75      16       15         6        2        59       6       158        94         11        0        -        12
    10         110     285      -       110        95       81        31      62       170      1110         57      312        -        40
    11         602     107       0       21        29       38        37      11       148       607         33       15       617       41
    12         196      29      11        4        17       31        30      80        92       322         13        4        30       22
    13          17      44       9        4         2        3        22       4        20       205         14        2        -         6
    14          48      -        5        6        10        5        15       4        17       167          8        4        -         8
    15         850     514      13       37        42       67       143      43       146      1390         53       36        -        37

    Mean       265     216      27       46        25       35        61      31       131       475         27       43       243       22
    SEM         80      77      12       16         7        9        18       9        41       131          6       21       140        6

    Range    17-850  6-1011   1-103    2-95      2-100    0-259     2-93    4-653    32-1650    2-84        2-84     0-312   29-617     3-80

    Table 55. (contd)

    PBBsb in tissue (µg/kg wet weight)

    Subject                           Heart           Kidney                                    Renal      Skeletal
    No.      Adrenal  Aorta   Brain   I. vent.   Cortex   Medulla   Liver   Lung     Pancreas   fat        muscle    Spleen   Thymus   Thyroid

    Tissue/
    renal
    fat:
    mean
    ratio     0.56    0.45    0.06     0.10      0.05     0.07      0.15    0.07      0.28       1.0        0.06     0.09     0.51      0.06

    a    From: Miceli et al. (1985).
    b    Measured (by GC) as the concentration of 2,2',4,4',5,5'-hexabromobiphenyl; limit of detection: 0.5 µg/kg.

    Table 56.  Adipose tissue and serum partitioning ratios of 2,2'4,4',5,5'-hexabromobiphenyl

    Exposed group collecteda        Year                Partition coefficient ratios       Correlation          Reference

    Male chemical workers
    (No. = 27)                      1976                           287:1                       0.96             Wolff et al. (1979a)
    (No. = 22)                     1975-80                       190-260:1                     0.89             Eyster et al. (1983)

    Farm residents, etc.
    Mixed sexes                    1974-75                         175:1                                        Humphrey & Hayner (1975)b
    (No. = 13)                                               (range: 61-370:1)

    Mixed sexes                    1975-76                    4752 (± 793):1                                    Meester & McCoy (1976)
    (No. = 116)                                            (range: 27-14 850:1)

    Mixed sexes                    1976-77                         363:1                       0.96             Landrigan et al. (1979)
    (No. = 132)

    Mixed sexes                     1976                           370:1                       0.94             Wolff et al. (1979b)
    (No. = 31)                     1976-77                         300:1
    (No. > 31)                  not specified                      320:1

    Mixed sexes                    1974-77                         358:1                       0.81d            Tuey & Matthews (1980)b,c
    (No. = 197)

    Pregnant females               1975-80                       140-180:1                     0.91             Eyster et al. (1983)
    (No. = 30)

    Non-pregnant females           1975-80                       193-230:1                     0.84             Eyster et al. (1983)
    (No. = 51)

    Males (No. 75)                                               325-329:1                     0.95             Eyster et al. (1983)

    Lactating women throughout      1976                           100:1                       0.72             Brilliant et al. (1978)
    Michigan (No. = 8)

    Table 56 (contd).

    Exposed group collecteda        Year                Partition coefficient ratios       Correlation          Reference

    Michigan general population     1978-79             370:1                              "high"               Selikoff & Anderson (1979)
    (No. = 396)

    Michigan general population     1978                300:1                              0.96                 Wolff et al. (1982)
    (No. = 588)

    a    No. = Number of paired samples.
    b    Use of "plasma" (instead of "serum").
    c    Values based on data of Gladen & Rogan (1979).
    d    Spearman correlation coefficient.

    
    Table 57.  Breast-milk (fat) and serum, partitioning ratios of
    2,2',4,4',5,5'-hexabromobiphenyl in Michigan women

    Year             Number of    Partition      Correlation     Reference
    collected        paired       ratios         coefficient
                     samples

    1974-75             5        70-132:1          0.78          Humphrey & Hayner (1975)

    1976                                           0.81          Brilliant et al. (1978)

    1976-77            21          122:1                         Landrigan et al. (1979)
                                (62-257:1)

    1975-80            46        107-119:1         0.95          Eyster et al. (1983)

    Not specified      92                          0.71a         Jacobson et al. (1984)

    a    Pearson product moment correlation.

    Table 58.  Adipose tissue and breast-milk (fat) partitioning ratios of
    2,2',4,4',5,5'-hexabromobiphenyl in Michigan women

    Year            Number of        Partition       Correlation      Reference
    collected       paired samples   ratios          coefficient

    1976                10             1.07:1          0.88           Brilliant et al. (1978)

    1975-80             24           1.1-1.5 :1        0.97           Eyster et al. (1983)

    
         Incidentally, in contrast to PBBs, PCB levels (examined
    additionally) were not significantly different in the maternal and
    cord serum when compared on a fat basis (Jacobson et al., 1984). PBB
    levels measured in children with known exposure to PBB in utero
    and/or through breast-milk (see Table 38: Weil et al., 1981) also
    indicate significant PBB transfer.

    Table 59.  Placental transfer of PBB: partitioning ratios of
    2,2',4,4',5,5'-hexabromobiphenyl between fetal and maternal tissues

    Year           No.a    Paired tissues      Ratios         Correlation     Reference
    collected                                                 coefficient

    1976-77         13     maternal serum/      7.04:1                        Landrigan et al.
                           cord serum        (1.5-10.3:1)                     (1979)

    1975-80         58     cord serum/        0.10-0.14:1        0.88         Eyster et al.
                           maternal serum                                     (1983)

    1975-80         56     placenta/          0.10-0.17:1        0.85         Eyster et al.
                           maternal serum                                     (1983)

    Not            153     maternal serum/                       0.81b        Jacobson et al.
    specified              cord serum                                         (1984)

    Not            107     maternal milk/                        0.39b        Jacobson et al.
    specified              cord serum                                         (1984)

    a    No. = Number of paired samples.
    b    Pearson product moment correlation.

    Table 60.  Mean PBB and lipid levels in cord serum and maternal serum and milka

                           No.          Mean PBBb levels        Mean lipid levels

    Cord serum             230          0.3 µg/litre             3.24 g/litre

    Maternal serum         205          1.7 µg/litre

                           206                                   6.181 g/litre

    Maternal milk          138          3.6 µg/litre                0.029%

    Maternal milk-fat      138          105.1 µg/kg

    a    From: Jacobson et al. (1984).
    b    Probably measured as concentration of 2,2',4,4',5,5'-hexabromobiphenyl.

         The results of analysis of fat and thymus specimens from 2
    infants, taken at autopsy, are shown in Table 61. The ratio of
    thymus/fat "hexabromobiphenyl" concentrations, expressed as
    percentage, were 13 and 37% (Corbett et al., 1978a).

    Table 61.  Fat and thymus concentrations of hexabromobiphenyl (HBB) in
    3-day-old infants

                              HxBB concentration (mg/kg)

                           Fat                         Thymus

    Patient I             0.091                    0.012 (13.2%)

    Patient II            0.062                    0.023 (37.1%)

    a    From: Corbett et al. (1978a).

         The distribution pattern of PBB congeners, other than
    2,2'4,4',5'5-hexabromobiphenyl (BB 153), has been studied by Wolff
    et al. (1979a). They examined the relative (to BB 153) distribution
    of PBB congeners (penta- to heptabromobiphenyls) in the fat and
    serum of Michigan chemical workers and farm residents, and found
    different partition ratios for different homologues.

         The distribution of PBBs among blood compartments was studied
    by Bekesi et al. (1979a,b), Greaves et al. (1984), and Roboz et al.
    (1980, 1985a,b). In  in vitro models (PBBs added to blood), the
    distribution of PBBs among plasma, erythrocytes, mononucleocytes
    (white cell fraction) and polymorphonucleocytes (white cell
    fraction) was found to be 89:9:< 1:< 1 (Roboz et al., 1985a,b). 
    When, however, the amount of PBBs per cell was considered, there was
    an approximately 100-fold excess of PBBs in the white cell fractions
    compared with the erythrocyte fraction (Roboz et al., 1985b). In
    environmentally contaminated human blood, PBBs were also present in
    higher concentrations per mg protein in lymphocytes than in
    erythrocytes (Bekesi et al., 1979a,b,; Roboz et al., 1980; see also
    Table 45).

         It is thought that the relatively large amounts of PBBs
    associated with the white blood cells are possibly the cause of the
    immunological dysfunctions that result from exposure to PBBs (Roboz
    et al., 1985b).

         In serum, 20% of the PBBs were not bound to protein. The
    remaining 80% were bound to apolipoproteins B and A in a 3:1 ratio
    (Greaves et al., 1984). Roboz et al. (1985b) reported a ratio of
    4:1, which was close to the ratio (by weight) of the lipid content
    of these apolipoproteins. For comparison: the ratio between their
    amino acid content was 1.6:1 (Roboz et al., 1985b). There was no
    evidence of differential binding of various PBB congeners (penta-,
    hexa-, heptabromobiphenyls) to any of the serum fractions (Greaves
    et al., 1984; Roboz et al., 1985a,b).

    6.3  Metabolic transformation

         Indirect evidence for vertebrate metabolism of some PBB
    congeners has been obtained by analysis of tissues from
    experimentally and environmentally exposed animals and humans (see
    section 6.5). While many PBB congeners tended to be persistent,
    others were frequently absent or diminished. However, the changes in
    the relative abundances can reflect differences in uptake,
    distribution, and excretion among the congeners, as well as
    differences in the metabolism (Moore et al., 1980).

         There are several  in vitro and  in vivo methods for studying
    the metabolism of PBB congeners and mixtures.

    6.3.1   In vitro studies

         Using  in vitro techniques, hepatic microsomes from rats (or
    rabbits: Kohli et al., 1978) were incubated with individual PBB
    congeners or a PBB mixture, in the presence of nicotinamide adenine
    dinucleotide phosphate (reduced) (NADPH) and atmospheric oxygen.
    Most of the authors measured rates of disappearance of congeners
    (Dannan et al., 1978b; Moore et al., 1980; Parkinson & Safe, 1982;
    Millis et al., 1985a,b; Mills et al., 1985). A second approach was
    to examine the incubation mixture for metabolites (Kohli et al.,
    1978; Purdy & Safe, 1980; Safe et al., 1980; Sparling et al., 1980).
    The initial studies (Dannan et al., 1978b; Moore et al., 1980)
    revealed that only two of twelve PBB congeners from FireMaster(R)
    were metabolized when incubated with microsomes isolated from rats,
    pretreated with phenobarbital (PB) or PBB, namely
    2,4,5,2',5'-pentabromobiphenyl and 2,3,6,2',4',5'-hexabromobiphenyl.
    No metabolism could be observed with control microsomes or
    microsomes from 3-methyl cholanthrene (MC)-treated rats. These and
    other investigations performed with a number of PBB congeners
    (Br1-Br7 = model congeners, FireMaster(R) components,
    photolysis products of several hexabromobiphenyls) and with liver
    microsomal enzymes induced by either PB or MC are summarized in
    Table 62.

         The results suggest that the rates of metabolism of PBB
    congeners are dependent upon the positions of bromine and the type
    of cytochrome induced (P-450:PB-induced; P-448:MC- induced).

         The following structure-activity relationships have been
    derived: PBB congeners that possessed adjacent non-brominated
    carbons  meta and  para to the biphenyl bridge on at least one
    ring were metabolized by PB-induced microsomes (Dannan et al.,
    1978b; Moore et al., 1980; Mills et al., 1985). In one case, even
    one free para position was reportedly sufficient for PB-induced
    metabolism (Moore et al., 1980). Increasing bromination of PBB
    congeners did not appear to prevent their metabolism (Moore et al.,
    1980; Mills et al., 1985). Significant metabolism by MC- pretreated
    microsomes required adjacent  ortho and  meta positions free of
    bromines on at least one ring of lower substituted congeners (up to
    Br4). Higher substituted congeners (Br5, Br6) were not
    metabolized, though they fulfilled this criterion (Mills et al.,
    1985).

         In contrast to the studies mentioned above, Purdy & Safe (1980)
    found that radiolabelled [3H]-2,2',4,4',5,5'-hexabromobiphenyl
    (purity: > 98%) was metabolized  in vitro by rat liver microsomal
    enzymes. They determined polar, lipophilic metabolites after
    incubation with control and PBB-induced microsomes, however, in
    quantities that were much smaller than those yielded from
    [3H]-4-bromobiphenyl.

         Mono- and dihydroxylated derivatives have been identified as
    major  in vitro metabolism products of lower brominated PBBs (Kohli
    et al., 1978; Purdy & Safe, 1980; Safe et al.; 1980, Sparling
    et al., 1980; Parkinson & Safe, 1982).

         Some PBB congeners may induce their own metabolism (Aust
    et al., 1983), and some PBB congeners may influence the metabolism
    of other PBB congeners (Purdy & Safe, 1980; Mills et al., 1985).
    However, it should be noted that PBB congeners that induce
    microsomal enzymes (see also section 8.8.1) are not necessarily
    metabolized (Aust et al., 1983).

         Some studies were carried out using AHH, specific DNA binding,
    and 7-ethoxyresorufin assays. The results showed that PBBs (FM FF-1)
    can induce  in vitro cytochromes P450 IA (P448) in the primary
    cultures of human, and newly-born rat, epidermal keratinocytes, and
    of a rat hepatoma cell-line (Yao et al., 1991).

    6.3.2   In vivo studies

          In vivo metabolism studies included attempts to find and
    identify PBB metabolites from intact animals. Hydroxylated
    derivatives have been reported most commonly as metabolites of
    vertebrates.

    Table 62.  Metabolism of PBB congeners with rat liver microsomes

                                              Evidence for metabolisma

    PBB congenerb             MC         Reference          PB         Reference
                           microsomesc                   microsomesd

    4-MoBB                    Yes                           Yes        Parkinson &
                             (172)                        (53.1)       Safe (1982)

    2,2'-DiBB                 Yes                           Yes        Mills et al. (1985)
                            (0.33)                        (201.7)
                                                            Yes        Moore et al. (1980)
                                                         (> 2100)      Dannan et al. (1978b)

    4,4'-DiBB                  -                            No         Moore et al. (1980)
                                                         (< 0.02)      Dannan et al. (1978b)

    3,4,4'-TrBB               Yes                           No         Mills et al. (1985)
                            (100.7)                       (0.02)

    2,4,2',4'-TeBB            Yes                           No         Mills et al. (1985)

    2,4,2',5'-TeBB            Yes                           Yes        Mills et al. (1985)
                            (43.5)                        (184.6)
                                                            Yes        Moore et al. (1980)
                                                           (24)

    2,4,2',6'-TeBB            Yes                           Yes        Mills et al. (1985)

    2,5,2',5'-TeBB            No                            Yes        Mills et al. (1985)
                             (0.0)                        (66.2)
                                                            Yes        Moore et al. (1980)
                                                           (27)

    2,6,2',6'-TeBB            No                            Yes        Mills et al. (1985)

    2,3,3',4'-TeBB            Yes                           Yes        Mills et al. (1985)
                            (57.6)                        (52.8)

    2,5,3',4'-TeBB            Yes                           Yes        Mills et al. (1985)
                            (49.7)                        (47.5)

    3,4,3',4'-TeBB            Yes                           No         Mills et al. (1985)
                            (58.8)                        (0.01)

    Table 62 (contd).

                                              Evidence for metabolisma

    PBB congenerb             MC         Reference           PB        Reference
                           microsomesc                   microsomesd

    3,4,3',5'-TeBB            Yes                           No         Mills et al. (1985)

    3,5,3',5'-TeBB            No                            No         Mills et al. (1985)
                            (0.06)                         (0.0)

                                                            Yes        Moore et al. (1980)

    2,4,6,2',4'-PeBB          No                            No         Mills et al. (1985)

    2,4,5,2',5'-PeBB          No                            Yes        Mills et al. (1985)
                            (0.02)                        (23.7)

                              No        Dannan et al.       Yes        Moore et al. (1980)
                                        (1978b)            (13)        Dannan et al. (1978b)

    2,4,6,2',6'-PeBB          No                            Yes        Mills et al. (1985)

    2,4,5,3',4'-PeBB          No                            No         Mills et al. (1985)
                            (0.05)                        (0.03)

                              No        Dannan et al.       No         Moore et al. (1980)
                                        (1978b)          (< 0.06)      Dannan et al. (1978b)

    3,4,5,3',4'-PeBB          No        Dannan et al.       No         Mills et al. (1985)
                                        (1978b)

    3,4,5,3',5'-PeBB          No        Dannan et al.       No         Mills et al. (1985)
                                        (1978b)

    2,3,4,2',4',5'-HxBBB      No                            No         Mills et al. (1985)
                            (0.16)                         (0.0)

                              No        Dannan et al.       No         Moore et al. (1980)
                                        (1978b)           (< 0.3)      Dannan et al. (1978b)

    2,3,6,2',4',5'-HxBBB      No        Dannan et al.       Yes        Moore et al. (1980)
                                        (1978b)            (19)        Dannan et al. (1978b)

    2,4,5,2',4',5'-HxBBB      No        Dannan et al.       No         Moore et al. (1980)
                                        (1978b)           (< 0.3)      Dannan et al. (1978b)

    Table 62 (contd).

                                              Evidence for metabolisma

    PBB congenerb             MC         Reference           PB        Reference
                           microsomesc                   microsomesd

    2,3,4,5,3',4'-HxBBB       No                            No         Mills et al. (1985)
                            (0.11)                         (0.0)

                              No                            No         Dannan et al. (1978b)

    2,4,5,3',4',5'-HxBBB      No                            No         Dannan et al. (1978b)

    3,4,5,3',4',5'-HxBBB      No                            No         Mills et al. (1985)
                            (0.20)                         0.0)

    2,3,4,5,2',4',5'-HpBB     No        Dannan et al.       No         Moore et al. (1980)
                                        (1978b)           (< 0.3)      Dannan et al. (1978b)

    a    Measured as the rate of substrate disappearance (in parentheses: values measured
         in pmol/min per mg protein).
    b    For expediency, a trivial numbering system was used.
    c    MC microsomes = 3-methylcholanthrene-induced microsomes.
    d    PB microsomes = phenobarbital-induced microsomes.
    
         As can be seen from Table 63, administration of lower
    brominated congeners resulted in low yields of, mainly, mono- or
    dihydroxy metabolites. However, most of the studies compiled
    suffered from the fact that the purities of the congeners used in
    these studies were not determined (Moore et al., 1980). The two
    studies with 2,2',4,4',5,5'-HxBB did not provide evidence of
    significant metabolism (Table 63).

         Various results were obtained after administering commercial
    PBB mixtures. No hydroxylated PBBs could be detected in the urine of
    cows given single 3-g doses of FireMaster(R) BP-6 (Willett &
    Irving, 1976) or in the milk of cows (accidentally contaminated by
    FireMaster(R) FF-1) with PBB residues as high as 900 µg/kg, on a
    whole milk basis (Gardner et al., 1976). Approximately 1% of the
    FireMaster(R) BP-6 administered to a pig was eliminated as an
    unidentified pentabromobiphenylol (Kohli & Safe, 1976). It is not
    clear whether this metabolite was formed from hexabromobiphenyl (by
    reductive debromination followed by hydroxylation) or directly from
    pentabromobiphenyl (by hydroxylation).

    Table 63. PBB in vivo metabolites reported in the literature

    Parent compound       Species        Yielda    Reported                    References
                          (tissue,                 metabolites
                          etc.)

    Monobromobiphenyls

    2-bromobiphenyl       rabbit         1%        2'-bromo-4-biphenylol       Kohli et al.
                          (urine)                                              (1978)
                                         traces    mono-hycroxybromobiphenyl

                          rat            (>)       2-bromo-4-4'-biphenyldiol   Sparling et al.
                                                                               (1980)

                                         (>)       2-bromo-4-4'-biphenyldiol

                                         (<)       2-bromo-4-biphenylol

    3-bromobiphenyl       rabbit         4%        3-bromo-4-biphenylol        Kohli et al.
                          (urine)                  or 5-bromo-2-biphenylol     (1978)

                                         < 1%      dihydroxybromobiphenyl

                          rat            (>)       3-bromo-4,4'biphenyldiol    Sparling et al.
                          (urine)                  and an unidentified diol    (1980)

                                         (<)       monohydroxybromobiphenyls

    4-bromobiphenyl       rabbit         4%        4'-bromo-4-biphenylol       Kohli et al.
                          (urine)        1.5%      4'-bromo-3,4-biphenyldiol   (1978)

                          rat            (>)       4'-bromo-4-biphenylos       Sparling et al.
                          (urine)        (<)       mono- and dihydroxylated    (1980)
                                                   species

                          pig            3%        4'-bromo-4-biphenylol       Kohli &
                          (urine)                                              Safe (1976)

                                         traces    monohydroxybromobiphenyl

                                         0.5%      4'-bromo-3-methoxy-
                                                   4-biphenylol

    Table 63 (contd).

    Parent compound       Species        Yielda    Reported                    References
                          (tissue,                 metabolites
                          etc.)

                          chicken        12.2%     4'-bromo-4-biphenylol       Jones et al.
                          (excreta)      9.8%      4'-bromo-3,4-biphenyldiol   (1979)

                          (eggs)         0%        no metabolites

    Dibromobiphenyls

    4,4'-dibromobiphenyl  rabbit         10%       4,4'-dibromo-3-biphenylol   Safe et
                          (urine)                                              (1976)
                                         1%        3,4'-dibromo-4-biphenylol

                                         2%        4'-bromo-4-biphenylol

                          pig            5%        4,4'dibromo-3-biphenylol    Kohli &
                          (urine)                                              Safe (1976)

                                         1%        3,4'-dibromo-4-biphenylol

                                         traces    dibromomethoxy-
                                                   biphenylol

                                         1%        4'-bromo-3-methoxy-
                                                   4-biphenylol

                                         traces    dibromomethoxybiphenyl

    Mixture of di-,       fish Salmo               dibromobiphenylol           Zitko &
    tri-, and tetra-      salar (whole                                         Hutzinger
    bromobiphenyls        animal)                                              (1976)

    Hexabromobiphenyls

    2,2',4,4',5,5'-       rat (urine     traces    "metabolites"               Safe et al.
    hexabromobiphenyl     and faeces)                                          (1978)
    (purity: 95%)

    Table 63 (contd).

    Parent compound       Species        Yielda    Reported                    References
                          (tissue,                 metabolites
                          etc.)

    2,2',4,4',5,5'-       rat            0%        no metabolites              Matthews et al.
    hexabromobiphenyl     (tissues)                                            (1977)
    (purity: 99%)

                          (bile and      traces    may be metabolites
                          faeces)        (1-4%)

    a    (>) and (<) = major and minor components (no further quantitative information).
    
         The faeces of dogs fed FireMaster(R) BP-6 contained a
    metabolite identified as 6-hydroxy-2,2',4,4',5,5'-hexabromobiphenyl
    (Gardner et al., 1979). However, the authors did not exclude
    microbial metabolism in the dog's gut, because no
    hydroxyhexabromobiphenyl was found in the liver of the dog, though
    PBB was present. Matthews et al. (1979) mentioned that dogs were
    able to metabolize 2,2',4,4',5,5'-hexachlorinated biphenyl, but were
    unable to metabolize the analogous PBB at an appreciable rate.

         Some investigations implied that fish may debrominate the more
    highly brominated components of PBB mixtures. Juvenile Atlantic
    salmon  (Salmo salar) experimentally exposed to FireMaster(R)
    BP-6, in water or in food, contained several mono- to
    pentabromobiphenyls, not present in FireMaster(R) BP-6 (Zitko,
    1977). Fish  (Salmo salar) fed octabromobiphenyl (Dow
    Chemical)-contaminated food contained unidentified penta-, hexa-,
    and heptabromobiphenyls in addition to the octabromo biphenyls. It
    was not known whether the partially debrominated biphenyls were
    generated by the fish, or by the associated microflora (Zitko,
    1977). Analyses of fish captured from natural waters may also
    indicate the possibility of the debromination reaction in fish,
    unless selective accumulation or elimination takes place (Stratton &
    Whitlock, 1979). In fish from water mainly contaminated with
    decabromobiphenyl, only the nona- and hexa bromobiphenyl congeners
    were present. However, in fish from FireMaster(R)
    BP-6-contaminated waters, only hexabromobiphenyl was detected.

    6.3.3  Metabolic pathway

         The most frequently reported route of PBB metabolism was
    hydroxylation. However, according to Zitko & Hutzinger (1976), a
    reductive debromination may be a degradative pathway of higher
    brominated biphenyls, because the carbon-bromine bond is less stable
    than, e.g., the carbon-chlorine bond.

         The hydroxylation reaction probably proceeds via both arene
    oxide intermediates (Safe et al., 1976, 1978, 1980; Kohli et al.,
    1978; Moore et al., 1980) and by direct hydroxylation (Kohli et al.,
    1978; Sparling et al., 1980; Moore et al., 1980). Schemes of
    possible metabolic routes have been published by Matthews (1982) and
    Safe (1989). The most important enzyme involved in the oxidation of
    xenobiotics, such as PBBs, is aryl hydrocarbon hydroxylase. It is a
    highly inducible, haem-containing mono oxygenase belonging to the
    family of cytochromes P-450 (e.g., Safe et al., 1980). A (partial)
    summary of the AHH-mediated metabolism is given by Safe et al.
    (1978).

         The formation of covalently bound macromolecular adducts has
    been reported. Less than 10% of the metabolites were present in the
    urine of rabbits in a bound form, e.g., as glucuronides (Safe
    et al., 1976).  In vitro metabolism also resulted in macromolecular
    conjugates (Kohli et al., 1978; Purdy & Safe, 1980; Safe et al.,
    1980; see also section 6.6). In general, the biotransformation of
    PBBs is a slow process, but the stereochemistry and molecular size
    vary so widely among PBBs that there are great differences in their
    metabolic activity.

    6.4  Elimination and excretion in expired air, faeces, urine

    6.4.1  Animal studies

         Elimination of PBBs from the body has been studied using hexa-
    and octabromobiphenyl. No information is available on
    decabromobiphenyl. Some data found in the literature (see also
    section 6.1) are compiled in Table 64 (14C-labelled single doses),
    Table 65 (14C-labelled multiple doses), and Table 66 (daily
    feeding).

         The only study conducted with octabromobiphenyl resulted in a
    much higher elimination from rats than was found for HxBB in another
    study on rats (Table 64). However, there are also reports on the
    rapid elimination of HxBB, e.g., by Willett & Irving (1976), who
    found a 50% recovery of HxBB after 168 h in the faeces of two cows
    given single intraruminal doses (3 g) of FireMaster(R) BP-6.
    However, relatively high concentrations of radioactivity or of HxBB,

    found, in some cases, in the faeces during the first few days after
    dosing or during daily dosing, may have been due to incomplete
    absorption (Tuey & Matthews, 1980). Approximately 60% of the total
    dose was also recovered in the faeces of rhesus monkeys (Rozman
    et al., 1982: Table 64).

         Elimination of PBBs was primarily via the bile and the
    intestine into the faeces and, in general, was found to be a slow
    process.

         Biliary concentrations have been measured in a Rhesus monkey
    (Rozman et al., 1982), in rats (Matthews et al., 1977), and in
    cattle (Willett & Irving, 1976; Willett & Durst, 1978). In rats,
    excretion of HxBB in the bile accounted for 0.68% of the total PBB
    dose between 0 and 4 h after intravenous (iv) administration.
    Twenty- four hours after an iv dose, 0.032% of the total dose was
    excreted in the bile in 1 h, and, 7 or 42 days after dosing
    concentrations were too low to quantify (Matthews et al., 1977).
    Because of this small amount cleared with the bile, enterohepatic
    recirculation of HxBB in rats is not important (Tuey & Matthews,
    1980). Concen trations of HxBB in the bile of cattle were two-three
    times greater than the concentration in the plasma (Willett &
    Irving, 1976; Willett & Durst, 1978).

         According to Fries (1985b), excretion of PBB in the urine is
    not expected, because of the insolubility of PBBs in water. He
    attributed the few instances in which low concentrations of PBBs
    were reported to cross-contamination with faeces. On the other hand,
    this route of excretion may account for minor or metabolized
    biphenyls (Damstra et al., 1982; see also Table 63). However,
    excretion of PBB metabolites may be of minor relevance, since the
    more abundant PBB congeners are not, or only slightly, metabolized
    (see also section 6.3). The amounts of urinary or faecal metabolites
    were low. A study on a pig that received a single intraperitoneal
    (ip) dose of FireMaster(R) BP-6 (100 mg/kg body weight) reported a
    yield of about 1% of pentabromobiphenylol in the urine and faeces,
    collected for 7 days (Kohli & Safe, 1976). The level of a hydroxy
    metabolite detected in the faeces of dogs fed FireMaster(R) BP-6
    was about an order of magnitude less than the PBB levels (Gardner
    et al., 1979). Yields of lower brominated urinary PBB metabolites
    are compiled in Table 63.

         In their study on cows, Willett & Durst (1978) did not find any
    direct relationships between the amount of PBBs fed and the
    concentration in the faeces. In contrast, Babish et al. (1975a) did
    find a linear correlation (r > 0.97) of dietary PBBs with excreta
    residues in Japanese quails. In another study on cows, it was also
    reported that relationships were approximately constant (Robl
    et al., 1978: Table 66).

    
    Table 64.  Faecal, urinary, and exhalative elimination of 14C activity as a percentage of a single dose of [14C-]PBB

    Species                 Agent; solvent; dose (mg/kg          Time                    % recovery in:                      Reference
                            body weight); route                              faeces          urine          expired air

    Rhesus monkey (male)    [14C-]HxBB in mineral oil; 2, oral   5 days        38           (0.18)               -           Rozman et al.
                                                                                                                             (1982)

    Rat (male)              [14C-]HxBB in Emulphor EL-620:                                                       -           Matthews et al.
                            ethanol: water (1:1:8)               24 h          7.9                                           (1977); Tuey &
                            1, oral                              24 h         0.96                                           Matthews
                            1, intravenous                       7 days       3.28           < 0.1                           (1978, 1980)
                            1, intravenous                       42 days       6.6       not detected

    Rat (male and female)   [14C-]OcBBa in corn oil; 1, oral     24 h          62                                            Norris et al.
                                                                 48 h          69                                            (1973)
                                                                 16 days       73             < 1               < 1

    Mink (Mustela vison)    [14C-]PBBb in propylene glycol                                                                   Bleavins et al.
    (pregnant female)       (1 µCi in 0.1 ml) intravenous        2 h            -            0.003               -           (1981)

    Ferret (Mustela                                              2 h            -            0.004
    puttorius (furo)
    (pregnant female)

    Dog                     [14C-]2,2',4,4',5,5'-hexabromo       25 days        8                                            Sipes et al.
                            biphenyl (solvent not specified)                                                                 (1979)
                            0.6, intravenous

    a    OcBB = technical octabromobiphenyl.
    b    Consisted of 2,2', 4,4', 5,5'-HxBB and 2,2', 3, 4,4', 5,5'-HpBB.

    Table 65.  Urinary and faecal elimination of HxBB and/or metabolites in male Rhesus monkeys and male rats,
    dosed repeatedly with [14C-]HxBB

    Species      Dose (mg/kg body          Days after      Urine             Faeces       Cumulative %      Reference
                     weight)               first dose    (µg/kg per        (µg/kg per     recovery of
                                                           day)               day)        total dose
                                                                                          in faeces

    Monkey       50                          1-10            3.2             5890         ca 60%            Rozman et al. (1982)
    (No. = 2)    in methyl cellulose;        11-17           2.5              5.0
                 oral on days 1 and 5       203-209    not detectable         3.5

    Rat          1                             7                                          ca 14%            Matthews et al. (1977)
    (No. = 3)    in corn oil; oral on
                 days 1, 2, 3, and 4

    Table 66.  Elimination of HxBB (2,2',4,4',5,5'-hexabromobiphenyl) in faeces and urine during the feeding of FireMaster(R)-mixtures

    Species      Intake of FireMaster              Sampling            Concentration in:             Approximate %      Reference
    (sex)            BP-6 or FF-1                    time                   (mg/kg)                  recovery in
                                                                     Faeces          Urine             faeces

    Dog          BP-6: in corn oil (capsule)      last day of          7                                                Gardner et al.
    (female)     1 mg/kg body weight per day        dosing                                                              (1979)
                 for 6 weeks

    Pig          BP-6: in corn oil                 at week 4                                                            Ku et al. (1978)
                 20 mg/kg diet                                       21.3a           0.015
                 200 mg/kg diet                                     182.0a           0.07
                 (ad libitum)
                 for > 4 weeks

    Cow          FF-1: in gelatin capsules;                                                                             Robl et al. (1978)
                 for 90 days
                 0.1 mg/kg diet                                      0.02           mostly           15% of
                 1.0 mg/kg diet                                      0.15            n.d.b           ingested
                 10 mg/kg diet                                        1.5                            dose

    Calf         BP-6:(capsule); 25 g daily          total           8045                            5% of total        Willet & Irving
    (male)       for 9 days                       collection                                         dose               (1976)

    Hen          BP-6: 20 mg/kg in the diet         weekly                                           9% of daily        Fries et al.
                 for 63 days                                                                         dose               (1976)

    Hen          FF-1: not specified             not specified                                       11% of daily       Ringer &
                                                                                                     dose               Polin (1977)

    a    Faecal samples oven-dried.
    b    nd = Not detected (detection limit = 0.005 mg/kg).

         Following withdrawal of PBBs (FireMaster(R) BP-6) from the
    diet of cows, the faecal concentrations of HxBB declined to 1-2% of
    faecal levels during dosing (Willett & Durst, 1978) and to less than
    5% in hens (Fries et al., 1976). Faecal concentrations were small in
    relation to body burden. Cows that received 250 mg FireMaster(R)
    BP-6 daily had HxBB concentration ratios in body fat to faeces of
    about 750 : 1. Their faeces to plasma ratio was 0.7 :1 (Willett &
    Durst, 1978). Cows environmentally contaminated (FireMaster(R)
    FF-1) 7-9 months before examination had comparable body fat to
    faeces ratios, but a different faeces to blood ratio of 4.2 : 1
    (Detering et al., 1975; Cook et al., 1978b; Fries et al., 1978a).
    Post-exposure lactating cows eliminated via milk fat three times the
    quantity of HxBB cleared in faeces (Willett & Durst, 1978).

         There have been some studies on the means to enhance the
    elimination of PBBs. PBBs used were: FireMaster(R) FF-1 (Cook
    et al., 1978b; Kimbrough et al., 1980; McConnell et al., 1980; Polin
    & Leavitt, 1984; Polin et al., 1985) and [14C-]HxBB (Rozman
    et al., 1982). The treatments included activated carbon in rats
    (McConnell et al., 1980) and cows (Cook et al., 1978b),
    cholestyramine in rats (McConnell et al., 1980) and monkeys (Rozman
    et al., 1982), colestipol in chickens (Polin & Leavitt, 1984; Polin
    et al., 1985), mineral oil in rats (Kimbrough et al., 1980), monkeys
    (Rozman et al., 1982), and chickens (Polin et al., 1985), high-fibre
    diets in rats (Kimbrough et al., 1980), and phenobarbital in cows
    (Cook et al., 1978b). The effects of restricted caloric intake,
    alone, or in combination with other treatments, was investigated in
    rats (McConnell et al., 1980) and chickens (Polin & Leavitt, 1984;
    Polin et al., 1985). The procedures were found not to be (Cook et
    al., 1978b; Kimbrough et al., 1980; McConnell et al., 1980), or to
    be only partially, effective (Rozman et al., 1982; Polin & Leavitt,
    1984; Polin et al., 1985) in reducing the body burden of PBBs
    (measured as concentrations of HxBB, total bromine levels, or
    14C-activity).

    6.4.2  Human studies

         The concentrations of PBBs in human bile and faeces represent a
    minor proportion of the total body burden, as has been demonstrated
    by Eyster et al. (1983), who determined HxBB levels in Michigan farm
    and chemical workers in 1975-80. Concen trations of HxBB observed in
    the bile and faeces were about 1/2 to 7/10 of the serum levels (on a
    whole-weight basis) and were estimated to be approximately 0.5% of
    the adipose tissue levels (Table 67).

         These findings are consistent with the theoretical predictions
    of Tuey & Matthews (1980), who calculated slow rates of faecal
    excretion in humans. In addition, these authors showed that the
    excretion rate in lean individuals exposed to HxBB would be higher
    than those in overweight individuals.

    6.5  Retention and turnover

    6.5.1  Animal studies

         The time course of PBB tissue concentrations has been studied
    predominantly in rats, and, to a lesser extent, in cattle, chickens,
    and guinea-pigs (Table 68). Incomplete data are available for mice,
    pigs, and monkeys. With the exception of 3 older studies (Norris
    et al., 1973; Lee et al., 1975a; Waritz et al., 1977), in which the
    behaviour of technical octabromobiphenyl in rats was observed, the
    majority of investigators used the FireMaster(R)- mixture (BP-6 or
    FF-1). Of the individual PBB congeners,
    2,2',4,4',5,5'-hexabromobiphenyl (Matthews et al., 1977; Millis
    et al., 1985b) and 3,3',4,4'-tetrabromobiphenyl (Millis et al.,
    1985b) were administered.

    Table 67.  Medians, range, and geometric means of 2,2',4,4',5,5'-
    hexabromobiphenyl (HxBB) for paired specimens of serum, faeces, and bile
    obtained from farm and chemical workersa

    Number      Paired         Median           Rangeb            Geometric
                specimen                                          mean

    51          serum          7 µg/litre       1-1540 µg/litre   14.4 µg/litre 
                faeces         5 µg/kg          nd-862 µg/kg      9.0 µg/kg

    20          serum          3.5 µg/litre     1-153 µg/litre    4.2 µg/litre 
                biliary fluid  2 µg/litre       nd-70 µg/litre    2.7 µg/litre

    a    From: Eyster et al. (1983).
    b    nd = Not detectable (detection limit: 1 µg/kg or µg/litre).
    
         Complex and varied relationships were found in tissue
    concentrations with time after PBB administration (see also Tables
    47, 48, and 49).

    
    Table 68.  Reported biological half-lifes of PBBs in mammals and birds, after single or repeated exposure

    Species                  PBBa (Dosing regimen)                Elimination          Calculated half-lifeb       References
    (sex)                    Observation period                   from:                (Kinetic phases)

    Rhesus Monkey (male)     [14C-]HxBB (50 mg/kg body weight     body                 > 4 years                   Rozman et al.
                             on days 1 and 5; oral) 209 days                                                       (1982)

    Rat (male)               [14C-]OcBB (1 mg/kg body weight;     faeces               < 24 h (1st phase)          Norris et al.
                             single dose; oral) 16 days                                > 16 days (2nd phase)       (1973)

    Rat                      [14C-]HxBB (1 mg/kg body weight;     faeces               2 days (1st phase)c         Birnbaum
                             single iv dose) 42 days                                                               (1985)
                                                                  "tissues"            ca 24 daysc                 Ecobichon et al.
                                                                  (blood, liver                                    (1983)
                                                                  muscle, skin)

    Rat (male)               FM BP-6 (1 mg/100 g body weight;     serum                23.1 weeks                  Miceli &
                             single ip dose; 36 weeks             fat                  69.3 weeks                  Marks (1981)
                                                                  adrenal              43.3 weeks
                                                                  brain                63.0 weeks (2nd phase)
                                                                  liver                11.5 weeks (2nd phase)
                                                                  lung                 11.2 weeks
                                                                  spleen               9.0 weeks

    Rat (male)               FM FF-1 (10 mg/kg body weight;       whole blood          3.27 h (')                  Domino et al.
                             single dose; oral) 112 days                               33.3 h (ý)                  (1982)
                                                                                       145 days (')

    Guinea-pig (lactating    FM FF-1 (50 mg/kg body weight;       tissues (fat,        ca 22 days                  Ecobichon
    females and pups)        single dose; oral) 60 days           liver, kidney,                                   et al. (1983)
                                                                  lung) of both

    Table 68 (contd).

    Species                  PBBa (Dosing regimen)                Elimination          Calculated half-lifeb       References
    (sex)                    Observation period                   from:                (Kinetic phases)

    Cow                      FM BP-6 (fed 10 mg/day for           milk fat             ca 58 days                  Fries &
                             60 days) 60 days (of withdrawal)                          (2nd phase)                 Marrow (1975)

    Cow                      FM BP-6 (fed 1.13 g/day for          milk                 10.5 days                   Gutenmann &
                             15 days; = 50 mg/kg in the diet)                                                      Lisk (1975)
                             15 days (of withdrawal)

    Cow                      FM FF-1 (environmentally             milk fat             ca 60 days                  Fries et al.
                             contaminated 1 year earlier;                              (range: 36-301 days)        (1978a); Cook
                             6 months of observation)                                                              et al. (1978b)

    Cow                      FM BP-6 (fed 0.25 mg-25 g/day        milk fat             > 6 monthsd                 Fries
                             for various periods) up to           (body)                                           (1985b)
                             3 years of observation

    Chicken (White           FM FF-1 (fed in the diet)            egg                  17 days                     Ringer &
    Leghorn hens)            28 days (of withdrawal)                                                               Polin (1977)

    Chicken (White           FM FF-1 (fed 0.2-125 mg/kg           egg                  17 days                     Polin &
    Leghorn hens)            in the diet for 5 weeks)                                                              Ringer (1978a)
                             56 days (of withdrawal)

                             (fed 1125 and 625 mg/kg in           liver                31 days
                             the diet for 5 weeks)
                             56 days (of withdrawal)

                             (fed 5-625 mg/kg in the diet         muscle               17 days
                             for 5 weeks) 56 days
                             (of withdrawal)

    Table 68 (contd).

    Species                  PBBa (Dosing regimen)                Elimination          Calculated half-lifeb       References
    (sex)                    Observation period                   from:                (Kinetic phases)

    Chicken (White           FM BP-6 (fed 20 mg/kg in the         egg                  28 days                     Fries et al.
    Leghorn hens)            diet for 63 days) 49 days                                 (2nd phase)                 (1976)
                             (of withdrawal)

    Chicken (White           FM BP-6 (fed 20 and 64 mg/kg         egg                  112 days                    Cecil &
    Leghorn hens)            in the diet for 8 weeks)                                  (late phase)                Bitman (1978)
                             266 days (of withdrawal)

    Chicken (White           FM BP-6 (fed 20 and 64 mg/kg         excreta              4-5 dayse                   Polin &
    Leghorn hens)            in the diet for 8 weeks)                                                              Leavitt (1984)
                             266 days (of withdrawal)

    a    HxBB = 2,2',4,4',5,5'-hexabromobiphenyl; OcBB = octobromobiphenyl (technical mixture);
         FM BP-6 = FireMaster(R) BP-6; FM FF-1 = FireMaster(R) FF-1.
    b    Referring to 2,2',4,4',5,5'-hexabromobiphenyl or [14C-]activity.
    c    Half-life calculated from data of Matthews et al. (1978); see also Fig. 6.
    d    Half-life calculated from data of Willett & Durst (1978).
    e    Half-life calculated from data of Fries et al. (1976).

    6.5.1.1  Time trends, retention: 2,2',4,4',5,5'-hexabromobiphenyl
             (BB 153)

    a) Rat

         When rats dosed with 2,2',4,4',5,5'-hexabromobiphenyl (Matthews
    et al., 1977; Tuey & Matthews, 1980) or with FireMaster(R) FF-1
    (Kimbrough et al., 1978; Domino et al., 1980b; 1982), BB 153
    concentrations in the blood were highest immediately after dosing,
    but fell rapidly during the first day (as PBBs are taken up from
    blood by the liver and muscle tissues, which are highly perfused
    tissues). Then, concentrations in the blood, liver, and muscle
    declined less quickly (as the dose was redistributed to the adipose
    tissue; Tuey & Matthews, 1980; Fries, 1985b), finally decreasing
    only very slowly. After a single intravenous dose of BB 153 (1 mg/kg
    body weight), adipose tissue contained more than 60% of the total
    body burden within four days (Tuey & Matthews, 1980; see Table 50).

         BB 153 concentrations in the adipose tissue peaked later than
    in other tissues and remained high throughout the period of
    observation (6 weeks: Matthews et al., 1977; 16 weeks; Domino
    et al., 1980b; 36 weeks: Miceli & Marks, 1981). For example, ratios
    between fat and serum levels in rats rose from 221 : 1 to 722 : 1
    between 6 and 36 weeks after a single dose exposure (Miceli & Marks,
    1981), reflecting the much more rapid clearance of BB 153 from serum
    than from fat.

         Kinetic models to describe the principal toxicokinetics of BB
    153 in the rat were constructed by Tuey & Matthews (1980; a blood
    flow-limited physiological compartmental model) and by Domino et al.
    (1982). The latter developed a three-compartment model. Tissues
    within a compartment showed similar kinetic characteristics, but
    concentrations could vary widely. Compartment 1 consisted of whole
    blood, spleen, kidney, and heart. Compartment 2 included liver,
    lung, cerebral grey and white matter, cerebellum, and testes, and
    compartment 3 consisted of subcutaneous fat. Jejunum could not be
    classified.

         However, results of Miceli & Marks (1981) (PBB levels monitored
    over longer periods) do not fit in well with this scheme. For
    example, these authors observed typical first-order-elimination
    kinetics of BB 153 in the serum of rats, but kinetics of disappear
    ance from heart and kidney (and pituitary) do not appear to be first
    order, though belonging to the same compartment (according to Domino
    et al., 1982). BB 153 concentrations in the brain and liver (both
    "compartment 2") declined rapidly during the interval from 6-12
    weeks after exposure, but, thereafter, (from week 12 to 36) brain
    concentrations fell far more slowly than those of the liver. The

    study of Miceli & Marks (1981) showed that the (long-term)
    retention, but not always the concentration, of BB 153 in lipid-rich
    tissues (brain, adrenal, adipose) was much greater than in most
    other tissues (see also Table 68).

         Corresponding to the small decline in BB 153 from the tissues
    of rats, the elimination rates in the faeces were slow (see Fig. 6). 
    Less than 7% of the dose was eliminated 42 days after a single iv
    dose, most, during the first 3-4 days (Tuey & Matthews, 1980).

         The kinetic models or calculations for BB 153 were based on the
    results of studies on adult male rats. In maternal rats the
    situation is more complex, and only a little information is
    available. For example, BB 153 levels in the liver and fat of
    maternal rats decreased during a period from the end of lactation

    (and exposure) until 14 weeks later (decline in fat: 50%), but BB
    153-concentrations in the mammary glands increased (5 times higher)
    during the same period (see also Table 48), indicating
    redistribution of BB 153 during the recovery period following
    lactation (McCormack & Hook, 1982).

         During continued exposure to FireMaster(R) BP-6, BB 153
    concentrations in the milk of lactating rats were determined 0, 3,
    5, 7, and 14 days following parturition and showed a decline from
    180 mg/litre (via 115, 89, 63 mg/litre) to 50 mg/litre (McCormack
    et al., 1979a).

         The kinetics of BB 153 in growing animals have not been
    frequently investigated. The differences in BB 153 levels and organ
    weights have been reported only between two ages. McCormack et al.
    (1980) showed that at 328 days of age, the concentrations of BB 153
    in the liver, kidney, and fat of rats were approximately 5, 10, and
    25% of the respective tissue concentrations at weaning (28 days of
    age; cessation of exposure).  Another long-term study (Groce &
    Kimbrough, 1984) compared BB 153 levels in the livers of perinatally
    exposed rats at the age of 2 months and 2 years and also found
    diminished values (see Table 52).

         Comparing BB 153 concentrations in the blood and adipose tissue
    of rats after 10 and 14 months recovery resulted in no "true"
    decrease (Kimbrough et al., 1978). Other studies also indicated a
    long retention of PBBs in the brain (Geller et al., 1979), thyroid,
    and liver (Allen-Rowlands et al., 1981), and in the adrenal glands
    (Castracane et al., 1982).

    b)  Other species

         The species, the second most often examined, was cattle, but
    the kinetic models used for cattle (e.g., Fries et al., 1978a) were
    less sophisticated than those described for rats (Fries, 1985b).

         In cows given FireMaster(R) BP-6, the BB 153 concentration in
    blood plasma was maximal 24 h after exposure (Willett & Irving,
    1976; Willett & Durst, 1978). When multiple doses were administered,
    plasma concentrations were at equilibrium by 15 days. When dosing
    was terminated, concentrations declined approximately 50% in 10 days
    and 66% by day 20. Thereafter, plasma residues did not fit a
    consistent decline model (Willett & Durst, 1978).

         While BB 153 was detectable in plasma within 2-4 h of exposure
    (Willett & Durst, 1978), it was detected in the milk of cows 13 h
    after exposure (Willett & Irving, 1976). With continued exposure, a
    steady state of BB 153 concentrations in milk fat was reached after
    20-40 days (Fries & Marrow, 1975; Willett & Durst, 1978; Fries
    et al., 1978a; Robl et al., 1978). When the feeding of PBBs was

    stopped, concentrations in milk fat declined rapidly for a short
    time (Fries & Marrow, 1975). When a new equilibrium was established,
    milk fat and body fat concentrations declined in a parallel manner
    (Fries, 1985b). An example of the biphasic decline is given in Fig.
    7. However, as Fries et al. (1978a) observed, the stage of lactation
    influenced the rate of elimination, and, in some cases, BB 153
    levels in milk increased shortly after calving.

         Data from Detering et al. (1975) indicated that BB 153 levels
    in cow's milk would decrease from 200-400 mg/kg in fat to 0.3 mg/kg
    in 120 weeks.

         Information on a time course of PBB levels in the body fat of
    cows is limited. According to Willett & Durst (1978), e.g., BB 153
    concentrations in the subcutaneous fat of cows had declined by 40%,
    20 days after exposure. Two measurements, one at parturition (ca.
    150 days later) and one after heavy lactation (ca. 200 days later)
    showed an increase in residues. During late lactation, significant
    declines occurred.

         Probably, a multicompartment system is necessary to describe
    the long-term behaviour of PBBs in lactating cows, with special
    trends when pregnancy, parturition, etc. occur (Willett & Durst,
    1978; Fries et al., 1978a; Fries, 1985b).

         The appearance and decline of BB 153 in faeces were reported
    for two cows given a single intraruminal dose of FireMaster(R)
    BP-6 (Willett & Irving, 1976) and for cows fed BP-6 daily for 60
    days (Willett & Durst, 1978). In the first case, BB 153 was detected
    12 h after administration, peaked between 20 and 36 h, and declined
    to about 2% of the peak concentration during the subsequent 48 h. By
    day 8, approximately 50% of the dose was detectable in the faeces
    (Willett & Irving, 1976). During daily exposure, BB 153
    concentrations in the faeces reached a steady state by day 10. After
    withdrawal of the PBBs, the levels of BB 153 declined within 10 days
    to approximately 1% of the concen tration present during exposure
    (Willett & Durst, 1978). Fries (1985b) inferred low rates of
    elimination in faeces, because faecal BB 153 concentrations in
    cattle that were no longer being exposed to PBBs were relatively low
    (Willett & Durst, 1978; Fries et al., 1978a).

         Another domestic species in which the kinetics have been
    examined is the chicken. Whole carcass analysis of male White
    leghorn chickens showed that, during the 2 weeks that
    FireMaster(R) FF-1 was fed at 0.1 or 1.0 mg/kg, the chickens
    retained 88 and 69%, respectively, of the FF-1 that was consumed
    (Polin & Leavitt, 1984). Withdrawal rates were determined in a
    similar study on egg- and meat-type chickens fed diets containing 1
    or 10 mg FF-1/kg. Body burdens of BB 153 in chickens, previously fed
    10 mg/kg, did not decrease significantly during a withdrawal period
    of 42 days (e.g., 3% loss by day 21 of withdrawal). In contrast,
    chickens, previously fed 1 mg/kg, eliminated up to 40% of the BB 153
    (Polin et al., 1985).

         Withdrawal of PBBs from the adipose tissue of laying hens fed
    FireMaster(R) FF-1 at different dietary levels (0.2, 1, 5, 25,
    125, or 625 mg/kg) has been followed by Polin & Ringer (1978a). BB
    153 levels remained unchanged over the 56 days of withdrawal. Lillie
    et al. (1975) calculated a 50% reduction after more than 16 weeks.
    Withdrawal from other tissues and from eggs was more rapid (Ringer &
    Polin, 1977; Polin & Ringer, 1978b).

         BB 153 levels in eggs laid by hens fed 20 or 64 mg
    FireMaster(R) BP-6/kg diet for 8-9 weeks reached a plateau by the
    third or fourth week of feeding. When feeding of BP-6 stopped,
    residues decreased in a two-phase rate pattern with a phase of rapid
    decline shortly after exposure had ceased and a late phase of slow
    decrease (Fries et al., 1976; Cecil & Bitman, 1978). In one study
    (Fries et al., 1976), the levels after 49 days were approximately
    10% of the values on day 0 of cessation; in the other study by Cecil
    & Bitman (1978), detectable amounts were still present 33 weeks
    after withdrawal of BP-6 from the diet.

         Excreta were analysed from hens fed 20 mg FireMaster(R)
    BP-6/kg for 63 days (Fries et al., 1976). After an initial rise and
    decline, the BB 153 levels remained fairly constant (at about
    2 mg/kg on a wet weight basis) during the feeding of PBBs. After
    withdrawal of PBBs, the residues dropped to a negligible level
    (< 0.1 mg/kg).

         Only some milk data during continued exposure are available for
    pigs. Milk of sows having received 10, 100, or 200 mg of
    FireMaster(R) BP-6/kg feed during the second half of gestation and
    during lactation was monitored until the 4th week. On a fat basis,
    concentrations of BB 153 were highest in the colostrum and decreased
    slowly during lactation (Werner & Sleight, 1981).

         Disappearance of BB 153 from the tissues of lactating
    guinea-pigs and of their pups was described by Ecobichon et al.
    (1983). The maternal animals had received a single oral dose of
    FireMaster(R) FF-1 (50 mg/kg body weight) within 6-12 h of
    parturition, and the residue levels of nursing young and the dams
    were measured up to 60 days after exposure (at intervals of 2, 4, 7,
    14, 28, 42, and 60 days: see Fig. 8). Following the initial 7 days
    during which there was obvious inter-tissue transportation and
    sequestration in body fat, a gradual, but similar, linear rate of
    decline was observed in the livers, kidneys, and lungs of both the
    young and their dams. A similar rate of reduction was observed in
    the body fat of both pups and dams.

         In a study on mice, BB 153 residue levels were measured 6 h
    after dietary intake of 100 mg/kg. FireMaster(R) BP-6 (for 14
    days) can be compared with those obtained 14 weeks after feeding. 
    There was a decline in all tissues including fat (see Table 48),
    however, to a different extent, resulting in changes in the relative
    BB 153-concentrations between tissues (Corbett et al., 1978a).

         BB 153 blood levels of rhesus monkeys, dosed with BB 153,
    markedly declined over time (day 5: 1.5 mg/kg, day 11: 0.2 mg/kg;
    day 25 < accurate measurement levels) (Rozman et al., 1982).

    6.5.1.2  Biological half-lives

         The biological half-lives of PBBs reported in the literature
    for various species have been compiled in Table 68. McDaniel &
    Lucier (1979) reported a half-life of BB 153 exceeding the lifetime
    of rats.

         In some cases the results obtained by different authors are
    similar, in other cases, large discrepancies exist. These deviations
    were, perhaps, caused by measuring the half-lifes under different
    circumstances of exposure and for different lengths of time (Fries,
    1985b). By means of simulation studies, Domino et al. (1982)
    demonstrated the effects of different amounts of body fat on the
    half-life of BB 153 in the rat (see Table 69).

         Tuey & Matthews (1980) have simulated the effects of a growing
    animal on the kinetics of BB 153 and found that, though
    concentrations of BB 153 in fat fell faster than in a stable animal,
    the "actual" half-life of the substance was prolonged, because of an
    increase in the relative fat proportions.

    6.5.1.3  Differences between individual congeners

         There are some reports on the differences in turnover and
    retention of individual PBB congeners. Mostly, they refer to changes
    in the relative abundances of certain FireMaster(R) components,
    namely: 2,2',4,5,5'-pentabromobiphenyl (BB 101),
    2,3',4,4',5-pentabromobiphenyl (BB 118), 2,2',3,4',5',6-hexa
    bromobiphenyl (BB 149), 2,2',4,4',5,5'-hexabromobiphenyl (BB 153),
    2,2',3,4,4',5'-hexabromobiphenyl (BB 138), 2,3',4,4',5,5'-
    hexabromobiphenyl (BB 167), 2,3,3',4,4',5-hexabromobiphenyl (BB
    156), 2,2',3,4,4',5,5'-heptabromobiphenyl (BB 180), and
    2,2',3,3',4,4'5-heptabromobiphenyl (BB 170). To describe such
    changes, the GC profile of the original FireMaster(R) mixture was
    compared with the GC profile obtained on analysis of tissues from
    animals treated with this mixture, by measuring either the area
    (e.g., Wolff & Aubrey, 1978; Domino et al., 1980b) or the height
    (e.g., McCormack et al., 1982a; Bernert & Groce, 1984; Groce &
    Kimbrough, 1984) of the GC peaks and by normalizing the values to BB
    153 as 100. A few other authors (Fries & Marrow, 1975; Fries et al.,
    1976) based their calculations on the assumption that each component
    (BB 153 and BB 180) was fed at the same rate in the diet. According
    to Fries (1985b), some differential behaviour may be due to
    analytical artefacts, introduced by differential recovery of the
    congeners or by adsorption of congeners on the glassware (Willett
    et al., 1978), but many changes appear real.

    Table 69. Effect of different amounts of body fat on the half-life of
    2,2',4,4',5,5'-hexabromobiphenyl in the rata

                                    Amount fat                Half-life
                                    (% normal fat)            (days)

         Emaciated                       25                     60.5
                                         50                     88.8
                                         75                    117
                                         90                    134

         Normal                          100                   145
                                         110                   156
                                         125                   173
                                         150                   200
                                         175                   228
                                         200                   256

         Obese                           250                   311

    a    From: Domino et al. (1982).
    
         The trends reported in the literature include the selective
    retention of 5 minor components of the FireMaster(R) mixture in
    the tissues of rats, pigs, cows, and chickens (Fries & Marrow, 1975;
    Fries et al., 1976, 1978a; Dannan et al., 1978b; Willett & Durst,
    1978; Wolff & Aubrey, 1978; Wolff & Selikoff, 1979; Domino et al.,
    1980b; McCormack et al., 1980, 1982a; Werner & Sleight, 1981; Groce
    & Kimbrough, 1984; Polin & Leavitt, 1984).  They can be summarized,
    as follows.

         With some exceptions, the concentrations of 2,2',4,5,5'-penta
    bromobiphenyl (BB 101) and 2,2',3,4,4',5,5'-heptabromobiphenyl (BB
    180) relative to BB 153 appeared to be lower in tissues from treated
    animals than in those fed FireMaster(R) mixture. The relative
    concentrations of 2,3',4,4',5-pentabromobiphenyl (BB 118) and
    2,3',4,4',5,5'-hexabromobiphenyl (BB 167) appeared to be higher or
    unchanged in many cases. 2,2',3,4',5',6-Hexabromo biphenyl (BB 149)
    was barely, or not, detected in the tissues of any animals.

         The results of a multigeneration study on rats also reflected
    the differential behaviour of certain PBB congeners (McCormack
    et al., 1981). Of the first eight peaks (penta- to
    heptabromobiphenyls) in the GC profile of FireMaster(R), all
    except peak 3 (BB 149) were detected in the livers of rats in the

    F1, F2, and F3 generations (experimental design: see Table
    54). For example, the concentration of
    2,3',4,4',5,5'-hexabromobiphenyl (BB 167) relative to BB 153 was
    higher in the livers of animals in the F1 generation than in the
    FireMaster(R) BP-6 standard, but decreased with each subsequent
    generation. Although F2-10 and F3-100 animals (10 and 100 mg/kg
    treatment, respectively; see Table 54) had similar hepatic
    concentrations of BB 153, the relative concentrations of other PBB
    congeners, including BB 167 appeared to be lower in the livers from
    F3-100 than F2-10 animals (McCormack et al., 1981).

         Domino et al. (1980b) found that 2,2',4,5,5'-pentabromobiphenyl
    (BB 101) penetrated the brain of rats more rapidly than
    2,3',4,4',5-pentabromobiphenyl (BB 118) or any of the higher
    relative molecular mass homologues. Fries et al. (1976) reported a
    faster clearance of 2,2',3,4,4',5,5'-heptabromobiphenyl (BB 180)
    (half-time = approximately 20 days) than of BB 153 (half-time =
    approximately 28 days) from eggs of hens after feeding stopped. 
    However, analyses of whole chicken carcasses resulted in unchanged
    ratios of BB 153/BB 180 on days 0, 21, and 42 of withdrawal (Polin &
    Leavitt, 1984). The authors judged that the dynamics for withdrawal
    of these two congeners from tissues of chickens were parallel. The
    withdrawal from milk of dairy cows was found to be more rapid for BB
    180 than for BB 153 (Fries & Marrow, 1975; Fries et al., 1978a; see
    also Fig. 7).

         In just one study (Millis et al., 1985b), equimolar doses of
    individual PBB congeners were administered to the test animals. 
    Immature male rats received a single oral dose (21.3 µmol/kg body
    weight) of 3,3',4,4',5,5'-hexabromobiphenyl or 3,3',4,4'-tetra
    bromobiphenyl and were analysed at various times up to 14 days after
    treatment. Adipose tissue and liver concentrations of
    3,3',4,4',5,5'-hexabromobiphenyl appeared unchanged over time
    whereas the tissue concentrations of 3,3',4,4'-tetrabromobiphenyl
    decreased in a biphasic manner.

    6.5.1.4  Octabromobiphenyl

         Some kinetic data are available for technical octabromo
    biphenyl. Bromine levels in the adipose tissue of rats dosed with
    octabromobiphenyl did not decrease during a period of 90 days
    (Norris et al., 1973) or 18 weeks (Aftosmis et al., 1972a; Waritz
    et al., 1977) after cessation of dosing, or, according to Lee et al.
    (1975a), levels even increased 18 weeks after exposure. A partial
    elimination of bromine was observed from the livers of these rats
    after recovery (Norris et al., 1973; Lee et al., 1975a; Waritz
    et al., 1977).

         The contents of total PBB (octabromobiphenyl plus an
    unidentified hexabromobiphenyl) in juvenile Atlantic salmon  (Salmo
     salar), fed 90 days with octabromobiphenyl (Dow
    Chemical)-contaminated food, also remained fairly constant after 28
    days of withdrawal (Zitko, 1977).

    6.5.2  Human studies

         Information on the time trends of BB 153 distribution or
    retention in humans is limited. As with animals, BB 153 seems to be
    highly persistent in humans. This conclusion has been drawn from
    monitoring BB 153 levels over time in both individual persons and
    the Michigan population.

         Most paired serial samples exist for serum (or plasma) from
    farmers, etc. (Humphrey & Hayner, 1975: sampled June/Autumn, 1974;
    Landrigan et al., 1979: sampled 1974/77; Wolff et al., 1979b:
    sampled 1976/77/78; Kreiss et al., 1982: sampled 1977/78/79;
    Sherman, 1991: sampled 1976/80/87) and chemical workers (Wolff
    et al., 1979b: sampled 1976/78; Bahn et al., 1980b and Bialik, 1982:
    sampled 1978/1981; Lambert et al., 1990) (in parentheses: references
    plus year of sampling). The values obtained indicated no, or little,
    decrease (see sections 5.2 and 5.3, and Table 38) with the exception
    of the results of Bahn et al. (1980b) and Bialik (1982) (see section
    5.3). Paired adipose analyses have been reported only by Meester &
    McCoy (1976) who found a consider able average decline in HxBB
    levels over six months (see also section 5.2). However, one of the
    16 persons tested had increasing or unchanged fat levels, while
    serum levels slowly dropped. The significance of these observations
    and the combined results of Bahn et al. (1980b) and Bialik (1982)
    are unclear. A most recent case report (Sherman, 1991) showed that
    "PBB" could be identified in the serum and fat of a cancer patient
    over an 11-year period (1976-87). Serial testing of 11 breast-milk
    samples from one lactating Michigan woman showed that HxBB
    concentrations varied between 0.1 and 0.2 mg/kg (expressed on a fat
    basis) during a three-month period, without any significant downward
    trend (Brilliant et al., 1978).

         Comparisons at the population level have been made for serum
    (Meester & McCoy, 1976), breast-milk (Miller et al., 1984), and
    adipose tissue (Miceli et al., 1985). Generally, the presence of
    PBBs in the tissues of Michigan people many years after the spill
    (1973) may be an indicator for its persistence (see Tables 38 and
    39). Meester & McCoy (1976) found that the average HxBB level in the
    serum of farmers during the first six months of 1976 was ten times
    lower than that during the last six months of 1975 (0.2 µg/litre
    versus 2.0 µg/litre). Miller et al. (1984) concluded from their
    analyses of breast-milk from 2986 lactating women during May 1976
    and December 1978 that HxBB levels were not declining. Approximately
    5 years after the Michigan PBB incident occurred, adipose tissue

    from live residents of a "high" exposure area (Muskegon County area)
    contained median HxBB levels of 500 µg/kg (Wolff et al., 1982).
    Approximately 10 years after exposure, postmortem adipose tissue
    contained median HxBB levels of 320 µg/kg (Miceli et al., 1985).

         On the basis of the two last values, Miceli et al. (1985)
    calculated a half-life of 7.8 years for HxBB (BB 153) in human
    adipose tissue. This prediction was close to the body burden
    half-time of 6.5 years estimated by Tuey & Matthews (1980) using
    pharmacokinetic data obtained from rats.

         A median serum half-life of BB 153 of 12 years (range: 4.6-94.7
    years) has been determined by comparing previous and more recent
    serum BB 153 levels of Michigan residents (Lambert et al., 1990).

         As Tuey & Matthews (1980) explained, the half-life may be
    longer in growing children or in persons gaining weight. However,
    calculating the effects of different amounts of body fat on the
    retention of BB 153, these authors also found that adipose tissue
    may act as a protective reservoir in mature humans, because the
    concentration of BB 153 in the blood (and possibly other more
    critical tissues) of obese persons should be significantly less than
    those of leaner individuals who received comparable exposures.

         There was some evidence for the differential retention of
    various PBB congeners in humans, when PBB congeners in serum samples
    from Michigan subjects were compared with FireMaster(R) BP-6. The
    main congeners assayed by using GC-MS analysis (Wolff & Aubrey,
    1978; Wolff et al., 1978) or Negative Chemical Ionisation
    Spectrometry (NCIMS) analysis (Roboz et al., 1982; Greaves et al.,
    1984) were as follows: 2,2',4,5,5'-pentabromo biphenyl (BB 101),
    2,3',4,4',5-pentabromobiphenyl (BB 118),
    2,2',3,4',5',6-hexabromobiphenyl (BB 149), 2,2',4,4',5,5'-hexa
    bromobiphenyl (BB 153), 2,2',3,4,4',5'-hexabromobiphenyl (BB 138),
    2,3',4,4',5,5'-hexabromobiphenyl (BB 167),
    2,2',3,4,4',5,5'-heptabromobiphenyl (BB 180). The most obvious
    changes refer to the two penta isomers and to the major
    heptabromobiphenyl. The 2,2',3,4,4',5,5'-heptabromobiphenyl was
    absent (Roboz et al., 1982) or greatly diminished in serum (Wolff &
    Aubrey, 1978; Wolff et al., 1979a; Greaves et al., 1984) in relation
    to the concentrations of BB 153 (taken as 100%). The relative
    amounts of 2,2',4,5,5'-pentabromobiphenyl (BB 101) were also greatly
    decreased (e.g., 80%: Greaves et al., 1984) in all samples. However,
    a marked decrease in 2,3',4,4',5-pentabromobiphenyl (BB 118)
    concentrations was observed only in the serum of farmers, taken
    several years after exposure (e.g., 60%: Greaves et al., 1984), but
    not in the serum of chemical workers (Wolff & Aubrey, 1978; Wolff
    et al., 1979a; Roboz et al., 1982).

    6.6  Reaction with body components

    6.6.1  Animal studies

         When a 14C-PBB mixture (FireMaster(R)) was incubated with
    rat liver microsomes, no binding to exogenous DNA was detected, and
    only a small amount of radioactivity was covalently bound to
    microsomal protein (Dannan et al., 1978b). The formation of low and
    high relative molecular mass adducts with PBB metabolites has been
    quoted elsewhere (section 6.3).

    6.6.2  Human studies

         Studies on human serum revealed that lipoproteins are the
    predominant protein carriers of PBBs in serum (Greaves et al.,
    1983). 80% of the PBBs were bound to apolipoproteins B and A in a 4
    : 1 ratio (Greaves et al., 1984; Roboz et al, 1985a).  According to
    Roboz et al. (1985b), the ratio was 3 : 1. No preferential binding
    of PBB congeners (2,2',4,4',5,5'-hexa-; 2,2',4,5,5'-penta-;
    2,2',4,5',6-pentabromobiphenyl) was found (Roboz et al., 1985a,b).

    7.  EFFECTS ON ORGANISMS IN THE ENVIRONMENT

         Only few data are available on effects of PBBs on organisms in
    the environment. They refer to microorganisms, water fleas,
    waterbirds, (rodents), and farm animals.

    7.1  Microorganisms

         The toxicity of technical decabromobiphenyl (Adine 0102)
    against bacteria  (Pseudomonas putida M.) was determined by the
    cell multiplication inhibition test (according to the ISO TC 147/SC
    5/WG 1/N 111 standard, and using 0.1-1% DMSO (dimethylsulf oxide) as
    a solvent. An EC10 of 53 mg/litre was found (Atochem, 1990).

    7.2  Aquatic organisms

         In a short-term test (according to the ISO standard 6341) the
    immobilization of  Daphnia magna (Crustacea) by technical
    decabromobiphenyl (Adine 0102) has been investigated. The following
    results were obtained after dissolution of the test material in DMSO
    because of its weak solubility in water:

    -    EC50 (24 h): > 66 mg/litre;

    -    The maximum concentration resulting in 0% immobilization
         24 h): < 2 mg/litre (Atochem, 1990).

    7.3  Terrestrial organisms

    7.3.1  Wildlife

         In 1977 and 1978, Haseltine et al. (1981) and Heinz et al.
    (1983) studied red-breasted mergansers  (Mergus serrator) nesting
    on islands in the northwestern Lake Michigan in order to determine
    whether environmental contaminants (organochlorines and metals) were
    producing effects on reproduction. Seventeen contaminants, including
    PBBs, were measured in randomly chosen eggs from 206 nests under
    study. Using a variety of statistical approaches, Heinz et al.
    (1983) looked for effects of individual contaminants and
    combinations of contaminants on reproductive measurements, such as
    nest desertion, failure of eggs to hatch, death of newly hatched
    ducklings, percentage hatching success, number of ducklings leaving
    the nest, and egg-shell thickness. PBBs and other chemicals were
    sometimes negatively correlated with shell thickness or thickness
    index, but not consistently so, as found for DDE. However, no
    contaminant or combination of contaminants measured seemed to have a
    pronounced effect on the aspects of reproduction mentioned above.
    The hatching success of the mergansers averaged 81.7% in 1977.
    According to Heinz et al. (1983), the hatching success averaged
    85.6% in 1978 (Haseltine et al., 1981).

         Although it is not valid to compare reproductive success among
    different species, it should be noted that dabbling ducks, whose
    eggs contained only a fraction of the contaminant burdens (e.g., no
    PBBs: Haseltine et al., 1981; see also Table 32), of the redbreasted
    mergansers had better hatching success (Heinz et al., 1983).

         An interesting observation on rodents living on a
    PBB-contaminated farm has been reported by Jackson & Halbert (1974).
    They observed that rats and mice were apparently eradicated when
    they came into contact with PBB-contaminated cattle feed pellets.

    7.3.2  Farm animals

         Farm animals in Michigan that ingested feed inadvertently
    containing PBB (FireMaster(R) FF-1) in place of magnesium oxide
    fell sick. First symptoms were observed in the cattle of several
    dairy herds and revealed this so-called "Michigan PBB incident".

    7.3.2.1  Cattle

         The exact doses of PBBs to which Michigan cattle were exposed
    are not known. Fries (1985b) estimated the maximum PBB doses of
    individual cattle based on milk or tissue fat concentration at the
    time of detection, which ranged from 9 to 24 months after the cattle
    had consumed contaminated feed. For example, if PBB were detected 9
    months after exposure, PBB concentrations of 0.1 mg/litre of milk
    and 0.25 mg/kg tissue would indicate that the cow had received a
    total dose of 1 mg/kg of body weight. Increased PBB concentrations
    in milk and tissue would indicate a proportionally higher dose. If
    detection were delayed for as long as 24 months, the above example
    for milk and tissue concen trations would indicate an exposure of
    6 mg/kg of body weight.

    a) High-level contamination in cattle

         Adverse effects of PBBs in lactating cows were first reported
    by Jackson & Halbert (1974).

         In reconstructing the accident, it was assumed that the cows on
    this farm (Halbert farm) consumed PBB-contaminated feed (PBB content
    from 3 to 4 g/kg; Isleib & Whitehead, 1975) over 16 days, and
    ingested about 20 g PBB/day, initially. The total average exposure
    of these cows was estimated to be 250 mg/kg body weight (Fries,
    1985b). The contaminated feed was also fed to a group of 6- to
    18-month-old calves. The dose might have been about 58 mg/kg body
    weight per day when feeding started, and the total doses may have
    reached 700 mg/kg body weight over 6 weeks (Fries, 1985b), if feed
    was consumed at the same rates as in experimental studies (Durst
    et al., 1977).

         The clinical signs of toxicity, described by Jackson & Halbert
    (1974), were anorexia (50% reduction in feed consumption) and a 40%
    decrease in milk production a few weeks after ingestion of the
    contaminated feed. Although the supplemented feed was discontinued
    within 16 days, milk production was not restored, and the cows
    continued to lose weight. An unspecified number of cows had
    increased frequency of urination and lacrimation and developed
    haematomas, abscesses, abnormal hoof growth, lameness, alopecia,
    hyperkeratosis, and cachexia, and several died within 6 months.
    Altogether, the death rate of Halbert cows was about 24/400.

         The death rate of the 6- to 18-month-old calves (heifers and
    bulls) to which the suspected feed was offered, was much higher. 
    About 50% of the calves died within 6 weeks. After 5 months, only
    two of twelve animals were alive, and they had developed
    hyperkeratosis over their entire bodies. There were also a variety
    of reproductive problems including embryo resorption, abortions,
    stillbirths, deaths shortly after births, delayed deliveries, and
    enlarged calves. The clinical signs were variable, and, with the
    exception of decreased milk production and weight loss, no
    particular symptom was predominant in the affected animals (Jackson
    & Halbert, 1974; Robertson & Chynoweth, 1975).

         Necropsy findings have been reported for some of the 24 mature
    cows that died during the 6 months following exposure (Jackson &
    Halbert, 1974). Gross lesions observed included somewhat enlarged
    livers, haematomas and abscesses in the thoracic and abdominal
    cavities, abomasal ulcers, necrotic metritis, suppurative
    bronchopneumonia, and pericarditis. As in all observations without
    controls, it was difficult to draw definitive conclusions as to
    which lesions were caused by PBBs and which were unrelated to PBBs
    (Fries, 1985b). Two of the twelve calves in a calf feeding trial had
    massive liver abscesses.

         Histopathological studies on ten of the cows revealed various
    liver and kidney changes. Liver lesions were reported in seven
    animals and included fatty changes and amyloidosis. Renal tubular
    nephrosis and interstitial nephritis were reported in four of the
    cows (Jackson & Halbert, 1974; Getty et al., 1977).

          Several clinical signs and pathological changes, reported by
    Jackson & Halbert (1974), were also described in cows in controlled
    feeding studies (Durst et al., 1977; Durst et al., 1978a,b; Moorhead
    et al., 1977, 1978; Robl et al., 1978; Willett et al., 1980; see
    also section 8). These included anorexia, dehydration, excessive
    lacrimation, emaciation, hyperkeratosis, reproductive difficulties
    (fetal death, enlarged calves, and difficulty in calving,

    hypospermatogenesis), and renal damage. Conditions described in the
    accidentally exposed cows, but not confirmed in the controlled
    studies, included haematomas, abscesses, abnormal hoof growth,
    extensive hair loss, liver abscesses, necrosis, and metritis (Fries,
    1983, 1985b).

         The Halbert herd was one of about 12 "highly" contaminated
    herds that had PBB concentrations of more than 30 mg/kg in milk fat,
    when detected. According to Fries (1985b), it is likely that all of
    these herds had some clinical signs of toxicosis. According to the
    same author, there was no comprehensive clinical examination of any
    herd that had milk concentrations in the range of 1-30 mg/litre, but
    it appears that most animals in these herds did not have clinical
    signs when the farms were depopulated. A preliminary report (cited
    by Getty et al., 1977) indicated that cows that had been exposed to
    PBBs 19 months earlier had levels of up to 80 mg/kg in body fat, but
    were apparently normal clinically and were producing normal
    quantities of milk. Gross or microscopic lesions that could be
    attributed to PBB exposure were not found.

    b) Low-level contamination in cattle

         Residue concentrations in the body fat or milk fat of cows,
    classed as having low-level contamination, rarely exceeded 1 mg/kg,
    and, for the most part, not even 0.3 mg/kg. There were several
    studies on Michigan cattle with such low exposures.

         Results of an evaluation of 72 low-level contaminated herds
    have been reported by Kay (1977) and Getty et al. (1977). 
    Production drop and sterility were two consistent signs and were
    regarded as interrelated. The retardation of growth of young stock
    was very significant, as it was in the Jackson & Halbert study
    (1974). Some other findings were not consistent. A mail
    questionnaire survey (Getty et al., 1977) showed similar
    observations.

         Cows (n = 46) from six herds across Michigan, whose body fat
    contained a mean concentration of 0.31 mg/kg and a maximum
    concentration of 1.8 mg/kg, were compared with a group of cows from
    Wisconsin (n = 40) that had not been exposed to PBB. The two groups
    were reared together and subjected to the same feeding and
    management system. There were no significant differences in the
    animals' milk production, body weight, weight gain, breeding and
    reproductive performance, incidence of commonly experienced health
    problems, calving rate, and the health of their calves. Also no
    pattern of gross or histopathological lesions was seen between test
    animals and control animals upon necropsy (Wastell et al., 1978).

         An epidemiological survey, which compared the health status of
    16 herds with low PBB exposure (traces to 1 mg/kg body fat or milk
    fat) with the status of 15 herds with no PBB exposure, also
    indicated that productivity and general health conditions between
    the two groups of herds were similar. Of the biochemical parameters
    tested (9 urinalyses, 13 serum chemistry parameters), three resulted
    in significantly different values. Serum concen trations of calcium,
    glucose, and cholesterol in contaminated herds were significantly
    lower than those of the control herds. But the relationship to PBB
    exposure was unknown (Mercer et al., 1976).

         Instead of specific clinical conditions, Fries (1983) evaluated
    the overall performance of exposed herds (residues in tissue or milk
    fat generally < 0.3 mg/kg) and of "relatively unexposed" herds
    (residues < 0.02 mg/kg) of comparable size, breed, and location by
    analysing Dairy Herd Improvement Association records. He found that
    no productive or reproductive character istics of the herds were
    affected by PBB exposure.

         It should be noted that the classification of herds as having a
    high or a low level of contamination refers to PBB levels at the
    time of detection. Thus, it is sometimes impossible to know whether
    there was a history of a short-term, high exposure or a long-term,
    low exposure, which may produce different syndromes.  For example,
    Fries (1985b) pointed out that feed that was contaminated by
    cross-contamination in the feed mills was being fed at the time of
    detection, in some cases. Under this circum stance, PBB intakes as
    low as 0.1 mg/kg of body weight per day could produce milk fat
    residues as high as 20 mg/kg (Fries & Marrow, 1975; Fries 1985b).

    7.3.2.2  Other farm animals

         Although it was cattle feed that was originally involved in the
    accidental substitution, all other feeds became involved by cross
    contamination, e.g., in the mixing machinery of feed companies that
    had been exposed to PBB (Dunckel, 1975). It is likely that other
    animals were not exposed to the same high levels as cattle.

    (i) Poultry

         There are no reports of clinical signs or problems associated
    with the accidental contamination of poultry feed. However, some
    controlled feeding studies have been published (see section 8).

    (ii) Pig

         Adverse health effects in pigs, identified as contaminated,
    were rarely reported. Only one review (Reggiani & Bruppacher, 1985)
    mentioned that abortions occurred in pigs. Two controlled feeding
    studies (Ku et al., 1978; Werner & Sleight, 1981) have been
    conducted (see section 8).

    (iii) Horse, rabbit, goat, sheep

         Other species of farm animals, including at least 2 horses, 32
    rabbits, 2 goats, and 19 flocks of sheep, were identified as
    contaminated and buried at Kalkaska, but details of ill effects were
    not recorded (Dunckel, 1975; Getty et al., 1977).

         One experimental feeding study on sheep (Gutenmann & Lisk,
    1975) is available (see section 8).

    7.4  Population and ecosystem effects

         No information available.

    7.5  Effects on the abiotic environment

         No information available.

    8.  EFFECTS ON EXPERIMENTAL ANIMALS AND  IN VITRO TEST SYSTEMS

         Differences in toxic responses between acute, high-level
    exposures and long-term, low-level exposures to halogenated aromatic
    compounds are mainly quantitative (McConnell & Moore, 1979).
    Moreover, the delayed onset of toxic signs and the persistence of
    PBBs in the body, which may cause long-term exposure of the target
    organs from a single dose, "tend to blur the usual distinctions that
    are made between acute and chronic exposure" (Fries, 1985b). For
    these reasons, symptoms after single and short-term exposures are
    reviewed together in section 8.2.  Another feature of the toxicity
    of PBBs and related classes of compounds is the latent period
    between the time of exposure and the time of death, which ranged
    from several days to weeks (Di Carlo et al., 1978; Safe, 1984;
    Hutzinger et al., 1985a; McConnell, 1985). Thus, the classical
    LD50 values and other mortality data found are summarized in one
    section (8.1).

    8.1  Lethality

         "Acute" toxicity data (LD50 and LC50 values) of commercial
    PBB mixtures have been compiled in Table 70. The LD50 values of
    all mixtures show a relatively low order of acute toxicity (LD50
    > 1 g/kg body weight) in rats, rabbits and quails, regardless of
    the route of administration, and range from > 1 to 21.5 g/kg body
    weight. Regarding the LC50 values for minks, this species may be
    highly sensitive to PBBs, but a direct comparison is complicated by
    differences in the experimental design.

         As with TCDD and PCBs (McConnell, 1984; Safe, 1984), the
    apparent toxicity of PBBs is higher with multiple-dose rather than
    single-dose administration. For example, the single oral LD50 of
    FireMaster(R) in rats was quoted to be 21.5 g/kg body weight, but,
    if given in small repeated doses, the total lethal dose was
    approximately 1-3 g/kg body weight (see Table 70).

         Deaths after exposure to PBBs are delayed (Di Carlo et al.,
    1978; Tables 71 and 72). Thus, Gupta & Moore (1979) have recommended
    that the LD50 of halogenated aromatic hydrocarbons or chemicals
    that may have a long-term build-up with delayed toxicity should be
    determined more accurately after multiple dosing and an extended
    period of observation.

         Generally, the susceptibility to the toxic effects of aryl
    hydrocarbons is dependent on the sex, age, species, and strain of
    the experimental animals (e.g., Safe, 1984; Hutzinger et al.,
    1985b).  In the case of PBBs, female rats dosed with FireMaster(R)
    FF-1 showed a lower LD50 than male rats (Gupta & Moore, 1979;
    Table 70).

    
    Table 70.  Toxicity of PBB mixtures

    PBB                 Species          Sex        Route       Observation    Parametera         Dose/         Details         References
                                                    (Strain)      period                      concentrationb

    FireMaster(R)       rat                         oral                       LD50           21.5              single dose     Di Carlo
                                                                                                                                et al.
                                                                                                                                (1978)

    FireMaster(R) FF1   rat (Fischer-    female     oral        90 days        LD50           1.43              22 doses        Gupta &
    (Lot No. 1312 FT)   344/N)                                                                                  (over 30        Moore
    (in corn oil)                        male       oral        90 days        LD50           3.28              days) 22        (1979)
                                                                                                                doses (over
                                                                                                                30 days)

    FireMaster(R) BP-6  rabbit                      dermal                     LD50           5                                 Aftosmis
                                                                                                                                et al. (1972b)

    FireMaster(R)       rabbit           male       dermal      14 days        ALD            5                 24 h of         Waritz et al.
    (Lot 635-71)        (New Zealand,                                                                           exposure        (1977)
    (in corn oil)       albino)

    FireMaster(R) FF1   mink             male,      in feed     313 days       LC50           3.95                              Ringer et al.
                        (Mustela vison)  female                                                                                 (1981)

    FireMaster(R)       Bobwhite quail              in feed     8 days         LC50           428               5 days of       Cottrell
                        (Colinus                                                                                treated diet    et al. (1984)
                        virginianus)

    Table 70 (contd).

    PBB                 Species          Sex        Route       Observation    Parametera         Dose/         Details         References
                                                    (Strain)      period                      concentrationb

    FireMaster(R)       Japanese quail              oral        not            LD50           > 1                               Strik
    (1973a)
                                                                specified

    Octabromobiphenyl   rat              male       oral                       LD50           2                 single dose     Aftosmis
                                                                                                                                et al. (1972a)

    Octabromobiphenyl   rat              male       oral        7 days         ALD            > 17              single or       Waritz et al.
    (Dow Lot 102-7-72)  (Sprague-Dawley)                                                                        repeated dose   (1977)
    (in acetone: corn
    oil = 15:85)

    Octabromobiphenyl   rabbit                      dermal                     LD50           > 10                              Aftosmis
                                                                                                                                et al. (1972b)

    Octabromobiphenyl   rabbit (New      male       dermal      14 days        ALD            > 10              24 h of         Waritz et al.
    (Dow Lot 102-7-72)  Zealand albino)                                                                         exposure        (1977)

    Octabromobiphenyl   Japanese quail              oral                       LD50           > 12.5            single dose     Aftosmis
                                                                                                                                et al. (1972a)

    Octabromobiphenyl   Bobwhite quail   male,      oral        14 days        ALD            > 12.5            single dose     Waritz et al.
    (Dow Lot 102-7-72)                   female                                                                                 (1977)
    (in corn oil)

    Nonabromobiphenyl   mouse (B6C3F1)   male,      oral        14 days        LD50           > 15              single dose     Momma (1986)
    (Bromkal 80-9D)                      female

    Table 70 (contd).

    PBB                 Species          Sex        Route       Observation    Parametera         Dose/         Details         References
                                                    (Strain)      period                      concentrationb
                                                                                                                                              
    Decabromobiphenyl   rat                         oral                       LD50           > 20              single dose     c

    Decabromobiphenyl   rat              male,      oral        14 days        LD50           > 5               single dose     Millischer
    (in corn oil)       (Sprague-Dawley  female                                                                                 et al.
                        CFY)             dermal                 14 days        LD50           > 5               single dose     (1979)

    Decabromobiphenyl   rat              oral                                  LD50           > 20              single dose     c

    Decabromobiphenyl   rabbit           dermal                                LD50           > 8                               c

    a    ALD = Approximate lethal dose.
    b    LD50 or ALD in g/kg body weight; LC50 in mg/kg diet (ppm).
    c    Consumer Product Testing Co. (1977) quoted by Di Carlo et al. (1978).

    Table 71.  Mortality associated with PBB administration: Commercial mixtures (dosing studies)

    PBBa            Species          Sex       Route          Doseb     Observation    Details      Mortality (in     Time to  References
                                     (No.)                              period                      percentage or     death
                                                                                                    No. dead/No.      (days)
                                                                                                    treated)

    FM FF1          rat              male      oral           0.03-30   60 days        22 doses     no mortality               Luster et al.
    (No. 1312 FT)                                                                      over 30                                 (1978)
    (in corn oil)

                    rat              female    oral           0.1-10    6 months       122 doses    no mortality               Luster et al.
                    (Fisher)                                                           over 6                                  (1980)
                                                                                       months

                    rat              female    oral           100       90 days        22 doses     100%              41-53    Gupta & Moore
                    (Fisher                                                            over 30                                 (1979)
                    344/N)                                                             days
                                     male      oral           100       90 days        22 doses     38%               50-73    Gupta & Moore
                                                                        over 30 days                                           (1979)

                                     female,   oral           300       90 days        9-21 doses   100%              14-29    Gupta & Moore
                                     male                                                                                      (1979)

                                     female,   oral           1000      90 days        6-10 doses   100%              9-14     Gupta & Moore
                                     male                                                                                      (1979)

    FM BP-6         rat                        inhalation     71 mg     not            1 h of       no mortality               Di Carlo et al.
                                                              per       specified      exposure                                (1978)
                                                              litre

    Table 71 (contd).

    PBBa            Species          Sex       Route          Doseb     Observation    Details      Mortality (in     Time to  References
                                     (No.)                              period                      percentage or     death
                                                                                                    No. dead/No.      (days)
                                                                                                    treated)

    FM FF-1         mouse            female    oral           0.03-30   60 days        22 doses     no mortality               Luster et al.
    (Lot No.                                                                           over 30                                 (1978)
    1312 FT in                                                                         days
    corn oil)       mouse            female    oral           0.1-10    6 months       122 doses    no mortality               Luster et al.
                                                                        over 6 months                                          (1980)

    FM              guinea-pig                 oral           50        60 days        single dose  no mortality               Ecobichon
                    (Hartley),                                                                      mentioned                  et al. (1983)
                    albino

    FM BP-6         cattle                     oral           25        60 days        daily doses  100% (animals     33-60    Irving et al.
    (finely                                                   g/dayc                                became moribund            (1976);Durst 
    ground)                                                                                         and were                   et al. (1977);
                                                                                                    necropsied)                Moorhead et al.
                                                                                                                               (1977, 1978)

    FM BP-6         cattle           female    oral           250       180 days       daily doses  no mortality               Durst et al.
    (finely                                                   mg/day                                                           (1978b)
    ground)

                    cattle           female    oral           0.3d      340 days       daily        no mortality               Robl et al.
                                                                                       doses over                              (1978)
                                                                                       158-228
                                                                                       days

    Table 71 (contd).

    PBBa           Species            Sex      Route             Doseb  Observation    Details       Mortality (in     Time to  References
                                      (No.)                             period                       percentage or     death
                                                                                                     No. dead/No.      (days)
                                                                                                     treated)

    FM BP-6        rainbow trout               intraperitoneal   150    15 days        single dose   no mortality               Elcombe & Lech
    (in corn oil)  (Oncorhynchus                                                       mentioned                                (1978)
                   mykiss)

    FM BP-6        brook trout                 oral              66.3   18 days        3 doses over  no mortality               Law & Addison
    (in dogfish    (Salvelinus                                                         5 days        mentioned                  (1981)
    oil)           fontinalis)

    FM FF-1        sheepshead                  intraperitoneal   15     56 days        single dose   no mortality               James & Little
                   (Archosargus                                                                                                 (1981)
                   probatocephalus)                              50     4-5 days       single dose   2/5 (remaining             James & Little
                                                                                                     3 moribund)

    OcBB           rat                female   oral              126-   14 days        single dose   no mortality               Norris et al.
    (in corn oil)  Sprague-                                      2000                                                           (1973)
                   Dawley)

    OcBB           rat                male     oral              1000   28 days        single dose   no mortality               Lee et al.
                   Sprague-                                                                                                     (1975b)
                   Dawley)

    OcBB           rat                male     inhalation        0.96   7 days         4 h of        no mortality               Waritz et al.
    (Dow Lot       (Sprague-                                     mg/                   exposure                                 (1977)
    102-7-72)      Dawley)                                       litre
                                                                 air

    Table 71 (contd).

    PBBa           Species            Sex      Route          Doseb     Observation    Details       Mortality (in     Time to  References
                                      (No.)                             period                       percentage or     death
                                                                                                     No. dead/No.      (days)
                                                                                                     treated)

    DeBB           rat                         inhalation     200       not            1 h of        no mortality               Di Carlo
                                                              mg/       specified      exposure                                 et (1978)
                                                              litre
                                                              air

    DeBB           rat                male,    inhalation     0.05-5    4 weeks        6 h/day;      no mortality               Millischer
                   (Sprague-                                  mg/                      5 days/week                              et al. (1979)
                   Dawley)                                    litre
                                                              air

    a    Commercial mixtures: FM = FireMaster(R); OcBB = octabromobiphenyl; DeBB = decabromobiphenyl.
    b    In mg/kg body weight per day, unless otherwise specified.
    c    Initially equivalent to 67.2 mg/kg body weight per day.
    d    Equivalent to 10 mg/kg feed.

    Table 72.  Mortality associated with PBB administration: Commercial mixtures (feeding studies)

    PBBa               Species          Sex         Dietary        Period of      Mortality (in          Time to       References
                                                    concentration  treatment      percentage or No.      death
                                                    (mg/kg feed)   observation    dead/No. treated)

    FM BP-6            rat (Sprague-    female      4.7-300        2/2 weeks      no mortality                         Dent et al. (1976a)
                       Dawley)                                     mentioned

    FM                 rat (Sprague-    male        1-500          30/30 days     no mortality                         Sleight & Sanger (1976)
                       Dawley)

    FM BP-6            mouse (BALB/c)   female      1000           9/9 days       70%                                  Fraker & Aust (1978);
                                                                                                                       Fraker (1980)

    FM BP-6            guinea-pig                   50             45/45          7/8                                  Vos & van Genderen
    (Lot No. 182 RP)                                                                                                   (1974)

    FM                 guinea-pig                   100            30/30 days     4/6                                  Sleight & Sanger (1976)

                       guinea-pig                   500            15/15 days     100%

    FM FF-1            mink             male,       1              313/313 days   no mortality                         Aulerich & Ringer (1979)
                       (Mustela vison)  female      2.5                           10%                    136 days
                                                                                  90%                    63-294 days   Ringer et al. (1981)
                                                                                  100%                   25-93 days

    FM                 pig                          20, 200        16/16 weeks    no mortality                         Ku et al. (1978)
                                                                                  mentioned

    FM FF-1            rhesus monkey    male        25             25/25 weeks    1/1                    25 weeks      Allen et al. (1978)
                       (adult)                      (total: 1 g)

                       (juvenile)       female      300            137/137 days   1/1                    137 days      Allen et al. (1978)
                                                    (total:
                                                    6.4 g)

    Table 72 (contd).

    PBBa               Species          Sex         Dietary        Period of      Mortality (in          Time to       References
                                                    concentration  treatment      percentage or No.      death
                                                    (mg/kg feed)   observation    dead/No. treated)

    FM BP-6            chicks (Hubbard  male        400            15/15 days     37%                                  Vos & van Genderen
    (Lot No. 182 RP)   Leghorn)                                                                                        (1974)

    FM BP-6            chicken (White               20-200         8/16 weeks     no mortality                         Cecil & Bitman (1978)
                       Leghorn)
                                                                   4/4 weeks      60% (control 10%)                    Cecil & Bitman (1978)

    FM FF-1            chicken (White               3125           4/4 weeks      100%                                 Polin & Ringer (1978a)
                       Leghorn)

    FM                 Japanese quail               10-100                        no mortality                         Babish et al. (1975a)
                                                    500-1000       "few" days     100%                                 Babish et al. (1975a)

    FM                 Bobwhite quail               100            5/8 days       no mortality                         Cottrell et al. (1984)
                                                    200            5/8 days       1/10                   8 days        Cottrell et al. (1984)
                                                    600            5/8 days       100% (10/10)           5.3 days      Cottrell et al. (1984)
                                                                                                         (mean)

    FM BP-6            Atlantic salmon              100            42/70 days     no mortality                         Zitko (1977)
                       (Salmo salar)                               (in excess of
                                                                   that of
                                                                   control fish)

    OcBB               rat (Sprague-    male        100-10 000     30/30 days     no mortality                         Norris et al. (1973)
                       Dawley)                                                    mentioned

    Table 72 (contd).

    PBBa               Species          Sex         Dietary        Period of      Mortality (in          Time to       References
                                                    concentration  treatment      percentage or No.      death
                                                    (mg/kg feed)   observation    dead/No. treated)

    OcBB               rat (Sprague-    male        1-1000         4/22 weeks     no mortality                         Lee et al. (1975a)
                       Dawley)

    OcBB (Dow          Atlantic salmon              100            74/96 days     no mortality (in                     Zitko (1977)
    Chemical)          (Salmo salar)                                              excess of that of
                                                                                  control fish)

    DeBB               rat (Sprague-    female,     1-2000         90/90 days     no mortality                         Millischer et al.
                       Dawley)          male                                      mentioned                            (1979)

    a    Commercial mixtures: FM = FireMaster(R); OcBB = octabromobiphenyl; DeBB = decabromobiphenyl.

         Although the studies, in most cases, are not directly
    comparable, species differences in the response to PBBs are
    reflected, in part, by the mortality data collated in Tables 71 and
    72. For example, minks appear to be more sensitive to the
    FireMaster(R) mixture than the other species of animals tested. 
    Compared to rats, guinea-pigs were far more susceptible to
    FireMaster(R) (Table 72).

         The few studies performed with commercial octa- and
    decabromobiphenyl mixtures did not result in any mortality in rats
    and fish (Tables 71 and 72). Of individual PBB congeners, only three
    hexa isomers have been tested. Apparently, 3,3',4,4',5,5'-
    hexabromobiphenyl is more toxic for rats than
    2,2',4,4',5,5'-hexabromobiphenyl (Table 73).

         With few exceptions, the cause of death by halogenated aryl
    hydrocarbons cannot usually be ascribed to pathology in a given
    organ or system as with most toxicants (McConnell & Moore, 1979;
    McConnell, 1984). At lethal doses, the affected animals develop, as
    a first indication of toxicity, a "wasting syndrome", i.e., a
    progressive loss of body weight, which may not be related simply to
    decreased food consumption. It is followed by weakness,
    debilitation, and finally death (Hutzinger et al., 1985a; McConnell,
    1985). Some authors (Allen et al., 1978) use the term "metabolic
    death".

         The extended course of the disease can be complicated by other
    diseases, usually of an infectious etiology (McConnell, 1984). For
    instance, parasitism, diarrhoea, and pulmonary infections have been
    observed in PBB-contaminated cattle (Jackson & Halbert, 1974;
    Willett & Irving, 1976; Moorhead et al., 1978). Many of the pigs
    that died during lactation after perinatal exposure to PBB had acute
    suppurative pneumonia (Werner & Sleight, 1981). Severely intoxicated
    rhesus monkeys may have succumbed finally to gastrointestinal and
    respiratory infections (Allen et al., 1978).  Male rats that were
    given 100 mg FireMaster(R) FF-1/kg body weight per day and died
    after 90 days had liver lesions (Gupta & Moore, 1979). Such
    overlying disease problems often result in difficulties in
    establishing a definitive etiological diagnosis in environmental
    exposures (McConnell, 1984).

    
    Table 73.  Mortality associated with PBB administration: Individual PBB congeners

    PBB                   Species                Sex      Exposure                   Dose           Mortality (in percentage   References
                                                                                     concentration  or No. dead/No. treated)

    2,2',4,4',5,5'-       rat (Sprague-Dawley)   male     in diet for 30 days           100a        no mortality               Akoso et al.
    hexabromobiphenyl                                                                                                          (1982a)

                          mouse (B6C3F1)         female   in diet for 10 days           750a        2/8                        Welsch &
                          (pregnant)                                                                                           Morgan (1985)

                          sheepshead                      intraperitoneal; single       20b         no mortality               James & Little
                          (Archosargus                    or multiple doses;                                                   (1981)
                          probatocephalus                 observation: 17-40 days

    3,3',4,4',5,5'-       rat (Sprague-Dawley)   male     in diet for 20 days           100a        1/2 (the remaining         Render et al.
    hexabromobiphenyl                                                                               rat was moribund)          (1982)

    2,3',4,4',5,5'        rat (Sprague-Dawley)   male     in diet for 30 days           100a        no mortality               Akoso et al.
    hexabromobiphenyl                                                                                                          (1982a)

    Mixture of di-,       Atlantic salmon                 in diet for 40 days plus      7.75a       (100% mortality)           Zitko &
    tri-, and             (Salmo salar)                   additional stress at day                                             Hutzinger (1976)
    tetrabromobiphenyls                                   4; observation: 42 days

    a    In mg/kg feed.
    b    In mg/kg body weight per day.

    8.2  Single and short-term exposures: general signs of toxicity

    8.2.1  PBB mixtures

    8.2.1.1  Overt clinical signs, food intake, and body weight changes

         In many acute and short-term studies, signs of PBB toxicity
    include reduction in feed consumption and weight loss or a decreased
    weight gain (see Tables 74 and 75). Most of the reports refer to the
    FireMaster(R) mixture, which was tested in rats, mice,
    guinea-pigs, pigs, cattle and avian species. From these studies with
    various protocols, the minimum effective doses of FireMaster(R)
    (FM) in the diet or by gavage ranged between 0.3 and 500 mg FM/kg
    feed or between 4 and 100 mg FM/kg body weight per day,
    respectively. Only a few studies have been performed with technical
    octabromobiphenyl and technical decabromobiphenyl; no effects were
    observed on feed consumption or body weight of rats (Tables 74 and
    75).

         Weight loss is not necessarily accompanied by decreased food
    intake (e.g., Allen et al., 1978; Lambrecht et al., 1978; Gupta &
    Moore, 1979) suggesting that PBBs may cause poor feed utiliz ation.
    On the other hand, increased efficiency of feed utilization has been
    reported in growing pigs (Ku et al., 1978) and weight loss in hens
    was accounted for completely by reductions in feed consumption in
    paired feeding studies (Cecil & Bitman, 1978; Ringer, 1978). If the
    concentrations of PBBs are high enough, a total refusal of feed will
    occur (Babish et al., 1975a; Gutenmann & Lisk, 1975; Ringer & Polin,
    1977; Cecil & Bitman, 1978; Polin & Ringer, 1978a; Aulerich &
    Ringer, 1979). At death, the loss in body weight can be as great as
    30-40% (Allen et al., 1978; Aulerich & Ringer, 1979; Durst et al.,
    1978b).

         At sublethal doses, decreased food intake and weight loss may
    be the only overt signs observed in many species. However, calves
    (fed 100 mg FireMaster(R) FF-1/kg body weight per day) also
    developed keratitis and lacrimation from day 35, and alopecia from
    day 50 (Robl et al; 1978). During a 16-week test period, some pigs
    receiving FireMaster(R) BP-6 at 200 mg/kg in the diet had
    dermatosis (Ku et al., 1978). Loss of hair (including eye lashes),
    dry scaly skin, and periorbital oedema were reported in a juvenile
    female rhesus monkey given 25 mg FireMaster(R) FF-1/kg feed for 50
    weeks (total dose: approximately 1.5 g), however, the time of onset
    of these symptoms was not specified (Allen et al., 1978). A
    decreased heart rate (bradycardia) was measured in White Leghorn
    cockerels fed 150 mg FireMaster(R) FF-1/kg feed for approximately
    9 weeks (Heinemann & Ringer, 1976; Ringer, 1978). Another
    characteristic sign in chickens was general oedema (Ringer & Polin,
    1977; see also section 8.2.1.3).

    
    Table 74.  Effects on feed consumption and changes in body and organ weights after single or short-term exposure to commercial
    PBB mixtures (dosing studies)

    PBBa             Species      Sex      Exposureb                Dosec      Feed         Weight (gain) changes                  References
    (carrier)        (strain)                                                  intaked      Bodyd      Organe

    FM FF-1          rat          male,    oral single dose         1000       n.r.         no effect  liver: increase             Kimbrough
    (in peanut oil)  (Sherman)    female   t.p.: 2 months                                                                          et al.
                                                                                                                                   (1978)

    M BP-6           rat          male     oral single dose 500     n.r.                    --         liver: increase             Bernert Jr &
    (Lot No. 5143    (Sherman)             t.p.: 1-8 weeks                                                                         Groce (1984)
    in corn oil)

    FM BP-6          rat          female   oral daily doses (9)     1          no effect    no effect  liver: increase; spleen     Harris
    (in olive oil)   (Sprague-             during pregnancy         (mg/day)                           kidney, adrenal, ovary      et al.
                                                                                                                                   (1978a)
                     Dawley)               t.p.: 13 days                                               gravid uterus, perirenal
                                           (after first dose)                                          fat pads: no effect

    FM FF-1          rat          male     oral multiple doses      3          n.r.         no effect  thymus spleen: decrease     Luster
    (Lot No.         (Fischer)             (22) over 30 days                                                                       et al.
    1312 FT)                               t.p.: 60 days            30         n.r.         reduced    thymus, spleen: decrease    (1978)
    (in corn oil)                          (after first dose)

    FM FF-1          rat          male,    oral multiple doses      100-1000   reduced      reduced    liver, spleen: increase     Gupta &
    (Lot No.         (Fischer     female   (22) over 30 days                   (day 10)                thymus: decrease            Moore (1979)
    (1312 FT)        344/N)                t.p.: up to 90 days
    (in corn oil)

                                  male                              30         no effect    reduced    --                          Gupta &
                                                                                            (day 15)                               Moore (1979)

                                  female                            30         variable     reduced    --
                                                                    (day 10)

    Table 74 (contd).

    PBBa             Species      Sex      Exposureb              Dosec      Feed         Weight (gain) changes                  References
    (carrier)        (strain)                                                intaked      Bodyd      Organe

                                  male,                           3          --           --         liver: increase (day 15)    Gupta et al.
                                  female                          30         no effect               thymus: decrease (day       (1981)
                                                                                          reduced    15); lung, heart, spleen,
                                                                                          (3 week)   kidney, adrenal, thyroid,
                                                                                                     testis, ovary, uterus,
                                                                                                     brain: no effect

    FM FF-1          rat          male     oral multiple doses    1-6        n.r.         no effect  liver, thyroid: increase    Allen-Rowlands
    (Lot No.         (Sprague-             (20) t.p.: 4 weeks                                        adrenal, testis:            et al. (1981);
    1312 FT)         Dawley)               (after 1 dose)                                            no effect                   Castracane
    (in lecithin                                                                                                                 et al. (1982)
    liposomes)

    FM               rat                   intraperitoneal        1000       n.r.         n.r.       liver: increase             Aftosmis
    (in corn oil)                          single dose                                                                           et al. (1972b)
                                           t.p.: 7 days

    FM BP-6          rat          female   intraperitoneal                   n.r.         no effect  liver: increase             Dent et al.
    (in peanut oil)  (Sprague-             single dose            150                                                            (1976b)
                     Dawley)               t.p.: 2 weeks

    FM FF-1          rat          female   intraperitoneal        200-1000   n.r.         no effect  liver: increase             Goldstein
    (in corn oil)    (Fischer)             single dose            (µmol/kg                                                       et al. (1979)
                                           t.p.: 4 days           body
                                                                  weight)

    FM FF-1          rat          male     intraperitoneal        90
    (in              (Sprague-             single dose
    polyethylene     Dawley)               t.p.: 1 week                      n.r.         n.r.       liver: increase             Dannan et al.
    glycol)                                                                                                                      (1978a)

    Table 74 (contd).

    PBBa             Species      Sex      Exposureb               Dosec     Feed         Weight (gain) changes                  References
    (carrier)        (strain)                                                intaked      Bodyd      Organe

                                           t.p.: 2 weeks                     n.r.         no effect  liver: increase;            Dannan et al.
                                                                                          no effect  spleen, thymus:             (1982c);
                                                                                                                                 Millis et al.
                                                                                                                                 (1985a)

    FM BP-6          rat          male     intraperitoneal (days   30        n.r.         n.r.       liver, spleen: increase     Robertson
    (Lot 7062)       (Wistar)              1 and 3) two doses      75        n.r.         n.r.       liver: increase; spleen,    et al. (1981b)
    (in corn oil)                          t.p.: 6 days                                              thymus: decrease
                                           (after 1 dose)

    FM BP-6          rat          male     intraperitoneal three   0.2       n.r.         n.r.       liver: increase             Ecobichon
    (in peanut       (Wistar)              doses (days 1, 2, 3)    mmol/kg                                                       et al. (1979)
    oil)                                   t.p.: 7 days            body
                                           (after 1 dose) weight

    FM BP-6          rat          male     intraperitoneal single  500       n.r.         reduced    liver: increase;            Andres et al.
    (in corn oil)    (Wistar)              or multiple doses (4)                                     thymus, spleen: decrease    (1983)
                                           t.p.: 15 days

    FM FF-1          mouse        female   oral multiple doses     30        n.r.         no effect  spleen: decrease            Luster et al.
    (Lot No.         (B6C3F1)              (22) over 30 days                                         thymus: no effect           (1978)
    1312 FT)                               t.p.: 60 days
    (in corn oil)                          (after 1 dose)

                     mouse        female   oral multiple doses     30        n.r.         no effect  spleen: increase;           Luster et al.
                     (B6C3F1)              (22) from gestational                                     thymus: decrease            (1980)
                     (pregnant)            day 0 until litters
                                           were weaned

    Table 74 (contd).

    PBBa             Species      Sex      Exposureb               Dosec     Feed         Weight (gain) changes                  References
    (carrier)        (strain)                                                intaked      Bodyd      Organe

    FM FF-1          mouse        male,    oral multiple doses     3-30      no effect    variable   liver: increase (day 15)    Gupta et al.
    (Lot No.         (B6C3F1/N)   female   (22) over 30 days                                         lung, heart, spleen,        (1981)
    FT 1312)                               t.p.: up to 90 days                                       kidney, adrenal thyroid
    (in corn oil)                                                                                    testis, ovary, uterus,
                                                                                                     brain: no effect

                                  male                             30        no effect    reduced    thymus: decrease
                                                                                          (only day  (only day 30)
                                                                                          30)
                                  female                           0.3, 3,   no effect    increased  thymus: no effect
                                                                   30                     (only
                                                                                          day 45)

    FM BP-6          mouse        female   intraperitoneal single  150       n.r.         n.r.       liver: increase (48,        Dent et al.
    (in peanut oil)  (NMRI)                dose t.p.: up to 192 h                                    96 h), no effect (24,       (1977a)
                                                                                                     192 h)

    FM BP-6          mouse        male     intraperitoneal         1.50      n.r.         no effect  liver: increase;            Robertson
    (in corn oil)    (C57BL/6J)            single dose             (mmol/kg                          thymus: decrease;           et al. (1984c)
                                           t.p.: 5 days            body                              spleen: no effect
                                                                   weight)

                     mouse        male     intraperitoneal         1.50      n.r.         no effect  liver: increase;
                     (DBA/2J)              single dose             (mmol/kg                          thymus, spleen:
                                           t.p.: 5 days            body                              no effect
                                                                   weight)

    FM FF-1          guinea-pig   female   oral single dose        50        n.r.         no effect  "tissues": no effect        Ecobichon
    (Lot FA          (Hartley,             t.p.: 2-60 days                                           (liver, kidney, lung,       et al. (1983)
    7042) (in        albino)                                                                         perirenal fat)
    peanut oil)      (pregnant)

    Table 74 (contd).

    PBBa             Species      Sex      Exposureb                Dosec      Feed         Weight (gain) changes                    References
    (carrier)        (strain)                                                  intaked      Bodyd         Organe

    FM BP-6          guinea-pig   male     intraperitoneal single   50         n.r.         --            liver, kidney: no effect   Smith
    (in peanut oil)  Hartley               dose t.p.: 120 h                                                                          et al.
                                                                                                                                     (1986)

                     hamster      male     intraperitoneal single   50         n.r.         --            liver, kidney: no effect
                     (golden               dose t.p.: 120 h
                     Syrian)

    FM (Lot          rabbit       male     dermal 24 h of           100-       n.r.         reduced       liver: increase            Waritz
    635-71)          (New                  exposure t.p.:           10 000                  (not                                     et al.
                     Zealand,              14 days                                          significant)                             (1977)
                     albino)

    FM BP-6          calf         male     oral daily doses         0.54       no effect    reduced       --                         Willett &
    (Lot RP-158)                           for 44 days              mg/day                                                           Irving
    (in milk)                                                                                                                        (1976)

    FM BP-6          cattle       female   oral daily doses         25 g       reduced      reduced       liver, kidney, perirenal   Irving
    (Lot             (pregnant)                                     per day    (day 4)      (day 20)      lymph nodes: increase      et al.
    6244 A)                                                                                               thymus: decrease           (1976);
                                                                                                          (days 33-66)               Willett
                                                                                                                                     & Irving
                                                                                                                                     (1976);
                                                                                                                                     Durst
                                                                                                                                     et al.
                                                                                                                                     (1977);
                                                                                                                                     Moorhead
                                                                                                                                     et al.
                                                                                                                                     (1977)

    Table 74 (contd).

    PBBa             Species      Sex      Exposureb              Dosec        Feed         Weight (gain) changes                References
    (carrier)        (strain)                                                  intaked      Bodyd         Organe

                                                                  250 mg       no effect    no effect     no effect
                                                                  per day

    FM FF-1          calf         male,    oral daily doses       100          reduced      reduced       --                     Robl et al.
                                  female                                       (day 36)     (day 35)                             (1978)

                     cattle       female   oral daily doses       0.3          no effect    no effect     --
                                           for 158 days
                                           t.p.: 340 days
                                           (after 1 dose)

    FM FF-1          dog          male,    oral daily doses       1            n.r.         --            liver: increase        Farber et al.
                     (Beagle)     female   for 7 weeks                                                                           (1976)

                     dog          male     oral daily doses       4            n.r.         reduced       --                     Farber et al.
                     (Beagle)                                                               (day 30)                             (1978)

    FM               Japanese              oral daily doses       25-1000      n.r.         reduced       liver: increase        Strik (1973b)
                     quail                 for 7 days

    FM BP-6          rainbow               intraperitoneal                     n.r.         n.r.          liver: no effect       Elcombe &
    (in corn oil)    trout                 single dose t.p.:                                                                     Lech (1978)
                     (Oncorhynchus         up to 15 days
                     mykiss)

    FM BP-6          brook trout           oral multiple          (200 mg/kg   n.r.         reduced       liver: no effect       Law & Addison
    (in dogfish      (Salvelinus           doses t.p.:            body                      (not                                 (1981)
    oil)             (fontinalis)          18 days (after         weight                                  significant)
                                           1 dose)                total dose)

    Table 74 (contd).

    PBBa             Species      Sex      Exposureb              Dosec        Feed         Weight (gain) changes                References
    (carrier)        (strain)                                                  intaked      Bodyd         Organe

    OcBB (in         rat          female   oral single dose       126-2000     n.r.         no effect     n.r.                   Norris et al.
    corn oil)        (Sprague-             t.p.: 14 days                                                                         (1973, 1975)
                     (Dawley)

    OcBB (in         rat          male     oral single dose       1000         no effect    no effect     liver: increase (days  Lee et al.
    corn oil)        (Sprague-             t.p.: 21 days                                                  2-11), no effect       (1975b)
                     Dawley)                                                                              (day 21)

                                           oral daily doses (2)   3000         no effect    no effect     liver: increase (up    Lee et al.
                                           t.p.: 28 days (after                                           to day 21), no effect  (1975b)
                                           lase dose)                                                     (day 28)

    OcBB (Dow        rat          male     oral single dose       3400-        n.r.         --            liver: increase        Waritz et al.
    Lot 102-7-72)    (Sprague-             t.p.: 7 days           17 000                                                         (1977)
    (in 40-50%       Dawley)
    acetone: corn
    oil = 15:85)

    OcBB (in         rat                   intraperitoneal        1000         n.r.         n.r.          liver: increase        Aftosmis
    corn oil)                              single dose t.p.:                                                                     et al. (1972b)
                                           7 days

                     rat                   inhalation 4 h         3.1          n.r.         n.r.          liver: no effect
                                           exposure for           µg/litre
                                           10 days                air

    OcBB             rat          male     inhalation 4 h         0.96         n.r.         n.r.          liver: increase (not   Waritz et al.
    (Dow Lot         Sprague-              exposure               mg/litre                                significant)           (1977)
    102-7-72)        Dawley)               t.p.: 7 days           air

    Table 74 (contd).

    PBBa             Species      Sex        Exposureb             Dosec       Feed         Weight (gain) changes                 References
    (carrier)        (strain)                                                  intaked      Bodyd         Organe

                     rat          not        inhalation            (25 g)      n.r.         n.r.          liver: no effect
                     (Sprague-    specified  23 h/day;                                                    (2-15 weeks) kidney,
                     Dawley)                 7 days/week for                                              thyroid: no effect
                                             2-15 weeks                                                   (15 weeks)

    OcBB             rabbit       male       dermal 24 h           100-        n.r.         n.r.          liver: increase (not    Waritz et al.
    (Dow Lot         (New                    exposure              10 000                                 significant)            (1977)
    102-7-72)        Zealand;                t.p.: 14 days
    (in corn oil)    albino)

                                  male       dermal 6 h/day;       1           n.r.         no effect     liver: increase
                                             5 days/week, for
                                             2 weeks t.p.:
                                             18 days (after last
                                             dose)

    OcBB             bobwhite     male,      oral single dose      12 500      n.r.         n.r.          any internal organs:
    (Dow Lot         quail        female     t.p.: 14 days                                                no effect
    102-7-72)
    (in corn oil)

    NoBB             mouse        male,      oral single dose      up to       n.r.         n.r.          liver: increase         Momma (1986)
                     (B6C3F1)     female     t.p.: 14 days         15 000

    DeBB (in         rat          male,      oral single dose      5000        n.r.         no effect     liver: no effect        Millischer
    corn oil)        (Sprague-    female     t.p.: 14 days                                                                        et al. (1979)
                     Dawley)

    Table 74 (contd).

    PBBa             Species      Sex        Exposureb             Dosec       Feed         Weight (gain) changes             References
    (carrier)        (strain)                                                  intaked      Bodyd         Organe

                     rat                     intraperitoneal       1000        n.r.         n.r.          liver: no effect    Aftosmis
                                             single dose                                                                      et al. (1972b)
                                             t.p.: 7 days

                     rat          male,      dermal 24 h           5000        n.r.         no effect     liver: no effect    Millischer
                     (Sprague-    female     exposure t.p.:                                                                   et al. (1979)
                     Dawley)                 14 days

                     rat          male,      inhalation 6 h/day,   0.05-5      no effect    no effect     liver: increase
                     (Sprague-    female     5 days/week for       mg/litre
                     Dawley)                 4 weeks               air

    a    Commercial PBB mixtures: FM = FireMaster(R); OcBB = octabromobiphenyl; NoBB = nonabromobiphenyl; DeBB = decabromobiphenyl.
    b    t.p. = time post-exposure.
    c    In mg/kg body weight per day, unless otherwise specified.
    d    n.r. = not recorded.
    e    Absolute or relative to body weight, respectively.

    Table 75.  Effects on feed consumption and changes in body and organ weights caused by short-term feeding of commercial PBB mixtures

    PBBa       Species         Sex      Dietary         Period of            Feed         Weight (gain) changes                   References
               (strain)                 concentration   treatment/           intakeb      Bodyb        Organsc
                                        (mg/kg feed)    observation

    FM BP-6    rat (Sprague-   female   75, 300         2/2 weeks            no effect    no effect    liver: increase            Dent et al.
               Dawley)                                                                                                            (1976a)

    FM         rat (Sprague-   male     100             30/30 days           no effect    no effect    liver: increase            Sleight &
               Dawley)                                                                                                            Sanger (1976)
                                        500             30/30 days           reduced      reduced      liver: increase;
                                                                                                       kidney: no effect

    FM BP-6    rat (Sprague-   male     50              3/3 weeks            no effect    no effect    liver: increase            Babish &
               Dawley)                                                                                                            Stoeswand
                                                                                                                                  (1977)

    FM BP-6    rat (Sprague-   female   50              day 8 of             n.r.         no effect    liver: increase            Dent et al.
               Dawley)                                  gestation through                                                         (1977b)
                                                        day 14 post-
                                                        partum

    FM BP-6    rat             male     5               variable             no effect    no effect    liver: increase (weeks     Garthoff
               (Holtzman)                                                                 (day 20)     2-5); kidney: decrease     et al. (1977)
                                                                                                       (week 3)

               rat             male     500             variable             no effect    reduced      liver: increase (weeks     Garthoff
               (Holtzman)                                                                 (day 20)     2-5); testis: no effect    et al. (1977)
                                                                                                       (week 3)

    Table 75 (contd).

    PBBa      Species         Sex          Dietary        Period of           Feed         Weight (gain) changes                  References
              (strain)                     concentration  treatment/          intakeb      Bodyb       Organsc
                                           (mg/kg feed)   observation

    FM BP-6   rat (Sprague-   not          50 (in         pre-, post- and     n.r.         n.r.        liver: increase            Cagen &
              Dawley)         specified    mother's or    perinatal                                                               Gibson (1978)
              pups            weanling's                  exposure/
                              diet)                                           of age
                                                                              15-49 age
                                                                              days

    FM BP-6   rat (Sprague-                               day 8 of
              Dawley)                                     gestation to day
                                                          15 postpartum

              mothers         female       50                                 n.r.         no effect   liver: increase; kidney,   Dent et al.
                                                                                                       mammary: no effect         (1978b)

              pups            male,        (50) (in       pre- post-, and     n.r.         no effect   liver: increase
                              female       mother's       perinatal
                                           diet)          exposure

    FM BP-6   rat (Sprague-   male,        (mothers       perinatal           n.r.         reduced     liver, spleen: increase    Harris et al.
              Dawley)         female       dose: 10       exposure                         (day 3 of   (day 60 of age) (males     (1978a)
              pups                         mg/day on                                       age)        more affected than
                                           gestation                                                   females
                                           days 7-15)

              adults          males        50-100         10/10 weeks         no effect    no effect   liver: increase            Harris et al.
                                           150, 200       10/10 weeks         no effect    reduced     liver: increase; adrenal,  (1978b)
                                                                                                       spleen, kidney, testes,
                                                                                                       seminal vesicles: no
                                                                                                       effect

    Table 75 (contd).

    PBBa       Species         Sex      Dietary         Period of            Feed         Weight (gain) changes                   References
               (strain)                 concentration   treatment/           intakeb      Bodyb        Organsc
                                        (mg/kg feed)    observation

                               female   600             10/10 weeks          reduced      reduced      n.r.

    FM BP-6    rat             male     50-500          5/5 weeks            n.r.         no effect    liver: increase            Kasza et al.
               (Holtzman)                                                                                                         (1978a)

    FM BP-6    rat (Sprague-   male     20              28/28 days           no effect    no effect    liver: increase            Chu et al.
               Dawley)                                                                                                            (1980)

    FM BP-6    rat (Sprague-   male,    100 (in         perinatal            n.r.         reduced      M: ventral                 Johnston
               Dawley)                  mothers or      exposure until                    (more        prostate: decrease         et al. (1980)
               pups                     weanlings       9 weeks of age                    pronounced
                                        diet)                                             in males)

    FM BP-6    rat (Sprague-   male     1-100           30/30 days           no effect    no effect    liver: increase; thymus,   Akoso et al.
               Dawley)                                                                                 spleen: no effect          (1982a)

                               male     100             30/30 days           no effect    no effect    thyroid: increase          Akoso et al.
                                                                                                                                  (1982b)

    FM BP-6    rat (Sprague-   male     100             9/9 days             no effect    no effect    liver, thyroid: increase   Render et al.
               Dawley)                                                                                 kidney: no effect          (1982)

    FM BP-6    rat (Fisher)    male     100             10/10 days           no effect    no effect    liver: increase            Raber &
                                                                                                                                  Carter (1986)

    FM BP-6    mouse           female   1000            11/11 days           n.r.            --        liver: increase            Corbett
               (Swiss,                                                                                                            et al. (1975)
               ICR)            male     1000            up to 14/14          n.r.         reduced      liver: increase (day 4);   Corbett
                                                        days                              (day 4)      testis: no effect          et al.
                                                                                                                                  (1978a)

    Table 75 (contd).

    PBBa      Species         Sex        Dietary        Period of            Feed         Weight (gain) changes                   References
              (strain)                   concentration  treatment/           intakeb      Bodyb        Organsc
                                         (mg/kg feed)   observation

    FM BP-6   mouse           female     50-200         2/2 weeks            no effect    no effect    liver: increase            Cagen et al.
              (Swiss,                                                                                                             (1977); Cagen
              Webster)                                                                                                            & Gibson
              adult                                                                                                               (1978)
              pups            not        50 (in         postnatal               --          --         liver: increase            Cagen &
                              specified  mothers        exposure until                                                            Gibson (1978)
                                         diet)          15 days of age

    FM        mouse           not        100            30/30 days           n.r.         no effect    liver: increase; thymus,   Fraker & Aust
              (BALB/c)        specified                                                                spleen: decrease           (1978)
                              not        1000           14/14 days           n.r.         reduced      liver: increase; thymus:
                              specified                                                                decrease (nearly athymic)

    FM BP-6   mouse           female     1, 10          30/30 days           n.r.         no effect    liver, spleen: no effect;  Fraker (1980)
              (BALB/c)                                                                                 thymus: decrease
                              female     100            30/30 days           n.r.         no effect    liver: increase; thymus,
                                                                                                       spleen: decrease

    FM FF-1   mouse           male       5              8/8 weeks            n.r.         no effect    liver: increase            Loose et al.
    (Lot No.  (BALB/c                                                                                                             (1981)
    7042)     ByJ)                       167            6/6 weeks            n.r.         no effect    liver: increase
                                         167            8/8 weeks            n.r.         reduced      liver: increase
                                         5              3/3 weeks            n.r.           --         thymus: no effect
                                         5              6-8/6-8 weeks        n.r.           --         thymus: decrease
                                         167            3-8/3-8 weeks        n.r.           --         thymus, spleen: decrease
                                         5, 167         3-8/3-8 weeks        n.r.           --         lung: no effect

    Table 75 (contd).

    PBBa      Species         Sex        Dietary        Period of            Feed       Weight (gain) changes                     References
              (strain)                   concentration  treatment/           intakeb    Bodyb          Organsc
                                         (mg/kg feed)   observation

    FM FF-1   mouse           male       mothers dose:  perinatal            n.r.       no effect      spleen: increase;          Luster et al.
    (Lot No.  (B6C3F1)                   10 mg/kg       exposure                                       thymus: no effect          (1980)
    1312 FT)  pups                       body weight
                                         per day
                                         (22 doses)

    FM BP-6   guinea-pig      not        10             45/45 days           n.r.       no effect      liver: increase            Vos & van
                              specified                                                                                           Genderen
                                                                                                                                  (1974)

    FM        guinea-pig      not        1, 10          30/30 days           no effect  no effect      liver: no consistent       Sleight &
                              specified                                                                effect                     Sanger (1976)
                                         100            up to 30 days        n.r.       reduced        liver: increase
                                                                                        (week 3)
                                         500            15/15 days           n.r.       reduced        liver: increase
                                                                                        (week 1)

    FM BP-6   pig             not        20, 200        16/16 weeks          reduced    reduced        liver, kidney: increase    Ku et al.
              (growing)       specified                                                                                           (1978)

              pig             not        100 (in        perinatal            n.r.       reduced        liver: increase (but no    Werner &
              (4-week-old)    specified  mothers        exposure                        (not           effect in sows)            Sleight
              (lactating)                diet)                                          significant)                              (1981)

              pig             not        100 (in        prenatal                --          --         thyroid: increase;
              (newborn)       specified  mothers diet)  exposure                                       liver: no effect

    Table 75 (contd).

    PBBa      Species         Sex        Dietary        Period of            Feed       Weight (gain) changes                     References
              (strain)                   concentration  treatment/           intakeb    Bodyb           Organsc
                                         (mg/kg feed)   observation

    FM FF-1   mink            female     1-1.54         several months       --         no effect       liver, kidney: increase   Aulerich &
                                         2.5            several months       --         no effect       (in animals that died     Ringer
                                                                                        (within first   during treatment)         (1979);
                                                                                        3 months,                                 Ringer et al.
                                                                                                                                  (1981)
                                                                                        later reduced)
                                         6-16           several months       (refused)  reduced

    FM FF-1   Rhesus          female     0.3            several months       no effect  reduced         --                        Allen et al.
              monkey                                                                                                              (1978)
              (adult)

              (infants)       not        0.3 (in        perinatal            --         reduced         --
                              specified  mothers        exposure;
                                         diet)          up to 12
                                                        weeks of age

              (juvenile)      female     300            up to 137            no effect  reduced         --
                                                        days                 (until a
                                                                             few days
                                                                             prior to
                                                                             death)

    Table 75 (contd).

    PBBa      Species         Sex        Dietary        Period of            Feed       Weight (gain) changes                     References
              (strain)                   concentration  treatment/           intakeb    Bodyb           Organsc
                                         (mg/kg feed)   observation

    FM        Japanese        male,      500, 1000      a few days           (refused)                                            Babish et al.
              quail           female                                                                                              (1975a)
                                         10-100         9/9 weeks            no effect  no effect       liver: increase

    FM        Bobwhite                   100-700        5/8 days             reduced    n.r.            n.r.                      Cottrell
              quail (Colinus                                                                                                      et al. (1984)
              virginianus)

    FM BP-6   chicks          male       400            15/15 days           n.r.       reduced         bursa of Fabricius:       Vos & van
    (Lot No.  (Hubbard                                                                                  decrease                  Genderen
    182 RP)   Leghorn)                   15, 30         63/63 days           n.r.       reduced         bursa of Fabricius,       (1974)
                                                                                                        spleen decrease

    "PBB"     pullet                     50, 200        4/4 weeks            n.r.       reduced         --                        Chang &
    (FM)                                                                                                                          Zindel (1975)

    FM        chicken         male       variable,      several weeks        --         --              liver, thyroid:           Ringer & Polin
              (White                     up to 200                                                      increase; comb:           (1977)
              Leghorn)                                                                                  decrease; testis:
                                                                                                        increase (low dose)
                                                                                                        decrease (higher dose)

                              female     125            several weeks        reduced    --              --

              chicks (White              75             several weeks        --         reduced         --
              Leghorn)

    Table 75 (contd).

    PBBa      Species         Sex        Dietary        Period of            Feed       Weight (gain) changes                     References
              (strain)                   concentration  treatment/           intakeb    Bodyb           Organsc
                                         (mg/kg feed)   observation

    FM BP-6   chicken         female     20, 64,        8/16 weeks           no effect  no effect       --                        Cecil &
              (White                     200            2/2 weeks            reduced    reduced         --                        Bitman (1978)
              Leghorn)                   640, 2000      2/2 weeks            (refused)  reduced         --

    FM FF-1   chicken         female     0-25           5/5 weeks            no effect  --              --                        Polin &
              (White                     125            5/5 weeks            reduced    --              --                        Ringer
              Leghorn)                   3125           5/5 weeks            refused    --              --                        (1978a)

    FM        chicks          male       75-250         up to 42             reduced    reduced         liver, thyroid:           Ringer (1978)
              (White                                    days                                            increase; comb, testes,
              Leghorn)                                                                                  spleen, bursa, thymus:
                                                                                                        decrease

    FM FF-1   cockerels       male       10, 100        28/28 days           no effect  no effect       liver: increase; bursa:   Dharma et al.
              (White                                                                                    decrease; thyroid,        (1982)
              Leghorn)                                                                                  spleen, testicles,
                                                                                                        comb: no effect

    OcBB      rat                        100            28/28 days           --         --              liver: increase           Aftosmis
                                                                                                                                  et al.
                                                                                                                                  (1972a)

    Table 75 (contd).

    PBBa       Species         Sex       Dietary        Period of            Feed       Weight (gain) changes                     References
               (strain)                  concentration  treatment/           intakeb    Bodyb           Organsc
                                         (mg/kg feed)   observation

    OcBB       rat (Sprague-   male      100-1000       30/30 days           no effect  no effect       liver: increase; heart,   Norris et al.
               Dawley)                                                                                  testes, brain: no         (1973, 1975)
                                         1000, 10 000   30/30 days                                      effect; kidney:
                                                                                                        increase

    OcBB       rat (Sprague-   male      100, 1000      2-4/2-4 weeks        no effect  no effect       liver: increase           Lee et al.
               Dawley)                                                                                                            (1975a)
                                         1000           4/22 weeks           no effect  no effect       liver: increase

    OcBB       rat             male      100, 1000      2-4/2-22             no effect  no effect       liver: increase           Waritz et al.
    (Dow Lot   (Sprague-                                weeks                                                                     (1977)
    102-7-72)  Dawley)

    DeBB       rat (Sprague-   male,     2000           13/13 weeks          no effect  no effect       liver: increase           Millischer
               Dawley)         female                                                                                             et al. (1979)

    a    Commercial PBB mixtures: FM = FireMaster(R); OcBB = octabromobiphenyl; DeBB = decabromobiphenyl.
    b    n.r. = Not recorded.
    c    Absolute or relative to body weight, resp.

         At lethal doses, the "wasting syndrome" (see section 8.1) can
    also be accompanied by other symptoms. Rats, which became moribund,
    had hunchback posture, sunken eyes, appeared dehydrated, and were
    lethargic (Gupta & Moore, 1979). Minks have been reported to show an
    unthrifty appearance (Aulerich & Ringer, 1979; Ringer et al., 1981).
    Cattle that died later showed many similar clinical signs, but they
    also had excessive lacrimation and salivation, diarrhoea and
    depressed heart and respiratory rates (Irving et al., 1976; Durst
    et al; 1977, 1978b; Moorhead et al., 1977). In two rhesus monkeys,
    the time to death was as long as 3-5 months. In addition to body
    weight loss, the dead animals exhibited alopecia and oedema,
    particularly on the face and eyelids (including loss of eyelashes),
    and dry scaly skin (Allen et al., 1978). Observations of intoxicated
    Bobwhite quails, prior to death, included asthenia, low carriage, an
    unkempt appearance, wing droop, diarrhoea, limited ataxia, and
    general lethargy (Cottrell et al., 1984).

    8.2.1.2  Haematology and clinical chemistry

    a) Haematology

         At lethal doses, leukopenia and erythropenia were observed in a
    rhesus monkey (Allen et al., 1978), but not in cattle (Moorhead
    et al., 1977). Packed cell volume, white blood cell count, and red
    blood cell count fell gradually in the monkey (dietary
    concentration: 300 mg/kg of feed; total dose: 6.4 g of
    FireMaster(R) FF-1), while changes in packed cell volume,
    haemoglobin content, total erythrocyte and leukocyte counts, and
    differential leukocyte counts were minimal in the cows (dose: 25 g
    FireMaster(R) BP-6 per day).

         At sublethal doses, haematological parameters of rhesus monkeys
    remained within normal limits (Allen et al., 1978). The same was
    true for cattle (Moorhead et al., 1977; Robl et al., 1978), with the
    exception of a calf dosed with 100 mg FireMaster(R) FF-1/kg body
    weight per day, the total leukocyte count of which was elevated
    (Robl et al., 1978). Rats given 30 mg FireMaster(R) FF-1/kg body
    weight per day for 30 days (22 total doses) showed a significant
    decrease in the packed cell volume, haemoglobin concentrations, and
    platelet counts at 30 days of exposure (Gupta et al., 1981) and at 6
    months after the start of dosing (Gupta & Moore, 1979), but were
    normal at 45, 60, or 90 days after the start of dosing (Gupta
    et al., 1981). White and red blood cell values were only
    occasionally reduced; for example, there was moderate lymphopenia in
    female animals at 30 days of exposure (Gupta & Moore, 1979; Gupta
    et al., 1981). No significant differences in values for the
    erythrocyte count, packed cell volume, haemoglobin, and total and
    differential leukocyte counts were found in male rats fed various

    levels of FireMaster(R) BP-6 (1-500 mg/kg diet) for 30-60 days
    (Sleight & Sanger, 1976; Garthoff et al., 1977; Sleight et al.,
    1978); only a possible increase in total white blood cell count was
    noted at the 500 mg/kg feed level (Garthoff et al., 1977). A mild
    but significant decrease in the packed cell volume and the number of
    platelets was observed in mice exposed to 30 mg FireMaster(R)
    FF-1/kg body weight per day for 30 days (22 total doses). The
    leukocyte values were within normal limits (Gupta et al., 1981).
    Growing pigs in a 16-week trial showed significant reductions in
    haemoglobin and haematocrit only after 6 weeks of feeding 200 mg
    FireMaster(R) BP-6/kg diet (Ku et al., 1978). There was no
    appreciable effect on standard haematological values of nursing pigs
    and their sows fed FireMaster(R) BP-6 (10-200 mg/kg feed) during
    pregnancy and lactation (Werner & Sleight, 1981). White Leghorn
    cockerels fed PBB (FireMaster(R) FF-1) at dietary concentrations
    of 75 and 150 mg/kg from 3 to 4 days of age until 5-9 weeks showed a
    significant decrease in packed cell volume and haemoglobin values
    (Heinemann & Ringer, 1976; Ringer, 1978).

         Technical octabromobiphenyl caused a significant decrease in
    packed cell volume and total red blood cell count in male rats fed
    dietary concentrations of 10 000 mg/kg for 30 days, but had no
    effect at dietary concentrations of 100 and 1000 mg/kg (Norris
    et al., 1973, 1975).

         Standard haematological determinations revealed no treatment-
    related changes in blood from rats exposed to technical
    decabromobiphenyl via diet (1-2000 mg/kg) for 4-12 weeks and via
    inhalation (0.005-5 mg/litre, 6 h/day, 5 days/week) for 4 weeks
    (Millischer et al., 1979).

    b) Clinical chemistry

         Clinical chemistry values examined in many studies refer to
    serum protein (total protein, specific fractions), serum enzymes,
    serum glucose, blood urea nitrogen, serum lipids, serum cholesterol,
    and urine.

    (i) Serum protein

         Decreases in total serum protein, due primarily to a reduction
    in the albumin fraction, occurred in severely intoxicated cattle
    (Durst et al., 1978a; Schanbacher et al., 1978) and monkeys (Allen
    et al., 1978). No consistent effect of dietary PBBs on total serum
    protein concentrations or electrophoretic profiles was observed in
    pigs fed FireMaster(R) BP-6 at levels of 20 or 200 mg/kg for 16
    weeks (Ku et al, 1978). In rats fed 5, 50, or 500 mg FireMaster(R)
    BP-6/kg for 3 weeks, total plasma protein was slightly increased by
    the highest concentration (Garthoff et al., 1977). A marked increase

    (50%) in serum protein was found in rats given 22 oral doses of
    FireMaster(R) FF-1 (30 mg/kg body weight per day) over a 30-day
    period and observed for some additional weeks. These changes were
    primarily associated with increased ß-globulin fractions (Gupta
    et al., 1981). Reductions in serum immuno globulin levels
    (gamma-globulin fractions) have been reported in mice given oral
    doses (30 mg/kg body weight per day) of FireMaster(R) FF-1 (Luster
    et al., 1978) or diets containing 167 mg FireMaster(R) FF-1/kg
    (Loose et al., 1981).

         No treatment-related changes in total serum protein were found
    in rats exposed to technical decabromobiphenyl (1-2000 mg/kg feed
    for 4-12 weeks; inhalation: 0.005-5 mg/litre; 6 h/day; 5 days/week
    for 4 weeks) (Millischer et al., 1979).

    (ii) Serum enzymes

         Alterations in serum enzymes, most of which are indicative of
    liver lesions, have been found in some instances.

         Gamma-Glutamyl transpeptidase (gamma-GTP) was elevated by oral
    doses of FireMaster(R) FF-1 (30 mg/kg body weight per day) in
    female rats and mice of both sexes (Gupta et al., 1981).

         No consistent increase in serum glutamic pyruvic transaminase
    (SGPT) occurred in rats after dietary (Garthoff et al, 1977;
    Matthews et al., 1978) or oral (Gupta et al., 1981) exposure to
    FireMaster(R). No changes were found in cows on diets containing
    up to 10 mg FireMaster(R) FF-1/kg (Robl et al, 1978). However, a
    gradual increase in SGPT activity was observed in lethally
    intoxicated rhesus monkeys (Allen et al., 1978). Technical
    decabromobiphenyl did not influence SGPT in rats (Millischer et al.,
    1979).

         Serum glutamic-oxaloacetic transaminase (SGOT) was
    significantly increased in cattle at high doses of PBBs (25 g FM
    BP-6 per day) (Moorhead et al., 1977; Durst et al., 1978b). It was
    unaffected in cattle given lower doses (250 mg FM BP-6/day: Moorhead
    et al., 1977; 0.01-10 mg FM FF-1/kg feed: Robl et al., 1978), as
    well as in pigs (Ku et al., 1978) or in rats (Sleight & Sanger,
    1976; Garthoff et al., 1977; Sleight et al., 1978) fed
    FireMaster(R) BP-6 (20 and 200 mg/kg diet or 1-500 mg/kg diet,
    respectively). A possible decrease in serum GOT has been reported in
    rats exposed to technical decabromobiphenyl via inhalation
    (Millischer et al., 1979).

         Lactic dehydrogenase (LDH) was within normal ranges in PBB-
    contaminated cows without clinical signs of toxicosis (Moorhead
    et al., 1977), but it was increased in a group of apparently
    intoxicated animals (dose: 25 g FM BP-6/day) (Moorhead et al., 1977;

    Durst et al., 1978b). A significant decrease was found in growing
    pigs (Ku et al., 1978), but not in nursing pigs and their sows
    (Werner & Sleight, 1981), fed FireMaster(R) BP-6.
    Electropherograms of LDH isozymes at 60 days, from rats given
    FireMaster(R) BP-6 (100 mg/kg feed), showed appreciable changes
    (Sleight et al., 1978).

         With the exception of calves (Robl et al., 1978) and newborn
    pigs (Werner & Sleight, 1981), alkaline phosphatase levels in
    animals were unaffected by FireMaster(R), e.g., rats (Sleight
    et al., 1978; Gupta et al, 1981), dogs (Farber et al, 1976), and
    growing pigs (Ku et al., 1978). Technical decabromobiphenyl also did
    not have any effect on alkaline phosphatase levels in rats
    (Millischer et al., 1979).

         Serum isocitrate dehydrogenase (sICDH) did not show any
    discernible rise in dairy cattle dosed with FireMaster(R) BP-6,
    until doses were sufficient to cause toxicosis (25 g/day). These
    cows showed moderate increases in sICDH (approximately a two-fold
    increase). Elevation of sICDH was coincident with fetal trauma. 
    Non-pregnant cows, equally intoxicated, showed minimal sICDH
    elevation (Schanbacher et al., 1987).

         Serum creatine phosphokinase levels in growing pigs were
    unaffected by 20 or 200 mg FireMaster(R) BP-6/kg feed (Ku et al.
    1978).

         In male Japanese quails, serum glutamate dehydrogenase levels
    were increased by "hexabromobiphenyl" (STRIK, 1973b).

    (iii) Serum glucose

         A slight decrease in serum glucose was observed in rats and
    mice administered 22 total doses of 30 mg FireMaster(R) FF-1/kg
    body weight (Gupta et al., 1981) and in rats fed 50 mg
    FireMaster(R) BP-6/kg diet for 3 weeks (Garthoff et al., 1977),
    but not in rats fed 500 mg/kg diet for the same period (Garthoff
    et al., 1977). FireMaster(R) did not produce any effects on
    glucose concentrations in either sublethally or lethally intoxicated
    cattle (Durst et al., 1978a; Robl et al., 1978), and
    decabromobiphenyl did not affect glucose levels in rats (Millischer
    et al., 1979).

    (iv) Blood urea nitrogen

         Values for blood urea nitrogen (BUN) remained in the normal
    range in mice (Gupta et al., 1981) and rats (Sleight & Sanger, 1976;
    Garthoff et al., 1977; Sleight et al., 1978; Gupta et al., 1981) or
    were elevated in rats at some concentrations (Sleight & Sanger,

    1976; Garthoff et al., 1977). A significant increase in BUN occurred
    in cows (Moorhead et al., 1977; Durst et al., 1978a) and a calf
    (Robl et al., 1978) that had received doses of FireMaster(R) high
    enough to produce overt signs of toxicosis (25 g FM BP-6 per day
    (equivalent to 50 mg/kg body weight per day, and 100 mg FM FF-1/kg
    body weight per day, respectively).

    (v) Serum lipids

         Characteristic alterations in serum phospholipid HPLC profiles,
    which were maintained for at least two months after dosing, were
    found in rats given a single oral dose of FireMaster(R) BP-6
    (500 mg/kg body weight) (Bernert et al., 1985).

    (vi) Serum cholesterol

         In rats, cholesterol levels appear to be the blood parameter
    most sensitive to PBBs. There were dose-related increases in
    cholesterol concentrations in short-term (Garthoff et al., 1977;
    Spear et al., 1990) and long-term (see 8.4: Bernert et al., 1983;
    Gupta et al., 1983a,b) studies, and these increases were significant
    at dietary concentrations of FireMaster(R) as low as 5 mg/kg
    (Garthoff et al., 1977). No noticeable effects of FireMaster(R) on
    cholesterol levels have been reported in cattle (Durst et al.,
    1978a) and pigs (Werner & Sleight, 1981). Rhesus monkeys showed a
    gradual decrease in serum cholesterol when they were lethally
    intoxicated (Allen et al., 1978).

    (vii) Urinalysis

         Tests of urine for pH, protein, glucose, ketones, bilirubin,
    occult blood, and specific gravity showed no significant changes due
    to FireMaster(R) in mice (Gupta et al., 1981) and rats (Sleight
    et al., 1978; Gupta et al., 1981) or due to technical decabromo
    biphenyl in rats (Millischer et al., 1979). Only Sleight & Sanger
    (1976) reported higher readings for protein in rats fed
    FireMaster(R). Differences in urinary protein patterns between
    control rats and rats given FireMaster were detected by means of
    two-dimensional electrophoresis (Myrick et al., 1987). The principal
    urine changes in cattle lethally intoxicated were decreased specific
    gravity and moderate proteinuria (Moorhead et al., 1977; Durst
    et al., 1978a).

    8.2.1.3  Morphological and histopathological changes

    a) Liver

         The liver is the site of the most prominent gross morphological
    and histopathological changes due to PBBs in many species.

         Enlargement of the liver was a characteristic response to
    exposure to FireMaster(R), technical octabromobiphenyl, and
    technical decabromobiphenyl, and it frequently occurred at
    concentrations lower than required to produce body weight changes
    (see Tables 74 and 75). Generally, increases in absolute or relative
    liver weights were dose and time dependent (e.g., Garthoff et al.,
    1977). A notable exception was in cows, which showed decreases in
    body weight as well as an increase in liver weights only at lethal
    doses (Table 74).

         Grossly, the livers of rats were often friable and had a
    mottled surface (Sleight & Sanger, 1976; Waritz et al., 1977; Akoso
    et al., 1982a; Render et al., 1982; Raber & Carter, 1986). Red
    fluorescence of liver (and other tissues) under UVR (366 nm)
    indicated excess porphyrin accumulation. In contrast to rats, which
    developed porphyria after long-term exposure, the liver of female
    mice given 30 mg FM FF-1/kg body weight per day (22 total doses)
    became porphyric after 45 days (Gupta et al., 1981). 
    FireMaster(R) FF-1 given orally at a dose rate of 22.5 mg/kg body
    weight per day for 4 days caused centrolobular accumulation of
    Oil-red O-staining lipids in the liver of rats (Kohli et al., 1981).

         The principal histopathological alterations in rodent species
    consisted of extensive swelling and vacuolation of hepatocytes and
    proliferation of smooth-surfaced endoplasmic reticulum (SER) (seen
    as "foamy cytoplasm" in light microscopy). The vacuoles were filled
    with fat indicating excess lipid accumulation. Proliferation of SER
    may be a morphological reflection of enhanced enzyme activity
    (Sleight & Sanger, 1976; Render et al., 1982). The changes depended
    on dose and length of exposure. They have been reported in rats
    after dietary intake of FireMaster(R) (Sleight & Sanger, 1976;
    Kasza et al., 1978a; Sleight et al., 1978; Hinton et al., 1979;
    Akoso et al., 1982a; Render et al., 1982; Raber & Carter, 1986) and
    of technical octabromobiphenyl (Norris et al., 1973; Lee et al.,
    1975a). The dietary concentrations ranged from 0.1 to 500 mg/kg for
    FireMaster(R) and from 100 to 10 000 mg/kg for octabromobiphenyl.
    Effects were seen as early as the tenth day of feeding 100 mg FM
    BP-6/kg (Raber & Carter, 1986). In contrast, during a 90-day feeding
    trial, technical decabromobiphenyl (dietary concentration: 100, 500,
    or 2000 mg/kg) caused hepatic damage only at the highest level
    (Millischer et al., 1979). Liver changes, as noted above, were
    observed also after a single i.p. injection (200-1000 µmol/kg) of
    FireMaster(R) (Goldstein et al., 1979), after single oral dosing
    (1000 mg/kg body weight) of FireMaster(R) (Kimbrough et al., 1978)
    and of octabromobiphenyl (Lee et al., 1975b), and after multiple
    oral dosing of FireMaster(R) (22 doses over a 30-day period:
    30 mg/kg body weight per day (Gupta & Moore, 1979; Gupta et al.,
    1981) and of octabromobiphenyl (two doses: 3000 mg/kg body weight;
    Lee et al., 1975b). As soon as 24 h (Kimbrough et al., 1978), 3 days
    (Lee et al., 1975b), or 4 days (Goldstein et al., 1979) after
    treatment, histological changes could be detected.

         Light and electron microscopic changes also reported in the
    liver of rats included reduction or disintegration of rough-
    surfaced endoplasmic reticulum (RER) (Lee et al., 1975a,b; Gupta
    et al., 1981; Akoso et al., 1982a; Raber & Carter, 1986), presence
    of myelin bodies (cytoplasmic inclusions; membrane whorls) (Lee
    et al., 1975a,b; Sleight & Sanger, 1976; Kasza et al., 1978a;
    Kimbrough et al., 1978; Sleight et al., 1978; Hinton et al., 1979;
    Gupta et al., 1981; Akoso et al., 1982a; Raber & Carter, 1986), di-
    or multinucleated cells (Kasza et al., 1978a; Kimbrough et al.,
    1978; Gupta & Moore, 1979; Hinton et al., 1979), diminution of
    glycogen (Millischer et al., 1979; Gupta et al., 1981; Raber &
    Carter, 1986) and mitochondria that were swollen and reduced in
    number or had degenerated as time passed (Sleight & Sanger, 1976;
    Kasza et al., 1978a; Akoso et al., 1982a). There was also necrosis
    of hepatocytes (Kimbrough et al., 1978; Gupta & Moore, 1979; Gupta
    et al., 1981), and these necrotic foci were infiltrated with
    polymorphonuclear cells and lymphocytes (Gupta et al., 1981).  With
    octabromobiphenyl, myelin configurations developed 7 days after
    treatment and subsequently disappeared one week later (Lee et al.,
    1975b).

         Changes in the hepatocytes were more advanced in the centri
    lobular and midzonal regions than in the periportal area of the
    liver lobule (Render et al., 1982; Raber & Carter, 1986). Fatty
    infiltration in the livers of male rats was much more pronounced
    than in those of female rats (Gupta & Moore, 1979).

         Male rats given 100 mg FM FF-1/kg body weight per day (22 total
    doses) and dying after 90 days had subacute to chronic hepatitis
    with marked focal proliferation of bile ducts (Gupta & Moore, 1979).

         Changes in the bile canaliculus (proliferation of microvilli)
    were also found in mice fed 1000 mg FM BP-6/kg for 4-14 days. 
    Changes in the hepatocytes of these mice were increase in cell size,
    decrease in RER, increase in SER, degeneration of mitochondria,
    decrease in glycogen, and increase in size and number of nucleoli
    (Corbett et al., 1978a). Fatty infiltration of the cytoplasm was
    reported only in another two studies on mice dosed with 30 mg FM
    FF-1/kg body weight per day (Gupta et al., 1981) or fed 167 mg FM
    BP-6/kg for 6 weeks (Loose et al., 1981). However, in (moribund)
    mice fed 167 mg FM BP-6/kg feed for 12 weeks, lipid vacuoles were
    not found within the cytoplasm, but, almost exclusively, within the
    nucleus (Martino et al., 1981).  Hepatocellular necrosis has also
    been observed (Loose et al., 1981).

         Hepatocytes of guinea-pigs were swollen and had many more large
    vacuoles than those of comparably dosed rats (Sleight & Sanger,
    1976), even at lower dietary concentrations (< 10 mg FM/kg). Liver
    damage was reported to be minimal at dietary levels of 50 mg FM/kg
    (Vos & van Genderen, 1974), but severe centrilobular fatty changes
    were found at 100 and 500 mg FM BP-6/kg (Sleight & Sanger, 1976).

         Livers of rabbits, dermally treated with FireMaster(R) at 5
    or 10 g/kg body weight, showed a mottled appearance, necrotic foci,
    and were friable. No gross pathological effects were seen in rabbits
    dermally exposed to octabromobiphenyl at 10 g/kg body weight (Waritz
    et al., 1977).

         Pigs fed FM BP-6 (up to 200 mg/kg) showed the following liver
    alterations: fatty change, centrolobular necrosis, swollen
    hepatocytes, and homogeneous cytoplasm (Werner & Sleight, 1981).

         Compared with other species, liver changes observed in cattle
    were less dramatic. Only an early stage of centrilobular fatty
    degeneration and glycogen depletion were found in the enlarged
    livers of lethally (25 g FM BP-6/day) dosed cows. In addition, there
    were changes in the gallbladder and bile duct (Mercer et al., 1978;
    Moorhead et al., 1978). Single calves exposed to FM FF-1 for 6-12
    weeks had slightly enlarged hepatocytes (dose: 1 mg/kg body weight
    per day) or necrosis of individual or small foci of hepatocytes
    (dose: 100 mg/kg body weight per day) (Robl et al., 1978).

         The only consistent histopathological lesion in mink which died
    (exposure: 6.25 mg FM FF-1/kg feed), was a fatty infiltration of the
    liver (Aulerich & Ringer, 1979).

         No hepatocellular damage was found in dogs given oral doses of
    FM BP-6 (1 mg/kg body weight per day) for seven weeks (Farber
    et al., 1976).

         Biopsies of the livers of two rhesus monkeys given a diet
    containing 25 mg FM FF-1/kg at 12 weeks revealed enlargement of
    hepatocytes and a marked proliferation of SER (Allen et al., 1978).

         Liver changes in avian species were similar to those observed
    in mammals. White Leghorn cockerels fed a diet of 10 or 100 mg FM
    FF-1/kg showed enlargement and vacuolation of hepatocytes, increased
    SER, swollen mitochondria, and disruption of mitochondrial cristae.
    But, unlike rats, increased SER was not a significant feature
    (Dharma et al., 1982).

    b) Thymus

         The thymus is also an organ sensitive to PBB exposure. 
    Decreases in thymus weights were observed in rats, mice, and cattle
    after oral or intraperitoneal doses (Table 74) and in mice after
    feeding (Table 75) of FireMaster(R) mixtures. There were no
    reports on thymus weight changes due to exposure to commercial octa-
    or decabromobiphenyl (Tables 74 and 75). The weight of the thymus
    was reduced as early as 6 (Robertson et al., 1981b) or 15 days
    (Gupta et al., 1981; Andres et al., 1983) after rats were given high
    doses of FireMaster(R) (Table 74). Frequently, decreases in thymus

    weights were accompanied by increases in liver weights (see: Tables
    74 and 75). But, in some cases, changes in thymus weights were seen
    at doses lower than those required for liver changes (Fraker, 1980),
    or vice versa (Akoso et al., 1982a). Rats (Akoso et al., 1982a) and
    mice (Fraker & Aust, 1978) both fed FireMaster(R) BP-6 (100 mg/kg
    feed) for 30 days differed in their thymic response in that rats
    remained unaffected and mice showed decreased thymic weight
    (Table 75). In contrast, rats appeared to be more sensitive than
    mice when given equal oral doses (30 mg/kg body weight per day for a
    period of 30 days) of FireMaster(R) FF-1 (Luster et al., 1978;
    Gupta et al., 1981: Table 74). Two strains of inbred mice are known
    to differ in their thymic sensitivity to FireMaster(R) (Robertson
    et al., 1984c: Table 74).

         In some studies, the histological appearance of the thymus of
    rats and mice that had survived exposure to FireMaster(R) was only
    minimally, or not, affected (Gupta & Moore, 1979; Gupta et al.,
    1981; Loose et al., 1981; Akoso et al., 1982a), even when organ
    weights were altered. In other studies, a preferential atrophy of
    the cortex of the thymus was found in rats and mice similarly
    exposed (Luster et al., 1978; Fraker, 1980). At high doses (1000 mg
    FM BP-6/kg feed), "surviving" mice (30%) were essentially athymic by
    day 14 (Fraker & Aust, 1978). The thymus was markedly involuted also
    in moribund rats. The normal architecture of the thymus was
    obliterated with marked atrophy and loss of demarcation between the
    cortical and medullary regions and disappearance of cortical
    thymocytes (Gupta & Moore; 1979).  Moderate to marked atrophy of the
    thymus was also observed in guinea-pigs (Vos & van Genderen, 1974)
    or cattle (Moorhead et al., 1978) that were lethally intoxicated.

         The bursa of Fabricius, an analogous organ in avian species,
    was also affected by FireMaster(R) (Table 75: Vos & van Genderen,
    1974; Ringer, 1978; Dharma et al., 1982). Reductions in weight
    occurred at exposures as low as 10 mg/kg feed in cockerels (Dharma
    et al., 1982). Histologically, the bursa showed depletion of the
    lymphoid cells especially in the medulla (Vos & van Genderen, 1974;
    Ringer, 1978; Dharma et al., 1982).

    c) Spleen

         Changes in spleen weights are given in Tables 74 and 75. 
    Feeding of FireMaster(R) (100-200 mg/kg equivalent to 10-20 mg/kg
    body weight per day) had no effect on the spleen weights of young
    rats (Harris et al., 1978b; Akoso et al., 1982a), but resulted in a
    decrease in the spleen weights of mice (equivalent to 15-30 mg/kg
    body weight per day) (Fraker & Aust, 1978; Fraker, 1980; Loose
    et al., 1981). An increase in spleen weights was observed in pups of
    both rats (Harris et al., 1978a) and mice (Luster et al., 1980)
    perinatally exposed to FireMaster(R). No effects were found in

    some oral dosing studies on rats (Harris et al., 1978a; Gupta
    et al., 1981); in another study, spleen weights were decreased
    (Luster et al., 1978), and in the highest-dosage study reported
    spleen weights increased (Gupta & Moore, 1979). On the other hand,
    rats that received i.p. injection of FireMaster(R) showed
    decreases in spleen weight at the higher doses (Robertson et al.,
    1981b; Andres et al., 1983) and increases at the lower dose
    (Robertson et al., 1981b). While female mice orally dosed with
    FireMaster(R) showed decreased spleen weights (Luster et al.,
    1978), pregnant and nursing females comparably dosed exhibited
    increased spleen weights (Luster et al., 1980). No effect was found
    in mice, 5 days after a single i.p. injection of FireMaster(R),
    though the liver and thymus were affected (Robertson et al., 1984c).
    Spleen weights of chicks fed FireMaster(R) were reduced (Vos & van
    Genderen, 1974; Ringer, 1978) or remained unaffected (Dharma et al.,
    1982).

         Significant histopathological changes in the spleen have not
    been reported, except in rats that were moribund from high doses of
    FireMaster(R). In these animals, the splenic lymphatic follicles
    were small because of a lack of periarterial lymphoid cells (Gupta &
    Moore, 1979).

    d) Thyroid

         Exposure to FireMaster(R) resulted in an increase in thyroid
    weight, if there was any weight change (see Tables 74 and 75). 
    Increases in thyroid weight have been observed in rats (Sleight
    et al., 1978; Allen-Rowlands et al., 1981; Akoso et al., 1982b;
    Render et al., 1982), newborn pigs (Werner & Sleight, 1981) and in
    chickens (Ringer & Polin, 1977; Ringer, 1978). When no weight change
    occurred (rats: Sleight et al., 1978; Gupta et al., 1981; mice:
    Gupta et al., 1981; chickens: Dharma et al., 1982), the extent of
    exposure was not always less than in the former studies. 
    Octabromobiphenyl tested in one inhalation study did not have any
    effect on thyroid weight in rats (Waritz et al., 1977).

         Histological changes in the thyroid gland developed in rats at
    dietary concentrations of FireMaster(R) BP-6 as low as 5 mg/kg
    (Kasza et al., 1978b). Hyperplasia of follicular cells occurred in
    rats (Kasza et al., 1978b; Sleight et al., 1978) and newborn pigs
    (Werner & Sleight, 1981). The normal low cuboidal follicular
    epithelium was altered to one that had a more columnar appearance
    (Kasza et al., 1978b; Sleight et al., 1978). The most prominent
    ultrastructural lesions found in rats fed 5-500 mg
    FireMaster(R)/kg for 5 weeks were dose-dependent. They included
    abnormal lysosomes and colloid droplets in the cytoplasm, vacuolated
    mitochondria with disrupted cristae, luminal surfaces with short and
    abnormally branched microvilli or devoid of microvilli, and abnormal
    cytoplasmic processes into the lumen (Kasza et al., 1978b).

    e) Kidney

         In most studies using rodents (Sleight & Sanger, 1976; Waritz
    et al; 1977; Harris et al., 1978a,b; Gupta et al., 1981; Render
    et al., 1982; Ecobichon et al., 1983; Smith et al., 1986), kidney
    weights did not change with PBB exposure (Tables 74 and 75).
    Increases in kidney weights were caused by FireMaster(R) in minks
    (Aulerich & Ringer, 1979) pigs (Ku et al., 1978), and cattle
    (Moorhead et al., 1977), and by octabromobiphenyl in rats (Norris
    et al., 1973). A single study reported a decrease in kidney weight
    in rats fed FireMaster(R) BP-6 (Garthoff et al., 1977).

         In cattle, kidneys were severely affected, and doubled in size
    in animals that were moribund from high doses of FireMaster(R)
    (Moorhead et al., 1977). The kidneys were distended with fluid, and
    pale tan to gray in colour. Perirenal lymph nodes were enlarged and
    oedematous. The principal histological lesions consisted of
    dilatation of collecting ducts and convoluted tubules, and tubular
    epithelial degenerative changes (Moorhead et al., 1977). Similar
    renal lesions were found in calves treated with different doses of
    FireMaster(R) (0.1-100 mg FM FF-1/kg body weight per day, for 2-12
    weeks). The severity of renal damage was related to dose level and
    length of exposure (Robl et al., 1978).  Despite the extensive
    morphological damage, effective renal plasma flow rates and
    glomerular filtration rates were not affected in cows (Mercer
    et al., 1978; Schanbacher et al., 1978).

         Ultrastructural analysis of kidneys of rats and mice given a
    single i.p. injection of 150 mg "PBB" (not specified)/kg body weight
    revealed proliferation of SER and increased numbers of peroxisomes
    in the proximal tubule of the rat, 15 days after dosing.
    Proliferation of SER was confined to only one segment (S3) of the
    proximal tubule. Mice had only marginal increases in SER and no
    significant increases in peroxisomes (Rush et al., 1986).

    f) Stomach

         Biopsies of the stomachs of two rhesus monkeys given
    FireMaster(R) FF-1 (25 mg/kg diet) were made at 12 weeks. In the
    gastric mucosa, there was evidence of early epithelial hyperplasia
    and penetration of the submucosa by glandular epithelium (Allen
    et al., 1978).

    g) Testicle

         Changes in the weights of the testes due to PBB exposure (see
    Tables 74 and 75) were not found in rats (Norris et al., 1973;
    Garthoff et al., 1977; Harris et al., 1978b; Gupta et al., 1981;
    Castracane et al., 1982) and mice (Corbett et al., 1978a; Gupta
    et al., 1981). The results of studies on chickens (Ringer & Polin,
    1977; Ringer, 1978; Dharma et al., 1982) were inconsistent (see
    Table 75).

         Histologically, treatment-associated changes (e.g.,
    hypospermatogenesis) were observed in the testes of male calves
    administered FireMaster(R) FF-1 (0.1-100 mg/kg body weight per
    day) for 2-12 weeks (Robl et al., 1978). Chickens fed
    FireMaster(R) (50 mg/kg of feed) showed lipid infiltration into
    the testicular parenchyma (Ringer & Polin, 1977).

    h) Fluid accumulation

         The presence of fluid accumulation, i.e., hydropericardium and
    ascites, was noted in chickens (Heinemann & Ringer, 1976; Ringer,
    1978). This lesion is known as "chick oedema disease" (McConnell,
    1980). Oedema were observed also in the skin of rhesus monkeys
    (Allen et al., 1978) and in the kidney, perirenal lymph nodes, and
    the gastrointestinal tract of cattle (Moorhead et al., 1978) that
    were lethally intoxicated.

         Occasionally, weight changes in organs other than those
    discussed above have been reported (see Tables 74 and 75, but they
    appear to be of minor importance.

         Some special effects occuring after single or short-term
    exposure to PBBs are reviewed in the respective sections.

    8.2.2  Individual PBB congeners and comparative studies

         A lot of individual PBB congeners have been examined for
    prominent general signs of toxicity, such as changes in body and
    relative organ weights (see Tables 76 and 77) and for histopatho
    logical changes (see Tables 78 and 79). It is evident from these
    records that individual PBB congeners differ in their pattern of
    toxicity. The more toxic isomers and congeners cause a decrease in
    thymus and/or body weight and produce pronounced histological
    changes in the liver and thymus. Despite variations in experimental
    protocols, a tendency can be seen that the most severe effects are
    elicited by congeners listed under category I. The relative severity
    of damage decreases in categories II and III with the least effects
    in the last group. Within a category, the degree of bromination may
    also influence toxicity. Categorization of halogenated biphenyls has

    been made on a structural basis (Parkinson et al., 1983; Safe,
    1984). Category I comprises isomers and congeners lacking
     ortho-substituents. They are referred to as coplanar PBBs.
    Mono- ortho-substituted derivatives constitute the second category.
    Other PBBs (mainly those with two or more  ortho-bromines) have
    been organized into the third category. Structure-activity
    relationships are discussed in detail by several authors (e.g.,
    Goldstein, 1979; Parkinson et al., 1983; Safe, 1984). 

         Orders of toxicity derived from comparative studies included
    only a limited number of congeners in any given study, but they
    agreed with the trends described above. Ecobichon et al. (1979)
    evaluated ultrastructural effects of lower and higher brominated
    congeners on hepatocytes of rats and showed that the highly
    brominated congeners (tetra-, penta-, hexa-, octabromobiphenyls)
    were more active than the low bromine-containing congeners (di-,
    tribromobiphenyls). Results of comparative studies dealing with
    higher brominated isomers and congeners, predominantly constituents
    of the FireMaster(R)-mixture, and the mixture itself have been
    summarized in Table 80.

         In all combinations tested, 3,3',4,4',5,5'-hexabromobiphenyl
    (BB 169) was found to be the most toxic PBB. This congener, only a
    very minor constituent of FireMaster(R), resembles 2,3,7,8-tetra
    chlorodibenzo- p-dioxin (TCDD), the typical and the most toxic
    member of the class of polyhalogenated hydrocarbons (e.g., Poland &
    Knutson, 1982). Of the major FireMaster(R) constituents,
    2,3,3',4,4',5-hexabromobiphenyl (BB 156) appeared to be the most
    toxic, followed by 2,3',4,4',5,5'-hexabromobiphenyl (BB 167) and
    2,3',4,4',5-pentabromobiphenyl (BB 118). The main component of the
    FireMaster(R)-mixture, 2,2',4,4',5,5'-hexabromobiphenyl (BB 153)
    was relatively nontoxic as well as the second most abundant
    constituent, 2,2',3,4,4',5,5'-heptabromobiphenyl (BB 180). Compared
    with the mixture itself, 3,3',4,4',5,5'-hexabromobiphenyl (BB 169)
    was consistently more toxic than FireMaster(R) and
    2,2',4,4',5,5'-hexabromobiphenyl (BB 153) less toxic. With
    2,3',4,4',5,5'-hexabromobiphenyl (BB 167), different results were
    obtained from a dosing study (Dannan et al., 1978a) and two feeding
    studies (Akoso et al., 1982a,b; Dharma et al., 1982). The latter
    attributed FireMaster(R) a higher toxicity than 2,3',4,4',5,5'-
    hexabromobiphenyl (BB 167); 2,2',4,5,5'-pentabromobiphenyl (BB 101)
    was less effective in producing adverse effects than
    2,3',4,4',5-pentabromobiphenyl (BB 118), which matched
    FireMaster(R) in some aspects (see Table 80).

    
    Table 76.  Effect of individual PBB congeners on body weight (or body weight gain) and relative organ weights of mice
    and rats (dosing studies)

    PBB congener           Dosea  Species         Sex    Exposureb                           Weight changesc in:             References
                                  (strain)               (solvent)
                                  (No.)                                                 Body        Liver        Thymus

    Categoryd I PBBs ("Coplanar" congeners)

    4,4'-di                       rat (Wistar)    male   intraperitoneal 3 doses        --          no effect    --          Ecobichon
                           600    (4-6)                  (days 1,2,3) (peanut oil)                                           et al. (1979)
                                                         t.p.: 7 dayse

    3,4,4',tri                    rat (Long       male   intraperitoneal single         no effect   increased    no effect   Parkinson et al.
                           250    Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    3,4,4'-tri                    rat (Wistar)    male   intraperitoneal 2 doses        --          increased    reduced     Robertson et al.
                           300    (3)                    (days 1,3) (corn oil)                                               (1982b)
                                                         t.p.: 5 dayse

    3,4,4',5-tetra                rat (Long       male   intraperitoneal single         reduced     increased    reduced     Parkinson et al.
                           250    Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    3,4,4',5-tetra                rat (Wistar)    male   intraperitoneal 2 doses        --          increased    reduced     Robertson et al.
                           60     (4)                    (days 1,3) (corn oil)                                               (1982)
                                                         t.p.: 5 dayse

    3,3',4,4'-tetra               rat (Sprague-   male   oral single dose (corn         no effect   no effect    (reduced)f  Millis et al.
                           21.3   Dawley) (3)            oil) t.p.: up to 14 days                                            (1985b)

    Table 76 (contd).

    PBB congener           Dosea  Species         Sex    Exposureb                           Weight changesc in:             References
                                  (strain)               (solvent)
                                  (No.)                                                 Body        Liver        Thymus

    3,3',4,4'-tetra               rat (Long       male   intraperitoneal single         no effect   increased    reduced     Parkinson et al.
                           250    Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    3,3',4,4'-tetra               rat (Wistar)    male   intraperitoneal single         reduced     increased    reduced     Andres et al.
                           150    (4-5)                  dose (corn oil)                                                     (1983);
                                                         t.p.: 2 weeks                                                       Robertson
                                                                                                                             et al. (1983b)

    3,3',4,4'-tetra               rat (Sprague-   male   intraperitoneal single         no effect   increased    no effect   Millis et al.
                           4.25g  Dawley) (6)            dose (polyethylene glycol)                                          (1985a)
                                                         t.p.: 2 weeks

    3,3',4,4'-tetra               rat (Wistar)    male   intraperitoneal 2 doses        --          increased    reduced     Robertson et al.
                           60     (4)                    (days 1,3) (corn oil)                                               (1982b)
                                                         t.p.: 5 dayse

    3,3',4,4'-tetra               mouse           male   intraperitoneal single         no effect   increased    reduced     Robertson et al.
                                  (C57BL/6J              dose (corn oil)                                                     (1984c)
                           1500   and DBA/2J)            t.p.: 5 days
                                  (10)

    3,3',4,4',5-penta             rat (Long       male   intraperitoneal single         reduced     increased    reduced     Parkinson et al.
                           100    Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    3,3',4,4',5-penta             rat (Wistar)    male   intraperitoneal 2 doses        --          increased    reduced     Robertson et al.
                           60     (4)                    (days 1,3) (corn oil)                                               (1982b)
                                                         t.p.: 5 dayse

    Table 76 (contd).

    PBB congener           Dosea  Species         Sex    Exposureb                           Weight changesc in:             References
                                  (strain)               (solvent)
                                  (No.)                                                 Body       Liver         Thymus

    3,3',4,4',5,5'-hexa           rat (Sprague-   male   oral single dose (corn         no effect  (increased)f  (reduced)f  Millis et al.
                           21.3   Dawley) (3)            oil) t.p.: up to 14 days                                            (1985b)

    3,3',4,4',5,5'-hexa           rat (Long       male   intraperitoneal single         reduced    increased     reduced     Parkinson et al.
                           100    Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    3,3',4,4',5,5'-hexa           rat (Sprague-   male   intraperitoneal single         no effect  increased     no effect   Millis et al.
                           3.19g  Dawley) (6)            dose (polyethylene glycol)                                          (1985a)
                                                         t.p.: 2 weeks

    3,3',4,4',5,5'-hexa           rat (Wistar)    male   intraperitoneal 2 doses        --         increased     reduced     Robertson et al.
                           60     (4)                    (days 1,3) (corn oil)                                               (1982b)
                                                         t.p.: 5 dayse

    3,3',4,4',5,5'-hexa           rat (Wistar)    male   intraperitoneal 3 doses        --         increased     --          Ecobichon et al.
                           600    (4-6)                  (days 1,2,3) t.p.: 7 daysd                                          (1979)

    Category II PBBs (Monoortho "coplanar" derivatives)

    2,3',4,4'-tetra               rat (Long       male   intraperitoneal single         no effect  no effect     no effect   Parkinson et al.
                           250    Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    2,3',4,4'-tetra               mouse           male   intraperitoneal single                                              Robertson et al.
                           1500                          dose (corn oil)                                                     (1984c)
                                                         t.p.: 5 days

    Table 76 (contd).

    PBB congener          Dosea   Species         Sex    Exposureb                           Weight changesc in:             References
                                  (strain)               (solvent)
                                  (No.)                                                 Body       Liver         Thymus

                                  (C57BL/6J)                                            no effect  no effect     no effect
                                  (5)
                                  (DBA/2J)                                              no effect  increased     no effect
                                  (5)

    2,3',4,4',5-penta             rat (Long       male   intraperitoneal single         no effect  increased     no effect   Parkinson et al.
                          250     Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    2,3',4,4',5-penta             rat (Sprague-   male   intraperitoneal single         reduced    increased     reduced     Dannan et al.
                                  Dawley) (6)            dose (polyethylene glycol)                                          (1982c)
                          164g                           t.p.: 2 weeks                  no effect  increased     no effect   Millis et al.
                                                                                                                             (1985a)

    2,3',4,4',5,5'-hexa           rat (Sprague-   male   intraperitoneal single         reduced    increased     (reduced)f  Dannan et al.
                          144g    Dawley) (4)            dose (polyethylene glycol)                                          (1978a)
                                                         t.p.: 7 days

    2,3,3',4,4',5-hexa            rat (Sprague-   male   intraperitoneal 2 doses        reduced    increased     reduced     Dannan et al.
                          144g    Dawley) (4)            dose (polyethylene glycol)                                          (1982a)
                                                         t.p.: 7 days

    2,3,3',4,4',5-hexa            rat (Wistar)    male   intraperitoneal 2 doses        --         no effect     --          Robertson et al.
                          3.8-60  (1-4)                  (days 1,3) (corn oil)                                               (1981a)
                                                         t.p.: 5 dayse

    2,3,3',4,4',5'-hexa           rat (Long       male   intraperitoneal single         no effect  no effect     no effect   Parkinson et al.
                          100     Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    Table 76 (contd).

    PBB congener          Dosea   Species         Sex    Exposureb                           Weight changesc in:             References
                                  (strain)               (solvent)
                                  (No.)                                                 Body       Liver         Thymus

    Category III PBBs (Others)

    4-mono                        rat (Wistar)    male   intraperitoneal 3 doses        --         no effect     --          Ecobichon et al.
                          600     (4-6)                  (day 1,2,3) (peanut oil)                                            (1979)
                                                         t.p.: 7 dayse

    2,2'-di                       rat (Sprague-   male   intraperitoneal single         --         no effect     --          Moore et al.
                          289g    Dawley) (3)            dose (polyethylene glycol)                                          (1979a)
                                                         t.p.: 2-22 days

    2,2'-di                       rat (Wistar)    male   intraperitoneal 3 doses        --         no effect     --          Ecobichon et al.
                          600     (4-6)                  (days 1,2,3) (peanut oil)                                           (1979)
                                                         t.p.: 7 dayse

    2,5'-di                       rat (Wistar)    male   intraperitoneal 3 doses        --         no effect     --
                          600     (4-6)                  (days 1,2,3) (peanut oil)
                                                         t.p.: 7 dayse

    2,2'5-tri                     rat (Wistar)    male   intraperitoneal 3 doses        --         no effect     --
                          600     (4-6)                  (days 1,2,3) (peanut oil)
                                                         t.p.: 7 dayse

    2,3',5-tri                    rat (Wistar)    male   intraperitoneal 3 doses        --         no effect     --
                          600     (4-6)                  (peanut oil) t.p.: 7 dayse

    2,4,6-tri                     rat (Wistar)    male   intraperitoneal 3 doses        --         no effect     --          Ecobichon et al.
                          600     (4-6)                  (peanut oil) t.p.: 7 dayse                                          (1979)

    2,4',5-tri                    rat (Wistar)    male   intraperitoneal 3 doses        --         increased     --
                          600     (4-6)                  (peanut oil) t.p.: 7 dayse

    Table 76 (contd).

    PBB congener          Dosea   Species         Sex    Exposureb                           Weight changesc in:             References
                                  (strain)               (solvent)
                                  (No.)                                                 Body       Liver         Thymus

    3,3',5,5'-tetra               rat (Wistar)    male   intraperitoneal 3 doses        --         increased     --
                          600     (4-6)                  (peanut oil) t.p.: 7 dayse

    2,3',4'5-tetra                rat (Wistar)    male   intraperitoneal 2 doses        --         no effect     --          Robertson et al.
                          150     (4)                    (days 1,3) (corn oil)                                               (1980)
                                                         t.p.: 5 dayse

    2,2',5,5'-tetra               rat (Long       male   intraperitoneal single         no effect  increased     no effect   Parkinson et al.
                          500     Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    2,2',5,5'-tetra               rat (Wistar)    male   intraperitoneal 3 doses        --         increased     --          Ecobichon et al.
                          600     (4-6)                  (peanut oil) t.p.: 7 dayse                                          (1979)

    2,4,4',6-tetra                rat (Long       male   intraperitoneal single         no effect  no effect     no effect   Parkinson et al.
                          500     Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    2,2',4,5',6-penta             rat (Wistar)    male   intraperitoneal 3 doses        --         increased     --          Ecobichon et al.
                          600     (4-6)                  (days 1,2,3) (peanut oil)                                           (1979)
                                                         t.p.: 7 dayse

    2,3',4,4',6-penta             rat (Long       male   intraperitoneal single         no effect  no effect     no effect   Parkinson et al.
                          500     Evans) (3)             dose (corn oil)                                                     (1983)
                                                         t.p.: 4 days

    2,2',4,5,5'-penta             rat (Long       male   intraperitoneal single         no effect  increased     no effect
                          500     Evans) (3)             dose (corn oil)
                                                         t.p.: 4 days

    Table 76 (contd).

    PBB congener          Dosea   Species         Sex     Exposureb                          Weight changesc in:             References
                                  (strain)                (solvent)
                                  (No.)                                                 Body       Liver         Thymus

    2,2',4,5,5'-penta             rat (Sprague-   male    intraperitoneal single        no effect  no effect     no effect   Dannan et al.
                          164g    Dawley) (4)             dose (polyethylene glycol)                                         (1982a)
                                                          t.p.: 7 days
                                  (6)                     t.p.: 14 days                 no effect  increased     no effect   Millis et al.
                                                                                                                             (1985a)

    2,2',3,4,4',5'-hexa           rat (Sprague-   male    intraperitoneal single        no effect  increased     no effect   Dannan et al.
                          144g    Dawley) (4)             dose (polyethylene glycol)                                         (1982a)
                                                          t.p.: 7 days

    2,2',4,4',6,6'-hexa           rat (Wistar)    male    intraperitoneal 3 doses       --         increased     --          Ecobichon et al.
                          600     (4-6)                   (days 1,2,3) (peanut oil)                                          (1979)
                                                          t.p.: 7 dayse

    2,2',4,4',5,5'-hexa           rat (Fischer    male,   oral 22 doses (over           no effect  increased     no effect   Gupta et al.
                          590g    344/N) (6)      female  30 days) (corn oil)                                                (1981)
                                                          t.p.: 15, 30, 45, 60,
                                                          90 dayse

    2,2',4,4',5,5'-hexa           rat (Fischer)   female  intraperitoneal single                                             Goldstein et al.
                                  (4)                     dose (corn oil)                                                    (1979)
                                                          t.p.: 4 days
                          40                                                            no effect  no effect     --
                          200,                                                          no effect  (increased)f  --
                          1000

    2,2',4,4',5,5'-hexa           rat (Long       male    intraperitoneal single        no effect  increased     no effect   Parkinson et al.
                          500     Evans) (3)              dose (corn oil)                                                    (1983)
                                                          t.p.: 4 days

    Table 76 (contd).

    PBB congener             Dosea   Species         Sex     Exposureb                         Weight changesc in:            References
                                     (strain)                (solvent)
                                     (No.)                                                Body        Liver       Thymus

    2,2',4,4',5,5'-hexa              rat (Sprague-   male    intraperitoneal single       no effect   increased   no effect   Moore et al.
                             144g    Dawley) (6)             dose (polyethylene glycol)                                       (1978b); Millis
                                                             t.p.: 2 weeks                                                    et al. (1985a)

    2,2',4,4',5,5'-hexa              rat (Wistar)    male    intraperitoneal 3 doses      --          increased   --          Ecobichon et al.
                             600     (4-6)                   (days 1,2,3) (peanut oil)                                        (1979)
                                                             t.p.: 7 dayse

    2,2',4,4',5,5'-hexa              mouse           male,   oral 22 doses (over          no effect   increased   no effect   Gupta et al.
                             590g    (B6C3F1/N)      female  30 days) (corn oil)                                              (1981)
                                     (6)                     t.p.: 15, 30, 45, 69,
                                                             90 dayse

    2,2',3,3',4,4'5-hepta    rat     (Sprague-       male    intraperitoneal single       no effect   increased   no effect   Dannan et al.
                             127g    Dawley) (4)             dose (polyethylene glycol)                                       (1982a)
                                                             t.p.: 7 days

    2,2',3,4,4',5,5'-hepta   rat     (Sprague-       male    intraperitoneal single       --          increased   --          Moore et al.
                             127g    Dawley) (3)             dose (polyethylene glycol)                                       (1979a)
                                                             t.p.: up to 22 days

    2,3,3',4,4',5,6-hepta    rat     (Wistar)        male    intraperitoneal 2 doses      --          no effect   --          Robertson et al.
                             6       (2)                     (days 1,3) (corn oil)                                            (1981a)
                                                             t.p.: 5 dayse

    2,2',3,3',4,4',5,5'-     rat     (not            male    intraperitoneal single       --          increased   --          Besaw et al.
    octa                     115g    specified)              dose (solvent not                                                (1978)
                                                             specified) t.p.: 7 days

    Table 76 (contd).

    a    Total dose in µmol/kg body weight.
    b    t.p. = Time post-exposure; --  = data not given.
    c    Only statistically significant changes; organ weight changes relative to body weight.
    d    Categorization according to Safe (1984); see also text in section 8.2.2.
    e    After first dose.
    f    Only absolute data given.
    g    Calculated from original value given in mg/kg body weight.

    Table 77.  Effect of various hexabromobiphenyl isomers on feed intake, body weight (or body weight gain)
    and (relative) organ weights (feeding studies)

    PBB congener      Species     Sex     Dietary        Feeding     Food            Effects                                          References
                      (strain)            concentration  period      intake      Weight changesa
                      (No.)               (mg/kg feed)   (days)c     Body       Liver      Thymus      Other organs

    Categoryb I PBBs

    3,3',4,4',5,5'-   rat         male    10             30          reduced    reduced    increased   reduced    spleen: reduced     Akoso et
    hexa              (Sprague-                                                                                   brain: no effect    (1982a,b)
                      Dawley)                                                                                     thyroid:
                      (6)                                                                                         increased

                      rat         male    1              9           no effect  no effect  no effect                                  Render
                      (Sprague-           10             9           reduced    reduced    increased   reduced                        et al.
                      Dawley)             100            9           reduced    reduced    increased   reduced                        (1982)
                      (6)
                      (2)                 100            20          refused
                                                                     (day 16)
    Category II PBBs

    2,3',4,4',5,5'-   rat         male    1, 10          30          no effect  no effect  no effect   no effect  brain: increased    Akoso
    hexa              (Sprague-                                                                                   thyroid: no effect  et al.
                      Dawley)             100            30          no effect  no effect  increased   no effect  brain: increased    (1982a,b)
                      (6)                                                                                         thyroid: no effect

                      cockerel    male    4, 10          28          no effect  no effect  no effect              bursa of            Dharma
                      (White                                                                                      Fabricius,          et al.
                      Leghorn)                                                                                    thyroid, spleen,    (1982)
                      (10)                                                                                        testicles, comb:
                                                                                                                  no effect

    Table 77 (contd).

    PBB congener      Species     Sex     Dietary        Feeding     Food            Effects                                          References
                      (strain)            concentration  period      intake      Weight changesa
                      (No.)               (mg/kg feed)   (days)c     Body       Liver      Thymus      Other organs

    Category III PBBs

    2,2',4,4',5,5'-   rat         male    1              30          no effect  no effect  increased   no effect  brain: increased    Akoso
    hexa              (Sprague-                                                                                   thyroid: no         et al.
                      Dawley)                                                                                     effect              (1982a,b)
                      (6)
                      (6)                 10, 100        30          no effect  no effect  increased   increased  brain: increased
                                                                                                                  thyroid: no
                                                                                                                  effect

                      rat         male    10             9           increased  no effect  increased   n.r.       kidney: no          Render
                      (Sprague-                                                                                   effect              et al.
                      Dawley)             100            9           no effect  no effect  increased   n.r.       kidney: no          (1982)
                      (6)                                                                                         effect

                      mouse       female  100, 300       gd 6        no effect  no effect  increased   n.r.                           Welsch &
                      (C57 BL),                          through                                                                      Morgan
                      pregnant                           15                                                                           (1985)
                      (3)                 500, 750       sacrifice   no effect  reduced    increased   n.r.
                                                         gd 17
                                          1000                       reduced    reduced    increased   n.r.

                      cockerel    male    10             28          no effect  no effect  no effect   n.r.       bursa of Fabri-     Dharma et al.
                      (White                                                                                      cius, thyroid,      (1982)
                      Leghorn)            62             28          no effect  no effect  increased   n.r.       spleen, testicles,
                      (10)                                                                                        comb, no effect
                                                                                                                  (both concen-
                                                                                                                  trations)

    Table 77 (contd).

    a    Only statistically significant changes; organ weight changes relative to body weight except for Render et al.
         (1982) giving absolute data.
    b    Categorization according to Safe (1984); see also text in section 8.2.2.
    c    gd = Gestation day.
    d    n.r. = Not recorded.

    Table 78.  Histopathology in relation to individual PBB congeners (dosing studies)

    PBB congener        Species         Sex      Exposurec                 Doseb          Histopathological effectsf     References
                        (strain) (No.)                                                 Liver    Thymus   Other organs

    Categorya I PBBs

    4,4'-di             rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.            Ecobichon et al.
                        (6)                      t.p.: 7 daysd                                                           (1977)

    3,3',4,4'-tetra     rat (Sprague-   male     oral single dose          21.3        +        ++       8 tissues:      Millis et al.
                        Dawley) (3)              t.p.: up to 14 days                                     0               (1985b)

                        rat (Sprague-   male     intraperitoneal single    4.25e       +        0        11 tissues:     Millis et al.
                        Dawley) (6)              dose t.p.: 2 weeks                                      0               (1985a)

                        rat (Wistar)    male     intraperitoneal single    150         +        ++       spleen,         Andres et al.
                        (4)                      dose t.p.: 2 weeks                                      kidney: 0       (1983); Robertson
                                                                                                                         et al. (1983b)

    3,3',4,4',5,5'-     rat (Sprague-   male     oral single dose          21.3        ++       ++       8 tissues:      Millis et al.
    hexa                Dawley) (3)              t.p.: up to 14 days                                     0               (1985b)

                        rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.            Ecobichon et al.
                        (4-6)                    t.p.: 7 daysd                                                           (1979)

    Categorya II PBBs

    2,3',4,4',5-penta   rat (Sprague-   male     intraperitoneal single    164e        +        0        9-11            Dannan et al.
                        Dawley) (6)              dose t.p.: 2 weeks                                      tissues: 0      (1982c); Millis
                                                                                                                         et al. (1985a)

    2,3',4,4',5,5'-     rat (Sprague-   male     intraperitoneal single    144e        ++       n.r.     9 tissues:      Dannan et al.
    hexa                Dawley) (4)              dose t.p.: 1 week                                       0               (1982a)

    Table 78 (contd).

    PBB congener        Species         Sex      Exposurec                 Doseb          Histopathological effectsf     References
                        (strain) (No.)                                                 Liver    Thymus   Other organs

    2,3,3',4,4',5-      rat (Sprague-   male     intraperitoneal single    144e        ++       ++       9 tissues:
    hexa                Dawley) (4)              dose t.p.: 1 week                                       0

    Categorya III PBBs

    4-mono              rat (Wistar)    male     intraperitoneal 3 doses   600         0        n.r.     n.r.            Ecobichon et al.
                        (4-6)                    t.p.: 7 daysd                                                           (1979)

    2,2'-di             rat (Sprague-   male     intraperitoneal single    289e        0        0        8 tissues:      Moore et al.
                        Dawley) (3)              dose t.p.: up to 22 days                                0               (1979a)

    2,5'-di             rat (Wistar)    male     intraperitoneal 3 doses   600         0        n.r.     n.r.            Ecobichon et al.
                        (4-6)                    t.p.: 7 daysd                                                           (1979)

    2,2',5-tri          rat (Wistar)    male     intraperitoneal 3 doses   600         0        n.r.     n.r.            Ecobichon et al.
                        (4-6)                    t.p.: 7 daysd                                                           (1979)

    2,3',5-tri          rat (Wistar)    male     intraperitoneal 3 doses   600         0        n.r.     n.r.
                        (4-6)                    t.p.: 7 daysd

    2,4,6-tri           rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.
                        (4-6)                    t.p.: 7 daysd

    2,4',5-tri          rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.
                        (4-6)                    t.p.: 7 daysd

    3,3',5,5'-tetra     rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.
                        (4-6)                    t.p.: 7 daysd

    2,2',5,5'-tetra     rat (Wistar)    male     intraperitoneal single    150         +        0        spleen,         Robertson et al.
                        (not specified)          dose t.p.: 2 weeks                                      kidney: 0       (1983b)

    Table 78 (contd).

    PBB congener        Species         Sex      Exposurec                 Doseb          Histopathological effectsf     References
                        (strain) (No.)                                                 Liver    Thymus   Other organs

                        rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.            Ecobichon et al.
                        (4-6)                    t.p.: 7 daysd                                                           (1979)

    2,2',4,5',6-penta   rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.            Ecobichon et al.
                        (4-6)                    t.p.: 7 daysd                                                           (1979)

    2,2',4,5,5'-penta   rat (Sprague-   male     intraperitoneal single    164e        +        0        9-11            Dannan et al.
                        Dawley)                  dose t.p.: 1-2 weeks                                    tissues: 0      (1982a); Millis
                        (4-6)                                                                                            et al. (1985a)

    2,2',3,4,4',5'-     rat (Sprague-   male     intraperitoneal single    144e        +        0        9 tissues:      Dannan et al.
    hexa                Dawley) (4)              dose t.p.: 1 week                                       0               (1982a)

    2,2',4,4',5,5'-     rat (Fischer    male,    oral 22 doses             1052e       +        0        16 tissues:     Gupta et al.
    hexa                344/N)          female   t.p.: up to 90 daysd                  0                 0               (1981)

    2,2',4,4',5,5'-     rat (Fischer)   male     intraperitoneal single    200-1000    +        n.r.     n.r.            Goldstein et al.
    hexa                (4)                      dose t.p.: 4 days                                                       (1979)

                        rat (Sprague-   male     intraperitoneal single    144e        +        0        8-11            Moore et al.
                        Dawley)                  dose t.p.: up to 14 days                                tissues: 0      (1978b); Millis
                        (3-6)                                                                                            et al. (1985a)

                        rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.            Ecobichon et al.
                        (4-6)                    t.p.: 7 daysd                                                           (1979)

    2,2',4,4',6,6'-     rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.
    hexa                (4-6)                    t.p.: 7 daysd

    Table 78 (contd).

    PBB congener        Species         Sex      Exposurec                 Doseb         Histopathological effectsf      References
                        (strain) (No.)                                                 Liver    Thymus   Other organs

    2,2',3,3',4,4',5-   rat (Sprague-   male     intraperitoneal single    127e        +        0        9 tissues:      Dannan et al.
    hepta               Dawley) (4)              dose t.p.: 1 week                                       0               (1982a)

    2,2',3,4,4',5,5'-   rat (Sprague-   male     intraperitoneal single    127e        +        0        8 tissues:      Moore et al.
    hepta               Dawley) (3)              dose t.p.: up to 22 days                                0               (1979a)

    2,2',3,3',4,4',     rat (not        male     intraperitoneal single    115e        +        0        several         Besaw et al.
    5,5'-octa           specified)               dose t.p.: 7 days                                       tissues: 0      (1978)
                        rat (Wistar)    male     intraperitoneal 3 doses   600         +        n.r.     n.r.            Ecobichon et al.
                        (4-6)                    t.p.: 7 daysd                                                           (1979)

    a    Categorization according to Safe (1984); see also text in section 8.2.2.
    b    Total dose in µmol/kg body weight.
    c    t.p. = Time post-exposure.
    d    After first dose.
    e    Calculated from original value given in mg/kg body weight.
    f    n.r. = Not recorded; 0 = Lesion not observed; + = Lesion observed (number of "+" denote severity).

    Table 79.  Histopathology to individual PBB congeners (feeding studies)

    PBB congener            Species           Sex      Dietary          Feeding     Histopathological effectsb            References
                            (strain)                   concentration    period
                            (No.)                      (mg/kg feed)     (days)      Liver    Thymus     Other organs

    Categorya I PBBs

    3,3',4,4',5,5'-         rat (Sprague-     male     1                10          +        0                            Render et al. (1982)
    hexa                    Dawley) (6)                10               10          ++       ++
                                                       100              10          ++       ++         spleen, lymph
                                                                                                        nodes: +

                            rat (Sprague-     male     1                30          +        0          thyroid: +        Akoso et al.
                            Dawley) (6)                10               30          ++       ++         thyroid,          (1982a,b)
                                                                                                        pituitary
                                                                                                        gland: +

    Categorya II PBBs

    2,3',4,4',5,5'-         rat (Sprague-     male     1, 10, 100       30          +        0          thyroid: +
    hexa                    Dawley) (6)

                            cockerels         male     10               28          +        n.r.       bursa of          Dharma et al. (1982)
                            (White Leghorn)                             Fabricius: +
                            (10)

    Categorya III PBBs

    2,2',4,4',5,5'-         rat (Sprague-     male     10, 100          10          +        0          18 tissues: 0     Render et al. (1982)
    hexa                    Dawley) (6)

                            rat (Sprague-     male     1, 10, 100       30          +        0          thyroid: +        Akoso et al.
                            Dawley) (6)                                                                                   (1982a,b)

    Table 79 (cont'd).

    PBB congener            Species           Sex      Dietary          Feeding     Histopathological effectsb            References
                            (strain)                   concentration    period
                            (No.)                      (mg/kg feed)     (days)      Liver    Thymus     Other organs

                            cockerel          male     4, 10            28          0        n.r.       bursa of          Dharma et al. (1982)
                            (White Leghorn)                                                             Fabricius: 0
                            (10)                       62               28          +        n.r.       bursa of
                                                                                                        Fabricius: +

    a    Categorization according to Safe (1984); see also text in section 8.2.2.
    b    n.r. = Not recorded; 0 = Lesion not observed; + = Lesion observed (number of "+" denote severity).

         Dannan et al. (1982b) recombined 9 purified FireMaster(R)
    constituents, namely BB 101 (2,2',4,5,5'-penta-,) BB 118
    (2,3',4,4',5-penta-), BB 153 (2,2',4,4',5,5'-hexa-), BB 138
    (2,2',3,4,4',5'-hexa-), BB 167 (2,3',4,4',5,5'-hexa), BB 156
    (2,3,3',4,4',5-hexa-), BB 180 (2,2',3,4,4',5,5'-hepta-), BB 170
    (2,2',3,3',4,4',5-hepta-), and BB 194 (2,2',3,3',4,4',5,5'-
    octabromobiphenyl), totalling 97% of either FireMaster(R) mixture,
    to form a reconstituted FireMaster(R) BP-6-like mixture and
    compared some effects of the reconstituted mixture to those of crude
    FireMaster(R) mixtures BP-6 and FF-1. Rats were treated with a
    single dose (90 mg/kg body weight of either mixture) and sacrificed
    one week later. Evaluating changes in body and selected organ
    (liver, thymus, spleen) weights, the conclusion was reached that
    adverse effects of FireMaster(R) (FF-1 or BP-6) must be due to the
    effects of the congeners studied. Moreover, it was found that the
    increase in liver weights was greater with FM BP-6 and the
    reconstituted mixture than with FM FF-1, consistent with the higher
    proportion of minor components (BBs: 118, 138, 167, 156) in FM BP-6
    (25% versus 15%).

         Differences in toxicity between PBBs were sometimes of a
    qualitative kind, but mostly they were quantitative. Some striking
    relations will be reviewed in detail according to the parameter
    tested.

    8.2.2.1  Food intake, overt clinical signs, body weight changes

         So far, in the congeners tested, food intake of rats was
    reduced only by 3,3'4,4',5,5'-hexabromobiphenyl (Table 77: Akoso
    et al., 1982a; Render et al., 1982). The effective dietary
    concentrations ranged from 1 to 100 mg/kg. A much higher
    concentration of 2,2',4,4',5,5'-hexabromobiphenyl (1000 mg/kg of
    feed) was needed to evoke reduction in the food consumption of mice
    (Table 77: Welsch & Morgan, 1985).

         Rats, moribund from 3,3',4,4',5,5'-hexabromobiphenyl treatment,
    had symptoms similar to those observed with FireMaster(R)
    toxicosis (see section 8.2.1.1). They became less active, had a
    roughened hair coat, developed sunken eyes, and were emaciated
    (Render et al., 1982).

         3,3',4,4',5,5'-Hexabromobiphenyl significantly decreased body
    weight (Render et al., 1982) or body weight gain (Akoso et al.,
    1982a) in rats, while the same concentrations of FireMaster(R)
    BP-6, 2,2',4,4',5,5'-hexa- and 2,3',4,4',5,5'-hexabromobiphenyl in
    the diet had no effects. When rats were injected i.p. with identical

    
    Table 80. Order of toxicity of higher brominated PBB congeners and the FireMaster(R) mixture on the basis of comparative studies

    Species    Parameter tested                                      PBBs testeda                              Order of      References
                                           FM    101   118   153   138    167    156    180     170    169     toxicity

    Dosing studies

    Rat        body weight gain            x                              x                                    167 > FM      Dannan et al.
                                                                                                                             (1978a)

    Rat        liver weight and            x                 x                                                 FM > 153      Moore et al.
               histopathology                                                                                                (1978b); Goldstein
                                                                                                                             et al. (1979)

    Rat        liver weight and            x                                            x                      FM > 180      Moore et al.
               histopathology                                                                                                (1979a)

    Rat        body and organ              x                 x                                                 FM > 153      Gupta et al.
    (Mouse)    weights, histopathology                                                                                       (1981)

    Rat        body and organ              x           x                                                       118 > FM      Dannan et al.
               weights, histopathology                                                                                       (1982c)

    Rat        body and organ              x                       x      x      x              x              156 > 167 >   Dannan et al.
               weights, histopathology                                                                         138, 170 >    (1982a)
                                                                                                               101

    Rat        body and organ                          x     x                                         x       169 > 118,    Parkinson et al.
               weights                                                                                         153           (1983)

    Rat        liver histopathology              x     x     x                                                 118, 153 >    Millis et al.
                                                                                                               101           (1985a)

    Table 80 (cont'd)

    Species    Parameter tested                                      PBBs testeda                              Order of      References
                                           FM    101   118   153   138    167    156    180     170    169     toxicity

    Feeding studies

    Rat        death, body and organ       x                 x                                         x       169 > FM      Sleight et al.
               weights, histopathology                                                                         > 153         (1981)

    Rat        feed intake, body and       x                 x            x                            x       169 > FM      Akoso et al.
               organ weights,                                                                                  > 167 > 153   (1982a,b)
               histopathology

    Rat        death, feed intake,         x                 x                                         x       169 > FM,     Render et al.
               body and organ weights,                                                                         153           (1982)
               histopathology

    Cockerel   organ weights,              x                 x            x                                    FM > 167      Dharma et al.
               histopathology                                                                                  > 153         (1982)

    a    FM = FireMaster(R) mixture (BP-6 or FF-1); PPB numbering according to Ballschmiter & Zell (1980):
         101, 118 = pentabromobiphenyls (2,2',4,5,5'-; 2,3',4,4',5-).
         153, 138, 167, 156, 169 = hexabromobiphenyls (2,2',4,4',5,5'-; 2,2',3,4,4',5'-; 2,3',4,4',5,5'-;
         2,3,3',4,4',5-; 3,3', 4,4', 5,5'-).
         180, 170 = heptabromobiphenyls (2,2',3,4,4',5,5'; 2,2',3,3',4,4'5-).

    amounts of several constituents of FireMaster(R) (BBs: 101, 138,
    167, 156, 170), only 2,3',4,4',5,5'-hexabromobiphenyl (BB 167) and
    2,3',4,4',5,5'-hexabromobiphenyl (BB 156) depressed body weight gain
    (Dannan et al., 1978a, 1982a). The body weight gain of rats treated
    with BB 167 was half that of FireMaster(R)-treated animals (Dannan
    et al., 1978a). Rats given BB 118 (2,3',4,4',5-hexabromo biphenyl)
    also gained less weight per day than those given FireMaster(R)
    (Dannan et al., 1982c).

         Liver weights in rats were increased by all treatments with
    congeners of category I, except for 4,4'-dibromobiphenyl. The lowest
    effective dose used was 2 mg/kg body weight (Millis et al., 1985a).
    Significant effects were seen as early as 4 days after dosing (e.g.,
    Parkinson et al., 1983). Many of the congeners listed under
    categories II and III were also capable of increasing liver weights
    (see Tables 76 and 77). Generally, all the changes in organ weights
    were dose-dependent. Gradual differences between congeners were also
    seen. Liver weights were significantly higher in rats given
    3,3',4,4',5,5'-hexabromobiphenyl than the liver weights in
    3,3',4,4'-tetrabromobiphenyl-treated rats, 6 days after a single
    dose (Millis et al., 1985b). In studies comparing the effects of
    five FireMaster(R) constituents (BB 101: 2,2',4,5,5'-penta; BB
    138: 2,2',3,4,4',5'-hexa; BB 167: 2,3',4,4',5,5'-hexa; BB 156:
    2,3,3',4,4',5-hexa; BB 170: 2,2',3,3',4,4',5-hepta), 7 days after
    dosing, 2,3,3',4,4',5-hexabromobiphenyl (BB 156) caused the largest
    increase in liver weights (60% increase) while 2,2',4,5,5'-
    pentabromobiphenyl (BB 101) failed to enlarge this organ. Increases
    caused by FireMaster(R) and BB 167 (2,3',4,4',5,5'-hexa) were
    similar (Dannan et al., 1978a, 1982a). The increases in liver
    weights due to BB 153 (2,2',4,4',5,5'-hexa), the main component of
    FireMaster(R), were far less than the increase in response to
    FireMaster(R), approximately 33% versus 60-80% (Moore et al.,
    1978b; Goldstein et al., 1979).

         Nevertheless, the increase was rapid with a 25% increase within
    two days of treatment (Moore et al., 1978b). The effect of
    2,2',3,4,4',5,5'-heptabromobiphenyl (BB 180), the second most
    abundant component of FireMaster(R), was also less than that
    caused by the mixture itself (Moore et al., 1979a). When
    FireMaster(R) BP-6, 2,3',4,4',5,5'-hexabromobiphenyl (BB 167),
    2,2',4,4',5,5'-hexabromobiphenyl (BB 153), and
    3,3',4,4',5,5'-hexabromobiphenyl (BB 169) were added to the diet of
    rats for 30 days, BB 153 and BB 169 significantly increased liver
    weights at 1 mg/kg, but FireMaster(R) and BB 167 did not. At 100
    mg/kg, FireMaster(R) increased liver weight more than BB 153 or BB
    167 (Akoso et al., 1982a).

         Thymus weights in rodents were decreased by most of the
    treatments with congeners of category I. Among congeners in category
    II, 2,2',4,4',5-pentabromobiphenyl (BB 118),
    2,3',4,4',5,5'-hexabromobiphenyl (BB 167), and
    2,3,3',4,4',5-hexabromobiphenyl (BB 156) were capable of reducing
    thymus weights. Congeners listed under the third category failed to
    reduce thymus weights (see Tables 76 and 77). Both 3,3',4,4'-tetra
    and 3,3',4,4',5,5'-hexabromobiphenyl caused a significant reduction
    in the thymus weights of rats, 3,3',4,4',5,5'-hexabromobiphenyl
    being more effective than 3,3',4,4'-tetrabromobiphenyl (Millis
    et al., 1985b). There was a 50-60% loss in thymic weight in rats
    injected i.p. with BB 167 or BB 156 and sacrificed 7 days later
    (Dannan et al., 1978a, 1982a). However, thymus weight: body weight
    ratios were not significantly affected when rats were fed BB 167 or
    FireMaster(R) BP-6 for 30 days (Akoso et al., 1982a). In the same
    study, 3,3',4,4',5,5'-hexabromobiphenyl (BB 169) significantly
    decreased the ratio, while there was an increase with
    2,2',4,4',5,5'-hexabromobiphenyl (BB 153).

         In cockerels fed FireMaster(R) FF-1, BB 153, or BB 167, for
    28 days, only FireMaster(R) FF-1 reduced relative bursal weights
    (Dharma et al., 1982).

         When young rats were fed diets containing FireMaster(R) BP-6,
    2,2',4,4',5,5'-hexa-, 2,3',4,4',5,5'-hexa-, or 3,3',4,4',5,5'-
    hexabromobiphenyl, for 30 days, thyroid weight was increased only by
    100 mg FireMaster(R) BP-6/kg feed and by 1 and 10 mg
    3,3'4,4',5,5'-hexabromobiphenyl/kg feed (Akoso et al., 1982b).

    8.2.2.2  Haematology and clinical chemistry

         Haematological and clinical chemistry findings were of minor
    importance in comparative studies. Gamma-Glutamyl transpeptidase
    (gamma-GTP) was elevated in female rats at high doses of both
    FireMaster(R) FF-1 (30 mg/kg body weight per day) and
    2,2',4,4',5,5'-hexabromobiphenyl (BB 153) (16.8 mg/kg body weight
    per day) 30 and 60 days after the last dose (Gupta et al., 1981).

    8.2.2.3  Morphological and histopathological changes

         Rats fed diets containing 100 mg FireMaster(R) BP-6/kg or 10
    or 100 mg 3,3',4,4',5,5'-hexabromobiphenyl (BB 169)/kg had friable
    yellow livers (Render et al., 1982). The architectural structure of
    the lobules was abnormal after feeding 3,3',4,4',5,5'-
    hexabromobiphenyl (Akoso et al., 1982a; Millis et al., 1985b), and
    bile duct hyperplasia was observed (Render et al., 1982).

         With the exception of the lower brominated congeners of
    category III, all PBB congeners caused histopathological changes in
    the liver (see Tables 78 and 79). The extent of the changes depended
    on the dose and the individual congener. The least severe effects

    were confined to a slight proliferation of hepatic SER (e.g.,
    4,4'-dibromobiphenyl: Ecobichon et al., 1977). More progressive,
    general changes were enlargement of hepatocytes and increased
    numbers of cytoplasmic lipid vacuoles. Corresponding ultrastructural
    lesions consisted mainly of increased SER and lipid vacuolation (see
    Tables 78 and 79). Additional changes seen with the more toxic
    congeners included myelin body formation (membrane whorls) (BBs:
    118, 167, 156, 169), disorganization of RER (BB 169), an increase in
    number of binucleated hepatocytes (BB 169), pycnotic nuclei (BB
    169), and, occasionally, multifocal areas of necrosis (BB 169)
    (Akoso et al., 1980, 1982a; Sleight et al., 1981; Dannan et al.,
    1982a,c; Render et al., 1982; Millis et al., 1985b).

         The thymus was affected by 3,3',4,4'-tetrabromobiphenyl (Andres
    et al., 1983; Millis et al., 1985b), possibly by BB 167 (Dannan
    et al., 1978a: "several" tissues: not accurately specified), by BB
    156 (Dannan et al., 1982a) and by BB 169 (Sleight et al., 1981;
    Akoso et al., 1982a; Render et al., 1982; Millis et al., 1985b). 
    There was a loss of thymocytes, especially in the cortex, the
    demarcation between cortex and medulla was indistinct, and
    macrophages were prominent in the remaining portion of the cortex.

         One study reported histological alterations in the thyroid of
    rats treated with 2,2',4,4',5,5'-hexa- (BB 153), 2,3',4,4',5,5'-hexa
    (BB 167), or 3,3',4,4',5,5'-hexabromobiphenyl (BB 169), and in the
    pituitary gland with BB 169 (Akoso et al., 1982b). Prominent lesions
    of the thyroid were extensive hyperplasia and hypertrophy of
    follicular cells and a lack of colloid. The pituitary gland showed
    swollen and vacuolated chromophobe cells.

         The spleen and lymph nodes of rats given 100 mg 3,3',4,4',5,5'-
    hexabromobiphenyl/kg feed for 10 and 20 days had an increased number
    of macrophages intermixed with mature lymphocytes. Changes were
    similar to those seen in the thymus, but were not as pronounced
    (Render et al., 1982).

         The main component of FireMaster(R),
    2,2',4,4',5,5'-hexabromobiphenyl (BB 153), is the congener most
    frequently examined and implicated in many comparative studies.

         The principal changes seen with BB 153 were vacuolation and
    enlargement of hepatocytes with proliferation of SER. They occurred
    in dosing studies (Moore et al., 1978b; Ecobichon et al., 1979;
    Goldstein et al., 1979; Gupta et al., 1981; Millis et al., 1985a) as
    well as in feeding studies (Sleight et al., 1981; Akoso et al.,
    1982a; Dharma et al., 1982), and were observed as early as two days
    after treatment (Moore et al., 1978b). Generally, the
    ultrastructural changes in BB 153-exposed rats were less severe than
    those in rats exposed to the FireMaster(R) mixture (e.g.,
    Goldstein et al., 1979; Gupta et al., 1981; Akoso et al., 1982a).
    Myelin figures and marked disorganization of RER, as seen with the

    FireMaster(R) mixture, were not observed with BB 153 in
    comparative studies (Gupta et al., 1981; Akoso et al., 1982a). 
    Moreover, changes caused by FireMaster(R) FF-1 in the livers of
    rats persisted, while the livers of rats dosed with BB 153 were
    comparable to those of the controls, 60 days after treatment (Gupta
    et al., 1981).

         The histological appearance of thymuses in rats was not
    affected by BB 153 (Tables 78 and 79), but, in cockerels, the
    lymphoid cells of the bursa of Fabricius were depleted by 62 mg BB
    153/kg feed, by 10 mg FireMaster(R) FF-1/kg feed, and by 10 mg BB
    167/kg feed (Dharma et al., 1982). When BB 153, the FireMaster(R)
    mixture, BB 167, and BB 169, were fed to rats, proliferation of SER,
    decreased RER, and increased fat droplets were seen in hepatocytes,
    with all chemicals, but, with BB 169
    (3,3',4,4',5,5'-hexabromobiphenyl), proliferation of SER was not as
    prominent as with the other three PBBs. In contrast, the RER was
    severely altered by BB 169 (Akoso et al., 1982a).

         Myelin bodies were observed in rats fed 100 mg BB 169/kg for 20
    days (Render et al., 1982) or FireMaster(R) BP-6 for 30 days
    (Akoso et al., 1982a), or BB 167 for 60 days (Akoso et al., 1980). A
    comparative experimental series testing single doses of six
    FireMaster(R) constituents, namely BB 118 (Dannan et al., 1982c;
    Millis et al., 1985a), BBs 101, 138, 167, 156, and 170 (Dannan
    et al., 1978a, 1982a) found the least severe histological changes
    with BB 101, and intermediate effects, which were limited to the
    proliferation of SER and cytoplasmic vacuolation in hepatocytes,
    with BB 138 and BB 170. The most pronounced changes resulted from
    BBs 118, 167, and 156 and consisted of proliferation of SER,
    increases in fat vacuoles and myelin figures in hepatocytes (BBs
    118, 167, 156) and thymus damage (BB 156). Rats given a single
    equimolar dose of 3,3',4,4',5,5'-hexabromobiphenyl (BB 169) or
    3,3',4,4'-tetrabromobiphenyl showed moderate to severe hepatic
    changes 14 days after treatment with BB 169, while the
    tetrabromobiphenyl-treated rats showed only mild hepatic changes
    (Millis et al., 1985b).

         The microscopic hepatic effects of
    2,2',3,4,4',5,5'-heptabromobiphenyl (BB 180) and of
    2,2',3,3',4,4',5,5'-octabromobiphenyl (BB 194) were reported to be
    similar to those of BB 153 (Besaw et al., 1978; Moore et al., 1979a,
    1980).

    8.3  Skin and eye irritation, sensitization, dermal lesions,
         and acne

         Common skin and eye irritation tests, as well as sensitization
    tests, resulted in no, or only mild, reactions due to the technical
    PBB mixtures tested, namely octabromobiphenyl and decabromobiphenyl
    (Table 81).

    
    Table 81.  Skin and eye irritation or sensitization tests of commercial PBB mixtures

    PBBa      Species            Application                  Test                         Observations              References

    OcBB      guinea-pig         50% (w/v) slurry in          irritation (intact           mild irritation           Waritz et al.
              (Hartley)          propylene glycol             shaved dorsal skin)                                    (1977)
                                 (0.05 ml)

    OcBB      guinea-pig                                      sensitization                no sensitization
              (Hartley)
                                 1) 1 x 50% (w/v) slurry      intact shaved skin
                                    in propylene glycol
                                 2) 9 x 50% slurry            abraded shaved skin
                                    (topical application)
                                 3) 2 weeks later:            abraded shaved skin
                                    1 x 50% slurry

    OcBB      guinea-pig                                      sensitization                no sensitization
              (Hartley)

                                 1) 1 x 50% (w/v) slurry      intact shaved skin
                                    in propylene glycol
                                 2) 4 x 1% (w/v) solution
                                    in dimethyl sulfoxide
                                    (intradermal injection)
                                 3) 2 weeks later:            abraded shaved skin
                                    1 x 50% slurry

    OcBB      rabbit                                          irritation                                             Norris et al.
              (New Zealand)                                                                                          (1973)
                                 dry solid (single and        intact shaved skin           no response
                                 multiple exposures)          abraded shaved skin          slight erythematous
                                                                                           and edematous response

    Table 81 (contd).

    PBBa      Species            Application                  Test                         Observations              References

    OcBB      rabbit             moistened with water
              (New Zealand)      (single exposure)            intact shaved skin           no response
                                 (repeated exposure)          intact shaved skin           slight erythematous
                                                                                           response

    OcBB      rabbit             moistened with water         abraded shaved skin          moderate erythematous
              (New Zealand)      (single and repeated                                      and slight oedematous
                                 exposures)                                                response

              rabbit             dry solid                    eye irritation               transient irritation
              (New Zealand)                                                                of the conjunctival
                                                                                           membranes

    OcBB      rabbit             powder (100 mg)              eye irritation               no irritating or corneal  Waritz et al.
                                                                                           effects; mild             (1977)
                                                                                           conjunctival redness and
                                                                                           swelling and a copious
                                                                                           discharge (disappeared
                                                                                           within 4 h)

    DeBB      rabbit             50% in olive oil             irritation                   mild irritation           Millischer et al.
                                                              (intact shaved skin)                                   (1979)

    DeBB      rabbit             50% in olive oil             eye irritation               no irritating effect

    DeBB      rabbit             powder                       eye irritation               mild irritating

    a    Commercial PBB mixtures: OcBB = Octabromobiphenyl; DeBB = Decabromobiphenyl.

         However, diverse lesions in the skin and skin appendages of
    certain animal species, e.g., rhesus monkeys and cattle, occurred
    after the ingestion of the FireMaster(R) mixture (Table 82). The
    main features were dry scaly skin and hair loss. Hyperkeratosis of
    the interfollicular epidermis and of the hair follicle, and atrophy
    and squamous metaplasia of the sebaceous glands were observed on
    microscopic examination of these lesions. As with related compounds,
    comparable epidermal changes have not generally been found in other
    laboratory animals, such as guinea-pigs or rats, but they were
    similar to those observed in humans following PBB exposure
    (section 9) and were described as chloracne (McConnell, 1980;
    Kimbrough, 1980b; Poland & Knutson, 1982).

         The rabbit ear (inner surface), but not any other part of the
    rabbit skin (Crow, 1983), is particularly sensitive to acne-causing
    compounds, which was first recognized by Adams et al. (1941). The
    reaction is hyperkeratosis. Painting the rabbit ear has become a
    standard bioassay to detect hyperkeratotic (acnegenic) activity. 
    Results of rabbit ear tests obtained with diverse PBBs (technical
    octabromobiphenyl, technical decabromobiphenyl FireMaster(R)
    mixture, fractions of this mixture, and purified PBB congeners) have
    been summarized in Table 83. The FireMaster(R) mixture itself
    produced hyperkeratosis, but its main components, BB 153
    (2,2',4,4',5,5'-hexa) and BB 180 (2,2',3,4,4',5,5'-hepta), did not. 
    Fractionation of FireMaster(R) indicated that most activity was
    associated with the more polar fraction containing minor compo nents
    (Needham et al., 1982). Sunlight irradiation of BB 153 also yielded
    products that caused severe hyperkeratosis. It is not clear whether
    one or more of the suspected PBBs is responsible for hyperkeratotic
    activity (Patterson et al., 1981). The model congener
    3,3',4,4',5,5'-hexabromobiphenyl and 3,3'4,4'-tetra bromobiphenyl
    were shown to be hyperkeratotic (Table 83).

    8.4  Long-term toxicity

         Toxic effects of PBBs, observed after long-term exposures, as
    well as a long time after exposure had ceased, are summarized in
    Tables 84 and 85. Experimental animals tested were rats, mice,
    cattle, minks, and rhesus monkeys. The majority of studies refer to
    the commercial FireMaster(R) mixture.

         The following comments refer mainly to the general signs of
    long-term toxicity. Other long-term effects will be reviewed in
    detail in the respective sections, e.g., carcinogenicity (section
    8.7), reproductive dysfunctions (section 8.5).

    
    Table 82.  Dermal lesions observed in cattle, rhesus monkeys, and rabbits after exposure to PBBs

    PBBa        Species    Route      Dose (duration)          Dermal lesions observed                               References

    FM BP-6     cattle     oral       25 g/day (for      subcutaneous emphysema and haemorrhage; changes             Moorhead et al.
                                      33-60 days)        in the eyelids: hyperkeratosis, with accumulations of       (1977, 1978)
                                                         keratin in hair follicles of the epidermis and squamous
                                                         metaplasia with keratin cysts in the tarsal glands

    FM FF-1     calf       oral       100 mg/kg body     keratitis, alopecia, hyperkeratosis involving the           Robl et al.
                                      weight (up to      head, cervical and dorsal thoracic region                   (1978)
                                      12 weeks)

                oral                  0.1, 10, 100       acanthosis, hyperkeratosis and/or dermal infiltrates
                                      mg/kg body         of mononuclear cells (dose-dependent severity)
                                      weight (up to
                                      12 weeks)

    FM FF-1     rhesus     in diet    25 mg/kg feed      alopecia, dry scaly skin, loss of eyelashes;                Allen et al.
                monkey                (for 25 weeks)     generalized subcutaneous oedema, marked oedema of           (1978)
                adult                 total dose:        the eyelids; keratinization of hair follicles
                (male)                approx. 1 g        and sebaceous glands

                juvenile   in diet    25 mg/kg feed      moderate loss of hair including eyelashes, dry
                (female)              (for 50 weeks)     scaly skin; periorbital oedema
                                      total dose:
                                      approx. 1.5 g

                juvenile   in diet    300 mg/kg feed     a rather generalized loss of hair, absent eyelashes;        Allen et al.
                (female)              (for 137 days)     considerable periorbital congestion and oedema;             (1978)
                                      total dose:        keratinization of hair follicles
                                      approx. 6.4 g

    Table 82 (contd).

    PBBa        Species    Route      Dose (duration)          Dermal lesions observed                               References

    FM FF-1     rhesus     in diet    1.5 mg/kg feed     periorbital oedema                                          Allen &
                monkey                (for over 5                                                                    Lambrecht (1978)
                                      months)
                                      total dose:
                                      approx. 75 mg

    OcBB        rabbit     dermal     not specified      erythema, exfoliation in the ear                            Norris et al.
                           (ear)      (1 month)                                                                      (1973)

    Various     rabbit     dermal     variable           hyperkeratosis in the ear                                   see Table 83
    PBBs                   (ear)

    FM = FireMaster(R); OcBB = Technical octabromobiphenyl.

    Table 83.  Hyperkeratotic activity of commercial PBB mixtures, the fractionateda FireMaster(R) mixture
    and purified PBB congeners, derived from the rabbit ear test

    PBBd                       Comments               Doseb (solvent)                       Hyperkeratosisc            References
                                                                                         not observed     observed

    DeBB (Adine 0102)                                 200, 2000 (acetone)                x                             Atochem (1990)

    OcBB                                              not specified                      x                             Norris et al.
                                                      (chloroform)                                                     (1973)

    FM FF-1 (lot FH 7042)

      mixture itself                                  60 (not specified)                                  x            Kimbrough
      polar fraction                                  not specified (not specified)                       x (+++)      et al.
      non-polar fraction                              not specified (not specified)                       x (+)        (1977)

    FM BP-6

      mixture itself                                  6.5 µg/kg body weight                               x            Hass et al.
                                                      (benzene-decane, 1:9)                                            (1978)
      fraction 1 (non-polar)   containing PBBs        6.5 µg/kg body weight                               x
                                                      (benzene-decane, 1:9)

    FM FF-1 (lot FH 7042)

      mixture itself                                  100 (toluene)                                       x (++)       Needham et al.
      less polar fractions                            50-210 (toluene)                   x                             (1982)
      more polar fraction      containing minor       185 (toluene)                                       x (+++)
                               components of the FM
                               mixture

      Compound 4               predominantly BB 153   5 (toluene)                        x

      Compound 8               predominantly BB 180   3.3 (toluene)                      x

    Table 83 (contd).

    PBBd                       Comments               Doseb (solvent)                       Hyperkeratosisc            References
                                                                                         not observed     observed

      2,2',4,4',5,5'-hexa-                            10 (not specified)                 x                             Patterson et al.
      bromobiphenyl (BB 153)                                                                                           (1981)
      (96% pure)

      sunlight degradation     mixture of BB 153      10 (not specified)                                  x (+++)      Patterson et al.
      products of BB 153       and other PBBs                                                                          (1981)
                               (probably BB 101,
                               BB 118 and 3,3',4,4'-
                               tetra-bromobiphenyl)

      3,3',4,4',5,5'-hexa-                            0.32-9.6 (toluene)                                  x (++)       Needham et al.
      bromobiphenyl                                                                                                    (1982)

      3,3',4,4'-tetra-                                0.245 and 0.02                                      x (++)
      bromobiphenyl                                   (not specified)

    a    The mixture was fractioned by different methods (on Florisil: Hass et al., 1978; on alumina:
         Kimbrough et al., 1977; by HPLC and GC: Needham et al., 1982).
    b    Total dose in mg/rabbit ear, unless otherwise specified.
    c    (+), (++), (+++) =  severity of hyperkeratosis.
    d    DeBB = technical decabromobiphenyl; OcBB = technical octabromobiphenyl; FM = FireMaster(R).
         BB 101 = 2,2',4,5,5'-pentabromobiphenyl; BB 118 = 2,3',4,4',5-pentabromobiphenyl;
         BB 153 = 2,2',4,4',5,5'-hexabromobiphenyl; BB 180 = 2,2',3,4,4',5,5'-heptabromobiphenyl.

    Table 84.  Long-term effects observed after exposure to PBBs by gavage

    PBBa                 Species      Sex       Dosage regimenc    Dosed       Observed effectse                              References
                         (strain)
                         (No.)b

    FM FF-1              rat          male,     single dose        1000        liver: lipid accumulation (more pronounced     Kimbrough et al.
    (lot FH 7042)        (Sherman)    female    t.p.: 6,10,14                  in males); uroporphyrin accumulation           (1977, 1978)
    (in peanut oil)      (5)                    months                         (females); histopathological changes;
                                                                               neo-plastic nodules; increase in relative
                                                                               weight

    FM FF-1              rat          male,     22 doses over      30          liver: marked hepatotoxic effects; atypical    Gupta &
    (lot No. 1312 FT)    (Fischer     female    30 days; t.p.:                 nodules                                        Moore (1979)
    (in corn oil)        344/N)                 6 months after
                         (9)                    first dose

    FM FF-1              rat          female    single dose        1000        liver: porphyria; neoplastic nodules; foci     Kimbrough et al.
    (lot. 7042)          (Sherman)              t.p.: 23 months                or altered areas; carcinoma; adenofibrosis     (1981)
    (in corn oil)        (65)

                         (16)         female    single dose        200         liver: neoplastic nodules; altered areas;
                                                t.p.: 22 months                multinucleated cells

                         (30)         female    12 doses over      100         liver: neoplastic nodules; foci or altered
                                                3 weeks; t.p.:                 areas; carcinoma; adenofibrosis
                                                24 months

    FM FF-1              rat          female    122 doses over     0.1, 1,     increased white blood cell and lymphocyte      Luster et al.
    (lot. FF 1312 FT)    (Fischer)              6 months t.p.:     3, 10       counts (0.1-10); decrease in body weight       (1980)
    (in corn oil)        (4-10)                 6 months after                 (3,10); decrease in thymus weight (3,10);
                                                first dose                     increase in relative spleen weight (3,10);
                                                                               decrease in adrenal weight (10); immune
                                                                               alterations (3,10)

    Table 84 (contd).

    PBBa                 Species      Sex       Dosage regimenc    Dosed       Observed effectse                              References
                         (strain)
                         (No.)b

    FM FF-1              rat          male,     22 doses over      30          decrease in body weight; increase in relative  Gupta et al.
    (lot 1312 FT)        (Fischer     female    30 days t.p.:                  liver weight; decrease in relative thymus      (1981)
    (in corn oil)        344/N)                 120 days after                 weight (F); increase in serum protein
                         (3)                    first dose                     (ß-globulin fraction); porphyria (F);
                                                                               pronounced hepatocellular alterations

    2,2',4,4',5,5'-      rat          male      22 doses over      16.8        increase in relative liver weight (M);
    hexabromobiphenyl    (Fischer     female    30 days t.p.:                  minimal hepatocellular changes
    (99% purity          344/N)                 120 days after
    (in corn oil)                               first dose

    FM FF-1              rat          male      single dose        500         no significant effects on body and liver       Bernert, Jr
    (lot 7042)           (Sherman)              t.p.: 18 months                weight; increase in serum cholesterol and      et al. (1983)
    (in corn oil)                                                              total serum phospholipids; enhancement of
                                                                               hepatic per-oxidation; reduced retinol
                                                                               levels in serum and liver microsomes;
                                                                               reduced alpha-tocopherol content in
                                                                               microsomes (but not in serum)

    FM FF-1              rat          male,     125 doses over     0.1, 0.3    no effect on food consumption; dose-related    Gupta et al.
    (lot. 1312 FT)       (Fischer     female    6 months; t.p.:    1, 3,       decrease in body weight gain; dose-related     (1983a)
    (in corn oil)        344/N)                 6 months after     10          increase in the absolute and relative liver
                         (10)                   first dose                     weights (Female: 0.1-10; Male: 0.3-10);
                                                                               decrease in thymus weight (0.3-10); increase
                                                                               in spleen weight (1-10); decrease in Hb and
                                                                               PCV values, in MCV and MCH values (10);
                                                                               dose-related increase in serum cholesterol;
                                                                               decrease in serum thyroid hormone levels;
                                                                               porphyrin accumulation in liver, bone, teeth
                                                                               (more pronounced in Female (1-10);

    Table 84 (contd).

    PBBa                 Species      Sex       Dosage regimenc    Dosed       Observed effectse                              References
                         (strain)
                         (No.)b

                                                                               dose-related hepatocellular alterations;
                                                                               increase in white blood cell count (Female:
                                                                               1-10); increase in serum GGTP (Female: 10);
                                                                               decrease in serum glucose (Female: 10);
                                                                               dose-related decrease in serum protein,
                                                                               primarily due to albumin (Female: 0.1-10);
                                                                               carcinoma in urinary bladder (Female:10);
                                                                               histopathological changes in the thyroid
                                                                               glands and kidneys (Male: 10); decrease in
                                                                               serum triglyceride (Male: 0.3-10)

    FM FF-1              rat          male,     125 doses over     0.1,0.3     dose-related body weight reductionso;          Gupta et al.
    (lot. 1312 FT)       (Fischer     female    6 months; t.p.:    1, 3,       dose-dependent porphyrogenic effects on        (1983b)
                         344)                   = up to 29         10          teeth, bones, liver (1-10); enlarged, pale,
                         (11-40)                months after                   or mottled livers with necrotic foci (1-10);
                                                first dose                     hepatocellular alterations (1-10);
                                                                               dose-dependent incidence of liver tumours
                                                                               and cholangiocarcinoma (higher doses);
                                                                               dose-dependent decline in survival time
                                                                               (Male: 1-10); chronic progressive nephropathy
                                                                               (Male: 1-10); gastric ulcers and hyperplastic
                                                                               gastropathy (Male: 3,10)

    FM FF-1              mouse        female    122 doses over     10          increase in body weight; increase in relative  Luster et al.
    (lot. FF 1312 FT)    (B6C3F1)               6 months; t.p.:                spleen weight; slight immune alterations       (1980)
    (in corn oil)        (4-10)                 6 months after
                                                first dose

    Table 84 (contd).

    PBBa                 Species      Sex       Dosage regimenc    Dosed       Observed effectse                              References
                         (strain)
                         (No.)b

    FM FF-1              mouse        male,     22 doses over      30          no effect on food consumption; increase in     Gupta et al.
    (lot 1312 FT)        (B6C3F1/N)   female    30 days; t.p.:                 relative liver weight, histopathological       (1981)
    (in corn oil)        (3)                    120 days after                 alterations in liver
                                                first dose

    2,2',4,4',5,5'-      mouse        male,     22 doses over      16.8        no effect on food consumption and body weight
    hexabromobiphenyl    (B6C3F1/N)   female    30 days; t.p.:                 gain; increase in relative liver weight;
    (99% purity)         (3)                    120 days after                 minimal hepatocellular alterations
    (in corn oil)                               first dose

    FM FF-1              mouse        male,     125 doses over     0.1, 0.3,   no effect on food consumption; decrease in     Gupta et al.
    (lot. 1312 FT)       (B6C3F1)     female    6 months           1, 3, 10    body weight gain (only Male: 10); increase     (1983a)
    (in corn oil)        (10)                                                  in body weight (only Female: 10); increase
                                                                               in absolute and relative liver weight
                                                                               (Female: 0.3-10; Male: 1-10); increase in
                                                                               spleen weight (Female: 10); decrease in
                                                                               uterine weight (Female: 10); haematological
                                                                               alterations: dose-related increase in red
                                                                               blood cell count; dose-related decrease in
                                                                               MCV; decrease in platelet counts (Female:
                                                                               3,10); leukocytosis (Female: 10); clinical
                                                                               chemistry changes: increase in serum levels
                                                                               of GGTP and SGPT (10) and alkaline
                                                                               phosphatase (10); decrease in serum glucose
                                                                               (Female: 10); dose-related hepatic porphyria
                                                                               (more pronounced in Female) pale and
                                                                               mottled livers (higher doses); dose-related
                                                                               microscopic changes in the liver (1-10)

    Table 84 (contd).

    PBBa                 Species      Sex       Dosage regimenc    Dosed       Observed effectse                              References
                         (strain)
                         (No.)b

    FM FF-1              mouse                  125 doses over     0.1, 0.3,   shortened survival time (Male: 10); hepatic    Gupta et al.
    lot. 1312 FT)        (B6C3F1)               6 months; t.p.:    1 ,3, 10    porphyria (Male: 3); slight reduction in body  (1983b)
    (in corn oil)        (8-27)                 up to 30                       weight (Male: 10); enlarged liver; fluid
                                                months after                   accumulation in peritoneal cavity; liver
                                                first dose                     carcinoma (10); metastasis to lung (Female:
                                                                               10); hyperplasia and adenoma of follicular
                                                                               cells of thyroid

    FM BP-6              cattle                 daily doses        250         no adverse clinicopathological chanages        Durst et al.
    (in gelatin          (6)                    for 60 days        mg/day                                                     (1978a)
    capsule)                                    t.p.: 80-190
                                                days after
                                                first dose

    FM BP-6              cattle                 daily doses        250         no gross or histopathological signs of         Moorhead et al.
    (in gelatin          (No. not               for 60 days        mg/day      toxicosis                                      (1978)
    capsule)             specified)             t.p.: 220
                                                days after
                                                last dose

    FM FF-1              cattle       female    daily doses        0.3         no effects on milk production, body weights,   Robl et al.
    (in gelatin          (6)                    for 158 days                   amount of food consumed; no effects on         (1978)
    capsule)                                    t.p.: 182                      haematological and clinical chemistry and
                                                days after                     urinalysis values;
                                                last dose                      (1 cow: overgrowth of hooves from day 129)

    Table 84 (contd).

    PBBa                 Species      Sex       Dosage regimenc    Dosed       Observed effectse                              References
                         (strain)
                         (No.)b

    FM BP-6              cattle       (Female)  daily doses        250         no effect on milk production, body weight,     Durst et al.
    (in gelatine                      (1-4)     for 60, 180        mg/day      number of infections or general injuries;      (1978b)
    capsule)                                    202 days                       increased frequencies of reproductive          Willett et al.
                                                t.p.: up to                    dysfunctions                                   (1980)
                                                1500 days
                                                after first
                                                dose

    a    FM = Fire Master.(R)
    b    No. = number of animals.
    c    t.p. = time post-exposure.
    d    In mg/kg body weight per day, unless otherwise specified.
    e    Hb = Haemoglobin; PCV = packed cell volume; MCV = mean corpuscular volume; MCH = mean corpuscular haemoglobin.

    Table 85.  Long-term effects of feeding PBBs to young or adult animals

    PBBa                  Species           Sex       Dietary         Feeding/       Observed effectsc                           References
                          (strain)                    concentration   observation
                          (No.)b                      (mg/kg feed)    period

    "Hexabromobiphenyl"   rat               female    50              7 months       increase in relative weights of liver,      Sepkovic &
    (Monsanto Co.,        (Sprague-                                                  ovary, and thyroid                          Byrne (1984)
    St. Louis)            Dawley) (8)

    FM BP-6               rat               female    1, 10, 50       5-7 months     no effect on food consumption, body         Byrne et al.
                          (Sprague-                                                  weight, and relative thyroid weight;        (1987)
                          Dawley) (10)                                               slightly elevated liver weight (10, 50);
                                                                                     primary hypothyroidism

    FM BP-6               rat               female    1, 5, 10,       5 or more      no effect on food consumption and relative  Byrne et al.
                          (Sprague-                   50              months         liver weight; decrease in relative adrenal  (1988)
                          Dawley) (10)                                               weight; depression of circulating levels
                                                                                     of adrenal cortex hormones

    OcBB                  rat               male,     0.01-1          180 days       no effect on food consumption and body      Norris et al.
    (Dow Chemical)        (Sprague-         female                                   weight                                      (1973)
                          Dawley) (not
                          specified)

    OcBB                  rat               male      100             4/22 weeks     return to normal liver weights              Lee et al.
    (Dow Chemical)        (Sprague-                                                                                              (1975a);
                          Dawley) (8)                 1000            4/22 weeks     increased liver weights;                    Waritz et al.
                                                                                     hepatocellular alterations                  (1977)

    OcBB                  rat               female    50              7 months       increase in relative liver weight           Sepkovic &
    (Monsanto Co.,        (Sprague-                                                                                              Byrne (1984)
    St. Louis)            Dawley) (8)

    Table 85 (contd).

    PBBa                  Species           Sex       Dietary         Feeding/       Observed effectsc                           References
                          (strain)                    concentration   observation
                          (No.)b                      (mg/kg feed)    period

    NoBB                  mouse             male,     100, 300        18 months      decrease in body weight (Male, Female);     Momma (1986)
    (Bromkal 80-9D)                         female                                   shortened survival time (300 mg/kg; Male);
                                                                                     enlargement of thyroid glands (300 mg/kg;
                                                                                     Female); decrease in triglyceride and
                                                                                     non-esterified fatty acids; reduction of
                                                                                     pentobarbital sleeping time (13 months);
                                                                                     liver carcinoma (Male, Female)

    FM FF-1               mink (9)          male,     6.25            210 days       deaths; decrease in body weight; increase   Aulerich &
                                            female                    (mean)         in relative liver and kidney weights;       Ringer (1979);
                                                                                     liver histopathology                        Ringer et al.
                                                                                                                                 (1981)

                          mink (8)          female    1-2.5           9 months       10% reduction in body weight (2.5);         Aulerich &
                                                                                     adverse effects on reproduction             Ringer (1979);
                                                                                                                                 Ringer et al.
                                                                                                                                 (1981)

    FM FF-1               rhesus            female    0.3             7 months-      weight loss; sterile abscesses (2/7);       Allen et al.
                          monkey                      (total dose:    > 1 year       reproductive dysfunctions                   (1978); Allen
                          (7)                         > 25 mg)                                                                   & Lambrecht
                                                                                                                                 (1978);
                                                                                                                                 Lambrecht
                                                                                                                                 et al. (1978)

                          rhesus            ?         1.5             > 5 months     weight loss; periorbital oedema;            Allen &
                          monkey                      (total dose:                   immunological alterations                   Lambrecht
                          (not                        approximately                                                              (1978)
                          specified)                  75 mg)

    Table 85 (contd).

    PBBa                  Species           Sex       Dietary         Feeding/       Observed effectsc                           References
                          (strain)                    concentration   observation
                          (No.)b                      (mg/kg feed)    period

    FM FF-1               rhesus            male      25              25 weeks       death; weight loss; haematological and      Allen et al.
                          monkey                      (total dose:                   clinical chemistry changes: decrease in     (1978)
                          (adult)                     approximately                  PCV, cholesterol, total serum protein and
                          (1)                         1 g)                           albumin; increase in serum GPT activity;
                                                                                     epidermal changes:
                                                                                     alopecia, dry scaly skin, loss of eyelashs;
                                                                                     keratinization of hair follicles and
                                                                                     sebaceous glands;
                                                                                     oedema:
                                                                                     generalized subcutaneous oedema and
                                                                                     marked oedema of eyelids; enlarged heart
                                                                                     and liver; hyperplastic gastroenteritis;
                                                                                     severe ulcerative colitis; hypoactive
                                                                                     seminiferous tubules; hyperplasia of bile
                                                                                     duct epithelium

    FM FF-1               rhesus            female    25              50 weeks       no weight gain: loss of hair (including     Allen et al.
                          monkey                      (total dose:                   eyelashes); dry scaly skin; periorbital     (1978)
                          (juvenile)                  approximately                  oedema; increase in serum GPT activity
                          (1)                         1.5 g)

    FM FF-1               rhesus            female    300             137 days       death; weight loss; haematological and
                          monkey                      (total dose:                   clinical chemistry changes: decrease in
                          (juvenile)                  approximately                  PCV, white blood cell count, red blood cell
                                                      6.4 g)                         count, serum cholesterol, serum protein;
                                                                                     increase in serum GPT activity
                                                                                     epidermal changes:
                                                                                     loss of hair (including eyelashes); atrophy
                                                                                     and squamous metaplasia of the sebaceous
                                                                                     glands; keratinization of hair follicles;

    Table 85 (contd).

    PBBa                  Species           Sex       Dietary         Feeding/       Observed effectsc                           References
                          (strain)                    concentration   observation
                          (No.)b                      (mg/kg feed)    period

                                                                                     periorbital congestion and oedema;
                                                                                     subcutaneous oedema; enlarged
                                                                                     hepatocytes; hyperplastic gastroenteritis;
                                                                                     hyperplasia of the epithelium of the
                                                                                     bladder and of the bile ducts; focal
                                                                                     areas of haemorrhage in the adrenal glands

    FM FF-1               rhesus            female    1.5             36 weeks       weight loss; decrease in serum              Lambrecht et al.
                          monkey                      (total dose:                   cholesterol enlarged hepatocytes with       (1978)
                          (adult)                     70 mg)                         moderate fatty infiltration (as indicated
                          (3)                                                        by liver biopsy)

                          rhesus            male,     25              14 weeks       weight loss (Male, adult) or lack of
                          monkey            female    (total dose:                   weight gain (Female, juvenile); decrease
                          (adult                      approximately                  in serum cholesterol; hyperplastic
                          juvenile)                   500 mg)                        gastritis
                          (2)

    a    FM = FireMaster; OcBB = technical octabromobiphenyl; NoBB = nonabromobiphenyl.
    b    No. = number of animals.
    c    PCV = packed cell volumes.

    8.4.1  Rat

    8.4.1.1  Overt clinical signs, body weight changes, food intake

         In rats, the low-dose, long-term feeding of FireMaster(R)
    (Byrne et al., 1987, 1988) or technical octabromobiphenyl (Norris
    et al., 1973) had no effect on food consumption and body weight
    (Table 85). Nevertheless, the fur of PBB-fed animals was slightly
    less dense and slightly coarser than that of control animals (Byrne
    et al., 1987). A dose-dependent decline in survival time (Gupta
    et al., 1983b), and body weight reductions or depressed rates of
    body weight gain as a function of time and dose (Luster et al.,
    1980; Gupta et al., 1981, 1983a,b) have been found in rats orally
    dosed with FireMaster(R) (Table 84); also there was no significant
    difference in food consumption between treated and control animals
    (Gupta et al., 1981, 1983a).

    8.4.1.2  Haematology and clinical chemistry

         Several haematological and clinical chemistry parameters were
    altered, some in only one sex (Table 84: Kimbrough et al., 1977;
    Luster et al., 1980; Bernert et al., 1983; Gupta et al., 1983a).
    Rats of both sexes had decreased haemoglobin and packed cell volume
    values (Gupta et al., 1983a), a dose-related increase in serum
    cholesterol (Bernert et al., 1983; Gupta et al., 1983a), and a
    dose-related hepatic porphyria (Gupta et al., 1983a). 

    8.4.1.3  Morphological changes

         Most of the livers of treated rats from higher dose groups were
    pale or slightly yellow and mottled (Gupta et al., 1983a) and
    contained white necrotic foci (Gupta et al., 1983b). Porphyrin
    accumulation in the liver, bone, and teeth, seen as red fluorescence
    under UVR, was more pronounced in treated females compared with
    treated males (Kimbrough et al., 1977; Gupta et al., 1983a,b). After
    withdrawal of treatment, visual fluorescence declined slightly in
    the lower dose groups (1 and 3 mg FM/kg body weight), but remained
    the same in the 10 mg FM/kg body weight dose groups (males and
    females) during lifetime observation (Gupta et al., 1983a,b).

         In long-term studies, an increase in the relative liver weights
    of rats exposed to FireMaster(R) or a related mixture was usually
    found (Kimbrough et al., 1978; Gupta et al., 1981, 1983a; Sepkovic &
    Byrne, 1984; Byrne et al., 1987), but in some instances (Bernert et
    al., 1983; Byrne et al., 1988), there was no effect on liver weight
    (see Tables 84 and 85). [During a six-month exposure to
    FireMaster(R), the increases in absolute and relative liver
    weights were dose-related (Gupta et al., 1983a)].

         Long-term feeding of commercial octabromobiphenyl (OcBB) also
    caused an increase in relative liver weights (Sepkovic & Byrne,
    1984; Table 85). Rats fed OcBB for 4 weeks still had increased liver
    weights at 18 weeks of recovery or had returned to near normal
    limits, depending on the concentration of OcBB in the test diet (Lee
    et al, 1975a; Table 85).

         The only individual PBB congener tested over the long-term,
    namely 2,2',4,4',5,5'-hexabromobiphenyl, caused an increase in the
    relative liver weight in male rats only (Gupta et al., 1981; Table
    84).

         Weight changes following PBB exposure, noted in organs other
    than the liver, included a decrease in the thymus (Luster et al.,
    1980; Gupta et al., 1981, 1983a), an increase in the spleen (Luster
    et al, 1980; Gupta et al., 1983a), a decrease in the adrenal glands
    (Luster et al., 1980; Byrne et al., 1988), and an increase in the
    thyroid and ovary (Sepkovic & Byrne, 1984) (see Tables 84 and 85).

    8.4.1.4  Histopathological changes

         Hepatocellular alterations (exclusive of hepatocellular
    carcinomas), observed in long-term studies with FireMaster(R) (see
    Table 84), consisted mainly of enlarged hepatocytes, fatty
    infiltration, proliferation and disorganization of RER, single cell
    necrosis, multinucleated cells, microabscesses, atypical foci, and
    bile duct proliferation (Kimbrough et al., 1977, 1978, 1981; Gupta
    et al., 1981, 1983a,b).

         In contrast to FireMaster(R)-treated rats, rats given
    2,2',4,4',5,5'- hexabromobiphenyl over 30 days tended to recover
    when examined during postexposure periods (Gupta et al., 1981). 

         Myelin figures, induced by the feeding of technical OcBB,
    persisted, together with fatty changes, as late as 18 weeks after
    withdrawal of a test diet containing 1000 mg OcBB/kg; however, the
    normal morphology of RER was restored independently of the
    occurrence of myelin figures, after treatment was discontinued (Lee
    et al., 1975a).

         Although there was no significant difference in the weights of
    the thyroid gland, slight to moderate microscopic changes were
    observed, primarily in male rats exposed for 6 months to 10 mg
    FireMaster(R)/kg body weight. The thyroid gland had thin, sparse,
    or bluish colloid with basophilic stippling and some follicles were
    lined with columnar epithelium and contained a few epithelial
    papillary projections (Gupta et al., 1983a). 

         The kidneys of male rats equally treated consistently showed
    atrophy of a few glomerular tufts with marked dilatation of Bowman's
    capsule, which contained amorphous eosinophilic staining material. A

    few glomerular tufts also appeared oedematous (Gupta et al., 1983a).
    Male rats, exposed to FireMaster(R) for 6 months (dose levels:
    1-10 mg/kg body weight per day) and observed for a lifetime, showed
    a higher incidence of chronic progressive nephropathy than the
    controls. Their kidneys were characterized by eosinophilic
    proteinaceous casts, sclerosis and thickening of glomerular tufts
    and Bowman's capsule, mononuclear leukocytic infiltration, and
    interstitial fibrosis (Gupta et al., 1983b).

         Gastric ulcers and hyperplastic gastropathy of the glandular
    portion of the stomach were found with significantly increased
    incidence in male rats held under the same conditions (dose levels:
    3 or 10 mg FM/kg body weight per day). Microscopic lesions consisted
    of hyperplasia of the mucosal epithelium, glandular metaplasia to
    goblet cells, hyperchromasia, and increased mitosis (Gupta et al.,
    1983b).

    8.4.2  Mouse

         As far as it has been tested (Table 84), FireMaster(R) has
    not produced any significant effects on food consumption in mice of
    both sexes (Gupta et al., 1981, 1983a). Interestingly, there were
    increases in the body weights of female mice with long-term exposure
    to FireMaster(R), while a decrease occurred only in males at the
    high dose (Luster et al., 1980; Gupta et al., 1983a,b). The high
    dose of FireMaster(R) also shortened the survival time of males
    (Gupta et al., 1983b). There were no significant differences in food
    consumption and body weight gain in mice treated with
    2,2',4,4',5,5'-hexabromobiphenyl (Gupta et al., 1982).

         A number of haematological and clinical chemistry changes have
    been found in mice exposed for 6 months to FireMaster(R) (Table
    84: Gupta et al., 1983a). Hepatic porphyrin levels were increased in
    a dose-related manner after a six-month exposure (Gupta et al.,
    1983a), but (unlike levels in rats) they tended to decrease
    following cessation of exposure (Gupta et al., 1983b).

         Organ weight changes noted in long-term studies on mice (Table
    84) consisted of an increase in liver (Gupta et al., 1981, 1983a,b)
    and spleen (Luster et al., 1980; Gupta et al., 1983a) weights and a
    decrease in uterine weights (Gupta et al., 1983a). Most of the
    affected mice observed for a lifetime contained serosanguineous
    fluid in the peritoneal cavity (Gupta et al., 1983b). The livers of
    mice with long-term exposure were pale and contained, primarily in
    males, grayish white foci (Gupta et al., 1981, 1983a).

         Microscopic alterations were marked swelling of hepatocytes,
    foamy or vacuolated cytoplasm with hyaline bodies, focal coagulative
    necrosis or scattered single cell necrosis of hepatocytes, and
    atypical hepatocellular foci (Gupta et al., 1983a). Hyperplasia was
    observed in the follicular cells of thyroid (Gupta et al., 1983b).

         Adverse effects (besides liver carcinoma; see section 8.7),
    observed after an 18-month exposure of mice to technical
    nonabromobiphenyl (Bromkal 80-9D), included decreases in body
    weight, enlargement of the thyroid gland, and biochemical
    alterations (Momma, 1986; Table 85).

    8.4.3  Cattle

         Except for a single animal, cattle with long-term exposure to
    low doses of FireMaster(R) FF-1 or BP-6, observed for up to 220
    days post-treatment (see Table 84) did not show any adverse effects
    with regard to food intake, clinical signs, clinicopatho logical
    changes, or performance (Durst et al., 1978a,b; Moorhead et al.,
    1978; Robl et al., 1978). However, reproductive dysfunction occurred
    more frequently (Willett et al., 1980; see also section 8.5). 

    8.4.4  Mink

         Minks were found to be very susceptible to PBB toxicity (Table
    85: Aulerich & Ringer, 1979). When fed with FireMaster(R) for
    several months, they responded with food rejection, loss of weight,
    an unthrifty appearance, and death. Upon necropsy of animals that
    died, increases in relative liver and kidney weights and a fatty
    infiltration of the liver were evident. A relatively low daily
    intake of FireMaster(R) by female mink had an adverse effect on
    their reproductive performance (see also section 8.5). 

    8.4.5  Rhesus monkey

         Rhesus monkeys are also among the species more sensitive to
    FireMaster(R) (Table 85: Allen et al., 1978; Allen & Lambrecht,
    1978; Lambrecht et al., 1978). At exposures of 1.5-300 mg FM/kg
    feed, they developed weight loss or a lack of weight gain,
    haematological and clinical chemistry changes, loss of hair, skin
    lesions, oedema, enlargement of the heart and liver, areas of
    haemorrhage in the adrenal glands; reduced spermatogenesis, and
    immune incompetence. Microscopic changes in the liver included
    enlarged hepatocytes with fatty infiltration. The most severe lesion
    was hyperplastic gastroenteritis and the accompanying ulcerations.
    Exposures to 25 or 300 mg FM/kg feed also caused death. The female
    monkeys fed with lower doses of FireMaster(R) (0.3 mg/kg diet),
    for over one year, did not develop any of the signs of intoxication
    noted above, except for weight loss. However, they were affected by
    reproductive dysfunctions (see also section 8.5).

    8.4.6  Pre- and perinatal exposure

         Long-term effects following pre- or perinatal exposure to
    FireMaster(R) have been recorded in rats and cattle.

         Stunted growth, increased mortality rates, and liver tumours
    were observed in the offspring of Sherman rats given 200 mg
    FireMaster(R) FF-1/kg body weight on days 7 and 14 of pregnancy,
    when a total of 50 male and 50 female offspring per group were
    followed until they were 2 years old (Groce & Kimbrough, 1984). 
    Sprague-Dawley rats (No. = 10), perinatally exposed (day 8 of
    pregnancy-28 days post partum) to FireMaster(R) BP-6 (100 mg/kg of
    feed) and weaned on to a PBB-free diet, had increased relative liver
    weights at 28 and 150, but not 328 days of age. Although the liver
    was not enlarged 10 months after weaning, hepatic histopathological
    alterations, such as cellular swelling, vacuolation, some necrosis,
    and eccentric and pyknotic nuclei were observed throughout this
    residual phase. Other long-lasting alterations were stimulation of
    renal and hepatic microsomal enzymes, and a reduction in the
    duration of anaesthesia produced by pentobarbital (McCormack et al.,
    1980). In a multigeneration study (McCormack et al., 1981), rats
    perinatally exposed to FireMaster(R) BP-6, as described above
    (F1-generation), were allowed to mature sexually and bred with
    littermates to produce the F2-generation. Even these F2-animals
    exhibited increased relative liver weights and histopathological
    liver changes at 28 days of age. The light microscopic changes
    included vacuolation, focal necrosis, pyknotic nuclei, swelling, and
    myelin bodies. However, the severity of lesions was much less
    prominent in F2-animals than in F1-animals.

         PBBs given to a single generation also produced hepatic and
    renal microsomal enzyme stimulation, a reduction in the duration of
    anaesthesia elicited by pentobarbital or a large dose of
    progesterone, and a decrease in the concentration of vitamin A in
    the liver, in both subsequent generations (F1 and F2). 

         Cows whose dams or granddams had received daily oral doses of
    FireMaster(R) BP-6 (up to 250 mg/day) for 60-202 days showed no
    general health problems, but they had conception difficulties
    (Willett et al., 1982).

    8.5  Reproduction, embryotoxicity, and teratogenicity

         Effects of PBBs on reproduction (reproductive system, overall
    reproductive performance, embryotoxicity, teratogenicity) have been
    summarized in Tables 86 and 87. Most of the studies refer to the
    FireMaster(R) mixture. Few reports deal with technical
    octabromobiphenyl (Aftosmis et al., 1972a; Waritz et al., 1977) or
    technical decabromobiphenyl (Millischer et al., 1979), and, among
    the individual PBB congeners, only 2,2',4,4',5,5'-hexabromobiphenyl
    has been evaluated by a few authors.

    8.5.1  PBB mixtures

    8.5.1.1  Mammals

    a) Reproductive system and performance.

         As listed in Tables 74 and 75, administration of
    FireMaster(R) by gavage and in the diet had no effect on the
    weight of male (Garthoff et al., 1977; Corbett et al., 1978a; Harris
    et al., 1978b, Gupta et al., 1981; Castracane et al., 1982) or
    female (Gupta et al., 1981) sex organs in rats and/or mice. An
    exception was an increase in the uterine weight of mice dosed for 6
    months with FireMaster(R) (Gupta et al., 1983a). Testes weights in
    rats fed commercial OcBB also remained unaffected (Norris et al.,
    1973). However, there was a reduction in the ventral prostate
    weight-to-body weight ratio in pubescent male rats (Johnston et al.,
    1980; Table 87) and a delay in vaginal opening in female rats after
    perinatal exposure to FireMaster(R) (Harris et al., 1978a;
    McCormack et al., 1981; Tables 86 and 87). Both findings may suggest
    retarded sexual maturation.

         Male rats, moribund from multiple doses of FireMaster(R),
    exhibited degenerative and hyperplastic changes in the ductus
    deferens (hyperplasia and squamous metaplasia with keratinization in
    the epithelial lining of the ductus deferens). However, such changes
    were not observed in surviving male rats, examined six months after
    the treatment. Lesions found in surviving animals were acute
    prostatitis (30 mg/kg body weight per day) and the presence of sperm
    granuloma in the epididymis (100 mg/kg body weight per day) (Gupta &
    Moore, 1979; Table 86). A rhesus monkey, exposed to FireMaster(R)
    in the diet, had hypoactive seminiferous tubules at death (Allen
    et al., 1978; Table 87). Little work was done on the possible
    impairment of spermatogenesis. Young bulls may develop testicular
    atrophy and reduced spermatogenesis when exposed to FM (Robl et al.,
    1978), but more numerous controlled studies are needed.

         The estrous cycle of cows (No. = 8) was not affected during
    administration of FireMaster(R) FF-1 (0.3 mg/kg body weight per
    day) for 158-228 days and during a recovery period of 112-182 days
    (Robl et al., 1978).

         The estrous cycle of female rats was increased in length after
    perinatal and subsequent dietary exposure to FireMaster(R) BP-6
    (Johnston et al., 1980; Table 87) at concentrations of 100 mg/kg
    (equivalent to 5 mg/kg body weight per day). Prolonged menstrual
    cycles were seen in rhesus monkeys after consuming FireMaster(R)
    FF-1 for six months at a concentration of 0.3 mg/kg (equivalent to
    0.02 mg/kg body weight per day). This alteration was correlated with
    decreased serum progesterone levels (Allen et al., 1978; Lambrecht
    et al., 1978; Table 87).

    
    Table 86.  Summary of effects of PBBs on reproduction (reproductive system, overall reproductive performance,
    embryotoxicity, teratogenicity): dosing studies

    PBB            Species      Exposurec         Dosed         Major effects                       Remarks                     References
                   (No.)b

    FM BP-6        rat          oral single       400, 800     reductions in fetal and placental                               Beaudoin
                   (Wistar)     dose one of                    weight; fetal death (primarily                                  (1977)
                   (3-15)       gd 6-14                        800 mg/kg body weight per day at
                                s.t.: gd 20                    day 7-12); malformed (cleft
                                                               palate; diaphragmatic hernia)
                                                               fetuses (400 mg/kg body weight
                                                               per day: 0-11.8%; 800 mg/kg body
                                                               weight per day: 0-60%)

    FM FF-1        rat (No.     oral multiple     100 (total   none                                no effects on number of     Ficsor &
                   not          doses (6) gd      dose: 600                                        fetuses, dead implants,     Wertz (1976);
                   specified    6-16 at 2 day     mg/kg body                                       fetal malformation          Wertz &
                   (15)         intervals         weight                                                                       Ficsor (1978)
                                s.t.: gd 19

    FM BP-6        rat          oral multiple     0.25-10      reduced fetal weight and            no effects on implantation  Harris
                   (Sprague-    doses gd 7-15     mg/day       crown-rump length (only             number of live fetuses or   et al. (1978a)
                   Dawley)      s.t.: gd 20                    0.25 mg/day)                        gross malformations
                   (6-8)

                                s.t.: 48, 60      10 mg/day    reductions in offspring weight      no effects on litter size   Harris
                                days of age                    (from 3 days of age onwards,        and birth weight            et al. (1978a)
                                                               more pronounced in male pups);
                                                               increased postnatal mortality (at
                                                               weaning 14.3% versus 1.5% in
                                                               control); delay in vaginal opening
                                                               of female offspring

    Table 86 (contd).

    PBB            Species      Exposurec         Dosed         Major effects                       Remarks                     References
                   (No.)b

    FM BP-6        rat          oral multiple     8-160 mg     reduced implantation rates          no malformed fetuses        Beaudoin
                   (Wistar)     doses gd 0-14     per animal   (80-160 mg); fetal death                                        (1979)
                   (No. not     on alternate      (total
                   specified)   days              dose)

    FM FF-1        rat          oral multiple     100          moribund rats: degenerative and                                 Gupta &
                   (Fischer     doses (22)                     hyperplastic changes in the ducts                               Moore (1979)
                   344/N)       over 30 days                   deferens (73 days after
                   (9 males)    s.t.: up to 6                  treatment); surviving rats: sperm
                                months                         granuloma in the epididymis (6
                                                               months after treatment; 1/2e)

                                                  30           acute prostatitis (4/9)e

    FM FF-1        rat          oral multiple     200          reduction in offspring survival                                 Groce &
                   (Sherman)    doses (2) gd 7                 rate-to-weaning                                                 Kimbrough
                   (16)         and 14 o.t.:                                                                                   (1984)
                                up to Weaning
                                (21 days of age)

    FM BP-6        rat          1) in vivo-       800          inhibited rate of embryo                                        Fisher (1980);
                   (Wistar)     treatment: oral                development in vitro (effects on                                Beaudoin &
                   (7)          single dose gd 9               axial rotation, heart rate, neural                              Fisher (1981)
                                s.t.: gd 10                    tube closure, formation of the
                                2) whole embryo                anterior limb buds, somite
                                culture: 24 h                  development, and establishment of
                                                               visceral yolk sac circulation);
                                                               reduction in DNA content;
                                                               pericardial oedema

    Table 86 (contd).

    PBB            Species      Exposurec         Dosed         Major effects                       Remarks                     References
                   (No.)b

    DeBB           rat          oral multiple     10-1000      none                                no teratogenicity or        Millischer
                   (Sprague-    doses gd 6-15                                                      embryotoxicity              et al. (1979)
                   Dawley)      s.t.: gd 21
                   (25)

    2,2',4,4'      mouse        oral multiple     0.3-32       none                                no fetotoxicity or          Lucier et al.
    5,5'-hexa-     (C.D. - 1)   doses gd 10-16                                                     teratogenicity; no effects  (1978)
    bromobiphenyl  (up to 25)   s.t.: gd 19                                                        on fertility, gestation,
    (purity                     o.t.: 4, 20                                                        viability, survival, and
    > 97%                       days of age                                                        lactation indices

    FM BP-6        cow (6)      oral multiple     25 g/day     abortion (3/6)e or fetal                                        Durst et al.
                                doses during                   death (3/6)e                                                    (1977, 1978b);
                                pregnancy for                                                                                  Moorhead
                                32-60 days                                                                                     et al. (1977)
                                o.t.: up to 60
                                days

    BM BP-6        cow          oral multiple     0.25 and     none                                                            Durst et al.
                   (3)          doses during      250 mg/day                                                                   (1978b)
                                pregnancy for
                                60 days
                   (1)          for 180 days      250 mg/day   stillbirth (due to dystocia)
                                o.t.: up to
                                305 days

    Table 86 (contd).

    PBB            Species      Exposurec         Dosed         Major effects                       Remarks                     References
                   (No.)b

    FM BP-6        cow (3-5)    oral multiple     0.25-250     high incidence of dystocia;         a total of 75 calves        Willett et al.
                   (4 dose      doses before      mg/day       increased birth weights of calves;  were studied; no effects    (1980, 1982)
                   groups)      breeding or                    stillbirths; increased number of    on growth, development,
                                during late                    inseminations required for          and survival of calves
                                pregnancy for                  conception in 1 and 2 generation    born alive
                                60-202 days                    offspring
                                o.t.: up to 5.5
                                years (1-5
                                parturition;
                                2 generations)

    a    FM = FireMaster(R); DeBB = technical decabromobiphenyl.
    b    No. = Number of females, unless otherwise specified.
    c    gd = Gestation day (in rodents sperm day = gd 0, of recorded); o.t. = observation time; s.t. = sacrifice time.
    d    In mg/kg body weight per day, unless otherwise specified.
    e    No. affected/no. treated.

    Table 87.  Summary of PBB effects on reproduction (reproductive system, overall reproductive performance,
    embryotoxicity, teratogenicity): feeding studies

    PBBa           Species          Treatmentc          Dietary           Major effects                    Remarks                 References
                   (No.)b                               concentrationd

    FM BP-6        rat (Sprague-    gd 7-18              100, 1000        decreasing fetal weight with     suggestion of late      Corbett
                   Dawley)          s.t.: gd 20                           increasing dosage                fetal mortality         et al.
                   (6-7)                                                                                   (high dose); no         (1975)
                                                                                                           teratogenicity

    FM BP-6        rat (Sprague-    gd 8-9th week           100           reduction in ventral             no effect on fetal      Johnston
                   Dawley) (at      of age s.t.:                          prostate weight of male          survival rate           et al.
                   least 8)         9th week of age                       offspring; increased length                              (1980)
                                                                          of estrous cycle of female
                                                                          offspring

    FM BP-6        rat (Sprague-    gd 8-Weaning            100           reduction in survival            no effects on length    McCormack
                   Dawley)          s.t.: Weaning                         rate-to-weaning (87% of          of gestation, litter    et al.
                                                                          control value); delay in         size, incidence
                   (8)              (28 days of                           vaginal opening in female        of gross external
                                    age)                                  offspring                        anomalies, pup body
                                                                          weight at birth

    OcBB           rat (not         gd 6-15             100, 1000,        gastroschisis (one fetus         abstract only (no       Aftosmis
                   specified)       s.t.: gd 20           10 000          at each level); anasarca         on number of fetuses    et al.
                                                                          (one fetus at each of the        information examined)   (1972a)
                                                                          two highest levels)

    OcBB           rat              gd 6-15             100, 1000,        no significant                   gastroschisis           Waritz et al.
                   (ChR-CD)         s.t.: gd 20           10 000          embryotoxicity or                (1/259e: 1000 mg/kg:    (1977)
                   (23-27)                                                teratogenicity                   1/1/283e
                                                                                                           10 000 mg/kg);

    Table 87 (contd).

    PBBa           Species          Treatmentc          Dietary           Major effects                    Remarks                 References
                   (No.)b                               concentrationd

                                                                                                           anasarca (1/259e: 1000
                                                                                                           mg/kg; 1/283e: 10 000
                                                                                                           mg/kg); no effects on
                                                                                                           growth or viability of
                                                                                                           embryos

    FM BP-6        mouse:           gd 7-18              50, 100,         dose-related decrease in fetal   incidence of            Corbett
                   (Swiss, ICR)     s.t.: gd 18            1000           weight with increasing dosage;   malformations           et al.
                   (9-12)                                                 exencephaly (5/295g: 100,        statistically           (1975,
                                                                          1000 mg/kg); cleft palate        significant only        1978b)
                                                                          (5/208g: all levelsg;            compared with pooled
                                                                          hydro-nephrosis (2/87:           historical controls
                                                                          1000 mg/kg)

    FM             mouse (Swiss-    gd 4-16              100, 200         increase in number of dead or    (abstract only)         Preache
                   Webster)         s.t.: gd 19                           resorbed fetuses (200 mg/kg)                             et al.
                   (No. not                                                                                                        (1976)
                   specified)       gd 8-16              100, 200         decrease in fetal body weight
                                    s.t.: gd 19                           (200 mg/kg)

                                    gd 8-16               50, 100         reduction in number of live      no effects on           Preache
                                    o.t.: up to 6                         offspring                        postnatal mortality or  et al.
                                    weeks of age                                                           body weight             (1976)

                                    days 1-29 pp          50, 100         increased mortality; decreased
                                    o.t.: up to                           body weight
                                    weaning

    Table 87 (contd).

    PBBa           Species          Treatmentc          Dietary           Major effects                    Remarks                 References
                   (No.)b                               concentrationd

    2,2',4,4'-     mouse            gd 6-15              100, 300,        at 300 mg/kg:                    17-182 fetuses were     Welsch &
    5,5'-hexa-     (C57BL)          o.t.: gd 17          500, 750,        decrease in pregnancy rates of   examined                Morgan (1985)
    bromobiphenyl  (2-22)                                  1000           plug-positive mice;
    (purity:                                                              at > 300 mg/kg:
    > 99%)                                                                reduced fetal body weight;
                                                                          malformed fetuses (cleft
                                                                          palate combined with a "cystic
                                                                          brain deviation": 5/166,
                                                                          3/172, 5/46, 6/17g,
                                                                          respectively, at 300-1000
                                                                          mg/kg; minor abnormalities of
                                                                          brain development); at >
                                                                          500 mg/kg: reduced gravid
                                                                          uterine weight

    FM BP-6        pig (2-4)        2nd half of        10, 100, 200       increased mortality during       no effect on litter     Werner &
                                    gestation and                         lactation                        size                    Sleight
                                    lactation o.t.:                                                                                (1981)
                                    up to weaning
                                    (4 weeks)

    FM FF-1        mink (8          for 9 months             1            reduced litter size; reduced     both male and female    Aulerich &
                   females;         (start before                         kit weight at birth and at 4     on PBB diet; no         Ringer
                   2 males)         breeding)                             weeks; increased mortality       effects on breeding or  (1979)
                                    4 weeks)                              (birth to periods; no            gestation
                                                                          teratogenicity

    Table 87 (contd).

    PBBa           Species          Treatmentc          Dietary           Major effects                    Remarks                 References
                   (No.)b                               concentrationd

    FM FF-1        rhesus           for over 1 year         0.3           prolonged menstrual cycles;                              Allen et al.
                   monkey           (start 7 months                       decreased serum progesterone                             (1978,
                   (7)              prior to breeding)                    levels (4/7e after 6 months);                            1979); Allen
                                                                          excessive and prolonged                                  & Lambrecht
                                                                          implantation bleeding (2/7e);                            (1978);
                                                                          abortion (1/7); stillbirth                               Lambrecht
                                                                          (1/7e); reduced weight of                                et al.
                                                                          infants at birth and at                                  (1978)
                                                                          weaning (4 months of age)

    FM FF-1        rhesus           for 25 weeks            25            hypoactive seminiferous tubules                          Allen et al.
                   monkey                                                 (at the time of death                                    (1978)
                   (1 male)

    FM BP-6        chicken (White   for 9 weeks             20            none                             no effect on            Cecil et al.
                   Leghorn) (35)                                                                           hatchability            (1974)

    "PBB"          chicken          for 8 weeks          5, 10, 20        none                             no effects on egg       Lillie et al.
                   (White                                                                                  production, egg         (1975)
                   Leghorn) (20)                                                                           weight, egg shell
                                                                                                           thickness, and
                                                                                                           fertility; no effects
                                                                                                           on hatchability,
                                                                                                           embryonal development
                                                                                                           and progeny health

    Table 87 (contd).

    PBBa           Species          Treatmentc          Dietary           Major effects                    Remarks                 References
                   (No.)b                               concentrationd

    FM BP-6        chicken          for 8 weeks             20            increased mortality of progeny   no effects on egg       Cecil &
                   (White                                                                                  production, egg         Bitman
                   Leghorn) (10)                                                                           weight, egg shell       (1978)
                                                                                                           thickness, fertility,
                                                                                                           hatchability, and
                                                                                                           embryonic death

                                    for 4-8 weeks        64, 200,         reduced egg production or stop
                                                         640, 2000        in egg production at 200-2000
                                                                          mg/kg; decreased hatchability
                                                                          of fertile eggs; increased
                                                                          mortality of progeny; reduced
                                                                          growth rate of progeny;
                                                                          embryonic deaths; embryonic
                                                                          abnormalities (subcutaneous
                                                                          oedema, oedematous cysts,
                                                                          unabsorbed yolk)

    FM FF-1        chicken          for 5 weeks          0.2-3125         decline in egg production                                Polin &
                   (White                                                 (MELf: 30-45 mg/kg); loss of                             Ringer
                   Leghorn) (24)                                          egg production (> 625 mg/kg,                             (1978a,b)
                                                                          within 2 weeks);

                                                                          reduced hatchability (MELf:
                                                                          30-45 mg/kg); dose-related
                                                                          increase in offspring
                                                                          mortality (MELf: 30-45 mg/kg;
                                                                          embryonic oedema

    Table 87 (contd).

    PBBa           Species          Treatmentc          Dietary           Major effects                    Remarks                 References
                   (No.)b                               concentrationd

    FM FF-1        chicken (10)     for 21 days             80            decline in hatchability; oedema  no effect on fertility  Polin et al.
                                                                          of embryos and newly hatched                             (1979)
                                                                          chicks

    2,2',4,4',     chicken (10)     for 21 days             52            none                             no decline in
    5,5'-hexa-                                                                                             hatchability; no
    bromobiphenyl                                                                                          oedema of chicks and
    (purity:                                                                                               and embryos
    not
    specified)

    FM             Japanese         for 9 weeks         10, 20, 100       at 100 mg/kg:                    no eggshell thinning    Babish
                   quail (No.                                             reduced egg production (17%                              et al.
                   not specified)                                         versus 68% in controls); no                              (1975a)
                                                                          hatchability; embryonal deaths

    FM FF-1        Japanese         for 5 weeks             80            reduced egg production           fertility and           Polin et al.
                   quail                                                                                   hatchability not        (1982);
                   (Coturnix                                                                               significantly           Bursian
                   coturnix                                                                                different from          et al.
                   japonica)                                                                               controls                (1983)
                   (36 males,
                   36 females)

    a    FM = FireMaster; OcBB = technical octabromobiphenyl.
    b    No. = Number of females, unless otherwise specified.
    c    gd = Gestation day (in rodents sperm day = gd 0, if recorded; exception: Waritz et al. (1977): sperm day = gd 1); pp = postpartum;
         o.t. = observed time; s.t. = sacrifice time.
    d    In mg/kg of feed, unless otherwise specified.
    e    No. affected/no. treated.
    f    MEL = Minimum effective level.
    g    As reported by Corbett et al. (1978a).

         The number of inseminations required for conception was
    increased in cows whose dams or grand dams had received oral doses
    of FireMaster(R) BP-6 (Willett et al., 1982; Table 86).

         Most of the studies evaluating the effects of PBBs on
    reproductive performance started with treatment during pregnancy
    (Tables 86 and 87). In few instances, were females exposed before
    mating (Allen et al., 1978; Aulerich & Ringer, 1979; Willett et al.,
    1980, 1982), and animals of both sexes were treated in only one
    study (Aulerich & Ringer, 1979). Under these conditions,
    FireMaster(R) reduced litter size in mice (Preache et al., 1976)
    and minks (Aulerich & Ringer, 1979), but not in rats (Harris et al.,
    1978a; McCormack et al., 1981) and pigs (Werner & Sleight, 1981). 
    The adverse effect on litter size was observed in minks given
    PBB-contaminated poultry as well as in those fed FireMaster(R),
    directly added to the diet (Aulerich & Ringer, 1979). Stillbirths
    occurred in cattle (Durst et al., 1978b; Willett et al., 1982) and
    rhesus monkeys (Allen et al., 1978; Lambrecht et al., 1978). 
    Reduced birth weights were reported in rhesus monkeys (Allen et al.,
    1978; Lambrecht et al., 1978), minks (Aulerich & Ringer, 1979), and
    mice (Corbett et al., 1978b) at intakes of 0.3, 1, or 50-1000 mg
    FireMaster(R)/kg feed, respectively (see Table 87). On the other
    hand, increased birth weights of calves resulted in a higher
    incidence of dystocia in cows (Durst et al., 1978b; Willett et al.,
    1980, 1982). The growth of progeny during lactation (indicated by
    weight at weaning) was also reduced by FireMaster(R) in rats
    (Harris et al., 1978a), mice (Preache et al., 1976), minks (Aulerich
    & Ringer, 1979), and rhesus monkeys (Allen et al., 1978; Lambrecht
    et al., 1978).

         In the study by Lambrecht et al. (1978), 14 female rhesus
    monkeys were used as an animal model (7 controls, 7 treated) to
    evaluate the toxicological effects of FM FF-1. The substance was
    added to the pelleted diet at a concentration of 0.3 mg/kg and 200 g
    of this diet was fed per day; after a dosing period of 7 months, the
    animals had ingested a total of 10.5 mg FM FF-1. Although the food
    consumption during this period was unaffected, there was a loss of
    7.4% of the initial body weight in the treated group. The total
    exposure is not stated, but, on the basis of information given in
    the paper, it appears that the dams had been exposed for a total of
    12.5 months at the time of the birth of the infants. After 6 months,
    menstrual cycles in 4/7 monkeys were lengthened (controls: 28 days;
    treated monkeys: 31 days). The treated animals showed a
    corresponding flattening of the progesterone peak. After mating, 5/7
    treated monkeys delivered normal-appearing but small infants (455 g
    vs 519 g in controls) with reduced weight gain in these infants
    during the postnatal period. Two out of 7 treated monkeys aborted a
    mummified fetus and a stillborn infant, respectively. All control
    animals delivered normal-appearing infants.

         The survival rate-to-weaning was adversely affected in the
    offspring of rats, mice, pigs, and minks, but not in calves (see
    Tables 86 and 87). FireMaster(R) levels producing the effects were
    200 mg/kg body weight per day (Groce & Kimbrough, 1984), or
    10 mg/day (Harris et al., 1978a), or 100 mg/kg feed (McCormack
    et al., 1981) in rats, 100 mg/kg feed in mice (Preache et al., 1976)
    and pigs (Werner & Sleight, 1981), and 1 mg/kg feed in minks
    (Aulerich & Ringer, 1979).

         For neurotoxic effects after perinatal exposure see section
    8.11.2.

         Ranges of maternal toxic parameters can be derived from Tables
    71, 72, 74, and 75.

    b) Embryotoxicity and teratogenicity

         PBBs were embryotoxic in rats, mice, cattle, and rhesus
    monkeys. Rats and cows appeared to be less susceptible than mice and
    rhesus monkeys (see Tables 86 and 87).

         Treatment of rats with a single high dose of FireMaster(R)
    (> 400 mg/kg body weight) on day 6 of pregnancy resulted in 100%
    embryo resorption. Generally, the number of fetal resorptions
    depended on the dose and the pregnancy stage at treatment. For
    example, after day 8 (400 mg/kg body weight dose) or day 12
    (800 mg/kg body weight dose), the embryolethal effect of
    FireMaster(R) declined abruptly (Beaudoin, 1977). Reductions in
    both fetal and placental weights were observed only at high doses
    (> 400 mg/kg body weight), and the most susceptible period of
    pregnancy was days 11-13 (Beaudoin, 1977).

         The long-term administration of lower doses (total dose: 8 or
    40 mg FireMaster(R)/animal) during pregnancy (from day 0) markedly
    increased embryonic death over that seen following administration of
    an equivalent single dose (Beaudoin, 1979). However, long-term
    intake of relatively low doses (see Tables 86 and 87) during late
    gestation (start: day 7) did not influence fetal survival rate
    (Corbett et al., 1975; Harris et al., 1978a; Johnston et al., 1980),
    but decreased fetal weight (Corbett et al., 1975; Harris et al.,
    1978a). A total dose of 600 mg FireMaster(R)/kg body weight, given
    at two-day intervals (start: day 6) had no effects on fetal death or
    fetal weight (Wertz & Ficsor, 1978).

         No significant effects on the growth or mortality of embryos
    were noted after the exposure of rats (Tables 86 and 87) to
    technical octabromobiphenyl (Waritz et al., 1977) or technical
    decabromobiphenyl (Millischer et al., 1979). Single cases of fetal
    oedema have been observed in OcBB-treated rats (Aftosmis et al.,
    1972a; Waritz et al., 1977).

         The incidence of dead or resorbed fetuses was increased in mice
    fed 200 mg FireMaster(R)/kg feed on days 4-16 of pregnancy
    (Preache et al., 1976). Feeding several concentrations of FM from
    day 7 (Corbett et al., 1975) or day 8 (Preache et al., 1976) of
    pregnancy reduced fetal weight (Table 87).

         Cattle given 25 g FM/day had 3 abortions and 3 dead fetuses
    from 6 treated animals (Durst et al., 1977; Table 86). The fetuses
    were oedematous and haemorrhagic, concomitant uterine lesions were
    haemorrhage and necrosis of the cotyledons (Moorhead et al., 1977).

         Two out of 7 rhesus monkeys fed FM (Table 87) had long
    implantation bleedings, one aborted a mummified fetus at 146 days of
    gestation and one gave birth to a stillborn infant at 154 days. The
    remaining 5 monkeys delivered small infants at 156-165 days of
    gestation (normal gestation: 165 days) (Allen et al., 1978;
    Lambrecht et al., 1978).

         Terata due to PBB exposure have been reported only in rats and
    mice (Tables 86 and 87). A single high dose of FireMaster(R)
    produced cleft palate and diaphragmatic hernia in rats (Beaudoin,
    1977). The majority of malformations were found following
    administration of 800 mg/kg body weight on day 11, 12, or 13 of
    gestation. No terata were noted in rats after multiple doses of
    FireMaster(R) (Table 86) (Harris et al., 1978a; Wertz & Ficsor,
    1978; Beaudoin, 1979) and after feeding diets containing up to
    1000 mg FireMaster(R)/kg feed (Corbett et al., 1975). In contrast
    to rats comparably treated (50-1000 mg FM/kg maternal diet), a
    higher incidence of exencephaly and cleft palate was seen in fetal
    mice, compared with pooled historical controls, but not compared
    with concurrent controls, though neither of these anomalies was seen
    in control fetuses (Corbett et al., 1975, 1978b).

         It is unclear whether the few cases of fetal gastroschisis,
    observed in rats fed technical OcBB (Table 87), are PBB-related or
    fortuitous (Aftosmis et al., 1972a; Waritz et al., 1977). No
    teratogenicity was found in rats exposed to DeBB (Millischer et al.,
    1979; Table 86).

         Embryo development was studied  in vitro. Maternal rats
    received a single, oral dose of 800 mg FM/kg body weight on
    gestation day 9, and the embryos were isolated on day 10 (24 h
    post-treatment) for cultivation over a 24- or 42-h period (Fisher,
    1980; Beaudoin & Fisher, 1981). Teratogenic effects observed (see
    Table 86) were not correlated with types of malformations found in
    earlier  in vitro experiments (Beaudoin, 1977). Some developmental
    disturbances tended to be corrected after 42 h of PBB-free culture.
    In addition to retarded development, there was a significant
    reduction in the DNA contents of cultured embryos (Fisher, 1980).
    The survival rate of embryos was not affected during the cultivation
    period (Beaudoin & Fisher, 1981).

    8.5.1.2  Avian species

         Avian reproduction was studied primarily in chickens. 
    Cockerels fed FM at various levels (10-250 mg/kg feed), for several
    weeks, showed inconsistent weight changes in the comb and testes
    (see Table 75: Ringer & Polin, 1977; Ringer, 1978; Dharma et al.,
    1982). Histologically, lipid infiltration into testicular parenchyma
    was noted (Ringer & Polin, 1977). No studies on the reproductive
    performance of these birds were made.

         Detrimental effects were seen when FireMaster(R) was fed to
    hens of both White Leghorn chickens and Japanese quails, the only
    two species studied (Table 87). Chickens (Cecil et al., 1974; Lillie
    et al., 1975; Cecil & Bitman, 1978; Polin & Ringer, 1978a,; Polin
    et al., 1979) appeared to be more sensitive to FireMaster(R) than
    the Japanese quails (Babish et al., 1975a; Bursian et al., 1983), on
    the basis of egg production and hatchability. Egg production in
    chickens was reduced by dietary levels of FireMaster(R) as low as
    30-45 mg/kg (Ringer & Polin, 1977), while the lowest effective level
    reported for Japanese quails was 80 mg/kg (Bursian et al., 1983).
    Chickens stopped laying when concentrations of FireMaster(R) in
    diets exceeded 600 mg/kg (Cecil & Bitman, 1978). The hatchability of
    eggs was adversely affected by 30-45 mg FireMaster(R)/kg feed in
    chickens (Ringer & Polin, 1977) and by 100 mg FireMaster(R)/kg
    feed in Japanese quails (Babish et al., 1975a).

         Increased mortality (Cecil & Bitman, 1978; Polin & Ringer,
    1978a, 1978b) and reduced growth rates (Cecil & Bitman, 1978) were
    seen in the offspring of chickens fed FireMaster(R) at low levels
    (< 64 mg/kg; Table 87).

         Embryonic deaths occurred in chickens (Cecil & Bitman, 1978;
    50% of deaths on the last day of incubation) and in Japanese quails
    (Babish et al., 1975b; 40% of deaths on the first day or two of
    development). The most common abnormality of embryos and newly
    hatched chicks after maternal feeding of FireMaster(R) was oedema
    (Cecil & Bitman, 1978; Polin & Ringer, 1978b; Polin et al., 1979).

         Although there was a reduction in the feed intake of exposed
    chickens, the decreased hatchability, higher incidence of
    abnormalities, and poorer progeny survival could not be reproduced
    by pair-fed control birds (Cecil & Bitman, 1978). At high dietary
    levels (> 600 mg FM/kg of feed), the direct effects of
    FireMaster(R) on egg production could not be separated from the
    effects of reduced food consumption (Cecil & Bitman, 1978).

         Adverse effects on the reproduction of chickens could return to
    normal after withdrawal of FireMaster(R) from the diet. Time for
    recovery depended on the concentration of PBB in the feed (Cecil &
    Bitman, 1978; Polin & Ringer, 1978a).

    8.5.2  Individual PBB congeners

         Individual PBB congeners have not been reported to cause weight
    changes in sex organs. Similarly, the testes of rats or cockerels,
    did not show any remarkable histological changes after treatment
    with 2,2'-dibromobiphenyl, 2,2',3,4,4',5,5'-heptabromobiophenyl,
    2,2',4,4',5,5'-hexabromobiphenyl (BB 153), 2,3',4,4',5,5' (BB 167),
    or 3,3',4,4',5,5'-hexabromobiphenyl (BB 169) (Moore et al., 1979a;
    Gupta et al., 1981; Akoso et al; 1982a; Dharma et al., 1982; Render
    et al., 1982). An exception was a decrease in the gravid uterine
    weight of pregnant mice given more than 500 mg BB 153/kg body weight
    (Welsch & Morgan, 1985).

         Embryotoxicity and other reproductive parameters have been
    studied only with BB 153 mice (Lucier et al., 1978; Welsch & Morgan,
    1985) or chickens (Polin et al., 1979). BB 153 did not cause the
    deleterious effects (decline in hatchability, oedema) that were
    produced by equivalent dietary levels of FireMaster(R) in chickens
    (Polin et al., 1979; Table 87). However, BB 153 was capable of
    producing cleft palate and cystic lesions in the region of the
    cerebellum in mouse embryos (Welsch & Morgan, 1985; Table 87). These
    adverse effects were observed at exposure concentrations that also
    cause toxicity in dams. Another less complete study (Lucier et al.,
    1978; Table 86) did not find developmental toxicity of BB 153 in
    mice, possibly because of lower exposure levels, later onset of
    exposure, and strain differences.

    8.6  Mutagenicity and related end-points

         The potential of PBBs for mutagenicity has been tested with
    several  in vitro and  in vivo assays referring to four major test
    categories: microbial and mammalian cell mutagenesis; mammalian cell
    chromosomal damage (cytogenetic tests;  in vitro and  in vivo);
    mammalian cell transformation  in vitro; and DNA damage and repair
    (UDS). Results have been summarized in Table 88. With one exception
    (Kohli et al., 1978), all studies failed to indicate any
    mutagenicity of individual PBB congeners or commercial PBB mixtures.
    Haworth et al. (1983) did not confirm the mutagenic effect of
    4-bromobiphenyl observed by Kohli et al. (1978), but they used
    different  Salmonella strains.

         However, FireMaster(R) gave positive results in a recently
    developed test, the Microscreen assay using lambda prophage
    induction in  Escherichia coli. This test has been found to be
    sensitive in detecting carcinogens which are negative in mutagenesis
    assays (Rossman et al., 1991).

    8.7  Carcinogenicity

    8.7.1  Carcinogenicity in long-term toxicity studies

         The carcinogenic effects of PBB in long-term toxicity studies
    have been compiled in Table 89. From this table, it is evident that
    the principal site of tumours was the liver. The incidence of
    hepatocellular carcinoma was significantly increased in both sexes
    of mice and rats receiving relatively high oral doses of the
    FireMaster(R) mixture.

         The results of one of these studies (Gupta et al., 1983b),
    carried out by the NCI/NTP (USA), were interpreted as
    FireMaster(R) showing carcinogenic effects (Haseman et al., 1984;
    Tennant et al., 1986). In this study, a statistically significant
    higher incidence of liver tumours was found at multiple doses of
    3 mg FM/kg body weight per day (male rats: 21%) and of 10 mg FM/kg
    body weight per day (female/male rats: 35/23%; female/male mice:
    88/95%). Atypical foci and neoplastic nodules were found at lower
    doses (Table 89). Dose-responses were statistically significant (P
    < 0.01) in male and female rats with regard to atypical foci,
    hepatocellular carcinoma, and cholangiocarcinoma, and, in female
    rats, also with regard to neoplastic nodules (Gupta et al., 1983b).
    Hepatocellular carcinoma could be produced, even after single dosing
    with FireMaster(R) (Kimbrough et al., 1981). Rats given a single
    dose of 1000 mg FM/kg or 12 doses of 100 mg FM/kg body weight, by
    gavage, developed incidences of carcinomas of 41.4 and 67.8%,
    respectively (Kimbrough et al., 1981). Liver tumours were also
    observed in female and male rats two years after perinatal exposure
    to FireMaster(R) (Groce & Kimbrough, 1984; Table 89). Although
    concurrent controls did not show such lesions, the IARC Working
    Group noted the lack of statistical significance (IARC, 1986).
    Nevertheless, the incidences of 5.9% (females) and 9.6% (males),
    respectively, exceeded the spontaneous incidence of carcinomas of
    the liver in this particular strain of rat, which is reportedly less
    than 1% (Groce & Kimbrough, 1984).

         Recently, NTP performed further carcinogenicity studies on
    FireMaster(R) to determine the following: (a) the effects of PBBs
    in F344/N rats and B6C3F1 mice receiving adult (F1) exposure only
    (0, 10, or 30 mg PBB/kg diet); (b) the toxic and carcinogenic
    effects of PBBs in rats and mice receiving perinatal (Fo) exposure
    only (10 mg/kg in rats and 30 mg/kg in mice); and (c) the effects of
    combined perinatal and adult exposure to PBBs (NTP, 1993). In an
    adult-only exposure study, both sexes in rats and mice receiving 10
    or 30 mg/kg (0.5 or 1.5 mg/kg body weight per day) showed increased
    incidences of hepatocellular adenoma/carcinoma, quite similar to
    the results of the previous studies (Gupta et al., 1983b).

    
    Table 88.  Summary of PBB genetic toxicity test results

    Assay                  Detailsb            Metabolic activation     PBBa                 Result  Remarks                   References

    Salmonella mutagenesis

    S. typhimurium         strains: TA 98      ± Aroclor 1254           FM FF-1                -                               Tennant
                                   TA 100      induced liver                                   -                               et al. (1986)
                                  TA 1535      S-9 from rats and                               -
                                  TA 1537      Syrian hamsters                                 -

    S. typhimurium         strains: TA 98      ± Aroclor 1254           hexabromobiphenylc     -                               Haworth et al.
                                   TA 100      induced liver                                   -                               (1983)
                                  TA 1535      S-9 from rats and                               -
                                  TA 1537      and Syrian hamsters

    S. typhimurium       strains: TA 1535      ± Aroclor                DeBB                   -                               Millischer
    (spot test; Ames)             TA 1537      induced rat                                     -                               et al. (1979)
                                  TA 1538      liver S-9                                       -

    S. typhimurium        strain: TA 1538      -                        DeBB                   -     mice receiving oral
    (host-mediated                                                                                   doses of 5, 10, and
    assay)                                                                                           20 g/kg body weight

    S. typhimurium         strains: TA 98      ± Aroclor 1254           2-bromobiphenyl        -                               Haworth et al.
                                   TA 100      induced liver                                   -                               (1983)
                                  TA 1535      S-9 from rats                                   -
                                  TA 1537      and Syrian hamsters                             -

    S. typhimurium         strains: TA 98      ± Aroclor 1254           3-bromobiphenyl        -
                                   TA 100      induced liver                                   -
                                  TA 1535      S-9 from rats and                               -
                                  TA 1537      Syrian hamsters                                 -

    Table 88 (contd).

    Assay                  Detailsb            Metabolic activation     PBBa                 Result  Remarks                   References

    S. typhimurium        strain: TA 1538      + Aroclor 1254           4-bromobiphenyld       +                               Kohli et al.
                                               induced rat liver S-9                                                           (1978)

                                               none                                            -

    S. typhimurium         strains: TA 98      ± Aroclor 1254           4-bromobiphenyle       -                               Haworth et al.
                                   TA 100      induced liver                                                                   (1983)
                                  TA 1535      S-9 from rats and
                                  TA 1537      Syrian hamsters

    Mammalian cell mutagenesis

    Adult rat liver (ARL)     HGPRT locus      none                     FM FF-1 (lot No.       -     at the highest non-toxic  Tong et al.
    epithelial cells                                                    1312-FS)                     dose of 10-3 mol          (1983); Williams
                                                                                                                               et al. (1984)

    Human fibroblasts         HGPRT locus      rat hepatocytes          FM FF-1 (lot No.       -     at the highest non-toxic
                                                                        1312-FS)                     dose of 10-4 mol

    Chinese hamster        HGPRT and Na-K      ± Aroclor 1254 induced   FM BP-6                -     cell survival             Kavanagh et al.
    V 79 cells                ATPase loci      rat liver S 15                                        unaffected (1-40 µg/ml)   (1985)

    Chinese hamster           HGPRT locus      ± Aroclor 1254 induced   3,3',4,4'-tetra-       -     cell survival
    V 79 cells                                 rat liver S 15           bromobiphenyl                unaffected (1-10 µg/ml)

    Chinese hamster           HGPRT locus      none                     2,2',4,4',5,5'-        -     reduced cell survival
    V 79 cells                                                          hexabromobiphenyl            (20-50 µg/ml)

    WB rat liver cells        HGPRT locus      -                        2,2',4,4',5,5'-        -     growth stimulation
                                                                        hexabromobiphenyl            effects (5-20 µg/ml)

    Table 88 (contd).

    Assay                  Detailsb            Metabolic activation     PBBa                 Result  Remarks                   References

    Chinese hamster         HGPRT locus        none                     3,3',4,4',5,5'-        -     reduced cell survival
    V 79 cells                                                          hexabromobiphenyl            (7-12 µg/ml)

    WB rat liver cells      HGPRT locus        -                        3,3',4,4',5,5'-        -     reduced cell survival
                                                                        hexabromobiphenyl

    Mammalian cell chromosomal
    damage in vitro

    Chromosome             CHO cells           ± Aroclor 1254           FM FF-1                -                               Tennant et al.
    aberrations                                induced rat                                                                     (1986)
    Sister chromatid       CHO cells           liver S-9                                       -
    exchange
    Chromosome             CHO cells           ± Aroclor 1254           hexabromobiphenyl      -                               Galloway et al.
    aberrations                                induced rat                                                                     (1987)
                                                                        liver S-9
    Sister chromatid       CHO cells                                                           ?f
    exchange

    Mammalian cell chromosomal
    damage in vivo
    (Cytogenetic effects)

    Chromosome             bone marrow cells   -                        FM                     -     colchicine-mitosis        Ficsor & Wertz
     aberrations           rat (pregnant)                                                            synergism                 (1976)
                           six oral doses of
                           100 mg/kg body
                           weight

    Table 88 (contd).

    Assay                  Detailsb            Metabolic activation     PBBa                 Result  Remarks                   References

    Chromosome             bone marrow cells   -                        FM                     -     no colchicine-mitosis     Wertz & Ficsor
    aberrations            mouse (male)                                                              synergism; increase in    (1978)
                           single dose of 50                                                         no. of gaps
                           or 500 mg/kg body
                           weight

    No. of cells in        rat (male) in diet for
     mitosis               5 weeks: 5-500 mg/kg
                           feed

    Chromosome             bone marrow cells;  -                        FM BP-6                -                               Garthoff et al.
    aberrations            spermatogonial                                                                                      (1977)
                           cells

    Micronucleus           bone marrow cells                            DeBB                   -                               Millischer
                           mouse (male and                                                                                     et al. (1979)
                           female) total dose
                           of 5, 10, or
                           20 g/kg body
                           weight at 2 doses

    Mammalian cell transformation
    in vitro

    Transformation         mouse Balb/c 3T3    ± non-induced            FM FF-1                -                               Tennant et al.
                           cells               male F 344 rat                                                                  (1986)
                                               hepatocytes

    Table 88 (contd).

    Assay                  Detailsb            Metabolic activation     PBBa                 Result  Remarks                   References

    DNA damage and repair
    (in vitro)

    Unscheduled DNA        hepatocyte primary  -                        FM FF-1                -     at the highest nontoxic   Tong et al.
    synthesis (UDS)        cultures (HPCs)                                                           doses of 10-3 mol (mice,  (1983);
                           from rat, hamster,                                                        hamsters) or 10-5 mol     Williams et al.
                           and mouse                                                                 (rats)                    (1984)

    DNA damage and repair
    (in vivo - in vitro)

    UDS                    hepatocyte primary  -                        FM FF-1                -                               Tennant et al.
                           cultures (HPCs)                                                                                     (1986)
                           from treated male
                           F 344 rats

    UDS                    hepatocyte primary  -                        FM FF-1                -     simultaneous measurement  Mirsalis et al.
                           cultures (HPCs)                                                           of hepatic cell           (1985)
                           from treated                                                              proliferative ability:
                           B6C3F1 mice (males                                                        increased cell
                           and females)                                                              proliferation

    a    Commercial PBB mixtures: FM = FireMaster(R); DeBB = decabromobiphenyl.
    b    HGPRT = hypoxanthine-guanine phosphoribosyl transferase.
    c    CAS No.: 36355-01-8; source: Pfaltz & Bauer.
    d    Source of PBB: Aldrich & Eastman Chemicals.
    e    Source of PBB: Pfaltz & Bauer.
    f    There was a very slight (16%) increase in SCEs without S-9 doses that produced severe cell cycle delay.

    Table 89.  Summary of carcinogenic effects of PBBs in long-term toxicity studies

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

    FM FF-1             rat            F, M   oral             1000             10 months     liver: neoplastic nodules           Kimbrough
    (lot no. 7042)      (Sherman)             single dose                                     (preliminary study) (F: 4/5;        et al. (1977,
    (in peanut oil)     (5)                                                     14 months     M: 0/5); (F: 3/5; M: 2/5);          1978)
                                                                                              (control: 0/5)
    FM FF-1             rat            F      oral             1000             23 months     liver: trabecular carcinoma         Kimbrough
    (lot no. 7042)      (Sherman)             single dose                                     (24/58 = 41.4% versus 0% in         et al. (1981)
    (in corn oil)       (65)                                                                  control) neoplastic nodules
                                                                                              (42/58 = 72.4% versus 0% in
                                                                                              control) foci or altered areas
                                                                                              (57/58 = 98.3% versus 1/53 in
                                                                                              control)

                        (16)                                   200              18-22         liver: no carcinoma
                                                                                months        neoplastic nodules
                                                                                              (5/16 = 31.2% versus 0% in
                                                                                              control) altered areas
                                                                                              (8/16 = 50% versus 1/19 in
                                                                                              control)

    FM BP-6             rat            F      oral two         total dose:      120 days      liver: small numbers of enzyme      Rezabek et
    (in corn oil)       (Sprague-             doses over       13 and 130                     altered foci (EAF)                  al. (1987)
                        Dawley)               24 h             mg/kg body
                                                               weight

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

    FM FF-1             rat            M      oral 22          30               6 months      liver: atypical nodules (2/9)       Gupta &
    (lot no. 1312       (Fischer              doses over                        (after 1      liver: atypical nodules (1/2)       Moore (1979)
    FT) (in corn        344/N)                4.5 weeks        100              dose)         epididymis: sperm granuloma (1/2)
    oil)                (9)

    FM FF-1             rat            F      oral 12          100              24 months     liver: trabecular carcinoma         Kimbrough
    (lot no. 7042)      (Sherman)             doses over                                      (17/28 = 60.7% versus 0% in         et al. (1981)
    (in corn oil)       (30)                  4 months                                        control) neoplastic nodules
                                                                                              (24/28 = 85.7% versus 1/25 in
                                                                                              control) foci or altered areas
                                                                                              (23/28 = 82.1% versus 1/25 in
                                                                                              control) adenocarcinoma
                                                                                              (1/28 = 3.6% versus 0% in control)
                                                                                              malignant tumour with metastases
                                                                                              to heart (1/28 = 3.6% versus 0%
                                                                                              in control)

                                                                                              Total malignant liver tumours:
                                                                                              19/28 (67.8% versus 0/25 in
                                                                                              controls)

    FM FF-1             rat            F, M   oral 125         0.1, 0.3,        6 months      liver: atypical foci (3/100);       Gupta et al.
    (lot no. 1312       (Fischer              doses over       1, 3, 10         (after 1      urinary bladder: squamous cell      (1983a)
    FT) (in corn        344/N)                6 months                          dose)         carcinoma (F: 1/51, high dose
    oil)                (51)

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

    FM FF-1             rat            F, M   oral 125                          lifetime                                          Gupta et al.
    (lot no. 1312       (Fischer              doses over                                                                          (1983b)
    FT) (in corn        344/N)                6 months
    oil)                (total: 320)          (sacrifice of
                                              10% animals
                                              alive, 23
                                              months post-
                                              treatment)

                                       F, M                    0.1                            liver: atypical foci
                                                                                              (M: 3/39 = 8%; F= 0/21)
                                                                                              neoplastic nodules
                                                                                              (M: 0/39; F: 2/21 = 10%)
                                                                                              carcinoma (M: 2/39 = 5%; F: 0/21)

                                                               0.3                            liver: atypical foci
                                                                                              (M: 12/40 = 30%, P < 0.01; F:
                                                                                              1/21 = 5%) neoplastic nodules
                                                                                              (M: 1/40 = 2%; F: 0/21) carcinoma
                                                                                              (M: 0/40; F: 0/21)

    FM FF-1             rat            F, M                    1                              liver: atypical foci                Gupta et al.
    (lot No. 1312       (Fischer                                                              (M: 11/31 = 35%, P < 0.01; F:       (1983b)
    FT) (in corn        344/N                                                                 2/11 = 18%) neoplastic nodules
    oil)                (total:                                                               (M: 4/31 = 13%, P < 0.05; F: 2/11)
                        320)                                                                  carcinoma

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

                                                               3                              liver: atypical foci
                                                                                              (M: 13/33 = 39%, P < 0.01; F:
                                                                                              4/19 = 21%) neoplastic nodules
                                                                                              (M: 4/33 = 12%; F: 5/19 = 26%,
                                                                                              P < 0.01) carcinoma
                                                                                              (M: 7/33 = 21%, P < 0.01; F:
                                                                                              3/19 = 16%)

                                                               10                             liver: atypical foci
                                                                                              (M: 12/31 = 39%, P < 0.01; F:
                                                                                              8/20 = 40%, P < 0.01 neoplastic
                                                                                              nodules (M: 1/31 = 3% F: 8/20 =
                                                                                              40%, P < 0.01 carcinoma (M:
                                                                                              7/31 = 23%, P < 0.01; F: 7/20 =
                                                                                              35%, P < 0.01; control: 0/33)
                                                                                              cholangiocarcinoma (M: 2/31 = 6 %,
                                                                                              F: 7/20 = 35%, P < 0.01)

    FM FF-1             rat            F, M   perinatal        total dose:      2 years       liver: neoplastic nodules           Groce &
    (lot 7042)          (Sherman)             exposure:        400 mg/kg        of age        (M: 2/41 = 4,9%, F: 9/51 = 17.6%)   Kimbrough
    (in corn oil)       (41-51)               two maternal     body                           trabecular carcinoma                (1984)
                                              oral doses       weight                         (M: 4/41 = 9.6%;
                                              on gestation                                    F: 3/51 = 5.9%; controls: 0%)
                                              days 7 and
                                              14

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

    FM FF-1             rat            F, M   adult only       0                24 months     liver: eosinophilic focus           NTP (1993)
    (lot FF 1312-       (Fischer              exposure (in                                    (M: 36%; F: 6%)
    FT)                 344/N)                diet for                                        oval cell hyperplasia
                        (50)                  24 months)                                      (M: 0%; F: 0%)
                                                                                              hepatocellular adenoma
                                                                                              (M 2%: F: 0%)
                                                                                              hepatocellular carcinoma
                                                                                              (M: 0%; F: 0%)

                                                               10                             liver: eosinophilic focus (M:
                                                                                              90%, p < 0.01; F: 94%, P < 0.01)
                                                                                              oval cell hyperplasia (M: 22%,
                                                                                              P < 0.01; F: 24%, P < 0.01)
                                                                                              hepatocellular adenoma (M: 20%;
                                                                                              F: 20%) hepatocellular carcinoma
                                                                                              (M: 4%; F: 4%) hepatocellular
                                                                                              adenoma/carcinoma (M: 24%, P
                                                                                              < 0.001; F: 24%, P < 0.001)

                                                               30                             liver: eosinophilic focus           NTP (1993)
                                                                                              (M: 92%, P < 0.01; F: 96%, P
                                                                                              < 0.01) oval cell hyperplasia
                                                                                              (M: 74%, P 0.01; F: 84%, P
                                                                                              < 0.01) hepatocellular adenoma
                                                                                              (M: 76%, P < 0.001; F: 76%, P <
                                                                                              0.001); hepatocellular carcinoma
                                                                                              (M: 38%, P < 0.001; F: 8%)
                                                                                              hepatocellular adenoma/carcinoma
                                                                                              (M: 82%, P < 0.001; F: 78%, P
                                                                                              < 0.001)

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

    FM FF-1             rat            F, M   perinatal only   10               24 months     liver: eosinophilic focus
    (lot FF-1312-       (Fischer              exposure                                        (M: 58%, P < 0.01; F: 38%, P
    FT)                 344/N)                (female parents                                 < 0.01) hepatocellular adenoma
                        (50)                  received                                        (M: 10%; F: 0%)
                                              FM-containing
                                              diet beginning
                                              60 days prior
                                              to breeding and
                                              throughout
                                              gestation,
                                              lactation, and
                                              up to 4 weeks
                                              postweaning)

    FM FF-1             rat            F, M   combined         1:3e             24 months     liver: eosinophilic focus           NTP (1993)
    (lot FF1312-        (Fischer              perinatal and                                   (M: 80%; F: 38%)
    FT)                 344/N)                adult exposure                                  oval cell hyperplasia (M: 8%;
                        (50)                                                                  F: 0%) hepatocellular adenoma
                                                                                              (M: 6%; F: 4%) hepatocelluar
                                                                                              carcinoma (M: 2%; F: 0%)

                                                               10:10f           24 months     liver: oval cell hyperplasia
                                                                                              (M: 46% versus 22% in 10 mg/kg
                                                                                              adult exposure group, P < 0.01
                                                                                              F: 68% versus 24% in 10 mg/kg
                                                                                              adult exposure group, P < 0.01)
                                                                                              hepatocellular adenoma

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

                                                                                              (M: 32% versus 20% in 10 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 70% versus 20% in 10 mg/kg
                                                                                              adult exposure group)
                                                                                              hepatocellular carcinoma
                                                                                              (M: 2% versus 4% in 10 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 16% versus 4% in 10 mg/kg
                                                                                              adult exposure group)
                                                                                              hepatocellular adenoma/carcinoma
                                                                                              (M: 32% versus 24% in 10 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 78% versus 24% in 10 mg/kg
                                                                                              adult exposure group, P < 0.001)

                                                               10:30g           24 months     liver: oval cell hyperplasia        NTP (1993)
                                                                                              (M: 82% versus 74% in 30 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 88% versus 84% in 30 mg/kg
                                                                                              adult exposure group)
                                                                                              hepatocellular adenoma
                                                                                              (M: 76% versus 76% in 30 mg/kg
                                                                                              adult exposure group
                                                                                              F: 90% versus 76% in 30 mg/kg
                                                                                              adult exposure group)
                                                                                              hepatocellular carcinoma
                                                                                              (M: 46% versus 38% in 30 mg/kg
                                                                                              adult exposure group
                                                                                              F: 44% versus 8% in 30 mg/kg
                                                                                              adult exposure group, P < 0.01)

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

    FM FF-1             mouse          F, M   oral 125 doses   10               6 months      liver: atypical foci                Gupta et al.
    (lot no. 1312       (B6C3F1)              over 6 months                                   (11/100 versus 1/20 in control)     (1983a)
    FT) (in corn        (50)                                                                  (M: 9/50; F: 2/50)
    oil)

    FM FF-1             mouse          F, M   oral 125 doses   0.1, 0.3,        lifetime      high dose: liver: carcinoma         Gupta et al.
    (lot no. 1312       (B6C3F1)              over 6 months    10                             (M: 21/22 = 95% versus 12/25 in     (1983b)
    FT) (in corn        (8-27)                (sacrifice of                                   control; P < 0.01; F: 7/8 = 88%
    oil)                                      10% animals                                     versus 0/13 in control; P < 0.01)
                                              alive 24                                        metastasis to lung
                                              months post-                                    (F: 3/8 = 38% versus 0/13 in
                                              treatment)                                      control; P < 0.05)

    FM FF-1             mouse          F, M   adult only       0                24 months     liver: eosinophilic focus (M: 6%;   NTP (1993)
    (lot FF1312-        (B6C3F1)              exposure (in                                    F: 2%) bile duct hyperplasia
    FT)                 (50)                  diet for 24                                     (M: 0%; F: 0%) hepatocellular
                                              months)                                         ademona (M: 18%; F: 8%)
                                                                                              hepatocellular carcinoma
                                                                                              (M: 16%; F: 2%)

                                                               10                             liver: eosinophilic focus (M: 33%,
                                                                                              P < 0.01; F: 36%, P < 0.01) bile
                                                                                              duct hyperplasia (M: 8%, < 0.01;
                                                                                              F: 18%, P < 0.01) hepatocellular
                                                                                              adenoma (M: 98%, P < 0.01; F: 78%,
                                                                                              P < 0.01) hepatocellular carcinoma
                                                                                              (M: 61%, P < 0.01; F: 44%, P <
                                                                                              0.01 hepatocellular adenoma/
                                                                                              carcinoma (M: 98%, P < 0.001;
                                                                                              F: 84%, P < 0.001)

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

                                                               30                             liver: eosinophilic focus           NTP (1993)
                                                                                              (M: 12%, F: 8%); bile duct
                                                                                              hyperplasia (M: 68%, P 0.01;
                                                                                              F: 81%, P < 0.01) hepatocellular
                                                                                              adenoma (M: 84%, P < 0.001;
                                                                                              F: 96%, P < 0.001); hepatocellular
                                                                                              carcinoma (M: 72%, P < 0.001;
                                                                                              F: 73%, P < 0.001) hepatocellular
                                                                                              adenoma/carcinoma (M: 96%, P <
                                                                                              0.001; F: 98%, P < 0.001)

    FM FF-1             mouse          F, M   perinatal only   30               24 months     liver: eosinophilic focus           NTP (1993)
    (lot FF-1312-       (B6C3F1)              exposure                                        (M: 40%, P < 0.01; F: 6%, P <
    FT)                 (50)                  (female parents                                 0.01) hepatocellular adenoma
                                              received                                        (M: 62%, P < 0.001; F: 38%, P <
                                              FM-containing                                   0.001) hepatocellular carcinoma
                                              diet beginning                                  (M: 34%, F: 8%) hepatocellular
                                              60 days prior                                   adenoma/carcinoma (M: 80%, P <
                                              to breeding and                                 0.001; F: 42%, P < 0.001)
                                              throughout
                                              gestation,
                                              lactation, and
                                              up to 4 weeks
                                              postweaning)

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

    FM FF-1             mouse          F, M   combined         10:10f           24 months     liver: eosinophilic focus           NTP (1993)
    (lot FF 1312-       (B6C3F1)              perinatal and                                   (M: 8% versus 33% in 10 mg/kg
    FT)                 (50)                  adult exposure                                  adult exposure group,
                                                                                              F: 32% versus 36% in 10 mg/kg
                                                                                              adult exposure group) bile duct
                                                                                              hyperplasia (M: 0% versus 0% in
                                                                                              10 mg/kg adult exposure group
                                                                                              (F 18% versus 18% in 10 mg/kg)
                                                                                              adult exposure group)
                                                                                              hepatocellular adenoma
                                                                                              (M: 94% versus 98% in 10 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 76% versus 78% in 10 mg/kg
                                                                                              adult exposure group)
                                                                                              hepatocellular carcinoma
                                                                                              (M: 63% versus 61% in 10 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 52% versus 44% in 10 mg/kg
                                                                                              adult exposure group)

    FM FF-1             mouse          F, M   combined         30:10h           24 months     liver: eosinophilic focus           NTP (1993)
    (lot FF 1312-       (B6C3F1)              perinatal and                                   (M: 0% versus 33% in 10 mg/kg
    FT)                 (50)                  adult exposure                                  adult exposure group, P < 0.01;
                                                                                              F: 8% versus 36% in 10 mg/kg
                                                                                              adult exposure group, P < 0.01)
                                                                                              bile duct hyperplasia
                                                                                              (M: 16% versus 0% in 10 mg/kg

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

                                                                                              adult exposure group, P < 0.01;
                                                                                              F: 12% versus 18% in 10 mg/kg
                                                                                              adult exposure group)
                                                                                              hepatocellular adenoma
                                                                                              (M: 96% versus 98% in 10 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 94% versus 78% in 10 mg/kg
                                                                                              adult exposure group)
                                                                                              hepatocellular carcinoma
                                                                                              (M: 80% versus 61% in 10 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 88% versus 44% in 10 mg/kg
                                                                                              adult exposure group)
                                                                                              hepatocellular adenoma/carcinoma
                                                                                              (M: 96% versus 98% in 10 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 100% versus 84% in 10 mg/kg
                                                                                              adult exposure group)

                                                               30:30i           24 months     liver: hepatocellular adenoma       NTP (1993)
                                                                                              (M: 96% versus 84% in 30 mg/kg
                                                                                              adult exposure group,
                                                                                              F: 87% versus 96% in 30 mg/kg
                                                                                              adult exposure group,
                                                                                              hepatocellular carcinoma
                                                                                              (M: 70% versus 72% in 30 mg/kg
                                                                                              adult exposure group;
                                                                                              F: 62% versus 73% in 30 mg/kg
                                                                                              adult exposure group)

    Table 89 (contd).

    PBB                 Species        Sexb   Treatment        Dose/            Observation   Site or type of tumourd             References
                        (strain)                               concentrationc   period
                        (No.a)

    NoBB                mouse          F, M   in diet for      100              18 months     liver: carcinoma: 300/100 mg/kg     Momma (1986)
    (Bromkal            (B6C3F1)              18 months        300                            (M: 28%/78%; F: 76%/17% versus
    80-9D)              (50)                                                                  14% (M), 0% (F) in controls)
                                                                                              neoplastic nodules: 300/100 mg/kg
                                                                                              (M: 96%/98%, F: 92%/72% versus
                                                                                              38% (M), 0% (F) in controls)
                                                                                              hepatoblastoma: 300 mg/kg
                                                                                              (M: 2%/12% versus 0% in controls)

    2,2',4,4',5,5'      rat            F      in diet for      10               180 days      liver: no neoplastic nodules;       Jensen &
    hexabromobiphenyl   (Sprague-             for 180 days                                    no EAF                              Sleight
    (BB 153)            Dawley) (3)                                                                                               (1986)

                                                               100              100 days      liver: neoplastic nodules (1/3)
                                                                                              small numbers of EAF

                        (6)            F      in diet          10               450 days      liver: no nodules, no carcinoma     Jensen &
                                              for 140 days                                                                        Sleight
                                                                                                                                  (1986)

    3,3',4,4',5,5'      rat (Sprague-  F      in diet          0.1              450 days      liver: no nodules, no carcinoma
    hexambromobiphenyl  Dawley)               for 140 days
    (BB 169)            (6)

    Mixture of BB       rat (Sprague-  F      in diet          10 plus          450 days      liver: no nodules, no carcinoma
    153 and BB 169      Dawley)               for 140 days     0.1 resp.

    Table 89 (contd).

    a    Number per experimental group, unless otherwise specified.
    b    F = female; M = male.
    c    In mg/kg body weight per day or in mg/kg feed, unless otherwise specified.
    d    Including nodules and atypical foci (numbers in parentheses: number affected/number treated); EAF = enzyme altered foci.
    e    F1 animals born after the perinatal exposure at dietary level of 1 mg/kg PBBs received diets containing 3 mg/kg PBBs up to 2 years.
    f    F1 animals born after the perinatal exposure at dietary level of 10 mg/kg PBBs received diets containing 10 mg/kg PBBs up to 2 years.
    g    F1 animals born after the perinatal exposure at dietary level of 10 mg/kg PBBs received diets containing 30 mg/kg PBBs up to 2 years.
    h    F1 animals born after the perinatal exposure at dietary level of 30 mg/kg PBBs received diets containing 10 mg/kg PBBs up to 2 years.
    i    F1 animals born after the perinatal exposure at dietary level of 30 mg/kg PBBs received diets containing 10 mg/kg PBBs up to 2 years.

         Perinatal-only exposure (through dietary administration of
    10 mg PBBs/kg to the dams) had no effect on the incidence of hepatic
    neoplasms in female rats, but, in male rats, this exposure was
    associated with a marginally increased incidence of hepatocellular
    adenomas. Perinatal exposure to 30 mg PBBs/kg showed significantly
    increased incidences of hepatocellular adenoma/carcinoma in male and
    female mice.

         Combined perinatal and adult exposure to PBBs confirmed the
    findings of the adult-only exposures in rats and mice. Although
    there were no enhancing effects of combined perinatal and adult
    exposure, perinatal exposure enhanced the susceptibility to the
    induction of liver tumours of adult female rats, exposed to 10 or
    30 mg/kg diet. In male and female mice, it was not possible to
    assess adequately the enhancing effects on hepatocellular tumours of
    combined perinatal and adult exposure, because adult-only exposure
    to 10 or 30 mg PBBs/kg resulted in high incidences (84-98%) of
    hepatocellular adenoma/carcinoma. However, with increased perinatal
    exposure, there were increases in the numbers of mice with
    hepatocellular carcinomas and mice with multiple hepatocellular
    adenomas, which suggests an enhancement of PBB-related
    hepatocellular carcinogenicity associated with perinatal exposure. A
    dietary dose of 3 mg/kg (0.15 mg/kg body weight per day) and pre-
    and perinatal exposure of the dam to 1 mg/kg (0.05 mg/kg body weight
    per day), the lowest dose in this combined perinatal and adult
    exposure, did not cause any adverse effects on rats.

         Feeding of 10-100 mg FireMaster(R) BP-6 or
    2,2',4,4',5,5'-hexa-bromobiphenyl (BB 153)/kg diet or of 0.1 mg
    3,3',4,4',5,5'-hexa-bromobiphenyl/kg diet did not cause
    hepatocellular carcinoma in rats, but neoplastic nodules were found
    at 100 mg FireMaster(R) or BB 153/kg of feed (Jensen et al., 1982;
    Jensen & Sleight, 1986).  However, the number of animals used was
    small, and the observation time less than 2 years.

         The incidence of hepatocellular carcinomas was increased in
    male and female mice receiving diets containing commercial
    nonabromobiphenyl (Bromkal 80-9D) at 100 or 300 mg/kg diet, for 18
    months; hepatoblastomas were also seen in males (Momma, 1986; Table
    89).

         The carcinogenic effects of commercial OcBB and DeBB have not
    been studied.

    8.7.2  Mechanisms of carcinogenicity

         Generally, the development of cancer is described as a
    multistage process consisting of initiation and promotion phases
    (e.g., Safe, 1984). The question of the mechanism of PBB-induced
    carcinogenicity is addressed in several studies.

    8.7.2.1  Tumour initiation

         As seen in section 8.6, there is no strong evidence for the
    mutagenicity or genotoxicity of PBBs, which is a property of known
    initiators. Additionally, PBBs (a mixture of almost exclusively BB
    153 and BB 180) did not bind to DNA (Dannan et al., 1978b).

         FireMaster(R) and BB 153 were also tested as tumour
    initiators (and promotors) in a two-stage mouse skin tumorogenesis
    assay (Haroz & Aust, 1979). A tumour promoter,
    12-0-tetradecanoyl-phorbol-13-acetate (TPA), was applied to the skin
    of a mouse of a tumour-susceptible strain (SENCAR). After 14 weeks
    of treatment, neither FM nor BB 153 exhibited tumour initiating (or
    promoting: see Table 90) activity. However,
    3,3',4,4'-tetrabromo-biphenyl, tested in a two-stage rat bioassay
    (promotion by phenobarbital), showed some evidence for weak
    initiating activity (Dixon et al., 1985, 1988). In contrast to
    3,3',4,4'-tetrabromobiphenyl which can be metabolized,
    FireMaster(R) has not been tested for initiating activity in this
    bioassay, since FireMaster(R) would persist in the tissues of the
    animals beyond the initiation phase and throughout the promotion
    phase (Rezabek et al., 1987).

    8.7.2.2  Tumour promotion

         Varied results (Table 90) were obtained with tumour promotion
    assays, in which PBBs were tested in combination with known
    carcinogens (2-acetylaminofluorene in rats, Schwartz et al., 1980;
    partial hepatectomy plus i.p. administration of  N-nitrosodiethyl
    amine in rats, Jensen et al., 1982, 1983, 1984; Jensen & Sleight,
    1986; Rezabek et al., 1987; Dixon et al., 1988; subcutaneous
    administration of  N-nitrosodiethylamine in hamsters, Wasito &
    Sleight, 1989; 7,12-dimethyl-benz [a]-anthracene by skin
    application in mice, Berry et al., 1978; Haroz & Aust, 1979;
     N-methyl- N-nitro- N-nitroso-guanidine by skin application in
    mice, Poland et al., 1982).

         On evaluating the development of tumours, hepatocellular
    carcinoma was found in rats (Jensen, 1983) and skin papilloma in
    mice (Poland et al., 1982). Other studies with FireMaster(R)
    resulted in negative findings (Berry et al., 1978; Haroz & Aust,
    1979; Schwartz et al., 1980). Only few hepatocellular carcinomas
    were present in initiated rats given
    2,2',4,4',5,5'-hexabromobiphenyl (BB 153) or
    3,3',4,4',5,5'-hexabromobiphenyl (BB 169) or a mixture of both
    (Jensen et al., 1982). In a mouse skin test, BB 169 was effective in
    promoting papillomas, but BB 153 was not (Poland et al., 1982).

         Another indicator of tumour-promoting ability in initiated rats
    was the counting and measuring of enzyme-altered foci (EAF;
    exhibiting gamma-glutamyltranspeptidase activity) and hepatic
    nodules, which were presumed to be precursor lesions of
    hepatocellular carcinomas (e.g., Sleight, 1985). In these studies
    (see Table 90) devised by Pitot et al. (1978), FireMaster(R)
    (Jensen et al., 1982, 1984; Jensen & Sleight, 1986; Rezabek et al.,
    1987) and its non-toxic major congener BB 153 (Jensen et al., 1982;
    Jensen & Sleight, 1986) acted as tumour promoters, FM being more
    effective than Bb 153 at dietary concentrations of 10 and 100 mg/kg
    (Jensen et al., 1982). Short-term feeding of FM was as effective as
    long-term feeding in enhancing the development of enzyme-altered
    foci (Jensen et al., 1984). Similarly, an oral 24-h administration
    of FM was sufficient to enhance EAFs (Rezabek et al., 1987). An oral
    dose of 13 mg FM/kg body weight was found to be close to a possible
    no-effect threshold level for the enhancement of EAF (Rezabek
    et al., 1987). BB 169 (3,3',4,4',5,5'- hexa) was tested positive
    only at a dose (1 mg/kg feed) that was hepatotoxic (Jensen et al.,
    1983). It was concluded (e.g., Sleight, 1985) that toxicity and
    carcinogenicity are not necessarily related. Synergistic as well as
    inhibitory effects on tumour-promoting ability could be elicited by
    special combinations of BB 153 and BB 169 (Sleight, 1985; Jensen &
    Sleight, 1986).

         Preliminary studies with FireMaster(R) BP-6 indicated that
    iron overload may enhance the hepatocarcinogenicity of PBBs in
    C57BL/10 ScSn male mice (Smith et al., 1990b).

         Interestingly, FireMaster(R) and
    2,2',4,4',5,5'-hexabromobiphenyl inhibited intercellular
    communication  in vitro at non-toxic doses, a property of known
    tumour promoters (e.g., Sleight, 1985), but
    3,3',4,4',5,5'-hexabromobiphenyl did not (Table 95; section 8.9). 
    Probably, non-toxic congeners, such as BB 153, have a direct
    tumour-promoting effect by interfering in normal cell-to-cell
    communication, whereas toxic congeners like BB 169 promote tumours
    secondarily to hepatic degeneration and necrosis (e.g., Sleight,
    1985).

    8.7.2.3  PBBs acting as complete carcinogens

         The development of tumours, hepatic nodules, or small numbers
    of EAF (Table 89) in PBB-exposed rodents that were not
    experimentally initiated has been interpreted in two ways: either
    PBBs (or some of them) have both initiating and promoting activity
    or the observed effects may have resulted from the promotion of
    "environmentally initiated" cells. As yet, neither of the two
    possibilities can be ruled out (Jensen et al., 1982; Sleight, 1985;
    Rezabek et al., 1987).

    
    Table 90.  Effects of PBB in tumour promotion assays

    PBB              Species         Initiation of               PBB             Observation     Effectsb                        References
                     (strain)        carcinogenesis              treatment       period after
                     (No.)a                                                      PBB treatment

    FM BP-6          rat (Sprague-   simultaneous treatment:     in diet 50      0               inhibition of 2-FAA induced     Schwartz
                     Dawley)         2-acetylaminofluorene       mg/kg for                       mammary and ear duct            et al. (1980)
                     (F, 8-12)       (2-FAA) in diet             57 weeks                        carcinogenesis; no significant
                                     (300 mg/kg feed)                                            effect on hepatic tumours
                                                                                                 (5/12 versus 3/8 in 2-FAA
                                                                                                 group)

    FM BP-6          rat (Sprague-   pretreatment: 70% partial   in diet 10      0               liver: neoplastic nodules       Jensen et al.
    (lot 6224 A)     Dawley)         hepatectomy plus N-nitro-   and 100 mg/kg                   (6/6) increase in EAF (P <      (1982)
                     (F,6)           sodiethylamine (DEN)        for 180 days                    0.05) (both levels)
                                     (single ip dose of 10
                                     mg/kg body weight)

    FM               rat (4)         pretreatment 70% partial    in diet 10      275 days        liver: carcinoma (4/4 versus 0  Jensen (1983)
                                     hepatectomy plus for        mg/kg                           in control)
                                     140 days DEN (single ip
                                     dose of 10 mg/kg
                                     body weight)

    FM BP-6          rat (Sprague-   pretreatment: 70% partial   in diet 100     0               liver: increase in EAF          Jensen et al.
    (lot 6224 A)     Dawley)         hepatectomy plus DEN        mg/kg for                       (P < 0.05)                      (1984)
                     (F,6)           (single ip dose of          for 15 days
                                     10 mg/kg body weight)       10 mg/kg for    0               liver: increase in EAF
                                                                 140 days                        (P < 0.05)

    Table 90 (contd).

    PBB              Species         Initiation of               PBB             Observation     Effectsb                        References
                     (strain)        carcinogenesis              treatment       period after
                     (No.)a                                                      PBB treatment

    FM BP-6          rat (Sprague-   pretreatment: two-thirds    oral two doses  120 days                                        Rezabek et al.
                     Dawley)         partial hepatectomy plus    over 24 h                                                       (1987)
                     (F,6)           DEN (single ip dose of      total dose:
                                     10 mg/kg body weight)       13 mg/kg and                    liver: increase in EAF (not
                                                                 130 mg/kg body                  significant) liver: increas
                                                                 weights                         in EAF (P < 0.05)

    FM BP-6          mouse CD1       pretreatment: 7,12-di-      dermal          0               skin: no papilloma              Berry et al.
                     (F,30)          methylbenz(a)anthracene     multiple doses                                                  (1978)
                                     (DMBA) (single dermal       (twice weekly
                                     dose of 200 nmol)           over 30 weeks)
                                                                 100 µg

    FM BP-6          mouse           pretreatment. DMBA          dermal          0               skin: no tumours                Haroz & Aust
                     (SENCAR)        (single dermal              multiple doses                                                  (1979)
                     (sex, no.:      subcarcinogenic dose)       (twice weekly
                     not                                         over 14 weeks)
                     specified)                                  dose: not
                                                                 specified

    FM FF-1          mouse           pretreatment: N-methyl-     dermal          0               skin: papilloma (9/15 = 60%)    Poland et al.
                     hairless        N'-nitro-N-                 multiple doses                                                  (1982)
                     HRS/J           nitrosoguanidine (MNNG)     (twice weekly
                     (F,20-26)       (single dermal dose of      over 20 weeks)
                                     5 µmol)                     2 mg, 5 weeks,
                                                                 then

    FM BP-6          hamster         pretreatment: DEN (single   in diet 100     133 days        respiratory tract: increase in  Wasito &
                     (Syrian         sc dose of 80 mg/kg         mg/kg for                       number of tracheal papillomas   Sleight (1989)
                     golden)         body weight                 140 days                        (P < 0.05)

    Table 90 (contd).

    PBB                 Species        Initiation of              PBB              Observation     Effectsb                      References
                        (strain)       carcinogenesis             treatment        period after
                        (No.)a                                                     PBB treatment

    3,3',4,4'-          rat (Sprague-  pretreatment: 70% partial  in diet 0.1,     0               liver: increase in EAF        Dixon et al.
    tetrabromobiphenyl  Dawley)        hepatectomy plus DEN       1, 5 mg/kg                       (significant at the high      (1988)
                        (F, 6)         (single ip dose of 10      for 180 days                     dose)
                                       mg/kg body weight)

    3,3',4,4'-          rat (Wistar)   pretreatment: DEN (oral    intraperitoneal  until 1 week    liver: increase in EAF        Buchmann
    tetrabromobiphenyl  (F,6)          dose of 10 mg/kg body      15 µmol/kg       and 9 weeks                                   et al. (1991)
                                       weight for 10 days)        body weight
                                                                  once weekly
                                                                  for 8 weeks

    2,2',4,4',5,5'-     rat (Sprague-  pretreatment: 70% partial  in diet 10       0               liver: neoplastic nodules     Jensen et al.
    hexabromobiphenyl   Dawley)        hepatectomy plus DEN       and 100 mg/kg                    (3/6) increase in EAF (P      (1982)
    (BB 153)            (F,6)          (single ip dose of 10      for 180 days                     < 0.05) neoplastic nodules
                                       mg/kg body weight)                                          (5/6) increase in EAF (P <
                                                                                                   0.05)

                                                                  in diet 10       0               liver: increase in EAF (P     Jensen &
                                                                  mg/kg for        70 days         < 0.05) increase in EAF (P    Sleight (1986)
                                                                  140 days         310 days        < 0.05) increase in hepatic
                                                                                                   nodules (P < 0.05) carcinoma
                                                                                                   (1/10 versus 0 in controls)

                        mouse          pretreatment: DMBA         dermal multiple  0               skin: no tumours              Haroz &
                        (SENCAR)       (single dermal             doses (twice                                                   Aust (1979)
                        (sex, no.:     sub-carcinogenic dose)     weekly over 14
                        not                                       weeks) dose:
                        specified)                                not specified

    Table 90 (contd).

    PBB                 Species        Initiation of              PBB              Observation     Effectsb                      References
                        (strain)       carcinogenesis             treatment        period after
                        (No.)a                                                     PBB treatment

    2,2',4,4',5,5'-     mouse          pretreatment MNNG          dermal           0               skin: no papilloma (0/22)     Poland et al.
    hexabromobiphenyl   hairless       (single dermal dose        multiple doses                                                 (1982)
                        HRS/J          of 5 µmol)                 (twice weekly
                        (F,20-26)                                 over 20 weeks)
                                                                  20 µg

    3,3',4,4',5,5'-     rat (Sprague-  pretreatement: 70%         in diet 0.1      0               liver: no effect on EAF       Jensen &
    hexabromobiphenyl   Dawley)        partial hepatectomy        mg/kg for        70 days         no effect on EAF              Sleight (1986)
    (BB 169)            (6)            plus DEN (single ip dose   140 days         310 days        no significant effect on
                                       of 10 mg/kg body weight)                                    hepatic nodules; carcinoma
                                                                                                   (1/11 versus 0 in controls)

    3,3',4,4',5,5'-     mouse,         pretreatment: MNNG         dermal multiple  0               skin: papilloma (12/20)       Poland et al.
    hexabromobiphenyl   hairless       (single dermal dose        doses (twice                                                   (1982)
                        HRS/J          of 5 µmol)                 weekly over 20
                        (f,20)                                    weeks) 20 µg

    Mixture of BB       rat (Sprague-  pretreatment 70% partial   in diet 10 mg    0               liver: synergistic effect     Jensen &
    153 and             Dawley)        hepatectomy plus DEN       BB 153/kg and    70 days         on development of EAF         Sleight (1986)
    BB 169                             (single ip dose of 10      0.1 mg BB        310 days        synergistic effect on
                                       mg/kg body weight)         169/kg feed for                  development of hepatic
                                                                  140 days                         nodules; carcinoma (1/11
                                                                                                   versus 0 in control)

                        rat (Sprague-                             in diet 100 mg   0               liver: inhibitory effect on   Jensen et al.
                        Dawley)                                   BB 153/kg and 1                  development of EAF            (1983)
                        F1 6)                                     mg BB 169/kg
                                                                  feed for 140
                                                                  days

    Table 90 (contd).

    a    No. = Number per experimental group; F = female.
    b    Numbers in parentheses signify No. affected/No. treated; EAF = Enzyme altered foci (exhibiting gamma glutamyl
         transpeptidase activity);
         DEN = N-nitrosodiethylamine; DMBA = 7,12-dimethyl-benz(a)anthracene; 2-FAA = 2-acetylaminofluorene;
         MNNG = N-methyl-N'-nitro-N-nitroso-guanidine.

         On the basis of the US National Toxicology Program (NTP) data,
    possible correlations between carcinogenicity and toxicity in
    laboratory rodents (Hoel et al., 1988) and between carcinogenicity
    and  in vitro genetic toxicity assays (Tennant et al., 1987;
    Benigni, 1989; Ashby & Tennant, 1991) have been analysed for a
    series of chemicals including the FireMaster(R) mixture. Results
    confirm that FireMaster(R) can be classified as a nongenotoxic
    (epigenetic) carcinogen (see also Loury et al., 1987; Williams
    et al., 1989).

    8.8  Biochemical toxicity

    8.8.1  Induction of microsomal enzymes

         One of the most intensively studied effects of the PBBs is
    their induction of mixed function oxidase (MFO) enzymes. Generally,
    MFO inducers and MFO systems are classified into two main groups,
    typified by phenobarbital (PB) and 3-methylcholanthrene (MC). The
    inducing capabilities of commercial PBB mixtures and individual PBB
    isomers and congeners have been summarized in Tables 91 and 92,
    respectively. The results were obtained from enzymatic, spectral,
    electrophoretic, immunochemical, and metabolic studies (see also
    section 6.3.1).

    8.8.1.1  Commercial PBB mixtures

         With one exception dealing with octabromobiphenyl (Ahotupa &
    Aitio, 1978), all studies available referred to the FireMaster(R)-
    mixture (Table 91).

         Consistently, FM was found to be a mixed-type inducer of
    hepatic microsomal enzymes in rats. Induction was observed at
    intakes as low as 1 mg FM/kg feed for 21 days (Babish & Stoeswand,
    1977). The no-effect level of a single ip dose was 8 µmol FM/kg body
    weight, corresponding to 4.7 mg FM/kg body weight (Goldstein et al.,
    1979). When FM was given for 5 days a week, over 30-50 days, changes
    in hepatic enzymes occurred with doses as low as 0.3 mg/kg body
    weight per day (Goldstein et al., 1979). The dose of FM BP-6
    effecting half maximal AHH (benzo[a]pyrene hydroxylase) induction
    was approximately 50 mg/kg body weight (Robertson et al., 1981c).
    Pre-, post-, or perinatal exposures were also effective in inducing
    microsomal enzymes in rats (Dent et al., 1977b,c, 1978b; Moore
    et al., 1978a; McCormack et al., 1978a, 1980, 1981). Nursing pups
    were approximately ten times more sensitive to these effects than
    the dams. The approximate no-effect level for microsomal enzyme
    induction in nursing rats was 0.1 mg FM/kg feed, in the diet of the
    adult (Moore et al., 1978a).

         Induction could be detected as early as 24 h after an ip
    administration of 150 mg FM/kg body weight (Dent, 1978; Dent et al.,
    1978a) or after an oral dose of 90 mg/kg body weight (Kluwe & Hook,

    1981). Although most of the investigations were short-term, there
    was some evidence for persistent stimulation of hepatic microsomal
    enzymes. For example, maternal rats fed 100 mg FM/kg feed, during
    pregnancy and lactation, had elevated enzyme activity 14 weeks after
    weaning their first litter or even after weaning a second litter
    (recovery period: 12-16 weeks) (McCormack & Hook, 1982). Perinatal
    exposure to FM induced microsomal enzymes in rats at 28, 150, and
    328 days of age (McCormack et al., 1980). Feeding of FM during
    pregnancy and lactation to F0-animals stimulated microsomal
    enzymes, not only in the F1-generation, but also in the
    F2-generation (McCormack et al., 1981). Also, persistence of an
    increased activity of microsomal enzymes, 120 or 125 days after
    cessation of exposure, was noted in rats exposed to FireMaster(R)
    BP-6 during hepatocarcinogenesis assays (Jensen et al., 1984;
    Rezabek et al., 1987).

         FM induced hepatic microsomal enzymes not only in the rat, but
    in all other animal species tested, i.e., mouse (Corbett et al.,
    1975; Dent et al., 1977a; Ahotupa & Aitio, 1978; Dannan et al.,
    1980; Ahmadizadeh et al., 1984; Robertson et al., 1984c), guinea-pig
    (Rush et al., 1982; Ecobichon et al., 1983; Smith et al., 1986),
    hamster (Rush et al., 1982; Smith et al., 1986), cattle (Schanbacher
    et al., 1978), pig (Werner & Sleight, 1981), dog (Farber et al.,
    1976), Japanese quail (Babish et al., 1975a,b; Bursian et al, 1983),
    and fish (Elcombe & Lech, 1978; Franklin et al., 1981; James &
    Little, 1981; Law & Addison, 1981). Unlike the mammalian situation,
    induction in several species of fresh- and saltwater fish was only
    of the MC-type (Table 91).

         Although the activities of microsomal enzymes were highest in
    the liver, induction was also found in extrahepatic tissues
    including the kidney (Dent et al., 1977c, 1978b; Ahotupa & Aitio,
    1978; McCormack et al., 1978a,b, 1979a,b, 1980, 1981; Kluwe & Hook,
    1981; Werner & Sleight, 1981; Ahmadizadeh et al., 1984; Rush et al.,
    1986; Smith et al., 1986), intestine (Manis & Kim, 1980; Traber
    et al., 1988a,b), mammary gland (Dent et al., 1977b,c, 1978b;
    McCormack et al., 1979a; McCormack & Hook, 1982) and lung (McCormack
    et al., 1979a). However, patterns of induction were organ specific.
    No induction was noted in the testes of rats (Kluwe & Hook, 1981)
    (see also Table 91).

         FM was also able to stimulate aryl hydrocarbon hydroxylase
    (AHH) activity in rat hepatoma cell culture (Garthoff et al., 1977).

         Commercial OcBB has been tested in only one study on mice and
    was found to be an inducer of drug-metabolizing enzymes. However,
    OcBB was a less potent inducer than FM (Ahotupa & Aitio, 1978).

    
    Table 91.  Induction of microsomal enzymes (MFOs) by commercial PBB mixtures

    PBBa              Species          Sex        Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    FM FF-1 (various  rat (Fischer     F          oral         9-22 doses    14-64          liver       x              PB + MC     Goldstein
    concentrations)   F 344/N)                                 over 30       days                                                  et al.
    (0.03-30 mg/kg                                             daysb                                                               (1979)
    body weight/day)

    FM FF-1 (lot no.  rat              M          oral         single        1-18 days      liver       x              MCd         Manis & Kim
    FF-1312-FT)       (Sprague-                                dose          1-3 days       intestine   x              MCd         (1980)
    (50-400 mg/kg     Dawley)                                                4-18 days      intestine          x
    body weight)

    (0.1 mg/day)                                  oral         25 doses      5 weeks        liver       x
                                                               over 5 weeks  5 weeks        intestine          x

    FM BP-6 (90       rat (Fischer     M          oral         single        9, 24, 72      liver       x              PB + MC     Kluwe &
    mg/kg body        344)                                     dose          216 h          kidney      x              only MC     Hook (1981)
    weight)                                                                                 testes             x

                                                               4 doses       7 days         liver       x              PB + MC
                                                               over 6 days                  kidney      x              only MC
                                                                                            testes             x

    FM BP-6 (25,      rat              F          intra-       single        12, 24, 48,    liver       x              PB + MC     Dent et al.
    150 mg/kg         (Sprague                    peritoneal   dose          192 h                                                 (1976b,
    body weight)      Dawley)                                                336 h                                                 1978a)

    Table 91 (contd).

    PBBa              Species          Sex        Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    FM BP-6 (150      rat (Sprague-    not        intra-       single        28 days        kidney      x              MC          McCormack
    mg/kg             Dawley)          specified  peritoneal   dose                                                                et al.
    body weight)      pups (7 or                                                                                                   (1978a)
                      11 days old)

    FM BP-6           rat (Wistar)     M          intra-       2 doses on    6 days         liver       x              MCd         Safe et al.
    (100 mg/rat)                                  peritoneal   days 1 & 3                                                          (1978)

    FM FF-1 (lot no.  rat              F          intra-       single        4 days         liver       x              PB + MC     Goldstein
    FF-1312 FT)       (Fischer)                   peritoneal   dose                                                                et al.
    (varied                                                                                                                        (1979)
    concentrations)
    (1.8-1000
    µmol/kg body
    weight)

    FM FF-1 (90       rat              M          intra-       single        2 weeks        liver       x              PB + MC     Dannan
    mg/kg body        (Sprague-                   peritoneal   dose                                                                et al.
    weight)           Dawley)                                                                                                      (1982c)

    FM BP-6 (1500     rat (Long        M          intra-       single        4 days         liver       x              PB + MC     Parkinson
    or 750 µmol/kg    Evans)                      peritoneal   dose                                                                et al.
    body weight)                                                                                                                   (1983);
                                                                                                                                   Haake et al.
                                                                                                                                   (1985)

    FM BP-6 (150      rat              M          intra-       single        5, 10, 15      kidney      x      x       MCd         Rush et al.
    mg/kg body        (Sprague-                   peritoneal   dose          days                       (day   (day                (1986)
    weight)           Dawley)                                                                           5,10)  15)

    Table 91 (contd).

    PBBa              Species          Sex        Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    FM BP-6 (6400     rat              M          intra-       4 doses       4 days         liver       x              PBe         Traber
    mg/kg body        (Sprague-                   peritoneal   over 4 days                  small                                  et al.
    weight; total     Dawley)                                                               intestine   x              PBe         (1988a,b)
    dose)

    FM BP-6           rat              F          in diet      2 weeks       2 weeks        liver       x              PB + MC     Dent et al.
    (4.6-200 mg/kg    (Sprague-                                                                                                    (1976a)
    of feed)          Dawley)

    FM BP-6 (50       rat (Sprague-    M          in diet      5-20 days     5-20 days      liver       x              PB + MC     Babish &
    mg/kg of feed)    Dawley)                                                                                                      Stoeswand
                                                                                                                                   (1977)

    FM BP-6 (50       rat (Sprague-    F          in diet      gd 8-day 14   day 14 post-   liver       x              at organ    Dent et al.
    mg/kg of feed)    Dawley)                                  postpartum    partum         kidney      x              specific    (1977b,c)
                      maternal                                                              mammary                    patterns
                                                                                            gland       x

    FM BP-6 (5, 50,   rat              M          in diet      2, 3, 5       2, 3, 5        liver       x              PBe         Garthoff
    500 mg/kg feed)   (Holtzmann)                              weeks         weeks                                                 et al.
                                                                                                                                   (1977)

    FM BP-6 (100      rat (Sprague-    F          in diet      3 months      3 months       liver       x              MC + PB     McCormack
    mg/kg feed)       Dawley)                                                               kidney      x              MC          et al.
                                                                                                                                   (1978a,b)

    FM FF-1 (lot      rat (Sprague-    F          in diet      18 days       18 days        liver       x              PB + MC     Moore
    7042) (0.1-10     Dawley)                                  postpartum                                                          et al.
    mg/kg feed)       lactating                                                                                                    (1978a)

    Table 91 (contd).

    PBBa              Species          Sex        Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    FM BP-6 (25-200   rat (Sprague-    F          in diet      gd 8-day 14   day 14 post-   lung        x              MCd         McCormack
    mg/kg feed)       Dawley)                                  postpartum    partum         kidney      x              MCd         et al.
                      lactating                                                             mammary                                (1979a)
                                                                                            gland       x              MCd
                                                                                            liver       x              MCd

    FM BP-6 (100      rat (Sprague-    M          in diet      30 days       30 days        liver       x              PB + MC     Akoso et al.
    mg/kg feed)       Dawley)                                                                                                      (1982a)

    FM BP-6 (100      rat              F          in diet      gd 8-day 28   W1 litter,     liver       x              PB + MC     McCormack &
    mg/kg feed)       (Sprague-                                postpartum    14 weeks       mammary                                Hook (1982)
                      Dawley)                                  weanling      after W1       gland       x              MC
                      maternal                                 (6 weeks)     and W2
                                                                             litters

    FM BP-6 (50       rat (pups)                  placental,   pre-, post-   at birth       liver       x              PB + MC     Dent et al.
    mg/kg feed in                                 milk or      or perinatal  or at day                                             (1977c,
    maternal diet)                                both                       15 post-                                              1978b)
                                                                             partum

    FM FF-1 (lot      rat                         milk         postnatal     day 18 post-   liver       x              PB + MC     Moore et al.
    7042) (0.1-10     (Sprague-                                              partum                                                (1978a)
    mg/kg feed in     Dawley)
    maternal diet     (pups) F1

    0.1-10 mg/kg      rat (Sprague-    F          milk and     postnatal     several        liver       x              PB + MC
    feed in maternal  Dawley)                     in diet      until mating  weeks
    diet plus 0.1-1   (lactating:                              and day 18
    mg/kg feed        F1)                                      postpartum

    Table 91 (contd).

    PBBa              Species          Sex        Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    0.1-10 mg/kg      rat (Sprague-               placental    perinatal     day 18 post-   liver       x              PB + MC
    feed in maternal  Dawley)                     and milk                   partum
    diet plus 0.1-1   (pups: F2)
    mg/kg feed

    FM BP-6 (100      rat (Sprague-               placental    perinatal     weanling       liver       x              PB + MC     McCormack
    mg/kg feed)       Dawley)                     and milk                   (28 days       kidney      x              MC          et al.
                                                                             of age)                                               (1980)

                                                                             150 days       liver       x              PB + MC
                                                                             of age         kidney      x              MC

                                                                             328 days       liver       x              PB + MC
                                                                             of age         kidney      x              MC

    FM BP-6 (10,      rat (Sprague-               placental    perinatal     W1             liver       x              PB + MC     McCormack
    100 mg/kg         Dawley)                     and milk     (F0: gd 8-                   kidney      x              MC          et al.
    feed)                                                      day 28                                                              (1981)
                                                               postpartum)
                                                                             W2             liver       x              PB + MC
                                                                                            kidney      x              MC

                                                                             W3             liver              x
                                                                                            kidney             x

    FM BP-6           mouse            F          intra-       single        24-192 h       liver       x              PB + MC     Dent et al.
    (150 mg/kg        (NMRI)                      peritoneal   dose                                                                (1977a)
    body weight)

    Table 91 (contd).

    PBBa              Species          Sex        Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    FM BP-6           mouse            M          intra-       single        10 days        liver       x              MCd         Ahotupa &
    (75 mg/kg         (C57)                       peritoneal   dose                         kidney                                 Aitio (1978)
    body weight)                                                                            lung               x

    FM BP-6           mouse            M          intra-       2 doses on    6 days         liver       x              PB + MC     Robertson
    (500 µmol/kg      (C57BL/)                    peritoneal   days 1 & 3                                                          et al.
    body weight)      6J)                                                                                                          (1984c)

                      mouse            M          intra-       2 doses on    6 days         liver       x              PB + (MC)
                      (DBA/2J)                    peritoneal   days 1 & 3

    FM BP-6           mouse            M          intra-       single        5, 10, 15      kidney             x                   Rush et al.
    (150 mg/kg        (ICR)                       peritoneal   dose          days                                                  (1986)
    body weight)

    FM BP-6 (1000     mouse            F          in diet      11 days       11 days        liver       x              not         Corbett
    mg/kg feed)       (Swiss/ICR)                                                                                      specified   et al.
                                                                                                                                   (1975)
    FM (100 mg/kg     mouse            M          in diet      28 days       28 days        liver       x              MCd         Ahmadizadeh
    feed)             (C57/6J)                                                              kidney      x              MCd         et al.
                                                                                                                                   (1984)

                      mouse            M          in diet      28 days       28 days        liver       x              MCd
                      (DBA/2J)                                                              kidney             x

    FM BP-6           guinea-          M          intra-       single        4 days         liver       x              MCd         Rush et al.
    (50 mg/kg         pig                         peritoneal   dose                         kidney      x              MCd         (1982);
    body weight)      (Hartley)                                                                                                    Smith et al.
                                                                                                                                   (1986)

    Table 91 (contd).

    PBBa              Species          Sex        Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    FM FF-1 (lot FA-  guinea-                     placental    prenatal      2 days         liver       x                          Ecobichon
    7042) (maternal,  pig                                      (from gd 65)                                                        et al.
    single oral       (Hartley)                   milk         postnatal     2-60 days      liver       x      x                   (1983)
    dose of 50 mg/kg  pups                                     (from 6-12 h  of age                     (2,4,  (14,
    body weight)                                               after                                    7,28   60,90
                                                               parturition)                             days   days
                                                                                                        of     of
                                                                                                        age)   age

    FM BP-6           hamster          M          intra-       single        4 days         liver       x              MCd         Rush et al.
    (50 mg/kg         (Golden                     peritoneal   dose                         kidney             x                   (1982);
    body weight)      Syrian)                                                                                                      Smith et al.
                                                                                                                                   (1986)

    FM BP-6 (lot      cattle           F          oral         90-180        90-180         liver       x                          Schanbacher
    6244 A)                                                    days/daily    days                                                  et al.
    (250 mg/day)                                               dose)                                                               (1978)

    FM BP-6           pig              F          in diet      2nd half of gestation and    liver       x                          Werner &
    (10-200 mg/kg     (sow)                                    lactation                    kidney      x                          Sleight
    feed)             (pups)                      placental    prenatal      at birth       liver              x                   (1981)
                                                                                            kidney             x
                                                  placental    perinatal     4 weeks        liver       x
                                                  and milk                   of age         kidney      x

    FM BP-6 (1        Beagle dog       M,F        oral         7 weeks       7 weeks        liver       x                          Farber
    mg/kg body                                                                                                                     et  al.
    weight per day)                                                                                                                (1976)

    Table 91 (contd).

    PBBa              Species            Sex      Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    FM (10-1000       Japanese           M,F      in diet      9 weeks       9 weeks        liver       x              PBe         Babish
    mg/kg feed)       quail                                                                                                        et al.
                                                                                                                                   (1975b)

    FM FF-1           Japanese           M,F      in diet      5 weeks       5 weeks        liver       x              PB + MC     Polin et al.
    (40, 80 mg/kg     quail                                                                                                        (1982);
    feed)             (Coturnix                                                                                                    Bursian
                      coturnix                                                                                                     et al.
                      japonica)                                                                                                    (1983)
                      (3 genetic
                      lines)

    FM BP-6           brook trout                 oral         18 days       18 days        liver       x              MC          Law &
    (200 mg/kg        (Salvelinus                              (multiple                                                           Addison
    body weight)      fontinalis)                              doses)                                                              (1981)

    FM BP-6           rainbow                     intra-       single        up to          liver       x              MC          Elcombe &
    (150 mg/kg        trout                       peritoneal   dose          2 weeks                                               Lech (1978)
                      (Oncorhynchus
                      mykiss)

    FM BP-6           rainbow                     parenteral   single        5 days         liver       x              MC          Franklin
    (150, 500 mg/kg   trout                                    dose                                                                et al.
    body weight)      (O. mykiss)                                                                                                  (1981)

    FM FF-1           sheepshead                  intra-       single        up to          liver       x              MCd         James &
    (15 mg/kg         minnow                      peritoneal   dose          56 days                                               Little
    body weight)      (Archosargus                                                                                                 (1981);
                      probatocephalus)                                                                                             James & Bend
                                                                                                                                   (1982)

    Table 91 (contd).

    PBBa              Species          Sex        Route               Period of                         MFO induction              References
    (Dose/            (strain)                                 Exposure      Observationc   Tissue        Induction    Type
    concentration)                                                                                      yes    no

    OcBB (FR 25013    mouse            M          intra-       single        10 days        liver       x              MCd         Ahotupa &
    A, Dow Chemical)  (C57)                       peritoneal   dose                         kidney             x                   Aitio (1978)
    (75 mg/kg                                                                               lung               x
    body weight)

    a    Commercial PBB mixtures; FM = FireMaster; OcBB = octabromobiphenyl.
    b    Dosing: 5 days per week for 30 days; examination points: 14 days (9 doses); 31 days (22 doses); 46 and 64 days (22 doses
         plus a 15-day and a 33-day recovery period, respectively.
    c    After first dose.
    d    Only MC-typical parameters recorded.
    e    Only PB-typical parameters recorded.
    Abbreviations:
         gd = gestation day; MFO = mixed function oxidase; MC = 3-methylcholanthrene; PB = phenobarbital.

    Table 92.  Induction of hepatic microsomal enzymes (MFOs) by PBB congeners

    PBBa              Species             Sex     Route                Period of            MFOc induction                   References
    (Dose/            (strain)                                 No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    4-mono-           rat                 M       intra-       3 doses       7 days         x                                Ecobichon
    (600)             (Wistar)                    peritoneal                                                                 et al. (1979)

    2,2'-di-          rat (Sprague-       M       intra-       single        2-22                       x                    Moore et al.
    (90 mg/kg body    Dawley)                     peritoneal   dose          days                                            (1979a)
    weight)

    (600)             rat                 M       intra-       3 doses       7 days                     x                    Ecobichon
                      (Wistar)                    peritoneal                                                                 et al. (1979)

    2,5'-di-          rat                 M       intra-       3 doses       7 days         x
    (600)             (Wistar)                    peritoneal

    4,4'-di-          rat                 M       intra-       3 doses       7 days         x                                Ecobichon
    (600)             (Wistar)                    peritoneal                                                                 et al. (1977,
                                                                                                                             1979)

    (300)             rat                 M       intra-       2 doses       6 days         x                   PB           Robertson
                      (Wistar)                    peritoneal                                                                 et al. (1982b)

    2,2',5-tri-       rat                 M       intra-       3 doses       7 days                     x                    Ecobichon
    (600)             (Wistar)                    peritoneal                                                                 et al. (1979)

    2,3',5-tri-       rat                 M       intra-       3 doses       7 days         x                                Ecobichon et al.
    (600)             (Wistar)                    peritoneal                                                                 (1979)

    2,4,6-tri-        rat                 M       intra-       3 doses       7 days         x
    (600)             (Wistar)                    peritoneal

    Table 92 (contd).

    PBBa              Species             Sex     Route                Period of            MFOc induction                   References
    (Dose/            (strain)                                 No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    2,4',5-tri-       rat                 M       intra-       3 doses       7 days         x
    (600)             (Wistar)                    peritoneal

    3,4,4'-tri-       rat                 M       intra-       single        4 days         x                   MC           Parkinson et al.
    (250)             (Long Evans)                peritoneal   dose                                                          (1983)

    (300)             rat                 M       intra-       2 doses       6 days         x                   MC           Robertson et al.
                      (Wistar)                                 peritoneal                                                    (1982b)

    2,2',5,5'-tetra-  rat                 M       intra-       single dose   2 weeks        x                   PB           Robertson et al.
    (150)             (Wistar)                    peritoneal                                                                 (1983b)

    (500)             rat (Long           M       intra-       single        4 days         x                   PB           Parkinson et al.
                      Evans)                      peritoneal   dose                                                          (1983)

    (600)             rat                 M       intra-       3 doses       7 days         x                                Ecobichon et al.
                      (Wistar)                    peritoneal                                                                 (1979)

    2,3',4,4'-tetra-  rat (Long           M       intra-       single        4 days         x                   PB + MC      Parkinson et al.
    (250)             Evans)                      peritoneal   dose                                                          (1983)

    (1500)            mouse               M       intra-       2 doses       6 days                     x                    Robertson et al.
                      (C57BL/6J)                  peritoneal                                                                 (1984c)

    (1500)            mouse               M       intra-       2 doses       6 days                     x
                      (DBA/2J)                    peritoneal

    2,3',4',5-tetra-  rat                 M       intra-       2 doses       6 days         x                   PB           Robertson et al.
    (150)             (Wistar)                    peritoneal                                                                 (1980)

    Table 92 (contd).

    PBBa              Species             Sex     Route                Period of            MFOc induction                   References
    (Dose/            (strain)                                 No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    2,4,4',6-tetra-   rat (Long           M       intra-       single        4 days         x                   PB + MC      Parkinson et al.
    (500)             Evans)                      peritoneal   dose                                                          (1983)

    3,3',4,4'-tetra-  rat (Sprague-       M       oral         single        1-10           x                   MC           Millis et al.
    (21.3)            Dawley)                                  dose          days                                            (1985b)

    (250)             rat (Long           M       intra-       single        4 days         x                   MC           Parkinson et al.
                      Evans)                      peritoneal   dose                                                          (1983)

    (2 mg/kg body     rat (Sprague-       M       intra-       single        2 weeks        x                   MC           Millis et al.
    weight)           Dawley)                     peritoneal   dose                                                          (1985a)

    (10, 60)          rat                 M       intra-       2 doses       6 days         x                   MC           Robertson et al.
                      (Wistar)                    peritoneal                                                                 (1982b); Andres et
                                                                                                                             al. (1983)

    (750)             mouse               M       intra-       2 doses       6 days         x                   MC           Robertson et al.
                      (C57BL/6J)                  peritoneal                                                                 (1984c)

    (1500)            mouse               M       intra-       2 doses       6 days         x                   MC
                      (DBA/2J)                    peritoneal

    3,3',5,5'-tetra-  rat                 M       intra-       3 doses       7 days                     x                    Ecobichon et al.
    (600)             (Wistar)                    peritoneal                                                                 (1979)

    (not specified)   chicken                     via shell    single        28 h                       x                    Poland & Glover
                      embryo                      into the     dose                                                          (1977)
                                                  air sac

    Table 92 (contd).

    PBBa              Species             Sex     Route                Period of            MFOc induction                   References
    (Dose/            (strain)                                 No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    3,4,4',5-tetra-   rat (Long           M       intra-       single        4 days         x                   MC           Parkinson et al.
    (250)             Evans)                      peritoneal   dose                                                          (1983)

    (60)              rat                 M       intra-       2 doses       6 days         x                   MC           Robertson et al.
                      (Wistar)                    peritoneal                                                                 (1982b)

    2,2',4,5,5'-      rat (Long           M       intra-       single        4 days         x                   PB           Parkinson et al.
    penta-            Evans)                      peritoneal   dose                                                          (1983)
    (BB 101) (500)

    (90 mg/kg body    rat (Sprague-       M       intra-       single        7-14           x                   PB           Dannan et al.
    weight)           Dawley)                     peritoneal   dose          days                                            (1982a); Millis
                                                                                                                             et al. (1985a)

    2,2',4,5',6-      rat                 M       intra-       3 doses       7 days         x                                Ecobichon et al.
    penta- (600)      (Wistar)                    peritoneal                                                                 (1979)

    2,3',4,4',5-      rat (Long           M       intra-       single        4 days         x                   PB + MC      Parkinson et al.
    penta-            Evans)                      peritoneal   dose                                                          (1983)
    (BB 118) (250)

    (90 mg/kg body    rat (Sprague-       M       intra-       single        2 weeks        x                   PB + MC      Dannan et al.
    weight)           Dawley)                     peritoneal   dose                                                          (1982c); Millis
                                                                                                                             et al. (1985a)
    (30, 150)         rat (Wistar)        M       intra-       2 doses       6 days         x                   PB + MC      Robertson et al.
                                                  peritoneal                                                                 (1980)

    (500)             mouse               M       intra-       2 doses       6 days         x                   PB + MC      Robertson et al.
                      (C57BL/6J)                  peritoneal                                                                 (1984c)

    Table 92 (contd).

    PBBa              Species             Sex     Route                Period of            MFOc induction                   References
    (Dose/            (strain)                                 No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    (500)             mouse               M       intra-       2 doses       6 days                     x
                      (DBA/2J)                    peritoneal

    2,3',4,4',6-      rat (Long           M       intra-       single        4 days         x                   PB + MC      Parkinson et al.
    penta- (500)      Evans)                      peritoneal   dose                                                          (1983)

    3,3',4,4',5-      rat (Long           M       intra-       single        4 days         x                   MC
    penta- (100)      Evans)                      peritoneal   dose

    (60)              rat                 M       intra-       2 doses       6 days         x                   MC           Robertson et al.
                      (Wistar)                    peritoneal                                                                 (1982b)

    2,2',3,4,4',5'-   rat (Sprague-       M       intra-       single        7 days         x                   PB + MC      Dannan et al.
    hexa-             Dawley)                     peritoneal   dose                                                          (1982a)
    (BB 138) (90
    mg/kg body
    weight)

    2,2',4,4',5,5'-   rat                 F       gavage       multiple      60 days        x                   PB           Goldstein et al.
    hexa- (BB 153)    (F 344/N)                                doses (over                                                   (1979)
    (16.8 mg/kg                                                30 days)
    body weight)

    (40-1000)         rat                 F       intra-       single        4 days         x                   PB
                      (Fischer)                   peritoneal   dose

    (500)             rat (Long           M       intra-       single        4 days         x                   PB           Parkinson et al.
                      Evans)                      peritoneal   dose                                                          (1983); Haake et
                                                                                                                             al. (1985)

    Table 92 (contd).

    PBBa              Species             Sex     Route                Period of            MFOc induction                   References
    (Dose/            (strain)                                 No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    (90 mg/kg body    rat (Sprague-       M       intra-       single        1-14           x                   PB           Moore et al.
    weight)           Dawley)                     peritoneal   dose          days                                            (1978b); Millis
                                                                                                                             et al. (1985a)

    (30 mg/kg body    rat                 M       intra-       single        72 h           x                   PB           Lubet et al.
    weight)           (F 344)                     peritoneal   dose                                                          (1990)

    (600)             rat                 M       intra-       3 doses       7 days         x                   PB           Ecobichon et al.
                      (Wistar)                    peritoneal                                                                 (1979)

    (100 mg/kg feed)  rat (Sprague-       M       in diet      30 days       30 days        x                   PB           Akoso et al.
                      Dawley)                                                                                                (1982a)

    (10, 100 mg/kg    rat (Sprague-       M       in diet      9 days        10 days        x                   PB           Render et al.
    feed)             Dawley)                                                                                                (1982)

    (150 mg/kg body   rainbow trout               parenteral   single        5 days                     x                    Franklin et al.
    weight)           (Oncorhynchus                            dose                                                          (1981)
                      mykiss)

    2,2',4,4',5,5'-   sheepshead                  intra-       single        17 days                    x                    James & Little
    hexa- (20 mg/kg   minnow                      peritoneal   dose                                                          (1981); James &
    body weight)      (Archosargus                                                                                           Bend (1982)
                      probatocephalus)

    (60, 100 mg/kg                                intra-       multiple      28-40                      x
    body weight)                                  peritoneal   doses         days

    Table 92 (contd).

    PBBa              Species             Sex     Route                Period of            MFOc induction                   References
    (Dose/            (strain)                                 No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    2,2',4,4',6,6'-   rat                 M       intra-       3 doses       7 days         x                                Ecobichon et al.
    hexa- (600)       (Wistar)                    peritoneal                                                                 (1979)

    2,3,3',4,4',5-    rat (Sprague-       M       intra-       single        7 days         x                   (PB) + MC    Dannan et al.
    hexa- (BB 156)    Dawley)                     peritoneal   dose                                                          (1982a)
    (90 mg/kg body
    weight)

    (3.75-60)         rat                 M       intra-       2 doses       6 days         x                   (PB) + MC    Robertson et al.
                      (Wistar)                    peritoneal                                                                 (1981a)

    2,3,3',4,4',5'-   rat (Long           M       intra-       single        4 days         x                                Parkinson et al.
    hexa- (100)       Evans)                      peritoneal   dose                                                          (1983)

    2,3',4,4',5,5'-   rat                 M       intra-       single        7 days         x                   PB + MC      Dannan et al.
    hexa- (BB 167)    (Sprague-                   peritoneal   dose                                                          (1978a)
    (90 mg/kg body    Dawley)
    weight)

    (100 mg/kg feed)  rat (Sprague-       M       in diet      30 days       30 days        x                   PB + MC      Akoso et al.
                      Dawley)                                                                                                (1982a)

    2,3',4,4',5',6-   rat (Long           M       intra-       single        4 days         x                   PB + MC      Parkinson et al.
    hexa- (BB 168)    Evans)                      peritoneal   dose                                                          (1983)
    (250)

    3,3',4,4',5,5',-  rat (Sprague-       M       oral         single        1-14 days      x                   MC           Millis et al.
    hexa- (21.3)      Dawley)                                  dose                                                          (1985b)

    Table 92 (contd).

    PBBa              Species             Sex     Route                Period of            MFOc induction                   References
    (Dose/            (strain)                                 No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    (100)             rat (Long           M       intra-       single        4 days         x                   MC           Parkinson et al.
                      Evans)                      peritoneal   dose                                                          (1983)

    (30 mg/kg body    rat                 M       intra-       single        72 h           x                   MC           Lubet et al.
    weight)           (F 344)                     peritoneal   dose                                                          (1990)

    (2, 30 mg/kg      rat (Sprague-       M       intra-       single        1-2            x                   MC           Dannan et al.
    body weight)      Dawley)                     peritoneal   dose          weeks                                           (1982c); Millis
                                                                                                                             et al. (1985a)

    30 mg/kg body     rat                 M       intra-       single        72 h           x                   MC           Lubet et al.
    weight            (F344)                      peritoneal   dose                                                          (1990)

    (60)              rat                 M       intra-       2 doses       6 days         x                   MC           Robertson et al.
                      (Wistar)                    peritoneal                                                                 (1982b)

    (600)             rat                 M       intra-       3 doses       7 days         x                                Ecobichon et al.
                      (Wistar)                    peritoneal                                                                 (1979)

    (1, 10 mg/kg      rat (Sprague-       M       in diet      30 days       30 days        x                   MC           Akoso et al.
    feed)             Dawley)                                                                                                (1982a)

    (10, 100 mg/kg    rat (Sprague-       M       in diet      9 days        10 days        x                   MC           Render et al.
    feed)             Dawley)                                                                                                (1982)

    (not specified)   chick                       via shell    single        24 h           x                   MC           Poland & Glover
                      embryo                      into the     dose                                                          (1977)
                                                  air sac

    Table 92 (contd).

    PBBa               Species            Sex     Route                Period of            MFOc induction                   References
    (Dose/             (strain)                                No. of doses  Observationb      Induction        Typed
    concentration)                                                                          yes         no

    (150 mg/kg body    rainbow trout              parenteral   single        5 days         x                   MC           Franklin et al.
    weight)            (Oncorhynchus                           dose                                                          (1981)
                       mykiss)

    2,2',3,3',4,4',5-  rat (Sprague-      M       intra-       single        7 days         x                   PB (+MC?)    Dannan et al.
    hepta- (BB 170)    Dawley)                    peritoneal   dose                                                          (1982a)

    2,2',3,4,4',5,5'-  rat                M       intra-       single        2-22 days      x                   PB           Moore et al.
    hepta- (BB 180)    (Sprague-                  peritoneal   dose                                                          (1979a)
    (90 mg/kg body     Dawley)
    weight)

    (150 mg/kg body    rainbow trout              parenteral   single        5 days                     x                    Franklin et al.
    weight)            (O. mykiss)                             dose                                                          (1981)

    2,3,3',4,4',5,6-   rat                M       intra-       2 doses       6 days                     x                    Robertson et al.
    hepta- (6)         (Wistar)                   peritoneal                                                                 (1981a)

    2,2',3,3',4,4',    rat                M       intra-       single        7 days         x                   PB           Besaw et al.
    5,5'-octa- (BB     (not speci-                peritoneal   dose                                                          (1978)
    194) (90 mg/kg
    body weight)

    (600)              rat                M       intra-       3 doses       7 days         x                   PB           Ecobichon et al.
                       (Wistar)                   peritoneal                                                                 (1979)

    Table 92 (contd).

    a    Total dose in µmol/kg body weight, unless otherwise specified.
    b    After first dose.
    c    MFO = Mixed function oxidase; PB = phenobarbital; MC = 3-methylcholanthrene.
    d    Only noted when categorized into PB- or MC- type by the authors themselves.

         The FM mixture was fractionated and reconstituted in order to
    test whether PBBs or contaminants (e.g., brominated dibenzofurans or
    dibenzodioxins, or brominated naphthalenes) were responsible for the
    inductive effects. The results indicated that most effects
    associated with the mixture were due to the brominated biphenyls
    (Safe et al., 1978; Robertson et al., 1981b; Dannan et al., 1982b).

    8.8.1.2  Individual PBB congeners

         The capability of individual PBB congeners to induce hepatic
    microsomal enzymes  in vivo is shown in Table 92. There was a broad
    range of responses, depending on the congener or species/strain
    tested. In addition to qualitative differences, the extent of the
    induction also differed between congeners (e.g., Ecobichon et al.,
    1979; Safe et al., 1981; Parkinson et al., 1983 and other references
    from Table 92). As far as they have been tested,  in vitro enzyme
    induction assays using rat hepatoma H-4-II-E cells in culture, have
    confirmed the results of the  in vivo studies (Andres et al., 1983;
    Bandiera et al., 1982, 1983).

         The most abundant components of the FM mixture, BB 153
    (2,2',4,4',5,5'-hexa-) and BB 180 (2,2',3,4,4',5,5'-hepta-), were
    strict PB-type inducers in rats. Congeners 118 (2,3',4,4',5-penta-),
    138 (2,2',3,4,4',5'-hexa-), and 167 (2,3',4,4',5,5'-hexa-) showed a
    mixed PB- and MC-type induction, and 156 (2,3,3',4,4',5-hexa-) was
    described (Robertson et al., 1981a; Dannan et al., 1982a) to be a
    very potent MC-type inducer (see Table 8.8/2).
    3,3',4,4'-tetrabromobiphenyl and the model congener
    3,3',4,4',5,5'-hexabromobiphenyl were pure MC-type inducers in rats
    (Table 92), 3,3',4,4'-tetrabromobiphenyl being less effective than
    3,3',4,4',5,5'-hexabromobiphenyl (Millis et al., 1985a,b). The
    ED50 value of 3,3',4,4',5,5'-hexabromobiphenyl determined in the
    chicken embryo was approximately 90 nmol/kg body weight (= 3.4 nmol
    per egg) (Poland & Glover, 1977). On the other hand,
    3,3',4,4'-tetrabromobiphenyl was at least 50 times more potent as an
    inducer of AHH activity than the commercial PBB mixture: ED50
    values (measured in rats) were 1-2 µmol/kg body weight for
    3,3',4,4'-tetrabromobiphenyl and 75-80 µmol/kg body weight for FM
    BP-6 (Robertson et al., 1982).

         Congeners that elicited PB-type induction in rats (e.g., BB 153
    and BB 180) failed to do so in fish, whereas MC-type inducers were
    effective in both rats and fish (Table 92).

         Correlations between the structure and microsomal enzyme-
    inducing activity (and toxicity) of individual PBB congeners have
    been demonstrated in several studies and reviews (e.g., Goldstein,
    1980; Moore et al., 1980; Aust et al., 1981; McKinney & Singh, 1981;
    Robertson et al., 1982b; Andres et al., 1983; Dannan et al., 1983;
    Parkinson et al., 1983; Safe, 1984; Safe et al., 1985).

         When 3,3',4,4',5,5'-hexabromobiphenyl was used to induce
    cytochrome P-450 in rats (at 10 µmol/kg body weight), it was found
    to be selectively associated with cytochrome P-450d (Voorman & Aust,
    1987).

    8.8.2  Endocrine interactions

         PBBs have been demonstrated to interact with the endocrine
    system.

    8.8.2.1  Thyroid hormones

         Rats (No. = 10), given oral doses of FM FF-1 (Lot No. 1312 FT)
    over 6 months, showed dose-related decreases in serum thyroxine
    (T4) and triiodothyronine (T3). Significant decreases in T4
    were seen at doses as low as 0.3 mg PBB/kg body weight per day in
    males, and 1 mg/kg body weight per day in females. The reduction in
    T3 was somewhat less and only significant at high doses (3-10
    mg/kg body weight per day) in females (Gupta et al., 1983a). A time-
    and dose-dependent reduction in plasma T4 levels was also found in
    male rats (n = 8-11) administered FM FF-1, by gavage, for 10 or 20
    days at 1, 3, or 6 mg/kg body weight per day (Allen-Rowlands et al.,
    1981). In addition, the reduced plasma T4 levels were correlated
    with an increase in thyroid stimulating hormone (TSH) at 20 days. At
    6 mg/kg body weight per day, the thyroid uptake of iodine was
    increased, but the incorporation of iodine in monoiodotyrosine was
    decreased. While short-term feeding (7 months) of female rats with
    commercial hexabromobiophenyl at dietary concentrations of
    1-50 mg/kg also resulted in an decrease in serum T3 and T4
    levels (Sepkovic & Byrne, 1984; Byrne et al., 1987), feeding of
    technical octabromobiphenyl had no effect on serum T3 levels
    (Sepkovic & Byrne, 1984). "PBB" (not specified) caused not only
    reduced serum T4 levels and elevated thyrotropin levels in rats,
    but also produced goitres (Bastomsky, 1986).

         Single ip injections of 3,3',4,4',5,5'-hexabromobiphenyl in
    juvenile male rats (20 and 40 mg/kg body weight) caused a
    significant decrease in serum T4 concentrations, while serum T3
    levels did not change significantly during the 28-day observation
    period. The decrease in serum T4 concentrations was dose-dependent
    (Spear et al., 1990).

         Serum concentrations of T3 and T4 were decreased in swine
    and their newborn piglets at 200 mg FM BP-6/kg feed. After nursing
    for 4 weeks, piglets born to sows fed 100 mg FM BP-6/kg feed also
    showed significant reductions in T3 and T4 (Werner & Sleight,
    1981).

    8.8.2.2  Sex hormones

         Hepatic microsomes, prepared from rats exposed to FM BP-6
    (100 mg/kg of feed) from day 8 of gestation until they were killed
    at 4-21 weeks of age, showed an increased metabolism of progesterone
    (Arneric et al., 1980), testosterone (Newton et al., 1980, 1982a),
    and of the estrogens estradiol, estrone, and ethynylestradiol
    (Bonhaus et al., 1981). In contrast to the increased hydroxylation
    reaction, reduction of testosterone was inhibited by pretreatment
    with PBBs (Newton et al., 1982a). The metabolism of exogenously
    administered and labelled steroid hormones including progesterone,
    testosterone, and estradiol, was also enhanced  in vivo in rats
    following perinatal exposure (gestation day 8-28 days postpartum) to
    10 or 100 mg FM BP-6/kg feed, as shown by diminished steroid action
    and reduced radio activity in serum and target organs (McCormack
    et al., 1979c). In contrast, endogenously produced concentrations of
    luteinizing hormone, prolactin, or corticosterone were not affected
    in rats treated with 100 mg FM BP-6/kg feed from gestation day 8
    until the ninth week of age (Johnston et al., 1980). Rats dosed with
    1, 3, or 6 mg FM FF-1/kg body weight per day for 20 days also did
    not show any alterations in plasma corticosterone or testosterone
    levels, but, at 6 mg/kg body weight per day, there was a significant
    reduction in plasma prolactin levels (Castracane et al., 1982). 
    Long-term, low-dose treatment with FM BP-6 (1, 10, or 50 m/kg feed
    for 5-7 months) caused cumulative and dose-dependent decreases in
    the serum corticosterone levels of female rats, as well as
    reductions in the circulating levels of dehydroepiandrosterone and
    dehydroepiandrosterone sulfate (Byrne et al., 1988). Alterations in
    the urinary metabolic profile in the corticosteroid region of the
    profile were observed after exposure (not specified) of rats to PBBs
    (not specified) (Vrbanac, 1984).

         Plasma corticosterone concentrations in female mice (BALB/c)
    fed 100 mg FM BP-6 for 24 or 30 days were only modestly elevated
    (Fraker, 1980).

         Endogenous concentrations of progesterone and estradiol
    determined in cows (No. = 2) administered toxic doses of FM BP-6
    (25 g/day for 39 or 50 days) were in the range normally expected
    (Willett et al., 1983a). The clearance rate of radiolabelled
    progesterone and estradiol from the blood of both cows was decreased
    (Willett et al., 1983a); elimination of radiolabel from these
    hormones in the urine and faeces also declined (Sprosty et al.,
    1979; Willett et al., 1983b).

         Ingestion of FM FF-1 by adult, female rhesus monkeys at
    concentrations of 0.3 mg/kg feed for 7 months (total dose:
    approximately 10 mg PBB) caused prolonged menstrual cycles and
    decreased concentrations of serum progesterone (Allen et al., 1978;
    Lambrecht et al., 1978; for details in study design see section
    8.5).

    8.8.2.3  Prostaglandins

         The effect of PBBs on prostaglandin has been examined in an
     in vitro study using rat liver microsomes. A single ip injection
    of FM BP-6 (100 mg/kg body weight) in male rats resulted in an
    elevated metabolism of prostaglandin E1, 7 days after dosing
    (Theoharides & Kupfer, 1981).

    8.8.3  Interaction with drugs and toxicants

         Several studies have demonstrated that PBBs have the ability to
    alter the biological activity of a variety of drugs and toxicants.
    In part, it may depend on the capability of the PBBs to induce
    microsomal enzymes involved in the activation or deactivation of
    xenobiotics. A summary of interactions, reported after the treatment
    of animals with a combination of PBBs and drugs or toxicants, is
    listed in Table 93 according to enhanced or miscellaneous effects.
    The majority of reports are limited to the FireMaster(R) mixture.
    One study (Halvorson et al., 1985) included several congeners, and
    it was found that the results of interaction (formation of aflatoxin
    metabolites) varied according to congener.

         The toxicities of carbon tetrachloride, bromobenzene,
    chloroform, trichloroethylene, and trichloroethane have been
    enhanced by FM in rodents (Roes et al., 1977; Kluwe et al., 1978,
    1979, 1982; Ahmadizadeh et al., 1984). Mirex-type compounds
    aggravated the histological damage due to PBBs in rats (Chu et al.,
    1980). Pretreatment with FM increased mortality during anaesthesia
    elicited by pentobarbital in Japanese quails (Cecil et al., 1975).
    On the other hand, a reduction in the toxicity of some toxicants has
    also been observed, e.g., a reduction in ouabain lethality (Cagen &
    Gibson, 1977a). Some other interactions are also recorded in Table
    93.

    8.8.4  Effects on vitamin A storage

         Like related compounds, PBBs cause profound alterations in
    vitamin A homeostasis. Significant reductions in hepatic vitamin A
    stores have been seen in rats after exposure to individual PBB
    congeners and the FireMaster(R) mixture (Table 94).
    2,2',4,4',5,5'- Hexabromobiphenyl was less potent in reducing
    vitamin A levels in the liver than the FM mixture and two other
    hexa-isomers (Table 94).

         Rats (Sherman, adult, male) given a single oral dose of 500 mg
    FM FF-1/kg body weight had lower levels of retinol in the serum and
    in liver microsomes compared with control animals, after an 18-month
    recovery period (Bernert et al., 1983).

    
    Table 93.  Interactions of PBBs with drugs and toxicants

    Species         PBB (dosage         Route of PBB      Drug/toxicant            Observed effects after                        References
    and sexa        regimen)            administration    (dose)                   combined treatmentd

    Enhancement of toxicity

    Rat (Sprague-   FM BP-6 (20 mg/kg   in diet           mirex and related        aggravation of histological changes due to    Chu et al.
    Dawley) M       feed for 28 days)                     compounds (Kepone,       PBB (additive rather than potentiative)       (1980)
                                                          photomirex)

    Rat (Sprague-   FM BP-6 (100 mg/kg  in diet           carbon tetrachloride     increase in CCl4-induced lethality and 48-h   Kluwe et al.
    Dawley) M       feed for 20 days)                     (CCl4) (single ip dose   growth retardation; increase in severity of   (1982)
                                                          of 0.03-2 ml/kg body     liver damage and renal tubular functional
                                                          weight)b                 impairment

    Mouse (NMRI)    FM BP-6 (single     intraperitoneal   bromobenzene (single     decrease in bromobenzene LT50c                Roes et al.
    F               dose of 150 mg/kg                     ip dose of 3150 mg/kg                                                  (1977)
                    body weight)                          body weight)b

    Mouse           FM BP-6 (1, 20,     in diet           chloroform (CHCl3)       increase in CHCl3-induced lethality (96-h     Kluwe et al.
    (ICR) M         25, or 100 mg/kg                      (single ip dose of       LD50; at 100 mg PBB/kg feed, P < 0.05);       (1978)
                    feed for 14-28                        various                  higher susceptibility to CHCl3-induced
                    days)                                 concentrations)b         renal and hepatic damage

    Mouse (C57      FM (100 mg/kg       in diet           chloroform (CHCl3)       enhancement of CHCl3 hepatoxicity (both       Ahmadizadeh
    BL/6J) and      feed for 28 days)                     (single ip doses of      strains); enhancement of nephrotoxicity       et al. (1984)
    (DBA/2J) M                                            0.025-0.25 ml/kg         (only in C57 strain)
                                                          body weight)

    Table 93 (contd).

    Species         PBB (dosage         Route of PBB      Drug/toxicant            Observed effects after                        References
    and sexa        regimen)            administration    (dose)                   combined treatmentd

    Mouse           FM BP-6 (1, 20,     in diet           carbon tetrachloride     increase in CCl4-induced lethality (96-h      Kluwe et al.
    (ICR) M         25, or 100 mg/kg                      (CCl4) (single ip        LD50; at 20 and 100 mg PBB/kg feed,           (1978, 1979)
                    feed for 14-28                        dose of various          P < 0.05); higher susceptibility to
                    days)                                 concentrations)b         CCl4-induced renal and hepatic damage
                                                                                   (e.g.: decrease in renal PAH accumulation
                                                                                   after 0.125 ml CCl4/kg body weight)

    Mouse           FM BP-6 (1, 20,     in diet           trichloroethylene (TRI)  potentiation of TRI-induced renal
    (ICR) M         25, or 100 mg/kg                      (single ip dose of       dysfunction (decrease in renal PAH
                    feed for 14-28                        1 ml/kg body weight)b    accumulation)
                    days)

                    FM BP-6 (1, 20,     in diet           1,1,2-trichloroethane    potentiation of TRI-induced renal
                    25, or 100 mg/kg                      (TCE) (single ip dose    dysfunction (decrease in renal PAH
                    feed for 14-28                        of 0.15 ml/kg body       accumulation)
                    days)                                 weight)b

    Japanese        FM BP-6 (single     gavage            pentobarbital (single    increased mortality during anaesthesia        Cecil et al.
    quail           dose of 100 mg/kg                     im dose of 50 (M) or     when the pentobarbital was administered       (1975)
                    body weight)                          60 (F) mg/kg body        2 h after PBB dosing; reduction in
                                                          weight)                  pentobarbital sleeping times 48 h
                                                                                   after PBB dosing

                    FM BP-6 (300 mg/kg  in diet           pentobarbital (single    reduction in pentobarbital sleeping
                    feed for 3 days)                      im dose of 50 (M) or     times
                                                          60 (F) mg/kg body
                                                          weight)

    Table 93 (contd).

    Species         PBB (dosage         Route of PBB      Drug/toxicant            Observed effects after                        References
    and sexa        regimen)            administration    (dose)                   combined treatmentd

    Miscellaneous effects

    Rat (Sprague-   FM BP-6 (single     intraperitoneal   N-methylnicotinamide     no effect on uptake of NMN                    Evers et al.
    Dawley) F       dose of 130-165                       (NMN) (incubation of                                                   (1977)
                    mg/kg body                            renal cortical slices
                    weight)                               with 6 x 10-6 mol/litre
                                                          [14C]-NMN)

                                                          p-aminohippuric acid     elevated uptake of PAH (significant
                                                          (PAH) (incubation of     only at 32 days after PBB dosing)
                                                          renal cortical slices
                                                          with 7.4 x 10-5 mol
                                                          per litre PAH)

    Rat (Sprague-   FM BP-6 (direct     in vitro          N-methylnicotinamide     no effect on uptake of NMN                    Evers et al.
    Dawley) F       exposure of renal                     (NMN) (incubation with                                                 (1977)
                    cortical slices                       6 x 10-6 mol/litre
                    from untreated                        [14]-NMN)
                    animals to animals
                    to 1 x 10-3
                    mol/litre or 1 x
                    10-6 mol/litre)

                                        in vitro          p-aminohippuric acid     no effect on uptake of PAH
                                                          (PAH) (incubation with
                                                          7.4 x 10-5 mol/litre
                                                          PAH)

    Table 93 (contd).

    Species         PBB (dosage         Route of PBB      Drug/toxicant            Observed effects after                        References
    and sexa        regimen)            administration    (dose)                   combined treatmentd

    Rat (Sprague-   FM BP-6 (50 and     pre- and/or       ouabain (single iv       enhanced hepatic uptake and transport         Cagen & Gibson
    Dawley)         100 mg/kg feed      postnatal         dose of 1 mg/kg body     of ouabain from plasma into bile in           (1977a,b,
                    in mother's diet)                     weight)b                 15-day-old rats                               1978); Cagen
                                                                                                                                 et al. (1977)

                                        postnatal         ouabain (single ip       elevated 24-h LD50 values in                  Cagen & Gibson
                                                          doses)b                  15-day-old rats                               (1977a)

    Rat (Sprague-   FM BP-6 (single     intraperitoneal   ouabain (in vitro        decrease in steady-state concentration        Eaton &
    Dawley)         dose of 200 mg/kg                     150 µmol in cell         of ouabain; tendency to increased             Klaassen
                    body weight;                          suspension)              rate of efflux                                (1979)
                    isolation of
                    hepatocytes: 3
                    days after dosing)

                                                          procaine amide           increased rate of efflux
                                                          ethobromide (PAEB)

    Rat (Sprague-   FM BP-6 (100 mg/kg  in diet           sulfobromophtalein       lower plasma concentrations of BSP;           Cagen & Gibson
    Dawley)         feed for 2 weeks)                     (BSP) (single iv dose    increased biliary excretion of BSP and        (1978)
                                                          of 120 mg/kg body        conjugated BSP
                                                          weight)b

    Rat (Fischer    FM BP-6 (100 mg/kg  in diet           cephaloridine (single    decrease in cephaloridine nephrotoxicity      Kuo & Hook
    344) M, F       feed for 10 days)                     ip dose of 1000-2000                                                   (1982)
                                                          mg/kg body weight)b

    Rat (Fischer    FM BP-6 (doses of   gavage            p-aminophenol (PAP)      marked reduction in nephrotoxicity            Newton et al.
    344) M          90 mg/kg body                         (100 or 200 mg/kg        produced by PAP                               (1982b)
                    weight per day                        body weight)b
                    for 2 days)

    Table 93 (contd).

    Species         PBB (dosage         Route of PBB      Drug/toxicant            Observed effects after                        References
    and sexa        regimen)            administration    (dose)                   combined treatmentd

    Rat (Fischer    FM BP-6 (doses of   gavage            N-acetyl-p-              accelerated excretion of mercapturic          Newton et al.
    344)            90 mg/kg body                         aminophenol (APAP)       acid; enhanced ability of APAP to             (1982c)
    (isolated       weight per day                        (3 x 10-8 mol/litre      deplete glutathione
    perfused        for 2 days)                           in the perfusate)b
    kidney)

    Rat (Sprague-   FM BP-6 (single     intraperitoneal   aflatoxin B1 (64 nmol    increase in in vitro metabolism of            Shepherd et al.
    Dawley) M       dose of 575 mg/kg                     per 5 ml incubation      aflatoxin B1 (to aflatoxin M1)                (1984)
    (isolated       body weight on                        mixture)
    liver           day 1; isolation
    microsomes)     of microsomes
                    on day 4)

    Rat (Wistar)    several PBBs (2     intraperitoneal   aflatoxin B1 (64 nmol                                                  Halvorson
    M (isolated     doses of 150                          per 5 ml incubation                                                    et al. (1985)
    liver           µmol/kg body                          mixture)
    microsomes)     weight on days 1
                    and 3; isolation
                    of microsomes on
                    day 6):

                    FM BP-6                                                        increase in in vitro metabolism of
                                                                                   aflatoxin B1 (to aflatoxin M1)

                    2,2',4,5,5'-penta-                                             increase in in vitro metabolism of
                    bromobiphenyl                                                  aflatoxin B1 (to aflatoxin Q1)

                    3,3',4,4'-tetra-                                               increase in in vitro metabolism of
                    bromobiphenyl                                                  aflatoxin B1 (to aflatoxin M1)

    Table 93 (contd).

    Species         PBB (dosage         Route of PBB      Drug/toxicant            Observed effects after                        References
    and sexa        regimen)            administration    (dose)                   combined treatmentd

                    2,3,4,4'5-penta-                                               increase in in vitro metabolism of
                    bromobphenyl                                                   aflatoxin B1 to aflatoxin M1);
                                                                                   decrease in metabolism to aflatoxin Q1

    Mouse (Swiss-   FM BP-6 (100, 200   in diet           ouabain (single iv       lower plasma ouabain concentrations           Cagen et al.
    Webster) F      mg/kg feed for                        dose of 0.1 mg/kg        no enhanced capacity for ouabain              (1977); Cagen
                    2 weeks)                              body weight)b            excretion                                     & Gibson
                                                                                                                                 (1978)

                                                          ouabain (diverse         no effect on ouabain 24-h LD50 values         Cagen et al.
                                                          single doses)                                                          (1977)

    Mouse (Swiss-   FM BP-6 (50 mg/kg   pre- and/or       ouabain (single iv       enhanced disappearance of ouabain from        Cagen & Gibson
    Webster)        feed in mother's    postnatal         dose of 1 mg/kg          the plasma; increase in ouabain excretion     (1977a,b,
                    diet)                                 body weight)b            in 15-day-old mice                            1978)

                                                          ouabain (ip dose)        no effect on ouabain 24-h LD50 values         Cagen & Gibson
                                                                                                                                 (1977a,b)

    Mouse (Swiss-   FM BP-6 (100, 150,  in diet           indocyanine green        enhanced initial disappearance of             Cagen et al.
    Webster)        200 mg/kg feed                        (ICG) (single iv dose    ICG from plasma (correlated with              (1977)
                    for 2 weeks)                          of 40 mg/kg body         higher hepatic ICG content)
                                                          weight)b

    Mouse           FM BP-6 (100 mg/kg  in diet           ethylene dibromide       decrease in renal and hepatic NPS             Kluwe et al.
    (ICR) M         feed for 18 days)                     (EDB) (single ip dose    (non-protein sulfhydryl)-depleting            (1981)
                                                          of 100 mg/kg body        effects of EDP
                                                          weight)b

    Table 93 (contd).

    Species         PBB (dosage         Route of PBB      Drug/toxicant            Observed effects after                        References
    and sexa        regimen)            administration    (dose)                   combined treatmentd

                                                          (diverse single          no significant effect on LD50 (220 mg/kg      Kluwe et al.
                                                          ip doses)                body weight versus 250 mg/kg in control)      (1981)

    Mouse           FM BP-6 (100 mg/kg  in diet           1,2-dibromo-3-chloro-    decrease in renal and hepatic NPS             Kluwe et al.
    (ICR) M         feed for 18 days)                     propane (DBCP) (single   (non-protein sulfhydryl)-depleting            (1981)
                                                          ip dose of 100 mg/kg     effects of DBCP
                                                          body weight)b

    Mouse           FM BP-6 (single     not               chloroform (CHCl3)       no significant effect on GPT or OCT           Plaa &
    M               dose of 500 mg/kg   specified         (single oral dose of     activity                                      Hewitt (1982)
                    body weight)                          0.1 ml/kg body
                                                          weight)b

    a    F = female; M = male.
    b    Administration after PBB treatment.
    c    LT50 = median time to death.
    d    GPT = Glutamic-pyruvic transaminase; OCT = ornithine carbamyl transferase; PAH = p-aminohippurate.

         Rats (Sprague-Dawley, female) treated with FM BP-6 (100 mg/kg
    diet for up to 140 days) had lower hepatic vitamin A and higher
    kidney vitamin A levels than controls, but showed an increase in
    serum retinol (Jensen & Zile, 1988).

         Short-term feeding of 3,3',4,4',5,5'-hexabromobiphenyl (1 mg/kg
    diet for 140 days) to rats (Sprague-Dawley, female) caused a severe
    decrease (approximately 20-fold) in hepatic retinol and retinyl
    esters and a 6-7-fold increase in retinol and retinyl esters in the
    kidneys, while serum concentrations of retinol were unaffected by
    PBB feeding (Jensen et al., 1987). Examination of liver enzymes in
    these rats revealed reductions of 50% and 63% of acetyl-CoA-retinol
    acetyltransferase and retinyl palmitate hydrolase, respectively
    (Jensen et al., 1987). Consistent with the previous studies, there
    was an increased accumulation of retinol and retinyl esters in the
    kidneys of rats given a single oral dose of
    3,3',4,4',5,5'-hexabromobiphenyl (2 mg/kg body weight) as well as a
    decrease in liver retinyl ester pools (Zile et al., 1989).

         In studies using radioactive retinyl acetate, a two-fold
    increase in the elimination of vitamin A metabolites in the urine
    and faeces was observed in rats (Sprague-Dawley, male) 12 h-8 days
    after a single anorectic, oral dose of
    3,3',4,4',5,5'-hexabromobiphenyl (2 mg/kg body weight). The
    potential effect of the PBB on the absorption of vitamin A was
    excluded by the experimental design in this study (Cullum & Zile,
    1985). Similarly, long-term, dietary administration of
    3,3',4,4',5,5'-hexabromobiphenyl (1 mg/kg diet for 140 days)
    resulted in a greatly increased faecal and urinary elimination of
    radioactivity, when rats (Sprague-Dawley, female) were given a
    physiological dose of [11-3H]retinyl acetate (Jensen et al.,
    1987).

         Changes in vitamin A metabolite patterns were found in tissues
    (liver, kidney, small intestinal mucosa) of rats after a single oral
    dose of 3,3',4,4',5,5'-hexabromobiphenyl (2 mg/kg body weight),
    which produced a shift of vitamin A metabolism towards the more
    polar forms of vitamin A, such as retinoic acid, its oxidation and
    conjugation products (retinoyl glucuronide), and polar retinoid
    metabolites (Zile et al., 1989).

         The influence of the PBB on the vitamin A balance was long
    lasting. As seen in Table 94, in a multigeneration study, FM BP-6
    produced a decrease in hepatic vitamin A concentration, even in the
    second generation of offspring (28 days of age) of rats when PBB was
    fed (100 mg/kg diet) only during the first pregnancy (day 8) until
    28 days post partum. At this time, all offspring (F1) were weaned
    onto a control diet, allowed to mature sexually, and bred with
    litter-mates to produce the F2-generation (McCormack et al.,
    1981).

    
    Table 94.  Reduction of hepatic vitamin A content in the rat by various PBBs (single congeners and commercial mixtures)

    Compound              Strain/sex         Dose and route of     Exposure period/                Reduction in hepatic    References
                                             administration        observation/period                 vitamin A
                                                                                                   concentration (%)

    2,2',4,4',5,5'-       Sprague-Dawley     100 mg/kg diet        30 days                                28               Akoso et al.
    hexabromobiphenyl     (male)                                   (1982a)

    2,3',4,4',5,5'-       Sprague-Dawley     100 mg/kg diet        30 days                                57
    hexabromobiphenyl     (male)

    3,3',4,4',5,5'-       Sprague-Dawley     10 mg/kg diet         30 days                                59
    hexabromobiphenyl     (male)

    3,3',4,4',5,5'-       Sprague-Dawley     1 mg/kg diet          140 days                               95               Jensen et al.
    hexabromobiphenyl     (female)                                 (1987)

    FireMaster(R) BP-6    Sprague-Dawley     100 mg/kg diet        30 days                                72               Akoso et al.
                          (male)                                   (1982a)

    FireMaster(R) BP-6    Sprague-Dawley     100 mg/kg diet        140 days                               92               Jensen & Zile
                          (female)                                 (1988)

    FireMaster(R) BP-6    Sprague-Dawley     100 mg/kg in          perinatal: day 8 of pregnancy           approximately   McCormack et al.
                          (female)           mother's diet         until 4, 8, or 14 weeks of              50              (1982b)
                                                                   age

    FireMaster(R) BP-6    Sprague-Dawley     100 mg/kg in          F0: perinatal: day 8 of                57               McCormack et al.
                          (female)           mother's diet         pregnancy until 28 days                                 (1981)
                                                                   post-partum/F1 (28 days of
                                                                   age)

    Table 94 (contd).

    Compound              Strain/sex         Dose and route of     Exposure period/                Reduction in hepatic    References
                                             administration        observation/period                 vitamin A
                                                                                                   concentration (%)

                                                                   F0: perinatal: day 8 of                28
                                                                   pregnancy until 28 days
                                                                   post-partum/F2 (28 days of
                                                                   age)

    a    F0 = parental generation; F1 = first filial generation; F2 = second filial generation.

         The influence of dietary levels of vitamin A on the toxicity of
    PBB has been studied. Vitamin A supplementation (up to 30 000 IU)
    provided only partial protection against decreases in body weight
    gain and thymic weight and against hyperplasia of the common bile
    duct in rats intoxicated with 100 mg FM BP-6/kg diet (Darjono
    et al., 1983). High dietary levels of vitamin A (200 000 IU) also
    had some inhibitory effect on carcinogenesis, i.e., on the promotion
    of hepatic-altered foci by 3,3',4,4',5,5'- hexabromobiphenyl in
    initiated rats (Rezabek et al., 1989).

         The mechanism by which PBBs influence vitamin A homeosta sis is
    not fully understood. Conflicting results may be because of
    analytical problems and biological variables. However, according to
    Zile et al. (1989), it is very likely that polyhalogenated aromatic
    hydrocarbons affect specific enzymes involved in the regulation of
    vitamin A storage and in the vitamin A metabolic pathway. Others
    have suggested that PCBs and related compounds may interfere with
    Vitamin A transport in the serum by inhibiting the formation of the
    serum transport protein complex carrying retinol and thyroxin
    (Brouwer & van den Berg, 1986).

    8.8.5  Porphyria

         Hexabromobiphenyl is able to produce chemical porphyria in
    Japanese quail (Strik, 1973b), rats, and mice (Gupta et al., 1983a;
    Hill, 1985). Following studies on adult Japanese quail, which were
    orally dosed with gelatin capsules or fed diet containing up to
    1000 mg/kg body weight FireMaster(R) BP-6, Strik (1978) stated
    that PBB porphyria was preceded by liver and kidney damage. 
    Accumulation of porphyrins in the liver is not solely due to an
    increase in delta-amino-levulinic acid synthetase activity, but
    rather to drug enzyme induction and the formation of a reactive
    intermediate that causes centrilobular liver damage and ultimately
    porphyria. The hepatic mitochondria decrease in number and are
    damaged (elevated serum glutamic acid dehydrogenase); the
    profilerated endoplasmic reticulum, including the haemoprotein
    P-450, is no longer capable of normal activity; uroporphyrinogen
    decarboxylase activity is reduced to zero; renal porphyrins
    accumulate and are excreted in the liver and via the bile.

         In tests with chick-embryo liver cell cultures, Debets et al.
    (1980) showed that pretreatment with inducers of the drug-
    metabolizing enzyme system markedly stimulated the accumulation of
    porphyrins, after exposure to FireMaster(R) BP-6. Inhibition of
    hepatic drug metabolism or the addition of compounds, known to trap
    electrophiles or radicals, protected against the porphyrinogenic
    action of FireMaster(R) BP-6  in vitro.

         In the same test system, a DeBB solution of 10 µg/ml medium did
    not show any porphyrogenic potential with, or without, pretreatment
    with ß-naphthoflavone (3 µg/ml medium) for 20 h (Koster et al.,
    1980). Gupta et al. (1983a) found dose-related, elevated hepatic
    prophyrin levels in Fischer 344/N rats and B6C3F1 mice, orally
    dosed with 0.1-10.0 mg FireMaster(R) BP-6/kg body weight (5
    steps), primarily in females.

         Hill (1985) studied the urinary porphyrin pattern by ion-pair
    chromatography in female Sherman rats given 0 or 1 g PBB/kg body
    weight. The route of administration was not stated. Chronic hepatic
    porphyria became evident about 55-60 days after dosing, as indicated
    by the large increase in uroporphyrin and heptacarboxylporphyrin and
    the corresponding ratios of these porphyrins to coproporphyrin.
    Between 85 and 100 days, chronic hepatic porphyria developed into
    its most severe form  (porphyria cutanea tarda).

         Summarizing all reported facts on porphyrin metabolism, Hill
    (1985) pointed out that chronic hepatic porphyria is characterized
    as a membrane disease in which there is damage to the membranes of
    the cell walls of the hepatocytes and organelles (i.e., mito
    chondria, endoplasmic reticulum) within the liver cell. The cause of
    damage is unknown. There is some evidence that PBBs produce changes
    in lipid metabolism, which in turn alters membrane structure
    (Bernert et al., 1983). This change in membrane structure may cause
    a change in membrane permeability (damage) so that porphyrins are
    excreted in the bile capillaries and the intercellular substance. In
    addition to these changes, PBBs, or their metabolites, cause the
    induction of delta-aminolevulinic acid synthetase and the inhibition
    of the enzyme uroporphyrinogen decarboxylase. The changes in enzyme
    activities produce a build-up of uroporphyrinogen and
    heptacarboxylporphyrinogen, and these precursors are excreted in the
    urine, where they are easily oxidized to uroporphyrin and
    heptacarboxylporphyrin.

         A marked sex difference in the development of uroporphyria
    occurred after administration to 10-week-old F344/N rats of 0.005%
    FireMaster(R) BP-6 added to the diet. Thus, the propensity of
    female rats to develop uroporphyria appeared to be a general
    response to this class of halogenated chemicals. Liver to body
    weight ratio, liver porphyrins, and the activity of a
    uroporphyrinogen decarboxylase inhibitor were significantly greater
    in both sexes compared with appropriate controls. Comparing treated
    males and females, the liver to body weight ratio and
    uroporphyrinogen decarboxylase inhibitor activity were significantly
    greater in males whereas the liver porphyrin content was greater in
    females. Levels of total cytochrome P-450 and pentoxyresorufin and
    benzyloxyresorufin dealkylase activities (associated with cytochrome

    P450IIB1) were greater in microsomes from control, and PBB-treated
    male rats compared with females. In contrast, ethoxyresorufin
    deethylase activity (associated with cytochrome P450 IA1) was
    significantly greater in females (Smith et al., 1990a).

         Iron potentiated the development of uroporphyria after oral
    exposure to FireMaster(R) BP-6 for 2 months (dose not stated) in 7
    to 10-week-old, male Ah-responsive C57Bl/10ScSn mice (Smith et al.,
    1990b).

    8.8.6  Miscellaneous effects

         Alterations in liver microsomal membrane lipid composition,
    increased peroxidation activities, and an increase in membrane
    fluidity were found after a single oral dose of 500 mg
    FireMaster(R) BP-6/kg body weight during short- and long-term
    observations (Bernert et al., 1983; Bernert & Groce, 1984).

         PBBs were found to inhibit rabbit muscle glycogen phosphorylase
    (1,4-alpha-D-glucan: orthophosphate alpha-D-glucosyltransferase, EC
    2.4.1.1), an enzyme that catalyzes the breakdown of glycogen to
    glucose 1-phosphate. The enzyme exists in two metabolically
    significant forms, phosphorylase a and b.
    2,2',4,4',5,5'-Hexabromobiphenyl and FireMaster(R) BP-6 were
    strong inhibitors of phosphorylase b (92% and 88% inhibition at
    60 µmol/litre, respectively; Ki = 15 µmol/litre), while exhibiting
    little or no inhibition of phosphorylase a (Mead et al., 1982).

         The activity of the enzyme uridine 5'-diphosphoglucuronyl-
    transferase (UDP-GT), responsible for the conjugation of a wide
    variety of substrates, was significantly increased in microsomes
    prepared from rats ip injected with 3,3',4'4',5,5'-hexabromobiphenyl
    at 20 mg/kg body weight (Spear et al., 1990).

         The influence of FireMaster(R) BP-6 on glutathione peroxidase
    activity, which is present in most mammalian species, was studied in
    the rat (liver cytosol). This enzyme is represented, on the one
    hand, by a selenium-containing enzyme, glutathione peroxidase (E.C.
    1.11.1.9), which is able to reduce hydrogen peroxide to water and
    organic hydroperoxides to the corresponding hydroxy compounds, and,
    on the other hand, by certain isozymes of glutathione transferase
    (E.C. 2.5.1.18). The activity of the selenium-dependent glutathione
    peroxidase was decreased to about 50% of control values on day 16
    following the ip administration of FireMaster(R) BP-6 (500 mg/kg
    body weight). Inversely, there was a potent induction of glutathione
    transferases during the 16-day period (Schramm et al., 1985).

         Adenylate cyclase [ATP pyrophosphatase lyase (cyclizing), EC
    4.6.1.1] catalyzes the conversion of adenosine triphosphate (ATP) to
    adenosine 3',5'-cyclic monophosphate (cyclic AMP), which acts as a
    central regulator of several diverse cell activities. In preliminary

    experiments, the  in vitro effect of FireMaster(R) BP-6 on
    adenylate cyclase activity in the plasma membranes of rat lung
    alveoli was determined. At concentrations of 10 µg/ml, the
    FireMaster(R) mixture stimulated the basal adenylate cyclase
    activity of plasma membranes 2- to 2.5-fold (Sidhu & Michelakis,
    1978). The authors discuss the possible immunological relevance of
    this observation.

    8.9  Effects on intercellular communication

         PBBs show a significant epigenetic activity. The
    FireMaster(R) mixture and some of its major components were found
    to be capable of inhibiting intercellular communication, measured by
    metabolic cooperation between HGPRT+ and HGPRT- cells in culture
    (Table 95). This inhibition occurred at non-cytotoxic
    concentrations. In contrast to FireMaster(R) and to its major
    constituents BB 153 and BB 180, 3,3',4,4',5,5'-hexabromobiphenyl and
    3,3',4,4'-tetrabromobiphenyl did not interrupt cell-cell
    communication at noncytotoxic concentrations. However, both
    congeners were markedly cytotoxic (Table 95). Congeners with
    intermediate toxicity such as 2,3'4'4',5-PeBB (BB 118),
    3,3',4,4',5'- PeBB (BB 127), and 2,3',4,4',5,5' HxBB (BB 167), were
    also shown to interfere with cell-cell communication at noncytotoxic
    concentrations. Both the cytotoxicity and the metabolic
    cooperation-inhibiting properties of PBB congeners seem to be
    related to their structure, i.e., presence or lack of ortho-
    substitution (Tsushimoto et al., 1982; Kavanagh et al., 1987; see
    also section 8.7.2.2).

         Recently, the ability of FireMaster(R) BP-6 to inhibit gap
    junction-mediated intercellular communication has been confirmed by
    the FRAP assay, using cultured rat liver epithelial cells (Rezabek
    et al., 1988). This assay, which has been described by Wade et al.
    (1986), evaluated the inhibition of fluorescence redistribution
    after photobleaching (FRAP), which occurs between cells loaded with
    a fluorescent dye.

         Results obtained by a similar new method, the scrape-
    loading/dye-transfer (SL/DT) technique (El-Fouly et al., 1987)
    confirmed the inhibitory potency of 2,2',4,4',5,5'-hexabromobiphenyl
    (Evans et al., 1988; Table 95).

         Several different cell types (human fibroblasts, rat kidney
    epithelial cells, rat liver oval cells, rat Leydig cells, rat glial
    cells, mouse keratinocytes) differ in their response to chemicals
    that alter gap junctional intercellular communication. After
    exposure to FireMaster(R) BP-6 (20 µg/ml), intercellular
    communication was inhibited to different extents in three (WB rat
    liver oval cells, RG-1 rat glial cells, JB-6 mouse keratinocytes)
    out of the six cell types tested, rat liver oval cell being the most
    sensitive cell (Bombick, 1990).

    
    Table 95.  Inhibition of intercellular communication by PBBs: results of in vitro assays testing metabolic cooperation
    between 6-thioguanine-sensitive (HGPRT+) and- resistant (HGPRT-) cells or testing dye transfera

    PBBa                            Cells in culture              Inhibition        Remark                           References
                                                                 Yes      No

    FM BP-6                         Chinese hamster              x                  non-lethal range of the          Trosko et al. (1981)
                                    V79 lung cells                                  chemical

    FM FF-1                         rat liver cells              x                  no cytotoxicity mentioned        Williams et al. (1984)

    FM BP-6                         human teratocarcinoma        x                  only slight effect on            Kavanagh et al. (1987)
                                    cells                                           cell survival

    FM BP-6                         rat liver epithelial cells   x                  at non-toxic FM concentration    Rezabek et al. (1988)
                                    (WB-F 344)

    3,3',4,4',-tetrabromobiphenyl   human teratocarcinoma                 x         moderately cytotoxic             Kavanagh et al. (1987)
    (BB 77)                         cells

    2,3',4,4',5-                    Chinese hamster              x                  inhibition before                Tsushimoto et al.
    pentabromobiphenyl (BB 118)     V79 cells                                       cytotoxicity occurs              (1982)

    3,3'4,5,5'-pentabromobiphenyl   Chinese hamster              x                  slight inhibition                Tsushimoto et al.
    (BB 127)                        V79 cells                                       before cytotoxicity              (1982)

    2,2',4,4',5,5'-                 Chinese hamster              x                  relatively nontoxic
    hexabromobiphenyl (BB 153)      V79 cells

                                    rat liver epithelial         x        x         at non-cytotoxic                 Evans et al.
                                    cells (WB-F344)                                 concentrations                   (1988)

    Table 95 (contd).

    PBBa                            Cells in culture              Inhibition        Remark                           References
                                                                 Yes      No

                                    human teratocarcinoma        x                  only slight effect               Kavanagh et al.
                                    cells                                           on cell survival                 (1987)

    2,3',4,4',5,5'-                 Chinese hamster              x                  inhibition before                Tsushimoto et al.
    hexabromobiphenyl (BB 167)      V79 cells                                       cytotoxicity occurs              (1982)

    3,3',4,4',5,5'-                 Chinese hamster              x                  highly cytotoxic                 Tsushimoto et al.
    hexabromobiphenyl (BB 169)      V79 cells                                                                        (1982)

                                    human teratocarcinoma        x                  highly cytotoxic                 Kavanagh et al.
                                    cells                                                                            (1987)

    2,2',3,4,4',5,5'-               Chinese hamster              x                  relatively non-cytotoxic         Tsushimoto et al.
    heptabromobiphenyl (BB 180)     V79 cells                                                                        (1982)

    2,2',3,3',4,4',5,5'-            Chinese hamster              x                  relatively non-cytotoxic
    octabromobiphenyl               V79 cells
    (BB 194)

    a    HGPRT = Hypoxanthine-guanine phosphoribosyl transferase locus.
    b    Purity of PBB congeners tested: > 99%; FM = FireMaster.

    8.10  Immunotoxicity

         The effects of PBBs (commercial mixtures and individual
    congeners) on the weight and histology of the thymus, bursa of
    Fabricius, and spleen have been reviewed in sections 8.2 (single and
    short-term exposures: 8.2.1.3, commercial mixtures; 8.2.2,
    congeners) and 8.4 (long-term exposures). In summary, atrophy of
    thymus was a frequent observation following PBB exposure.

         Other indicators of a suppressed immune function have been
    compiled in Table 96. These data refer only to the FireMaster(R)-
    mixture, because information on OcBB, DeBB, or individual PBB
    congeners (with the exception of 3,3',4,4'-tetrabromobiphenyl) is
    lacking.

         In addition to the thymus or spleen, other lymphoid tissues
    were affected by PBB, e.g., bone marrow and the lymph nodes of dogs
    (Farber et al., 1978; Table 96).

         Serum immunoglobulin levels in mice were changed following
    short-or long-term exposure to FireMaster(R) (Luster et al., 1978,
    1980; Loose et al., 1981). Suppression of antibody response to sheep
    erythrocytes (or bovine gamma globulin) was reported after the
    short-term exposure of mice (Fraker & Aust, 1978; Luster et al.,
    1978; Fraker, 1980; Loose et al., 1981) and after a six-month
    exposure of rats (Luster et al., 1980). Conditions of study are
    summarized in Table 96.

         Interestingly, mice showed no response in the 6-month study
    (Luster et al., 1980). A decrease in antibody titres to tetanus
    toxoid was observed in guinea-pigs (Vos & van Genderen, 1974; Table
    96).

         Although mortality rates following infection with  Listeria
     monocytogenes were not affected by FireMaster(R) exposure in
    mice exposed long-term, an increased susceptibility to infection
    with Listeria was suggested, because a decrease in time to death
    occurred (Luster et al., 1980; Table 96). No effects on mean
    survival time were observed in mice fed 5 or 167 mg/kg feed for 3 or
    6 weeks and then challenged by  Plasmodium berghei (murine malaria)
    infection (Mudzinski et al., 1979; Loose et al., 1981).

         An increased susceptibility to endotoxin was found in mice
    after short-term (Mudzinski et al., 1979; Loose et al., 1981) or
    perinatal (Luster et al., 1980) exposure to FireMaster(R) (Table
    96). Mice with long-term exposure did not show endotoxin sensitivity
    (Luster et al., 1980). Of the individual PBB congeners, 3,3'4,4'-
    tetrabromobiphenyl was found to increase sensitivity to endotoxin
    (lipopolysaccharide from  Escherichia coli) 1-2 days after
    administration (single intraperitoneal dose of 150 µmol/kg body
    weight) to rats (Shedlofsky et al., 1991).

    
    Table 96.  Immunotoxicity of FireMaster(R)a

    PBBb                Species       Route      Dosing                Period of     Observed effectsd                             Reference
                        (strain/                                       exposure
                        sex)c

    FM FF-1             rat           gavage     22 doses of 0.03,     30 days       depression of T-cell responsiveness to        Luster
    (lot FF 1312 FT)    (Fischer)                0.3, 3, or 30 mg/kg                 mitogens (PHA: overall dose response:         et al.
                        (M)                      body weight                         P < 0.01; 3 and 30 mg/kg per day:             (1978)
                                                                                     P < 0.05; Con A: overall dose response:
                                                                                     P < 0.1; 30 mg/kg per day; P < 0.05)

    FM FF-1             rat           gavage     122 doses of 0.1,     6 months      depression of both B-(10 mg/kg per day)       Luster
    (lot FF 1312 FT)    (Fischer)                0.3, 1, 3, or 10                    and T-(1,3, or 10 mg/kg per day) cell         et al.
                        (F)                      mg/kg body weight                   mitogenic (PHA, Con A, PWM) and               (1980)
                                                                                     allo-geneic responses (P < 0.05 or 0.01);
                                                                                     decreased antibody responses to bovine
                                                                                     globulin (10 mg/kg per day; P < 0.1);
                                                                                     suppressed delayed hypersensitivity
                                                                                     reactions (3 and 10 mg/kg per day;
                                                                                     P < 0.05)

    FM FF-1             mouse         gavage     22 doses of 0.03,     30 days       depression of T- and B-cell responsiveness    Luster
    (lot FF 1312 FT)    (B6C3F1)                 0.3, 3, or 30 mg/kg                 to mitogens PHA, Con A, and LPS (overall      et al.
                        (F)                      body weight                         dose response: P < 0.01; 3 mg/kg per day:     (1978)
                                                                                     PHA, Con A and 30 mg/kg per day: PHA,
                                                                                     Con A, LPS: P < 0.10 or 0.01); decreased
                                                                                     antibody responses to SRBC (30 mg/kg per
                                                                                     day; 27% reduction): decrease in serum IgM
                                                                                     and IgG2 levels (30 mg/kg per day;
                                                                                     P < 0.01 and 0.10, respectively)

    Table 96 (cont'd).

    PBBb                Species       Route      Dosing                Period of     Observed effectsd                             Reference
                        (strain/                                       exposure
                        sex)c

    FM FF-1             mouse         gavage     122 doses of 0.1,     6 months      enhanced number of bone marrow colony         Luster
    (lot FF 1312 FT)    (B6C3F1)                 0.3, 1, 3, or 10                    forming units (only F at 1 and 10 mg/kg       et al.
                        (F,M)                    mg/kg body weight                   body weight per day; P < 0.01); decrease      (1980)
                                                 per day                             in serum IgG, IgM, and IgA levels (10 mg/kg
                                                                                     body weight per day P < 0.01 or 0.05);
                                                                                     increase in serum IgG (1 mg/kg body weight
                                                                                     per day; P < 0.01) and IgA (0.3 mg/kg body
                                                                                     weight per day; P < 0.1); depression of B-
                                                                                     and T-cell responisiveness to mitogens
                                                                                     (PHA, Con A, LPS) at 10 mg/kg body weight
                                                                                     per day (P < 0.05): increased
                                                                                     susceptibility to infection with Listeria
                                                                                     mono-cytogenes (10 mg/kg body weight
                                                                                     per day)

    FM FF-1             mouse         perinatal  maternal doses of     gestation     enhanced number of bone marrow colony         Luster
    (lot FF-1312 FT)    (B6C3F1                  0.3, 1, 3, or 10      day 0 until   forming units (F: 1 mg/kg body weight         (1980)
                        (F,M)                    mg/kg body weight     weaning (on   per day; P < 0.05): increased
                                                 per day               alternate     susceptibility to endotoxin (LPS,
                                                                       day)          E. coli) (marginal dose response
                                                                                     P = 0.06)

    FM BP-6             mouse         in diet    1, 10, 100 mg/kg      30 days       reduced antibody responses to SRBC            Fraker &
                        (BALB/c)                 feed                                (10, 100 mg/kg: P < 0.001)                    Aust (1978)

                                                 1000 mg/kg feed       14 days       survivors incapable of mounting an            Fraker
                                                                                     antibody-mediated response to SRBC            (1980)

    Table 96 (cont'd).

    PBBb                Species       Route      Dosing                Period of     Observed effectsd                             Reference
                        (strain/                                       exposure
                        sex)c

    FM FF-1             mouse         in diet    167 mg/kg feed        3 or 6        increase in endotoxin (LPS;                   Loose
    (lot No. 7042)      (BALB/cByJ)                                    weeks         Salmonella typhosa) sensitivity (P < 0.05);   et al.
                        (M)                                                          reduced primary antibody reaction to          (1981)
                                                                                     SRBC (only at 3 weeks)

                                                 5 mg/kg feed          3 or 6        reduced serum IgM levels (at 3 and 6
                                                                       weeks         weeks; (P < 0.05)

    FM BP-6             guinea-pig    in diet    10, 50 mg/kg feed     45 days       reduction in antibody titres to tetanus       Vos & van
                        (F)                                                          toxoid (P < 0.025) P < 0.05); reduced serum   Genderen
                                                                                     IgG levels (at 6 weeks, P < 0.05) reduced     (1974)
                                                                                     serum IgM levels (at 3 and 6 weeks;
                                                                                     P < 0.05)

    FM BP-6             pig           in diet    100, 200 mg/kg        last half     decreased responses of peripheral blood       Howard
                        (sows)                   feed                  of            lymphocytes to mitogen (PHA, PWM)             et al.
                                                                       gestation     stimulation (200 mg/kg; P < 0.05)             (1980)
                                                                       and 4
                                                                       weeks of
                                                                       lactation
                                                                       (12 weeks)

    FM BP-6             pig           perinatal  100, 200 mg/kg        last half of  normal mitogen (PHA, PWM) responses at
                        (piglets)                feed                  gestation     birth; decreased mitogen responses at
                                                                       and 4 weeks   4 weeks of age (PWM = 200 mg/kg;
                                                                       of lactation  P < 0.002)
                                                                       (12 weeks)

    Table 96 (cont'd).

    PBBb                Species       Route      Dosing                Period of     Observed effectsd                             Reference
                        (strain/                                       exposure
                        sex)c

    FM BP-6             dog           gavage     0.06-4 mg/kg          61 days       degenerating lymphocytes in blood smears      Farber
                                                 body weight                         (all levels); depletion of lymphocytes in     et al.
                                                 per day                             the lymph nodes, (4 mg/kg); reduced           (1978)
                                                                                     erythro-poiesis in bone marrow (4 mg/kg);
                                                                                     reduction in IgG-containing lymphocytes in
                                                                                     popliteal lymph nodes (4 mg/kg)

    a    Exclusive of effects on the weight and histology of thymus and spleen, which are noted in another section.
    b    FM = FireMaster(R).
    c    M = Male; F = Female.
    d    Con A = Concanavalin A; LPS = bacterial lipolysaccharide; PHA = phytohemagglutinin; PWM = pokeweed mitogen;
         SRBC = sheep red blood cells.

         FireMaster(R) depressed lymphoproliferative (B- and/or
    T-cell) responsiveness to mitogens in rats (Luster et al., 1978,
    1980), mice (Luster et al., 1978, 1980), and pigs (Howard et al.,
    1980). Response to mitogens was variable among the species tested
    (Table 96), e.g., rats exposed long-term were more sensitive (dose
    required: < 10 mg/kg body weight per day) than mice (dose required
    = 10 mg/kg body weight per day) in the same study (Luster et al.,
    1980).

         Delayed hypersensitivity reactions were depressed in adult rats
    at higher doses of PBBs (Luster et al., 1980; Table 96), but they
    were comparable to controls in mice, exposed perinatally and
    long-term (Luster et al., 1980).

         Some haematological parameters of immunological interest, e.g.,
    changes in peripheral lymphocyte and leukocyte counts are reported
    in sections 8.2.1.2. and 8.4.

         In summary, there was a wide spectrum of immunotoxic effects of
    FireMaster(R) in different animal species, but immune
    dearrangement was often recorded at doses that produced other signs
    of toxicity.

    8.11  Neurotoxicity

         Behavioural and neurological parameters have been examined in
    rodents and rhesus monkeys treated with the commercial
    FireMaster(R) mixture or with its main component, 2,2',4,4',5,5'-
    hexabromobiphenyl (BB 153).

    8.11.1  Exposure of adult animals

         Adult rats (Fischer 344/N) and mice (B6C3F1) of both
    sexes were exposed to oral doses of 0.03-30 mg FM FF-1/kg body
    weight per day or 0.168-16.8 mg 2,2',4,4',5,5'-hexabromobiphenyl per
    kg body weight per day (5 days per week) for a total of 22 doses.
    Neurobehavioural toxicity was assessed at the end of the 30-day
    dosing regimen and also 30 days after cessation of dosing (Tilson
    et al., 1978; Tilson & Cabe, 1978, 1979). Additionally, rats having
    received 130 oral doses of 3 or 10 mg FM FF-1/kg body weight per day
    (5 days per week) were tested after 6 months of dosing (Tilson &
    Cabe, 1979). Mainly at the higher doses, FM FF-1, and, to a much
    lesser extent, BB 153 led to neuromuscular dysfunction, such as
    decreased motor activity, depressed neuromuscular reflexes, and
    impaired forelimb grip strength. Rats were generally more affected
    than mice. Visual placement responses were also decreased in male
    rats and mice by FM FF-1 and BB 153. Hypothermia (decreased rectal
    temperature) was caused by FM FF-1 in mice. In general, rats tended
    to remain the same or get worse during the 30 days of no dosing,
    while mice tended to improve. In another study (Geller et al.,
    1979), the influence of PBB on cognitive function was evaluated.

    Male rats (Sprague-Dawley) received "hexabrominated biphenyl" (not
    specified) at 1 mg/kg body weight per day (5 days per week) for a
    total of 20 doses during a one-month period and were then trained
    for a simple auditory discrimination task. PBB-treated animals did
    not significantly differ from controls with respect to accuracy on
    the discrimination task. However, throughout 24 weeks of
    discrimination training, PBB rats made many more extra responses and
    showed longer response times (response latencies), thereby reducing
    their efficiency. Upon completion of the behavioural study, a group
    of rats, dosed concurrently with the behavioural animals, was
    sacrificed immediately after the end of dosing, and the brains were
    used to prepare both intact synaptosomes and synaptic plasma
    membranes (Gause et al., 1979). Both calcium binding to synaptic
    plasma membranes and calcium uptake by intact synaptosomes was
    significantly reduced in the brains of rats administered 1 mg PBB/kg
    body weight per day. From these results, the authors derived that
    both spontaneous and evoked transmitter release could be reduced
    during PBB treatment.

    8.11.2  Perinatal exposure

         Functional impairment of offspring after perinatal exposure to
    PBBs has been observed at PBB concentrations not causing overt
    maternal toxicity. Locomotor activity was decreased in the offspring
    of Swiss-Webster-mice fed FireMaster(R) (100 mg/kg feed) during
    lactation (postnatal days 1-29). Increased mortality and decreased
    body weight were also seen in the pups (Preache et al., 1976). Prior
    to breeding, female rats (Sprague-Dawley) were dosed orally for 20
    days (5 days/week) with FireMaster(R) FF-1 (0.5 or 5 mg/kg body
    weight), and the male offspring were used for measurements of motor
    activity (Gause et al., 1984), pain threshold (Gause et al., 1984),
    operant behaviour, and response to central nervous system-active
    drugs (Gause et al., 1984; Geller et al., 1985). The first two of
    these four measurements started from weaning and resulted (over a 6
    week period) in higher levels of activity and in changes in the pain
    threshold in animals exposed to PBB. Both of the last tests were
    conducted with the adult (> 75 days of age) offspring: There were
    no detectable effects of PBB on the acquisition or performance of
    the operant discrimination task; however, the pharmacological
    challenge showed that F1 males from PBB-treated dams were less
    sensitive to both phenobarbital and d-amphetamine than F1 males
    from control dams. In another study, pregnant rats (Sprague-Dawley)
    received oral doses of 0.2 or 2 mg FireMaster(R) BP-6/kg body
    weight per day from day 6 of gestation through day 24 postpartum
    (Henck & Rech, 1986).  Several signs of neurobehavioural toxicity
    were found in male and female offspring of dams given 2 mg
    FireMaster(R) BP-6/kg per day, a dose that produced tissue levels
    within the range of those measured in highly exposed Michigan
    people. There were significant effects on the acquisition of
    foreword locomotion, cliff avoidance, cage emergence, and open field
    activity (Henck, 1986). At 6 months of age, the offspring were

    tested for a series of operant responses of increasing difficulty.
    It was found that the learning of various operant behavioural
    patterns was impaired in a relatively subtle manner, and that both
    sexes can differ in their responses (Henck, 1986; Henck & Rech,
    1986).

    8.12  Factors modifying toxicity, toxicity of metabolites

    8.12.1  Contaminants affecting toxicity

    8.12.1.1  Polybrominated naphthalenes (PBNs)

         PBNs have been identified as contaminants of the commercial
    FireMaster(R) mixture (at concentrations of the order of
    200 mg/kg: see section 2.1.2). In structure, they resemble other
    classes of halogenated aromatic hydrocarbons, such as
    polychlorinated naphthalenes, polyhalogenated biphenyls,
    dibenzodioxins, and dibenzofurans, and may elicit similar
    qualitative effects (e.g., Kimbrough, 1980a,b). A summary of
    biologic and toxicological responses reported on PBNs is given in
    Tables 97 and 98. It shows that some PBNs are potent toxicants and
    teratogens. PBNs were teratogenic in mice at dose levels below those
    capable of producing overt maternal toxicity (Miller & Birnbaum,
    1986). Compared with FireMaster(R) (consult also previous
    sections), PBN mixtures were much more potent in causing adverse
    effects. For example, a PBN mixture was at least 10 times more
    effective than FM BP-6 in producing maximal induction of aryl
    hydrocarbon hydroxylase (30 µmol/kg body weight versus 300 µmol/kg;
    Robertson et al., 1981a, 1984a). Although PBNs are present only at
    low levels in the FireMaster(R) mixture, some authors (Robertson
    et al., 1984a; Miller & Birnbaum, 1986) believe that they may
    contribute to the toxicity of FireMaster(R).

    8.12.1.2  Mixed polybromo-chlorobiphenyls

         At present, only a monochloropentabromobiphenyl has been
    identified as a trace impurity in FireMaster(R) FF-1 (see section
    2.1.2). No information is available on its toxicological properties. 
    However, there is one study by Andres et al. (1983) in which the
    biological and toxic effects are compared of a series of laterally
    substituted 3,3',4,4'-tetrahalobiphenyls containing the following
    variable molecular Cl/Br ratios: Br4, Br3Cl, Br2Cl2 (two
    isomers), BrCl3, and Cl4. Parameters examined included: growth
    rate, effects on the thymus, and hepatic microsomal enzyme induction
    in male Wistar rats, as well as enzyme induction in rat hepatoma
    cells in culture and relative binding affinities to the rat
    cytosolic receptor protein. Data obtained demonstrated that the
    activity of these (mixed) halogenated biphenyls was enhanced with
    increasing bromine (and decreasing chlorine) substitution.

    Table 97.  LD50 values of several polybrominated naphthalenes (PBN)
    in guinea-piga,b

    PBN                                                        LD50
                                                        (µg/kg body weight)

    2,3,6,7-tetrabromonaphthalene                               242
    1,2,4,6,7-pentabromonaphthalene                             200
    1,2,3,4,6,7-hexabromonaphthalene                            361
    1,2,3,5,6,7-hexabromonaphthalene                         > 3610

    a    From: McKinney & McConnell (1982).
    b    Hartley strain guinea-pigs given a single oral dose (gavage) and
         observed for 30 days.

    8.12.2  Toxicity of metabolites

         No experimental data are available on the toxicity of PBB
    metabolites.

    8.12.3  Toxicity of photolysis and pyrolysis products

    8.12.3.1  Photolysis products

         Studies of the FireMaster(R) mixture and its main component,
    2,2',4,4',5,5'-hexabromobiphenyl, showed that the photolysis
    products were more toxic than the original PBB. The parameters of
    toxicity compared were liver and thymus weight changes, liver
    histology, hepatic microsomal enzyme induction, and binding affinity
    to the cytosolic receptor in rats, as well as development of
    hyperkeratosis in the rabbit ear (Table 99). Probably, one or more
    of the lower brominated PBBs formed by photolysis (see section
    4.2.1) are responsible for the increased potency. It is believed
    that the increased potency of irradiated
    2,2',4,4',5,5'-hexabromobiphe nyl is due mostly to
    2,3',4,4',5-pentabromobiphenyl and, because of metabolism, to a
    lesser extent to 3,3',4,4'-tetrabromobiphenyl (Millis et al.,
    1985a). The enhanced toxicity of the photolysed FireMaster(R)
    mixture may be explained similarly by increased concentrations of
    2,3',4,4',5-pentabromobiphenyl and of congeners containing no ortho
    bromines (Robertson et al., 1983a).

    
    Table 98.  Summary of reported biological alterations and toxic effects of polybrominated naphthalenes

    Species           Sexa       PBNb             Dosage regimenc                       Observed effects                         Reference

    Pathological features

    Rat               M      1,2,3,4,6,7-HBN      oral doses of 5 mg/kg body     centrilobular hepatic accumulation of lipid     Kohli et al.
                                                  weight per day for 4 days                                                      (1981)

    Mouse             F      synthetic HBN        oral doses of 0.5, 1.0, 2.5,   decrease in body weight (at 7.5 and 10.0        Miller &
    (C57 BL/6N)              mixture (mainly      5.0, 7.5, or 10.0 mg/kg        mg/kg); increase in relative liver weight       Birnbaum
    (pregnant)               1,2,3,4,6,7-HBN      body weight per day on         (at all levels); wasting, listlessness,         (1986)
                             and 2,3,4,5,6,7-     gd 6-15; s.t.: gd 18           vaginal bleeding, death (at 5-10 mg/kg)
                             HBN)

    Rat               F      2,3,6,7-TBN (not     2 daily ip doses of 0.2        increased liver weight; histological            Goldstein
    (Fischer)                identified in        mmol/kg body weight per        liver changes                                   et al. (1979)
                             FireMaster)          day; s.t.: 3 days after
                                                  last dose

    Rat               M      3 synthetic          single ip dose of 0.3          decrease in body weight gain; enlarged          Robertson
    (Wistar)                 PBN mixtures         mmol/kg body weight            livers; decreased thymuses; histological        et al. (1984a)
                                                  on day 1; s.t.: day 15         changes in liver and thymus;

    Hepatic microsomal enzyme induction

    Rat               F      2,3,6,7-TBN (not     2 ip doses of 0.2 mmol         MC-type induction: approximate                  Goldstein
    (Fischer)                identified in        per kg body weight per         ED50 = 40 µmol/kg (18 mg/kg)                    et al. (1979)
                             FireMaster(R))       day; s.t.: 3 days              (approximately 10-fold more potent than
                                                  after last dose                FM FF-1)

    Table 98 (contd).

    Species           Sexa       PBNb             Dosage regimenc                       Observed effects                         Reference

    Rat               M      3 synthetic          ip doses of 15 or 150          MC-type induction                               Robertson
    (Wistar)                 PBN mixtures         µmol/kg body weight per        (ED100 = at most 30 µmol/kg)                    et al. (1984a)
                             (5-6 bromines        day on days 1 and 3;
                             per naphthalene)     s.t.: day 6

    Fetal toxicity

    Mouse             -      synthetic HBN        maternal oral doses of         dose-related increases in fetal mortality       Miller &
    (C57 BL/6N)              mixture              0.5-10 mg/kg body weight       (at 5-10 mg/kg); dose-related increase in       Birnbaum
                                                  per day on gd 6-15;            incidence of various teratogenic effects        (1986); Miller
                                                  s.t.: gd 18                    (all dose levels):                              et al. (1985)
                                                                                 - kidney lesions (100% of fetuses at
                                                                                   1 mg/kg)d
                                                                                 - reduction in size of thymus and spleen
                                                                                 - cleft palate (4.8% of fetuses at 1 mg/kg;
                                                                                   98.6% of fetuses at 2.5 mg/kg)
                                                                                 - subcutaneous edema
                                                                                 - sternebral anomalies
                                                                                 - delayed cranial ossification

    a    F = female; M = male.
    b    PBN = polybrominated naphthalene(s); HBN = hexabrominated naphthalene(s); TBN = tetrabrominated naphthalene(s).
    c    gd = gestation days; s.t. = sacrifice time; ip = intraperitoneal.
    d    Estimated NOEL (no-observed-effect level) = 0.1-0.25 mg/kg per day.

    8.12.3.2  Pyrolysis products

         Recently, the toxicity of the pyrolyzed FireMaster(R) mixture
    has been determined  in vitro by measurements of EC50 values for
    the induction of aryl hydrocarbon hydroxylase (AHH) and
    ethoxyresorufin  O-deethylase (EROD) in rat hepatoma H-4-II E
    cells, and,  in vivo by measurements of ED50 values for hepatic
    microsomal AHH and EROD induction, body weight loss, and thymic
    atrophy in immature male Wistar rats (Zacharewski et al., 1988).
    FireMaster(R) BP-6 was pyrolyzed at 800 °C, and the residue was
    extracted with toluene. Solvents used for the application of the
    test material to the cell cultures and for ip injection of the
    animals were DMSO and corn oil, respectively. Both the  in vitro
    and  in vivo dose-response effects were compared with the relative
    activity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and expressed
    as the concentrations of "2,3,7,8-TCDD equivalents".

    The calculated  in vitro and  in vivo "2,3,7,8-TCDD equivalents"
    (µg/g sample) for the six bioassays ranged between 480 and 1680 µ/g
    (Table 100).

         Several polybrominated dibenzofurans (PBDFs) have been
    identified in the highly complex combustion mixture of
    FireMaster(R) (see section 4.3.2). However, toxicity tests have
    been conducted for only one PBDF congener, namely 2,3,7,8-dibenzo
    furan (Moore et al., 1979b).

         Generally, PBDFs may have a higher toxicity than the chloro
    analogues (Poland & Knutson, 1982).

         The toxicity of pyrolyzed technical octabromobiphenyl (Dow, Lot
    102-7-72) has been studied in a less sophisticated manner than that
    of FireMaster(R). Rats were exposed, via inhalation, to OcBB,
    which had been heated at 290 °C (4 h/day, for up to 10 days) and
    examined for liver damage. Atmospheric concentrations of
    > 2.5 µg/litre (as Br) of brominated 290 °C pyrolysis products caused
    liver enlargement; microscopic abnormalities in the liver were not
    detected (Aftosmis et al., 1972b; Waritz et al., 1977).

    8.13  Mechanism of toxicity including carcinogenicity

         PBB and related halogenated compounds are known to elicit a
    large number of different effects in animal species. However, the
    underlying mechanisms of toxicity are unknown. It is likely that
    several molecular mechanisms may operate (e.g., Silberhorn et al.,
    1990).

    
    Table 99.  Summary of comparative toxicology data of photolysed PBBs

    PBB                   Irradiation         Parametera                              Effects of                           References
                          (solvent during     (species)                   PBB                   irradiated PBB
                          irradiation)

    FM BP-6               300 nm              thymus weight         dose-related decreases      dose-related decreases;    Robertson
    (lot 7062)            (cyclohexane)       (rat, immature)       significant at 75 mg/kg     decreases significant at   et al.
                                                                    body weight                 25 mg/kg body weight       (1981b,c)

                                              AHH-induction         ED50 = 50 mg/kg             ED50 = 9 mg/kg
                                              (rat, immature)       body weight                 body weight

                                              displacement of       EC50 = 300 µmol             EC50 = 2 µmol              Robertson
                                              [3H] TCDD from the                                                           et al. (1981b)
                                              Ah receptor
                                              (rat, immature)

    2,2',4,4',5,5'-       sunlight            hyperkeratosis        no hyperkeratosis           severe hyperkeratosis      Patterson
    hexabromobiphenyl     (hexane)                                  (rabbit ear)                                           et al. (1981)
    (BB 153)

                          254 nm              hepatic microsomal    PB-type                     mixed type                 Millis et al.
                          (hexane)            enzyme induction                                  (PB and MC)                (1985a)
                                              (rat, outbred)

                                              liver weight          increase                    increase (more than
                                              (rat, outbred)                                    with BB 153)

    Table 99. (cont'd).

    PBB                   Irradiation         Parametera                              Effects of                           References
                          (solvent during     (species)                   PBB                   irradiated PBB
                          irradiation)

                                              liver histology       hepatocyte                  moderate to severe
                                              (rat, outbred)        enlargement                 hepatocyte enlargement

    a    AHH = benzo[a]pyrene hydroxylase; TCDD = 2,3,7,8-tetrachlorodibenzo-p-dioxin.
    b    MC = 3-methylcholanthrene; PB = phenobarbital.

    
    Table 100. FireMaster(R) BP-6 pyrolysate: in vitro and in vivo determination
    of "2,3,7,8-TCDD equivalents"a

    Bioassayb                                         FireMaster(R) BP-6 pyrolysatec:
                                                      Sample "2,3,7,8-TCDD equivalents"d
                                                                    (µg/g)

    AHH induction (in vitro)                                         1400

    EROD induction (in vitro)                                         480

    AHH induction (in vivo)                                           540

    EROD induction (in vivo)                                          520

    Body weight loss (in vivo)                                        760

    Thymic atrophy (in vivo)                                         1680

    a    From: Zacharewski et al. (1988).
    b    AHH = aryl hydrocarbon hydroxylase; EROD = ethoxyresorufin O-deethylase.
    c    Pyrolysis temperature: 800 °C.
    d    2,3,7,8-TCDD = 2,3,7,8-tetrachlorodibenzo-p-dioxin.
    
         As has been discussed in a number of comparative studies and
    reviews, there is good evidence relating the effects of PBB
    congeners that are MC inducers to a receptor-mediated model of
    toxicity (Poland & Glover, 1977, 1980; Poland et al., 1979;
    Goldstein, 1980; Moore et al., 1980; McKinney & Singh, 1981;
    Parkinson & Safe, 1981; Bandiera et al., 1982, 1983; McKinney &
    McConnell, 1982; Nebert et al., 1982; Poland & Knutson, 1982;
    Robertson et al., 1982b, 1984c,d; Safe et al., 1982, 1985; Aust
    et al., 1983; Dannan et al., 1983; Lai, 1984; Safe, 1984). The
    particular PBB-induced toxic syndrome of wasting, and other effects
    that are common to related halogenated compounds isosteromeric to
    TCDD, are related to an interaction with the cytosolic Ah - or TCDD
    - receptor protein. The Ah receptor is believed to be a member of
    the steroid/retinoid/thyroid hormone nuclear receptor superfamily,
    however, no endogenous ligands have been detected so far for the Ah
    receptor (Nebert et al., 1990; Poellinger et al., 1992). Activation
    of the Ah receptor, translocation into the nucleus, and binding to
    responsive elements on DNA are complex processes involving heat
    shock protein 90 and several other unknown, or less well described,
    steps (Poellinger et al., 1992). This activation of the Ah receptor
    leads by less well understood mechanisms to altered expression of a
    number of different genes (among these at least 6 drug- metabolizing

    enzymes) resulting in a pleiotypic response (Nebert et al., 1990).
    Furthermore, TCDD, apparently via activation of the Ah receptor, has
    an antiestrogenic effect by down-regulation of the nuclear estrogen
    receptor and affects the epidermal growth factor (EGF)
    receptor-binding (DeVito et al., 1991; Safe et al., 1991). The most
    active TCDD-like PBBs are those lacking ortho bromine substitution,
    being coplanar and approximate isostereomers to TCDD. It should be
    noted that the interaction between ligands and the Ah receptor, as
    well as the action on different genes and species differences, are
    only partly understood.

         Under certain conditions, TCDD can elicit programmed cell death
    (apoptosis) in freshly isolated thymocytes from young rats (McConkey
    et al., 1988). This has been suggested as an important mechanism for
    the effects of TCDD on cells in the thymus. It is not known whether
    this effect is mediated via the receptor or whether it can occur
    with coplanar PBBs. For tissues in general, apoptosis is believed to
    be important for differentiation, normal cell turnover,
    hormone-dependent atrophy, and tumour promotion (Nebert et al.,
    1990).

         PBBs also have a number of other effects at the molecular and
    biochemical levels, e.g., increased cell proliferation in the B633F1
    mouse liver (Mirsalis et al., 1985, Table 88; Loury et al., 1987;
    Mirsalis et al., 1989; Mirsalis & Steinmetz, 1990), and effects on
    membranes (Bernert & Groce, 1984) or membrane-mediated processes in
    rats (Shukla & Albro, 1987). PBBs substituted at the  ortho
    positions cause PB-type microsomal induction. The mechanism of this
    type of enzyme induction is unknown. This group of PBBs also causes
    inhibition of intercellular communication (Trosko et al., 1981;
    Tsushimoto et al., 1982; Williams et al., 1984; Kavanagh et al.,
    1987; Rezabek et al., 1988), which has been suggested to be
    important for the promotion phase in the carcinogenic process.

         PBB microsomal enzyme induction, as well as the induction of
    other drug metabolizing enzymes, may lead to a number of secondary
    events with enhanced metabolic conversions of both xenobiotica and
    endogenous compounds, such as steroid hormones.  Furthermore, a high
    level of P450 enzymes could lead to the generation of oxygen
    radicals. A relationship between the induction of cytochrome P-450
    enzymes (see section 8.8.1) and liver tumour promoting activity has
    been noted for a number of chemicals including PBBs (e.g., Lubet
    et al., 1989; Beebe et al., 1991; Buchmann et al., 1991).

         Some of the toxic effects of PBBs could also be mediated via
    changes in the metabolism of vitamin A (retinol compounds and
    retinoic acid), which is important for cellular growth and
    differentiation. However, the mechanism of the effects of PBBs on
    vitamin A metabolism is still unknown.

    9.  EFFECTS ON HUMANS

         The human health effects of PBBs have been reviewed by Safe
    (1984), Reggiani & Bruppacher (1985), Fries (1985b), IARC (1986),
    Kimbrough (1987), Anderson (1989), Silberhorn et al. (1990), and
    Waldron (1990).

    9.1  General population exposure

    9.1.1  Acute toxicity-poisoning incidents

         Most information on the effects of PBBs on humans was obtained
    as the result of a poisoning incident in Michigan, USA, 1973, when
    several hundred kg PBBs were introduced into cattle feed through a
    labelling accident. Widespread human exposure in this area resulted
    from direct contact with contaminated feed and from the consumption
    of PBBs in meat, eggs, and dairy products. During an interval of
    more than 9 months between the accident, the identification of its
    cause, the beginning of statewide testing and the establishment of
    quarantines, commercially marketed products entered the Michigan
    food chain.

         For exposure data see sections 5.2 and 5.3.

         There was no instance of acute PBB toxicosis in humans with
    which to compare the potential effects at lower exposures (Fries,
    1985b).

    9.1.2  Epidemiological studies

         In the epidemiological studies reviewed below, efforts have
    been made to evaluate the relationship between PBB exposure and a
    large number of adverse effects, including behavioural effects and
    subjective complaints. However, most studies suffer from major
    failures in design introducing confounders that make it difficult,
    or impossible, to draw conclusions regarding the relationship
    between PBB exposure and possible health effects.

         A number of studies had no comparison groups. In other reports,
    small groups of patients were selected because of existing illness
    and not because their PBB body burdens were particularly elevated.
    Some of the outcomes measured, such as urinary porphyrin levels,
    liver function tests, and immunological tests, did not show any
    clinically relevant changes or were not positively correlated with
    PBB body burdens. The clinical relevance of some of the tests is
    also not known, at present, because no reference values exist. Most
    of these reports dealt with cross sectional studies of heterogeneous
    groups of people. No detailed reports exist on long-term, follow-up
    studies.

    9.1.2.1  Studies conducted by the Michigan Department of Public
             Health (MDPH studies)

         The health status of 165 persons living on PBB-quarantined
    farms was compared with that of 133 persons living on unexposed
    farms in the same area. Although a variety of symptoms were reported
    by both groups, no consistent pattern of differences between the
    groups was observed. Physical examinations did not show any
    abnormalities of the heart, liver, spleen, or nervous system that
    could be related to PBB exposure. There were no differences between
    groups in urine analysis and blood counts (Humphrey & Hayner, 1975).

         A cohort study of Michigan residents (4545 persons), exposed to
    PBBs, was conducted to examine, among other things, whether there
    was an increased incidence of acute or subacute illness in relation
    to PBB exposure, 4 years after the accident. Six groups with various
    levels of potential exposure were included in the cohort. The groups
    were quarantined farm residents, farm product recipients, chemical
    workers and their families, pilot study control participants,
    self-referred individuals who resided on farms that were
    contaminated with low amounts of PBBs, and self-referred individuals
    who had no direct connection with contaminated farm premises. Mean
    and median serum concen trations of PBBs were much higher in the
    first three groups than in the latter three. The prevalence of
    selected symptoms by group was examined. Symptoms generally were
    most prevalent in the two self-selected groups and were least
    prevalent in the group composed of chemical workers and their
    families. An evaluation of dose-response relationships was
    undertaken by dividing the cohort into seven segments on the basis
    of serum PBB levels. No positive associations were found between
    serum concentrations of PBB and reported symptom frequencies.
    Symptom-prevalence rates (excluding volunteers) were slightly higher
    in persons with no detectable PBBs in serum than in those with
    measurable quantities. Relationships between symptom-prevalence
    rates and serum PBB levels were also examined within each enrolment
    group, and no positive trends were found; in all groups, including
    chemical workers and quarantined farm residents, the highest
    prevalence rates occurred in persons with the lowest serum PBB
    levels (Landrigan et al., 1979).

    9.1.2.2  Studies conducted by the Environmental Science Laboratory,
             Mount Sinai School of Medicine, New York (ESL studies)

         Anderson et al. (1978b, 1979) reported on a study of PBB-
    exposed farmers and residents in Michigan and a control group of
    unexposed Wisconsin dairy farmers, who were examined in November
    1976 and March 1977, respectively. The results were given on the
    basis of the examination of 933 exposed persons and 229 controls in
    the 1978 report, and of 993 exposed subjects and 228 controls in the
    1979 report.

         The study included four groups: families chosen randomly from
    Michigan farms, consumers of produce bought directly from
    participating farms, self-selected Michigan families, and Wisconsin
    dairy farmers not exposed to PBBs. All subjects completed
    comprehensive questionnaires on medical histories and 43 symptoms,
    and they were subjected to physical examination and certain
    laboratory tests. Statistical analysis of the prevalence of symptoms
    at the time of examination or during the preceding year in the
    Michigan and Wisconsin populations studied, found the Michigan group
    to have a significantly higher prevalence of skin, neurological, and
    musculoskeletal symptoms. The increase was seen among the younger
    age groups of 16-35 years and 36-55 years. Michigan females had a
    higher prevalence of neurological symptoms than Michigan males
    (Anderson et al., 1978b).

         No statistically significant, positive correlations were found
    between serum PBB values and any individual current symptom. Liver
    function tests showed that serum glutamic pyruvic transaminase
    (SGPT), serum glutamic oxaloacetic transaminase (SGOT), and lactate
    dehydrogenase (LDH) elevations were significantly more prevalent in
    the Michigan group (chi square test). No differences were seen for
    alkaline phosphatase. Within the Michigan group, males had a higher
    prevalence of SGPT and LDH increases than females, and comparing
    males in both groups, Michigan males had a significantly higher
    prevalence of SGPT and SGOT increases than Wisconsin males (Anderson
    et al., 1979).

         The comparison of findings among residents on Michigan dairy
    farms (quarantined and non-quarantined farms) and corresponding
    consumers of produce purchased from these farms (cross-sectional
    clinical survey of 1029 persons) gave the following results:
    prevalence of symptoms (dermatological, neurological,
    musculoskeletal, and gastrointestinal) in consumers of farm products
    from quarantined farms was similar to that found in farmers on
    quarantined farms; the prevalence was lower in consumers of products
    from non-quarantined farms. The prevalence of liver function
    abnormalities (increase in alkaline phosphatase, SGOT, SGPT, and
    LDH) was similar in dairy farmers and consumers. The distribution,
    mean and median values of serum PBB levels in consumers were found
    to be similar to those in dairy farmers (Lilis et al., 1978).

         Although some results of the ESL studies were at times
    interpreted differently from the results of the MDPH studies, there
    was one area of consistent agreement. Neither set of studies
    demonstrated a positive dose-response relationship between PBB
    concentrations in serum or adipose tissue and the prevalence of
    symptoms or abnormal clinical measurements (Fries, 1985b).

    9.1.3  Special studies

    9.1.3.1  Examination of subjects with complaints

         In the original cohort (Landrigan et al., 1979) a subset of
    individuals (19 males and 4 females), predominantly from the
    quarantined farms, was identified who had a number of disabling
    health complaints.

         This group was systematically evaluated at a hospital together
    with a group of 28 PBB workers selected randomly from a pool of 100
    people with previous occupational PBB exposure. The physical
    examination of this group of exposed farmers demonstrated a
    relatively high prevalence of hepatomegaly. Eight patients (35%)
    showed evidence of liver enlargement, defined as greater than 11 cm
    of vertical height in the midclavicular line. Liver scanning
    confirmed the presence of hepatomegaly in four of these individuals
    (17%), and two of them had a history of substantial alcohol intake.
    Ten individuals (43%) had skin lesions, but these were common
    dermatological problems, such as superficial mycoses and actinic
    keratosis, which are not uncommon in the general population and in
    people working outdoors. Biochemical and haematological testing
    revealed few abnormalities, and electro myograms, nerve conduction
    velocities, endocrine studies, and lymphocyte transformation studies
    did not provide any objective findings that correlated with
    subjective complaints. Psychiatric evaluation revealed a high
    prevalence of depression (78%) among the farmers. Multiple tests of
    intelligence, memory, and functional ability did not demonstrate
    abnormalities. There was no relation ship between fat PBB levels and
    physical or laboratory findings (Stross et al., 1981). The present
    study did not use epidemiological methods to evaluate the
    relationship between health effects and exposure to PBB and should,
    thus, be regarded as a report on cases in a group with known, but
    unquantified, PBB exposure.

    9.1.3.2  Cutaneous effects

         Three years after the Michigan PBB incident, the cutaneous
    effects were examined in a multidisciplinary study of the farming
    population (498 persons). Results were divided into two categories:
    subjective findings or symptoms of which subjects complained, and
    objective findings or signs, which were detected on physical
    examination. The results of the subjective findings were: 32% of
    adult residents and consumers associated with quarantined and
    non-quarantined farms complained of the development of unexplained
    cutaneous itching in a 3-year period from the PBB contamination
    episode to the time of the examination, compared with 22% reported
    by the control group. There was also a higher proportion of dryness
    reported; 32% of the quarantined and non-quarantined farm adults
    compared with 24% of the control group. Similarly, 17% of the farm

    study groups complained of the development of unexplained peeling
    and scaling during the same period compared with an incidence of 9%
    in the control group. The prevalence of erythema in the combined
    farm study groups was 12% compared with a prevalence of 5% in the
    controls. Increased unexplained nail growth was reported by 8% of
    the quarantined and non-quarantined adults compared with none in the
    controls. Increased abnormal sweating was a complaint of 22% of the
    quarantined and non-quarantined group compared with 13% in the
    controls. Unexplained hair loss was a complaint of 12% of the
    quarantined and non-quarantined group compared with 5% in the
    control group. All exposed groups had a significantly increased
    prevalence of skin symptoms compared with the comparison group. Of
    the symptoms elicited in a physician interview, rash was the most
    frequently reported. Among the farmers, rash was reported by 14%
    compared with 9% in the control group.

         Objective findings, determined by examination, were diffuse
    unexplained alopecia in 4% of the combined quarantined and
    non-quarantined farm groups, compared with none in controls (P <
    0.005) (Chanda et al., 1982).

         Because of major flaws in the study design and biases
    introduced during the selection processes in the cohort and a poor
    response rate, no causal association with PBBs could be deduced from
    this study.

    9.1.3.3  Effects on liver function

         The serum activities of SGOT, SGPT, LDH, and alkaline
    phosphatase were measured in 614 Michigan adults exposed to PBB and
    141 unexposed Wisconsin adults. The Michigan groups had a higher
    prevalence of elevated SGOT (P < 0.005) and SGPT (P < 0.005). A
    clear sex difference was observed. Michigan men had a higher
    prevalence of elevated SGPT (P < 0.005) and LDH (P < 0.005) than
    Michigan women, and a higher prevalence of elevated SGOT than
    Wisconsin men (P < 0.005) and SGPT (P < 0.01). On the basis of
    serum PBB analyses, no obvious relationship was observed between PBB
    values and liver function tests (Anderson et al., 1978d).

    9.1.3.4  Porphyria

         In 1977, urine samples were collected from members of farm
    families in Michigan, who had ingested PBB-contaminated meat and
    dairy products, beginning in 1973, and from members of farm families
    in Wisconsin with no known exposure to PBB (control group).

         The total porphyrin excretion of both groups was below
    200 µg/litre. Therefore, at this level, this parameter cannot be
    used as an indication of exposure of humans to PBB.

         Out of a group of 142 persons, at least 47% were found with
    secondary coproporphyrinuria or with chronic hepatic porphyria Type
    A, demonstrating an abnormal porphyrin pattern. The incidence of
    this indicator of liver malfunction was higher in the PBB-exposed
    group than in the controls (6%). The study was limited to an
    assessment of liver damage as manifested by porphyrin excretion
    (Strik et al., 1979).

    9.1.3.5  Effects on spermatogenesis

         Analysis of semen from 52 PBB-exposed men compared with
    analysis of semen from a control group of 52 men not exposed to PBB
    revealed no differences in the distribution of sperm counts,
    motility, or morphology (Rosenman et al., 1979).

    9.1.3.6   Paediatric aspects

         In 1976, the paediatric aspects of PBB exposure were studied in
    Michigan children, using Wisconsin children as a control group
    (Barr, 1978, 1980).

         Examination of the data from 292 Michigan farm children showed
    that the prevalence of symptoms was related to the quarantine status
    of the farm and to the method of invitation into the study. Serum
    PBB levels were related to the quarantine status of the farm, but
    not to the method of invitation into the study. No significant
    effects of age or sex were found on the prevalence of symptoms or
    serum PBB levels, except that the teenage (13-16 years of age) males
    had somewhat higher PBB levels. Despite the frequent reporting of
    symptoms of ill health, physical examination failed to reveal any
    objective alterations that could be attributed to PBBs. The most
    striking finding was a statistically significant negative
    correlation between the prevalence of symptoms and the serum PBB
    levels.

         The effects of PBBs on 33 children born between September 1,
    1973, and December 31, 1975, were evaluated in September, 1977. 
    These children, born to families who lived on quarantined farms,
    were compared with 20 children who had not been exposed to PBBs. The
    birthdate interval was selected to obtain children who were exposed
     in utero or in early infancy, or both, the two time periods when
    damage to developing tissues and organ systems should have been
    maximal. The results of these studies failed to identify any effects
    on physical growth, physical examination, or neurological
    assessment, though the parents indicated by historical review that
    the exposed children had more illnesses, especially respiratory,
    than the control children. There were some indications of an inverse
    relationship between fat PBB levels and performance on selected
    developmental tests (Weil et al., 1981).

         Seagull (1983) studied 19 of these children between the ages of
    2 years 5 months and 3 years 11 months using five tests of the
    McCarthy Scales of Children's Abilities and concluded that four of
    the five tests had significant (P < 0.05) correlations with PBB
    exposure, i.e., the higher the PBB levels in the adipose tissue, the
    lower the child's developmental abilities.

         Schwartz & Rae (1983) later studied these same children between
    the ages of 4 years 1 month and 6 years 1 month (N = 18 because one
    family refused to participate in the follow-up study) with the
    entire battery of McCarthy Scales of Children's Abilities, plus the
    Wechsler Preschool and Primary Scale of Intelligence, and concluded
    that no significant (P > 0,05) differences existed.

         These different conclusions from studies on the same children
    were summarized by Nebert et al. (1983) and commented on from
    statistical, clinical paediatric, and toxicological points of view.

         The authors stated that different approaches to the analysis of
    the data were used and that, in one case, the ability tests of only
    five children were selected, because of time limitations in the
    study situation.

         Comparison of fetal death rates among residents of Michigan's
    Lower Peninsula counties with a high percentage of quarantined farms
    and among residents of Upper Peninsula counties with no quarantined
    farms revealed no important differences in rates or trends after the
    contamination. Since counts of early spontaneous abortions were
    lacking, a complete assessment of the possible impact on
    reproductive outcome could not be made (Humble & Speizer, 1984).

    9.1.3.7  Neurological and neuropsychiatric aspects

         Neurological symptoms were the earliest and most prominent
    symptoms recorded in Michigan farm residents exposed to PBBs
    compared with an unexposed control farm population in Wisconsin. The
    prevalence and incidence of neurological symptoms were analysed in
    over 620 adults from Michigan and 153 from Wisconsin. Subsamples of
    both groups were examined in objective performance tests used for
    the assessment of neuropsychological dysfunction. In Michigan
    (particularly among males), those who exhibited the most marked
    symptoms tended to show diminished performance. Low indices of
    performance were also significantly correlated with intake of
    home-produced foodstuffs, particularly during the years 1972-74 and
    store-bought products during the years 1975-76. Between 1972 and
    1976, the Michigan farm residents studied made significant changes
    in their consumption patterns of products suspected to be
    contaminated with PBBs compared with those of Wisconsin farm

    residents. Serum PBB levels were not found to be significantly
    higher in Michigan males and females exhibiting the most prominent
    neurological symptoms. Serum PBB levels were negatively correlated
    with performance test scores, particularly in males in older age
    groups (Valciukas et al., 1978, 1979).

         Twenty-one persons exposed to PBBs were compared with hospital
    volunteers on a battery of tests measuring memory, motor strength
    and coordination, cortical-sensory perception, personality, and
    higher cognitive functioning. Patients exposed to PBBs were selected
    for the study only if they had persistent medical complaints. The
    adipose PBB levels were not correlated with performance on any test
    in the battery. The two groups did differ on the Minnesota
    Multiphasic Personality Inventory, suggesting an adjustment reaction
    with depressive symptoms and somatizing defences. Persons exposed to
    PBBs were also impaired compared with control subjects in tests of
    prose recall, short-term memory, concentration, and cognitive
    flexibility. However, these differences vanished when group
    differences on education and personality were statistically held
    constant. The selective admission criteria for the study limited the
    possibility of generalizing these findings (Brown & Nixon, 1979).

         Forty-six persons (37 men and 9 women) with known exposure to
    PBBs were examined in a study designed to evaluate neurobehavioural
    complaints (Stross et al., 1979). These people complained of a
    serious deterioration in their health status and were unable to
    engage in their previous occupations. Comprehen sive medical
    investigations were carried out including neurological studies and
    psychological evaluation. Electromyograms were abnormal in six
    patients (13%) with no consistent or diagnostic findings. Nerve
    conduction studies were abnormal in 19 patients (41%), with slowing
    in sensory nerve latencies the predominant finding. The abnormal
    values averaged 4.7 milliseconds compared with the normal value of
    < 3.9 milliseconds. There was an excellent correlation between
    patients with objective findings on neurological examination and
    abnormal nerve conduction studies (r value not stated). There was no
    relationship between the presence of these abnormalities and serum
    or fat PBB levels.

         Despite the fact that an extensive battery of tests was
    administered in the psychological evaluation, few objective
    abnormalities were documented. The most common findings were those
    of somatic preoccupation, irritability, and mild depression. The
    tests of motor function were normal, while the tests of sensory
    modalities showed minor differences that were not outside normal
    limits. Most had IQs of between 100 and 140 with no differences
    between estimated and observed levels. Although most patients
    complained of memory difficulties, no objective deterioration in
    memory could be elicited.

         The results of the psychiatric interviews showed that 31
    patients (67%) were depressed. No evidence of endogenous depression
    was noted, and it was the opinion of the psychiatrists involved that
    the findings were characteristic of reactive depression.

    9.1.3.8  Lymphocyte and immune function

         The immunotoxicology of PBBs has been reviewed by Amos (1986)
    and Steele et al. (1989).

         Bekesi et al. (1983b) summarized the findings of lymphocyte and
    immunological function studies, conducted in 1976 on 45 adult
    Michigan dairy farm residents who had consumed PBB-contaminated food
    products for periods ranging from three month to three years. Test
    comparisons were made with a group of 46 dairy farm residents in
    central Wisconsin who had not been exposed to PBB-contaminated food
    and to a group of 76 healthy subjects from the New York Metropolitan
    area (Bekesi et al., 1978, 1979a,b).

         Marked changes in various immunological parameters were noted
    among the Michigan dairy farm residents compared with both the
    Wisconsin and New York control populations. The peripheral blood
    lymphocytes of only 27 of the 45 Michigan subjects exhibited a
    normal response to the T-cell mitogens phytohaemagglutinin and
    concanavalin A, to the alloantigens in the mixed leukocyte culture
    reaction, and to the B-cell mitogen (pokeweed mitogen). In the
    remaining 18 subjects, the lymphocytes showed an impaired functional
    response to all mitogens and alloantigens.

         The lymphocytes of all 45 PBB-exposed study subjects showed a
    reduced proliferative T-cell response in mixed leukocyte cultures.
    The group of 18 individuals with decreased T-cell function had
    values measuring one-third to one-quarter of those obtained from the
    normal controls. The number of viable cells in the various
    subpopulations of peripheral blood lymphocytes were measured
    according to their ability to form stable rosettes with sheep
    erythrocytes in the case of the T-cells, while the B-lymphocytes
    were quantified by either direct immunofluorescence or by sheep
    erythrocytes sensitized with antibody and complement. The 27
    Michigan farm residents with normal lymphocyte functions also
    exhibited the normal distribution of T- and B-lymphocytes. Eighteen
    of the 45 subjects with lymphocyte dysfunction showed significantly
    reduced populations of T-cells. Despite the marked changes in the
    characteristic cell surface markers detected in the peripheral blood
    lymphocytes of the PBB-exposed Michigan farm residents, the marker
    for monocytes, determined by peroxidase staining or latex digestion,
    did not differ from that of either control group. Thus, the most
    significant deviation from the control samples was a marked increase
    in lymphocytes without detectable surface markers.

         Five years later, Bekesi et al. (1983a,b) examined the same
    individuals and the data strongly suggested a persistent PBB-induced
    immune suppression. The findings were characterized by a decrease in
    the percentage and absolute number of T-lymphocytes, with a
    concomitant increase in the occurrence of lymphocytes without
    detectable membrane surface markers, and, in as many as 30% of the
    subjects retested, a reduction in the T-cell function.

         Silva et al. (1979) assessed T- and B-lymphocyte numbers and
    lymphocyte transformation to 3 mitogens (phytohaemagglutinin,
    concanavalin A, and pokeweed mitogen) in 41 persons with a high
    exposure to PBBs (mean serum level 787 µg/litre, range
    529-2560 µg/litre) and 57 persons with a low exposure (mean serum
    level 3 µg/litre, range 1-11 µg/litre). In contrast to the findings
    of Bekesi et al. (1978) there were no significant differences in the
    percentages of T- and B-lymphocytes among persons who experienced
    high or low PBB exposure or in control groups. Similarly, no
    significant depression of lymphocyte mitogenic responsiveness were
    found in those who experienced high or low PBB exposure compared
    with controls. No correlation was found between serum PBB levels and
    lymphocyte numbers or function.

         In a comprehensive immunotoxicological study, 336 adult
    Michigan farm residents, 117 general consumers (for comparison), and
    75 dairy farm residents in Wisconsin, who had not eaten
    PBB-contaminated food, were examined, as were 79 healthy subjects in
    New York City. Abnormalities in the Michigan groups included:
    hypergammaglobulinaemia, exaggerated hypersensitive response to
    streptococci, significant decreases in absolute numbers and
    percentages of T- and B-lymphocytes, and increased numbers of
    lymphocytes with no detectable surface markers ("null cells"). 
    Significant reduction of  in vitro immune function was noted in
    20-25% of the Michigan farm residents who had eaten food containing
    PBBs. The decreased immune function detected among the PBB-exposed
    farm residents tended to affect families as a unit and was
    independent of the age or sex of exposed individuals,
    contraindicating the possibility of genetic predisposition (Bekesi
    et al., 1987).

         Lipson (1987) evaluated the effects of PBBs on the function and
    on the synthesis of immunoglobulins by peripheral blood lymphocytes.
    Concentrations of PBBs as low as 0.001 µg/105 cells decreased
    lymphocyte response to pokeweed mitogen: higher concentrations of
    PBBs stimulated the  in vitro synthesis and release of
    immunoglobulins. PBBs had no effect on the quantity of
    E-rosette-forming cells, the total T- or B-cells, or the ratio of
    helper to suppressor T-cell subpopulations. Enhanced release of IgG
    was identified in lymphocyte cultures obtained from blood specimens
    of PBB-exposed Michigan farmers. The data from this study suggest
    that PBBs had exerted an adverse effect on cell function, but had
    produced a non-specific activation of B lymphocytes.

    9.1.3.9  Carcinogenic embryonic antigen plasma levels

         Carcinogenic embryonic antigen (CEA) titres were determined for
    611 Michigan farmers exposed to PBBs and for a control unexposed
    population of 138 Wisconsin farmers. The overall prevalence of
    elevated CEA titres was slightly higher in the Michigan study group,
    but the difference was not statistically significant. Serum PBB
    concentrations appeared to be positively correlated with CEA titres.
    The authors discussed the possibility that the effect of PBBs may be
    additive to that of other factors that are known to result in an
    increased prevalence of elevated CEA titres (Anderson et al.,
    1978c).

         The possibility of long-term effects of PBBs, such as cancer,
    cannot be ruled out. The induction of liver tumours in rodents is a
    matter of concern (Fries, 1985b).

    9.1.3.10  Biochemical effects

         Two hundred and sixty-two residents with a geometric mean serum
    PBB level of 19.9 µg/litre submitted at least one blood sample for
    clinical chemistry tests of 9 parameters during 4 different years.
    No consistent significant correlation with serum PBB levels was
    shown for any parameter (Kreiss et al., 1982). The authors suggested
    that tests with greater sensitivity and specificity for hepatic
    microsomal enzyme induction should be developed for future
    evaluations.

         Lambert et al. (1987) were the first to study the effects of
    PBB exposure on the human cytochrome P-450 system, as determined by
    the caffeine breath test (CBT), in healthy non-smoking adults from
    rural Michigan with, and without, detectable serum PBB levels
    (concentration not stated) and in prepubescent children with known
    perinatal exposure to PBBs. The results were compared with the CBT
    results obtained from unexposed urban adult non-smokers and
    age-matched children. The unexposed and PBB-exposed children had
    similar CBT data. The adult groups were not significantly different
    from each other, except for the rural adults with detectable PBB
    levels who had significantly higher CBT values than the unexposed
    urban adults.

         Lambert et al. (1990) conducted a field biochemical
    epidemiology study using the Michigan cohort consisting of 51 rural
    residents exposed to PBBs. The CBT and CMR (caffeine urinary
    metabolite ratio) were elevated in the subjects exposed to PBBs
    compared with the values obtained from urban non-smokers and were
    similar to those found in adults who smoked. A gender effect was
    seen in the PBB-exposed subjects, the median CBT and CMR values of
    the females being lower than the values of the males. There was a
    correlation between the CBT and the serum HxBB values (r2 = 0.2,
    p = 0.01) but not between CMR and serum HxBB values.

         PBBs induce hepatic cytochrome P-450IA2 enzyme activity in the
    human adult, but not in the child. Lambert et al. (1991) there fore
    investigated, in a prospective longitudinal study of 14 male and 15
    female children exposed transplacentally and transmammil lary to
    PBBs in 1973-75, whether PBB exposure altered the normal decrease in
    P-450IA2 activity that occurs during puberty. P-450IA2 activity was
    monitored via the CBT every 2 years, beginning in 1985, and compared
    with the P-450IA2 activity in gender- and Tanner stage-matched
    children not exposed to PBBs. Unlike the adult, PBBs did not alter
    P-450IA2 activity in the child or in the mid-pubescent adolescent
    (Wilcoxon rank, P > 0.05).

    9.2  Occupational exposure

    9.2.1  Epidemiological studies

         Anderson et al. (1978a) investigated the health status of 55
    employees (52 men and 3 women) of the Michigan Chemical Corporation,
    which manufactured PBBs from 1970 to 1974, in addition to a variety
    of other halogenated fire retardant chemicals. Ten of those examined
    had formerly worked directly in the PBB production area, the other
    45 persons worked in other departments in the plant. For these 55
    workers, the route and quality of occupational exposure were
    probably different from those of farmers, since they could have been
    directly exposed to PBBs. The results were compared with those from
    a group of male farm residents and consumers from Michigan.

         The prevalence of chest and skin symptoms among chemical
    workers as a group was significantly greater than among farmers. 
    Significantly fewer symptoms were reported in the musculoskeletal
    category. The PBB department workers experienced symptoms in the
    skin category significantly more frequently than non-PBB workers.
    Blood chemistry results were similar for workers and farmers.
    However, both groups exhibited a significantly higher prevalence of
    elevated liver function tests (SGOT, SGPT) than a control population
    of unexposed farmers. Considering only workers with more than five
    years in the plant, a significantly higher prevalence of elevated
    CEA titres was present compared with the farmers.

    9.2.2  Clinical studies

         The only abnormality noted during physical examination in a
    group of PBB-exposed chemical workers consisting of 24 males and 4
    females whose ages ranged from 23 to 62 years with a mean of 40
    years, was the presence of hepatomegaly in two patients (7%), both
    of whom heavily indulged in alcoholic beverages, and abnormal skin
    examination in four patients (14%). In numerous biochemical tests,
    only minor elevations of serum uric acid, serum iron, and serum
    cholesterol were found in 20% of the chemical workers.

         Elevation of triglyceride levels was noted in 50% of the
    chemical workers, with a mean of 185 mg % (SD ± 50 mg %), with an
    upper limit of normal of 150 mg %. No abnormalities in lymphocyte
    number or function could be determined, and there was no
    relationship between PBB levels and physical or laboratory
    abnormalities (Stross et al., 1981).

    9.2.3  Special studies

    9.2.3.1  Cutaneous effects

              Halogen acne was observed on physical examination in 13%
    of 53 Michigan chemical workers exposed to PBBs compared with none
    in unexposed controls (P < 0.001) (Chanda et al., 1982).

    9.2.3.2  Memory performance

         Twenty-five chemical workers, who manufactured PBBs, were given
    objective tests of learning and memory. Although this group had high
    concentrations of PBBs in adipose tissue, mean scores on all memory
    tests were normal. The PBB concentration was not correlated with
    memory performance; the most contaminated workers showed no evidence
    of memory dysfunction (Brown et al., 1981).

    9.2.3.3  Thyroid effects

         Thyroid function was investigated in a cohort of 35 male
    workers, selected from 86 identified workers exposed for at least 6
    weeks, manufacturing decabromobiphenyl, decabromobiphenyl ether, and
    bromine. The study revealed four cases of primary hypothyroidism
    (11.4%), but none in 89 control subjects. The bromine compounds were
    the only common exposure. A significantly higher number of the
    exposed workers had detectable serum levels of DeBB
    (0.5-1340 ng/ml), but not DeBBO (Bahn et al., 1980a,b).

         Bialik (1982) investigated thyroid dysfunction in workers
    exposed for at least 240 h to decabromobiphenyl and
    decabromobiphenyl oxide over a 4-year period. The average period of
    employment was 3.9 years, mean age, 34.7 years. Medical
    questionnaires, physical examinations, and laboratory tests were
    conducted. For exposure data see section 5.3. Thyroid nodules were
    seen in 3 out of 18 workers exposed for 3 years or longer.

         No detectable PBBs were found in the serum.

    9.2.3.4  Reproductive effects

         Bialik (1982) also studied reproductive effects in the same PBB
    workers.

         A significant correlation was seen between length of employment
    and concentrations of follicle stimulating hormone (FSH). An
    abnormal FSH value was found in only one worker. A testicular cyst
    was found in one exposed worker, and epididymal nodules in two
    others. No testicular or epididymal nodules were seen among
    controls. No definite statement could be made concerning adverse
    effects on the prevalence of testicular and epididymal nodules,
    because of their prevalence in the general population.

    9.2.3.5  Lymphocyte function

         Decreased lymphocyte function occurred in four out of ten
    Michigan chemical workers. The decrease was related to higher plasma
    levels of PBBs (40-1200 µg/litre) (Bekesi et al., 1979b).

    9.2.3.6  Mortality

         A historical prospective mortality study was conducted by Wong
    et al. (1984) on 3579 white male workers employed between 1935 and
    1976 at chemical plants with potential exposures to brominated
    compounds. Because of the lack of quantitative data, potential
    exposures of workers to PBBs were categorized as "routine" and
    "non-routine". None of 91 individuals of the cohort potentially
    exposed to PBBs on a routine basis died during the study period.

         Among the 237 "non-routinely" exposed, two deaths were
    observed, though 6.36 were expected. One was due to cancer of the
    large intestine, the other was coded as arteriosclerotic heart
    disease.

    10.  PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

         The International Agency for Research on Cancer (1986, 1987)
    evaluated the polybrominated biphenyls and concluded that there is
    sufficient evidence for the carcinogenicity to experimental animals
    of a commercial preparation of PBBs (FireMaster FF-1, various lots),
    composed primarily of hexabromobiphenyl with smaller amounts of
    penta- and heptabrominated isomers. There is considered to be
    inadequate evidence for their carcinogenicity in humans. Commercial
    mixtures of PBBs were thus classified into Group 28, possibly
    carcinogenic to humans.

         The European Community added PBBs to the chemicals banned or
    severely restricted to certain uses owing to their effects on human
    health and the environment (CEC, 1988).

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    ABBREVIATIONS USED IN THE MONOGRAPH

    1.  PBB nomenclature

    PBB  = polybrominated biphenyl
    MoBB = monobromobiphenyl
    DiBB = dibromobiphenyl
    TrBB = tribromobiphenyl
    TeBB = tetrabromobiphenyl
    PeBB = pentabromobiphenyl
    HxBB = hexabromobiphenyl
    OcBB = octabromobiphenyl
    NoBB = nonabromobiphenyl
    DeBB = decabromobiphenyl

    FM   = FireMaster(R)

    PBB congener numbering system used (Table 3). 

    2.  Enzyme nomenclature

         Designation of the cytochrome P-450-dependent mixed function
    monooxygenase (P-450) system, as relevant for PBBs:

    Systematic nomenclaturea                     Trivial names

    PB (phenobarbital)-inducible

    P-450 II                                     P-450

    P-450 II B 1                                 P-450b

    P-450 II B 2                                 P-450e

    MC (3-methylcholanthrene)-inducible

    P-450 I                                      P-448

    P-450 I A 1                                  P-450c

    P-450 I A 2                                  P-450d

    a    From: Nebert et al. (1987, 1989).

    3.  Other compounds

    AHH       aryl hydrocarbon hydroxylase
    AP        alkaline phosphatase
    BUN       blood urea nitrogen
    DBBO      decabromobiphenyloxide
    DMBA      7,12-dimethyl-benz (a)anthracene
    GOT       glutamic-oxaloacetic transaminase
    GPT       glutamic-pyruvic transaminase
    GTP       glutamyl transpeptidase
    LDH       lactic dehydrogenase
    MFO       mixed function oxidase
    MNNG       N-methyl- N'-nitro- N-nitroso-guanidine
    PBCDD     polybrominated/chlorinated dibenzo- p-dioxin
    PBCDF     polybrominated/chlorinated dibenzofuran
    PBDD      polybrominated dibenzo- p-dioxin
    PBDF      polybrominated dibenzofuran
    PCDD      polychlorinated dibenzo- p-dioxin
    PCDF      polychlorinated dibenzofuran
    PEG       polyethylene glycol
    TPA       12- O-tetradecanoylphorbol-13-acetate

    4.  Other abbreviations

    ALD       approximate lethal dose
    F         female
    GLC       gas liquid chromatography
    HPLC      high pressure liquid chromatography
    ip        intraperitoneal
    IPCS      International Programme on Chemical Safety
    LC50    lethal concentration, median
    LD50    lethal dose, median
    M         male
    NCI       National Cancer Institute (USA)
    No.       number of animals
    NTP       National Toxicology Program (USA)
    RER       rough-surfaced endoplasmic reticulum
    SER       smooth-surfaced endoplasmic reticulum
    t.p.      time post-exposure
    UV        ultraviolet
    WHO       World Health Organization

    RESUME ET EVALUATION, CONCLUSIONS ET RECOMMANDATIONS

    1.  Résumé et évaluation

    1.1  Identité, propriétés physiques et chimiques, méthodes
         d'analyse

         On désigne par biphényles polybromés ou polybromobiphényles
    (PBB) un groupe d'hydrocarbures halogénés obtenus par substitution
    des hydrogènes du noyau biphényle par le brome. On ne les connaît
    pas à l'état naturel. Leur formule brute est
    C12H(10-x-y)Br(x+y) dans laquelle x et y peuvent prendre
    toutes les valeurs de 1 à 5. Il y a théoriquement 209 homologues
    possibles. On n'en a synthétisé et caractérisé que quelques-uns. Les
    PBB produits dans un but commercial consistent essentiellement en
    hexa-, octa-, nona- et décabromobiphényles, mais ils contiennent
    également d'autres homologues. Ce sont des retardateurs de flammes
    de type additif et, en mélange avec les polymères ou solides secs,
    ils exercent une action retardatrice sur les flammes par filtrage,
    avec libération de bromure d'hydrogène en cas d'inflammation.

         Les PBB sont préparés au moyen d'une réaction du type Friedel
    et Crafts, par action du brome sur le biphényle avec ou sans solvant
    organique et en présence de chlorure d'aluminium, de bromure
    d'aluminium, de fer, etc, comme catalyseur.

         La plupart des recherches ont été consacrées au FireMaster(R)
    BP-6 et au FF1 qui étaient impliqués dans la catastrophe du Michigan
    où ce composé a été ajouté par inadvertance à de la nourriture pour
    animaux à la place d'oxyde de magnésium.  L'intoxication des animaux
    qui s'en est suivie a abouti à la perte de milliers de bovins, porcs
    et moutons et de millions de poulets.

         La composition du FireMaster(R) varie d'un lot à l'autre mais
    il est principalement composé de 2,2',4,4',5,5'-hexabromobiphényle
    (60 à 80%) et de 2,2',3,4,4',5,5'-heptabromobiphényle (12 à 25%) à
    côté d'homologues inférieurs dus à une bromation incomplète.  Parmi
    les constituants mineurs du FireMaster(R) on a également observé
    la présence de bromochlorobiphényles et de polybromo naphtalènes. Le
    FireMaster FF-1 (poudre blanche) est du FireMaster BP-6 (paillettes
    brunes) auquel on a ajouté 2% de silicate de calcium comme
    antiagglomérant.

         Les PBB sont des solides dont la faible volatilité décroît à
    mesure qu'augmente le nombre d'atomes de brome. Ils sont
    pratiquement insolubles dans l'eau, solubles dans les graisses et
    légèrement à fortement solubles dans divers solvants organiques; la
    solubilité diminue également à mesure qu'augmente le nombre d'atomes

    de brome. Ces composés sont relativement stables et chimiquement
    inertes, encore que des mélanges de PBB fortement substitués
    subissent une photodégradation avec débromation réductrice sous
    l'action du rayonnement ultraviolet.

         Les produits de la décomposition thermique expérimentale des
    PBB dépendent de la température, de la quantité d'oxygène présente
    et d'un certain nombre d'autres facteurs. L'étude de la pyrolyse du
    FireMaster BP-6 en l'absence d'oxygène (600 à 900 °C) a montré qu'il
    se forme des bromobenzènes et des bromobiphényles inférieurs mais
    pas de polybromofuranes. En revanche, la pyrolyse en présence
    d'oxygène (700 à 900 °C) conduit à la formation de
    bromodibenzofuranes bi- à hepta substitués. Des quantités plus
    importantes ont été trouvées en présence de polystyrène et de
    polyéthylène. La pyrolyse du FireMaster BP-6 en présence de PVC à
    800 °C a fourni un mélange de bromochlorobiphényles. On ignore
    qu'elle est la nature des produits d'incinération des matériaux
    contenant des PBB. On manque également de données sur la toxicité
    des dioxines et des furanes bromés et chlorobromés, mais on estime
    qu'elle doit être à peu près du même ordre que celle des dioxines et
    des furanes chlorés.

         Après la catastrophe du Michigan, la principale technique
    d'analyse qu'on a utilisée pour la surveillance biologique des PBB
    dans des échantillons de tissus et de liquides biologiques ou
    provenant de l'environnement, était la chromatographie en phase
    gazeuse avec détection par capture d'électrons. Le dosage des
    différents homologues peut s'effectuer par chromatographie en phase
    gazeuse en tube capillaire avec détection par spectrométrie de masse
    à sélectivité ionique. En raison du nombre élevé d'homologues
    possibles, les recherches sont gênées par le manque d'étalons de
    synthèse convenables. On utilise, pour extraire les PBB des
    échantillons biologiques, des méthodes du type de celles qu'on
    applique aux pesticides. Les PBB sont extraits avec la fraction
    lipidique puis purifiés.

         Le fait que l'on ait récemment découvert des homologues des PBB
    dans des échantillons biologiques prélevés dans l'environne ment
    général n'implique pas forcément que la concentration de ces
    produits y soit en augmentation. La mise au point de techniques
    d'analyse plus sensibles comme la spectrométrie de masse avec
    production d'ions négatifs par ionisation chimique, pourrait en être
    la cause. Il est donc urgent de procéder à des études
    rétrospectives. L'amélioration des méthodes de purification devrait
    permettre d'effectuer le dosage spécifique des homologues
    coplanaires toxiques car des données sont également nécessaires à
    leur sujet.

    1.2  Sources d'exposition humaine et environnementale

         La production commerciale du FireMaster(R) a commencé aux
    Etats-Unis en 1970. Elle a été arrêtée après la catastrophe du
    Michigan (novembre 1974). On estime qu'entre 1970 et 1976 les
    Etats-Unis ont produit 6000 tonnes de PBB (produits du commerce). La
    production de l'octabromobiphényle et du décabromobiphényle s'est
    poursuivie aux Etats-Unis jusqu'en 1979. En outre, l'Allemagne a
    produit jusqu'à la moitié de 1985 un mélange de PBB fortement
    bromés, le Bromkal 80-9 D. La France produit actuellement du
    décabromobiphényle (Adine 0102) de qualité technique. Autant qu'on
    sache, c'est le seul PBB qui soit actuellement produit.

         Les PBB ont fait leur apparition sur le marché comme
    retardateurs de flamme au début des années 1970. Avant novembre
    1974, l'hexabromobiphényle était le principal PBB produit dans le
    commerce aux Etats-Unis; il était incorporé aux résines ABS
    (acrylonitrile-butadiène-styrène) dans la proportion de 10% et
    utilisé principalement pour la fabrication de divers accessoires
    d'automobiles, les peintures et les vernis ainsi que dans la mousse
    de polyuréthanne. Les autres retardateurs de flamme à base de PBB
    ont des applications similaires.

         Des PBB peuvent passer dans l'environnement au cours du
    processus normal de production à la faveur d'émissions dans l'air,
    dans les eaux usées, ou encore par libération dans le sol et dans
    les décharges, mais les concentrations correspondantes se sont
    révélées faibles en général.

         Ces produits peuvent également passer dans l'environnement lors
    du transport et de la manipulation ou par suite d'accidents comme
    cela s'est produit dans le Michigan.

         Il y a également risque de pénétration dans l'environnement
    lors de l'incinération de produits contenant des PBB ou lors
    d'incendies au cours desquels il se forme d'autres substances
    toxiques comme des polybromodibenzofuranes ou des dérivés mixtes
    bromochlorés.

         La majeure partie du volume totale de ces produits finit de
    toute façon par se retrouver dans l'environnement soit tels quels,
    soit sous forme de produits de décomposition.

    1.3  Transport, distribution et transformation dans l'environnement

         Il n'est pas démontré que les PBB puissent être transportés à
    longue distance dans l'atmosphère, mais la présence de ces composés
    chez les phoques de l'Arctique indique qu'ils sont largement
    disséminés sur la planète.

         Les principales voies de pénétration des PBB dans l'environne
    ment aquatique sont, d'une part la pollution des eaux réceptrices,
    les décharges de déchets industriels et, d'autre part le lessivage
    de dépotoirs de déchets industriels, ou encore, l'érosion de sols
    pollués. Les PBB sont pratiquement insolubles dans l'eau et on les
    retrouve principalement dans les sédiments des lacs et des rivières
    pollués.

         La pollution du sol peut trouver son origine dans des sources
    polluantes ponctuelles comme par exemple des unités de production de
    PBB ou des dépotoirs. Une fois qu'ils ont pénétré dans le sol, les
    PBB ne semblent pas être facilement mobilisables. On a constaté
    qu'ils étaient 200 fois plus solubles dans le produit de lessivage
    d'une décharge que dans l'eau distillée; cela pourrait entraîner une
    plus large distribution dans l'environnement. Du fait de leurs
    propriétés hydrophobes, les PBB sont facilement adsorbés sur le sol
    à partir des solutions aqueuses. On a observé que les différents
    homologues étaient adsorbés préférentiellement en fonction des
    caractéristiques du sol (par exemple la teneur en matières
    organiques) ainsi que de la position et du nombre des atomes de
    brome.

         Les PBB sont stables et persistants; ils sont lipophiles et ne
    sont en outre que légèrement solubles dans l'eau; certains
    homologues sont peu métabolisés et s'accumulent dans la fraction
    lipidique des organismes vivants. Une fois libérés dans
    l'environnement, ils peuvent entrer dans la chaîne alimentaire où
    ils subissent une concentration.

         On a décelé des PBB dans les poissons de diverses régions. Les
    PBB peuvent pénétrer dans l'organisme des mammifères et des oiseaux
    par suite de l'ingestion de ces poissons.

         Il est improbable que les PBB subissent une dégradation
    chimique purement abiotique (à l'exclusion d'une photodécompo
    sition). On a fait état d'une persistance des PBB sur le terrain. 
    Des échantillons de sol prélevés sur l'emplacement d'une ancienne
    unité de production de PBB ont été analysés plusieurs années après
    l'accident du Michigan; ils contenaient encore des PBB mais la
    proportion des divers homologues était différente, ce qui indique
    qu'il y avait eu décomposition partielle des résidus de PBB dans les
    échantillons en question.

         Au laboratoire, les PBB sont facilement décomposés par le
    rayonnement ultraviolet. La photodécomposition d'un mélange
    commercial (FireMaster(R)) a provoqué une diminution de la
    concentration des homologues les plus substitués. La vitesse et le
    degré de photolyse des PBB dans l'environnement n'ont pas été
    déterminées avec précision, encore que l'observation sur le terrain
    montre que les PBB de départ sont très tenaces, avec dégradation
    partielle des homologues les moins bromés.

         D'après les études en laboratoire, les mélanges de PBB semblent
    assez résistants à la dégradation microbienne.

         On ne connaît pas d'exemple de fixation ou de décomposition des
    PBB par les végétaux. Par contre, les PBB sont facilement absorbés
    par l'organisme animal et bien qu'ils se soient révélés très
    persistants chez les animaux, on a tout de même retrouvé de petites
    quantités de métabolites. Ces métabolites consistaient
    principalement en dérivés hydroxylés et, dans certains cas, il y
    avait des traces de PBB partiellement débromés. Aucune étude sur les
    métabolites soufrés analogues à ceux des PCB n'a été publiée.

         La bioaccumulation des PBB a été étudiée dans les poissons. En
    ce qui concerne les animaux terrestres, on l'a étudiée chez
    différentes espèces d'oiseaux et de mammifères. Les données ont été
    fournies par des observations sur le terrain, par l'étude des
    conséquences de la catastrophe du Michigan et par des études
    d'alimentation contrôlée. En général, on a constaté que
    l'accumulation des PBB dans les graisses de l'organisme était liée à
    la dose et à la durée d'exposition.

         La bioaccumulation des différents homologues des PBB augmente
    avec le degré de bromation, au moins jusqu'aux dérivés tétrabromés.
    On peut penser que les homologues plus substitués s'accumulent dans
    une proportion encore plus importante. Toutefois, on ne dispose
    d'aucun renseignement sur le décabromobiphényle; il est possible
    qu'il soit peu absorbé.

         On a signalé la présence de dibenzofuranes bromés et de PBB
    partiellement débromés comme produits de la décomposition thermique
    des PBB. La formation de ces composés dépend de plusieurs variables
    (par exemple, température, oxygène).

    1.4  Concentrations dans l'environnement et exposition humaine

         On ne dispose que d'un seul rapport sur la concentration des
    PBB dans l'atmosphère. Il s'agit d'une étude au cours de laquelle on
    a mesuré la concentration de ces composés au voisinage des trois
    unités de production et de traitement des PBB aux Etats-Unis
    d'Amérique.

         La concentration des PBB dans les eaux de surface du même
    secteur ainsi que dans la décharge du Comté de Gratiot (Michigan,
    Etats-Unis d'Amérique) qui avait reçu entre 1971 et 1973 plus de 100
    000 kg de déchets contenant 60 à 70% de PBB, a fait l'objet d'une
    surveillance.

         Les données relatives à la surveillance des eaux souterraines
    au voisinage de la décharge du Comté de Gratiot ont révélé la
    présence de traces de PBB, même au-delà du voisinage immédiat de la
    décharge; toutefois aucun de ces composés n'a été décelé dans les
    puits d'eau potable du secteur.

         On dispose de données sur la pollution tellurique par les PBB
    dans les secteurs où des PBB ont été ou sont produits, utilisés ou
    rejetés et également sur la pollution tellurique des terrains
    agricoles du Michigan contaminés par ces composés.

         Lors de la catastrophe du Michigan, du FireMaster(R) a été
    ajouté par inadvertance à de la nourriture pour animaux. Il a fallu
    presque une année pour qu'on s'aperçoive de cette erreur et pour que
    les analyses révèlent que les PBB étaient en cause. Pendant cette
    période (de l'été 1973 à mai 1974), des animaux et des produits
    animaux contaminés ont été utilisés pour l'alimentation humaine et
    ont pénétré dans l'environnement de l'Etat du Michigan. Des
    centaines d'exploitations agricoles ont été affectées; il a fallu
    abattre et enterrer des milliers d'animaux et détruire des milliers
    de tonnes de produits agricoles.

         La plupart des données concernant la contamination de la faune
    sauvage par les PBB concernent des poissons et des oiseaux des
    Etats-Unis d'Amérique et d'Europe (essentiellement la sauvagine
    vivant à proximité des sites industriels) ainsi que des mammifères
    marins.

         Selon des rapports récents sur la contamination de poissons, de
    mammifères terrestres ou marins et d'oiseaux aux Etats-Unis
    d'Amérique et en Europe, ces composés seraient très disséminés.  La
    composition en homologues dans les échantillons de poissons est très
    différentes de celle qu'on trouve dans des produits commerciaux.
    Pour les principaux, ils pourraient dans beaucoup de cas résulter
    d'une débromation photochimique du décabromobiphényle (BB 209), mais
    cela n'a pas été confirmé.

         On a observé une exposition professionnelle chez des employés
    d'usines chimiques aux Etats-Unis d'Amérique, ainsi que chez des
    ouvriers agricoles, à la suite de l'accident du Michigan. Les taux
    médians de PBB dans le sérum et les tissus adipeux étaient plus
    élevés chez les employés de l'industrie chimique. On ne dispose pas
    de renseignements en provenance d'autres pays ou d'autres
    entreprises sur l'exposition professionnelle lors de la fabrication,
    de la formulation et de l'utilisation commerciale de ces produits.

         On ne dispose pas, pour la plupart des populations humaines,
    d'une documentation qui fournisse des données de première main sur
    l'exposition aux PBB de diverses origines. Dans le Michigan, on a
    observé de très nombreux cas d'exposition humaine résultant d'un

    contact direct avec de la nourriture pour animaux contaminée et pour
    l'essentiel, de la consommation de viande, d'oeufs et de produits
    laitiers qui avaient également été contaminés par des PBB.  Au moins
    2000 familles (principalement des exploitants agricoles et leurs
    voisins) ont été fortement contaminées. En Allemagne, on a récemment
    décelé des PBB dans du lait de vache et du lait humain.

         La composition en homologues de ces échantillons diffère de
    celle que l'on trouve dans le poisson. La concentration relative du
    BB 153 est plus élevée dans le lait humain que dans le poisson.

         Les voies d'exposition de la population générale aux PBB sont
    mal connues. Pour autant que l'on sache, ils ne sont pas présents à
    fortes concentrations dans l'air ambiant ni dans l'eau. Plus
    importants à cet égard sont probablement les produits alimentaires
    riches en lipides tirés d'eaux contaminées. On ne possède aucun
    renseignement sur le niveau d'exposition dans l'air intérieur ni sur
    l'exposition par voie percutanée par suite d'un contact avec des
    retardateurs de flammes à base de PBB.

         La composition en homologues observée dans le lait humain
    prélevé en Allemagne rappelait celle que l'on trouvait dans le lait
    de vaches de la même région, mais à concentrations sensiblement plus
    élevées.

         Pour évaluer l'apport journalier de PBB par l'intermédiaire de
    la nourriture dans la population générale, on ne dispose que de très
    peu de données. Si l'on suppose que le poisson contient 20 µg de
    PBB/kg de matières grasses et 5% de matières grasses et qu'une
    personne de 60 kg consomme 100 g de poisson par jour, on arrive à
    une ingestion journalière de 0,002 µg/kg de poids corporel. Avec une
    concentration de PBB de 0,05 µg/kg de matières grasses dans le lait
    (4% de matières grasses) et une consommation de lait de
    500 ml/jour, la même personne en ingèrera quotidiennement environ
    0,00002 µg/kg de poids corporel.

         Un nourrisson de 6 kg consommant 800 ml de lait humain (3,5% de
    matières grasses) par jour ingèrera 0,01 µg de PBB/kg de poids
    corporel, si le lait contient de 2 µg de PBB/kg de matières grasses.

    1.5  Cinétique et métabolisme

         La résorption des PBB dans les voies digestives varie selon le
    degré de bromation, les composés les moins bromés étant les plus
    facilement résorbés.

         Les données relatives à la résorption du DeBB et de l'OcBB/NoBB
    sont insuffisantes.

         On retrouve des PBB dans l'ensemble du règne animal et des
    populations humaines, les concentrations d'équilibre les plus
    élevées étant observées dans les tissus adipeux. Les concentrations
    sont relativement élevées également dans le foie, particulièrement
    en ce qui concerne les homologues les plus toxiques qui semblent se
    concentrer dans cet organe. Le coefficient de partage des différents
    homologues varie d'un tissu à l'autre. En général, on note une
    tendance marquée à la bioaccumulation. Chez les mammifères, la
    transmission des PBB à la descendance se produit par la voie
    transplacentaire et par le lait maternel. On a constaté la présence
    de 2,2',4,4',5,5'-hexabromobiphényles dans du lait humain à des
    concentrations 100 fois plus élevées que dans le sérum maternel.
    Lors d'une étude portant sur plusieurs générations de rats,
    l'administration de PBB à une seule génération a entraîné la
    présence de résidus décelables dans plus de deux des générations
    suivantes. Chez les oiseaux, la teneur en PBB de l'organisme
    maternel entraîne également la présence de résidus dans les oeufs.

         Des nombreux homologues des PBB persistent dans les systèmes
    biologiques. Ainsi, les constituants les plus abondants du
    FireMaster(R), de même que l'octabromobiphényle et le décabromo
    biphényle, n'ont pas paru être métabolisés ou excrétés dans une
    proportion sensible. Les études métaboliques  in vitro montrent que
    l'on peut établir des relations structure-activité dans le cas du
    métabolisme de PBB. Les PBB pourraient être métabolisés par les
    microsomes induits par le phénobarbital à la condition de posséder
    des atomes de carbone adjacents non bromés, en  méta et en  para
    du pont biphényle, sur au moins un des cycles. La métabolisation des
    homologues inférieurs par les microsomes induits par le
    3-méthylcholanthrène nécessite la présence d'atomes de carbone non
    bromés en  ortho et  méta du pont biphényle sur au moins un des
    cycles; en outre, un degré important de bromation empêche la
    métabolisation. Chez les vertébrés, les principaux produits de
    métabolisation  in vitro et  in vivo des homologues inférieurs
    sont des dérivés hydroxylés. Le rendement métabolique observé est
    relativement faible. La réaction d'hydroxylation d'effectue
    probablement par l'intermédiaire d'un oxyde d'arène ou par
    hydroxylation directe.

         L'homme, le rat, le singe rhésus, le porc, la vache et le
    poulet éliminent les PBB, principalement dans leurs matières
    fécales. Dans la plupart des cas, il semble que la vitesse
    d'excrétion soit faible. Les concentrations de
    2,2',4,4',5,5'-hexabromobiphényles observées dans la bile et les
    matières fécales de sujets humains étaient égales à environ 50-70%
    des taux sériques et à environ 0,5% des taux dans les tissus
    adipeux. Les traitements administrés en vue d'améliorer
    l'élimination des PBB chez l'animal ou l'homme n'ont guère eu de
    succès. Le lait constitue une autre voie d'élimination des PBB.

         Après administration de PBB à des rats et à d'autres animaux,
    on a constaté que les relations entre la concentration tissulaire
    des PBB et le temps étaient complexes et variables. Ces relations
    ont pu être établies en utilisant divers modèles comportementaux. On
    a calculé que la demi-vie d'élimination du 2,2',4,4',5,5'-hexa
    bromobiphényles à partir des tissus adipeux du rat était d'environ
    69 semaines. Dans le cas des singes rhésus, on a trouvé une demi-vie
    de plus de quatre ans. Chez l'homme, on estime que la demi-vie
    moyenne se situe dans le cas de ce composé entre 8 et 12 ans. Dans
    la littérature, on trouve des valeurs allant de 5 à 95 ans. On
    constate quelques différences dans la rétention et le "turnover" des
    divers homologues. Les résultats fournis par l'analyse du sérum des
    agriculteurs et des travailleurs de l'industrie chimique en vue de
    doser le 2,3',4,4',5-pentabromobiphényle étaient incohérents. Cette
    incohérence est probablement due à la diversité des sources
    d'exposition. Les ouvriers étaient exposés à la totalité des
    constituants du FireMaster(R) alors que la population du Michigan
    n'avait consommé que de la viande et du lait contaminés contenant
    des mélanges de PBB différents par suite de la métabolisation des
    produits initiaux par les animaux de boucherie. Après administration
    d'octobromobiphényle à des rats, on n'a pas noté de diminution des
    taux de brome dans les tissus adipeux. On ne dispose d'aucune donnée
    sur la rétention du décabromobiphényle.

         L'organisme humain a davantage tendance à retenir certains
    homologues des PBB que celui des animaux de laboratoire. C'est un
    facteur à prendre en considération lorsqu'on évalue le danger pour
    la santé humaine que représentent ces composés.

         En conclusion, toutes les données disponibles indiquent que les
    PBB ont une forte tendance à s'accumuler et à persister dans les
    organismes vivants. Ils sont peu métabolisés et leur demi-vie chez
    l'homme est de 8 à 12 ans ou davantage.

    1.6  Effets sur les êtres vivants dans leur milieu naturel

         On ne dispose que de quelques données au sujet des effets que
    les PBB exercent sur les êtres vivants dans leur milieu naturel. 
    Elles portent sur les microorganismes, les puces d'eau, les oiseaux
    aquatiques et les animaux d'élevage.

         Les oiseaux aquatiques qui nichent sur les îles du nord-ouest
    du lac Michigan ont été étudiés afin de voir si les polluants du
    milieu étaient susceptibles d'affecter leur reproduction. On a ainsi
    procédé au dosage de 17 polluants et notamment de PBB, dont aucun
    n'a paru avoir d'effets notables sur la reproduction.

         Les animaux d'élevage qui avaient ingéré une nourriture à
    laquelle avait été ajouté par inadvertance du FireMaster(R) FF-1 à
    la place d'oxyde de magnésium, sont tombés malades. Dans la première
    ferme fortement contaminée que l'on ait observée, l'exposition
    moyenne estimative des vaches était égale à 250 mg/kg de poids
    corporel. Les signes cliniques d'intoxication consistaient dans une
    réduction de 50% de la consommation de nourriture (anorexie) et une
    diminution de 40% de la production laitière, dans les semaines
    suivant l'ingestion des aliments contaminés. Bien qu'en l'espace de
    16 jours on ait cessé de donner aux animaux la nourriture en
    question, la production laitière n'est pas revenue à sa valeur
    normale. Certaines vaches ont présenté une pollakiurie, un
    larmoiement, avec en outre des hématomes, des abcès, une croissance
    anormale des sabots, une boiterie, une alopécie, une hyperkératose
    et une cachexie; plusieurs animaux sont morts dans les six mois
    suivant l'exposition. Au total, la mortalité dans cette exploitation
    a été de 24/400. Chez les veaux âgés de six à 18 mois, elle était
    beaucoup plus élevée. Environ 50% d'entre eux sont morts dans les
    six semaines avec seulement deux survivants sur 12 au bout de cinq
    mois. Ces animaux étaient atteints d'hyperkératose sur l'ensemble du
    corps. On a également noté divers problèmes affectant la
    reproduction.

         Les résultats des autopsies sont connus pour certaines des
    vaches qui étaient mortes dans les six mois suivants l'exposition.
    L'étude histopathologique a révélé la présence d'altérations
    variables au niveau du foie et des reins.

         Plusieurs des signes cliniques et des altérations
    anatomopathologiques indiqués ci-dessus ont été confirmés par la
    suite par des études d'alimentation contrôlée (anorexie,
    déshydratation, hyperlarmoiement, émaciation, hyperkératose,
    problèmes de reproduction, modification d'un certain nombre des
    paramètres biochimiques, lésions rénales).

         Chez les troupeaux faiblement contaminés, on a noté une chute
    de la production et des cas de stérilité. Ces résultats contrastent
    avec ceux des études contrôlées, qui n'ont pas révélé des
    différences sensibles entre les troupeaux faiblement contaminés et
    les troupeaux témoins.

         A l'origine, la substitution accidentelle concernait des
    aliments pour bovins, mais d'autres types de nourriture animale ont
    subi une contamination croisée, notamment par l'intermédiaire du
    matériel servant à la préparation de ces aliments. Il est probable
    que l'exposition qui s'en est suivie n'a pas été aussi intense que
    dans le cas des bovins. La contamination d'autres animaux a été
    signalée (volailles, porcs, chevaux, lapins, chèvres et moutons) et
    ces animaux ont été abattus; toutefois, les troubles dont ils
    auraient pu souffrir n'ont pas été précisés.

         On ne dispose d'aucun renseignement au sujet des effets des PBB
    sur l'écosystème.

    1.7  Effets sur les animaux d'expérience et les systèmes d'épreuve
          in vitro

         Les valeurs de la DL50 pour les mélanges du commerce corre
    spondent à une toxicité aiguë relativement faible (DL50 > 1 g/kg
    de poids corporel) pour le rat, le lapin et la caille, après
    administration par voie orale ou percutanée. Une fois la dose de PBB
    administrée, il y a d'ailleurs un certain délai avant l'apparition
    des manifestations toxiques et la mort. C'est la dose totale
    administrée qui détermine l'ampleur de l'intoxication, qu'elle soit
    donnée en une seule fois ou qu'elle soit fractionnée et administrée
    sur une courte période (jusqu'à 50 jours). La toxicité des PBB s'est
    révélée plus importante après des doses multiples qu'après une dose
    unique. L'exposition aux PBB n'entraîne pas immédiatement la mort.

         Les quelques études effectuées sur des mélanges commerciaux
    d'octo- et de décabromobiphényles n'ont pas provoqué de mortalité
    chez les rats ni les poissons. En ce qui concerne les différents
    homologues des PBB, on n'a étudié que trois hexaisomères, le
    3,3',4,4',5,5'-HxBB et le 2,3',4,4',5,5'-HxBB étant plus toxiques
    pour le rat que le 2,2',4,4',5,5'-HxBB. Sur la base des données
    disponibles qui restent limitées, l'OcBB et le DeBB se révèlent
    moins toxiques et sont moins bien résorbés que les mélanges de PBB.

         De nombreuses études destinées à faire ressortir les effets
    aigus et les effets à court terme ont montré que, parmi les signes
    d'intoxication par les PBB (la plupart du temps, du FireMaster),
    figurait une réduction de la consommation de nourriture. Aux doses
    mortelles, on ne peut pas attribuer la mort à des lésions
    anatomopathologiques affectant un organe déterminé mais plutôt à un
    syndrome "cachectique" qui se développe chez l'animal et constitue
    le premier signe d'intoxication. Au moment de la mort, la perte de
    poids peut atteindre 30 à 40%. Les quelques études consacrées à
    l'OcBB et au DeBB techniques n'ont pas révélé d'effets de ce genre.

         C'est essentiellement au niveau du foie que l'on observe les
    altérations morphologiques et histopathologiques imputables à
    l'exposition aux PBB. Ainsi l'hypertrophie du foie s'observe
    fréquemment à des doses plus faibles que celles qui entraînent une
    perte de poids. Chez les rongeurs, les principales altérations
    histopathologiques pourraient être un gonflement et une
    vacuolisation généralisée des hépatocytes, la prolifération du
    réticulum endoplasmique agranulaire et la nécrose des cellules
    individuelles. La gravité des lésions dépend de la dose et de la
    composition du mélange administré.

         On a observé une diminution du poids du thymus chez des rats,
    des souris et des bovins après absorption de FireMaster(R), mais
    non d'OcBB ou de DeBB.

         On a fait état d'une augmentation du poids de la thyroïde et de
    modifications histologiques au niveau de cette glande chez le rat à
    des concentrations faibles.

         Il est évident que les différents homologues des PBB ne
    présentent pas le même type de toxicité. Les isomères et les
    homologues les plus toxiques provoquent une réduction du poids du
    thymus ou du corps et déterminent des altérations histologiques
    marquées au niveau du foie et du thymus. On a classé les byphényles
    halogénés en fonction de leur structure. La catégorie 1 comporte les
    isomères et les homologues qui n'ont pas de substi tuants en  ortho
    (PBB coplanaires). Les dérivés monosubstitués en  ortho
    constituent la deuxième catégorie. Les autres PBB (principalement
    ceux qui comportent deux bromes ou davantage en  ortho) sont
    classés dans la troisième catégorie. Les homologues de la catégorie
    1 ont tendance à provoquer les effets les plus graves alors que ceux
    de la deuxième et de la troisième catégorie entraînent des effets
    toxicologiques qui vont diminuant. A l'intérieur d'une même
    catégorie, le degré de bromation peut également avoir une influence
    sur la toxicité.

         Sur toutes les combinaisons étudiées, c'est le
    3,3',4,4',5,5'-HxBB qui s'est révélé le plus toxique. Cet homologue
    est présent à faibles concentrations dans le FireMaster(R). Parmi
    les principaux constituants du FireMaster(R), c'est le
    2,3,3',4,4',5-HxBB qui s'est révélé le plus toxique devant le
    2,3',4,4',5,5'-HxBB et le 2,3',4,4',5-PeBB, dans cet ordre. Le
    principal constituant du FireMaster(R), le 2,2',4,4'5,5'-HxBB
    s'est révélé relativement non toxique, de même que le
    2,2',3,4,4',5,5'-HpBB, qui vient en seconde position par ordre de
    concentration.

         On ne connaît pas très bien la toxicité des mélanges d'OcBB et
    de DeBB techniques eu égard à leur teneur en divers homologues (et
    autres contaminants éventuels).

         Les tests habituels d'irritation cutanée et oculaire de même
    que les tests de sensibilisation qui ont été effectués sur des
    mélanges de PBB techniques (OcBB et DeBB) n'ont révélé aucune
    réaction ou du moins, seulement des réactions légères. Toutefois on
    a relevé une hyperkératose et une alopécie chez les bovins exposés
    et des lésions rappelant la chloracné ont été observés chez les
    singes rhésus après ingestion de FireMaster(R). Le FireMaster(R)
    a produit une hyperkératose de la surface interne de l'oreille chez
    le lapin, mais ses deux principaux constituants (le
    2,2',4,4',5,5'-HxBB et le 2,2',3,4,4',5,5'-HpBB) ne produisaient pas

    cet effet. En fraction nant le FireMaster(R), on a constaté que
    l'essentiel de son activité était le fait des fractions les plus
    polaires contenant des constituants mineurs. En traitant des lapins
    avec de l'HxBB exposé à la lumière solaire, on a constaté
    l'apparition d'une hyperkératose grave au niveau de l'oreille.

         L'administration de faibles doses d'OcBB technique pendant une
    longue période à des rats n'a pas affecté leur consommation de
    nourriture ni leur poids corporel, mais on a constaté chez les rats
    qui avaient reçu pendant sept mois une dose de 2,5 mg/kg de poids
    corporel, une augmentation du poids relatif du foie. L'adminis
    tration pendant une longue durée à des rats de FireMaster(R) mêlé
    à leur nourriture à la dose de 10 ng/kg de poids corporel pendant
    six mois, est restée sans effet sur leur consommation de nourriture. 
    En revanche à la dose de 1 mg/kg de poids corporel administrée sur
    une période de six mois, on constatait une modification du poids du
    foie. Chez les rattes qui recevaient 0,3 mg/kg de poids corporel de
    FireMaster(R), on constatait une réduction du poids du thymus. Des
    altérations histopathologiques ont également été observées. Des
    études d'alimentation contrôlées poursuivies pendant une longue
    période sur des bovins exposés à de faibles doses de
    FireMaster(R), n'ont pas fait ressortir d'effets nocifs, à en
    juger par la prise de nourriture, les signes cliniques, les
    modifications clinicopathologiques ou le rendement du bétail. Les
    visons, les cobayes et les singes se sont révélés plus sensibles à
    l'intoxication par les PBB.

         On a observé chez le rat des effets à long terme attribuables à
    la rétention des PBB après administration de fortes doses de
    FireMaster(R) au cours de la période prénatale ou périnatale.

         Les effets délétères les plus fréquemment observés sur la
    reproduction consistaient en une résorption du foetus et une moindre
    viabilité de la progéniture. Chez les visons, on observait encore
    certains effets à la concentration de 1 mg/kg de nourriture. Une
    réduction de la viabilité de la progéniture a été observée chez des
    singes rhésus après 12,5 mois d'exposition au FireMaster(R) (dose:
    0,3 mg/kg de nourriture). Les singes ont reçu une dose quotidienne
    de ce mélange, égale à 0,01 mg/kg de poids corporel et la dose
    totale était de 3,8 mg/kg de poids corporel. Il n'a pas été possible
    d'évaluer les études de reproduction ni les études
    neurocomportementales effectuées sur des singes et des rats à
    faibles doses, car les publications en question n'étaient pas
    suffisamment explicites quant au protocole expérimental des essais.
    Chez les rongeurs, on a observé un faible pouvoir tératogène à des
    doses élevées, susceptibles d'être toxiques pour les mères.

         Les PBB perturbent les fonctions endocrines. Chez des rats et
    des porcs on a observé une réduction des taux sériques de thyroxine
    et de triiodothyronine qui était liée à la dose. Les PBB
    perturberaient également, dans la plupart des cas, les taux
    d'hormones stéroïdiennes. L'ampleur des effets dépend de l'espèce
    ainsi que de la dose et de la durée de l'administration.

         Les PBB ont également produit une porphyrie chez des rats et
    des souris mâles à des doses quotidiennes ne dépassant pas
    0,3 mg/kg de poids corporel. La dose quotidienne maximale sans
    effets était de 0,1 mg/kg de poids corporel. On constatait une
    influence marquée des PBB sur l'accumulation de vitamine A ainsi que
    des effets sur la métabolisme intermédiaire.

         Après exposition aux PBB, on observe fréquemment une atrophie
    du thymus et on a constaté que d'autres tissus lymphoïdes étaient
    également affectés. On a également mis en évidence d'autres
    indicateurs témoignant d'une dépression des fonctions immunitaires
    par le FireMaster(R). On manque de données concernant l'OcBB, le
    NoBB, le DeBB ou les différents homologues des PBB.

         Un des effets des PBB qui ait été le plus intensivement étudié
    est l'induction des oxydases à fonction mixte. De fait, on a
    systématiquement constaté que le FireMaster(R) se comportait comme
    un inducteur de type mixte des enzymes microsomiennes du foie chez
    le rat et chez toutes les autres espèces étudiées. Cette induction a
    été également observée dans d'autres tissus, mais dans une moindre
    mesure. L'aptitude à induire les enzymes microso miennes hépatiques
    varie d'un homologue à l'autre. On a mis en évidence des
    corrélations entre la structure et l'aptitude à induire les enzymes
    microsomiennes.

         Plusieurs études ont montré que les PBB étaient capables de
    modifier l'activité biologique de divers médicaments et substances
    toxiques. Cela s'explique peut-être en partie par le fait que les
    PBB sont capables d'induire les enzymes microsomiennes qui
    interviennent dans l'activation ou la désactivation des substances
    xénobiotiques.

         Le FireMaster(R) et certains de ces principaux constituants
    se sont révélés capables d'inhiber la communication intercellulaire
    in vitro. Cette inhibition s'est produite à des concentrations non
    cytotoxiques. Cette cytotoxicité, de même que la capacité d'inhiber
    la coopération métabolique paraît liée à la structure et plus
    précisément à la présence ou à l'absence de substitution en  ortho.

         Les épreuves  in vitro et  in vivo (mutagénèse des cellules
    microbiennes et mammaliennes, altération des chromosomes de cellules
    mammaliennes, transformation des cellules mammaliennes, lésion et
    réparation de l'ADN) n'ont pu mettre en évidence de mutagénicité ou
    de génotoxicité imputables aux divers homologues des PBB ou aux
    mélanges qui sont vendus dans le commerce.

         Les études de toxicité à long terme ont montré que le foie
    était la principale cible des effets cancérogènes du PBB. Chez des
    souris et des rats, mâles et femelles, qui recevaient du
    FireMaster(R) par voie orale, on a noté une augmentation sensible
    de l'incidence des carcinomes hépatocellulaires. Des effets
    cancérogènes sur le foie ont également été observés chez des souris
    qui avaient reçu pendant 18 mois une alimentation contenant une dose
    totale de 100 mg/kg ou davantage de Bromkal 80-9D
    (nonabromobiphényle technique) en doses quotidiennes de 5 mg/kg de
    poids corporel. La dose quotidienne de PBB la plus faible qui ait
    produit des tumeurs (pour la plupart, des adénomes) chez des
    rongeurs, était de 0,5 mg/kg de poids corporel pendant deux ans. Les
    rats qui en avaient reçu quotidiennement 0,15 mg/kg de poids
    corporel, en plus de ce qu'il leur avait été administré pendant la
    période prénatale et périnatale, n'ont pas présenté le moindre effet
    indésirable. La pouvoir cancérogène de l'octabromobiphényle et du
    décabromobiphényle techniques n'a pas été étudié.

         Ni le FireMaster BP-6 ni le 2,2',4,4',5,5'-hexabromobiphényle
    ne se sont comportés comme des initiateurs tumoraux (en utilisant le
    TPA comme promoteur) ou comme des promoteurs tumoraux (en utilisant
    la DMBA comme initiateur) lors d'épreuves bio logiques sur
    l'épiderme de souris. Toutefois, en utilisant le même modèle
    (épiderme de souris) et avec du DMBA ou de la MNNG comme initiateur,
    le FM FF-1 et le 3,3',4,4'5,5'-hexabromo biphényle mais non pas le
    2,2',4,4'5,5'-hexabromobiphényle, ont présenté une activité
    tumoro-promotrice. Lors d'une épreuve biologique sur foie de rat
    effectuée en deux temps, et avec du phénobarbital comme promoteur,
    on a constaté que le 3,3',4,4'- tétrabromobiphényle se comportait
    comme un initiateur faible. Avec ce même modèle animal, en présence
    de diéthylnitrosamine et après hépatectomie partielle, on a constaté
    que le FM, le 3,3',4,4'-tétrabromobiphényle et le
    2,2',4,4',5,5'-hexabromobi phényle, mais non pas le
    3,3',4,4',5,5'-hexabromobiphényle, se comportaient comme des
    promoteurs tumoraux.

         Les résultats des études sur la communication cellulaire, les
    résultats négatifs fournis par les études de génotoxicité et de
    mutagénicité, ainsi que ceux des épreuves de promotion tumorale,
    montrent que les mélanges de PBB et les divers homologues étudiés
    provoquent l'apparition de cancers par un mécanisme épigéné tique.
    On ne dispose d'aucun renseignement sur l'octa-, le nona-, le
    décabromobiphényles techniques.

         Le mode d'action qui est à la base des nombreuses manifes
    tations de la toxicité des PBB et des composés apparentés reste
    inconnu. Toutefois, certains des effets observés, comme le syndrome
    cachectique, l'atrophie du thymus et l'hépatotoxicité, les
    manifestations dermatologiques et les effets délétères sur la
    fonction de reproduction peuvent être attribués à une interaction
    avec les récepteurs Ah ou TCDD, interaction qui entraîne une
    modification de l'expression d'un certain nombre de gènes.
    L'interaction avec ces récepteurs varie selon les divers homologues,
    les homologues coplanaires étant les plus actifs.

         Nombre des effets des PBB s'observent après une exposition de
    longue durée. Cela s'explique peut-être par le fait que certains
    homologues s'accumulent fortement et que l'organisme ne les
    métabolise et ne les élimine que difficilement. Il s'en suit une
    accumulation de ces composés dans l'organisme qui finit par
    submerger les mécanismes de compensation et entraîne des effets
    délétères.

         Certains contaminants connus du FireMaster(R), en
    l'occurrence des polybromonaphtalènes (PBN) sont fortement toxiques
    et tératogènes. Bien qu'ils ne soient présents qu'en petites
    quantités dans le FireMaster(R), il n'est pas exclu qu'ils
    contribuent à sa toxicité.

         Les études portant sur le FireMaster(R) et son principal
    constituant le 2,2',4,4'5,5'-HxBB, ont montré que leurs produits de
    photolyse étaient plus toxiques que les composés initiaux. Les
    produits du pyrolyse du FM provoquent l'induction des oxydases à
    fonction mixte, une perte de poids et une atrophie du thymus. On a
    également observé que les produits de pyrolyse de l'OcBB technique
    produisaient une hypertrophie du foie.

    1.8  Effets sur l'homme

         On ne connaît aucun exemple d'intoxication aiguë par les PBB
    chez l'homme auquel on puisse comparer les effets potentiels à
    faibles doses résultant de l'accident survenu dans le Michigan aux
    Etats-Unis d'Amérique en 1973. Les principales études
    épidémiologiques ont été menées par le Michigan Department of Public
    Health (MDPH) et l'Environmental Science Laboratory de la Mount
    Sinaï School of Medicine, New York (ESL).

         On estime que les personnes les plus fortement contaminées
    avaient consommé 5 à 15 g de PBB sur une période de 230 jours par
    l'intermédiaire du lait. Il est possible que la consommation de
    viande ait constitué une source de contamination supplémentaire. 
    Chez certains des agriculteurs et chez la plupart des membres de la
    population générale du Michigan, le niveau d'exposition était
    beaucoup plus faible, la dose totale étant de 9 à 10 mg. Il est

    possible cependant que certaines personnes aient reçu une dose
    totale d'environ 800 à 900 mg. (Une dose totale de 9 mg correspond à
    0,15 mg/kg de poids corporel et une dose de 900 mg, à 15 mg/kg de
    poids corporel pour un adulte moyen de 60 kg; pour un enfant, la
    dose par kg/poids corporel serait plus élevée).

         En 1974, la première étude du MDPH a consisté à comparer l'état
    de santé des personnes travaillant dans les fermes mises en
    quarantaine, à celui du personnel des fermes de la même région qui
    n'étaient pas frappées par cette mesure. Dans les deux groupes, on a
    constaté divers symptômes, mais sans pouvoir dégager de différences.
    Aucune anomalie inhabituelle n'a été constatée, qu'il s'agisse du
    coeur, du foie, de la rate, du système nerveux, des résultats de
    l'analyse d'urine et de la NFS, non plus qu'en ce qui concerne tous
    les autres paramètres médicaux examinés. Une étude ultérieure très
    complète menée par le MDPH et portant sur des groupes soumis à une
    exposition de degré variable, n'a pas permis de mettre en évidence
    de corrélation positive entre les taux sériques de PBB et la
    fréquence des symptômes ou des affections observés. L'ESL a étudié
    environ 990 personnes vivant sur des exploitations agricoles, 55
    travailleurs de l'industrie chimique et un groupe de producteurs de
    lait du Wisconsin qui ont fait office de témoins. Les symptômes
    étaient plus fréquent chez les exploitants du Michigan que chez ceux
    du Wisconsin. C'est dans le cas des symptômes neurologiques et
    musculo-squelettiques, au sens large, que les différences étaient
    les plus importantes. De même les taux sériques de certaines enzymes
    hépatiques et de l'antigène carcino-embryonnaire étaient plus
    fréquemment élevés chez les fermiers du Michigan que chez ceux du
    Wisconsin. La prévalence des symptômes respiratoires et cutanés
    était plus forte chez les travailleurs de l'industrie chimique avec
    également des symptômes musculo-squelettiques moins fréquents que
    chez les agriculteurs. Les résultats des travaux de l'ESL n'ont pas
    toujours été interprétés de la même manière que ceux d'autres études
    comparables, mais tous sont d'accord sur un point. Aucune de ces
    séries d'études n'a mis en évidence de corrélation dose-réponse
    positive entre les taux de PBB dans le sérum ou les tissus adipeux
    et la prévalence des symptômes ou des anomalies cliniques. Un
    certain nombre d'aspects cliniques ont été étudiés de manière plus
    intensive par des méthodes spéciales. En particulier, l'examen des
    aspects neurologiques au moyen de tests objectifs de performance a
    révélé, dans une étude tout du moins, l'existence d'une corrélation
    négative entre les taux sériques de PBB et les résultats des tests,
    en particulier chez les hommes d'âge mûr. Quant aux autres études,
    elles n'ont pas mis en évidence de relation entre la concentration
    des PBB dans le sérum ou les tissus adipeux et les résultats d'une
    batterie de tests portant sur la mémoire, la force musculaire, la
    coordination, la perception cortico-sensorielle, la personnalité,
    les fonctions cognitives supérieures et d'autres fonctions. Les
    aspects pédiatriques de l'exposition aux PBB ont été étudiés dans
    les familles examinées par l'ESL. Bien que de nombreux symptômes

    aient été signalés, l'examen médical n'a pas révélé d'anomalie
    objective attribuable à l'exposition au PBB. Des opinions
    différentes se sont exprimées à propos des effets
    neurospychologiques plus subtils observés dans la descendance de ces
    personnes et les résultats des études portant sur la capacité de
    développement sont également controversés. Cela vaut aussi pour
    l'étude des lymphocytes et de la fonction immunitaire. C'est ainsi
    que selon plusieurs auteurs, il n'y avait pas de différences entre
    les groupes à fort et faible taux sérique de PBB pour ce qui
    concerne le nombre de lymphocytes et les fonctions lymphocytaires,
    alors que d'autres ont constaté une réduction sensible des
    sous-populations de lymphocytes T et de lymphocytes B chez environ
    40% des personnes exposées dans le Michigan, par rapport aux groupes
    non exposés, avec en outre une altération de la fonction
    lymphocytaire, à savoir une diminution de la réponse aux mitogènes.

         Dans les études épidémiologiques qui ont été passées en revue,
    on s'est efforcé d'évaluer la relation entre l'exposition aux PBB et
    un grand nombre d'effets sur le comportement et de symptômes
    subjectifs. Cependant, la plupart des ces études présentent de
    graves insuffisances au niveau de la conception et en particulier,
    elles laissent subsister des facteurs de confusion qui rendent
    difficile, voire impossible, toute conclusion sur la relation
    éventuelle entre l'exposition aux PBB et d'éventuels effets sur la
    santé. On ne dispose pas d'un recul suffisant pour pouvoir évaluer
    les effets cancérogènes éventuels de ces composés.

         On a identifié deux petits groupes de travailleurs exposés de
    par leur profession à un mélange de PBB ou à du DeBB et du DBBO. Des
    lésions rappelant une chloracné ont été observées chez 13% des
    travailleurs exposés au mélange de PBB, alors que ceux qui avaient
    été exposés au DeBB ne présentaient pas de telles lésions. Toutefois
    la prévalence de l'hypothyroïdie était plus élevée dans ce groupe.

    1.9  Evaluation globale de la toxicité et de la cancérogénicité

         La seule étude toxicologique qui ait été effectuée à vie sur
    des animaux d'expérience a été menée récemment dans le cadre du
    Programme national de toxicologie (National Toxicology Programme,
    NTP) sur des rats et des souris. La dose la plus faible étudiée qui
    produisait encore des effets cancérogènes était égale à 0,5 mg/kg de
    poids corporel et par jour (formation de tumeurs hépatiques chez les
    rongeurs). D'autres études du même genre ont mis en évidence un
    effet cancérogène à la dose quotidienne de 3 mg/kg de poids
    corporel, sur une durée de six mois. L'étude de six mois montre
    qu'une exposition pendant une durée inférieure à la vie normale de
    l'animal à des doses voisines, entraîne également des effets
    délétères analogues. Il est possible qu'à plus faibles doses, les
    PBB exercent des effets sur la reproduction des primates
    sous-hominiens et des visons.

         En outre, l'étude de deux ans effectuée dans le cadre du NTP a
    montré qu'une dose quotidienne de 0,15 mg/kg de poids corporel avec
    exposition prénatale et périnatale de la mère à une dose quotidienne
    de 0,05 mg/kg de poids corporel, ne produisait aucun effet nocif.
    Par conséquent, la dose totale absorbée quotidienne ment à partir de
    la nourriture, de l'eau, de l'air et du sol devrait être inférieure
    à 0,15 µg/kg de poids corporel, si l'on extrapole les résultats
    obtenus concernant la dose sans effet nocif observable lors d'une
    étude de cancérogénicité positive, en appliquant à cet effet un
    coefficient d'incertitude (coefficient de sécurité) de 1000, puisque
    ces composés induisent probablement des cancers par un mécanisme
    épigénétique.

         On estime que la dose totale reçue par le sous groupe de
    population du Michigan se situait entre 0,15 et 15 mg/kg de poids
    corporel sur une période de 230 jours. Si on rapporte cette dose à
    la durée moyenne de vie normale d'un être humain, cela
    correspondrait, pour cette population, à une dose quotidienne de 0,6
    ng à 6 µg/kg de poids corporel.

         On estime que pour les adultes de la population générale,
    l'apport quotidien total de PBB par kg de poids corporel à partir
    des sources répertoriées, est de l'ordre de 2 ng; il est de 10 ng
    pour les nourrissons nourris au sein. Il convient de noter que ces
    estimations reposent sur des données régionales très limitées.

         Ces calculs reposent sur l'hypothèse que la concentration des
    PBB n'atteindra pas un état stationnaire au cours de l'existence et
    que l'on peut substituer une exposition forte sur une courte durée à
    une exposition faible sur une longue durée, étant donné que ces
    composés sont très mal métabolisés et excrétés.

         On ne dispose pas de données suffisantes pour l'OcBB, le NoBB
    et le DeBB pour calculer quel serait l'apport quotidien total
    maximal ne produisant pas d'effets indésirables.

    2.  Conclusions

         La plupart des homologues des PBB qui entrent dans la
    composition des retardateurs de flammes vendus dans le commerce,
    sont lipophiles, persistants et s'accumulent dans les biotes. Ces
    composé subissent une bioamplification le long des réseaux
    trophiques et constituent une menace, en particulier pour les
    organismes qui se trouvent en fin de réseau. En outre, certains
    constituants des PBB sont les précurseurs de dibenzofuranes
    polybromés toxiques qui se forment lors de la combustion.

         Outre les émissions qui se produisent au cours de la
    fabrication et de l'utilisation des PBB, ceux-ci pénètrent dans
    l'environnement du fait de la très large utilisation des
    retardateurs de flammes dont ils sont les constituants. Une part
    très importante des PBB produits finit par passer dans
    l'environnement du fait de la très grande stabilité de ces composés.

         On trouve également des PBB dans des échantillons prélevés dans
    l'environnement et sur des sujets humains, en des lieux éloignés des
    endroits où l'on sait que ces composés sont produits.  La
    composition en homologues des PBB dans les échantillons provenant de
    l'environnement ne correspond pas à celle que l'on trouve dans les
    produits techniques, ce qui indique qu'il y a transformation dans le
    milieu, peut-être à la suite d'une débromation photochimique.

         On dispose actuellement des très peu de données sur l'ampleur
    de l'exposition de la population générale aux PBB. Toutefois, dans
    les quelques cas où on a procédé à des mesures, on a pu mettre en
    évidence des traces de PBB. Actuellement, cette exposition ne cause
    pas d'inquiétude, mais il faudrait éviter que ces composés ne
    continuent à s'accumuler. D'après les observations faites sur
    l'homme à la suite de l'accident du Michigan, il semblerait que les
    personnes contaminées aient été exposées à des doses de plusieurs
    ordres de grandeur supérieures à celles que l'on observe dans la
    population générale. On n'a pas observé dans la population du
    Michigan d'effets concluants qui puissent être attribués à
    l'exposition aux PBB, encore que la période de suivi ne soit pas
    suffisante pour permettre à d'éventuels cancers de se manifester. 
    Etant donné que les taux de PBB dans les tissus adipeux et le sérum
    restent élevés dans la population du Michigan, il y a poursuite de
    l'exposition interne. En revanche, on a bien observé des effets
    toxiques chez les bovins de cette région. On explique cette
    discordance par le fait que les bovins avaient été davantage
    exposés.

         L'exposition professionnelle n'a été étudiée que dans deux
    unités de production des Etats-Unis d'Amérique. Il semble que chez
    les travailleurs employés à la production des PBB, il puisse y avoir
    apparition de lésions rappelant une chloracné; quant aux
    travailleurs exposés au DeBB, ils peuvent présenter une
    hypothyroïdie. Aucune enquête n'a été menée chez les travailleurs
    qui confectionnent des produits commerciaux à base de deca-, d'octa-
    ou de nona-bromobiphényles.

         Les PBB sont extrêmement persistants chez les organismes
    vivants et ils peuvent conduire à une intoxication chronique et à
    des cancers. Bien que la toxicité aiguë soit faible, on constate
    l'apparition de cancers à des doses quotidiennes de 0,5 mg/kg de
    poids corporel avec une dose sans effet observable de 0,15 mg/kg de

    poids corporel et par jour. On a observé un certain nombre d'effets
    toxiques chroniques chez les animaux de laboratoire à des doses
    quotidiennes de l'ordre de 1 mg/kg de poids corporel, administrées
    pendant de longues périodes.

    3.  Recommandations

    3.1  Généralités

         Le Groupe de travail estime qu'il faut éviter à l'homme et à
    l'environnement d'être exposés aux PBB en raison de la forte
    persistance et de la forte bioaccumulation de ces composés ainsi que
    des effets nocifs qu'ils peuvent provoquer en cas d'exposition de
    longue durée à de faibles doses. Aussi convient-il de ne plus
    utiliser de PBB dans des produits du commerce.

         Comme les données dont on dispose sur la toxicité du DeBB et de
    l'OcBB sont limitées, qu'ils sont extrêmement persistants et
    susceptibles d'être dégradés dans l'environnement et qu'en outre,
    leur combustion entraîne la formation de dérivés encore plus
    toxiques, ils ne doivent pas être utilisés dans le commerce, du
    moins tant qu'on aura pas démontré que cet usage est sans danger.

         La cohorte du Michigan est toujours en observation et il est
    nécessaire que les données obtenues soient publiées.

    3.2  Recherches futures

         Il convient de développer la surveillance des PBB chez l'homme
    et dans l'environnement, et en particulier sur les lieux de travail,
    qu'il s'agisse de la fabrication proprement dite des PBB ou de leur
    utilisation; cette surveillance devra porter sur chaque homologue en
    particulier et englober également l'OcBB, le NoBB et le DeBB. Ces
    composés doivent figurer dans les programmes de surveillance des
    dérivés halogénés actuellement en cours. On devra notamment
    continuer à suivre la tendance des concentrations de PBB dans
    l'environnement et leur distribution géographique. On procédera
    également à un relevé des décharges où des PBB sont susceptibles de
    passer dans l'environnement.

         Il faudrait procéder à des expériences de thermolyse simulant
    les conditions d'un incendie accidentel ou de l'incinération de
    déchets municipaux. Des travaux complémentaires devront également
    être consacrés à l'étude du mécanisme de la toxicité et de la
    cancérogénicité des PBB et des composés apparentés. Les PBB peuvent
    être utilisés comme modèles pour ces recherches. Tous ces travaux
    devront utiliser des homologues purifiés.

         Les effets des PBB sur la reproduction restent mal connus.
    Aussi serait-il souhaitable d'effectuer des études de longue durée
    bien conçues, concernant l'effet des faibles doses sur la
    reproduction, en utilisant une espèce vulnérable.

         Il importe également d'obtenir davantage de renseignements sur
    la biodisponibilité et la toxicocinétique de l'OcBB/NoBB, du DeBB et
    d'un certain nombre d'homologues.

    RESUMEN Y EVALUACION, CONCLUSIONES Y RECOMENDACIONES

    1.  Resumen y evaluación

    1.1  Identidad, propiedades físicas y químicas y métodos analíticos

         Los bifenilos polibromados o polibromobifenilos (PBB) son un
    grupo de hidrocarburos halogenados formados por sustitución del
    hidrógeno del bifenilo por bromo. No se conoce ningún PBB de origen
    natural. Estas moléculas responden a la fórmula
    C12H(10-x-y)Br(x+y), donde x e y están comprendidos entre 1 y
    5. Por consiguiente, teóricamente son posibles 209 formas
    moleculares, pero sólo se han sintetizado individualmente y
    caracterizado un reducido número. Los PBB fabricados para uso
    comercial consisten principalmente en hexa-, octa-, nona-, y
    decabromobifenilos, pero contienen también otros productos de la
    misma familia. Son pirorretardantes que se emplean como aditivos, y
    que mezclados con material polimérico líquido o sólido seco le
    confieren propiedades pirorretardantes de tipo filtrante; en caso de
    ignición se produce una liberación química de ácido bromhídrico.

         La fabricación de los PBB se basa en una reacción de
    Friedel-Crafts entre el bifenilo y el bromo, en presencia de un
    disolvente orgánico en ocasiones, y de un catalizador que puede ser
    cloruro de aluminio, bromuro de aluminio o hierro.

         La mayor parte de las investigaciones realizadas se refieren a
    los productos FireMaster BP-6 y FF-1, responsables de la catástrofe
    que se produjo en Michigan cuando, inadvertidamente, fueron
    agregados al pienso de los animales en lugar del óxido de magnesio
    que correspondía. La consiguiente contaminación acarreó la muerte de
    miles de cabezas de ganado vacuno, porcino y ovino, así como de
    millones de pollos.

         La composición de la mezcla FireMaster(R) varía de un lote a
    otro, pero sus principales componentes son el 2,2',4,4',5,5'-
    hexabromobifenilo (60-80%) y el 2,2',3,4,4',5,5'-heptabromobifenilo
    (12-25%), junto con los cuales se hallan también otros compuestos
    menos bromados que son el resultado de una reacción de bromación
    incompleta. Se han detectado también bromoclorobifenilos y
    naftalenos polibromados como componentes minoritarios de
    FireMaster(R). FireMaster FF-1 (polvo blanco) se obtiene a partir
    de FireMaster BP-6 (escamas pardas), por adición, como agente
    antiaglutinante, de silicato de calcio al 2%.

         Los PBB son sólidos de baja volatilidad; ésta disminuye al
    aumentar el número de átomos de bromo. Son prácticamente insolubles
    en agua, solubles en grasas, y entre poco y muy solubles en diversos
    disolventes orgánicos; la solubilidad también disminuye al aumentar

    el número de átomos de bromo. Son compuestos relativamente estables
    y químicamente inertes, pero las mezclas de PBB muy bromados se
    fotodegradan y sufren una debromación reductiva al ser expuestas a
    la radiación ultravioleta.

         Los productos de la descomposición térmica experimental de los
    PBB dependen de la temperatura, de la cantidad de oxígeno presente y
    de otros varios factores. Las investigaciones realizadas sobre la
    pirólisis de FireMaster BP-6 en ausencia de oxígeno (600-900 °C) han
    demostrado que se forman bromobencenos y bifenilos menos bromados,
    pero no así furanos polibromados. Por el contrario, la pirólisis en
    presencia de oxígeno (700-900 °C) generó una cierta cantidad de di-
    a heptabromodibenzofuranos. En presencia de poliestireno y
    polietileno se hallaron niveles más altos. La pirólisis de
    FireMaster BP-6 en presencia de PVC a 800 °C dio lugar a una mezcla
    de bromoclorobifenilos. No se dispone de información sobre la
    naturaleza de los productos de incineración de los materiales que
    contienen PBB. Poco se sabe acerca de la toxicidad de las dioxinas y
    furanos bromados y bromados/clorados, pero se estima que debe ser de
    aproximadamente la misma magnitud que la de las dioxinas y furanos
    clorados.

         La principal técnica analítica empleada para el control
    biológico de los PBB en muestras del medio y en tejidos y líquidos
    biológicos tras la catástrofe de Michigan fue la cromatografía de
    gases con detector de captura de electrones. Los diversos productos
    de la familia pueden determinarse individualmente mediante cromato
    grafía de gases capilar, y aún es posible conseguir una detección
    más específica si se emplea la espectrometría de masas de control de
    determinados iones. Como el número de posibles miembros de esta
    familia de productos es muy elevado, las investigaciones se ven
    dificultadas por la falta de patrones sintéticos adecuados. Los
    métodos empleados para extraer PBB de muestras biológicas se han
    venido basando en los usados con los plaguicidas. Los PBB son
    extraídos con la grasa, y purificados a continuación.

         El hallazgo reciente de PBB en muestras biológicas de fondo no
    significa necesariamente que su concentración esté aumentando en el
    medio: ello podría deberse a la aparición de técnicas analíticas más
    sensibles, como la espectrometría de masas de ionización química de
    iones negativos. De ahí la necesidad de realizar cuanto antes
    estudios retrospectivos. Los métodos mejorados de purificación
    exhaustiva permiten realizar análisis específicos de los PBB
    coplanares tóxicos, datos que son igualmente necesarios.

    1.2  Fuentes de exposición humana y ambiental

         La producción comercial de FireMaster(R) comenzó en los
    Estados Unidos en 1970, pero se interrumpió tras la catástrofe de
    Michigan (noviembre de 1974). La producción estimada de PBB en los

    Estados Unidos entre 1970 y 1976 fue de 6000 toneladas (cantidades
    comerciales); hasta 1979 se siguió produciendo en el país
    octabromobifenilo y decabromobifenilo. En Alemania se produjo hasta
    mediados de 1985 una mezcla de PBB altamente bromados conocida como
    Bromkal 80-9 D. Actualmente se produce en Francia decabromobifenilo
    (Adine 0102) de calidad técnica. Al parecer, esos son los únicos PBB
    que se siguen produciendo hoy en día.

         Los PBB se introdujeron a principios de los años setenta como
    pirorretardantes. Hasta noviembre de 1974 el PBB más importante
    comercialmente en los Estados Unidos era el hexabromobifenilo,
    producto que se incorporaba a los plásticos (10% de contenido de
    PBB), de acrilonitrilo-butadieno-estireno (ABS), material usado
    principalmente en la fabricación de pequeños utensilios y
    componentes de automóvil, revestimientos, barnices y espuma de
    poliuretano. Los otros PBB pirorretardantes tienen aplicaciones
    similares.

         Durante el proceso normal de producción pueden tener lugar
    pérdidas de PBB en el medio ambiente, por emisión a la atmósfera o
    por su incorporación a aguas residuales, suelos o vertederos,
    pérdidas que sin embargo, según se ha observado, son por lo general
    de escasa importancia.

         Estos compuestos pueden llegar también al medio durante su
    transporte y manipulación, así como de manera accidental, como
    ocurrió en Michigan.

         Existe también la posibilidad de que pasen al medio de resultas
    de la incineración de materiales que contienen PBB, o a causa de
    fuegos accidentales, formándose en estos casos otros productos
    tóxicos, como polibromodibenzofuranos o derivados mixtos de bromo y
    cloro.

         La mayor parte de los compuestos así formados acaban
    difundiéndose a la larga al medio, como tales o en forma de
    productos de degradación.

    1.3  Transporte, distribución y transformación en el medio ambiente

         No hay pruebas de que los PBB se propaguen por la atmósfera a
    grandes distancias, pero la presencia de estos compuestos en
    muestras de focas del Artico pone de manifiesto una amplia
    distribución geográfica.

         Las principales vías conocidas de llegada de los PBB al medio
    acuático son los vertidos de desechos industriales y los lixiviados
    de lugares de vertimiento industrial que alcanzan las aguas, así
    como la erosión de suelos contaminados. Los PBB son casi insolubles
    en agua y se hallan sobre todo en los sedimentos de lagos y ríos
    contaminados.

         Los focos de contaminación del suelo pueden ser las fábricas o
    los depósitos de residuos de PBB. Los PBB que llegan a penetrar en
    el suelo no se desplazan fácilmente. Se ha observado que los PBB son
    200 veces más solubles en el lixiviado de un vertedero que en el
    agua destilada, lo que puede significar una mayor propagación en el
    medio ambiente. Debido a sus propiedades hidrofóbicas, cuando están
    en solución acuosa estos productos son fácilmente adsorbidos por los
    suelos. Se observó una adsorción preferencial de determinados PBB en
    función de las características del suelo (por ejemplo de su
    contenido orgánico) y del número y posición de los radicales de
    bromo.

         Los PBB son estables y persistentes, lipofílicos, y sólo
    ligeramente solubles en agua; algunos de los compuestos de esta
    familia apenas son metabolizados y se acumulan en los compartimentos
    lipídicos de la biota. Una vez liberados en el medio ambiente,
    pueden alcanzar la cadena alimentaria y concentrarse en ella.

         Se han detectado PBB en el pescado capturado en varias
    regiones. La ingestión de pescado es una vía de transmisión de PBB a
    los mamíferos y las aves.

         Se considera improbable que los PBB se degraden mediante
    reacciones químicas puramente abióticas (excluidas las reacciones
    fotoquímicas). Se ha notificado la persistencia de PBB en el
    terreno. Al cabo de varios años del accidente de Michigan, el
    análisis de muestras del suelo de un antiguo centro de fabricación
    de PBB reveló la presencia, aún, de ese tipo de productos, aunque el
    perfil de los PBB era distinto, debido a la degradación parcial
    sufrida por los residuos en la muestra de suelo.

         En condiciones de laboratorio los PBB son degradados fácilmente
    por la radiación ultravioleta. La fotodegradación de la mezcla
    comercial FireMaster(R) se refleja en una menor concentración de
    los PBB que presentan más sustituyentes. No se han determinado con
    exactitud ni la velocidad ni la magnitud de las reacciones
    fotolíticas que sufren los PBB en el medio, pero las observaciones
    realizadas sobre el terreno muestran una elevada persistencia de los
    PBB originales, o bien una degradación parcial a formas menos
    bromadas.

         En las investigaciones de laboratorio las mezclas de PBB
    parecen bastante resistentes a la degradación microbiana.

         No se ha descrito ningún fenómeno de captación o degradación de
    PBB por las plantas. En cambio, los PBB son fácilmente absorbidos
    por los animales, en los que se ha observado que son muy
    persistentes, aun cuando se han detectado pequeñas cantidades de

    metabolitos. Los principales productos metabólicos eran
    hidroxiderivados, y en algunos casos se hallaron indicios de la
    existencia de PBB parcialmente debromados. No se ha descrito
    investigación alguna sobre posibles metabolitos sulfurados análogos
    a los de los PCB.

         Se ha investigado la bioacumulación de PBB en el pescado, así
    como la que se produce en animales terrestres, en este caso mediante
    el estudio de especies de mamíferos y aves. Los datos obtenidos
    proceden de observaciones sobre el terreno, de la evaluación de la
    catástrofe de Michigan, y de estudios controlados de alimentación de
    los animales. Por lo general se observó que la acumulación de PBB en
    la grasa corporal dependía de la dosis y de la duración de la
    exposición.

         Al analizar individualmente los PBB, se observa que su
    bioacumulación aumenta con el grado de bromación, al menos hasta los
    tetrabromobifenilos. Cabe suponer que los productos más bromados de
    la familia se acumulan aún en mayor medida. No obstante, no se
    dispone de información sobre el decabromo bifenilo, cuya absorción
    es posiblemente escasa.

         Se ha notificado la generación de dibenzofuranos bromados o PBB
    parcialmente debromados como productos de la descomposición térmica
    de los PBB. Su aparición depende de varios factores, como por
    ejemplo la temperatura, el oxígeno, etc.

    1.4  Niveles ambientales y exposición humana

         Tan sólo se dispone de los resultados de un estudio sobre los
    niveles de PBB en la atmósfera. En dicho estudio se determinaron las
    concentraciones de esos productos en las proximidades de tres
    plantas de fabricación o procesamiento de PBB de los Estados Unidos.

         Se analizaron también los niveles alcanzados en las aguas
    superficiales en esas mismas inmediaciones y en el vertedero del
    distrito de Gratiot/Michigan (EE.UU.), al que entre 1971 y 1973
    fueron a parar más de 100 000 kg de desechos, constituidos en un
    60-70% por PBB.

         El análisis de las aguas subterráneas del vertedero del
    distrito de Gratiot reveló la presencia de cantidades ínfimas de PBB
    incluso fuera de la zona del vertedero, pero no se detectaron PBB en
    los pozos de agua de bebida del entorno.

         Se dispone de datos sobre la contaminación del suelo por PBB en
    zonas de fabricación, empleo o evacuación de PBB, así como en los
    suelos de los campos de las granjas de Michigan contaminadas por
    PBB.

         La catástrofe de Michigan sobrevino porque, por inadvertencia,
    se añadió FireMaster(R) al pienso destinado a los animales. No fue
    sino al cabo de casi un año cuando se descubrió el error de mezcla,
    y los análisis efectuados mostraron que el origen del problema eran
    los PBB. Durante ese periodo (verano de 1973 a mayo de 1974), los
    animales contaminados y sus productos se difundieron entre los
    suministros de alimentos para el hombre y en el medio en el estado
    de Michigan. Centenares de granjas se vieron afectadas, y miles de
    animales tuvieron que ser sacrificados y enterrados, al igual que
    hubo que enterrar miles de toneladas de productos agrícolas.

         La mayor parte de los datos disponibles sobre la contaminación
    de la fauna por PBB se refieren a peces y aves de los Estados Unidos
    y Europa, sobre todo aves acuáticas, de las inmediaciones de centros
    industriales, y mamíferos marinos.

         Los últimos estudios sobre la contaminación por PBB de peces,
    mamíferos terrestres y marinos y aves de los Estados Unidos y Europa
    muestran una amplia distribución de esos compuestos. El perfil de
    los PBB hallados en las muestras de pescado es muy distinto del
    hallado en los productos comerciales. Muchos de los picos más
    importantes podrían ser el resultado de la debromación fotoquímica
    del decabromobifenilo (BB 209), hipótesis no confirmada.

         Tras el accidente de Michigan se observaron casos de exposición
    profesional entre los empleados de fábricas de la industria química
    de los Estados Unidos, así como entre los trabajadores agrícolas.
    Los niveles medianos de PBB en suero y tejido adiposo eran mayores
    entre los trabajadores de la industria química. No se dispone de
    información de otros países o compañías sobre la exposición
    profesional asociada a la fabricación, formulación y usos
    comerciales de esos productos.

         Respecto a la mayoría de las poblaciones humanas, no se han
    notificado datos directos sobre la exposición a PBB a partir de
    diversas fuentes. En relación con el caso de Michigan (Estados
    Unidos) se ha notificado la exposición humana masiva resultante del
    contacto directo con pienso contaminado y, sobre todo, del consumo
    de carne, huevos y productos lácteos que contenían PBB. Al menos
    2000 familias (principalmente agricultores y sus vecinos) se vieron
    expuestas a muy altos niveles. Recientemente se han detectado PBB en
    muestras de leche de vaca y leche humana en Alemania.

         El perfil de los PBB de estas muestras difiere del hallado en
    el pescado. Así, la concentración relativa de BB 153 es mayor en la
    leche humana que en el pescado.

         Las vías de exposición de la población general a los PBB no se
    conocen con precisión. A tenor de los conocimientos actuales, el
    aire y el agua ambientales no contienen niveles elevados. Los
    alimentos ricos en lípidos, sobre todo los procedentes de aguas
    contaminadas, son probablemente muy importantes a ese respecto. No
    se dispone de información sobre los niveles de exposición en el aire
    de espacios interiores ni sobre la exposición cutánea a materiales
    con PBB pirorretardantes.

         El perfil de los PBB detectados en la leche humana analizada en
    Alemania era parecido al hallado en la leche de vaca de la misma
    región, pero los niveles detectados en las muestras humanas eran
    considerablemente mayores.

         Son muy pocos los datos disponibles para fundamentar el cálculo
    de la ingesta diaria de PBB a través de los alimentos por parte de
    la población general. Si suponemos que el pescado contiene 20 µg
    PBB/kg de lípido y un 5% de lípidos y que una persona de 60 kg
    consume 100 g de pescado al día, la ingesta resultante es de 0,002
    µg/kg de peso corporal al día. Para esa misma persona, una
    concentración de PBB de 0,05 µg/kg de lípido en la leche (4% de
    lípidos) y un consumo de leche de 500 ml/día determinarían una
    ingesta de PBB de aproximadamente 0,00002 µg/kg de peso corporal al
    día.

         Si suponemos que la leche materna contiene 2 µg PBB/kg de
    lípido, un lactante de 6 kg que consuma 800 ml de esa leche (3,5% de
    lípidos) al día ingerirá 0,01 µg PBB/kg de peso corporal al día.

    1.5  Cinética y metabolismo

         La absorción gastrointestinal de los PBB varía según el grado
    de bromación; así, los compuestos menos bromados se absorben más
    fácilmente.

         La información disponible sobre la absorción de DeBB y
    OcBB/NoBB es insuficiente.

         Los PBB están distribuidos en todas las especies animales y en
    el hombre y alcanzan su mayor concentración de equilibrio en el
    tejido adiposo. También se han hallado niveles relativamente altos
    en el hígado, sobre todo de los PBB más tóxicos, que al
    parecertienden a concentrarse en ese órgano. Los coeficientes de
    reparto de los diversos PBB entre varios tejidos parecen diferir.
    Por lo general se observa una marcada tendencia a la bioacumulación.
    En los mamíferos la transferencia de PBB a la descendencia se
    produce a través de la placenta y de la leche. Se observó que la
    leche humana contenía niveles de 2,2',4,4',5,5'-hexabromobifenilo
    más de 100 veces superiores a los niveles séricos maternos. En un
    estudio realizado sobre varias generaciones de ratas, tras

    administrar PBB a una de las generaciones se observaron residuos
    detectables en más de dos generaciones sucesivas. Los huevos de
    especies aviares también se vieron afectados por el contenido
    corporal materno de PBB.

         Muchos PBB tienden a persistir en los sistemas biológicos. No
    se obtuvieron indicios de un metabolismo o excreción importantes de
    los componentes más abundantes en la mezcla FireMaster(R) ni del
    octa- o decabromobifenilo. Los estudios metabólicos  in vitro
    mostraron que hay relaciones estructura-actividad que explican el
    metabolismo de los PBB. Los microsomas inducidos por FB
    (fenobarbital) sólo metabolizaban los PBB que poseían carbonos
    adyacentes no bromados,  meta y para respecto al puente bifenilo en
    al menos uno de los anillos. La metabolización por microsomas
    inducidos por MC (3-metilcolantreno) estaba condicionada por la
    presencia de posiciones adyacentes  orto y meta no bromadas en al
    menos un anillo del PBB, que debía tener pocos sustituyentes, ya que
    una mayor bromación parecía impedir el metabolismo. Se ha observado
    que, en los vertebrados, los derivados hidroxilados son unos de los
    principales productos del metabolismo,  in vitro e
     in vivo, de los bifenilos menos bromados; la intensidad de la
    transformación metabólica fue relativamente baja. La hidroxilación
    se produce probablemente tanto mediante la generación previa de
    óxidos de hidrocarburos aromáticos como de forma directa.

         El hombre, la rata, el rhesus, el cerdo, la vaca y la gallina
    eliminan los PBB fundamentalmente por las heces. En la mayoría de
    los casos la velocidad de excreción parece ser baja. Las
    concentraciones de 2,2',4,4',5,5'-hexabromobifenilo observadas en la
    bilis y las heces humanas equivalían aproximadamente a entre 1/2 y
    7/10 de los niveles séricos y a aproximadamente el 0,5% de los
    niveles observados en el tejido adiposo. Los tratamientos aplicados
    para facilitar la eliminación de los PBB por los animales o el
    hombre fueron de escasa o nula eficacia. Otra forma de eliminación
    es la excreción a través de la leche.

         Tras la administración de PBB a ratas y otros animales, las
    concentraciones tisulares del producto evolucionaron con el tiempo
    de forma compleja y diversa. Esa evolución se ha descrito mediante
    modelos de varios compartimentos. Se calculó una semivida de
    aproximadamente 69 semanas para la eliminación del
    2,2',4,4',5,5'-hexabromobifenilo de la grasa corporal de la rata. En
    el rhesus se observó una semivida de más de cuatro años. En el
    hombre se calcula que la semivida de ese mismo compuesto oscila como
    promedio entre 8 y 12 años; pero, según lo publicado, ese margen
    podría estar comprendido entre 5 y 95 años. Hay algunas diferencias
    de retención y de recambio entre los distintos PBB. Los resultados
    de los análisis del suero de agricultores y trabajadores de la
    industria química por lo que se refiere al
    2,3',4,4',5-pentabromobifenilo fueron incongruentes, probablemente

    porque las fuentes de exposición eran distintas. Los trabajadores de
    la industria estaban expuestos a todos los componentes de la mezcla
    FireMaster(R), mientras que la población de Michigan estuvo
    expuesta a carne y leche contaminadas por otra combinación de PBB,
    debido a los cambios metabólicos sufridos por los compuestos en los
    animales de trabajo. En un estudio realizado en ratas, los niveles
    de bromo del tejido adiposo no disminuyeron cuando se administró
    octabromobifenilo de calidad técnica. No se dispone de información
    sobre la retención del decabromobifenilo.

         El hombre presenta quizá una mayor tendencia a retener
    determinados PBB que la observada en los animales de
    experimentación. Este factor debería tenerse en cuenta a la hora de
    evaluar los riesgos que entrañan esos productos químicos para la
    salud humana.

         En resumen, todos los datos disponibles indican que los PBB
    presentan una marcada tendencia a la bioacumulación y la
    persistencia. Se metabolizan lentamente, y sus semividas en el
    hombre son del orden de al menos 8 a 12 años.

    1.6  Efectos en los seres vivos del medio ambiente

         Los pocos datos de que se dispone sobre los efectos de los PBB
    en los seres vivos del medio ambiente se refieren a micro
    organismos, pulgas de agua, aves acuáticas y animales de trabajo.

         Se realizó un estudio sobre las aves acuáticas que anidaban en
    las islas del noroeste del lago Michigan para averiguar si los
    contaminantes del medio tenían alguna influencia en su reproduc
    ción. Se determinaron los niveles de 17 contaminantes, incluidos
    diversos PBB, pero al parecer ninguno tenía efectos pronunciados
    sobre la reproducción.

         El ganado de labor que ingirió el pienso que por error contenía
    FireMaster(R) FF-1 en lugar de óxido de magnesio enfermó. El valor
    promedio estimado de la exposición sufrida por las vacas de la
    primera explotación en que se observó una alta contaminación fue de
    250 mg/kg de peso corporal. Los signos clínicos de toxicidad
    consistieron en una reducción del 50% del consumo de pienso
    (anorexia) y una disminución del 40% de la producción de leche,
    manifestaciones observadas algunas semanas después de la ingestión
    del pienso contaminado. Aunque la administración del pienso
    suplementado se interrrumpió a los 16 días, la producción de leche
    no se reanudó. Algunas de las vacas presentaron una mayor frecuencia
    miccional y lacrimación y desarrollaron hematomas, abscesos,
    crecimiento anormal de las pezuñas, cojera, alopecia,
    hiperqueratosis y caquexia; varias murieron menos de seis meses
    después de la exposición. Globalmente, la tasa de mortalidad en esa
    explotación fue de 24/400. Sin embargo, entre los terneros de 6 a 18

    meses la tasa de mortalidad fue mucho más alta: aproximadamente un
    50% murieron al cabo de menos de seis semanas, y sólo dos de 12
    sobrevivieron más de cinco meses. Los animales desarrollaron
    hiperqueratosis por todo el cuerpo. Se observaron también diversos
    problemas relacionados con la reproducción.

         Se han notificado los resultados de las autopsias de algunas de
    las vacas adultas que murieron durante los primeros seis meses tras
    la exposición. Los estudios histopatológicos revelaron alteraciones
    de diverso tipo del hígado y los riñones.

         Varios de los signos clínicos y cambios patológicos señalados
    anteriormente fueron confirmados más tarde mediante estudios
    controlados de administración de pienso (anorexia, deshidratación,
    lacrimación excesiva, emaciación, hiperqueratosis, problemas de
    reproducción, ciertos cambios de los parámetros químicos clínicos y
    lesiones renales).

         Se notificó una caída de la producción y la aparición de
    esterilidad en las manadas afectadas por un bajo nivel de
    contaminación. Esto contrasta con los resultados de unos estudios
    controlados en los que no se halló ninguna diferencia significativa
    entre los rebaños sometidos a una contaminación baja y los rebaños
    testigo.

         Aunque el error que provocó el accidente afectó originalmente
    al pienso del ganado vacuno, el pienso de otros animales también se
    vio afectado por la contaminación cruzada que se produjo, por
    ejemplo, en los mezcladores de las compañías productoras del pienso.
    Probablemente la exposición no llegó a ser tan alta como la del
    ganado vacuno. Se notificó también la contaminación de otros
    animales que fueron igualmente sacrificados (aves de corral, cerdos,
    caballos, conejos, cabras y ovejas), pero sin concretar las
    manifestaciones de la enfermedad.

         No se dispone de información sobre los efectos de los PBB en el
    ecosistema.

    1.7  Efectos en los animales de experimentación y en los sistemas
         de prueba  in vitro

         Las DL50 de las mezclas comerciales administradas por vía
    oral o cutánea muestran un nivel relativamente bajo de toxicidad
    aguda (DL50 > 1 g/kg de peso corporal) en la rata, el conejo y la
    codorniz. En estos casos la muerte y las manifestaciones agudas de
    toxicidad aparecieron con mayor retraso tras la administración de
    PBB. La dosis total administrada determinó el grado de toxicidad, ya
    se tratase de una dosis única, ya de dosis repetidas durante breves

    periodos (hasta 50 días). La toxicidad de los PBB fue mayor cuando
    se administraron varias dosis que cuando se administró una sola
    dosis. Se observa un efecto dilatorio sobre la mortalidad tras la
    exposición a los PBB.

         Los escasos estudios realizados con mezclas comerciales de
    octa- y decabromobifenilo no revelaron ninguna influencia en la
    mortalidad de ratas y peces. Por lo que se refiere al análisis
    individual de los PBB, sólo se han analizado tres hexaisómeros:
    3,3',4,4',5,5'-HxBB, 2,2',4,4',5,5'-HxBB y 2,3',4,4',5,5'-HxBB, el
    último de los cuales es más tóxico para la rata que el anterior. A
    juzgar por los datos limitados de que se dispone, el OcBB y el DeBB
    parecen menos tóxicos que las mezclas de PBB y son peor absorbidos.

         En numerosos estudios sobre los efectos agudos y a corto plazo,
    entre los signos de toxicidad por PBB (sobre todo por FireMaster) se
    ha observado una disminución del consumo de pienso. A dosis letales,
    la muerte no se puede atribuir a la alteración patológica de un
    determinado órgano sino más bien a un «síndrome de emaciación» que
    desarrollan los animales como primera manifes tación de toxicidad.
    En el momento de la muerte la pérdida de peso puede ser de hasta un
    30-40%. Los pocos estudios realizados con OcBB y DeBB de calidad
    técnica no revelaron ningún efecto de ese tipo.

         Los cambios morfológicos e histopatológicos causados por la
    exposición a los PBB afectan sobre todo al hígado. El aumento de
    tamaño de este órgano se produce con frecuencia a dosis inferiores a
    las requeridas para inducir cambios en el peso corporal. En las
    especies roedoras las alteraciones histopatológicas consisten
    principalmente en la hinchazón y vacuolación masivas de los
    hepatocitos, la proliferación del retículo endoplasmático liso y una
    necrosis de células aisladas. La gravedad de las lesiones depende de
    la dosis y del tipo de PBB administrados.

         Se observó una disminución del peso del timo en la rata, el
    ratón y el ganado vacuno tras la exposición a FireMaster(R), pero
    no así a OcBB o DeBB.

         En algunas publicaciones se menciona un aumento del peso de la
    glándula tiroides y cambios histológicos en el tiroides de la rata,
    efectos observados a bajas concentraciones.

         Está demostrado que los distintos PBB difieren en cuanto al
    perfil de toxicidad. Los PBB más tóxicos provocan una disminución
    del peso del timo y/o del organismo y causan cambios histológicos
    pronunciados en el hígado y el timo. Se ha propuesto una
    clasificación de los bifenilos halogenados basada en criterios
    estructurales. La clase 1 abarca los productos de la familia (con
    sus distintos isómeros) que carecen de sustituyentes en posición

    orto (PBB coplanares). La segunda clase abarca los monoderivados con
    sustituyente en posición orto. Los otros PBB (principalmente los que
    poseen dos o más orto-bromos) pertenecen a la tercera clase. Los PBB
    de la clase 1 son los que suelen tener efectos más graves, mientras
    que los productos de la segunda y la tercera clases presentan una
    toxicidad decreciente. Dentro de cada clase la toxicidad depende
    también del grado de bromación.

         En todas las combinaciones analizadas, el PBB más tóxico
    resultó ser el 3,3',4,4',5,5'-HxBB. Este compuesto está presente a
    baja concentración en la mezcla FireMaster(R). De los principales
    componentes de ésta, el más tóxico fue el 2,3,3',4,4',5-HxBB,
    seguido del 2,3',4,4',5,5'-HxBB y el 2,3',4,4',5-PeBB. El principal
    componente de la mezcla FireMaster, el 2,2',4,4',5,5'-HxBB, era
    relativamente atóxico, al igual que el 2,2',3,4,4',5,5'-HpBB,
    segundo componente más abundante.

         La influencia del contenido de los diversos PBB (y de otros
    posibles contaminantes) sobre la toxicidad de las mezclas de calidad
    técnica de OcBB y DeBB no se conoce con tanto detalle.

         Las pruebas habituales de irritación cutánea y ocular y de
    sensibilización efectuadas con las mezclas PBB de calidad técnica
    analizadas (OcBB y DeBB) fueron negativas, o a lo sumo revelaron una
    reacción moderada. No obstante, se observaron hiperqueratosis y
    pérdida de pelaje en el ganado vacuno, y lesiones parecidas al
    cloracne en el rhesus, provocadas en los animales por la ingestión
    de FireMaster(R). Esta mezcla provocó hiperqueratosis en la
    superficie interna de la oreja del conejo, cosa que no ocurrió con
    sus principales componentes (2,2',4,4',5,5'-HxBB y
    2,2',3,4,4',5,5'-HpBB). El fraccionamiento de la mezcla
    FireMaster(R) mostró que la mayor parte de la actividad
    correspondía a las fracciones más polares, que contenían componentes
    minoritarios. La aplicación de HxBB irradiado con luz solar provocó
    una grave hiperqueratosis en la oreja del conejo.

         En trabajos realizados en la rata, la administración prolongada
    de dosis bajas de OcBB de calidad técnica no influyó ni en el
    consumo de pienso ni en el peso corporal, pero se observó un aumento
    del peso relativo del hígado de las ratas expuestas a dosis de 2,5
    mg/kg de peso corporal durante 7 meses. La administración prolongada
    de FireMaster(R) a ratas a dosis de 10 mg/kg de peso corporal
    durante 6 meses no influyó en el consumo de alimento. La
    administración durante 6 meses de dosis de 1 mg/kg de peso corporal
    afectó al peso del hígado. El peso del timo disminuyó en las ratas
    hembras a las que se administraron 0,3 mg/kg de peso corporal. Se
    observaron también cambios histopatológicos. Los estudios
    prolongados y controlados de administración de pienso a ganado

    vacuno expuesto a dosis bajas de FireMaster(R) no pusieron de
    manifiesto ningún efecto adverso por lo que se refiere a ingesta de
    alimentos, signos clínicos, cambios clinicopatológicos o desarrollo
    físico. El visón, el cobayo y el mono parecen más susceptibles a la
    toxicidad por PBB.

         Se han estudiado los efectos a largo plazo provocados en la
    rata por los PBB retenidos tras la exposición pre- o perinatal a
    dosis altas de FireMaster(R).

         Los efectos adversos más frecuentes sobre la reproducción
    fueron los embarazos malogrados o perdidos y la disminución de la
    viabilidad de la descendencia. Se observaron aún ciertos efectos en
    el visón a concentraciones de 1 mg/kg de alimento. Se observó
    también una disminución de la viabilidad de la descendencia de
    rhesus expuestos durante 12,5 meses a FireMaster(R) (0,3 mg/kg de
    alimento). Los monos recibieron una dosis diaria de 0,01 mg/kg de
    peso corporal y una dosis total de 3,8 mg/kg de peso corporal. Los
    resultados de los estudios sobre reproducción y neurología del
    comportamiento realizados con monos y ratas expuestos a dosis bajas
    no pudieron ser evaluados debido a que la información aportada en
    los artículos publicados acerca del diseño de los experimentos era
    insuficiente. Se observó un débil efecto teratógeno en experimentos
    realizados con roedores, a dosis elevadas que podrían haber causado
    una cierta toxicidad en la madre.

         Los PBB interaccionan con el sistema endocrino. En la rata y el
    cerdo se observaron disminuciones dosis-dependientes de la tiroxina
    y la triyodotironina séricas. También se ha notificado que los PBB
    alteran los niveles de las hormonas esteroides en la mayoría de los
    casos. La intensidad del efecto depende de la especie, así como de
    la dosis y la duración del tratamiento.

         Los PBB provocan porfiria en la rata y en el ratón macho a
    dosis de sólo 0,3 mg/kg de peso corporal al día. El nivel sin efecto
    fue de 0,1 mg/kg de peso corporal al día. Se observó una pronunciada
    influencia de los PBB sobre la acumulación de vitamina A, así como
    efectos sobre el metabolismo intermediario.

         Una observación frecuente tras la exposición a PBB fue la
    atrofia del timo, y se han observado también efectos en otros
    tejidos linfoides. Se ha demostrado asimismo la existencia de otros
    signos de depresión de la función inmunitaria en respuesta a la
    mezcla FireMaster(R). No hay datos disponibles sobre los OcBB,
    NoBB y DeBB ni sobre PBB particulares.

         Uno de los efectos más estudiados de los PBB es la inducción
    que provocan de las enzimas de actividad oxidasa de función mixta
    (MFO). Como era de esperar, se descubrió que FireMaster(R) era un
    inductor de tipo mixto de las enzimas microsómicas hepáticas tanto

    en la rata como en todas las demás especies animales estudiadas.
    Este fenómeno de inducción se observó también en menor medida en
    otros tejidos. La capacidad de inducción de las enzimas microsómicas
    hepáticas variaba de un PBB a otro; no obstante, se han descubierto
    correlaciones entre su estructura y la actividad de inducción de las
    enzimas microsómicas.

         Varios estudios han puesto de manifesto que los PBB pueden
    modificar la actividad biológica de diversos fármacos y sustancias
    tóxicas. Esto se debe quizá en parte a la capacidad de los PBB para
    inducir las enzimas microsómicas implicadas en la activación o
    desactivación de los productos xenobióticos.

         Se observó que FireMaster(R) y algunos de sus principales
    componentes podían inhibir la comunicación intercelular in vitro;
    esta inhibición se produce a concentraciones no citotóxicas. Tanto
    la citotoxicidad como las propiedades de inhibición de la
    cooperación metabólica parecen guardar relación con la estructura de
    los PBB, concretamente con la presencia o ausencia de sustituyentes
    en posición orto.

         Los ensayos realizados  in vitro e  in vivo (mutagénesis de
    células microbianas y de mamífero, lesiones cromosómicas de células
    de mamífero, transformación de células de mamífero, lesión y
    reparación del ADN) no han revelado ningún tipo de mutagenicidad o
    genotoxicidad causadas por PBB particulares o por mezclas
    comerciales de los mismos.

         Los estudios de toxicidad prolongados han revelado que el
    principal órgano de manifestación de los efectos carcinógenos de los
    PBB es el hígado. La incidencia de carcinoma hepatocelular aumentó
    significativamente en las ratas y los ratones machos y hembras a los
    que se administró la mezcla FireMaster(R) por vía oral. Se han
    notificado efectos carcinógenos en el hígado de ratones sometidos a
    dietas que contenían Bromkal 80-9D (nonabromobifenilo de calidad
    técnica) a dosis de 100 mg/kg (5 mg/kg de peso corporal al día) o
    más durante 18 meses. La dosis más baja de PBB que produjo tumores
    (fundamentalmente adenomas) en los roedores fue de 0,5 mg/kg de peso
    corporal al día durante 2 años. Las ratas que recibieron 0,15 mg/kg
    de peso corporal al día además de la exposición pre- y perinatal no
    sufrieron ningún efecto adverso. No se ha estudiado la
    carcinogenicidad del octabromobifenilo y el decabromobifenilo de
    calidad técnica.

         En un bioensayo realizado sobre la piel del ratón no se observó
    ninguna actividad de iniciación tumoral (usando
    12-O-tetradecanoilforbol-13-acetato (TPA) como agente activador) o
    activación tumoral (usando 7,12-dimetil-benz(a)antraceno (DMBA) como
    iniciador) por parte de FireMaster BP-6 o del 2,2',4,4',5,5'-

    hexabromobifenilo. Sin embargo, en otros modelos basados en la piel
    del ratón (en los que se empleó DMBA o DN-metil- N'-nitro-
     N-nitroso-guamidina (MNNG) como iniciadores), FM FF-1 y el
    3,3',4,4',5,5'-hexabromobifenilo, pero no así el 2,2',4,4',5,5'-
    hexabromobifenilo, tuvieron efecto como activadores tumorales. En un
    bioensayo de dos fases realizado con hígado de rata usando
    fenobarbital como activador, el 3,3',4,4'-tetrabromobifenilo mostró
    una débil actividad iniciadora. En el modelo de dos fases utilizado
    con el hígado de rata, con empleo de dietilnitrosamina y
    hepatectomía parcial, la mezcla FM, el 3,3',4,4'-tetrabromobifenilo
    y el 2,2',4,4',5,5'-hexabromobifenilo, pero no así el
    3,3',4,4',5,5'-hexabromobifenilo, tuvieron efecto como activadores
    tumorales.

         Los resultados de los estudios sobre la comunicación celular,
    los resultados negativos de los estudios de genotoxicidad y
    mutagenicidad y los resultados de los ensayos de activación tumoral
    indican que las mezclas y los miembros de la familia estudiados
    provocan cáncer por mecanismos epigenéticos. No se dispone de
    información sobre los octa-, nona-, o decabromo bifenilos de calidad
    técnica.

         Se desconocen los mecanismos de acción subyacentes a las
    numerosas manifestaciones de toxicidad de los PBB y de otros
    compuestos relacionados. No obstante, algunos de los efectos, como
    el síndrome de emaciación, la atrofia del timo, la hepatotoxicidad,
    los trastornos cutáneos y la toxicidad sobre el sistema reproductor
    podrían guardar relación con la interacción con el llamado receptor
    Ah- o TCDD, que alteraría la expresión de una serie de genes. Los
    distintos PBB difieren en lo que respecta a esa interacción con el
    receptor, y en ese sentido los coplanares son más activos.

         Muchos de los efectos de los PBB se observan sólo después de
    una exposición prolongada. La razón podría ser la marcada
    acumulación de algunos de ellos y la escasa capacidad del organismo
    para metabolizarlos y eliminarlos. Ello determina la progresiva
    concentración del producto en el organismo; los mecanismos de
    compensación se ven desbordados y aparecen los efectos adversos.

         Algunos naftalenos polibromados (PBN), que se sabe son
    contaminantes de FireMaster(R), tienen potentes efectos tóxicos y
    teratógenos. Las concentraciones de PBN presentes en esa mezcla son
    bajas, pero es posible que contribuyan a su toxicidad.

         Los estudios realizados sobre la mezcla FireMaster(R) y su
    principal componente, el 2,2',4,4',5,5'-HxBB, mostraron que los
    productos de fotólisis eran más tóxicos que el PBB original. Los
    productos de la pirólisis de FM causaron la inducción del sistema
    enzimático MFO, pérdida de peso corporal y atrofia tímica. Los
    productos de pirólisis del OcBB de calidad técnica provocaron un
    aumento del tamaño del hígado.

    1.8  Efectos en el hombre

         No había ningún ejemplo de toxicosis aguda por PBB en el hombre
    con el que poder comparar los efectos potenciales de las bajas
    exposiciones que siguieron a la intoxicación accidental acaecida en
    Michigan (Estados Unidos) en 1973. Los principales estudios
    epidemiológicos fueron realizados por el Departamento de Salud
    Pública de Michigan (MDPH) y el Laboratorio de Ciencias del Medio
    Ambiente (ESL) de la Facultad de Medicina Mount Sinai de Nueva York.

         Se calculó que las personas más expuestas habían consumido
    entre 5 y 15 g de PBB durante un periodo de 230 días a través de la
    leche. Podría haberse producido una cierta exposición adicional a
    través de la carne. La exposición de algunos de los agricultores y
    de la mayoría de la población general de Michigan fue mucho menor:
    9-10 mg de exposición total. No obstante, algunas de estas últimas
    personas podrían haber recibido una dosis total de aproximadamente
    800-900 mg. (Una dosis total de 9 mg corresponde a 0,15 mg/kg de
    peso corporal, y 900 mg, a 15 mg/kg de peso corporal, cifras
    referidas a un adulto de 60 kg de peso como valor promedio; la
    dosis/kg de peso corporal sería mayor en los niños).

         En 1974, en el primer estudio llevado a cabo por el MDPH se
    procedió a comparar el estado de salud de las personas de las
    granjas sometidas a cuarentena con el de las personas de las
    explotaciones no sometidas a cuarentena de la misma zona. Los dos
    grupos declararon diversos síntomas, pero no se observó ninguna
    diferencia entre ambos. No se detectaron alteraciones inhabituales
    del corazón, hígado, bazo, sistema nervioso, orina, sangre o
    cualquiera de los otros parámetros médicos examinados. En un estudio
    completo llevado a cabo más adelante por el MDPH, que abarcaba
    grupos sometidos a distintos niveles de exposición, no se observó
    relación alguna entre las concentraciones séricas de PBB y la
    incidencia de los síntomas o enfermedades notificados. En los
    estudios del ESL se examinó aproximadamente a 990 residentes de las
    explotaciones agrícolas, a 55 trabajadores de la industria química y
    a un grupo de trabajadores de la industria láctea que fueron
    utilizados como testigos. La incidencia de síntomas entre los
    agricultores de Michigan fue mayor que la hallada entre los
    agricultores de Wisconsin. Las mayores diferencias fueron las
    observadas dentro del amplio apartado de síntomas neurológicos y
    musculoesqueléticos. En los agricultores de Michigan se halló una
    mayor prevalencia de aumentos de las concentraciones séricas de
    algunos antígenos carcinoembrionarios y enzimas hepáticas que en los
    agricultores de Wisconsin. Los trabajadores de la industria química
    presentaron una mayor prevalencia de síntomas torácicos y cutáneos y
    una menor prevalencia de síntomas musculoesqueléticos que los
    agricultores. Aunque la interpretación de los resultados de los
    estudios del ESL divergió en ocasiones de la de otros resultados de

    estudios comparables, hubo un aspecto en que los datos coincidieron:
    ninguno de los estudios puso de manifiesto una relación dosis-
    respuesta positiva entre los niveles de PBB en el suero o el tejido
    adiposo y la prevalencia de síntomas o trastornos clínicos. Se
    investigaron varios aspectos clínicos mediante estudios especiales
    más detallados. En uno de ellos, el examen del sistema neurológoco
    mediante pruebas funcionales objetivas reveló una correlación
    negativa entre los niveles séricos de PBB y los resultados de las
    pruebas funcionales, sobre todo entre los varones de los grupos de
    edad avanzada. Los otros estudios no mostraron ninguna relación
    entre las concentraciones de PBB en el suero o la grasa y la
    actividad funcional determinada mediante una batería de pruebas en
    las que se analizaron la memoria, fuerza motora, coordinación,
    percepción corticosensorial, personalidad, funciones cognitivas
    superiores y otro tipo de funciones. Se examinaron los aspectos
    pediátricos de la exposición a PBB en algunas de las familias
    estudiadas por el ESL. Se notificaron numerosos síntomas, pero la
    exploración física no reveló ningún trastorno objetivo que pudiera
    atribuirse a los PBB. Hubo opiniones discrepantes acerca de los
    efectos neuropsicológicos en la descendencia, más sutiles, y los
    resultados de las investigaciones sobre los signos de desarrollo de
    las capacidades siguen siendo objeto de polémica. Lo mismo ocurre
    con la investigación sobre los linfocitos y la función inmunitaria.
    Algunos autores no hallaron ninguna diferencia numérica o funcional
    entre los linfocitos de los grupos que presentaban niveles altos y
    bajos de PBB en el suero, mientras que otros autores detectaron una
    disminución significativa de las subpoblaciones de linfocitos T y B
    en aproximadamente un 40% del grupo expuesto de Michigan en
    comparación con los grupos no expuestos, así como trastornos de la
    función linfocitaria, concretamente una menor respuesta a los
    mitógenos.

         El análisis de los estudios epidemiológicos realizados muestra
    que se ha procurado evaluar la relación entre la exposición a PBB y
    un elevado número de efectos adversos, incluidos efectos sobre la
    conducta y trastornos subjetivos. No obstante, la mayoría de esos
    estudios adolecen de fallos graves de diseño pues introducen
    imprecisiones que hacen difícil, por no decir imposible, extraer
    conclusiones acerca de la relación entre la exposición a PBB y los
    posibles efectos sobre la salud. Además, el seguimiento no se ha
    prolongado lo necesario para poder evaluar los posibles efectos
    carcinógenos.

         Se identificó a dos pequeños grupos de trabajadores que habían
    sufrido exposición ocupacional a una mezcla de PBB o a DeBB y
    decabromobifenilóxido. Se observaron lesiones parecidas al cloracne
    en el 13% de los trabajadores expuestos a la mezcla de PBB, lesiones
    ausentes en cambio en los trabajadores expuestos al DeBB. No
    obstante, en este último grupo se observó una prevalencia
    significativamente mayor de hipotiroidismo.

    1.9  Evaluación global de la toxicidad y carcinogenicidad

         El único estudio realizado con una mezcla de PBB y prolongado
    durante todo el ciclo de vida fue el bioensayo llevado a cabo hace
    poco con ratas y ratones en el marco del Programa Nacional de
    Toxicología (NTP) de los Estados Unidos. La dosis más baja con
    efectos carcinógenos fue de 0,5 mg/kg de peso corporal al día
    (tumores hepáticos en roedores). En otros estudios realizados al
    efecto se observó una respuesta carcinógena con 3 mg/kg de peso
    corporal al día administrados durante 6 meses. El estudio prolongado
    durante 6 meses demuestra que una exposición a dosis análogas
    limitada a parte del ciclo de vida tiene también efectos adversos
    similares. A dosis inferiores se observan efectos sobre el sistema
    reproductor en los primates y el visón.

         Además, en el estudio llevado a cabo durante 2 años por el NTP
    con ratas, una dosis diaria de 0,15 mg/kg de peso corporal al día y
    la exposición prenatal y perinatal de la madre a 0,05 mg/kg de peso
    corporal al día no provocó ningún efecto adverso. Así pues, la
    ingesta diaria total a partir de los alimentos, el agua, el aire y
    el suelo debería ser inferior a 0,15 µg/kg de peso corporal al día,
    cifra extrapolada del NOAEL (nivel sin efectos adversos observados)
    observado en un estudio de carcinogenicidad que arrojó resultados
    positivos, usando un factor de incertidumbre (seguridad) de 1000,
    dado que estos compuestos probablemente producen cáncer por un
    mecanismo epigenético.

         Se calculó que la dosis total recibida por la subpoblación de
    Michigan había sido de entre 0,15 y 15 mg/kg de peso corporal
    durante un periodo de 230 días. Para esa población, la división de
    esas dosis por el valor promedio de la duración de la vida del ser
    humano arrojaría una cifra equivalente a una dosis diaria de entre 6
    ng y 0,6 µg/kg de peso corporal al día.

         Se ha calculado una ingesta total de 2 ng PBB/kg de peso
    corporal al día, de fuentes conocidas, para los adultos de la
    población general, y de 10 ng/kg de peso corporal al día para los
    lactantes alimentados con leche materna. No debe olvidarse que estos
    cálculos están basados en datos de carácter muy limitado y regional.

         Estos cálculos se basan en el supuesto de que durante el ciclo
    de vida los PBB no alcanzan un estado estacionario, y de que una
    exposición alta y breve equivale a una exposición baja y prolongada,
    toda vez que estos compuestos son metabolizados y excretados con
    suma lentitud.

         La información disponible sobre los OcBB, NoBB, y DeBB no es
    suficiente para poder calcular una ingesta diaria total carente de
    efectos adversos.

    2.  Conclusiones

         La mayoría de los PBB presentes en los pirorretardantes
    comerciales son lipofílicos, persistentes y bioacumulables. Estos
    compuestos tienden a concentrarse en las tramas alimentarias del
    medio y suponen una amenaza, especialmente para los organismos que
    ocupan los niveles superiores de esas tramas. Además, en caso de
    combustión, algunos PBB generan dibenzofuranos polibromados tóxicos.

         Aparte de las emisiones que se producen durante su fabricación
    y empleo, los PBB pasan al medio como consecuencia del uso
    generalizado de pirorretardantes. Debido a la gran estabilidad de
    los PBB, una parte considerable de ellos alcanza en un momento u
    otro el medio.

         También se detectan PBB en muestras ambientales o humanas de
    lugares alejados de los focos conocidos. El perfil de PBB de las
    muestras del medio no se corresponde con el hallado en los productos
    de uso industrial, lo que indica que éstos sufren transformaciones
    en el medio ambiente, posiblemente como resultado de una debromación
    fotoquímica.

         Se dispone actualmente de muy poca información sobre el grado
    de exposición de la población general a los PBB. No obstante, en los
    pocos casos en que se determinaron sus niveles se descubrieron
    cantidades ínfimas. En la actualidad, ese nivel de exposición no
    resulta preocupante, pero deberá evitarse que prosiga la
    acumulación. Los datos sobre las personas afectadas en Michigan
    indican que en este caso las exposiciones fueron varios órdenes de
    magnitud superiores a la de la población general. No se han
    observado efectos concluyentes sobre la salud atribuibles a la
    exposición a PBB en la población de Michigan, pero el periodo de
    seguimiento no ha sido lo suficientemente dilatado para descartar la
    aparición de cáncer. Los niveles de PBB en el tejido adiposo y el
    suero de la población de Michigan siguen siendo altos, por lo que la
    exposición interna continúa. Por el contrario, sí se observó la
    aparición de toxicidad en el ganado vacuno de Michigan. Esta
    discrepancia se explica por el diferente grado de exposición del
    ganado.

         Sólo se han estudiado casos de exposición profesional en dos
    fábricas de los Estados Unidos. Parece que los trabajadores que
    producen PBB pueden desarrollar lesiones parecidas al cloracne, y
    los expuestos a DeBB, hipotiroidismo. No se han realizado estudios
    sobre los trabajadores que incorporan deca- u octa-/nona-
    bromobifenilo en productos comerciales.

         Los PBB persisten durante mucho tiempo en los organismos vivos,
    y se ha demostrado que producen toxicidad crónica y cáncer en los
    animales. Así, se indujo cáncer a una dosis de 0,5 mg/kg de peso

    corporal al día, pese a la baja toxicidad aguda asociada a esa
    dosis, y el nivel sin efectos observados fue de 0,15 mg/kg de peso
    corporal al día. Se han observado diversos efectos tóxicos crónicos
    en animales de experimentación tras la exposición prolongada a dosis
    de aproximadamente 1 mg/kg de peso corporal al día.

    3.  Recomendaciones

    3.1  Recomendaciones generales

         El Grupo Especial de Trabajo considera que el hombre y el medio
    ambiente no deben verse expuestos a los PBB, habida cuenta de su
    elevada persistencia y bioacumulación y de los efectos adversos que
    pueden aparecer tras la exposición prolongada a muy bajos niveles.
    Por consiguiente, deberá interrumpirse todo uso comercial de los
    PBB.

         Respecto al DeBB y el OcBB, teniendo en cuenta los escasos
    datos sobre su toxicidad, su extrema persistencia y su posible
    degradación en el medio ambiente, así como la mayor toxicidad de los
    compuestos persistentes generados durante la combustión, no deberán
    ser empleados comercialmente, a menos que se demuestre su inocuidad.

         Es sabido que se siguen formulando observaciones sobre la
    cohorte de Michigan, información que convendría fuese publicada.

    3.2  Futuras investigaciones

         La futura vigilancia de los PBB en el hombre y en el medio,
    incluida la vigilancia en el lugar de trabajo en las industrias de
    fabricación o uso de esos productos, deberá ampliarse, deberá
    centrarse en PBB específicos, y deberá incluir los OcBB/NoBB y DeBB.
    Es preciso incorporar también estos compuestos en los programas en
    curso de vigilancia de otros productos halogenados. La evolución
    temporal y la distribución geográfica de los niveles de PBB en el
    medio ambiente deberán seguir siendo objeto de vigilancia. Habrá que
    controlar también la liberación de PBB en el medio a partir de los
    lugares de evacuación de desechos.

         Deberán efectuarse experimentos de termólisis mediante la
    simulación de fuegos accidentales y la incineración municipal.
    Conviene realizar nuevas investigaciones sobre los mecanismos de
    toxicidad y carcinogenicidad de los PBB y de otros compuestos
    relacionados. Los PBB podrían servir como modelo para el estudio de
    esos mecanismos, y en las investigaciones al efecto deberán
    emplearse PBB purificados.

         Los efectos de los PBB sobre la reproducción no están bien
    dilucidados. Por consiguiente, deberán realizarse estudios bien
    diseñados y prolongados sobre los efectos de las dosis bajas en la
    reproducción, usando para ello una especie vulnerable.

         Es preciso disponer también de más información sobre la
    biodisponibilidad y toxicocinética de los OcBB/NoBB y DeBB, así como
    de determinados productos de la misma familia.
    See Also:
       Toxicological Abbreviations
       Polybrominated Biphenyls  (IARC Summary & Evaluation, Supplement7, 1987)
       Polybrominated Biphenyls  (IARC Summary & Evaluation, Volume 18, 1978)
       Polybrominated Biphenyls (IARC Summary & Evaluation, Volume 41, 1986)