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
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venture of the United Nations Environment Programme, the International
Labour Organisation, and the World Health Organization. The main
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carried out by the IPCS include the development of know-how for coping
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 identifica