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    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY







    ENVIRONMENTAL HEALTH CRITERIA 205





    POLYBROMINATED DIBENZO-p-DIOXINS AND DIBENZOFURANS


    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 C. Melber and Dr J. Kielhorn, Fraunhofer
    Institute of 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, and produced within the framework of the
    Inter-Organization Programme for the Sound Management of Chemicals.



              World Health Organization
              Geneva, 1998

         The International Programme on Chemical Safety (IPCS),
    established in 1980, is a joint venture of the United Nations
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    WHO Library Cataloguing in Publication Data

    Polybrominated dibenzo- p-dioxins and dibenzofurans.

         (Environmental health criteria ; 205)

         1.Dioxins                     2.Benzofurans
         3.Environmental exposure      4.Occupational exposure
         I.International Programme on Chemical Safety      II.Series

         ISBN 92 4 157205 1            (NLM Classification: QD 405)
         ISSN 0250-863X

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    CONTENTS

    ENVIRONMENTAL HEALTH CRITERIA FOR POLYBROMINATED DIBENZO- p-DIOXINS
    AND DIBENZOFURANS

    PREAMBLE

    ABBREVIATIONS

    1. SUMMARY

         1.1. Identity, physical and chemical properties,
              and analytical methods
         1.2. Formation and sources of human and
              environmental exposure
         1.3. Environmental transport, distribution,
              and transformation
         1.4. Environmental levels and human exposure
         1.5. Kinetics and metabolism
         1.6. Effects on laboratory mammals and  in vitro
              test systems
         1.7. Effects on humans
         1.8. Effects on other organisms in the laboratory
              and field

    2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND ANALYTICAL
         METHODS

         2.1. Identity
         2.2. Physical and chemical properties
              2.2.1. Appearance, melting and boiling
                        points, water solubility, vapour pressure,
                        octanol/water partition coefficient,
                        and sorption coefficient
              2.2.2. Stability of PBDDs/PBDFs
                        2.2.2.1   Photolysis
                        2.2.2.2   Thermolytic degradation
                                  of PBDDs/PBDFs
              2.2.3. Chemical reactions

         2.3. Conversion factors
         2.4. Analytical methods
              2.4.1. General aspects
              2.4.2. Sampling and extraction
                        2.4.2.1   Ambient air, airborne dust,
                                  automobile exhaust, flue gas,
                                  and products of thermolysis
                        2.4.2.2   Water and aqueous samples
                        2.4.2.3   Environmental samples: soil,
                                  sediment, and sewage sludge
                        2.4.2.4   Flame retardants, polymers,
                                  fly ash samples, dust, soot,
                                  and fire residues

                        2.4.2.5   Biological matrices: human
                                  milk, blood/plasma, tissues,
                                  and fish samples
              2.4.3. Sample clean-up
              2.4.4. Separation
              2.4.5. Detection, quantification, and confirmation
                        of PBDDs/PBDFs by MS techniques
              2.4.6. The need for analysis of
                        2,3,7,8-substituted congeners
              2.4.7. Interfering substances
              2.4.8. Standards

    3. FORMATION AND SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

         3.1. Synthesis and use
         3.2. By-products of brominated organic chemicals
              (including flame retardants)
         3.3. Formation from the photochemical degradation
              of brominated organic chemicals
         3.4. Formation from the laboratory thermolysis of
              bromine-containing flame retardants
         3.5. Formation during production of plastic materials
              and presence in consumer products containing
              flame retardants
              3.5.1. Formation during production processes
              3.5.2. Presence in resins and polymer products
         3.6. Emissions from flame-retarded consumer products
         3.7. Presence in fire residues, smoke condensates,
              and gases after fires
              3.7.1. Experimental fires
              3.7.2. Accidental fires
         3.8. Formation from incineration of fuels
         3.9. Formation during waste disposal and treatment
              3.9.1. Incineration
              3.9.2. Disposal
              3.9.3. Recycling
                   3.9.3.1   Plastics
                   3.9.3.2   Metals
         3.10. Presence in automotive exhaust
         3.11. Formation during textile processing

    4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

         4.1. Transport and distribution between media
              4.1.1. Air
              4.1.2. Water and sediments
              4.1.3. Soil
              4.1.4. Biota
         4.2. Environmental transformation
              4.2.1. Photochemical degradation
              4.2.2. Microbial degradation
         4.3. Bioaccumulation and biomagnification

    5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

         5.1. Environmental levels
              5.1.1. Air
                   5.1.1.1   Ambient air
                   5.1.1.2   Indoor air
              5.1.2. Water and sediment
              5.1.3. Soil, sewage sludge, and biocompost
              5.1.4. Food and feed
              5.1.5. Other products
              5.1.6. Terrestrial and aquatic organisms
                   5.1.6.1   Plants
                   5.1.6.2   Animals
         5.2. General population exposure
              5.2.1. Exposure data
              5.2.2. Monitoring of human tissues and fluids
         5.3. Occupational exposure
              5.3.1. Workplace monitoring data
                   5.3.1.1   Flame retardant/polymer industry
                   5.3.1.2   Offices/studios
                   5.3.1.3   Recycling plants
                   5.3.1.4   Other workplaces
              5.3.2. Monitoring of human tissues and fluids

    6. KINETICS AND METABOLISM

         6.1. Absorption
              6.1.1. Dibenzo- p-dioxins
              6.1.2. Dibenzofurans
         6.2. Distribution
              6.2.1. Levels in organs and blood
                   6.2.1.1   Dibenzo- p-dioxins
                   6.2.1.2   Dibenzofurans
              6.2.2. Transfer to offspring
         6.3. Metabolic transformation
              6.3.1. Dibenzo- p-dioxins
              6.3.2. Dibenzofurans
         6.4. Elimination and excretion
              6.4.1. Dibenzo- p-dioxins
              6.4.2. Dibenzofurans
         6.5. Retention and turnover
              6.5.1. Animal studies
              6.5.2. Human studies

    7. EFFECTS ON LABORATORY MAMMALS AND  IN VITRO TEST SYSTEMS

         7.1. Single exposure
              7.1.1. Dibenzo- p-dioxins
              7.1.2. Dibenzofurans
              7.1.3. Remarks on the lethality of PBDDs/PBDFs
         7.2. Short-term exposure
              7.2.1. Dibenzo- p-dioxins
              7.2.2. Dibenzofurans

         7.3. Long-term exposure
         7.4. Skin and eye irritation, sensitization, dermal
              lesions, and acne
         7.5. Reproductive and developmental toxicity
              7.5.1. Reproductive toxicity
              7.5.2. Developmental toxicity
         7.6. Mutagenicity and related end-points
         7.7. Carcinogenicity
              7.7.1. Short-term studies
              7.7.2. Long-term studies
         7.8. Other special studies
              7.8.1. Immunotoxicity
                   7.8.1.1   Dibenzo- p-dioxins
                   7.8.1.2   Dibenzofurans
              7.8.2. Effects on intermediary metabolism:
                        Porphyrin effects
              7.8.3. Effects on vitamin A storage
              7.8.4. Endocrine interactions
              7.8.5. Interaction with drugs and toxicants
              7.8.6. Induction of microsomal enzymes
                   7.8.6.1   Dibenzo- p-dioxins
                   7.8.6.2   Dibenzofurans
                   7.8.6.3   Combustion products
         7.9. Mechanisms of toxicity -- mode of action
         7.10. Experimental data on selected PBDDs/PBDFs
              and their relevance to the toxicity equivalency
              factor (TEF) concept

    8. EFFECTS ON HUMANS

         8.1. General population exposure
         8.2. Occupational/accidental exposure
         8.3. Subpopulations at special risk

    9. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD

    10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE
         ENVIRONMENT

         10.1. Hazard evaluation
         10.2. Exposure evaluation
         10.3. Risk evaluation

    11. CONCLUSIONS AND RECOMMENDATIONS FOR PROTECTION OF HUMAN HEALTH
         AND THE ENVIRONMENT

         11.1. Conclusions
         11.2. Recommendations

    12. FURTHER RESEARCH

    13. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

    REFERENCES

    APPENDICES

    RÉSUMÉ

    RESUMEN
    

    NOTE TO READERS OF THE CRITERIA MONOGRAPHS


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         This publication was made possible by grant number 5 U01
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    Environmental Health Criteria

    PREAMBLE

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    FIGURE 1


    WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR POLYBROMINATED
    DIBENZO- p- DIOXINS AND DIBENZOFURANS

     Members

    Dr A.P.J.M. de Jong, Laboratory of Organic Analytical Chemistry,
    National Institute of Public Health and Environment, Bilthoven, The
    Netherlands

    Ms J. Diliberto, National Health and Environmental Effects
    Research Laboratory, Experimental Toxicology Division, US
    Environmental Protection Agency, Research Triangle Park, North
    Carolina, USA

    Dr M. Feeley, Toxicology Evaluation Section, Bureau of Chemical
    Safety, Health Canada, Tunney's Pasture, Ottawa, Ontario, Canada
     (Rapporteur)

    Dr H. Fiedler, Bayerisches Institut für Abfallforschung BIFA
    GmbH, Augsburg, Germany

    Professor B. Jansson, Institute of Applied Environmental Research,
    Stockholm University, Stockholm, Sweden  (Chairman)

    Dr Y. Kurokawa, Biological Safety Research Center, National
    Institute of Health Sciences, Tokyo, Japan

    Dr C. Melber, Fraunhofer Institute for Toxicology and Aerosol
    Research, Hanover, Germany

    Professor D. Neubert, Institute for Clinical Pharmacology and
    Toxicology, Berlin, Germany

    Professor C. Rappe, Institute of Environmental Chemistry,
    University of Umea, Umea, Sweden

     Observer

    Dr B. Schatowitz, Environmental and Trace Analysis Consumer
    Care Division, Ciba-Geigy AG, Basel, Switzerland (Representing the
    European Centre for Ecotoxicology and Toxicology of Chemicals)


     Secretariat

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

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

    Dr I. Mangelsdorf, Fraunhofer Institute for Toxicology and Aerosol
    Research, Hanover, Germany

    Dr F.X.R. van Leeuwen, Chemical Safety, European Centre for
    Environment and Health, Bilthoven Division, De Bilt, The Netherlands

    ENVIRONMENTAL HEALTH CRITERIA FOR POLYBROMINATED DIBENZO- p-DIOXINS
    AND DIBENZOFURANS

         A WHO Task Group on Environmental Health Criteria for
    Polybrominated Dibenzo- p-dioxins and Dibenzofurans met at the
    Fraunhofer Institute for Toxicology and Aerosol Research, Hanover,
    Germany from 11 to 15 November 1996. Professor U. Heinrich opened the
    meeting and welcomed the participants on behalf of the host institute.
    Dr H. Galal-Gorchev, IPCS, welcomed the participants on behalf of the
    Director, IPCS, and the three IPCS cooperating organizations
    (UNEP/ILO/WHO). The Task Group reviewed and revised the draft criteria
    monograph and made an evaluation of the risks for human health and the
    environment from exposure to polybrominated dibenzo- p-dioxins and
    dibenzofurans.

         Dr J. Kielhorn and Dr C. Melber, Fraunhofer Institute for
    Toxicology and Aerosol Research, Hanover, Germany, prepared the first
    draft of this monograph. They also prepared the second draft,
    incorporating comments received following the circulation of the first
    draft to the IPCS Contact Points for Environmental Health Criteria
    monographs.

         Dr H. Galal-Gorchev, IPCS Central Unit, was responsible for the
    overall scientific content and Ms M. Sheffer, Scientific Editor,
    Ottawa, Canada, for the linguistic editing.

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

    ABBREVIATIONS

    ABS                 acrylonitrile-butadiene-styrene
    Ah                  aromatic hydrocarbon
    AHH                 arylhydrocarbon hydroxylase
    BB                  bromobiphenyl
    BDE                 bromodiphenyl ether
    CAS                 Chemical Abstracts Service
    CYP                 cytochrome P-450
    DBB/decaBB          decabromobiphenyl
    DBDE/decaBDE        decabromodiphenyl ether
    DD/DF               dibenzo- p-dioxin/dibenzofuran
    DiBDD               dibromodibenzo- p-dioxin
    DiBDF               dibromodibenzofuran
    DiXDF               mixed dihalogenated dibenzofuran
    EC50                median effective concentration
    ED50                median effective dose
    EI-SIM-MS           electron impact-selective ion monitoring-mass
                        spectrometry
    EPA                 Environmental Protection Agency (USA)
    EROD                ethoxyresorufin- O-deethylase
    GC                  gas chromatography
    HexaBB              hexabromobiphenyl
    HIPS                high-impact polystyrene
    HpBDD/heptaBDD      heptabromodibenzo- p-dioxin
    HpBDF/heptaBDF      heptabromodibenzofuran
    HPLC                high-performance liquid chromatography
    HRGC                high-resolution gas chromatography
    HRMS                high-resolution mass spectrometry
    HxBDD/hexaBDD       hexabromodibenzo- p-dioxin
    HxBDF/hexaBDF       hexabromodibenzofuran
    HxCDD/hexaCDD       hexachlorodibenzo- p-dioxin
    I-TEF               international toxicity equivalency factor
    I-TEQ               international toxic equivalent
    LD50                median lethal dose
    LOAEL               lowest-observed-adverse-effect level
    LOEL                lowest-observed-effect level
    MI-IR               matrix isolation infrared spectrometry
    MoBDD/monoBDD       monobromodibenzo- p-dioxin
    MoBDF/monoBDF       monobromodibenzofuran
    MS                  mass spectrometry
     n                   sample size
    NCI                 negative ion chemical ionization
    n.d.                not detected
    NOAEL               no-observed-adverse-effect level
    NOEL                no-observed-effect level
    n.sp.               not specified
    OBDE/octaBDE        octabromodiphenyl ether
    OcBDD/octaBDD       octabromodibenzo- p-dioxin
    OcBDF/octaBDF       octabromodibenzofuran
    OCDD/OcCDD/octaCDD  octachlorodibenzo- p-dioxin
    PAH                 polycyclic aromatic hydrocarbon

    PBB                 polybrominated biphenyl
    PBDD                polybrominated dibenzo- p-dioxin
    PBDE                polybrominated diphenyl ether
    PBDF                polybrominated dibenzofuran
    PBT                 polybutylene terephthalate
    PCB                 polychlorinated biphenyl
    PCDD                polychlorinated dibenzo- p-dioxin
    PCDE                polychlorinated diphenyl ether
    PCDF                polychlorinated dibenzofuran
    PeBDD/pentaBDD      pentabromodibenzo- p-dioxin
    PeBDE/pentaBDE      pentabromodiphenyl ether
    PeBDF/pentaBDF      pentabromodibenzofuran
    PeCDF/pentaCDF      pentachlorodibenzofuran
    PeHDD               pentahalogenated dibenzo- p-dioxin
    PeHDF               pentahalogenated dibenzofuran
    PHDD                polyhalogenated dibenzo- p-dioxin (used as
                        collective term including PCDD, PBDD, PXDD)
    PHDF                polyhalogenated dibenzofuran (used as collective
                        term including PCDF, PBDF, PXDF)
    PVC                 polyvinyl chloride
    PXDD                mixed (brominated/chlorinated) halogenated
                        dibenzo- p-dioxin
    PXDF                mixed (brominated/chlorinated) halogenated
                        dibenzofuran
    RI                  retention index
    RIA                 radioimmunoassay
    RMM                 relative molecular mass
    SD                  standard deviation
    T3                  triiodothyronine
    T4                  thyroxin
    TBBPA               tetrabromobisphenol A
    TBCDD               2,3-dibromo-7,8-dichlorodibenzo- p- dioxin
    TBDD/2,3,7,8-TeBDD  2,3,7,8-tetrabromodibenzo- p-dioxin
    TBDF/2,3,7,8-TeBDF  2,3,7,8-tetrabromodibenzofuran
    TBPI                bis-tetrabromo-phthalimide ethylene
    TCDD/2,3,7,8-TeCDD  2,3,7,8-tetrachlorodibenzo- p-dioxin
    TCDF/2,3,7,8-TeCDF  2,3,7,8-tetrachlorodibenzofuran
    TeBDD/tetraBDD      tetrabromodibenzo- p-dioxin
    TeBDF/tetraBDF      tetrabromodibenzofuran
    TEF                 toxicity equivalency factor
    TeHDD               tetrahalogenated dibenzo- p-dioxin
    TEQ                 toxic equivalent
    TeXDD/tetraXDD      mixed tetrahalogenated dibenzo- p- dioxin
    THDF                2,3,7,8-tetrahalogenated dibenzofuran
    TrBDD/triBDD        tribromodibenzo- p-dioxin
    TrBDF/triBDF        tribromodibenzofuran
    TrHDD/triHDD        trihalogenated dibenzo- p-dioxin
    TV                  television
    TxDD                2,3,7,8-substituted mixed tetrahalogenated
                        dibenzo- p-dioxin
    UV                  ultraviolet
    WHO                 World Health Organization

    1.  SUMMARY

    1.1  Identity, physical and chemical properties, and analytical
         methods

         Polybrominated dibenzo- p-dioxins (PBDDs) and polybrominated
    dibenzofurans (PBDFs) are almost planar tricyclic aromatic compounds.
    Theoretically, 75 PBDDs and 135 PBDFs are possible. In addition, a
    large number of mixed halogenated congeners -- 1550
    brominated/chlorinated dibenzo- p-dioxins (PXDDs) and 3050
    brominated/chlorinated dibenzofurans (PXDFs) -- are theoretically
    possible. Because of the complexity of the analytical procedures and
    paucity of analytical reference standards, it has been possible to
    characterize and determine only a small number of these compounds. The
    most toxic congeners are those substituted at positions 2, 3, 7, and
    8. There are 7 2,3,7,8-substituted PBDDs and 10 2,3,7,8-substituted
    PBDFs, as well as 337 possible 2,3,7,8-substituted PXDDs and 647
    possible 2,3,7,8-substituted PXDFs.

         PBDDs/PBDFs have higher molecular weights than their chlorinated
    analogues, high melting points, low vapour pressures, and low water
    solubilities. They are generally soluble in fats, oils, and organic
    solvents. There are very few experimental data on the physical and
    chemical properties of PBDDs/PBDFs.

         Photolysis occurs at a more rapid rate for PBDDs/PBDFs than for
    polychlorinated dibenzo- p-dioxins (PCDDs) and polychlorinated
    dibenzofurans (PCDFs). PBDDs/PBDFs are thermostable. The temperatures
    of formation and destruction of PBDDs/PBDFs depend on several
    conditions, including the presence or absence of oxygen, polymers, and
    flame retardant additives, such as antimony trioxide (Sb2O3).

         In the presence of excess chlorine, bromine is substituted by
    chlorine to give PXDDs/PXDFs.

         Because of the toxic nature of these compounds and their
    photolytic properties, care must be taken during sampling and
    analysis. Highly sensitive, selective, and specific analytical methods
    (gas chromatography/mass spectrometry, or GC/MS) are required because
    of the large number of PBDD/PBDF congeners. Sampling procedures are
    identical for all polyhalogenated dibenzo- p-dioxins (PHDDs) and
    polyhalogenated dibenzofurans (PHDFs), but separation and
    determination of PBDDs/PBDFs (and PXDDs/PXDFs) differ slightly from
    those of their chlorinated analogues. PBDDs/PBDFs have higher
    molecular weights and longer GC retention times than the chlorinated
    analogues, as well as different MS isotopic cluster patterns and
    interference compounds. Exact identification of specific brominated
    congeners is very limited owing to the small number of reference
    standards currently available. For the same reason, determination of
    mixed halogenated congeners is almost impossible.

    1.2  Formation and sources of human and environmental exposure

         PBDDs/PBDFs are not known to occur naturally. They are not
    intentionally produced (except for scientific purposes) but are
    generated as undesired by-products in various processes. They can be
    formed by chemical, photochemical, or thermal reactions from
    precursors and by so-called  de novo synthesis.

         PBDDs/PBDFs have been found as contaminants in brominated organic
    chemicals (e.g. bromophenols) and, in particular, in flame retardants,
    such as polybrominated diphenyl ethers (PBDEs), decabromobiphenyl
    (decaBB or DBB), 1,2-bis(tribromophenoxy)ethane, tetrabromobisphenol A
    (TBBPA), and others. They have been detected in distillation residues
    of some bromophenols and bromoanilines and in wastes from chemical
    laboratories.

         PBDFs and, to a lesser extent, PBDDs have been detected as
    photochemical degradation products of brominated organic chemicals,
    such as PBDEs and bromophenols.

         Laboratory thermolysis experiments showed the formation of
    PBDDs/PBDFs from bromophenols, PBDEs, polybrominated biphenyls (PBBs),
    and other brominated flame retardants (pure or in a polymer matrix).
    There was a broad range of yields, from zero to maximum values
    (reached from PBDEs) in the g/kg range. Generally, PBDFs were much
    more abundant than PBDDs. The optimum PBDF formation temperature of a
    series of pure flame retardants was in the range of 600-900°C. The
    presence of polymers or synergists (e.g. Sb2O3) resulted in a
    decrease in the optimum formation temperature (down to 400°C). In
    addition to temperature and the presence of polymer matrix or
    synergists, several other factors, such as metals, metal oxides,
    water, oxygen, and the type of combustion apparatus used, influenced
    the yield and pattern of PBDDs/PBDFs. In ternary mixtures of PBDE,
    polymer matrix, and Sb2O3, tetrabromodibenzo furans (tetraBDFs or
    TeBDFs) were frequently the most abundant homologue group.
    2,3,7,8-Substituted PBDDs/PBDFs (tetra to hepta) were found at varying
    concentrations; for example, 2,3,7,8-TeBDF was found at up to 2000
    mg/kg in pyrolysates of polymers containing octabromodiphenyl ether
    (octaBDE or OBDE).

         In the manufacture of plastics, elevated temperatures (150-300°C)
    occur during several processes. Studies of the exhaust streams from
    machines processing polymers -- such as
    acrylonitrile-butadiene-styrene (ABS) and polybutylene terephthalate
    (PBT) -- containing different types of brominated flame retardants
    showed that PBDDs/PBDFs (di to octa) can be formed at these
    temperatures. OBDE and decabromodiphenyl ether (decaBDE or DBDE)
    produced the highest amounts of PBDDs/PBDFs, the major portion
    consisting of PBDFs. Levels observed with TBBPA or
    bis-tetrabromo-phthalimide ethylene (TBPI) were several orders of
    magnitude lower. No PBDDs/PBDFs were detected during processing of ABS
    flame-retarded by brominated styrene or

    1,2-bis(tribromophenoxy)ethane. 2,3,7,8-Substituted congeners were not
    determined (processing of DBDE), were detected at trace levels
    (processing of OBDE), or were not detected (processing of TBBPA and
    TBPI).

         Various plastic materials at several processing stages were
    analysed for PBDDs/PBDFs. These included (granulated) resins and
    moulded parts whose flame retardant additives were known as well as
    samples from commercial electrical appliances (television sets,
    printers, computers) whose flame retardant additives were unknown. The
    highest levels of PBDDs/PBDFs were found in materials flame-retarded
    with PBDEs and were in the range of several thousand µg/kg, thus
    exceeding the levels of other flame retardant/polymer systems by
    orders of magnitude. Factors influencing the extent of formation are
    temperature and the duration of such processes as blending, extrusion,
    and moulding. Again PBDFs dominated, with some exceptions, over PBDDs,
    with the highly brominated (>tetra) derivatives being prevalent. Peak
    concentrations were seen with pentabromodibenzofurans (pentaBDFs or
    PeBDFs) and hexabromodibenzofurans (hexaBDFs or HxBDFs). The latter
    reached levels as high as 3000 µg/kg in casing parts. Printed circuit
    boards contained tetra- and pentaBDFs at maximum concentrations of
    1300 and 1400 µg/kg, respectively. Total PBDF (mono to hexa)
    concentrations were in the range of 3.6-3430 µg/kg.
    2,3,7,8-Substituted PBDDs/PBDFs were not determined, were not
    detectable, or were present at relatively low concentrations. Maximum
    concentrations of 2,3,7,8-substituted PBDFs (tetra to hexa) in casings
    or printed circuit boards ranged from 11 µg/kg (tetra) to 203 µg/kg
    (hexa).

         Experiments to determine whether PBDFs were released from
    television sets or similar appliances during use showed air levels
    ranging from not detected to 1800 pg total PBDFs (tetra to hexa) per
    appliance.

         Burning of products containing brominated compounds caused
    emission of PBDDs/PBDFs. In experimental fire tests simulating real
    fire conditions with electrical appliances such as television sets,
    printers, computer terminals, and their casings, high PBDF (mono to
    hexa) concentrations were detected in the combustion residues
    (thousands of mg/kg), in smoke condensate (hundreds of µg/m2), and in
    smoke (up to 1700 µg/m3). PBDD concentrations amounted to about 3% of
    the detected levels of PBDDs/PBDFs. The 2,3,7,8-substituted isomer was
    mostly below 3% of the total tetraBDFs. 2,3,7,8-Substituted penta- and
    hexaBDFs yielded between 1 and 16% of the corresponding totals.
    Burning of test vehicles resulted in PBDF (mono to octa)
    concentrations of up to 4.3 µg/kg in the fire residues.

         During real fire accidents in private residences (television sets
    involved), offices (computers involved), and other buildings,
    concentrations measured were in most cases below the values found in
    the model experiments described above, but the qualitative composition
    of the samples was similar. PBDFs were found in almost all samples,
    but PBDDs were not always detected; if present, their concentrations

    were low. The PBDF concentrations in combustion residues were mainly
    in the µg/kg range (low to high), but single maximum values (sum of
    mono to hexa) of up to 107 mg/kg were also observed. The PBDF (mono to
    hexa) area contaminant concentrations in close vicinity to the fire
    site ranged between 0.1 and 13 µg/m2 in most cases. Additionally,
    relevant concentrations of PXDDs/PXDFs could be detected. The
    proportion of 2,3,7,8-substituted PBDDs/PBDFs was relatively low in
    most of the samples examined. For example, maximum proportions of 3,
    10, or 18% of the corresponding totals of tetra-, penta-, or hexaBDFs,
    respectively, were reported from fire accidents with television sets.
    Soot samples collected after a fire in a computer room contained
    2,3,7,8-substituted tetra- and pentabromodibenzo- p-dioxins
    (tetra/pentaBDDs or TeBDD/PeBDD) and tetra- and pentaBDFs, with a
    maximum concentration of 48 µg/kg for 2,3,7,8-TeBDF (TBDF).

         PXDDs were detected in ash from a wood-fired boiler. However, the
    sort of wood (treated or untreated) was not specified. No data were
    available on the incineration of other fuels, such as coal, peat, or
    fuel oil.

         The presence of PBDDs/PBDFs and/or PXDDs/PXDFs has been reported
    in fly ash and/or flue gas of municipal, hospital, or hazardous waste
    incinerators. The majority of these compounds are probably produced in
    the incinerator itself, by formation from precursors at high
    temperatures in the flame or by  de novo synthesis at low
    temperatures in the post-combustion zone of the incinerator. The
    formation of PXDDs/PXDFs is explained by the extensive
    bromine-chlorine exchange reactions (with chlorine donors in waste)
    observed under several test conditions. The quantities of PBDDs/PBDFs
    and PXDDs/ PXDFs measured in fly ash of incinerators were in the range
    of ng/kg to µg/kg. In most cases, the concentrations of
    dibenzo- p-dioxins exceeded those of dibenzofurans, and PXDDs/PXDFs
    were more abundant than PBDDs/PBDFs. Of 2,3,7,8-substituted congeners,
    a mixed tetrahalogenated dibenzo- p-dioxin (tetraXDD or TeXDD)
    (Br2Cl2DD) was found.

         Analyses of waste samples from some disposal sites showed the
    presence of PBDDs/PBDFs and PXDDs/PXDFs at concentrations of several
    hundred to several thousand ng/kg dry weight. The concentration of
    dibenzo- p-dioxins (up to 580 ng/kg) was below that of dibenzofurans
    (up to 4230 ng/kg). Generally, the homologue profile was dominated by
    the lower halogenated (mono to tetra) derivatives. Chemical laboratory
    waste contained PBDDs/PBDFs, with a peak concentration of 15 500 ng/kg
    for hexaBDFs.

         PBDDs/PBDFs were present in plastic materials (with or without
    metals) of several recycling stages. The samples originated mainly
    from office machines, printed circuit boards, and other electronic
    scrap. In some cases, the sum concentration of eight selected PBDD/
    PBDF congeners having the 2,3,7,8-substitution was as high as 65
    µg/kg. Metal reclamation was also found to be a source of PBDDs and/or
    PXDDs/PXDFs. PBDDs/PBDFs have also been detected in textile industries

    where brominated flame retardants have been used. PBDFs were found in
    the exhaust air, in the textiles before and after processing, and in
    the chimney depositions.

         PBDDs/PBDFs and PXDDs/PXDFs (along with PCDDs/PCDFs) have been
    detected in emissions of motors using leaded petrol, in emissions of
    motors using unleaded petrol with and without catalytic converters,
    and in emissions of diesel engines. Because of the brominated and
    chlorinated scavengers (dibromo- and dichloroethane) used in leaded
    petrol, the highest levels of PHDDs/PHDFs (several thousand ng/m3)
    were found with this type of petrol. Unleaded petrol produced much
    lower emissions of PHDDs/PHDFs (approximately two orders of magnitude
    lower). A further reduction was seen after catalytic gas cleaning. The
    values for diesel engines were somewhat higher than those found with
    the Otto motors (spark ignition engines) run on unleaded petrol. In
    exhaust gases from combustion of leaded petrol, PBDDs/PBDFs were more
    abundant than PXDDs/PXDFs and PCDDs/PCDFs. Generally, the
    concentrations of dibenzofurans exceeded those of dibenzo- p-dioxins,
    and there was a dominance of lower substituted homologues (mono to
    tri). Similar patterns were seen in residues adhering to mufflers.

    1.3  Environmental transport, distribution, and transformation

         There are very few data available on the environmental transport
    and distribution of PBDDs/PBDFs. Generally, their physicochemical
    properties suggest similarities to PCDDs/PCDFs. Therefore, if released
    to the environment, they may be preferably distributed into carbon- or
    fat-rich compartments, as with PCDDs/PCDFs.

         Airborne PBDDs/PBDFs were found to be transported in both the
    particulate and vapour phase, the partitioning ratio depending on the
    degree of bromination.

         No experimental data are available on the movement of PBDDs/
    PBDFs in water or soil. For PBDFs (tri to penta), adsorption to
    sediment was reported. Owing to the low water solubility of PBDDs/
    PBDFs, leaching through the soil may be limited but may be increased
    in the presence of organic solvents or humic acids.

         There are no experimental data on processes for the transport and
    distribution of PBDDs/PBDFs between environmental media and biota or
    within biota. Based on the similar high octanol/water partition
    coefficients calculated for selected PCDDs/PCDFs, PBDDs/PBDFs, and
    PXDDs/PXDFs, a bioavailability comparable to that of PCDDs/ PCDFs is
    expected.

         Photolysis of PBDDs/PBDFs and PXDDs/PXDFs was studied in organic
    solvents and on quartz surfaces in the laboratory, as well as in soil
    and on soot (and dust) particles under outdoor conditions. The slowest
    photolytic reactions were observed under the latter, more
    environmentally relevant, conditions. Reductive debromination was
    found to be a major photochemical pathway. The rate of decomposition

    of different congeners depended on their bromine substitution pattern.
    Generally, higher brominated congeners and those with lateral bromines
    had shorter half-lives. Calculated half-lives were in the order of
    minutes (use of direct sunlight or ultraviolet [UV] light and quartz
    vials), hours (use of solid films or soot or dust particles and
    sunlight), or hundreds to thousands of hours (use of soil and
    sunlight). For example, the estimated sunlight-induced half-lives for
    2,3,7,8-TeBDD (TBDD) were 0.8 min (in organic solution) or 32 h
    (dispersed as solid films). A half-life of 3-6 months was estimated
    for tetraBDD isomers in surface soil. Compared with PCDDs/PCDFs, the
    brominated counterparts were photochemically less stable. PXDDs/PXDFs
    preferentially lost their bromine atoms during photolysis and
    therefore were transformed into PCDDs/PCDFs, which had longer
    photolytic half-lives. Such a transformation of PXDDs/PXDFs to
    PCDDs/PCDFs also occurs during incineration processes.

         PBDDs/PBDFs seem to be poorly degradable by microorganisms.

         The presence of PBDDs/PBDFs in animals and in humans, as seen in
    a few studies, is indicative of their accumulation potential.
    2,3,7,8-TeBDD accumulated in rats during subchronic administration.
    Bioaccumulation, bioconcentration, or biomagnification factors for
    PBDDs/PBDFs or PXDDs/PXDFs are not available.

    1.4  Environmental levels and human exposure

         To date, in contrast to PCDDs/PCDFs, PBDDs/PBDFs have not been
    frequently included in monitoring programmes. The few studies
    performed indicate a limited occurrence.

         In ambient air, PBDFs were found more frequently than PBDDs. Only
    lower brominated PBDDs (mono to tetra) were detected at concentrations
    ranging from not detected (n.d.) to about 0.85 pg/m3 for
    monobromodibenzo- p-dioxins (monoBDDs or MoBDDs) in a motor way
    tunnel and an underground garage. Of PBDFs, mono- to hexabrominated
    homologues were found, their concentrations ranging from n.d. to 74
    pg/m3. The concentrations (mean values) of total PBDDs/ PBDFs (tri to
    hexa) measured, for example, in Germany in a motorway tunnel, in a
    city, and in a suburban area amounted to 23 pg/m3, 2 pg/m3, and 0.59
    pg/m3, respectively; 2,3,7,8-TeBDD was not detected, and the maximum
    concentrations of 2,3,7,8-TeBDF and 1,2,3,7,8-PeBDF were 0.28 pg/m3
    and 0.08 pg/m3, respectively. PXDFs were identified in
    traffic-related air samples at concentrations up to 41 pg/m3
    (Cl1Br1DFs). Outdoor dust samples (mainly from motorways) also
    showed a predominance of PBDFs/PXDFs (maxima of several thousand
    ng/kg) over PBDDs/PXDDs (maxima of up to some hundred ng/kg).

         Indoor air samples taken from rooms equipped with a number of
    operating electronic appliances (television and/or computer monitors)
    showed the presence of PBDFs (tetra to hepta) at total concentrations
    ranging from 0.23 to 1.27 pg/m3. PBDDs were not detected. Dust
    samples collected in computer rooms yielded total PBDF levels of

    2.4-5.5 µg/kg dust. In contrast to air, the homologue pattern in dust
    was dominated by hexaBDFs and heptabromodibenzofurans (heptaBDFs or
    HpBDFs). Only in dust samples were low concentrations of tetraBDDs (up
    to 1 µg/kg) and of 2,3,7,8-substituted tetra- and pentaBDFs (up to
    0.07 µg/kg) detectable. PBDF concentrations in the one sample of house
    dust were lower by a factor of 10. The sum concentration of
    PBDDs/PBDFs equalled that of PCDDs/PCDFs in dust from computer rooms
    but was lower than that of PCDDs/PCDFs in house dust. Dust from an
    underground garage contained lower halogenated PBDFs (mono and di) and
    PXDFs (di to tetra), with a maximum concentration of 4.3 µg/kg for
    mixed dihalogenated dibenzofurans (DiXDFs).

         No data are available on levels of PBDDs/PBDFs in water samples.

         In river and marine sediment samples from an industrialized zone,
    tetraBDDs (up to 0.006 µg/kg dry weight) and tetra- to hexaBDFs (sum
    up to 0.37 µg/kg dry weight) were detected. Sediment from road
    drainage contained PBDFs (sum of mono to tri: 2.5 µg/kg; sum of tetra
    to hepta: 0.3 µg/kg) and PXDFs (sum of di and tri: 1.85 µg/kg), but no
    PBDDs.

         Similarly, soil samples taken near a motorway contained
    monobromodibenzofurans (monoBDFs or MoBDFs) and dibromodibenzofurans
    (DiBDFs) (sum: 1.3 µg/kg), tetra- and pentaBDFs (sum: 0.02 µg/kg), and
    PXDFs (sum: 1 µg/kg), but no PBDDs. Soil samples taken from an
    incineration field and near a metal reclamation factory gave total
    PBDF concentrations of up to 100 µg/kg, but no PBDDs were detected. In
    a series of sewage sludge samples from municipal wastewater treatment
    plants, total PBDF concentrations ranged from n.d. to 3 µg/kg. In one
    case, traces of tetraBDDs and 2,3,7,8-TeBDF were detected. A
    biocompost sample was nearly free of PBDDs/ PBDFs (tetraBDFs: <0.003
    µg/kg).

         There are no quantitative data on levels of PBDDs/PBDFs in food.

         In grass and pine needle samples collected near motorways, lower
    halogenated PBDFs/PXDFs (mono to tetra) and traces of PBDDs/ PXDDs
    (mono to tri) were detectable.

         No PBDDs/PBDFs were found in the few wildlife samples tested.

         In cow's milk collected at dairy farms in the vicinity of a
    municipal waste incinerator, tribromodibenzofurans (triBDFs or
    TrBDFs), a tetraBDF, and a pentaBDF (not having the
    2,3,7,8-substitution pattern) were tentatively identified.

         PBDDs/PBDFs have not been detected in the few tested samples of
    human adipose tissues or milk samples from the general public.

         Contamination by PBDDs/PBDFs is possible at a variety of
    workplaces involved in the production, processing, use, or disposal of
    certain flame retardants or their products, especially where processes
    involve elevated temperatures. The magnitude of worker exposure

    depends not only on the compounds involved but also on the quality of
    the air and ventilation conditions. There are only limited workplace
    monitoring data from plastic producing or processing facilities, from
    offices/studios with large numbers of electrical appliances
    continuously in use, and from recycling workplaces (including
    secondary copper plants). Generally, PBDFs were more abundant than
    PBDDs, and PBDF air concentrations were highest at workplaces where
    DBDE-containing polymers were produced. In many samples,
    2,3,7,8-substituted PBDFs/PBDDs were detectable. PBDD/PBDF
    contamination was also found at the work area under the fume hood of a
    chemical laboratory. Monitoring data at waste incineration facilities
    are lacking.

    1.5  Kinetics and metabolism

         Most of the studies refer to 2,3,7,8-TeBDD and, to a lesser
    extent, 1,2,7,8-TeBDF. Half-life calculations have included some
    additional congeners.

         2,3,7,8-TeBDD was absorbed in rats after oral, intratracheal, and
    dermal administration, the percent absorption varying with route and
    dose. Single doses of 1 nmol 2,3,7,8-TeBDD/kg body weight led to an
    absorption of 80% (oral and intratracheal routes) or 12% (dermal
    route) of the administered dose. The dermal absorption of 1 nmol
    1,2,7,8-TeBDF/kg body weight was about 29%. Oral absorption of
    2,3,7,8-TeBDD appeared to be comparable to that of
    2,3,7,8-tetrachlorodibenzo- p-dioxin (2,3,7,8-TeCDD or TCDD).
    However, dermal absorption of 2,3,7,8-TeBDD was about one-third that
    of an equimolar dose of 2,3,7,8-TeCDD.

         2,3,7,8-TeBDD or 1,2,7,8-TeBDF administered to rats, by any
    route, was distributed throughout the entire body, with major deposits
    found in liver and adipose tissue, followed by skin and muscle. For
    example, 3 days after single oral doses of 2,3,7,8-TeBDD (1 nmol/kg
    body weight), the portions in these tissues amounted to 20%, 20%, 11%,
    and 4%, respectively, whereas thymus and adrenals contained 0.03% and
    0.4%, respectively, of the administered dose. The partitioning of
    2,3,7,8-TeBDD between liver and adipose tissue of rats was found to be
    influenced by dose, route of exposure, and time post-dosing. The
    ratios of liver : fat concentrations measured under different
    conditions ranged from 0.2 to 6.5 (range for single doses of
    2,3,7,8-TeBDD in rats). No experimental data were available on the
    transfer of PBDDs/PBDFs to offspring.

         TetraBDD/BDF metabolites were detected in bile and faeces from
    rats. They were mainly formed by aromatic hydroxylation and hydrolytic
    debromination. The rate of metabolism (indirectly determined as the
    rate of biliary excretion) differed between 2,3,7,8-TeBDD (about 7%)
    and 1,2,7,8-TeBDF (about 50%). Three days after an intravenous dose of
    2,3,7,8-TeBDD (1 nmol/kg body weight), 14% of the administered dose
    was found as metabolites in the faeces of rats.

         Elimination and excretion of 2,3,7,8-TeBDD were studied in rats
    using oral, intravenous, intratracheal, and dermal routes of
    administration. In all studies, the major route of elimination was
    through the faeces, the eliminated radioactivity ranging from 2%
    (dermal route) to 42% (oral route) of the administered dose (1 nmol
    [3H]2,3,7,8- TeBDD/kg body weight) in faeces samples, and from 0.2 to
    1% in urine samples. Similarly, in studies with 1,2,7,8-TeBDF in rats,
    excretion was mainly through the faeces, only 2-3% of the intravenous,
    oral, or dermal doses being excreted in urine. During the first days
    following oral doses, unabsorbed material and biliary excretion
    appeared to be the major sources of eliminated compound in faeces. The
    portions of parent 2,3,7,8-TeBDD found in faeces of rats after
    administration of 1 nmol 2,3,7,8-TeBDD/kg body weight were 53% (oral
    route), 43% (intratracheal route), and 10-20% (intravenous route). A
    few days after oral application of 2,3,7,8-TeBDD (1 nmol/kg body
    weight), about 20% of the dose administered was eliminated as parent
    compound.

         Data on retention and turnover are available for some PBDDs/
    PBDFs. The relative body burden of 2,3,7,8-TeBDD (and other congeners)
    in rats depends on the route of exposure and on the dose administered,
    reflecting differences in absorption. Half-lives were calculated for
    several PBDDs/PXDDs and PBDFs in various tissues and faeces of rats.
    They ranged between 1 day (1,2,7,8-TeBDF from body) and 99 days
    (2,3,4,7,8-PeBDF from liver). The estimated half-lives of 17, 18, and
    58 days for 2,3,7,8-TeBDD in liver, faeces, and adipose tissue,
    respectively, were similar to those reported for 2,3,7,8-TeCDD in
    liver and faeces, but higher (by a factor of >2) than those reported
    for 2,3,7,8-TeCDD in adipose tissue. Despite differences in early
    retention, half-lives of 2,3,7,8-TeBDF and
    2,3,7,8-tetrachlorodibenzofuran (2,3,7,8-TeCDF or TCDF) in liver were
    comparable.

         As with PCDDs/PCDFs, half-lives calculated for humans are much
    longer than those for rats. There are estimations of 3-11 years (mean:
    5.9 years) for 2,3,7,8-TeBDD and of 1-2 years (mean: 1.5 years) for
    2,3,7,8-TeBDF. The persistence of these compounds in humans was also
    seen in the case of a chemist who had synthesized 2,3,7,8-TeBDD and
    2,3,7,8-TeCDD in 1956. Thirty-five years after exposure, markedly
    elevated levels of 2,3,7,8-TeBDD were found in his blood.

    1.6  Effects on laboratory mammals and in vitro test systems

         Most studies were concerned with the toxicity of 2,3,7,8-TeBDD,
    but some information was also available on other PBDDs/PBDFs and
    PXDDs/PXDFs.

         2,3,7,8-TeBDD caused typical 2,3,7,8-TeCDD-like effects,
    including wasting syndrome, thymus atrophy, and liver toxicity.
    Additionally, liver damage described as peliosis hepatis, which has
    not been reported after exposure of rats to 2,3,7,8-TeCDD, was
    observed. The pattern of lesions (lethality, histopathology, liver and

    thymus weights) found in guinea-pigs after a single exposure and in
    rats after short-term exposure to 2,3,7,8-TeBDF was similar to that of
    2,3,7,8-TeCDF.

         2,3,7,8-TeBDD interacts with the endocrine system. In rats,
    dose-related changes in circulating thyroid hormones and impairment of
    spermatogenic activity have been observed.

         The oral LD50 (28-day observation period) of 2,3,7,8-TeBDD in
    Wistar rats was about 100 µg/kg body weight for females and about 300
    µg/kg body weight for males. Oral LD50 values for 2,3,7,8- TeCDD
    obtained from other studies ranged between 22 and >3000 µg/kg body
    weight. Equimolar doses of 2,3,7,8-TeBDF and 2,3,7,8-TeCDF resulted in
    comparable mortality rates in guinea-pigs. For example, 100% mortality
    was seen after treatment with both 2,3,7,8-TeBDF (0.03 µmol/kg body
    weight, 15.8 µg/kg body weight) and 2,3,7,8-TeCDF (0.03 µmol/kg body
    weight, 10 µg/kg body weight). Pre-peliotic lesions and changes in
    thyroid hormones were seen in rats after a single dose of 100 µg
    2,3,7,8-TeBDD/kg body weight.

         In Wistar rats administered 2,3,7,8-TeBDD orally for 13 weeks,
    evidence for decreased spermatogenic activity, defective and necrotic
    spermatocytes, signs of severe peliosis hepatis, and changes in
    circulating thyroid hormones and organ weights were observed. The
    no-observed-adverse-effect level (NOAEL) was 0.01 µg/kg body weight
    per day.

         2,3,7,8-TeBDF administered orally to Sprague-Dawley rats for 4
    weeks caused dose-dependent growth retardation and histopathological
    changes in liver and thymus. The NOAEL was 1 µg/kg body weight per
    day.

         Developmental toxicity of some 2,3,7,8-substituted PBDDs/ PBDFs
    occurred in mice at subcutaneous and oral doses that produced no
    maternal toxicity and no fetal mortality. The lowest-observed-effect
    levels (LOELs) (in µg/kg body weight) for hydronephrosis and cleft
    palate after a single oral exposure of pregnant mice were,
    respectively, as follows: 3 and 48 for 2,3,7,8-TeBDD, 25 and 200 for
    2,3,7,8-TeBDF, 400 and 2400 for 2,3,4,7,8-PeBDF, and 500 and 3000-4000
    for 1,2,3,7,8-PeBDF. Compared on a molar basis, 2,3,7,8-TeBDD and
    2,3,7,8-TeCDD were almost equipotent in induction of hydronephrosis.
    Compared on a weight basis, generally the brominated isomers were
    slightly less potent than the chlorinated ones in induction of
    hydronephrosis and cleft palate. However, 2,3,7,8-TeBDF was more
    active than 2,3,7,8-TeCDF.

         No information was found on the mutagenicity of PBDDs/PBDFs or
    related end-points.

         No long-term toxicity and carcinogenicity studies with PBDDs/
    PBDFs were available. 2,3,7,8-TeBDD tested positive in a cell
    transformation assay using murine peritoneal macrophages. However, the
    transforming potency of 2,3,7,8-TeBDD was seven times less than that

    of 2,3,7,8-TeCDD. Later, tumours developed in nude mice after
    subcutaneous injection of the resulting established cell lines.

         A series of several PBDDs and PXDDs (tetra and penta) given
    intraperitoneally to immature male Wistar rats caused body weight
    losses 14 days after injection. On the basis of molar ED50 values,
    the most toxic compounds tested were 2,3,7,8-TeBDD,
    2-Br1-3,7,8-Cl3- DD, and 2,3-Br2-7,8-Cl2-DD (TBCDD), which are
    substituted only in the four lateral positions. The relative potencies
    of the other PBDDs examined followed the order 2,3,7,8- >
    1,2,3,7,8- > 1,2,4,7,8- > 1,3,7,8-DD. In other experiments, there
    were only slight differences in the ED50 values (on a molar basis)
    for body weight loss, thymic atrophy, and hepatic enzyme induction
    between 2,3,7,8-TeCDD and 2,3,7,8-TeBDD.

         Thymic atrophy and other signs of immunotoxicity (e.g.
    haematological parameters, alterations of certain lymphocyte
    subpopulations) were seen with several PBDDs/PXDDs and 2,3,7,8-TeBDF
    in the rat and with 2,3,7,8-TeBDD and TBCDD in the marmoset monkey
     (Callithrix jacchus). It was concluded that, on a molar basis, the
    potency of 2,3,7,8-TeBDD was comparable to that of 2,3,7,8-TeCDD in
    rats and monkeys. For example, a significant effect on certain
    lymphocyte subpopulations in monkeys was found after a single
    subcutaneous dose of 30 ng 2,3,7,8-TeBDD/kg body weight versus 10 ng
    2,3,7,8-TeCDD/kg body weight. Effects on immunotoxicity after
    perinatal exposure to PBDDs/PBDFs have not been investigated.

         After subchronic dosing of either 2,3,7,8-TeBDD or 2,3,7,8-TeCDD
    by oral gavage in mice, there was a dose-dependent increase in total
    hepatic porphyrins.

         After single oral doses of 2,3,7,8-TeBDD and 2,3,7,8-TeCDD,
    reductions in concentration and total amount of vitamin A were
    observed in the liver of rats, with 2,3,7,8-TeBDD being slightly less
    potent than 2,3,7,8-TeCDD (on a molar basis).

         2,3,7,8-TeBDD and 2,3,7,8-TeBDF produced hyperkeratosis in the
    rabbit ear assay at a dose of 100 µg/rabbit, but not at 10 µg/rabbit.
    A no-observed-effect level (NOEL) for 2,3,7,8-TeCDD was 0.01
    µg/rabbit.

         Several tetra- (Br1Cl3DDs, Br2Cl2DDs) and penta- (Br1Cl4DD)
    halogenated congeners with 2,3,7,8-substitution were found to have an
    antiestrogenic potency similar to that of 2,3,7,8-TeCDD, as examined
    in cultures of human breast cancer cells.

         In rats, 2,3,7-tribromodibenzo- p-dioxin (2,3,7-triBDD/TrBDD)
    depressed the disappearance of ouabain from plasma, its excretion into
    bile, and bile flow to a slightly lesser extent than 2,3,7,8-TeCDD.

         PBDDs/PBDFs and PXDDs/PXDFs are potent inducers of certain
    cytochrome P-450 (CYP)-dependent microsomal enzymes. ED50 values of
    0.8-1 nmol/kg body weight for CYP1A1 induction and about 0.2 nmol/kg

    body weight for CYP1A2 induction in rat liver were estimated after
    single oral doses of 2,3,7,8-TeBDD. CYP1A1 induction (arylhydrocarbon
    hydroxylase [AHH] and/or ethoxyresorufin- O-deethylase [EROD]
    induction) was observed in a variety of species and tissues
    in vivo  and in rat cell cultures  in vitro. A lot of different
    congeners were found to be active, as well as pyrolysates from certain
    flame retardants. Generally, enzyme induction proceeded
    dose-dependently at non-toxic concentrations, started soon after
    exposure, and was long-lasting. It was measurable at exposures as low
    as the pmol range. The induction potency varied over several orders of
    magnitude for different congeners, depending on their chemical
    structure. The most potent inducers were TCDD, TBDD, and TBCDD.
    Compared (on a molar basis) with their chlorinated analogues, the
    PBDDs and PXDDs had more or less similar potency. In contrast to TCDD,
    whose relative induction potency was independent of the tissue
    examined, TBDD was five times more potent at inducing EROD activity in
    the liver than in skin and lung following subchronic exposure of mice.
    The ranking order for induction of EROD activity in marmoset monkeys
    was TCDD > 2,3,4,7,8-pentachlorodibenzofuran
    (2,3,4,7,8-pentaCDF/PeCDF) > 2,3,4,7,8-PeBDF when enzyme activities
    were compared with the hepatic concentrations.  In vitro tests with
    rat cell cultures resulted in similar molar EC50 values of AHH and
    EROD induction potencies between corresponding PXDFs and PCDFs.

         PBDDs/PBDFs are believed to share a common mechanism of action
    with PCDDs/PCDFs and other related halogenated aromatic hydrocarbons
    (Ah). Binding to the cytosolic Ah receptor, which plays a central role
    in mediating 2,3,7,8-TeCDD-like toxicity, was confirmed for several
    PBDDs and PXDDs/PXDFs. Their receptor-binding affinities varied by
    several orders of magnitude but were comparable to those of their
    chlorinated analogues.

    1.7  Effects on humans

         There are no data on the exposure of humans to PBDDs/PBDFs or on
    their effects on the health of the general population.

         Two cases of acute health problems due to 2,3,7,8-TeBDD/ TeCDD
    exposure have been reported, with symptoms including chloracne.

         In another study, male personnel of a chemical plant with
    documented exposure to PBDDs/PBDFs originating from the use of
    brominated flame retardants (OBDE and DBDE) were subjected to
    immunological and additional clinical laboratory tests. Although there
    were indications of minor changes in immunological parameters, the
    overall evaluation of their health status did not reveal an impact of
    2,3,7,8-TeBDD/TeBDF body burden on the immune system.

         There are no reports on cancer mortality caused by PBDDs/ PBDFs.

    1.8  Effects on other organisms in the laboratory and field

         There is only limited information on the effects of PBDDs/PBDFs
    on microorganisms, plants, or invertebrate or vertebrate wildlife
    species.

         Using the rainbow trout  (Oncorhynchus mykiss) sac fry early
    life stage mortality bioassay, a series of PBDD/PBDF congeners were
    tested and found to be active. This bioassay also demonstrated that
    for both PBDDs and PBDFs, there was a decreased potency with increased
    bromine substitution. Both 2,3,7,8-TeBDD and 2,3,7,8-TeBDF were more
    potent than their chlorinated analogues.

    2.  IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND ANALYTICAL METHODS

    2.1  Identity

         PHDDs/PHDFs are almost planar tricyclic aromatic compounds. There
    are eight positions on both the dibenzo- p-dioxin and the
    dibenzofuran molecules where halogen substitution can occur. The
    positions are numbered as shown in Fig. 1 for PBDDs and PBDFs.

         Each series consists of eight homologous groups (groups of
    congeners having the same number of bromine atoms), and in each group
    there are different numbers of isomers (see Table 1). Theoretically,
    75 PBDDs and 135 PBDFs are possible, as well as a large number of
    mixed halogenated congeners -- 1550 PXDDs and 3050 PXDFs (Buser,
    1987a). There are 7 2,3,7,8-substituted PBDDs and 10
    2,3,7,8-substituted PBDFs (see Table 2), as well as 337 possible
    2,3,7,8-substituted PXDDs and 647 possible 2,3,7,8-substituted PXDFs
    (Ballschmiter & Bacher, 1996). PCDDs/PCDFs are discussed in a separate
    Environmental Health Criteria monograph (WHO, 1989).

         Because of the complexity of the analytical procedures (see
    section 2.4), it has been possible to characterize only a small number
    of PBDDs/PBDFs and PXDDs/PXDFs. Tables 3 and 4 show the Chemical
    Abstracts Service (CAS) numbers that have been allocated to some of
    these compounds.

    2.2  Physical and chemical properties

    2.2.1  Appearance, melting and boiling points, water solubility, vapour
           pressure, octanol/water partition coefficient, and sorption coefficient

         Experimental data on the physical and chemical properties of
    PBDDs/PBDFs are scarce (see Table 5). In many cases, only predicted
    values are available. It should be noted that for PCDDs, experimental
    data are often lower than the calculated values (Shiu et al., 1988;
    Fiedler & Schramm, 1990). This is also to be expected for the
    brominated and for the mixed halogenated compounds (Fiedler & Schramm,
    1990). Measured values for the aqueous solubility of PCDDs decrease
    dramatically with increase in chlorine substitution and temperature
    (Shiu et al., 1988).

         PBDDs/PBDFs have higher molecular weights than their chlorinated
    analogues, high melting points, and low water solubilities, but they
    are generally soluble in fats, oils, and organic solvents (see Table
    5). PBDDs/PBDFs have, like their chlorinated analogues, very low
    vapour pressures, and at ambient temperatures they are mostly found
    bound to particles. For the lower substituted compounds, PBDDs/PBDFs
    have higher calculated p Kow values than the chlorinated congeners
    (Fiedler & Schramm, 1990) and are therefore more lipophilic.

        Table 1.  Number of isomers, elemental composition, and molecular weight for PBDDs/PBDFs
                                                                                            

    Compound            Number of isomers                  Elemental               Molecular
                    Total          2,3,7,8-Substituted     composition             weight
                                                                                            

    MoBDD           2              -                       C12H7O2Br               263.1
    DiBDD           10             -                       C12H6O2Br2              342.0
    TrBDD           14             -                       C12H5O2Br3              420.9
    TeBDD           22             1                       C12H4O2Br4              499.8
    PeBDD           14             1                       C12H3O2Br5              578.7
    HxBDD           10             3                       C12H2O2Br6              657.6
    HpBDD           2              1                       C12HO2Br7               736.5
    OcBDD           1              1                       C12O2Br8                815.4

    MoBDF           4              -                       C12H7OBr                247.1
    DiBDF           16             -                       C12H6OBr2               326.0
    TrBDF           28             -                       C12H5OBr3               404.9
    TeBDF           38             1                       C12H4OBr4               483.8
    PeBDF           28             2                       C12H3OBr5               562.7
    HxBDF           16             4                       C12H2OBr6               641.6
    HpBDF           4              2                       C12HOBr7                720.5
    OcBDF           1              1                       C12OBr8                 799.4

                                                                                            
    
    FIGURE 2

    Table 2.  PBDDs/PBDFs brominated at the
              2,3,7,8-positions
                                                 

    PBDD congenera          PBDF congenera
                                                 

    2,3,7,8-TeBDD*          2,3,7,8-TeBDF*
    1,2,3,7,8-PeBDD*        1,2,3,7,8-PeBDF*
                            2,3,4,7,8-PeBDF*
    1,2,3,4,7,8-HxBDD*      1,2,3,4,7,8-HxBDF
    1,2,3,6,7,8-HxBDD*      1,2,3,6,7,8-HxBDF
    1,2,3,7,8,9-HxBDD*      1,2,3,7,8,9-HxBDF
                            2,3,4,6,7,8-HxBDF
    1,2,3,4,6,7,8-HpBDD     1,2,3,4,6,7,8-HpBDF
                            1,2,3,4,7,8,9-HpBDF
    OcBDD                   OcBDF
                                                 

    a  The congeners marked with an asterisk (*)
       are cited in the German Dioxin Directive (1994)
       (see Appendix I).


    2.2.2  Stability of PBDDs/PBDFs

    2.2.2.1  Photolysis

         In the presence of laboratory light or sunlight, photolysis
    occurs at a more rapid rate for PBDDs/PBDFs than for PCDDs/PCDFs
    (Buser, 1988; Chatkittikunwong & Creaser, 1994a; for details, see
    section 4.2.1). This should be taken into consideration when analyses
    of these compounds are carried out (see sections 2.4.1 and 4.2.1).

         Photolysis on quartz surfaces under sunlight is a much slower
    process than photolysis in organic solvents (Buser, 1988). PBDDs/
    PBDFs adsorbed on incinerator soot particles remained relatively
    stable and degraded only slowly during a 6-h period (Lutes et al.,
    1990, 1992a,b). Studies of PBDDs in soil showed that for the same
    congeners, the half-lives in this matrix are four times longer than in
    solution (Chatkittikunwong & Creaser, 1994a).

         Under conditions of ambient temperature and protection from
    light, there is no appreciable (>1%) degradation of crystalline
    PBDDs/ PBDFs and no significant change (0.6%, with the exception of
    octaBDD [9.7%]) in standard solution (solvent:  n-nonane)
    concentrations over a period of 3 years (Re et al., 1995).

        Table 3. CAS numbers for some PBDDs/PBDFs

                                                                                

    PBDD congenera       CAS number         PBDF congenera           CAS number
                                                                                

    Br1DD                103456-34-4        Br1DF                    103456-35-5
    1-Br1DD              105908-71-2        2-Br1DF                  86-76-0
    2-Br1DD              105906-36-3
    Br2DD                103456-37-7        Br2DF                    103456-40-2
    1,6-Br2DD            91371-14-1         2,7-Br2DF                65489-80-7
    2,7-Br2DD            39073-07-9         2,8-Br2DF                10016-52-1
    2,8-Br2DD            105836-96-2
    Br3DD                103456-38-8        Br3DF                    103456-41-3
                                            1,2,8-Br3DF              84761-81-9
                                            2,3,8-Br3DF              84761-82-0
    Br4DD                103456-39-9        Br4DF                    106340-44-7
    1,2,3,4-Br4DD        104549-41-9        1,2,7,8-Br4DF            84761-80-8
    2,3,7,8-Br4DD        50585-41-6         2,3,7,8-Br4DF            67733-57-7
    Br5DD                103456-36-6        Br5DF                    68795-14-2
    1,2,3,7,8-Br5DD      109333-34-8        1,2,3,7,8-Br5DF          107555-93-1
                                            2,3,4,6,7-Br5DF          124388-77-8
                                            2,3,4,7,8-Br5DF          131166-92-2
    Br6DD                103456-42-4        Br6DF                    103456-33-3
    1,2,3,4,7,8-Br6DD    110999-44-5        1,2,3,4,6,7-Br6DF        124388-78-9
    1,2,3,6,7,8-Br6DD    110999-45-6        1,2,3,6,7,8-Br6DF        107555-94-2
    1,2,3,7,8,9-Br6DD    110999-46-7
    Br7DD                103456-43-5        Br7DF                    62994-32-5
                                            1,2,3,4,6,7,8-Br7DF      107555-95-3
    Br8DD                2170-45-8          Br8DF                    103582-29-2

                                                                                

    a The homologue groups are underlined.
    
    2.2.2.2  Thermolytic degradation of PBDDs/PBDFs

         As discussed in chapter 3, the temperature of formation and
    destruction of PBDDs/PBDFs depends on several conditions, such as
    residence time, the presence/absence of oxygen, polymers, and
    additives such as Sb2O3, as well as the efficiency of the apparatus
    used for the thermal degradation. In laboratory experiments on the
    thermolysis of polybrominated flame retardants (see section 3.4; Table
    11), the PBDDs/PBDFs formed were destroyed at 800°C in an air
    atmosphere after a 2.0-second residence time (Striebich et al., 1991).
    PBDDs/PBDFs formed at 600°C from the thermolysis of plastics
    containing DBDE or PBDE were no longer detectable at 800°C (Lahaniatis
    et al., 1991). However, Thoma et al. (1987b) found that PBDDs/PBDFs
    are still formed at 900°C. There is thus no definitive information on
    the temperature needed to destroy PBDDs/PBDFs.

        Table 4. CAS numbers for some PXDDs/PXDFs
                                                                                           

    PXDD congenera             CAS number               PXDF congenera           CAS number
                                                                                           

    Br1Cl1DD                   109007-09-02             Br1Cl1DF                 109264-70-2
    Br1Cl2DD                   107227-59-8              Br1Cl2DF                 107227-60-1
    Br1Cl3DD                   107227-75-8              Br1Cl3DF                 107227-56-5
                                                        8-Br1-2,3,4-Cl3DF        n.g.b
    Br1Cl4DD                   109264-61-1              Br1Cl4DF                 109302-36-5
                                                        1-Br1-2,3,7,8-Cl4DF      104549-43-1
                                                        4-Br1-2,3,7,8-Cl4DF      115656-08-1
    Br1Cl5DD                   109264-65-5              Br1Cl5DF                 107103-81-1
    Br1Cl6DD                   109264-67-7              Br1Cl6DF                 107207-47-6
    Br1Cl7DD                   109264-69-9              Br1Cl7DF                 109302-40-1

    Br2Cl1DD                   107227-58-7              Br2Cl1DF                 107227-57-6
    Br2Cl2DD                   107227-74-7              Br2Cl2DF                 107227-55-4
    Br2Cl3DD                   109031-99-4              Br2Cl3DF                 107227-53-2
    Br2Cl4DD                   109264-62-2              Br2Cl4DF                 107207-48-7
    Br2Cl5DD                   109264-66-6              Br2Cl5DF                 107207-45-4
    Br2Cl6DD                   109264-68-8              Br2Cl6DF                 109302-39-8

    Br3Cl1DD                   n.g.b                    Br3Cl1DF                 107227-54-3
    Br3Cl2DD                   n.g.b                    Br3Cl2DF                 107227-52-1
    Br3Cl3DD                   n.g.b                    Br3Cl3DF                 107207-46-5
    Br3Cl4DD                   n.g.b                    Br3Cl4DF                 107207-42-1
    Br3Cl5DD                   n.g.b                    Br3Cl5DF                 n.g.b

    Br4Cl1DD                   n.g.b                    Br4Cl1DF                 107227-51-0
    Br4Cl2DD                   n.g.b                    Br4Cl2DF                 107207-44-3
    1,2,3,4-Br4-7,8-Cl2DD      134974-39-3
    Br4Cl3DD                   n.g.b                    Br4Cl3DF                 107207-41-0
    Br4Cl4DD                   n.g.b                    Br4Cl4DF                 n.g.b
    1,2,3,4-Br4-6,7,8,9-Cl4DD  124728-12-7

    Br5ClxDD                   n.g.b                    Br5Cl1DF                 107207-49-8
                                                        other Br5ClxDF           n.g.b

    Br6Cl1DD                   107207-38-8              Br6Cl1DF                 n.g.b
    Br6Cl2DD                   n.g.b                    Br6Cl2DF                 107207-36-3
    1,2,4,6,7,9-Br6-3,8-Cl2DD  2170-44-7

    Br7Cl1DD                   n.g.b                    Br7Cl1DF                 107207-37-4
                                                                                           

    a  The homologue groups are underlined.
    b  n.g. = CAS numbers not found (probably not yet allocated).
    

        Table 5.  Physical and chemical properties of some PBDDs/PBDFs

                                                                                                                                         

    Compound          Appearance           Melting point           Boiling point   Water         Vapour        Octanol/water  Sorption
                                           (°C) (observed)         (°C)            solubility    pressure      partition      coefficient
                                                                   (predicted)     [log S]       [log P]       coefficient    [log Koc]
                                                                                   (mol/litre)   (Pa at 25°C)  [log Kow]      (mol/litre)
                                                                                   (predicted)   (predicted)   (predicted)    (predicted)
                                                                                                                                         

    PBDDs
    1-MoBDD           white needles        104-106a                338.2b                        3.5 × 10-3b
    2-MoBDD           n.g.c                93-94.5a                338.2b          -6.12d        4.0 × 10-3b   5.62d          4.39d
                                           (90-92)a
    1,6-DiBDD                              207e                    375b                          1.5 × 10-4b
    2,3-DiBDD         n.g.c                157.2-158f              375b            -6.90d        1.6 × 10-4b   6.25d          4.74d
    2,7-DiBDD                              174-176a                375b                          1.5 × 10-4b
                                           193-194e
    2,8-DiBDD                              149.5-151a              375b                          1.7 × 10-4b
                                           (145-150)a
    3,7-DiBDD                                                                      -7.24d                      6.53d          4.89d
                                                                                   -7.99d                      7.14d          5.22d
    1,2,3,4-TeBDD                                                                                6 × 10-7g
    2,3,7,8-TeBDD     white granules       334-336a,f              438.3b          -8.72d        6.4 × 10-7b   7.74d          5.54d
                                                                                                               6.50h
                                                                                                               7.73i

    1,2,3,7,8-PeBDD                                                                -9.45d                      8.32d          5.87d
    1,2,3,4,6,7,                                                                   -10.89d                     9.50d          6.50d
    8-HpBDD
    OcBDD                                  376j                    523.2b          -11.69d       4.1 × 10-11b  10.08d         6.82d
                                                                                                 9.3 × 10-16g
    PBDFs

    monoBDF                                                                                      2.89-3.26k
    2-MoBDF                                                                        -5.42d                      5.05d          4.08d
    diBDF                                                                                        4.35-4.46k    5.58-6.09k
    2,7-DiBDF                                                                      -6.25d                      5.95d          4.47d
    triBDF                                                                                       5.36-5.47k    6.49-6.79k

    Table 5.  (Continued)

                                                                                                                                         

    Compound          Appearance           Melting point           Boiling point   Water         Vapour        Octanol/water  Sorption
                                           (°C) (observed)         (°C)            solubility    pressure      partition      coefficient
                                                                   (predicted)     [log S]       [log P]       coefficient    [log Koc]
                                                                                   (mol/litre)   (Pa at 25°C)  [log Kow]      (mol/litre)
                                                                                   (predicted)   (predicted)   (predicted)    (predicted)
                                                                                                                                         
    1,2,8-TrBDF +     colourless           144-148l
    2,3,8-TrBDF       prismsl
    2,3,7-TrBDF                                                                    -7.26d                      6.55d          4.90d
    tetraBDF                                                                                     6.35-6.41k    7.72-8.72k
    1,2,7,8-TeBDF     colourless needlesl  240.5-242l                                                          6.20h
    2,3,7,8-TeBDF     colourless needlesl  301-302l                                -7.99d                      7.14d          5.22d
                                                                                                               5.98h
    2,3,4,6-TeBDF                                                                  -7.99d                      7.14d          5.22d
    pentaBDF                                                                                     7.25-7.45k
    1,2,3,7,8-PeBDF                                                                                            7.04h
                                                                                                               7.56i
    2,3,4,7,8-PeBDF                                                                -8.71d                      7.73d          5.54d
    hexaBDF                                                                                      8.34k
    2,3,4,6,7,                                                                     -9.43d                      8.31d          5.86d
    8-HxBDF
    1,2,3,4,6,7,                                                                                 9 × 10-11g
    8-HpBDF
                                                                                                                                         

    a     From Gilman & Dietrich (1957). Melting points in parentheses are values from other sources
          reported by these authors.
    b     From Rordorf (1987).
    c     n.g. = not given.
    d     Predicted; from Fiedler & Schramm (1990). Sorption coefficient [log Koc] = distribution
          coefficient between compound adsorbed to soil organic carbon and the compound in solution.
    e     From Tomita et al. (1959)
    f     From Kende & Wade (1973).
    g     From Rordorf et al. (1990).
    h     From Jackson et al. (1993), estimated from measured reverse-phase high-performance liquid
          chromatography (HPLC) retention times.

    Table 5.  (Continued)

    i     From Jackson et al. (1993), calculated.
    j     From Denivelle et al. (1960).
    k     From Watanabe & Tatsukawa (1990).
    l     From Tashiro & Yoshiya (1982).
    

    2.2.3  Chemical reactions

         Aromatic carbon-bromine bonds are generally weaker than similar
    carbon-chlorine bonds, and, consequently, bromine can be substituted
    more easily. In general, the reductive substitution of halogens in
    aromatic structures becomes easier as the halogen atoms' size
    increases (Wania & Lenoir, 1990).

         In the presence of excess chlorine, bromine can be substituted by
    chlorine to give PXDDs/PXDFs -- for example, under conditions such as
    those present in municipal incinerators (Wilken et al., 1990; Luijk et
    al., 1992a).

         Wania & Lenoir (1990) investigated the effect of heating
    1,2,3,4-TeBDD (20 µg) in the presence of copper (1 g) at 100, 120,
    150, or 210°C for a duration of 30 seconds to 1 h. With increasing
    heating time, the spectrum of PBDD shifted from tetraBDD to lower
    brominated congeners, and the sum of the quantities decreased. The
    reaction rate increased with increasing temperature. At 210°C for 30
    min, all PBDDs had disappeared, but the dibenzo- p-dioxin ring
    structure remained intact.

         In a further experiment, it was shown that the presence of water
    (10 or 100 µg/litre) considerably increased the yield of debrominated
    products.

         On heating monoBDD and 1 g copper to 150°C, the debrominated
    product dibenzo- p-dioxin and dimers of this compound were
    identified. On heating hexaBDD and octaBDD to 150°C in the presence of
    copper, it was found that appreciable quantities of the original
    compounds could still be detected after 1 h. The reaction was
    considerably slower than in the comparable experiment with tetraBDD.

         The debromination reactions proceed faster than the respective
    dechlorination reactions with PCDDs (Hagenmaier et al., 1987).

    2.3  Conversion factors

         At 25°C and 101.3 kPa, conversion factors for converting airborne
    concentrations from ppm to mg/m3 for a particular PBDD/ PBDF congener
    can be calculated from the relative molecular mass (RMM):

              1 ppm = RMM/24.45 mg/m3
              1 mg/m3 = 24.45/RMM ppm

    For example, for monoBDF, 1 ppm = 247.1/24.45 = 10.1 mg/m3.
    Similarly, 1 mg/m3 = 0.099 ppm.

    2.4  Analytical methods

    2.4.1  General aspects

         Some PBDD/PBDF congeners are highly toxic (see chapter 7). Using
    the principles of Good Laboratory Practice, great precautions should
    be taken in handling the samples. Additionally, precautions must be
    taken owing to the photochemical instability of the brominated and
    mixed brominated/chlorinated congeners (see also sections 2.2.2.1 and
    4.2.1). The use of amber-coloured glassware and filters on lamps and
    windows is mandatory.

         Sampling, sample treatment (extraction and clean-up), and
    analysis for PBDDs/PBDFs and PXDDs/PXDFs follow largely the methods
    and techniques currently used for PCDDs/PCDFs (Donnelly et al.,
    1989a,b, 1990; US EPA, 1990, 1992 [Methods 1613 and 8290]; Maier et
    al., 1994; Ballschmiter & Bacher, 1996). The large number of isomers
    in some homologous groups (see Table 1) makes the separation and
    quantification of individual congeners difficult. Using highly
    selective, specific, and sensitive analytical methods,
    2,3,7,8-substituted PBDDs/PBDFs can be detected, although co-elution
    with other isomers cannot be excluded.

         Accurate identification of specific congeners is limited by the
    small number of reference standards available. The large number of
    PXDDs/PXDFs (see section 2.1) makes it impossible to identify and
    quantify individual congeners. Homologue groups, however, can be
    analysed semi-quantitatively. Major steps in the analytical procedures
    are as follows:

    -    spiking of the homologous sample with labelled standards
    -    use of matrix-specific extraction procedures (pretreatment of the
         sample before extraction where necessary)
    -    clean-up by column chromatography, liquid-liquid extraction, HPLC
    -    concentration of the eluate (addition of a high-boiling solvent
         as a keeper where necessary); addition of a recovery standard
    -    analysis by GC/MS.

         Many of the analytical methods for PCDDs/PCDFs have been
    validated in the past decade in interlaboratory studies organized,
    among others, by: the World Health Organization (WHO) for biological
    samples (WHO/EURO, 1989, 1991; Stephens et al., 1992; WHO/ECEH, 1996);
    the European Community Bureau of Reference for environmental samples,
    including fly ash (Maier et al., 1994), and for milk powder (Schimmel
    et al., 1994; Tuinstra et al., 1996); and the European Committee for
    Standardization for emissions by stationary sources (Bröker, 1996). To
    avoid systematic errors in the individual steps from sampling to
    analysis, recoveries must be controlled by the addition of appropriate
    stable isotope labelled standards before extraction of the sample,
    clean-up, and final quantification.

    2.4.2  Sampling and extraction

         The sampling procedures recommended for PCDDs/PCDFs (WHO, 1989
    and citations in second paragraph of section 2.4.1) also apply for the
    brominated congeners.

    2.4.2.1  Ambient air, airborne dust, automobile exhaust, flue gas, and 
             products of thermolysis

         Experience from PCDD/PCDF analysis has shown critical or weak
    points in current gas sampling (ambient air, indoor air, exhaust gas)
    techniques. Requirements are as follows:

    -    representativeness of samples; special attention must be given to
         isokinetic sampling of particles in emission samples
    -    stability of the sample on the sampling medium during the
         sampling period; the filter should be kept below 120°C and
         protected from light
    -    recovery of the analytes from the sampling train (as checked by
         appropriate spiked standards)
    -    use of clean equipment to avoid contamination of the sample (as
         checked by appropriate blanks)
    -    complete trapping of gas and particle phases (aerosols) to avoid
         sample losses.

         Quartz fibre filters with polyurethane foam plugs have been used
    to sample ambient air up to 1000 m3 (Wagel et al., 1989; Päpke et
    al., 1990; Harless et al., 1992; Watanabe et al., 1992). (Note: There
    may be interferences from brominated organic aromatic flame retardants
    in polyurethane foam.)

         Haglund et al. (1988) described a method to collect both the
    particulate phase (using a Teflon-coated filter) and the gas phase
    (cryotechnique) in vehicle exhaust.

         Hutzinger et al. (1990) used the so-called Grimmer apparatus to
    sample automobile exhaust: the sampling train consists of a large
    glass condenser and a non-impregnated fibreglass filter. Typically, 50
    m3 of automobile exhaust were taken per sample; the temperature at
    the muffler outlet was kept below 50°C. The experiments were carried
    out as stationary motor tests. The total emissions of the motor were
    sucked through the sampling train by a pressure-controlled blower.

         Emissions from a laboratory furnace experiment were collected by
    a sampling train, including a high-efficiency quartz fibre filter (to
    collect organic-laden particulate material) and an XAD-2 resin (to
    adsorb semivolatile organic compounds) (Riggs et al., 1992).

         Thermolytic products have been collected as condensate in a
    quartz-wool-filled condenser tube (Neupert et al., 1989b).

    2.4.2.2  Water and aqueous samples

         Analysis of water samples should follow a different approach. If
    the samples are free of particles, a normal liquid-liquid extraction
    is sufficient. If, however, the samples contain particles, both the
    particles and the water phase should be extracted separately -- the
    solids by methods recommended for solids, the water phase as described
    above.

    2.4.2.3  Environmental samples: soil, sediment, and sewage sludge

         For environmental samples, problems arise in obtaining a
    representative sample. For soil sampling, a method was described by
    Fortunati et al. (1994).

         Prior to the extraction, appropriate measures should be taken to
    ensure that PHDDs/PHDFs in the sample material are fully accessible to
    the extraction solvent. In a number of applications, this includes a
    digestion of the sample (solids) and/or the complete removal of water
    (wet solid samples) prior to extraction clean-up; a chemical
    destruction of non-persistent chemicals can be useful by incubating
    the sample in neat sulfuric acid (H2SO4). PHDDs/PHDFs are shown to
    be stable. Treatment with (strong) bases should be avoided, as
    PHDDs/PHDFs may degrade.

         For the study of sewage samples, Hagenmaier et al. (1992) dried,
    powdered, and extracted the samples with toluene for 18 h. After
    concentration, the extracts were treated with concentrated sulfuric
    acid.

         Proven digestion and water removal methods are treatment with
    hydrochloric acid (10% HCl) and Dean Stark collector (US EPA, 1990;
    Rappe et al., 1996), respectively. Sediments should be treated with
    copper powder to eliminate sulfur (Kjeller et al., 1993).

    2.4.2.4   Flame retardants, polymers, fly ash samples, dust, soot, and
              fire residues

         In general, the analysis of plastics is performed by dissolving
    the polymer in a suitable solvent. Non-dissolvable plastics should be
    powdered and Soxhlet-extracted.

         Dibromomethane was used to dissolve samples of PBDE (Tondeur et
    al., 1990). Ranken et al. (1994) noted that this solvent must first be
    specially purified before use to remove the colour, which caused
    quantitative interferences in the mass spectrometer. TBBPA can be
    dissolved in methanol (Tondeur et al., 1990; Ranken et al., 1994).

         PBT resins (extruded beads/powder) were extracted best with
    1,1,1-trichloroethane/phenol followed by water partitioning of phenol;
    powdered high-impact polystyrene (HIPS) samples by toluene/reflux; and
    powdered ABS samples by dichloromethane (Donnelly et al., 1989a).

         Kieper (1996) used toluene for Soxhlet extraction from samples of
    flame-retarded polymers: DBDE (with polystyrene/polystyrenebutadiene),
    1,2-bis(tribromophenoxy)ethane (with polystyrene), TBBPA-carbonate
    oligomer (with PBT), dibromostyrene, and tribromostyrene (both with
    polyamide 66).

         Samples of burnt plastic, PBT material, ash/slag, and soil were
    Soxhlet-extracted with dichloromethane (Neupert & Pump, 1992). Clausen
    et al. (1987) used Soxhlet extraction with hexane. ABS was extracted
    under reflux with methylene chloride (Donnelly et al., 1990).

         Dry fly ash was treated with 10% HCl, dried, and neutralized.
    After further drying, the sample was Soxhlet-extracted with toluene
    (Hosseinpour et al., 1989). Similar procedures were used by Tong et
    al. (1991) and Huang et al. (1992a,b).

         PBDDs/PBDFs from dust samples and smoke condensate were
    Soxhlet-extracted with toluene (UBA, 1992; Funcke et al., 1995).
    Samples from fire residues were ground and extracted with toluene;
    wipe samples of soot were extracted with hexane (Harms et al., 1995).

    2.4.2.5   Biological matrices: human milk, blood/plasma, tissues, and
              fish samples

         For biological samples, most appropriate extraction methods are
    those giving the highest yields (or recovery) for the lipids in the
    sample (i.e. milk, blood, tissue).

         Neupert et al. (1989a,b) quantified PBDDs/PBDFs in rat liver,
    adipose tissues, and faeces. After homogenization with sodium sulfate,
    extraction was performed on a multiple-layer column using
    dichloromethane/hexane.

         Fish samples were ground with sodium sulfate and homogenized.
    Methanol and sodium oxalate were added to milk samples (De Jong et
    al., 1992). Diethyl ether and hexane were used to extract PHDDs/ PHDFs
    from the fat fraction of the milk and fish samples.

         For PBDD/PBDF determination, samples of human adipose tissue were
    homogenized, extracted with dichloromethane, dried with sodium
    sulfate, and solvent-exchanged into hexane (Cramer et al., 1990a).
    This method was also used by Zober et al. (1992).

         Fat removal can be performed utilizing a semipermeable membrane
    technique (Bergqvist et al., 1993), which enables larger amounts of
    fat (sample size up to 200 g) to be eliminated from the sample matrix
    (>95%) and improved detection limits.

         Lyophilization has been used successfully in the analysis of TBDD
    in biological matrices such as rat livers or marmoset monkey tissues
    (Schulz-Schalge et al., 1991a,b; Schulz et al., 1993; Nagao et al.,
    1995/96).

    2.4.3  Sample clean-up

         Sample clean-up is carried out to remove those materials that
    might otherwise interfere with the analysis. A variety of liquid
    chromatography separations have been used, including silica, florisil,
    alumina, and various combinations of these columns. Usually an
    acid/base wash followed by alumina column chromatography is used to
    remove the bulk of interferences, and carbon column chromatography is
    used to remove residual interferences (Donnelly et al., 1986, 1987,
    1989b).

         Where PBDEs are likely contaminants, a modification of separation
    techniques is necessary. Alumina columns are ineffective in separating
    PBDFs from PBDEs. Carbon columns were found to be more effective, but
    the higher brominated PBDFs could be removed from the column only by
    back-flushing with an aromatic solvent (Donnelly et al., 1987; Hileman
    et al., 1989). Bonilla et al. (1990) introduced an HPLC step to the
    clean-up procedure. The sample was passed through an AX21 carbon
    column. The column was washed in the forward direction with
    dichloromethane/cyclohexane and dichloromethane/methanol/benzene and
    back-flushed with toluene. This procedure decreased the PBDE
    concentration in the final sample by six orders of magnitude.

         Depending on the aim of the analysis (general surveying or
    specific search and quantification of 2,3,7,8-substituted congeners),
    a number of 13C standards are required to be added at several stages
    during sampling and analysis.

         In the WHO interlaboratory calibration study for the analysis of
    PCDDs/PCDFs in human blood and milk, the basic clean-up/ separation
    methods used by some laboratories were activated carbon as the primary
    PCDD/PCDF isolation step followed by alumina; the remaining
    laboratories used other procedures, mostly H2SO4 followed by
    alumina. Nearly all methods used a step involving some type of carbon
    chromatography (Stephens et al., 1992).

    2.4.4  Separation

         GC is used for the separation of PBDDs/PBDFs. PBDDs/PBDFs have
    much higher retention times and elution temperatures (30-40°C higher)
    than their chlorinated analogues (Buser, 1991). The higher brominated
    congeners have extremely long retention times, so non-polar (SE 54),
    medium-length (up to 25-m) columns are generally used. Such a column
    is suitable for separating the PBDD and PBDF homologues. Elution
    temperatures on a 25-m SE 54 high-resolution gas chromatography (HRGC)
    column range from 184-188°C for monoBDDs/BDFs to 260-273°C for
    pentaBDDs/BDFs. Hexa-, hepta-, and octa-homologues elute during the
    isothermal phase at 280°C (Buser, 1986a, 1991). Cross-linked columns
    allow higher temperatures, reducing analysis times (Hutzinger et al.,
    1990). Table 6 gives retention indices (RIs) of some PBDDs/PBDFs as
    well as PBDEs, which are possible contaminants (Donnelly et al.,
    1987). A 30-m DB-5 or DB-5MS fused capillary column has been found to

    be quite useful for the GC/MS analysis of tetra- through
    hepta-substituted PBDDs/PBDFs (Ranken et al., 1994).

    Table 6.  Retention indices (RIs) of PBDDs,
    PBDFs, and PBDEsa,b

                                                

    Congener                                RI
                                                

    PBDDs
    2-MoBDD                                 1868
    2,8-DiBDD                               2174
    1,3,7-TrBDD                             2423
    2,3,7-TrBDD                             2475
    2,3,7,8-TeBDD                           2800
    1,2,7,8-TeBDD                           2811
    1,2,4,7,8-PeBDD                         3072
    1,2,3,7,8-PeBDD                         3145
    1,2,3,4,7,8-HxBDD                       3412
    1,2,3,6,7,8-HxBDD                       3475
    1,2,3,7,8,9-HxBDD                       3798
    1,2,3,4,6,7,8-HpBDD                     3763
    OcBDD                                   4219

    PBDFs
    2-MoBDF                                 1834
    2,8-DiBDF                               2133
    1,2,8-TrBDF                             2416
    2,3,8-TrBDF                             2433
    1,2,7,8-TeBDF                           2740
    2,3,7,8-TeBDF                           2791
    1,2,3,7,8-PeBDF                         3103
    1,2,3,6,7,8-HxBDF                       3479
    1,2,3,4,6,7,8-HpBDF                     3806
    OcBDF                                   4231

    PBDEs
    HexaBDE                                 2888
    HexaBDE                                 3004
    HexaBDE                                 3015
    HexaBDE                                 3030
    HexaBDE                                 3051
    HexaBDE                                 3095
    HexaBDE                                 3286
    HexaBDE                                 3314
    HexaBDE                                 3369
    HexaBDE                                 3411
    OctaBDE                                 3525
    OctaBDE                                 3577
    OctaBDE                                 3601
    OctaBDE                                 3627

    Table 6.  (Continued)

                                                

    Congener                                RI
                                                
    OctaBDE                                 3654
    OctaBDE                                 3737
    OctaBDE                                 3786
    NonaBDE                                 3951
    NonaBDE                                 4003
    DecaBDE                                 4310
                                                

    a         From Donnelly et al. (1987).
    b         Chromatographic conditions:
              30 m x 0.32 mm DB-5 GC column;
              He carrier gas at ca. 7 psi head
              pressure; temperature programmed
              from 10 min at 170-320 °C at
              8 °C/min.

         The elution of PCDDs/PCDFs and PBDDs/PBDFs occurs in the order of
    the molecular weights. PXDDs/PXDFs elute between the corresponding
    chloro- and bromo-analogues (Buser, 1987a). However, mixed congeners
    containing bromine elute earlier than expected on a molecular weight
    basis, relative to the chloro-compounds (e.g. BrCl5 before Cl7)
    (Buser, 1991). (For isomer-specific analysis, columns of different
    polarity should be used.)

         Owing to the lack of PBDD/PBDF (and PXDD/PXDF) standards, it has
    not been possible to identify all congeners. Instead, a combination of
    MS and GC RI identification has to be used for the analysis of
    2,3,7,8-substituted PBDDs/PBDFs, PCDDs/PCDFs, and PXDDs/ PXDFs. An RI
    model has been developed to predict the GC retention times for 1700 of
    these compounds (Donnelly & Sovocool, 1991; Donnelly et al., 1991a,b).

    2.4.5  Detection, quantification, and confirmation of PBDDs/PBDFs
            by MS techniques

         Detection, quantification, and confirmation are usually performed
    by MS, as only this technique shows sufficient selectivity to
    distinguish PBDDs/PBDFs from other halogenated compounds (e.g. PBDEs)
    that are present in the sample. MS allows the determination of the
    number and type of halogens present from characteristic isotope
    distribution patterns,