NCEA-C-1315
ERASC-002F
March 2005
MEMORANDUM: RESPONSE TO ECOLOGICAL RISK ASSESSMENT FORUM
REQUEST FOR INFORMATION ON THE BENEFITS OF
PCB CONGENER-SPECIFIC ANALYSES
by
David Cleverly
United States Environmental Protection Agency
Office of Research and Development
National Center for Environmental Assessment
Washington, DC
Eras C
Ecological Risk Assessment Support Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH

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ACKNOWLEDGMENTS
This document was prepared by David Cleverly of EPA's National Center for
Environmental Assessment (NCEA), Office of Research and Development (ORD) in response to
a request received by ORD's Ecological Risk Assessment Support Center (ERASC) from the
Ecological Risk Assessment Forum (ERAF). Scientific contributions were made by Kathleen
Walker, former Post Doc with NCEA, and Arthur Chiu, NCEA. Internal (within EPA) peer
review of the document was conducted by Lawrence Burkhard of ORD's National Health and
Environmental Effects Research Laboratory, Chris Cubbison, NCEA, and Andy Beliveau, EPA
Region 1. External peer review was conducted by Mace Barron, P .E.A.K. Research/ASE,
Colorado, and Sean Kennedy, EcoToxicology Consulting, Ontario, Canada. Steve Wharton,
EPA Region 8, Tala Henry, Office of Water/Office of Science and Technology, and Debdas
Mukerjee, NCEA, also provided helpful comments. Programmatic review of the document was
conducted by the Trichairs of EPA's Ecological Risk Assessment Forum: Susan Roddy, EPA
Region 6; Bethany Grohs, Office of Solid Waste and Emergency Response, Office of Superfund
Remediation and Technology Innovation (0SWER70SRTI); and Brenda Jones, EPA Region 5.
Finally, we would like to acknowledge the efforts of Bruce Duncan, EPA Region 10, and
Clarence Callahan, formerly with EPA Region 9, in initiating the original request.
This document has been both internally and externally scientifically peer reviewed in
accordance with Agency guidance.
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
National Center for Environmental Assessment
Washington, DC 20460
NCEA Washington Office (8623D)
January 6, 20031
MEMORANDUM

\
.SB,
pro*4-0

SUBJECT: Response to the ERAF Request for Information on the Benefits of PCB
Congener-Specific Analyses
FROM: David H. Cleverly, Environmental Scientist
Exposure Analysis and Risk Characterization Group (8623D)
TO:
Michael Kravitz, Director
Ecological Risk Assessment Support Center
NCEA-Cin
In August, 2001, the Ecological Risk Assessment Forum (ERAF) submitted a formal
question to the Ecological Risk Assessment Support Center (ERASC) on the benefits of
evaluating PCB congeners in environmental samples. This question was developed by ERAF
members Bruce Duncan and Clarence Callahan. ERASC contacted NCEA's Exposure Analysis
and Risk Characterization Group for assistance in responding to the request. The purpose of this
memorandum is to formalize the response.
Central question being asked: What information is provided by performing PCB congener
analysis as compared with Aroclor or total PCB reporting of the results of environmental
sampling?
The production of PCBs ceased in the late 1970's. Monsanto produced commercial
mixtures known as Aroclors that differed by the total amount of chlorine present as well as the
PCB congener composition. In the environment, various biotic and abiotic processes shift the
PCB congener composition from the original commercial products such that environmental
samples no longer resemble PCB Aroclors. Hence using Aroclor technical standards to
qualitatively determine PCB levels present in the environment may provide an inaccurate
depiction of the current PCB congener mixtures present in environmental media and biota. This
technical response is divided as follows:
1 Revised March, and August 2004 in accordance with internal and external peer review
comments

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I	A review of the historical production and use of PCBs
II	A brief review of the PCB congener composition of Aroclors
III	Alterations of PCB congener profiles as a result of environmental weathering
IV	Alterations of PCB congener profiles as a result of bioaccumulation and biomagnification
in ecological food chains
V	Utility of PCB congener-specific analyses - two examples
VI	PCB congeners common to environmental matrices
VII	Conclusions regarding PCB congener-specific analyses for environmental samples
I.	Historical Production and Use of PCBs
As a prelude to the discussion of the benefits of congener-specific analysis, it is useful to
briefly review the history of the domestic and global production and use of PCBs. PCBs were
once perceived as highly valuable manmade chemicals. Their high boiling points and resistance
to thermolytic breakdown made them useful in a broad array of industrial applications.
Furthermore, since PCBs do not conduct electric current, they were useful for commercial
purposes as insulating material and dielectric fluid. Global production of commercial PCB
mixtures from 1929 to 1980 has been estimated to be greater than 1.1 million metric tons
(Erickson, 1997). U.S. production has been estimated to be approximately 568,000 metric tons
(U.S. EPA, 1976). Maximum U.S. production occurred in 1970 with a volume of 38,500 metric
tons (IARC, 1978). In 1972, Monsanto Corporation, the major U.S. producer, voluntarily
restricted the sale of PCBs to uses as dielectric fluids in "closed electrical systems." This
restriction was prompted by growing evidence of PCBs' persistence in the environment,
tendency to bioaccumulate in animal tissues and toxic effects. Annual production fell to 18,000
metric tons in 1974. Monsanto ceased PCB manufacture in mid-1977 and shipped the last
inventory in October 1977 (Erickson, 1997). Regulations issued by EPA beginning in 1.977,
principally under the Toxic Substances Control Act (TSCA) (40 CFR 761), have strictly limited
the production, import, use, and disposal of PCBs.
Monsanto Corporation marketed technical grade mixtures of PCBs primarily under the
patented trade name Aroclor. The Aroclors are identified by a four-digit numbering code in
which the last two digits indicate the approximate chlorine content of the formulation by weight
percent. The exception to this coding scheme is Aroclor 1016, which contains only mono-
through hexa-chlorinated congeners with an average chlorine content of 40 percent. The uses of
Aroclors containing mixtures of PCB congeners can be classified into three categories (Erickson,
1997; U.S. EPA, 1976):
1.	Completely closed electrical systems such as electrical capacitors and transformers. In
these cases, PCB dielectric fluids are self-contained within the electrical apparatus in
sealed steel vessels.
2.	Semi-closed applications. In these cases, PCBs are used as lubricants in high
temperature environments. Examples include hydraulic and heat transfer systems and
vacuum pumps.
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3. Open-ended applications. These uses are varied but refer to coatings, dyes, paints, inks,
adhesives, pesticide extenders, plasticizers, synthetic rubber, carbonless copy paper,
cutting oils, lubricating oils, and casting waxes.
Estimates of PCB usage in the United States by usage category during the period 1930-
1975 are presented in Table 1. Prior to voluntary restrictions by Monsanto Corporation in 1972
on sales for uses other than "closed electrical systems," approximately 13 percent of the PCBs
were used in "semi-closed applications," and 26 percent were used in "open-end applications."
Most of this usage of PCBs for "semi-closed" and "open-end" applications occurred between
1960 and 1972 (U.S. EPA, 1976). Table 2 shows the percentage of total Aroclor production
contributed by specific Aroclors during the years.1957-1977. EPA has estimated that
approximately 5 percent of the PCBs used in closed electrical systems were released into the
open environment; 60 percent of the PCBs used in semi-closed applications were released; 25
percent of the PCBs used for plasticizers were released; and 90 percent of PCBs used for
miscellaneous industrial uses had escaped into the environment (U.S. EPA, 1976). The
reliability of these release estimates was assumed to be +30 percent (U.S. EPA, 1976). Prior to
the enactment of legislation, approximately 132,000 metric tons of PCBs were buried in
unsecured sanitary landfills (U.S. EPA, 1976). This total was comprised of 50,000 metric tons
from capacitor and transformer production wastes, 36,000 metric tons from disposal of obsolete
electrical equipment, and 46,000 metric tons from disposal of material from open-end
applications. An additional 14,000 metric tons of PCBs, although still in service in various semi-
closed and open-end applications in 1976 were estimated to ultimately be destined for disposal in
landfills.
Table 1. Estimated U.S. "Usage of PCBs by Use Category (193Q-1975)
Category
Type of Product
Total Use
Completely closed electrical
systems'
Transformers, capacitors, electrical
insulating and cooling applications
61% before 1971
100% after 1971
Semi-closed applications
Hydraulic fluids, heat transfer fluids,
lubricants
13% before 1971
0% after 1971
Open-end applications
Plasticizers, surface coatings, ink and
dye earners, adhesives, pesticide
extenders, carbonless copy paper, dyes
26% before 1971
0% after 1971
Source: NRC (2000)
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Table 2. Percentage of Total Aroclor Production Contributed by Specific Aroclors During the Years
1957 - 1977		
Aroclor
1957-1977 U.S. Production (%)
1016
12.88
1221
00.96
1232
00.24
1242
51.76
1248
06.76
1254
15.73
1260
10.61
1262
00.83
1268
00.33
Source: Brown (1994)
II. PCB Congener Composition of Aroclors
Frame et al. (1996) has reported on the detailed analyses of the PCB congener
distributions present in Aroclors 1016, 1242, 1248, and 1254. Because of variation to the
chlorination process during chemical synthesis, no two batches of the same Aroclor had identical
PCB congener distributions. In fact, substantial differences in congener profiles between batches
of the same Aroclor could lead to significant differences in biological effects (Kodavanti et al.,
2001). Nevertheless the work by Frame et al. (1996) has yielded typical congener patterns
present in the PCB formulations. The typical percent distribution of congeners by PCB
homologue groupings is depicted in Table 3. Note that the most abundant homologue groups are
the di- and tri-chlorinated biphenyls for the low chlorinated Aroclors (1016 and 1242) while
penta-chlorinated biphenyls were more abundant in the higher chlorinated Aroclors (1248,1254
and 1260). Tetra-chlorinated biphenyls were abundant in both low chlorinated and higher
chlorinated Aroclors.
Table 3. Typical PCB Homologue Composition (% wt) of Five PCB Aroclors
PCB
Aroclor 1016
Aroclor 1242
Aroclor 1248
Aroclor 1254
Aroclor 1260
Homologue
(%)
(%)
(%)
(%)
(%)
Mono-CB
0.7
0.8
0
0
0
Di-CB
17.5
15.0
0.4
0.2
0.1
Tri-CB
54.7
44.9
22.0
1.3
0.2
Tetra-CB
26.6
32.6
56.6
16.4
0.5
Penta-CB
0.5
6.4
18.6
53.0
8.6
Hexa-CB
0
0.3
2.0
26.8
43.4
Hepta-CB
0
0
0.6
2.7
38.5
Octa-CB
0
0
0
0
8.3
Nona-CB
0
0
0
0
0.7
Deca-CB
0
0
0
0
0
Source: Frame et al. (1996)
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III.	Alterations of PCB Congener Profiles as a Result of Environmental Weathering
In the environment PCBs occur as mixtures of congeners, but their composition will
differ from the commercial Aroclors. The chemical and physical properties largely affects the
environmental distribution of PCBs. The National Research Council (2000) recently reviewed
the fate processes that tend to change the environmental mixtures of PCBs from what was
initially released into the environment. The term 'weathering' refers to the sum effect of these
fate processes. When released into the environment, PCBs tend to partition to the organic
component of soil, water and sediment. Within an aquatic system, PCBs can exist in three
abiotic phases: freely dissolved in water; associated with dissolved organic carbon in the water
column; and sorbed to particles (NRC, 2000). Freely dissolved light molecular weight PCB
congeners may volatilize from the water and into the atmosphere. PCB congeners sorbed to
organic carbon in the water column can cross the sediment-water interface and can move below
the surficial sediments through the process of diffusion (NRC, 2000). Particle-bound PCB
congeners eventually settle to become incorporated into the sediments. The NRC (2000) has
noted the following generalizations with respect to the environmental distribution of PCB
congeners:
1.	The less chlorinated PCB congeners are more water soluble, more volatile and more
susceptible to biodegradation. This tends to cause lower concentrations of these PCB
congeners in sediments as compared with their distribution in the Aroclor that was
discharged into the environment.
2.	Higher chlorinated PCB congeners are less soluble, sorb more readily to organic
substrates, are less volatile and less susceptible to biodegradation. These PCB congeners
are persistent in sediments and tend to bioaccumulate in ecological food webs.
3.	At the interface of surface water and the atmosphere, the lower chlorinated PCB
congeners have higher vapor pressures and tend to volatilize from the water body into the
atmosphere. By this process the atmosphere tends to become enriched in the lower
chlorinated congeners relative to the water column, leaving the water body depleted of
low molecular weight PCB congeners.
4.	As a result of weathering, the PCB congener mixtures that occur in the environment
differ substantially from the PCB congener composition of the original industrial release
(Bazzanti et al., 1997).
IV.	Alterations of PCB Congener Profiles as a Result of Bioaccumulation and
Biomagnification in Ecological Food Chains
Measures of Aroclor mixtures or total PCB concentrations may not provide adequate data
on PCB exposure and health risks to wildlife. Although there are 209 possible congeners, only
about half are prevalent in the environment and, of those, only a limited number both accumulate
in animal tissues and exhibit significant toxic effects (McFarland and Clarke, 1989; Chiu et al.,
2000; Letcher et al., 2000). Furthermore, differences in uptake, metabolism and
bioaccumulation of PCB congeners can lead to significant differences between congener profiles
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in predators feeding high on aquatic and terrestrial food webs, and congener profiles in
contaminated sediments and soils in the same ecosystems or in the original Aroclor mixtures
(NRC, 2000; Chiu et al., 2000; Wagman et al., 2001).
Toxicity of different congener groups
Accurate information on specific congener body burdens is important as toxicological
effects vary greatly. PCB congener-specific toxic effects in mammals are believed to include
developmental and reproductive toxicity, dermal toxicity, endocrine effects, hepatotoxicity and
carcinogenesis (Safe, 1993; ATSDR, 2000). Coplanar congeners, those having two para-, two or
more meta- and no ortho- chlorine substituents, and their mono-ortho analogs may be
responsible for much of the observed toxicity of PCB mixtures present in the environment (Safe,
1994; van den Berg et al., 1998). Coplanar PCBs have similar chemical structures to dioxins,
have a common mechanism of toxicity, and invoke a similar battery of toxic responses as
2,3,7,8-tetrachlorodibenzo-/?-dioxin (TCDD). Because of a shared mechanism of toxicity with
certain dioxins and dibenzofurans, the concept of toxicity equivalence has been applied for
translating complex mixtures of chlorodibenzo-p-dioxins, chlorodibenzofurans and coplanar
PCBs present in tissues or diet into 2,3,7,8-TCDD toxicity equivalent concentrations (TEC)
using a toxicity equivalence factor (TEF) (Safe, 1994). A TEF is an estimate of the potency,
relative to 2,3,7,8-TCDD, of an individual polychlorinated dibenzo-/?-dioxin, dibenzofiiran or
biphenyl congener, using careful scientific judgment after considering all available relative
potency data. Coplanar PCBs behave like TCDD by binding to the aryl hydrocarbon (Ah)
receptor, a common pathway for dioxin-like toxicity. The dioxin/PCB-receptor complex then
enters the cell nucleus and induces a variety of toxicologically-relevant changes, including
enzyme induction (e.g., aryl hydrocarbon hydroxylase, AHH) and possibly competition for other
nuclear proteins that regulate cell differentiation. Thus the PCB congeners that also induce AHH
activity are referred to as dioxin-like. Several different methods for calculating TEFs have been
developed using particular animal species and toxic endpoints (Leonards et al., 1995). In
conducting human health and wildlife risk assessments, EPA generally recommends the use of
the-TEF procedure developed by the World Health Organization (WHO) as reviewed by van den
Berg et al. (1998). Table 4 displays the WHO-TEFs developed for mammals, birds and fish.
The toxicity equivalence concept is applied by multiplying the TEF of each congener present in
a mixture by the respective mass concentration and the products are summed to represent the
2,3,7,8-TCDD TEC of the mixture, as in the following equation:
TEC = Yj, n(Congener; x TEF,)+ {congene^ x TEFy)+	(Congenern x TEFn)
The assumption of additivity is inherent to the TEF approach. There are limitations to
the predictive value of the TEF approach for PCB mixtures as the biological activity of some
congeners may change in the presence of other congeners (Safe, 1994, 1998; van den Berg et al.,
1998). Nonetheless, considerable experimental data for ecologically relevant exposures and
toxicity endpoints, such as early life stage mortality, support the additivity assumption with no
evidence of antagonism or synergism (Walker and Peterson, 1991; Walker et al., 1996; Zabel et
al., 1995; Tillet et al., 1996). In general, the four congeners considered most toxic, based on
dioxin-like activity, are the non-ortho (coplanar) PCBs with the IUPAC numbers 77 (chlorinated
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on carbons 3,3',4,4'), 81 (3,4,4',5), 126 (3,3',4,4',5) and 169 (3,3V4,4',5,5') (van den Berg et al.,
1998). Some congeners may cause toxic effects indirectly through a variety of mechanisms
involving the cytochrome P450 (CYP) mixed-function oxidase system (Letcher et al., 2000).
While induction of CYP may help to remove contaminants, it may also harm the organism by
turning otherwise nontoxic contaminants into cytotoxic or genotoxic metabolites (McFarland and
Clarke, 1989). In addition, ortho-substituted congeners may have neurotoxic effects (Kodavanti
et al., 2001).
Table 4. World Health Organization Toxicity Equivalence Factors (TEF) for Mammals, Birds and Fish
Congener |
TEF Mammals
TEF Birds
TEF Fish
2378-TCDD
1
1
1
12378-PeCDD
1
1
1
123478-HxCDD
0.1
0.05
0.5
123678-HxCDD
0.1
0.01
0.01
123789-HxCDD
0.1
0.1
0.01
1234678-HpCDD
0.01
0.001
0.001
OCDD
0.0001
0.0001
0.0001
2378-TCDF
0.1
1
0.0001
12378-PeCDF
0.05
0.1
0.05
23478-PeCDF
0.5
1
0.5
123478-HxCDF
0.1
0.1
0.1
123678-HxCDF
0.1
0.1
0.1
123789-HxCDF
0.1
0.1
0.1
234678-HxCDF
0.1
0.1
0.1
1234678-HpCDF
0.01
0.01
0.01
1234789-HpCDF
0.01
0.01
0.01
OCDF
0.0001
0.0001
0.0001
IUPAC PCB-81
0.0001
0.1
0.0005
IUPAC PCB-77
0.0001
0.05
0.0001
IUPAC PCB-126
0.1
0.1
0.005
IUPAC PCB-169
0.01
0.001
0.00005
IUPAC PCB-105
0.0001
0.0001
0.000005
IUPAC PCB-114
0.0005
0.0001
0.000005
IUPAC PCB-118
0.0001
0.00001
0.000005
IUPAC PCB-123
0.0001
0.00001
0.000005
IUPAC PCB-156
0.0005
0.0001
0.000005
IUPAC PCB-157
0.0005
0.0001
0.000005
IUPAC PCB-167
0.00001
0.00001
0.000005
IUPAC PCB-189
0.0001
0.00001
0.000005
Source: van den Berg et al. (1998)
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Persistence and bioaccumulation of different congeners
PCB mixtures change as these contaminants move through abiotic media into food chains
(Chiu et ah, 2000; NRC, 2000). Some congeners exhibit preferential uptake, metabolism or
bioaccumulation by different organisms (Goerke and Weber, 2001; Jackson et al., 1998, 2001;
Traas et al., 2001; Willman et al., 1997). Organisms acquire PCBs either through contact with or
ingestion of contaminated sediments, water or soil, or through their food. Once the PCBs enter
an organism, individual congeners are either cleared through metabolism and/or excretion or are
sequestered, usually in lipid tissues. The rate of clearance of a PCB congener through non-
metabolic processes is usually inversely proportional to its preferential solubility in lipids,
measured as the octanol-water partition coefficient Kovv (Thomann, 1989). Metabolic clearance
also depends on chemical structure of the congener and the induction of appropriate enzyme
pathways in the organism.
Several factors tend to influence the bioaccumulation tendency of different congeners,
including the number of chlorine (CI) substituents and their positions on the two phenyl rings. In
general, the more chlorinated congeners exhibit a higher level of persistence in vertebrates and
will concentrate to higher levels in tissues of predators than in the surrounding environmental
media or prey organisms. This phenomenon has been observed in field populations of fish
(salmon - Jackson et al., 2001), birds (cormorants - Guruge and Tanabe, 1997; seabirds - Braune
et al., 2001) and mammals (seals - Bernt et al., 1999) and corroborated in controlled laboratory
studies (rats - Kodavanti et al., 1998). Wagman et al. (2001) observed similar congener
specificity for persistence and elimination in invertebrates (earthworms) exposed to PCB
mixtures. In earthworms, elimination was observed to be enhanced for lower chlorinated PCB
compounds (e.g., PCB-45) and slowest for nonpolar PCB congeners having 6 or 7 chlorine
substituents (e.g., PCB-169). The position of CI substituents on the ortho, meta or para positions
also affects bioaccumulation (Boon et al., 1994). Congeners can be classified as either persistent
or readily cleared based on the absence or presence, respectively, of neighboring meta-para
hydrogen substituents (m,p-H) on at least one phenyl ring (kestrels - Drouillard et al., 2001;
weasel/otters - Leonards et al., 1998; cormorants - Guruge and Tanabe, 1997; crustaceans and
fish - Porte and Albaiges, 1994). At the bottom of the food chain, phytoplankton were observed
to preferentially take up coplanar congeners rather than those with ortho- chlorine substituents
(Swackhamer and Skoglund, 1991). The effect of degree of chlorination at ortho positions on
bioaccumulation is more complex and variable in vertebrates (Bruhn et al., 1995; Boon et al.,
1994). In general, bioaccumulation in both vertebrates and invertebrates changes the congener
profile relative to the surrounding environment.
It should be stressed that patterns of persistence of certain congeners do not hold across
species. For example, the highly toxic non-ortho PCB congeners IUPAC 77, 126 and 169 are
metabolized and not abundant in body tissues of some predators experiencing high levels of PCB
exposure (seal - Nakata et al., 1997; salmon - Willman et al., 1997; porpoise - Bruhn et al., 1995)
but congeners 126 and 169 do appear to preferentially bioaccumulate in other predator species
(weasel/otters - Leonards et al., 1998; cormorants - Guruge and Tanabe, 1997). Some general
patterns may, however, exist. In their review of the occurrence and abundance of PCB
congeners across species, including humans, McFarland and Clarke (1989) observed that tetra-,
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penta- and hexa-chlorinated congeners seemed to predominate in biological tissues. In addition,
accumulated PCBs are further bioconcentrated at each succeeding trophic level in a food web,
causing high-order predators to experience the highest overall environmental exposure to PCBs.
The frequency and severity of adverse effects, however, depend not just on the level of exposure
but also on the particular species' sensitivity to PCBs.
Biomagnification of different congeners in aquatic food chains
More highly chlorinated congeners tend to bioaccumulate most readily, and PCBs tend to
biomagnify in the food chain, reaching relatively high, toxic concentrations at higher trophic
levels, such as in piscivorus birds (e.g., gulls, terns, and cormorants) and mammals (e.g., minks,
otters, seals, and sea lions) (ATSDR, 2000). As PCBs are passed through a food chain, certain
congeners are more likely to biomagnify than others (Jackson et al., 1998; Trowbridge and
Swackhamer, 2002). How congener patterns change depends upon the number of trophic levels
in a food web and the varying capacities of the different species to metabolize the contaminants.
In an aquatic food web that included plankton, macro invertebrates, alewife and salmon in Lake
Michigan, Jackson et al. (1998, 2001) found that the degree of biomagnification generally
increased with the degree of congener chlorination. More specifically, the largest components of
the total PCB mixture in plankton, the base of the pelagic food web, were tetra- and
pentachlorobiphenyls, but in the macro invertebrates Mysis and Diporeia and in salmon, the PCB
mixture was predominantly hexachlorobiphenyls. A similar pattern was observed in earlier
research in Lake Michigan by Willman et al. (1997), in which penta-, hexa- and heptachloro
congeners were more concentrated while trichloro congeners were depleted as the PCB mixtures
moved from sediments to plankton to fish. Within groups of congeners with the same degree of
chlorination (homologues), congeners with no or few ortho- chlorine substituents have shown a
tendency to bioaccumulate in lower trophic levels in a study by Swackhamer and Skoglund
(1991) but not in a study by Willman et al. (1997). In a follow-up study, Trowbridge and
Swackhamer (2002) confirmed that dioxin-like PCB congeners preferentially bioaccumulate in
the trophic transfer from the dissolved phase to phytoplankton and from phytoplankton to
zooplankton of freshwater lakes. Trowbridge and Swackhamer (2002) found that the
biomagnification of dioxin-like PCB congeners are twice the rate of other PCBs for each of the
trophic transfer steps. This observation is consistent with the hypothesis that the environmental
distribution and trophodynamics of mono- and non-ortho substituted PCB congeners differs from
other PCB congeners, with the result that dioxin-like PCBs preferentially bioaccumulate in lower
trophic levels. In a Lake Ontario study focusing on mono- and non-ortho congeners, Metcalfe
and Metcalfe (1997) found that these more toxic congeners were a larger percentage of the PCB
profiles in plankton than in higher organisms in the food web. These congeners did
preferentially bioaccumulate at certain trophic transfer points, specifically between invertebrates
and fish, and between fish and herring gulls.
V.. Utility of PCB Congener-specific Analyses - Two Examples
Example 1. Reproductive toxicity of PCBs in mink
The limitations of wildlife risk assessments based only on total PCBs is illustrated in the
case of mink {Mustela vison). Mink are fish-eating mammals and may be exposed through their
diet to high levels of PCBs in contaminated ecosystems (Giesy et al., 1994). Mink are highly
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sensitive to PCBs and experience adverse reproductive effects including reduced litter size and
high (up to 100%) kit mortality even when exposed to fairly low levels of PCB contamination in
their diet (Heaton et al., 1995; Restum et al., 1998; Brunstrom et al., 2001). PCB concentrations
in the food sources of wild populations of mink have been assessed in the Great Lakes region,
while the practice of mink farming has allowed controlled laboratory experiments to determine
the effects of PCBs on mink directly. Estimates of reproductive risks from PCB congeners can
be based on analyses of diet or on mink body burdens. The reproductive effects appear to be
caused by the dioxin-like congeners (Brunstrom et al., 2001). Ortho-congeners such as IUPAC
153 (2,2',4,4',5,5') and IUPAC 136 (2,2',3,3',6,6') may exhibit neurological effects (Aulerich et
al., 1985).
In their review of recent literature, Giesy and Kannan (1998) observed that laboratory
mink feeding studies using commercial Aroclor mixtures calculated higher low/no observable
effect levels (LOEL/NOEL) and EC50 than did studies using weathered PCB mixtures as found in
wild food sources (fish). In other words, weathered PCB mixtures were more toxic than the
commercial mixtures, indicating that the congener profile changed as the contaminants moved
through abiotic media and into the aquatic food web (e.g., Giesy et al., 1994). In an earlier
review of experimental data, Leonards et al. (1995) found it difficult to determine a dose-
response curve or reference dose for reproductive effects such as litter size or kit survival based
on total PCB in the mink diet. However, a dose-response curve that matched laboratory
observations could be calculated based on mink whole-body concentration of dioxin-like PCB
congeners estimated using TEF calculations developed by Safe (1993). Further laboratory work
by Brunstrom et al. (2001) confirmed that reproductive effects in mink are correlated with high
levels of non- and mono-ortho-substituted-biphenyls (dioxin-like congeners) in their food, while
no reproductive effects are observed among mink exposed to high concentrations of 2-4-ortho-
substituted-biphenyls only. These studies clearly indicate the importance of using more refined
measurements than total PCB concentrations to assess risks to sensitive wildlife.
Example 2. A study of the effects of PCB on the hormonal system ofpolar bears
Braathen et al. (2004) studied the relationship between the uptake of PCB congeners and
thyroid hormones (THs) and retinal within male and female polar bears. This provides a second
example of the use of PCB congener-specific analysis to understand the toxicity of PCBs on
mammals. The authors noted that alterations of THs can have observable effects on behavior
and on the neurological system. In addition, hypothyroidism is associated with menstrual
dysfunction, anaovulation and miscarriages.
The polar bear (Ursus maritimus) is at the top of the Arctic food web and preys on
marine mammals, e.g., ringed and harp seals. PCB exposures to the polar bear are through their
diet in that marine mammals have a tendency for accumulating PCBs present in the environment
through the process of biomagnification up trophic systems. This study examined the
relationship of the body burden of twenty-eight PCB congeners in polar bears (PCB-99, 105,
118, 138,153, 156, 157, 170, 180,194, 206 and 209 were listed by the authors) to alterations in
their hormonal system. Six congeners were analyzed to represent the twenty-eight since many of
the PCB congeners were found to be correlated to one another, that is, when one is present the
other is also present in polar bear tissues (i.e., PCB-99 correlated with 138; 118 with 105; 156
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with 157; 180 with 170; and 194 with 206+209). Blood samples were collected (17 female and
29 male mature bears) for PCB, TH and retinal analysis. When evaluating a possible cause and
effect relationship between PCBs and the alteration of TH, these six PCB congeners were
summed to represent all twenty-eight congeners. The investigators observed a statistically
significant negative correlation between plasma PCB-levels and the plasma levels of five and
two TH variables in female and male polar bears, respectively, i.e., decreases in plasma levels of
specific thyroid hormones. Females were found to be more susceptible to TH suppression by
PCBs than males, and the TH hormone, T3, was decreased to the greatest extent. The authors
noted a need for research to relate the apparent TH imbalance in females caused by PCBs to
adverse functional effects on the endocrine system. No statistically significant effect was
observed between plasma PCB-levels and retinal in either male or female bears. In this study,
the utility of PCB congener specific analysis was to identify PCB congeners that should be
further studied for their propensity for endocrine disruption.
VI. PCB Congeners Common to Environmental Matrices
Hansen (2001) identified a series of PCB congeners that are most commonly detected in
environmental matrices, including sediments, soils and biota. Hansen based his list of
congeners, summarized in Table 5, on a review of numerous data sets published in the scientific
literature. Together, the congeners in Table 5 account for >60% of all PCBs measured. This
table may serve as a basis for agreement on PCB congeners in need of analytical delineation.
Table 5. Hansen's List of Major PCB Congeners Detected and Characteristic of Steady State PCB
Residues
IUPAC No.
Ring Chlorination
IUPAC No.
Ring Chlorination
153
245-245
201
2345-2356
138
234-245
56 + 60
23-34 + 234-4
180
2345-245
66 + 95
24-34 + 236-25
118
245-34
163
2356-34
74
245-4
128 + 167
234-234 + 245-345
146
235-245
194
2345-2345
170
2345-234
196 + 203
2345-2346 + 23456-245
99
245-24
70 + 76
25-34 + 345-2
187
2356-245
77
34-34
28+31
24-4 + 25-4
81 .
345-4
156
2345-34
126
345-34
105+ 132
234-34
169
345-345
183
2346-245


Notes: Two congeners separated by a + sign indicates that they are seldom resolved and coelute.
Source: Hansen (2001)
VII. Utility of PCB Congener Patterns Analysis in Environmental Samples.
PCB congener-specific analysis can provide information necessary to resolve likely
sources of environmental contamination. Termed "fingerprinting," congener patterns present in
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aquatic sediments or other environmental media can be matched against a database of PCB
congener profiles of source releases to link sources with receptors.
For example, Ikonomou et al. (2004) compared the PCB congener distribution in
Dungeness crab (Cancer inagister) to the PCB congener distributions measured in sediments at
various locations in Victoria Harbor, British Columbia. The crab was used as a biomonitor with
the intent of identifying sources of PCB contamination. Statistical analysis (factor analysis and
principal component analysis) was applied to the PCB congener patterns discerned in crab and
sediment. A remarkable similarity in the PCB congener patterns was found between crab and
sediment close to the outfall of a former bleached chlorine pulp and paper mill. In both matrices
the congener pattern resembled a 45:55 mixture of Aroclors 1254 and 1260. Ikonomou et al.
(2004) applied a direct mixing model to the PCBs associated with the mill operations, and,
considering the weathering of PCBs in sediments with the passage of time, they predicted the
PCB congener distributions in the sediments. From this procedure, the investigators found a
good fit between the PCB congener profile measured in the sediments at the outfall to the
wastewater discharge at the mill with the predicted congener profile resulting from the mixing
model. With these two lines of evidence, i.e., a PCB fingerprint match between crab and
sediment, and a PCB fingerprint match between measured and predicted sediment PCB
distribution, Environment Canada concluded that the likely source of PCB contamination in
Victoria Harbor was the past operation of the paper mill.
A study of the Lower Fox River in Wisconsin (Stratus Consulting, 1999) provides a
second example of the utility of PCB congener pattern analysis. In an effort to identify the
source of PCB contamination in the river sediments, the investigators relied on the comparison
of PCB congener patterns in relation to four locations within the watershed area: Lower Fox
River (LFR), Inner Green Bay, Outer Green Bay, and Lake Michigan. A suspected source of
contamination was the congregation of several paper mills along the LFR reach. These mills
were the center of the production of carbonless copy paper in which PCBs were used as a
coating. Based on reviews of historical facility records, industrial processes and waste disposal
practices, and PCB concentrations in paper products and waste, it was estimated that paper mills
along the LFR had released a total of 300,000 kg of PCBs into the Lower Fox River. Sediment
concentrations were lowest upstream of the location of the mills and reached maxima near the
cluster of the mills on the LFR. The spatial and temporal pattern of PCB contamination in LFR
sediments was found to be consistent with the transport and weathering of PCBs discharged from
the paper mills. PCB congeners 028+031 (coeluted), 056+060, 066+095, and 070+076 were
common to all sampling areas. However, the LFR was found to be more enriched in the lower
chlorinated congeners (those with low congener numbers) than the other three sampling areas.
Lake Michigan samples appeared to be relatively enriched in the higher chlorinated congeners
(those with high congener numbers). Analysis of PCB congener patterns indicated that PCBs in
Green Bay were derived from those in the LFR (and ultimately the paper mills), and Lake
Michigan PCBs probably originated from outer Green Bay.
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VIII. Conclusions
PCB congener-specific data provide the best and most scientifically defensible basis for
evaluating the ecological hazards that may be associated with PCB contamination in the
environment. Information and examples presented in this memorandum give scientific
support to this premise.
The weathering of PCBs, coupled with PCB bioaccumulation in ecosystems,
considerably alters the mixture of PCB congeners present in the environment. This
means that, with the passage of time, the PCB congener patterns that initially comprised
commercial PCB formulations are less likely to resemble the PCB congener patterns
currently observed in the environment.
Specifying the PCB congener profiles in environmental samples adds important
information to the risk assessment process that otherwise would be obscured by only
reporting Aroclor equivalents or total PCBs in the samples. PCBs exhibit a wide
spectrum of toxicologic effects in various species, including humans (ATSDR, 2000).
This has created two major groups of PCB congeners: 1) the dioxin-like (co-planar)
PCBs, and (2) the non-dioxin-like PCBs. In specifying the PCB congener profiles for
purposes of human health and ecological risk assessments, such groupings are useful.
PCB congener fingerprinting techniques can lead to the identification of likely sources of
PCB contamination. This involves the matching of the PCB congener patterns present in
the environment to the PCB congener profiles associated with the use of specific PCB
Aroclors by local point sources, and accounting for the weathering of PCBs. The
application of statistical pattern recognition techniques to the data (e.g., principal
component analysis) may greatly assist this effort.
A central question for this analysis is whether PCB congener distributions can be
estimated for historical environmental measurements in which the data is reported in
Aroclor equivalents or the sum of PCBs present in the sample. The work of Ikonomou et
al. (2004) has demonstrated that it is theoretically possible to predict PCB congener
patterns based on an assumption of the weathering of specific Aroclors that may have
been used by specific sources. This can be achieved through the application of
sophisticated environmental mixing models. It may be possible to run these models
backwards from the current measurement of the PCB congener patterns present in the
environment to a prediction of the distribution of PCB congeners that may be present in
environmental matrices in cases where environmental measurements are represented only
as Aroclor equivalents. However, such analysis would be highly uncertain and results
would be difficult to verify. Until research has reached a point where one can readily
identify clear and unambiguous PCB congener patterns in all environmental matrices,
and the physical/chemical processes of weathering are more accurately defined, it is not
possible to reach a firm conclusion as to the scientific validity of retrospectively
reconstructing the likely PCB congener distributions in these historical environmental
studies.
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It is recommended that the results of analyses for PCB contamination in environmental
matrices be expressed in terms of PCB congener-specific, total PCB, and Aroclor
equivalent concentrations. This will provide useful information on the proportion of
specific PCB congeners relative to the sum of all congeners that is needed in order to
scientifically address the use of historical data. A second benefit of this approach is that
ecological risk assessment metrics have, in many cases, been developed around
exposures to total PCBs and Aroclor equivalents in the environment, and not on a single
congener. The reporting of total PCBs and Aroclor equivalents in environmental studies
will provide continuity in terms of the utilization of available bioaccumulation factors
and ecotoxicity benchmarks in site-specific ecological risk assessments.
Current state-of-the-art laboratory methods makes it possible to analytically identify and
quantify the presence or absence of all 209 PCB congeners in environmental samples
(e.g., EPA Method 1668A; U.S. EPA, 1999). The PCBs that can be determined by this
Method are the 12 polychlorinated biphenyls (PCBs) designated as having dioxin-like
activity and the remaining 197 PCBs. Approximately 125 of the PCB congeners are
resolved adequately on an SPB-octyl gas chromatographic column to be determined as
individual congeners. The remaining 70 congeners are determined as mixtures, e.g., they
coelute with other congeners. The overarching question then shifts away from analytical
chemistry capabilities to one of defining a subset of 209 PCB congeners that should be
routinely identified as PCB congener mixtures in specific environmental media and biota.
Hansen (2001; Table 5 of this document) has provided an interim list of major
(commonly reported) congeners characteristic of steady state PCB residues.
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Braathen, M; Derocher, AE; Wiig, 0; et al. (2004) Relationships between PCBs and thyroid
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ADDITIONAL REFERENCES ON PCBs NOT CITED IN THIS MEMORANDUM
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