Relationship of serum levels of individual PCB, dioxin, and furan congeners and DDE with Great Lakes sport-caught fish consumption

Great Lakes (GL) sport fish consumption is a potential route of exposure for environmentally persistent organochlorine contaminants, which may have human health effects. In this report, relationships are explored among individual congeners in a large cohort of frequent and infrequent GL sport fish consumers. Blood samples were obtained in 1993-1995 and analyzed for 1,1-bis(4-chlorophenyl)-2,2-dichloroethene (DDE) and for 62 noncoplanar polychlorinated biphenyls (PCBs), 4 coplanar PCBs, 8 polychlorinated dibenzo-p-dioxin (dioxin), and10 dibenzofuran (furan) congeners. All GL fish eaters and referents had detectable levels of DDE, total noncoplanar PCBs, total coplanar PCBs, total dioxins, and total furans. Noncoplanar PCBs were higher in GL sport fish consumers than in a referent population from the same geographic area, were associated with GL sport-caught fish (GLSCF) consumption, and varied significantly by Great Lake. DDE, lower chlorinated dioxin and furan toxic equivalents (TEQs), and coplanar PCB TEQs were positively associated with noncoplanar PCBs but were not associated with GL sport fish consumption independent of PCB level. Highly chlorinated dioxin and furan congener TEQs were not significantly associated with noncoplanar PCBs or GL sport fish consumption, suggesting that participants were acquiring some of these TEQs from a source other than GLSCF. In epidemiologic studies, it may be important to include populations with higher organochlorine exposures as well as background exposures and to consider the effects of individual congeners or mixtures of congeners on health outcomes.     

Mortality among frequent consumers of Great Lakes sport fish

Commercial and sport-caught fish provide a healthy source of dietary protein, omega-3 fatty acids, and other micronutrients. Regular fish consumption has been associated with decreased risk of heart disease and health professionals encourage adults to include fish in their weekly diets. However, fish harvested from contaminated waters can contain higher levels of persistent, bioaccumulative chemicals such as methylmercury, PCBs, dieldrin, and DDT. To assess the beneficial effects of fish intake and the adverse effects of contaminant exposure, underlying and contributing causes of death were obtained from the National Death Index for 342 deceased members of a cohort of 2538 Great Lakes charterboat captains, 180 Wisconsin anglers, and 1141 referents who were established in 1993-1995. Multivariate analysis of death rates confirmed a dose-related protective effect of fish intake against all-cause and cardiovascular disease mortality, including coronary heart disease, among the referent group. This effect was not observed among consumers of Great Lakes sport fish, however. Cancer mortality was not associated with fish intake in either exposure group. While the number of deaths among this cohort is currently too small to support rigorous statistical analysis, these preliminary findings are consistent with other studies that have shown a protective effect of commercial fish on human health and longevity and raise concerns regarding the effect of persistent environmental contaminants that continue to be detected in fish from the Great Lakes Basin. It is hoped that continued monitoring of this cohort will improve our understanding of the complex interactions that exist between nutrients and contaminants found in fish harvested from the Great Lakes.     

Uterine leiomyomata in a cohort of Great Lakes sport fish consumers

Diet and endocrine disrupting persistent organic pollutants (POPs) have been associated with gynecologic conditions including uterine leiomyomata (UL), endometriosis, and ovarian cysts. Great Lakes sport fish consumption is a source of exposure to POPs such as p,p′-diphenyldichloroethene (DDE) and polychlorinated biphenyls (PCBs). This study was designed to examine retrospectively the effects Great Lakes sport fish consumption on the incidence of UL and to examine the effects of DDE and PCB serum levels on prevalent UL in women participating in the Great Lakes Fish Consumption Study. We hypothesized that associations of exposures with UL would be modified by breastfeeding status. Years of sport fish consumption, demographic, health, and reproductive data were assessed by survey. In a subgroup, serum was collected and tested for DDE and PCB levels. Effects of years of Great Lakes sport fish and sport fish consumption were modeled using time-dependent Cox proportional hazards regression and effects of POP exposures on UL were modeled using multiple logistic regression. Years of sport fish consumption were associated with UL, with an incidence rate ratio of 1.2 (95% CI 1.0–1.3) for each 10-year increment of fish consumption. Summary measures of POP exposures in the overall group were not associated with UL. In the subgroup of women who never breastfed and in whom PCB measurements were available, however, UL was significantly associated with PCBs and groupings of estrogenic, antiestrogenic, and dioxin-like PCBs. These findings support the possibility that PCB exposures from fish consumption may increase the risk of UL and highlight the importance of additional studies exploring biologic pathways by which they could be acting.     

Exploratory assessment of sportfish consumption and polybrominated diphenyl ether exposure in New York State anglers

A cross-sectional study was conducted to examine the influence of sportfish consumption on body burden of nine polybrominated diphenyl ether (PBDE) congeners in 36 New York State (NYS) anglers. Participating anglers who had previously reported consuming sportfish from Lake Ontario and its tributaries were found to have significantly higher blood plasma levels of BDE-28, BDE-47, BDE-99, BDE-100, and the sum of measured PBDE congeners (ΣPBDE), than anglers who had previously reported no consumption of sportfish from these waters. Bivariate analysis was used to evaluate potential dietary predictors of PBDE plasma levels, including indicators of consumption of sportfish, as well as commercial fish, wild waterfowl, dairy products, and beef. The number of years of reported consumption of Lake Ontario sportfish between 1980 and 1990 was found to be correlated with plasma levels of BDE-47, BDE-85, BDE-99, BDE-100, BDE-153, BDE-154, and ΣPBDE. The number of meals, eaten in the year prior to study participation, of Lake Ontario sportfish species known to have high levels of other persistent organic pollutants (POPs) was correlated with plasma levels of BDE-28, BDE-47, BDE-85, BDE-99, BDE-100, BDE-154, and ΣPBDE. Multiple linear regression revealed that the number of years consuming Lake Ontario sportfish between 1980 and 1990, after adjusting for plasma lipids, was a weak, but statistically significant, predictor of ΣPBDE plasma levels (β=0.130, 95% CI: 0.007-0.254). These results suggest that sportfish consumption can contribute measurably to PBDE body burden in NYS anglers, although there are likely to be additional, more significant, sources of exposure.     

Profiles of ortho-polychlorinated biphenyl congeners, dichlorodiphenyldichloroethylene, hexachlorobenzene, and Mirex among male Lake Ontario sportfish consumers: the New York State Angler cohort study

Great Lakes sportfish consumption is a recognized human exposure source to environmental organochlorine compounds. Using data collected as part of the New York State Angler Cohort Study, 203 males were considered with regard to history of Lake Ontario sportfish consumption and sera levels of 57 ortho-substituted polychlorinated biphenyl (PCB) congeners, dichlorodiphenyldichloroethylene, hexachlorobenzene, and Mirex. Consumption of six species of highly contaminated Lake Ontario sportfish during the years 1980 to 1990 was considered. Exposure was weighted by average annual frequency of consumption, whole-fish PCB estimates, and meal size to determine a continuous index of exposure. This index was dichotomized to compare "consumers" to "nonconsumers" in several procedures. Recovery and lipid-adjusted serum values for PCB congener IUPAC Nos. 138+163 (rsp=0.3), 183 (rsp=0.3), 187 (rsp=0.4), and 188 (rsp=0.3) and Mirex (rsp=0.4) were significantly correlated with the index of fish consumption (P<0.001). A logistic regression model, using forward stepwise selection procedures (alpha in/out=0.002/0.004), was employed to account for high intercorrelations among organochlorine predictor variables. Mirex was the sole statistically significant predictor variable of "consumer/nonconsumer." A one-unit increase in log Mirex was associated with a 92.0% increase in the odds of having reported sportfish consumption (OR=1.92, 95%CI=1.43, 2.58). Age, body mass index, cigarette smoking, water/wildfowl consumption, and year of sampling were considered covariates. The results of this study support the premise that long-term dietary consumption of Lake Ontario sportfish, even at comparatively low levels, contributes significantly to the body burden of organochlorine compounds in western New York anglers and sportsmen.     

Respondent driven sampling in a biomonitoring study of refugees from Burma in Buffalo,New York who eat Great Lakes fish

Background

Refugees from Burma who consume fish caught from local waterbodies have increased risk of exposure to environmental contaminants. We used respondent driven sampling (RDS) to sample this hard-to-reach population for the first Biomonitoring of Great Lakes Populations program. In the current study, we examined the interview data and assessed the effectiveness of RDS to sample the unique population.

Risks and benefits of consumption of Great Lakes fish

Background: Beneficial effects of fish consumption on early cognitive development and cardiovascular health have been attributed to the omega-3 fatty acids in fish and fish oils, but toxic chemicals in fish may adversely affect these health outcomes. Risk–benefit assessments of fish consumption have frequently focused on methylmercury and omega-3 fatty acids, not persistent pollutants such as polychlorinated biphenyls, and none have evaluated Great Lakes fish consumption.Objectives: The risks and benefits of fish consumption have been established primarily for marine fish. Here, we examine whether sufficient data are available to evaluate the risks and benefits of eating freshwater fish from the Great Lakes.Methods: We used a scoping review to integrate information from multiple state, provincial, and federal agency sources regarding the contaminants and omega-3 fatty acids in Great Lakes fish and fish consumers, consumption rates and fish consumption advisories, and health effects of contaminants and omega-3 fatty acids.Data synthesis: Great Lakes fish contain persistent contaminants—many of which have documented adverse health effects —that accumulate in humans consuming them. In contrast, data are sparse on omega-3 fatty acids in the fish and their consumers. Moreover, few studies have documented the social and cultural benefits of Great Lakes fish consumption, particularly for subsistence fishers and native communities. At this time, federal and state/provincial governments provide fish consumption advisories based solely on risk.Conclusions: Our knowledge of Great Lakes fish has critical gaps, particularly regarding the benefits of consumption. A risk–benefit analysis requires more information than is currently available on the concentration of omega-3 fatty acids in Great Lakes fish and their absorption by fish eaters in addition to more information on the social, cultural, and health consequences of changes in the amount of fish consumed.     

Quantifying the fate of mercury in the Great Lakes Basin: toward an ecosystem approach

We argue that the need to reduce human exposure to mercury in the Great Lakes Basin and thus reduce the risk of adverse effects can be accomplished only by reducing the quantity of all mercury species cycling in the ecosystem. It is pointed out that much can be learned from experiences with PCBs. PCB concentrations and exposures have been reduced, in part, because a clear picture has been established of relative sources and PCB' s environmental fate in the form of mass balance models, which document the "big picture" of PCB behavior at a range of scales. It is suggested that a similar strategy is needed for mercury as part of the effort to protect human health throughout the entire Great Lakes ecosystem.     

Organochlorine Exposure and Incidence of Diabetes in a Cohort of Great Lakes Sport Fish Consumers

Background

Studies have demonstrated ubiquitous human exposure to persistent organic pollutants (POPs) such as p,p′-diphenyldichloroethene (DDE) and polychlorinated biphenyls (PCBs). Although there is considerable evidence that POP exposures are associated with prevalent diabetes, these studies do not establish causality because the cross-sectional study design does not allow for assessment of temporality of the exposure–disease association. Prospective studies, however, have been lacking.

Objectives

This study was designed to determine whether POP body burdens are related to incidence of diabetes in a cohort of Great Lakes sport fish consumers.

Methods

The cohort was established in the early 1990s and followed through 2005. We tested serum for DDE and PCB congeners and assessed diabetes diagnosis, demographics, and fish consumption. Associations of diabetes with exposures were examined prospectively in participants without diabetes in 1994–1995, followed through 2005. Annual percent changes in DDE and PCB-132/153 from 1994 to 2005 were examined by diabetes status.

Results

DDE exposure was associated with incident diabetes. Incident diabetes was not associated with mono-ortho PCB-118, total PCBs, or years of sport fish consumption. Annual percent change in DDE and PCB-132/153 did not differ significantly by diabetes status.

Conclusions

This study demonstrates an association between DDE exposure and incident diabetes. The findings of an association of DDE with incident diabetes and the lack of effect of diabetes on annual percent change in POPs do not support the hypothesis that associations of POPs with diabetes are attributable to reverse causality. Additional studies should address the biological pathways by which DDE could affect glucose homeostasis.     

Mercury concentrations in fish from Canadian Great Lakes areas of concern: an analysis of data from the Canadian Department of Environment database

The tissue mercury concentrations in six species of fish collected at the 17 Areas of Concern identified by the International Joint Commission on the Canadian side of the Great Lakes were analyzed using an Environment Canada database. A linear increase in mercury concentration with fish length was found, but slopes differed among locations. The temporal pattern over the period 1971-1997 differed across species in fish collected in Lake St. Clair; in at least two species there was evidence of increased mercury concentration during the 1990s that had been suggested in an earlier analysis. Areas of Concern differed significantly in observed tissue concentrations. Differences observed did not consistently parallel expectations associated with the historical presence of chlor-alkali plants in the vicinities of some locations. An attempt to correlate the fish tissue mercury concentration with the frequency of occurrence of infantile cerebral palsy at Areas of Concern was unsuccessful.     

Spatial and temporal patterns in mercury contamination in sediments of the Laurentian Great Lakes

Data from recent sediment surveys have been collated and mapped in order to determine the spatial distribution of mercury in sediments across the entire Great Lakes basin. Information from historical surveys has also been collated in order to evaluate temporal trends. Lake Huron (2002) exhibited the lowest mercury concentrations (lakewide average concentration, 0.043 microg/g); Lakes Michigan (1994-1996) and Superior (2000) also exhibited relatively low levels (lakewide averages of 0.088 and 0.078 microg/g, respectively). The western basin of Lake Erie (1997-1998, 0.402 microg/g) and Lake Ontario (0.586 microg/g) exhibited the highest levels. Sources of mercury contamination in Lakes Erie and Ontario are primarily attributed to loadings from historical sources, including chlor-alkali production in the Detroit, St. Clair, and Niagara Rivers. The spatial distributions of mercury in sediments of Lakes Huron and Superior suggest that natural geochemical factors are an influence. Surficial sediment mercury contamination was found to have decreased markedly since the late 1960s and 1970s. Decreases in lakewide average sediment concentrations of mercury over this time period ranged from approximately 25% for Lake Ontario to 80% for Lake Huron.     

Modeling the atmospheric transport and deposition of mercury to the Great Lakes

A special version of the NOAA HYSPLIT_4 model has been developed and used to estimate the atmospheric fate and transport of mercury in a North American modeling domain. Spatial and chemical interpolation procedures were used to expand the modeling results and provide estimates of the contribution of each source in a 1996 anthropogenic US/Canadian emissions inventory to atmospheric mercury deposition to the Great Lakes. While there are uncertainties in the emissions inventories and ambient data suitable for model evaluation are scarce, model results were found to be reasonably consistent with wet deposition measurements in the Great Lakes region and with independent measurement-based estimates of deposition to Lake Michigan. Sources up to 2000 km from the Great Lakes contributed significant amounts of mercury through atmospheric transport and deposition. While there were significant contributions from incineration and metallurgical sources, coal combustion was generally found to be the largest contributor to atmospheric mercury deposition to the Great Lakes.     

Plasma concentrations of persistent organochlorines in relation to thyrotropin and thyroid hormone levels in women

Objectives: There is a concern that persistent organohalogen toxicants, such as polychlorinated biphenyls (PCBs), might display endocrine-disrupting effects in exposed populations. In this study the correlations between PCBs and thyrotropin (TSH) and thyroid hormone concentrations in plasma were assessed in adult women. Methods: The study group consisted of 182 fishermen's wives from the Swedish east coast, with a median age of 42 years (range 23–62) and a median current consumption of contaminated fatty fish from the Baltic Sea of two meals per month (range 0–12). TSH, free (FT₃) and total (TT₃) triiodothyronine and free (FT₄) and total (TT₄) thyroxin in plasma were analyzed by immunofluorometric assays, and 2,2′,4,4′,5,5′-hexachlorobiphenyl (CB-153) in plasma was analyzed by gas chromatography with electron capture detection. Twenty other PCB and two hydroxy-PCB congeners were analyzed in subgroups of the women. Plasma lipid analyses were performed with enzymatic techniques. Results: The CB-153 concentration in plasma (range 16–776 ng/g lipid) was negatively correlated with the TT₃ concentrations (range 1.0–3.0 nmol/l, r_s=−0.29, P < 0.001). This association remained after age adjustment. Conclusions: The present study gives some support for the notion that dietary exposure to persistent organochlorine compounds (POCs) might weakly affect peripheral thyroid hormone concentrations in adult women. Received: 9 June 2000 / Accepted: 31 October 2000     

Absence of cardiovascular benefits and sportfish consumption among St. Lawrence River anglers

The benefits of sportfish consumption and omega-3 fatty acid (omega3-FA) intake for cardiovascular risk factors were evaluated in a sample of 112 male fishers from the St. Lawrence River in the Montreal area during the 1996 winter and fall fishing seasons. A questionnaire on fishing practices and fish consumption was administered, and fasting blood samples were collected for lipid and phospholipid determination. Linear regression analyses, which considered the confounding effect of major risk factors, did not show any significant association between measured omega3-FAs or reported fish intake and blood lipids or blood pressure. This study is limited by its low statistical power due to the small sample size and the possibility that the fish eaten by the participants were low in omega3-FAs or that the participants diets contained foods high in cholesterol-raising fat.     

Fish Acquisition and Consumption in the African Great Lakes Region through a Food Environment Lens: A Scoping Review

Effective actions for the fishery and aquaculture sectors to contribute toward improving nutrition rely on an understanding of the factors influencing fish intake, particularly amongst vulnerable populations. This scoping review synthesises evidence from 33 studies in the African Great Lakes Region to examine the influence of food environments on fish acquisition and consumption. We identified only two studies that explicitly applied a food environment framework and none that linked policy conditions with the contribution of fish to diets. Economic access to fish was represented in the largest number of included studies (21 studies), followed by preferences, acceptability and desirability of fish (17 studies) and availability and physical access (14 studies). Positive perceptions of taste and low cost, relative to other animal-source foods, were drivers of fish purchases in many settings; however, limited physical and economic access were frequently identified as preventing optimal intake. In lakeside communities, fish were increasingly directed toward external markets which reduced the availability and affordability of fish for local households. Few studies considered intra-household variations in fish access according to age, gender or physiological status, which represents an important knowledge gap. There is also scope for future research on seasonal influences on fish access and the design and rigorous evaluation of programmes and policies that address one or more constraints of availability, cost, convenience and preferences.     

Catfish consumption as a contributor to elevated PCB levels in a non-Hispanic black subpopulation

The human body burden of polychlorinated biphenyls (PCBs) sharply declined after production was banned in the US in 1979. For the 10% of the US population that remains most exposed to PCBs, fish consumption is the primary source. National Health and Nutrition Examination Survey (NHANES) data indicates that the highest remaining PCB levels exist in a non-Hispanic black subpopulation. Our review suggests that catfish consumption may be a significant PCB source for the one million non-Hispanic black anglers who fish for catfish. In comparison to non-Hispanic white anglers, non-Hispanic black anglers consume more catfish, are more likely to eat the whole fish rather than just the fillets that contain less PCBs, and are more likely to fish in watersheds with high PCB contamination.Efforts to diminish potential racial disparities in PCB exposure are challenged by geographic, economic, cultural, and educational barriers. In response, we propose that a fish consumption survey be performed that identifies the extent of subsistence fishing by non-Hispanic black anglers for catfish in watersheds with PCB contamination, the type and quantity of catfish subsistence fishing provides, and what actions would help moderate PCB exposure due to subsistence fishing for catfish in such areas. Understanding the contamination and consumption factors that contribute to higher PCB body burdens will help identify and offer solutions to racial disparities in exposure to PCBs due to subsistence fishing while providing a model to prevent similar disparities in exposure to toxics ranging from mercury to polybrominated diphenyl ethers.     

Prenatal concentrations of polychlorinated biphenyls, DDE, and DDT and overweight in children: a prospective birth cohort study

Background: Recent experimental evidence suggests that prenatal exposure to endocrine-disrupting chemicals (EDCs) may increase postnatal obesity risk and that these effects may be sex or diet dependent.Objectives: We explored whether prenatal organochlorine compound (OC) concentrations [polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (DDE), and dichlorodiphenyltrichloroethane (DDT)] were associated with overweight at 6.5 years of age and whether child sex or fat intakes modified these associations.Methods: We studied 344 children from a Spanish birth cohort established in 1997–1998. Overweight at 6.5 years was defined as a body mass index (BMI) z-score ≥ 85th percentile of the World Health Organization reference. Cord blood OC concentrations were measured and treated as categorical variables (tertiles). Children’s diet was assessed by food frequency questionnaire. Relative risks (RRs) were estimated using generalized linear models.Results: After multivariable adjustment, we found an increased RR of overweight in the third tertile of PCB exposure [RR = 1.70; 95% confidence interval (CI): 1.09, 2.64] and the second tertile of DDE exposure (RR = 1.67; 95% CI: 1.10, 2.55), but no association with DDT exposure in the population overall. Associations between overweight and PCB and DDE concentrations were strongest in girls (p-interaction between 0.01 and 0.28); DDT was associated with overweight only in boys. For DDT we observed stronger associations in children with fat intakes at or above compared with below the median, but this interaction was not significant (p-interaction > 0.05).Conclusions: This study suggests that prenatal OC exposures may be associated with overweight in children and that sex and high-fat intake may influence susceptibility.     

An ecosystem approach to the health effects of mercury in the Great Lakes basin ecosystem

New concerns about the global presence and human health significance of mercury have arisen as a result of recent epidemiological data demonstrating subtle neurological effects from consumption of mercury-contaminated fish. In the Great Lakes Basin, the complexity of the diverse sources, pools, and sinks of mercury and of the pathways of distribution, fate, and biotransformation requires an ecosystem approach to the assessment of exposures of Great Lakes' human populations. Further epidemiological research is needed to verify preliminary indications of harmful effects in people living near the Great Lakes. Great Lakes fish are valuable resources for subsistence nutrition, recreation, and commerce, but the benefits of fish consumption must be balanced by concern for the hazards from the contaminants that they may contain. The efficacy of fish consumption advisories in reducing exposures should continue to be evaluated while planning continues for remedial actions on contaminated sediments from historic industrial activities and for regulatory action to control sources.     

Seafood intake and blood cadmium in a cohort of adult avid seafood consumers

Although the benefits of fish consumption are widely recognized, seafood may also be a source of exposure to heavy metals such as cadmium. Many types of seafood are rich in cadmium, but bioavailability and potential for toxicity after consumption is less clear. This study investigates the relationship between seafood intake and the level of cadmium (Cd) in the blood in a 252 person cohort of avid seafood consumers in the Long Island Study of Seafood Consumption (New York). Blood cadmium is an established biomarker of cadmium exposure, reflecting both recent and decade-long exposure. Data on the amounts and frequency of eating various types of seafood were self-reported by avid seafood consumers recruited in 2011–2012. After adjusting for age, BMI, sex, current smoking status, and income in a linear regression model, we found no association between regular seafood intake (β = −0.01; p = 0.11) but did identify an association between salmon intake in cups/week (ln transformed) (β = 0.20; p = 0.001) and blood cadmium. After accounting for salmon, no other types of seafood were meaningfully associated with blood cadmium. No association was found between rice intake, blood zinc, or dietary iron or calcium and blood cadmium. Results suggest that seafood is not a major source of cadmium exposure, but that salmon intake does marginally increase blood cadmium levels. Given that cadmium levels in salmon are not higher than those in many other seafood species, the association with salmon intake is likely attributed to higher consumption of salmon in this population.     

Associations of organochlorines with endogenous hormones in male Great Lakes fish consumers and nonconsumers

This study investigated the relationships of steroid and thyroid hormones with total noncoplanar polychlorinated biphenyls (PCBs), total toxic equivalents (TEQs) from dioxins-like organochlorines, and dichlorodiphenyl dichloroethene (DDE) in 56 male frequent and infrequent Great Lakes sport caught fish consumers. Significant negative associations were found for triiodothyronine (T3), thyroxine (T4), thyroid stimulating hormone (TSH), and sex hormone binding globulin (SHBG)-bound testosterone with PCBs, for TSH with total TEQs, and for estrone sulfate with DDE, adjusting for age, body mass index, and medication use. Follicle-stimulating hormone, luteinizing hormone, free testosterone, and SHBG were not significantly associated with organochlorines. Models that accounted for exposure to both PCBs and TEQs predicted T4, estrone sulfate, and SHBG-bound testosterone better than models that included either PCBs or TEQs alone, with the lowest hormone levels occurring in the participants with both higher PCB levels and lower TEQ levels. These data suggest that exposure to PCBs, dioxin-like organochlorines, and DDE, alone and potentially in combination, may be associated with effects on the endocrine system in adult males. Further studies should help delineate specific exposure effects and effects of exposures to other common environmental contaminants alone and in combination with PCBs.