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Persistent organic pollutants (POPs) are heterogeneous carbon-based compounds that can seriously affect human health. The aim of this study was to measure serum concentrations of POPs in women residing in the Euro-Arctic Region of Russia. A total of 204 women from seven rural settlements of the Nenets Autonomous Okrug (NAO) took part in the study. We measured serum concentrations of 11 polychlorinated biphenyls (PCBs) and 17 organochlorine pesticides (OCPs) across the study sites and among Nenets and non-Nenets residents. Measurement of POPs was performed using an Agilent 7890A gas chromatograph equipped with an Agilent 7000 series MS/MS triple quadrupole system. The concentrations of all POPs were low and similar to findings from other Arctic countries. However, significant geographic differences between the settlements were observed with exceptionally high concentrations of PCBs in Varnek located on Vaygach Island. Both ΣDDT (p = 0.011) and ΣPCB (p = 0.038) concentrations were significantly lower in Nenets. Our main findings suggest that the serum concentrations of the legacy POPs in women in the Euro-Arctic Region of Russia are low and similar to those in other Arctic countries. Significant variations between settlements, and between Nenets and non-Nenets residents, were found. Arctic biomonitoring research in Russia should include studies on the associations between nutrition and concentrations of POPs.

Abstract The application of toxic equivalency factors (TEFs) or toxic units to estimate toxic potencies for mixtures of chemicals which contribute to a biological effect through a common mechanism is one approach for filling data gaps. Toxic Equivalents (TEQ) have been used to express the toxicity of dioxin-like compounds (i.e., dioxins, furans, and dioxin-like polychlorinated biphenyls (PCBs)) in terms of the most toxic form of dioxin: 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). This study sought to integrate two data gap filling techniques, quantitative structure–activity relationships (QSARs) and TEFs, to predict neurotoxicity TEQs for PCBs. Simon et al. (2007) previously derived neurotoxic equivalent (NEQ) values for a dataset of 87 PCB congeners, of which 83 congeners had experimental data. These data were taken from a set of four different studies measuring different effects related to neurotoxicity, each of which tested overlapping subsets of the 83 PCB congeners. The goals of the current study were to: (i) evaluate an alternative neurotoxic equivalent factor (NEF) derivations from an expanded dataset, relative to those derived by Simon et al. and (ii) develop QSAR models to provide NEF estimates for the large number of untested PCB congeners. The models used multiple linear regression, support vector regression, k-nearest neighbor and random forest algorithms within a 5-fold cross validation scheme and position-specific chlorine substitution patterns on the biphenyl scaffold as descriptors. Alternative NEF values were derived but the resulting QSAR models had relatively low predictivity (RMSE ∼0.24). This was mostly driven by the large uncertainties in the underlying data and NEF values. The derived NEFs and the QSAR predicted NEFs to fill data gaps should be applied with caution. Highlights • Two data gap filling techniques were integrated QSARs and TEFs to predict neurotoxicity (NEFs) for PCBs. • Alternative NEFs were derived from an expanded dataset and compared to those derived in Simon et al. (2007). • QSAR models to predict NEFs were developed using 4 machine learning approaches. • The developed QSAR models had low predictivity. • Predictivity was limited by the quality and quantity of underlying experimental data. [ABSTRACT FROM AUTHOR]

Background Managing and recycling electronic waste (e-waste), while useful and necessary, has resulted in significant contamination of several environments in China. The area around Tianjin, China has become one of the world's largest e-waste disposal centers, where electronics are processed by manually disassembly or burning, which can result in serious exposure of workers to a multitude of toxicants. Objective The present study assessed potential genomic damage in workers involved in recycling e-waste. Methods To detect cytogenetic and DNA damage, chromosomal aberrations (CA), cytokinesis blocking micronucleus (CBMN) and the comet assay were performed. Concentrations of some trace elements, markers of oxidative stress and polychlorinated biphenyls (PCBs) in whole blood or serum were measured, and relationships among the markers described above, age, and duration of exposure were analyzed. The profiles of expression of genes in lymphocytes in peripheral blood were assessed to determine the status of the regulation of genes involved in genome stability. Results Concentrations of 28 PCB congeners in the whole blood of the exposed group were significantly ( P < 0.001) greater than those in the control individuals. Frequency of CA (8.01%) and CBMN (26.3‰) in lymphocytes and the level of DNA damage in the lymphocytes and spermatozoa of the exposed men were also significantly ( P < 0.0001) greater than those of the controls. There were significant relationships between CA, CBMN, DNA damage and duration of exposure. Concentrations of malondialdehyde (MDA) and lead (Pb) in the blood serum were significantly greater, but activities of superoxide dismutase (SOD), glutathione (GSH) and concentrations of calcium (Ca) and magnesium (Mg) were lower in the serum of the exposed men. MDA, Pb, Ca and Mg were associated with the duration of exposure to handling e-waste. In males involved in handling of e-waste, there were 13 genes — ATM, ATR, ABL1, CHEK1, CHEK2, GADD45A, CDK7, GTSE1, OGG1, DDB1, PRKDC, XRCC1 and CCNH — for which expression of mRNA was up-regulated and 7 genes — BRCA1, GTF2H1, SEMA4A, MRE11A, MUTYH, PNKP and RAD50 — for which the expression of mRNA was down-regulated. Conclusions A strong correlation between indicators of damage of DNA, which could result in instability of the genome, and duration of processing e-waste was observed. If proper procedures are not followed, there are significant risks to the health of the individuals involved in such activities. [ABSTRACT FROM AUTHOR]

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Five fish species (Mackerel, Bream, Red mouth grouper, common Pandora and Parrotfish) and two benthic invertebrates (Shrimp and Crab) were collected from Red Sea coasts in Yanbu city in Saudi Arabia. Concentrations of 14 organochlorine pesticides (DDT and its metabolites, HCH isomers, Chlordane, Heptachlor and HCB) and seven PCB congeners (28, 52, 101, 118, 153, 138 and 180) were studied. The mean concentrations of PCB s and OCPs in marine biota were 23 ng.g-1 lipid wt and 651.7 ng.g-1 lipid wt, respectively. Levels of studied chemical pollutants were significantly higher in industrial area (IA) when compared with Yanbu al Bahr (YB) and the Sharam area (Sh) reflecting the effects of the industrial activities on OC concentrations in marine organisms. However, these levels were clearly lower than the maximum residue values for human consumption fixed by the international organizations (FAO/WHO/FDA). In consequence, the consumption of marine products from Red Sea in KSA is generally safe as regarded to OCs. Levels of contamination by OCs were also markedly lower in invertebrate species when compared to fish species due may be to the lower lipid contents in these benthic organisms. [ABSTRACT FROM AUTHOR]

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that accumulate in tissues of exposed animals and humans. This case report refers to n = 3 dairy cows accidentally exposed to non-dioxin-like PCBs (ndl-PCBs) of unknown origin on a German farm. At study start they had a cumulative total of 122-643 ng/g fat in milk and 105–591 ng/g fat in blood, consisting mainly of PCBs 138, 153, and 180. Two cows calved during the study and their calves were raised on their mothers' milk, resulting in cumulative exposure until slaughter. A physiologically based toxicokinetic model was developed to describe the fate of ndl-PCBs in the animals. The toxicokinetic behavior of ndl-PCBs was simulated in individual animals, including transfer of contaminants into calves via milk and placenta. Both the simulations and experimental data indicate that contamination via both routes is significant. In addition, the model was used to estimate kinetic parameters for risk assessment. [Display omitted] • Fully parameterized model describing the transfer of PCBs 138, 153 and 180 from mother cow to calf. • Similar amount of PCBs transferred from mother cow to calf via milk and placenta after roughly 70–80 days of suckling. • Derivation of several parameters relevant for risk assessment such as biotransfer factors and half lives. [ABSTRACT FROM AUTHOR]

Millions of pounds of polychlorinated biphenyl (PCB) compounds have been produced in multiple countries for industrial applications over the last several decades. PCB exposure induces various adverse health effects in animals and humans. Environmental and occupational exposures to PCBs have been associated with liver, kidney, endocrine, and neurodevelopmental adverse effects. We have collected and reviewed animal and human data cited in the US National Library of Medicine from 2000 to 2010. In brief, our review shows new evidence, that is, in animal studies, exposure to one of the PCBs, A1221, induces a significant alteration of serum luteinizing hormone. The effects were more profound in the F2 generation, particularly with respect to fluctuations in hormones and reproductive tract tissues across the estrous cycle. Morphological analyses of brain tissue from rats exposed to A1254 confirmed the results of an earlier work which showed that the relative size of the intra- and infrapyramidal (II-P) mossy fibers was smaller than that in the controls and also reduction in growth was selective for the II-P mossy fibers. PCB exposure increased anogenital distance and prostate size but decreased epididymal weight, epididymal sperm count, and motile epididymal sperm count. No effects were observed on testicular weight or size. The epidemiological data showed an association between diabetes mellitus prevalence and elevated concentrations of PCB 153. Additionally, prenatal PCB exposure studies were associated with a smaller thymic index at birth and could adversely affect immune responses to childhood vaccinations and resistance to respiratory infections. PCB exposure was also reported to adversely affect enamel development in children in a dose-dependent manner. Because PCBs and their metabolites are potential health hazards, understanding the risk factors associated with individual PCBs, PCB mixtures, and PCB metabolites is important. PCB exposures of vulnerable populations (pregnant women, fetuses, infants, and children) are of particular concern because of heightened sensitivity during this period of brain development. [ABSTRACT FROM AUTHOR]

The Hudson River, NY, USA is contaminated for over 300 km with polychlorinated biphenyls (PCBs) released from two General Electric (GE) capacitor plants. We collected adult and juvenile mallards ( Anas platyrhynchos ) from four different areas of the river; an area upstream of the GE plants (n = 38), two areas directly downstream of the GE plants (n = 41, n = 38), and an area more than 100 km downstream in the freshwater tidal river (n = 20). Collections occurred during July and August (2008) when ducks were flightless to ensure ducks were “resident” and exposures were local. Fat and muscle tissue were analyzed for PCBs. PCBs were detected in all samples, and mallards below the GE plant sites on the Hudson River had orders of magnitude higher concentrations of PCBs than those above the plants. Juvenile mallards from areas directly downstream of the GE plant sites tended to have higher PCB concentrations in fat than adults. The patterns of PCB congeners and homolog groups varied across the study areas, with areas directly downstream of the GE plants dominated by tetra-chloro biphenyls whereas samples from upstream and the freshwater tidal river tended towards higher chlorinated congeners. Congener patterns between male and female and juvenile and adult mallards were generally similar within study areas, with the exception of one area downstream of the GE plants where adult birds exhibited different patterns than juveniles. Evidence of PCBs from the GE plant sites was detected in the tidal Hudson River, more than 100 km downstream of the plant sites. More than 90% of the ducks collected in areas downstream of the GE plants but above the tidally influenced river exceed the USFDA tolerance level for PCBs in poultry, which should be a concern for consumers of waterfowl taken in proximity to the upper Hudson River. [ABSTRACT FROM AUTHOR]

PCBs (polychlorinated biphenyls) were determined in sediment/soil profiles to a depth of 30 cm from three different wetlands (i.e., ditch wetlands, riparian wetlands and reclaimed wetlands) of the Pearl River Estuary to elucidate their levels, distribution and toxic risks along a 100-year chronosequence of reclamation. All detected PCB congeners and the total 15 PCBs (∑15 PCBs) decreased with depth along sediment/soil profiles in these three wetlands. The ∑15 PCBs concentrations ranged from 17.68 to 169.26 ng/g in surface sediments/soils. Generally, old wetlands tended to have higher PCB concentrations than younger ones. The dominant PCB congeners at all sampling sites were light PCB homologues (i.e., tetra-CBs and tri-CBs). According to the sediment quality guideline, the average PCB concentrations exceeded the threshold effects level (TEL, 21.6 ng/g) at most of the sampling sites, exhibiting possible adverse biological effects, which were dominantly caused by light PCB congeners. The total toxic equivalent (TEQ) concentrations of 10 dioxin-like PCBs (DL-PCBs) detected at all sampling sites ranged from 0.04 to 852.7 (10 −3 ng/g), mainly affected by PCB126. Only DL-PCB concentrations in ditch and riparian wetland sediments with 40-year reclamation histories (i.e., D40 and Ri40) exhibited moderate adverse biological effects according to SQGQ values. Principal component analysis indicated that PCBs in three wetland sediments/soils mainly originated from Aroclor 1016, 1242, and 1248. Correlation analysis showed that sediment/soil organic carbon content had a significant correlation with the concentrations of several PCB congeners (P < 0.05), whereas no significant correlations were observed between any PCBs congeners and grain size or aggregate content (P > 0.05). [ABSTRACT FROM AUTHOR]

Polychlorinated biphenyls (PCBs) have been detected at relatively high concentrations in harbor seals, apex predators in the northwest Atlantic. As part of an ongoing assessment of the effects of PCBs on population health, we analyzed tri- to deca-PCBs in the liver of 56 harbor seals (6 adult males, 50 pups) and in 11 blubber samples (4 adult males, 7 pups) and examined tissue-specific accumulation patterns, biomagnification potential, and toxic implications of current PCB concentrations. Hepatic ∑ 30 PCB concentrations (overall mean ± standard deviation: 76,860 ± 111,800 ng/g lipid weight, lw) were higher than blubber concentrations (48,180 ± 69,420 ng/g lw). Regional trends were suggestive of fresh PCB inputs from the industrialized, densely populated southern coast of New England versus the rural north. The lack of temporal trends confirmed that tissue concentrations of PCBs have plateaued since the early 1990s. Tissue distribution of PCBs varied significantly by age and, surprisingly by gender among the pups. Principal Component Analysis (PCA) revealed that lighter PCBs are selectively transferred from mother to pup blubber in relation to lipid solubility (log K ow ), but heavier PCBs may be efficiently transferred during late lactation from mother to pup liver. Biomagnification factors (BMFs) for ∑ 6 PCBs from prey fish to adult male seals ranged from 90 to 547 in the liver and 88 to 532 in the blubber, and suggested that molecular structure and metabolic capacity were more important influences than log K ow on the retention of PCBs. Blubber concentrations of ∑ 30 PCBs in 87% of the pups were an order of magnitude higher than recent toxic reference values (TRVs) calculated for ∑ 154 PCBs in nursing harbor seals, suggesting that the pups are at risk for PCB-mediated toxicity at a vulnerable stage of development. Given the recurring pattern of epizootics in these seals, the health of the population is of concern. [ABSTRACT FROM AUTHOR]

Highlights: [•] We analyzed 27 organochlorine compounds in human milk samples from Croatia. [•] p,p′-DDE, PCB-153, PCB-138 and PCB-180 were found in the highest concentrations. [•] TEQ values were higher in samples from Zadar in comparison to Zagreb. [•] Organochlorine compounds levels decreased significantly in 10 years period. [ABSTRACT FROM AUTHOR]

Highlights: [•] PCB mass spectra can provide structural information beyond mw and no. of Cls. [•] 2,2′- and 2,2′,6-substitution show largest effects in mass spectra. [•] Chlorine loss fragment (ortho effect) studied for all 209 congeners. [•] Combined with complementary chromatographic ortho effect. [•] Permits recognition of incorrect structural assignments. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the levels of some persistent organic pollutants in the surface sediments from the Zahuapan and Atoyac rivers (Tlaxcala, Mexico), as well as to determine the genotoxic potential, by the micronucleus test inVicia faba, of the sediments and agricultural soils irrigated with water from these rivers. This document is the first study on the presence of POPs in surface sediments of the above-mentioned rivers; among the compounds analyzed are the HCH isomers, DDT and its metabolite DDE, HCB, mirex, aldrin, and 41 PCB congeners. The concentrations of HCB, ΣDDTs, ΣHCHs, and ΣPCBs ranged from 138–510, 45–450, 3–27, and 59–1876 μg kg−1dry weight, respectively. The highest levels of HCB, HCH isomers, and PCB congeners were found in the Atoyac River, and these compounds have the potential for causing an environmental impact. On the other hand, biological testing shows that both sediments and agricultural soils possess a genotoxic potential, given that the micronuclei frequency inV. fabais increased. [ABSTRACT FROM AUTHOR]

Among the chemicals known as persistent organic pollutants responsible to cause serious harmful effects both on environment and health, the class belonging to polychlorinated biphenyls (PCB) still arise problems related to instrumental techniques detection in order to enhance the analytical performances. In this context special preparative methods have been developed, such as solid—phase—micro—extraction, when a magnesium silicate matrix, fluorisil, can be successfully used to increase sensitivity and to decrease the detection limits. The aim of this paper is to provide experimental data on kinetics and equilibrium of adsorption of nine PCB congeners on fluorisil matrix. Correlation of adsorption parameters with structural characteristics results in differentiation of adsorption efficiency between two PCB groups, depending on whether one or both biphenyl rings are substituted with chlorine atoms. Adsorption correlations are discussed in terms of molecular volumes and areas, hydrophobicity, dipole moment and polarizability, which determine a perpendicular or parallel arrangement of PCB molecules of two PCB groups on magnesium silicate sorbent. Adsorption modeling of kinetic data indicates an intra-particle diffusion mechanism and a C type isotherm for equilibrium data is checked. [ABSTRACT FROM PUBLISHER]

Abstract: Background: Reliable techniques to measure polychlorinated biphenyl (PCB) congeners make the clearer definition of their effects on human health possible. Given that PCBs are classified as endocrine disrupters, we sought to explore the expression of some key genes involved in sex steroid metabolism. Objectives: To examine common classification schemes of PCB congeners and determine whether exposure to groups classified by mechanism of action alter the gene expression (GE) of CYP17, CYP19, and ESR1 and ESR2. Methods: GE and exposure to various classifications of lipid-adjusted PCB congeners were examined in 139 daughters of the Michigan Fisheaters'' Cohort. Using mixed models analyses and adjusting for age, menopausal status, and current use of oral contraceptives and hormone replacement therapy, GE data were regressed on exposure to PCB congener groupings based on mechanism of action. Results: Three novel findings are elucidated: first, that up-regulation of CYP19 expression is associated with exposure to PCB groupings containing dioxin-like, potentially anti-estrogenic, immunotoxic congeners, including PCB IUPAC #74, #105, #118, #138, #156, #157, #158, #167, and #170 from this cohort. Second, that exposure to similar congeners (PCB IUPAC #105, #156, #157, #158, and #167 in this cohort) but using a classification based solely on hormonal mechanisms of action is associated with increased expression of ESR2. Third, that increased expression of CYP17 is of borderline significance when associated with exposure to PCB IUPAC #118, #138, and #156. Conclusions: These findings are both counter-intuitive and intriguing. Rather than exhibiting anti-estrogenic effects alone, they suggest that these congeners up-regulate the major enzyme involved in estrogen synthesis and tend to confirm previous findings of links between AhR and ER signaling pathways. Replication of these findings, expansion of the number of genes examined, exploration of mixtures of environmental chemicals, and subsequent study of health outcomes in a larger cohort are future priorities. [Copyright &y& Elsevier]

Introduction: Ambient air and bulk deposition samples were collected between June 2008 and June 2009. Eighty-three polychlorinated biphenyl (PCB) congeners were targeted in the samples. Discussion: The average gas and particle PCB concentrations were found as 393 ± 278 and 70 ± 102 pg/m, respectively, and 85% of the atmospheric PCBs were in the gas phase. Bulk deposition samples were collected by using a sampler made of stainless steel. The average PCB bulk deposition flux value was determined as 6,020 ± 4,350 pg/m day. The seasonal bulk deposition fluxes were not statistically different from each other, but the summer flux had higher values. Flux values differed depending on the precipitation levels. The average flux value in the rainy periods was 7,480 ± 4,080 pg/m day while the average flux value in dry periods was 5,550 ± 4,420 pg/m day. The obtained deposition values were lower than the reported values given for the urban and industrialized areas, yet close to the ones for the rural sites. The reported deposition values were also influenced by the type of the instruments used. The average dry deposition and total deposition velocity values calculated based on deposition and concentration values were found as 0.23 ± 0.21 and 0.13 ± 0.13 cm/s, respectively. [ABSTRACT FROM AUTHOR]

Polychlorinated biphenyls (PCBs) are persistent toxic pollutants occurring as complex mixtures in the environment. Humans are known genetically to have > 60-fold differences in hepatic cytochrome P450 1A2 (CYP1A2) levels and > 12-fold differences in aryl hydrocarbon receptor (AHR) affinity, both of which could affect PCB pharmacokinetics. Thus, we compared Ahrb1_Cyp1a2(+/+) high-affinity AHR wild-type, Ahrd_Cyp1a2(+/+) poor affinity AHR wild-type, Ahrb1_Cyp1a2(−/−) knockout, and Ahrd_Cyp1a2(−/−) knockout mouse lines. We chose a mixture of three coplanar and five noncoplanar PCBs to reproduce that seen in human tissues, breast milk, and the food supply. The mixture was given by gavage to the mother on gestational day 10.5 (GD10.5) and postnatal day 5 (PND5); tissues were collected from pups and mothers at GD11.5, GD18.5, PND6, PND13, and PND28. Ahrb1_Cyp1a2(−/−) pups showed lower weight at birth and slower rate of growth postnatally. Absence of CYP1A2 resulted in significant splenic atrophy at PND13 and PND28. Presence of high-affinity AHR enhanced thymic atrophy and liver hypertrophy in the pups. Concentrations of each congener were analyzed at all time points: maximal noncoplanar congener levels in maternal tissues were observed from GD18 until PND6, whereas the highest levels in pups were found between PND6 and PND28. Coplanar PCB concentrations were generally higher in Ahrd-containing pup tissues; these findings are consistent with earlier studies demonstrating the crucial importance of AHR-mediated inducible CYP1 in the gastrointestinal tract as a means of detoxication of oral planar polycyclic aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

Abstract: We analyzed 15 polychlorinated biphenyls (PCBs) and five organochlorine pesticides (OCPs) in fat tissue of 27 loggerhead sea turtles (Caretta caretta) from eastern Adriatic Sea with the curved carapace length ranging from 25.0 to 84.5cm. The PCB profile was dominated by hexa- and hepta-chlorinated congeners, with PCB-153 (median: 114.9ngg−1 wet mass), PCB-138 (80.0ngg−1 w.m.), and PCB-180 (26.7ngg−1 w.m.) detected with the highest levels. Toxic mono-ortho congeners PCB-118, PCB-105 and PCB-180 with dioxin-like toxicity were found in >70% samples. 4,4′-DDE (81.0ngg−1 w.m.) prevailed the OCP signature, accounting for 80% of the total DDTs. A significant increasing trend in accumulation with size was found for PCB-52 (rs =0.512, p <0.01) and PCB-114 (rs =0.421, p <0.05). Comparison of our results with organochlorine contaminant (OC) pattern in some prey taxa suggest that contamination occurs primarily through the food web, with biomagnification factors of 0.14–6.99 which were positively correlated with the octanol–water partition coefficient (log K ow; p <0.05). This study, based upon a fairly large sample size collected mostly from incidentally captured animals over a short time period (June 2001–November 2002), present a temporal snapshot of OC contamination in wild, free-ranging loggerheads from Adriatic feeding grounds and provide a baseline for monitoring the regional OC trends in this endangered species. [ABSTRACT FROM AUTHOR]

Polychlorinated biphenyls (PCBs) are known to reduce serum thyroxine (T4) in rats, but the relative effects of individual PCB congeners on thyroid hormones are not known. Thus, male Sprague-Dawley rats were administered Aroclor 1254, Aroclor 1242 (4, 8, 16, or 32 mg/kg/day), PCB 95 (2,2′,3,5′,6-pentachlorobiphenyl), PCB 99 (2,2′,4,4′,5-pentachlorobiphenyl), PCB 118 (2,3′,4,4′,5-pentachlorobiphenyl) (2, 4, 8, or 16 mg/kg/day), PCB 126 (3,3′4,4′,5-pentachlorobiphenyl) (2.5, 5, 10, 20, or 40 μg/kg/day), TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) (0.14, 0.43, 1.3, or 3.9 μg/kg/day), or corn oil via oral gavage for 7 days. Rats were necropsied 24 h after the last dose. Serum thyroid hormone levels were evaluated by radioimmunoassay, and induction of hepatic Cyp1a (a TCDD-inducible protein) and Cyp2b (a phenobarbital [PB]-inducible protein) activity was determined by ethoxyresorufin-O-deethylase and pentoxyresorufin-O-deethylase assays, respectively. Significant increases in Cyp1a activity occurred in response to PCBs, except PCB 95 and PCB 99. Aroclor 1254, PCB 99, and PCB 118 significantly induced Cyp2b activity. Serum total T4 and free T4 were dramatically reduced in response to each of the seven treatments in a dose-dependent manner. The marked T4 reductions occurred in response to Aroclor 1254, PCB 99 (a PB-type congener), and PCB 118 (a mixed-type congener). In contrast, reductions in serum triiodothyronine (total and free) were variable and mild, and serum thyroid-stimulating hormone was not significantly affected by any of the compounds. These data indicate that the PB and mixed-type PCB congeners are more effective than the TCDD-type PCB congeners at reducing serum T4. [ABSTRACT FROM PUBLISHER]

Abstract: Concentrations of polychlorinated biphenyls (PCBs) were measured in composited samples of walleyes Sander vitreus and their prey during 2005–2007 from Saginaw Bay, Lake Huron. There was a linear relationship between fish length and PCB concentrations in walleyes between 356 and 608mm, but fish 680mm had lesser concentrations than 608-mm fish. When fish 222–550mm from 1990 were compared with those from 2007, there was a decrease of 1315ng PCBs/g wet wt (ww). Concentrations of PCBs in gizzard shad Dorosoma cepedianum (190ng PCBs/g ww) were three-fold less than fish collected in 1990 (516ng PCBs/g ww). Round gobies Neogobius melanostomus collected from the Saginaw River had the greatest concentrations of PCBs (range: 200–350ng PCBs/g ww) compared with other prey fishes (45–190ng PCBs/g ww). Concentrations of PCBs in Saginaw River round gobies were three-fold greater than those from Saginaw Bay. Zooplankton from 1990 and 2008 contained 8.0 and 32ng PCBs/g ww, respectively, while zebra mussels Dreissena polymorpha from 2008 contained 351ng PCBs/g ww. Principal components analysis showed that PCB congeners differed between the largest walleyes and other fish. There are several possible explanations for lesser concentrations of PCBs observed in 2007. These include effects of dredging, changes in the food web related to round gobies, loss of alewife Alosa pseudoharengus, which was a major walleye prey item in 1990, and replacement by yellow perch Perca flavescens, or decreases in release of PCBs from sediments due to weathering, burial, or diffusion. [Copyright &y& Elsevier]

Polychlorinated biphenyl compounds (PCBs) were analyzed in sediments and clams’ soft tissues from sampling sites in the Mekong River delta from the border with Cambodia to the coast of South China Sea. Concentrations of 13 individual PCB congeners are reported. Median concentration of ΣPCB congeners was 0.279 ng g−1 dry weight (range 0.106–2.016 ng g−1 dry weight) in sediments, and 5.20 ng g−1 dry weight (range 1.89–19.37 ng g−1) in clams. Distribution and bioaccumulation of PCBs in the delta are discussed. It is concluded that in the Mekong River delta PCB concentrations were generally lower than in other regions of Vietnam and their likely sources have been waste discharges from repair workshops and other facilities in the delta cities. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the rhizosphere effect of rape plants on polychlorinated biphenyls (PCB) dissipation in soils spiked with seven indicator congeners. Depletion of PCB in the rhizosphere was significantly higher in the soil with lower organic matter content. While in the Chernozem soil, 87% of PCB related to bulk soil were found in the 1st mm from roots, only 62%–69% were found in the Fluvisol soil with no significant influence of increased initial PCB concentration. Further from the roots, the concentration of lower chlorinated congeners decreased, which indicates their greater biodegradation in comparison with more chlorinated ones. [ABSTRACT FROM AUTHOR]

Abstract: Background: Polychlorinated biphenyls are toxic and slowly degrading substances that have been in widespread industrial use in the 1960s and 1970s. Despite a worldwide reduction, environmental exposure remains an issue; the assessment of an individual’s level of exposure at a given time in retrospect requires valid toxicokinetic modeling of the different PCB congeners. Objectives: To develop and verify a toxicokinetic model of the in vivo-degradation of PCB 28 and 52 in adult humans. Methods: The plasma concentrations of PCB congeners were measured in 583 persons working in a contaminated building for an average of 14.7±9.6 years. The values were adapted to a simple pharmacokinetic model (y t = y 0 ×(1−e−kt )); the steady state concentration y 0 was estimated based on the median values of persons working exposed more than 10 years. Results: The steady state concentration of PCB 28 was 0.10μg/l, that of PCB 52 0.02μg/l. The half-life of the congeners was estimated based on a logarithmic regression analysis according to the model mentioned above; it was 2.18 (95% CI: 1.91–2.54) years for PCB 28 and 3.95 (95% CI: 3.55–4.45) years for PCB 52, respectively. Stepwise elimination of persons with very long employment duration did not reduce the estimated half-life. Conclusions: The estimated half-life is higher than previously published data especially for PCB 52. Possible reasons and implications of this finding are discussed. [Copyright &y& Elsevier]

Accumulation and distribution of seven indicator PCB congeners(IUPACNo. 28,52, 101,118,138, 153 and 180) in carrots grown on spiked soils (100 μg of each PCB congener per kg of soil) with different physical and chemical characteristics were investigated during two vegetation seasons. Results showed that the concentrations of the sum of the tested congeners (PCB7) in edible parts of carrots were significantly higher compared to shoots. The differences in PCB7 concentration in carrot roots among treatments were observed only during the first experimental year. The highest value, 1280±130 μg PCB7.kg-1, was found in carrot roots planted on the soil with the lowest organic matter content. The differences in accumulation of individual congeners were more obvious in the second experimental yeas, in terms of higher accumulation rate of more chlorinated biphenyls. The effect of soil type was not significant. In both years, congener profiles of all soils sampled after the harvest of carrots were characterized by a larger proportion of highly chlorinated PCB congeners. [ABSTRACT FROM AUTHOR]

Organisms differ widely in their ability to metabolize and eliminate polychlorinated biphenyls (PCBs). We evaluated the retention of PCB congeners, reference standard mixture, experimentally injected into cockroach Blattella germanica, in relation to sex and time, and its elimination through the feces, exuviae and oothecae. The nymphs that died prematurely had a higher average PCB retention than those with a longer lifetime, 88% of the injected dose for those that died within 1 to 10 days, and 76% for those within 11-20 days. Diverse PCB congeners showed differential retention, and particularly the more volatile, low weight congeners were recovered in lower concentrations, the medium-weight ones were intermediate, while the high-weight congeners attained the highest concentration. PCBs were also detected in the excrements and in exuviae, which may therefore act as detoxification paths, and in the oothecae, thus showing that PCBs can be transferred from mother to progeny. [ABSTRACT FROM AUTHOR]

Abstract: Atlantic croaker (Micropogonias undulatus) were exposed to the polychlorinated biphenyl (PCB) mixture (Aroclor 1254) or one of three individual congeners (planar PCB 77 or ortho-substituted PCB 47 and PCB 153) in the diet for 30 days to investigate the effects of PCBs on circulating thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Aroclor 1254 (0.2 and 1.0 mg/kg body mass/day) decreased plasma T3 levels consistently, but the effects on T4 levels were inconsistent from year to year. Exposure to PCB 153 (0.1 and 1.0 mg/kg body mass/day) significantly lowered both T4 and T3, while PCB 47 at the same doses had no effect on thyroid hormone levels. The lower doses of PCB 77 (0.004, 0.01 and 0.02 mg/kg body mass/day) had no effect on T4 or T3, whereas the highest dose (0.1 mg/kg body mass/day) increased T4 levels significantly. The results of the present study demonstrate that exposure to PCBs at environmentally realistic concentrations can have profound effects on the thyroid status of Atlantic croaker. The ortho-substituted PCB 153 appears to contribute at least partially to the deleterious effects of Aroclor 1254 on thyroid status, whereas the planar PCB 77 at concentrations present in the mixture is unlikely to alter thyroid hormone levels. [Copyright &y& Elsevier]

Abstract: A novel application of a commonly used statistical approach was used to examine differences in polychlorinated biphenyl (PCB) congener patterns among locations and sample matrices in tree swallows (Tachycineta bicolor) nesting in the Housatonic River watershed in western Massachusetts, USA. The most prevalent PCB congeners in tree swallow tissue samples from the Housatonic River watershed were Ballsmitter Zell numbers 153, 138, 180, 187, 149, 101, and 170. These congeners were seven of the eight most prevalent congeners in Aroclor® 1260, the PCB mixture that was the primary source of contamination in the Housatonic River system. Using paired-Euclidean distances and tolerance limits, it was demonstrated that congener patterns in swallow tissues from sites on the main stem of the Housatonic River were more similar to one another than to two sites upstream of the contamination or from a nearby reference area. The congener patterns also differed between the reference area and the two upstream tributaries and between the two tributaries. These pattern differences were the same in both pipper (eggs or just hatched nestlings) and 12-day-old nestling samples. Lower-chlorinated congeners appeared to be metabolized in nestlings and pippers compared to diet, and metabolized more in pippers compared to nestlings. Euclidean distances and tolerance limits provide a simple and statistically valid method to compare PCB congener patterns among groups. [Copyright &y& Elsevier]

Abstract: We have demonstrated previously [Pérez-Reyes, P.L., Sánchez-Alonso, J.A., López-Aparicio, P., Recio, M.N., Pérez-Albarsanz, M.A., 2001. Different molecular capacity in the induction of apoptosis by polychlorinated biphenyl congeners in rat renal tubular cell cultures. Biosci. Rep. 6, 765–778] that the polychlorinated biphenyls (PCBs) cause loss of cell viability and accelerate apoptosis in cell kidney cultures. Further investigations are necessary to elucidate the mechanism of apoptosis induction. In this way, we have analyzed in the present work the effects of PCBs on protein kinase C (PKC, a protein family intimately involved in the regulation of cell survival) and the expression of two proapoptotic (caspase-3 and Bax) and one antiapoptotic (Bcl-2) proteins. Aroclor 1248 (a commercial PCB mixture with 48% chlorine by weight), PCB 153 (2,2′,4,4′,5,5′-hexachlorobiphenyl, a di-ortho-substituted nonplanar congener) and PCB 77 (3,3′,4,4′-tetrachlorobiphenyl, a non-ortho-substituted planar congener), significantly increased PKCα activity compared to control cells in the cytosolic and particulate cell fractions, and increased the PKCα protein content in the particulate fraction. The nonplanar PCB 153 showed stronger effects than the coplanar congener PCB 77. In addition, Aroclor 1248 decreased both, procaspase-3 levels and the Bcl-2/Bax protein ratio. These findings indicate that PCBs, particularly nonplanar congeners, can induce apoptosis in primary renal tubular cells through the PKCα, caspase-3 and Bcl-2/Bax pathway. [Copyright &y& Elsevier]

Each environmental exposure matrix contains a unique mixture of PCB congeners. Since several congener types have multiple and distinct biological actions, it is important to characterize congener profiles in exposure sources. The Fox River Environment and Diet Study (FRIENDS) is assessing the human health effects of consumption of PCB-contaminated fish from the Fox River in northeastern Wisconsin. Concurrent laboratory studies required the formulation of a dosing solution which closely mimicked the human PCB exposure from fish. PCB congener profiles from Fox River walleye were compared to profiles for various theoretical mixtures having different relative percentages of Aroclors by weight. The theoretical mixture which provided the best approximation of the Fox River fish PCB profile contained 35% 1242, 35% 1248, 15% 1254, and 15% 1260. A PCB mixture was formulated to match this theoretical construct, and the congener profile for the mixture of Aroclors was determined by capillary column gas chromatography with electron capture detection (GC/ECD). The relative percent of each congener was compared to the PCB congener profile of the theoretical Aroclor mixture and that for Fox River walleye. The specific congeners differed on average by 17% from the theoretical Aroclor mixture predicted values, and the specific congeners measured in the mixture were on average within 71% of those reported for Fox River fish. The mixture was found to have relatively low AhR activity but high RyR activity. Indirect comparisons suggest that in vivo toxicity was slightly greater than that for Aroclor 1254. This illustrates that Aroclor mixtures are useful for formulating dosing solutions which closely approximate actual environmental exposures. [ABSTRACT FROM AUTHOR]

Abstract: Approximately 80 000kg polysulfide sealant containing 10 000–18 000kg polychlorinated biphenyls (PCB) was deposited at a Swedish municipal landfill station during 1965–1973. Investigations during 1994 showed that soil layers underneath the landfill had concentration of PCB not alarmingly high. The concentration of PCB congeners in ground water samples was elevated 4–750 times compared to a reference sample. Based on samples of ground water, leachate water, and flux chambers measuring evaporation of PCB from the landfill surface, the emission of PCB was estimated to be 1g ΣPCB/yr. This very low rate was attributed to the high sorptive capacity of the sealant. Compared to a reference site, the evaporation flux was elevated for the most volatile congeners, but factors 20–1400 lower than from another landfill which was contaminated with PCB in paper-pulp fibres. [Copyright &y& Elsevier]

In order to investigate the residual amounts of organochlorines and polychlorinated biphenyls (PCBs) in Korean human tissues (blood, adipose tissue, liver, kidney cortex, and lung), the samples were collected from the autopsied cadavers of 40 men and 40 women (from teens to seventies of age) α-BHC, β-BHC, γ-BHC, σ-BHC, p,p′-DDT, p,p′-DDD, p,p′-DDE, endrin, dieldein, aldrin, and 7 marker PCBs (28, 52, 101, 118, 138, 153, and 180) were determined in human tissues. The levels of organochlorines and PCB congeners indicated that they have been widely distributed in Korean human body. Positive correlations in terms of age were observed for the following cases: p,p′-DDE, p,p′-DDT, θ-DDT, PCB 118, PCB 138, PCB 153, and θ-PCB in the adipose tissue, and p,p′-DDE in the lung. Concentration of these compounds showed a significant age-related increase. Accumulation of these compounds in aged people revealed that these compounds were more slowly eliminated in our environment and risk assessment was necessary for further proper action. Significant differences in the levels of PCBs between genders were found for PCB 118 in the adipose tissue and PCB 138 in the liver. Positive correlation coefficients between tissues were detected with p,p′-DDE and β-BHC. [ABSTRACT FROM AUTHOR]

Nine hand-collected sediment cores were obtained for PCB concentration analysis and dating from the Upper Sheboygan River, Wisconsin, USA. The primary PCB Aroclors in the Upper Sheboygan River were 1248 (50%) and 1254 (50%). The total PCB concentrations in the sediments ranged from 0.1-1 04 ppm (based on dry weight). The PCB data obtained from the sampling were analyzed using a factor analysis (FA) model with non-negative constraints in order to identify PCB sources and congener patterns. The factor loadings obtained from the FA model represent a general dechlorination profile common to most of the higher concentration samples and another associated with contamination from upstream dredging during 1989-1991. Anaerobic dechlorination is occurring in Upper Sheboygan River sediments and is most significant at high concentrations (≳ 20 ppm). Observation of elevated amounts of lower chlorinated congeners such as congeners 4 (2-2), 8 (2-4), 25 (24-3), and 26 (25-3) indicates the presence of anaerobic dechlorination activities. Based on the data from the FA model, anaerobic dechlorination was occurring according to dechlorination activities M and P. All possible dechlorination pathways involving marker congeners were considered. A significant improvement (86-91%) in similarity between the original Aroclor profile and the altered ones was found. [ABSTRACT FROM AUTHOR]

Levels and patterns of polychlorinated biphenyls (PCBs) were studied in surface soil samples collected in the coastal part of Croatia within and surrounding four different airports and in the vicinity of two partially devastated electrical transformer stations. The compounds accumulated from air-dried soil samples by multiple ultrasonic extraction with an n -hexane : acetone 1 : 1 mixture were analysed by capillary gas chromatography with electron capture and ion-trap detection. PCBs were quantified against a standard Aroclor 1242/Aroclor 1260 mixture and a standard mixture of 17 individual PCB congeners (IUPAC No.: 28, 52, 60, 74, 101, 105, 114, 118, 123, 138, 153, 156, 157, 167, 170, 180, and 189). The mass fractions of total PCBs in 18 soil samples collected within the airport premises ranged from 3 to 41 327 µg/kg dry weight (dw) (median: 533 µg/kg dw), and those in 21 samples collected at a distance ranging from several metres to 5 km away from the airport fence, from <1 to 39 µg/kg dw (median: 5 µg/kg dw). The highest PCB levels were determined in soils along the airport aprons where the aircrafts were serviced and refuelled. The PCB pattern was very similar to technical Aroclor 1260 in all airport soils. The PCB pattern in 22 soils collected in the vicinity of electrical transformer stations was dominated by congeners contained in Aroclor 1242. These soils contained 7 to >400 µg/kg dw of total PCBs. One highly PCB-contaminated airport soil sample was analysed for polychlorinated dibenzo- p -dioxins (PCDDs) and dibenzofurans (PCDFs). With an international toxic equivalent (I-TEQ) of 9.7 ng/kg dw, the airport soil contamination was within values typical for urban and rural areas, and the congener patterns gave no clear indication for PCBs as the only source of PCDDs/PCDFs. [ABSTRACT FROM AUTHOR]

During the past 20 years a number of studies have found neurological and immunological effects in the developing fetus and infants exposed to background or only slightly elevated levels of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs). To address concerns arising from possible increased human exposure in the Arctic and possible effects of POPs, all circumpolar countries agreed in 1994 to monitoring of specific human tissues for contaminants in the Arctic under the Arctic Monitoring and Assessment Program (AMAP). Mothers in eight circumpolar countries contributed blood samples that were analysed at a single laboratory for 14 PCB congeners (IUPAC No. 28, 52, 99, 105, 118, 128, 138, 153, 156, 170, 180, 183, 187) and 13 organochlorine pesticides (aldrin, beta-hexachlorocyclohexane (beta-HCH), dichlordiphenyltrichloroethane (p,p′-DDT), diphenyldichloroethylene (p,p′-DDE), dieldrin, heptachlorepoxide, hexachlorobenzene (HCB), mirex, and the chlordane derivatives alpha-chlordane, gamma-chlordane, cis-nonachlor, oxychlordane and trans-nonachlor). Inuit mothers from Greenland and Canada have significantly higher levels of oxychlordane, transnonachlor and mirex than mothers from Norway, Sweden, Iceland and Russia. Inuit mothers from Greenland also have significantly higher levels of these contaminants than Inuit mothers from Canada and Alaska. These differences among Inuit groups may represent regional dietary preferences or different contaminant deposition patterns across the Arctic. Levels of PCBs are also elevated among some arctic populations due to their consumption of marine mammals and are in the range where subtle effects on learning and the immune system have been reported. The Russian mothers who consume mainly food imported from southern Russia have elevated levels of DDT, DDE, beta-HCH and a higher proportion of lower chlorinated PCB congeners. This study has allowed an assessment of the variation of contaminants such as PCBs and various organochlorine pesticides (DDT, chlordane, etc.) in human populations around the circumpolar north. [Copyright &y& Elsevier]

Polychlorinated biphenyls including coplanar congeners were measured in the liver of different species of skates and ghostsharks. The mean concentrations of PCBs in skates (314 ng/g wet wt) were comparable with those in ghostsharks (285 ng/g wet wt). The specific analysis of PCB congeners in skates hepatic tissue revealed a profile dominated by hexa-, penta-, and heptachlorinated congeners followed by trichlorobiphenyls, tetra- and decachlorobiphenyls. A different profile dominated by hexa-, tri-, and pentachlorinated congeners, followed by heptachlorobiphenyl and decachlorobiphenyls was found in ghostsharks liver. The estimated 2,3,7,8-tetrachlorodibenzo-p-dioxin toxic equivalents (TEQs) of coplanar PCBs in skates and ghostsharks were 0.48 and 0.33 pg/g wet weight, respectively, with mono-ortho congeners PCB105, 118 and 156 contributing more than 90% to the TEQs. [Copyright &y& Elsevier]

New reliable and extensive polychlorinated biphenyl (PCB) partition equilibrium data between real world PCB contaminated St. Lawrence River sediments (SLRS) and two supercritical fluids (SCFs), scCO2 and scCO2/5 mol% MeOH, are presented. Three real world SLRS samples with similar physical properties and PCB congener distribution patterns but different PCB concentration levels were used to conduct experiments at 313, 323, and 333 K and SCF densities from 5.5 to 18 mol/l. The experimental results are presented as partition coefficients, K, for 16 PCB congeners and for the total PCBs in the SLRS. The presence of methanol in the SC phase increases PCB desorption, as expected. Two partition equilibrium models are employed to correlate these data sets for each of the two SCFs used. The effects of SCF density on K and the parameters of the models are presented for each PCB congener in both systems of scCO2 and scCO2/MeOH. Preferential desorption is found among the PCB congeners and it is suggested that the partition coefficients increase roughly in the order of PCB molar weight. These models can be used in the design of large scale PCB desorption equipment. [Copyright &y& Elsevier]

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants, some of which may be neurotoxic depending on the chemical structure of the congeners. This study investigated the neurotoxic potential of 3,3′,4,4′-tetrachlorobiphenyl (TCB) (PCB 77, a non-ortho-substituted planar congener) and 2,2′,4,4′,5,5′-hexachlorobiphenyl (HCB) (PCB 153, a di-ortho-substituted nonplanar congener) by assessing cell viability and apoptotic cell death in neuronal cell cultures. We have combined morphological and biochemical techniques to establish the relevance of apoptosis in neuronal cell death induced by the two selected PCB congeners. Treatment with both planar and nonplanar congeners caused the loss of cell viability and accelerated apoptosis in a time- and concentration-dependent manner. However, the extent of apoptosis generated was greater for the non-ortho-substituted planar congener (PCB 77) than for the di-ortho-substituted nonplanar congener (PCB 153). This was correlated with the loss of cell viability since the planar congener was more cytotoxic. Based on our findings, the apoptosis induced by PCBs involves the increase of caspase-3 activity in neuronal cell cultures. It is reasonable to assume that PCB-induced apoptosis may be linked to the neurotoxic effect of these toxicants and that different molecular mechanisms may operate in the induction of apoptosis depending on the planarity or nonplanarity of the PCB congeners. [Copyright &y& Elsevier]

Seven EPA PCB congeners (28, 52, 101, 118, 138, 153, and 180) were determined in samples of early human milk collected from 18 mothers in Novi Sad, using GC-ECD (HP 5890) supplied with a Quadra fused silica column 5% Ph for PCBs. The sum of seven PCB congeners was 3.26±3.90 (), median 1.25, range 0.4–14.31 and the range of individual congeners was for: 28: 0.04–0.37; 52: 0.04–0.44, 101: 0.04–1.21; 118: 0.05–0.62; 138: 0.13–4.61; 153: 0.13–4.81; 180: 0.10–3.07, ng/g wet. No correlation was found between maternal age and seven PCB congeners. In two primiparous mothers below 30 years, the sum of seven PCB congeners was three to fourfold, and in one multiparous twofold higher than the average for the group. Unchanged level of assumed total PCBs in early human milk in 2003, compared with measured total PCBs in 1993, suggest the continuous inlet of these chemicals into the environment. [Copyright &y& Elsevier]

Persistent organic pollutants (POPs) are heterogeneous carbon-based compounds that can seriously affect human health. The aim of this study was to measure serum concentrations of POPs in women residing in the Euro-Arctic Region of Russia. A total of 204 women from seven rural settlements of the Nenets Autonomous Okrug (NAO) took part in the study. We measured serum concentrations of 11 polychlorinated biphenyls (PCBs) and 17 organochlorine pesticides (OCPs) across the study sites and among Nenets and non-Nenets residents. Measurement of POPs was performed using an Agilent 7890A gas chromatograph equipped with an Agilent 7000 series MS/MS triple quadrupole system. The concentrations of all POPs were low and similar to findings from other Arctic countries. However, significant geographic differences between the settlements were observed with exceptionally high concentrations of PCBs in Varnek located on Vaygach Island. Both ΣDDT (p = 0.011) and ΣPCB (p = 0.038) concentrations were significantly lower in Nenets. Our main findings suggest that the serum concentrations of the legacy POPs in women in the Euro-Arctic Region of Russia are low and similar to those in other Arctic countries. Significant variations between settlements, and between Nenets and non-Nenets residents, were found. Arctic biomonitoring research in Russia should include studies on the associations between nutrition and concentrations of POPs. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide fluid extraction (SFE) has been used for selective extraction of nine aliphatic hydrocarbons, Aroclor 1260, Aroclor 5460, and four PCB congeners from chicken liver. Alumina was used as adsorbent and methanol as modifier. Recoveries were between 53 and 100% for aliphatic hydrocarbons, 83 and 95% for Aroclor 1260 and Aroclor 5460, and 81 and 98% for PCB congeners. [ABSTRACT FROM AUTHOR]