Highly toxic coplanar PCBs: occurrence, source, persistency and toxic implications to wildlife and humans

Isomer-specific determinations of PCB congeners in a wide variety of animal species such as fish, marine mammals (whale, dolphin and porpoise) and terrestrial mammals (dog, cat and human) revealed the environmental occurrence of highly toxic coplanar 3,3',4,4'-tetrachlorobiphenyl (T(4)CB), 3,3',4,4',5-pentachlorobiphenyl (P(5)CB) and 3,3',4,4',5,5'-hexachlorobiphenyl (H(6)CB) within a range of few pg g(-1) to several ten ng g(-1) in fat tissues (except fish) on a wet weight basis. Detection of these toxic residues in wild specimens collected from remote areas such as the North Pacific suggests the already widespread distribution of coplanar PCBs as in the case of general PCB pollution. The clear positive correlations between concentrations of total PCBs and each of the three coplanar PCBs obtained in all mammals analysed suggest that the sources of coplanar PCB contamination to the environment are mainly commercial PCB preparations. Comparison of the composition of three toxic coplanar PCBs in commercial PCB mixtures and in the various animals indicates the relative metabolisability of these congeners as follows: 3,3',4,4'-T4CB>3,3',4,4',5-P5CB>3,3',4,4',5,5'-H6CB. Moreover, marine mammals seem to have lower potency to metabolise the coplanar PCBs in comparison with terrestrial mammals. In human adipose tissues, the concentrations of coplanar PCBs were found to be much higher than 2,3,7,8-tetrachlorodibenzo-p-dioxin (T(4)CDD), 2,3,4,7,8-pentachlorodibenzofuran (P(5)CDF) and other toxic congeners. 'T(4)CDD-equivalent' analysis based on the enzyme induction potencies and the residues of these toxic chemicals indicates that 3,3',4,4',5-P(5)CB may impose a greater toxic threat than dioxins and furans to the humans and probably to wildlife also.     

Polychlorinated biphenyls (PCBs) in sediments in Hong Kong: a congener-specific approach to the study of coplanar PCBs in aquatic ecosystems

Patterns of contamination by polychlorinated biphenyls (PCBs) were investigated in fourteen samples of coastal sediments from Hong Kong. Congener-specific analyses revealed nine sediment samples from Junk Bay to contain PCBs at concentrations ranging from 31 to 2200 ng g(-1) dry weight, concentrations generally increasing with distance north in the Bay. By contrast, five sediments from the Tolo area to the north-east of Hong Kong exhibited total PCB levels of only 6.6 to 45 ng g(-) dry weight. The patterns of relative abundance of PCB congeners in the northern Junk Bay sediments suggested the existence of ongoing source(s) of PCBs in this area; biphenyls of lower chlorination were present at high concentration in these samples. Three coplanar PCBs (3', 4, 4'-tetrachlorobiphenyl; 3,3',4,4',5-pentachlorobiphenyl; and 3,3',4,4',5,5'-hexachlorobiphenyl) were found to be present in Junk Bay sediments; these are highly toxic and are cause for concern in aquatic environments. The abundance of the three coplanar PCBs in the sediments studied was similar to that in commercial PCB mixtures, suggesting that these congeners are not enriched over other PCBs by the sediments of coastal ecosystems. It is concluded that the preferential enrichment of coplanar PCBs occurs in the biosphere, rather than in sediments.     

Comparison of seven indicator PCBs and three coplanar PCBs in beef, pork, and chicken fat

The risk assessment of polychlorinated biphenyls (PCBs) is difficult since complex congeners were used in many industrial applications for a long period of time and the residue monitoring in foods of animal origin and the environment were not established in comparable systems. The relationships of determined concentrations in indicator PCB congeners (mono- and di-ortho PCBs) and coplanar PCB congeners (non-ortho PCBs) in livestock products are presented in this study. The concentrations of seven indicator PCBs were compared with three coplanar PCBs in beef, pork, and chicken fat. Distributions of concentration for the indicator PCBs in three different animal species were similar except for that of PCB-118 (2,3',4,4',5-pentachlorobiphenyl) in pork fat. The congeners with the highest concentration were PCB-138 (2,2',3,4,4',5'-hexachlorobiphenyl) in beef and pork fat and PCB-28 (2,4,4'-trichlorobiphenyl) in chicken fat. The bioaccumulation and metabolism of PCBs in animal species represent different congener profiles in livestock products. The percentage of the total concentration of three coplanar PCBs was about 2% of the total concentration of the seven indicator PCBs. Relatively high concentration of mono-ortho and di-ortho PCBs in fat samples of livestock products may be calculated with the concentration of coplanar PCBs that can be usually determined on a sequential procedure with dioxin analysis. Therefore, the relationship of the amounts between seven indicator PCBs and three coplanar PCBs may be useful to derive the composition and level of contaminants in beef, pork, and chicken.     

Biodegradation of coplanar polychlorinated biphenyls by anaerobic microorganisms from estuarine sediments.

In this study, we investigated the biodegradability of biphenyl and 5 congeners (one non-planar and four coplanar) of polychlorinated biphenyl (PCB). Biphenyl, the non-planar congener 2,3',4',5-tetrachlorobiphenyl (25-34 CB), and the four coplanar congeners 3,3',4,4'-tetrachlorobiphenyl (34-34 CB), 3,4,4',5-tetrachlorobiphenyl (345-4 CB), 3,3',4,4',5-pentachlorobiphenyl (345-34 CB), and 3,3',4,4',5,5'-hexachlorobiphenyl (345-345 CB) were amended at a concentration of 10 mg/L into anoxic sediment slurries collected from the estuaries of the Tansui River and the Erjen River. During 2 years' incubation under sulfidogenic conditions, biphenyl was persistent, while all other chlorinated congeners, except for 345-345 CB, were dechlorinated with or without a lag period in sediment slurries collected from both rivers. Dechlorination of coplanar and non-planar congeners began with para chlorine removal. All para chlorines from the mono-, di-, and trichlorobiphenyl groups could be removed by sediment slurries from both rivers. Microbial communities in sediment from the Erjen River additionally fostered meta-dechlorination activity, but only after removal of all the para chlorines. Addition of Tween 20 (0.05%, v/v) into sediment slurries from the Tansui River did not enhance dechlorination rates or extents, but the addition of toluene- or 3-chlorobenzoate-adapted sediments enhanced dechlorination of 34-34 CB and 345-4 CB.     

Mussels as bioindicators of PCB pollution: a case study on uptake and release of PCB isomers and congeners in green-lipped mussels (Perna viridis) in Hong Kong waters

The uptake and release of PCB isomers and congeners were examined in green-lipped mussels (Perna viridis) through a transplantation experiment in two locations in Hong Kong waters. Rapid rates of uptake and release of relatively less lipophilic lower-chlorinated PCBs were observed in the mussels, indicating that the primary mechanism of bioaccumulation of lipophilic pollutants in P. viridis complies with the concept of equilibrium partitioning. Thus, data for contaminant concentrations are most appropriately based upon lipid weights of samples when using mussels as bioindicators of aquatic PCB pollution. Considering the kinetic parameters of PCBs based on lipid weight-related data, it is concluded that P. viridis has the ability to respond rapidly to changes in ambient levels of PCBs. This is significant in determining the usefulness and limitations of mussels as bioindicators for monitoring programmes investigating aquatic pollution by PCBs.     

Bioaccumulation profiles of polychlorinated biphenyls including coplanar congeners and possible toxicological implications in Baikal seal (Phoca sibirica)

Isomer specific concentrations of individual polychlorinated biphenyls (PCBs) including toxic non-ortho (IUPAC 77, 126, 169), mono-ortho (105, 118, 156) and di-ortho (137, 138, 153, 180) coplanar congeners were determined in the blubber of 40 Baikal seals (Phoca sibirica) and as their fish diet collected from Lake Baikal, Siberia. Residue levels of total PCBs in Baikal seals were noticeably high and comparable to those reported for seals from the North Sea, suggesting the recent usage of this compound in the watershed of Lake Baikal. Non-, mono-, and di-ortho coplanar congeners were also detected in Baikal seals and fish. An approach to estimate bioaccumulation profiles of PCB congeners revealed that the non-ortho PCBs, IUPAC 77, 126 and 169 seemed to be less persistent than other congeners. Furthermore, selective biotransformation of PCB congeners having either meta-para vicinal H atoms or both adjacent chlorinated meta-para and ortho-meta positions has been suggested. Comparison of 2,3,7,8-TCDD toxic equivalents (TEQ) of non-, mono- and di-ortho coplanar congeners in Baikal seals with those for other marine mammals suggested higher enrichment of mono-ortho congeners, particularly IUPAC 105 and 118, which contributed significantly to the total TEQs in Baikal seals. Results imply that the TCDD-like toxicity is relatively serious in Baikal seals, because of the enrichment of these toxic PCB congeners in tissues.     

Determination of coplanar and ortho substituted PCBs in some sewage sludges of Switzerland using HRGC/ECD and HRGC/MSD

The three most toxic coplanar PCB congeners PCB 77, 126 and 169 as well as 7 mono-and di-ortho-PCBs (PCB 28, 52, 101, 118, 153, 138, 180) were measured in 19 sewage sludges. Concentrations of the coplanar PCBs ranged between 231–5050 ng/kg dw for PCB 77, 43–1511 ng/kg dw for PCB 126 and 29–273 ng/kg dw for PCB 169. Comparable results were obtained with mass selective detection in the single ion monitoring mode (MSD-SIM) except for PCB 169, where MSD-SIM was less sensitive than ECD. The sum of the 7 mono-and di-ortho-PCBs, which are routinely measured as representatives of the PCB fraction, reached levels between 43–550 μg/kg dw and agreed well with results previously obtained in our laboratory. Based on our data, a selective accumulation of the coplanar PCBs could not be observed. Sludges that received industrial effluents clearly showed higher PCB levels than rural ones. Finally, calculation of TEQ equivalents of the coplanar PCBs in the sewage sludges revealed that, based on application rates normally used in Switzerland, the contribution of the sludges to soil pollution seems to be of minor importance.     

Individual PCBs as predictors for concentrations of non and mono-ortho PCBs in human milk

32 Dutch human milk samples were analyzed for PCBs with either HRGC-ECD or HRGC-LRMS in the NCI mode. Samples were collected from three different locations in The Netherlands: Amsterdam, Rotterdam and Groningen. Quantitatively, no differences could be observed between the three localities, while in addition the congener specific pattern showed a striking similarity for all individual samples. Only principal component analysis revealed slight individual differences. Based on similarities in the PCB profiles, linear relationships were calculated between 2,3′4,4′,5-PnCB (#118) or 2,2′4,4′5,5′HxCB (#153) and the most relevantnon andmonoortho PCBs exhibiting dioxinlike activity. These PCBs included 2,3,3′,4,4′-PnCB (#105), 3,3′,4,4′5-PnCB (#126) 2,3,3′,4,4′,5-HxCB (#156), 2,3,3′,4,4′,5′-HxCB (#157), 2,3′,4,4′,5,5′-HxCB (#167) and 3,3′,4,4′,5′5-HxCB (#169). Good linear relationships were observed between individual PCBs. Based on the results of this study, PCB #118 can be used to predict concentrations of the PCBs #105 and #126. PCB #153 can be used as a predictor for the PCBs #156, #157, #167 and #169, but also for the total toxic equivalencies (TEQs) ofnon andmonoortho PCBs present in human milk. This method using certain PCBs as predictors for other toxicological relevant congeners, can be useful and cost effective, e.g. for epidemiological studies. However, before applied a number of conditions should be met. These are:

1. A stable composition of the PCB matrix should be established.
2. A possible time dependent change in composition of the matrix should first be excluded when used over different time periods.

     

Persistent organochlorines in beluga whales (Delphinapterus leucas) from the St Lawrence River estuary--I. Concentrations and patterns of specific PCBs, chlorinated pesticides and polychlorinated dibenzo-p-dioxins and dibenzofurans

Blubber samples from beluga whales (Delphinapterus leucas) in the St Lawrence River estuary were analysed for PCB congeners (ortho- and non-ortho-substituted) and other persistent organochlorines as well as chlorinated dibenzo-dioxins/furans (PCDD/Fs). Major individual components (mean concentrations > 1 microg g(-1)) were 4,4'-DDE, -DDD and -DDT, T12 (a toxaphene-related compound), trans-nonachlor, oxychlordane, mirex, HCB, tris(p-chlorophenyl) methane and dieldrin. Concentrations of SigmaPCBs (8.3-412 microg g(-1)), SigmaDDT (3.36-389 microg g(-1)) and mirex (0.18-6.8 microg g(-1)) were particularly elevated relative to other odontocetes in Canadian waters. SigmaDDT, PCBs (as Aroclor), mirex and T12 concentrations were positively correlated with age of adult females (> 10 years) but only weakly, or not significantly, correlated with age of adult males. PCDD/Fs were present at low ng kg(-1) levels and consisted mainly of penta- and hexachlorofurans, and hepta- and octachlorodioxin. CB126 (3,3',4,4',5-PCB) was the most prominent non-ortho-substituted PCB congener in beluga blubber. Total TCDD toxic equivalents averaged 330 ng kg(-1) in females and 1400 ng kg(-1) in males and were dominated by CB126, and the mono-ortho-substituted congeners CB105 and CB118. Biomagnification factors (BMFs) for mirex and SigmaPCB from fish to beluga ranged from 11 to 16, and were similar to BMFs in Arctic animals, indicating that elevated levels in St Lawrence animals are a consequence of relatively high levels of recalcitrant organochlorines in prey of the beluga in the St Lawrence river system.     

Embryotoxicity of polycyclic aromatic hydrocarbons (PAHs) in three domestic avian species, and of PAHs and coplanar polychlorinated biphenyls (PCBs) in the common eider

The embryotoxicity of an artificial mixture of 18 polycyclic aromatic hydrocarbons (PAHs) was tested by injection into the yolk sacs of eggs of four avian species: chicken Gallus domesticus, turkey Meleagris gallopavo, domestic duck Anas platyrhynchos and common eider Somateria mollissima. A dose of 2.0 mg kg egg(-1) of the PAH mixture increased the mortality among the embryos of all four species. In the domestic duck, but not in the three other species, there was a significantly increased embryonic mortality at a dose of 0.2 mg kg(-1) of this mixture. All 18 individual compounds in the mixture were tested for embryotoxicity in the chicken. The compound most toxic to chick embryos was benzo[k]fluoranthene. This substance also proved to be highly embryotoxic in the three other species. Previous studies have shown coplanar polychlorinated biphenyls (PCBs) to be much more embryotoxic in the chicken than in other avian species studied. In accordance with this, eider duck embryos proved to be considerably less sensitive to 3,3',4,4'-tetrachlorobiphenyl and 3,3',4,4',5-pentachlorobiphenyl than was previously found for chick embryos. For PAHs, however, chick embryos did not have a higher sensitivity than the other species tested.     

Application of an ELISA for PCB 118 to the screening of dioxin-like PCBs in retail fish

A commercially available enzyme-linked immunosorbent assay (ELISA) kit was evaluated for the determination of toxic equivalents (TEQs) of dioxin-like polychlorinated biphenyls (PCBs) in retail fish. The ELISA was highly specific for 2,3',4,4',5-pentachlorobiphenyl (PCB 118), which is generally the most abundant dioxin-like PCB isomer found in fish. The quantitative limit of the ELISA (using 3,3',4'-trichloro-4-methoxybiphenyl as a surrogate standard for PCB 118) was 10 ng ml(-1) (125 pg assay(-1)) in the standard curve, corresponding to 50 pg PCB 118 g(-1) in the tested sample. Good recoveries of PCB 118 (78.7-112.3%) were obtained for spiked purified fish extracts according to the ELISA. Good linearity was also obtained in dilution tests using purified fish extracts. No significant interference of the matrix was observed in the ELISA when this purification procedure was used. Recovery tests in which PCB 118 was added to fish samples also resulted in acceptable recoveries (60.2-82.3%) in the ELISA following purification. The ELISA results for fish samples correlated well with the TEQ concentrations of dioxin-like PCBs obtained by high-resolution gas chromatography/high-resolution mass spectrometry (r = 0.92, n = 26). These data indicate that the ELISA kit is suitable for screening retail fish for the TEQs of dioxin-like PCBs.     

Concentrations and composition of organochlorine contaminants in different species of cephalopod molluscs from the Italian waters (Adriatic Sea)

Persistent organochlorines, such as polychlorinated biphenyls including coplanar congeners and DDT compounds were measured in the liver of different species of mollusc cephalopods: broadtail squid (Illex coindetii), horned octopus (Eledone moschata) and spider octopus (Octopus salutii) collected in two different areas of the Adriatic Sea (central and southern Adriatic Sea). The concentration of PCBs exceeded DDT ones in horned octopus (PCBs: 617.0 ngg(-1) lipid weight, DDTs: 188.0 ngg(-1) lipid weight) and in spider octopus (PCBs: 590.0 ngg(-1) lipid weight, DDTs: 293.0 ngg(-1) lipid weight), while in broadtail squid PCB load (748.0 ngg(-1) lipid weight) was similar to those of DDTs (514.5 ngg(-1) lipid weight). No significant difference in PCB levels was observed among species, while DDT concentrations were higher in broadtail squid than in horned octopus and spider octopus. DDTs composition showed slight differences in relation to species, thought p,p'-DDE was the predominant compound in all cephalopod species (broadtail squid: 88.1%, horned octopus 94.1%, spider octopus: 97.5%). PCB isomer profiles were similar among species being hexachlorinated isomers the most abundant, followed by penta- and heptachlorobiphenyls, while tri- and tetrachlorobiphenyls made up a small percentage of the total PCB residues. Regarding coplanar congeners, non-ortho PCBs were below the detection limit in all samples and the 2,3,7,8-TCDD toxic equivalent (TEQ) concentrations were very low. The influence of biological and ecological factors (size/weight and location) on the bioaccumulation of organochlorine compounds has been discussed.     

Background levels of non-ortho-substituted (coplanar) polychlorinated biphenyls in human serum of Missouri residents

This study characterizes the levels of polychlorinated biphenyls (PCB) congeners PCB 77, PCB 81, PCB 126, and PCB 169, in a group of 150 men and women with no documented exposure to PCBs. Its purpose is to provide current referent levels of coplanar PCBs in Missouri residents and to compare those levels to levels reported in the literature from the United States and other countries. Although this study used an extensive questionnaire assessing potential sources of exposure, no positive relations were found between these exposure sources and participants' PCB levels. The PCB levels for the four congeners measured were lower than any reported in the literature. PCBs 126 and 169 are only two of the dioxin-like congeners; however, their contribution makes up 11% of the total TEQ. Age was significantly related to PCB 126 and PCB 169. For every one-year increase in age, both PCB congeners increased by approximately 0.4 parts per trillion (ppt). There was no gender difference for PCB 126; however, PCB 169 levels were 3 ppt higher in males than females.     

Bioaccumulation of PCBs in the cuttlefish Sepia officinalis from seawater, sediment and food pathways

The cuttlefish Sepia officinalis was selected as a model cephalopod to study PCB bioaccumulation via seawater, sediments and food. Newly hatched, juvenile cuttlefish were exposed for 17 days to environmentally realistic concentrations of (14)C-labeled 2,2',4,4',5,5'-hexachlorobiphenyl (PCB#153) (18 ng PCB l(-1) seawater; 30 ng PCB g(-1) dry wt sediments; Artemia salina exposed to 18 ng PCB l(-1) seawater). Accumulation of PCB#153 was followed in three body compartments: digestive gland, cuttlebone and the combined remaining tissues. Results showed that (1) uptake kinetics were source- and body compartment-dependent, (2) for each body compartment, the accumulation was far greater when S. officinalis was exposed via seawater, (3) the cuttlebone accumulated little of the contaminant regardless of the source, and (4) the PCB congener showed a similar distribution pattern among the different body compartments following exposure to contaminated seawater, sediment or food with the lowest concentrations in the cuttlebone and the highest in the remaining tissues. The use of radiotracer techniques allowed delineating PCB kinetics in small whole organisms as well as in their separate tissues. The results underscore the enhanced ability of cephalopods to concentrate organic pollutants such as PCBs, and raise the question of potential risk to their predators in contaminated areas.     

Study of transportation and distribution of PCBs using an ecologically simulated growth chamber

This study was designed to investigate the transportation, distribution, and bioaccumulation of PCBs in various environmental media and compartments using an ecologically simulated growth chamber. Spatial and temporal trends of PCBs in the growth chamber were discussed. The release of PCB congeners in soil was affected by the amount of rainfall with the transporting direction moving away from PCBs contaminated point. Two pathways of PCBs accumulation in plants were the uptake of roots and the deposition on shoots/leaves. There were 29 PCB congeners been found in the lalang grass. Higher concentrations of lower chlorinated PCBs were identified than higher chlorinated PCBs because of relatively higher vapor pressure for lower chlorinated congeners. After 10months of monitoring, PCBs were detected in water samples which were contributed by the release of PCBs from leached soil. Analysis of sediment showed that the percentages of low- and mid-chlorinated biphenyls were decreased 1% and 13%, respectively compared to the increase (14%) of high-chlorinated biphenyls. The increase of high-chlorinated PCBs was possibly caused by their low hydrophilicity which had resulted higher adsorption rate in sediment. All of five species of fish had been found significant amount of PCBs accumulation ( summation operatorPCBs: 21.7-102.1 microg/g-lipid). The concentrations of PCBs in fish were varied significantly among species. The range of bioaccumulation factors (BAFs) among different species of fish could be as much as 5 times depending on the consumption habits of fish. The mass balance of PCBs distribution in the growth chamber was also discussed.     

Elimination of 10 polybrominated diphenyl ether (PBDE) congeners and selected polychlorinated biphenyls (PCBs) from the freshwater mussel, Elliptio complanata

Mussel biomonitors are widely used as screening tools for polybrominated diphenyl ethers (PBDEs) in marine and aquatic environments. This study determined elimination rate coefficients (k(tot)) for eight PBDE and five PCB congeners in the freshwater mussel, Elliptio complanata, over a 120d depuration period. Elimination of BDE 15, 28, 47, 75 and 100 was similar to PCBs of equivalent hydrophobicity and negatively related to chemical K(OW). Rapid elimination of BDE 190 and an inferred rapid elimination of BDE 183 indicate mussels are capable of biotransformation of certain highly brominated PBDEs. Time to 90% steady state ranged from 48 to 66d for di- and tribromoDE congeners and from 91 to >250d for tetra- to hexabromoDE congeners. Given the long time periods required for steady state, mussel accumulated PBDE residues should be interpreted in the context of calibrated bioaccumulation models.     

Organochlorine residues (PCBs and DDTs) in two Torpedinid species liver from the Southeastern Mediterranean Sea

Purpose  

Polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and PCB congeners accumulation profile were measured in the liver of two torpedinid species (Torpedo nobiliana and Torpedo marmorata) from the Mediterranean Sea (Adriatic Sea) in order to investigate the relative toxicological impact of these highly toxic PCBs in the organisms in question.     

PCB problems in the future: foresight from current knowledge

The present paper overviews the forthcoming PCB problems from current knowledge of their use, environmental contamination and toxicology. From a global point of view, PCB levels in the environmental media and biota are unlikely to decline in the near future due to the greater quantities of PCBs still in use than the quantity that has already escaped into the open environment. Considering all the information on the occurrence, distribution and behaviour of PCBs in the ecosystems, the marine mammals are probably the most vulnerable and possible target organisms in forthcoming long-term PCB toxicity. The recent isomer-specific analyses suggest that the intrinsic toxicity of PCBs principally resulted from the coplanar PCB congeners which may impose a greater toxic threat than chlorinated dioxins and furans to humans and wildlife. The measures necessary to reduce further discharge of PCBs into the environment should be set in motion immediately, otherwise there may be a subsequent deleterious biological impact.     

Occurrence and accumulation of organochlorine contaminants in swordfish from Mediterranean Sea: a case study

Polychlorinated biphenyls including coplanar congeners and DDT compounds were measured in the liver of a teleost species: namely, Xiphias gladius. PCB concentrations (median: 1121 ng/g lipid wt) were comparable with DDT levels (median: 1236 ng/g lipid wt). PCBs revealed a profile dominated by hexa-, penta- and heptachlorinated congeners. Among DDTs, the compound in the greatest concentration was p,p'-DDE, representing 70% of the total DDT burden, followed by o,p'-DDT>p,p'-DDT>p,p'-DDD=o,p'-DDD. Mean total 2,3,7,8-TCDD equivalent of five coplanar PCBs was 8.83 pg/g lipid weight. The isomers with higher TEQs values were non-ortho congeners than mono-ortho ones.     

Accumulation properties of polychlorinated biphenyl congeners in Yusho patients and prediction of their cytochrome P450-dependent metabolism by in silico analysis

In what has become known as the Yusho incident, thousands of people in western Japan were poisoned by the accidental ingestion of rice bran oil contaminated with polychlorinated biphenyls (PCBs) and various dioxins and dioxin-like compounds. In this study, we investigated the accumulation patterns of 69 PCB congeners in the blood of Yusho patients in comparison with those of non-exposed controls. The blood samples were collected at medical check-ups in 2004 and 2005. To compare the patterns of PCB congeners, we calculated the concentration ratio of each congener relative to the 2,2′,4,4′,5,5′-hexaCB (CB153) concentration. The concentration ratios of tetra- and penta-chlorinated congeners in the blood of Yusho patients were significantly lower than those of controls. To examine the cytochrome P450 (CYP)-dependent metabolic potential of the 2,3′,4,4′5-pentaCB (CB118), CB153, and 2,3,3′,4,4′5-hexaCB (CB156) congeners, we conducted PCB-CYP (CYP1A1, CYP1A2, CYP2A6, and CYP2B6) docking simulation by in silico analysis. The docking models showed that human CYP1A1, CYP2A6, and CYP2B6 isozymes have the potential to metabolize CB118 and CB153. On the other hand, it was inferred that CB156 is difficult to be metabolized by these four CYP isozymes. These results indicate that CYP1 and CYP2 isozymes may be involved in the characteristic accumulation patterns of PCB congeners in the blood of Yusho patients.