PCB in soils and estimated soil-air exchange fluxes of selected PCB congeners in the south of Sweden

PCB concentrations were studied in different soils to determine the spatial variation over a region of approximately 11 000 km(2). PCB congener pattern was used to illustrate the spatial differences, as shown by principal component analysis (PCA). The relationship to different soil parameters was studied. PCB concentrations in soil showed a large variation between sampling-areas with median concentrations ranging between 2.3 and 332 ng g(-1) (dw). Highest concentrations were found at two sites with sandy soils, one with extremely high organic carbon content. Both sites were located on the west coast of southern Sweden. Soils with similar soil textures (i.e. sandy silt moraine) did not show any significant differences in PCB concentrations. PCB congener composition was shown to differ between sites, with congener patterns almost site-specific. PCB in air and precipitation was measured and the transfer of chemicals between the soil and air compartments was estimated. Soil-air fugacity quotient calculations showed that the PCBs in the soil consistently had a higher fugacity than the PCBs in the air, with a median quotient value of 2.7. The gaseous fluxes between soil and air were estimated using standard modelling equations and a net soil-air flux estimated by subtracting bulk deposition from gaseous soil-air fluxes. It was shown that inclusion of vertical sorbed phase transport of PCBs in the soil had a large effect on the direction of the net soil-air exchange fluxes.     

Combined effect of microwave and activated carbon on the remediation of polychlorinated biphenyl-contaminated soil

The application of microwave and activated carbon for the treatment of polychlorinated biphenyl (PCB) contaminated soil was explored in this study with a model compound of 2,4,5-trichlorobiphenyl (PCB29). PCB-contaminated soil was treated in a quartz reactor by microwave irradiation at 2450MHz with the addition of granular activated carbon (GAC). In this procedure, GAC acted as microwave absorbent for reaching high temperature and reductant for dechlorination. A sheltered type-K thermocouple was applied to record the temperature rising courses. It was shown that the addition of GAC could effectively promote the temperature rising courses. The determination of PCB residues in soil by gas chromatography (GC) revealed that rates of PCB removal were highly dependent on microwave power, soil moisture content, and the amount of GAC added. GC with mass spectrum (MS) detector and ion chromatography were employed for the analysis of degradation intermediates and chlorine ions, respectively. It was suggested that microwave irradiation with the assistance of activated carbon might be a potential technology for the remediation of PCB-contaminated soil.     

PCB congener distributions in muscle,liver and gonad of Fundulus heteroclitus from the lower Hudson River Estuary and Newark Bay

Gradients in sediment polychlorinated biphenyl (PCB) concentrations and PCB congener profiles exist along the Hudson River (NY, USA). We evaluated site and tissue differences in PCB concentration and congener profiles in resident mummichog (Fundulus heteroclitus) collected from PCB-contaminated sites in the lower Hudson River and the New York/New Jersey Harbor Estuary. Fish were collected from three PCB-contaminated sites Piermont Marsh (P), Iona Marsh (I), and Newark Bay (NB), and from two reference sites (Flax Pond, NY; Succotash Salt Marsh, RI). Congener profiles were statistically analyzed using principal component analysis (PCA) and general linear model (GLM) profile analysis. Contaminated fish had PCB tissue concentrations approximately 10-fold higher than those of reference fish. There were no site differences in PCB body burden (all tissues combined) among the contaminated site fish. However, relative PCB concentration did differ between organs: NB fish (gonad=liver>muscle); I and P fish (gonad>liver>muscle). In contrast to PCB content, PCB congener profiles did show site differences; NB mummichog being depleted in the less chlorinated congeners relative to I and P fish, likely reflecting different PCB sources to these populations. Within a site, however, PCB congener patterns were similar between liver, gonad and muscle. In conclusion, PCA and GLM analyses gave complementary results, both analyses indicating differences in site, but not tissue, distributions of PCB congeners. This study also demonstrates that unlike congener profiles, total PCB content does differ dramatically amongst tissues and further, that PCB differences among tissues (gonad vs. liver vs. muscle) can vary with site.     

Characterization and risk assessment of polychlorinated biphenyls in soils and vegetations near an electronic waste recycling site, South China

This study aimed at identifying the levels of PCBs generated from e-waste recycling, and their potential impacts on the soils and vegetations as well. The ΣPCBs concentrations in soil and plant samples ranged from 7.4 to 4000 ng g(-1) and from 6.7 to 1500 ng g(-1), respectively. For the plant samples, Chrysanthemum coronarium L. from vegetable field and the wild plant Bidens pilosa L. from the burning site showed relatively higher PCB concentrations than other species. For the soil samples, the e-waste burning site had relatively higher PCB concentrations than the adjacent areas, and vegetable soils had higher PCB concentrations than paddy soils. The PCB concentrations showed a clear decreasing trend with the increasing distance from the e-waste recycling site. PCB 28, 99, 101, 138, 153, and 180 were the predominant congeners. Principal component analysis results showed a potential fractionation of PCB compositions from the burning site to the surroundings. The PCB congener pattern at the burning site was similar to Arochlor 1260, pointing to an input of non-domestic e-waste. Similar PCB congeners were found in soils and related vegetables, indicating they derived from the same source. The consumption of vegetables grown in soils near e-waste recycling sites should be strictly avoided due to the high PCBs in the plant tissues.     

PCB and DDT contamination in cultivated and wild sea bass from Ria de Aveiro, Portugal

Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) and metabolites were quantified in muscle and liver of sea bass (Dicentrarchus labrax) collected in Ria de Aveiro and in two fish farms. Sea bass from natural environment showed lower levels than fish from farming, which may be partly attributed to the higher lipid content of cultivated fish. PCB congener distribution in tissues of sea bass from the two farms resembled that of diet pellets suggesting that commercial diet is a major source of PCBs. However, fish in the two sites were fed with diet of similar PCB and DDT contamination but showed distinct levels in its tissues not explained by lipid content.     

Influence of activated carbon amendment on the accumulation and elimination of PCBs in the earthworm Eisenia fetida

In this study we investigated the use of activated carbon (AC) as a soil amendment for reducing bioavailability of polychlorinated biphenyls (PCBs) to the earthworm Eisenia fetida. Artificial soil was contaminated with PCBs and used in bioaccumulation experiments fresh or after aging for 19 months. PCB bioaccumulation in earthworms was reduced by 68% when AC was placed as a layer without mixing and by 94% when AC was manually mixed into the soil. Aging of the same AC mixed soil for 19 months resulted in an overall reduction of 99% in PCB biouptake. AC-treated aged soil also showed two orders of magnitude lower equilibrium aqueous concentrations of PCBs compared to untreated aged soils. The findings from this study indicate that application of engineered sorbents like AC to PCB impacted soils may greatly reduce PCB uptake at the base of the terrestrial food chain.     

Organic carbon effects on aerobic polychlorinated biphenyl removal and bacterial community composition in soils and sediments

Certain organic compounds, including biphenyl and salicylic acid, stimulate polychlorinated biphenyl (PCB) degradation by microorganisms in some environments. However, the usefulness of these amendments for improving PCB removal by microorganisms from diverse habitats has not been extensively explored. This study evaluated the effects of biphenyl, salicylic acid, and glucose on changes in aerobic PCB removal and bacterial communities from an agricultural soil, a wetland peat soil, a river sediment, and a mixture of these samples. PCB removal patterns were significantly different between soils and sediments amended with carbon compounds: (i) terrestrial soil microorganisms removed more PCBs than river sediment microorganisms, particularly with regard to PCBs with >4 chlorine substituents, (ii) glucose-supplemented, agricultural soil microorganisms removed more hexachlorobiphenyl than unsupplemented samples, (iii) biphenyl-supplemented, river sediment microorganisms removed more di- and tri-chlorobiphenyls than unamended samples. Carbon amendments also caused unique shifts in soil and sediment bacterial communities, as determined by specific changes in bacterial 16S rRNA denaturing gradient gel electrophoresis banding patterns. These results indicate that organic carbon amendments had site-specific effects on bacterial populations and PCB removal. Further work is needed to more accurately characterize PCB degrading communities and functional gene expression in diverse types of environments to better understand how they respond to bioremediation treatments.     

Seasonal variation of the distribution of PCBs in sediments and biota in a PCB-contaminated estuary

To elucidate the effects of seasonal variation of precipitation on the distribution of polychlorinated biphenyls (PCBs) in estuarine sediments and benthic feeders, PCB concentrations of river surface sediments and mullet fish (Liza macrolepis) were investigated in the estuary of Er-Jen River near former PCB contamination sites before and after each wet season from 2002 to 2004. Analyses of grain size distribution and organic matter revealed that the pre-existing surface sediments were covered by and mixed with the soil particulates brought by surface runoff after each wet season. Obvious increment of PCB content and significantly elevated fraction (p < 0.005) of light PCBs of the river mouth’s sediments after each wet season indicated that the invading particles were rich in unweathered PCBs. PCBs previously buried in the surface soil of heavily contaminated sites were flushed into this estuary through surface runoff. The precipitation altered the PCB patterns in sediment organic matter, the dietary source of mullet, and consequently changed that of mullets accordingly, which all possessed significant greater fraction of light PCBs. In this study, it was demonstrated that seasonal summer precipitation affected the distribution of PCBs on surface sediments and the mullets of this estuary. PCB residuals retained in this region still pose potential threats to biota resided here.     

Dynamics of PCB removal and detoxification in historically contaminated soils amended with activated carbon

Activated carbon (AC) can help overcome toxicity of pollutants to microbes and facilitate soil bioremediation. We used this approach to treat a Histosol and an Alluvial soil historically contaminated with PCB (4190 and 1585 mg kg⁻¹, respectively; primarily tri-, tetra- and pentachlorinated congeners). Results confirmed PCB persistence; reductions in PCB extractable from control and AC-amended soils were mostly due to a decrease in tri- and to some extent tetrachlorinated congeners as well as formation of a bound fraction. Mechanisms of PCB binding by soil and AC were different. In addition to microbial degradation of less chlorinated congeners, we postulate AC catalyzed dechlorination of higher chlorinated congeners. A large decrease in bioavailable PCB in AC-amended soils was demonstrated by greater clover germination and biomass. Phytotoxicity was low in treated soils but remained high in untreated soils for the duration of a 39-month experiment. These observations indicate the utility of AC for remediation of soils historically contaminated with PCB.     

Assessing the potential for rhizoremediation of PCB contaminated soils in northern regions using native tree species

Rhizosphere bioremediation of polychlorinated biphenyls (PCBs) offers a potentially inexpensive approach to remediating contaminated soils that is particularly attractive in remote regions including the Arctic. We assessed the abilities of two tree species native to Alaska, Salix alaxensis (felt-leaf willow) and Picea glauca (white spruce), to promote microbial biodegradation of PCBs via the release of phytochemicals upon fine root death. Crushed fine roots, biphenyl (PCB analogue) or salicylate (willow secondary compound) were added to microcosms containing soil spiked with PCBs and resultant PCB disappearance, soil toxicity and microbial community changes were examined. After 180 d, soil treated with willow root crushates showed a significantly greater PCB loss than untreated soils for some PCB congeners, including the toxic congeners, PCB 77, 105 and 169, and showed a similar PCB loss pattern (in both extent of degradation and congeners degraded) to biphenyl-treated microcosms. Neither P. glauca (white spruce) roots nor salicylate enhanced PCB loss, indicating that biostimulation is plant species specific and was not mediated by salicylate. Soil toxicity assessed using the Microtox bioassay indicated that the willow treatment resulted in a less toxic soil environment. Molecular microbial community analyses indicated that biphenyl and salicylate promoted shifts in microbial community structure and composition that differed distinctly from each other and from the crushed root treatments. The biphenyl utilizing bacterium, Cupriavidus spp. was isolated from the soil. The findings suggest that S. alaxensis may be an effective plant for rhizoremediation by altering microbial community structure, enhancing the loss of some PCB congeners and reducing the toxicity of the soil environment.     

The influence of soil contamination on the concentrations of PCBs in milk in Siberia

Although atmospheric deposition is generally the dominant pathway of PCBs into agricultural food chains, soil ingestion by livestock can be important in some cases. The relationship between PCB levels in cow's milk and in pasture soil was studied in the Irkutsk region in Siberia where an historical atmospheric source(s) of PCBs has led to widespread contamination of soil. Milk samples were collected in spring and again in autumn from 18 different farms and analyzed for PCBs. Pasture soil samples were also collected and analyzed. The PCB concentrations in both milk and soil ranged over more than an order of magnitude between the farms. A good correlation was obtained between PCB levels in autumn milk and in soil. This together with a range of other evidence suggested that ingestion of pasture soil was the dominant source of the PCB contamination in the milk. The average soil ingestion rate was estimated to be 1700 g/d, which is at the upper end of values reported in the literature. This may be due to the arid summer climate or the animal husbandry practices in Siberia.     

Remediation of PCB contaminated soils using iron nano-particles

In this study, iron nano-particles were used to remediate PCB contaminated soil and an attempt was made to maximize PCB destruction in each treatment step. The results show that nano-particles do aid in the dechlorination process and high PCB destruction efficiencies can be achieved. The destruction efficiency during the preliminary treatment (mixing of soil and iron nano-particles in water) can be increased by increasing the water temperature. The maximum thermal destruction (pyrolysis/combustion of soil after preliminary treatment) of soil-bound PCBs occurs at 300 degrees C in air. A minimum total PCB destruction efficiency of 95% can be achieved by this process. The effect of changing treatment parameters such as type of mixing, time of mixing and mixing conditions and application of other catalysts like iron oxide and V(2)O(5)/TiO(2) was also investigated. It was found that at 300 degrees C in air, iron oxide and V(2)O(5)/TiO(2) are also good catalysts for remediating PCB contaminated soils.     

Enhanced metal and metalloid concentrations in the gut system comparing to remaining tissues of Gammarus pulex L

Invertebrate shredders such as Gammarus pulex are key species in contaminated stream ecosystems. Although a number of previous studies examining differences in metal accumulation between the gut system and remaining tissues of invertebrates exist, few focus on wide range of metals and metalloids that are relevant to contaminated systems. This study compared accumulation of the commonest (at study site) 15 metals and metalloids between the gut system including feces and remaining tissues of G. pulex. All metals and metalloids measured were significantly higher (p<0.001, except Cu p<0.005) in the gut system including feces than remaining tissues of G. pulex. Metals and metalloids in body tissues without the gut system including feces were significantly lower (Al, Cr, Fe and Mn (p<0.005), Sr and U (p<0.01), Co (p<0.05)) in content for a number of elements when compared to washed, whole G. pulex specimens. As well, all elements measured were significantly higher (all elements (p<0.005) except Cu and Co (p<0.05)) in gut system including feces than washed, whole G. pulex specimens. These results indicate that in G. pulex the uptake of all 15 metals and metalloids examined across the gut epithelium is minimalized or that sequestration of these elements in gut epithelial cells may occur.     

Polychlorinated biphenyls in digested UK sewage sludges

Twelve sewage sludges from rural, urban and industrial waste water treatment works in north west England were analysed for polychlorinated biphenyls by capillary GC-ECD. The total polychlorinated biphenyl content ranged between 106 to 712 μg/kg, with a mean of 292 μg/kg. Di- and penta-chlorinated congeners made the greatest contribution to the ΣPCB concentrations at most sites. The 6 IUPAC congeners were found in the following order of abundance, 101>180>153>138>52>28. Industrial inputs would appear to influence levels of ΣPCB in the sludge.

If these sludges were ploughed into arable land at typical rates only a slight elevation in soil ΣPCB levels would result. Alternatively, if the same quantity of sludge were applied to the surface of pasture grassland, significant elevations in the potential transfer of PCBs to grazing livestock may result.     

Removal of PCBs in contaminated soils by means of chemical reduction and advanced oxidation processes

Although the chemical reduction and advanced oxidation processes have been widely used individually, very few studies have assessed the combined reduction/oxidation approach for soil remediation. In the present study, experiments were performed in spiked sand and historically contaminated soil by using four synthetic nanoparticles (Fe⁰, Fe/Ni, Fe₃O₄, Fe_3???x Ni _x O₄). These nanoparticles were tested firstly for reductive transformation of polychlorinated biphenyls (PCBs) and then employed as catalysts to promote chemical oxidation reactions (H₂O₂ or persulfate). Obtained results indicated that bimetallic nanoparticles Fe/Ni showed the highest efficiency in reduction of PCB28 and PCB118 in spiked sand (97 and 79 %, respectively), whereas magnetite (Fe₃O₄) exhibited a high catalytic stability during the combined reduction/oxidation approach. In chemical oxidation, persulfate showed higher PCB degradation extent than hydrogen peroxide. As expected, the degradation efficiency was found to be limited in historically contaminated soil, where only Fe⁰ and Fe/Ni particles exhibited reductive capability towards PCBs (13 and 18 %). In oxidation step, the highest degradation extents were obtained in presence of Fe⁰ and Fe/Ni (18–19 %). The increase in particle and oxidant doses improved the efficiency of treatment, but overall degradation extents did not exceed 30 %, suggesting that only a small part of PCBs in soil was available for reaction with catalyst and/or oxidant. The use of organic solvent or cyclodextrin to improve the PCB availability in soil did not enhance degradation efficiency, underscoring the strong impact of soil matrix. Moreover, a better PCB degradation was observed in sand spiked with extractable organic matter separated from contaminated soil. In contrast to fractions with higher particle size (250–500 and <500 μm), no PCB degradation was observed in the finest fraction (≤250 μm) having higher organic matter content. These findings may have important practical implications to promote successively reduction and oxidation reactions in soils and understand the impact of soil properties on remediation performance.     

The assimilation of dioxins and PCBs in conventionally reared farm animals: occurrence and biotransfer factors

The assimilation of PCDD/Fs and PCBs in chickens, pigs and sheep was investigated in studies using conventional animal husbandry practices. Closely matched samples of muscle (meat), liver, kidneys, eggs, milk, feed, soil and grass were collected of which 105 were analysed. The data obtained were consistent with the PCB and PCDD/F TEQ concentrations to be expected in rural background locations. A slight decline in TEQ values in meat with increasing age was evident in pigs, sheep and broiler chickens. Higher TEQ values in meat from outdoor pigs compared to those raised indoors, and an increase in TEQs in eggs as a result of free-range conditions might be attributable to additional contaminant intakes from soil. TEQ values in samples of sheep meat were slightly higher than those for pigs and chickens and market ready lowland sheep showed higher meat TEQs than the highland species. PCDD/F TEQs were considerably higher in the liver than meat. Contaminant transfer from dietary sources was investigated using biotransfer factors (BTFs) which tended to be higher in chickens than in sheep or pigs. BTFs for all animals declined in magnitude with age, but on average, BTFs for pigs and chickens showed a sharper initial decline than for sheep. The relative magnitude of the BTFs usually followed the order: (highest first) PCB 153, PCB 169, PCB 126, 1,2,3,7,8-PeCDD/2,3,4,7,8-PeCDF and 2,3,7,8-TCDD. This may suggest that higher chlorinated congeners accumulate more readily in meat tissues. Congener-specific BTF variations were found to be associated with variables such as dietary composition during rearing, differences between feed and animal species.     

Physiological and molecular responses of the earthworm <Emphasis Type="Italic">Eisenia fetida</Emphasis> to polychlorinated biphenyl contamination in soil

Polychlorinated biphenyls (PCBs) are a class of man-made organic compounds ubiquitously present in the biosphere. In this study, we evaluated the toxic effects of different concentrations of PCBs in two natural soils (i.e. red soil and fluvo-aquic soil) on the earthworm Eisenia fetida. The parameters investigated included anti-oxidative response, genotoxic potential, weight variation and biochemical responses of the earthworm exposed to two different types of soils spiked with PCBs after 7 or 14 days of exposure. Earthworms had significantly lower weights in both soils after PCB exposure. PCBs significantly increased catalase (CAT), superoxide dismutase (SOD), and guaiacol peroxidase (POD) activity in earthworms exposed to either soil type for 7 or 14 days and decreased the malondialdehyde (MDA) content in earthworms exposed to red soil for 14 days. Of the enzymes examined, SOD activity was the most sensitive to PCB stress. In addition, PCB exposure triggered dose-dependent coelomocyte DNA damage, even at the lowest concentration tested. This response was relatively stable between different soils. Three-way analysis of variance (ANOVA) showed that the weight variation, anti-oxidant enzyme activities, and MDA contents were significantly correlated with exposure concentration or exposure duration (P < 0.01). Furthermore, weight variation, CAT activity, and SOD activity were significantly affected by soil type (P < 0.01). Therefore, the soil type and exposure time influence the toxic effects of PCBs, and these factors should be considered when selecting responsive biomarkers.     

Polychlorinated biphenyls contamination in urban soil of Shanghai: level, compositional profiles and source identification

Surface soil samples taken from 55 sampling sites at the urban areas of Shanghai were collected and analyzed for the occurrence of 144 polychlorinated biphenyls (PCBs) by GC-μECD. The results showed that totally 74 PCB congeners were identified and the mean concentration of total PCBs was 3057 ng kg⁻¹ with a range of 232 to 11325 ng kg⁻¹. Compared with the related reports, the level of PCBs contamination in this study was approximately equal to the global background value in soils, but higher than Chinese background for rural and urban soils. According to the compositional profiles of PCBs homologues, a higher proportion of low chlorinated (from tri-CBs to hexa-CBs) was observed. The results indicated that PCB15 + 13, PCB18, PCB28, PCB104 + 47 and PCB153 were the most dominant congeners among the identified PCBs. Through homologues analysis, cluster analysis and principal component analysis (PCA), it was found that PCBs were stretched from mixed local sources, and appeared to be mostly originated by Aroclor 1260- and 1254-like mixtures as well as some samples influenced by Aroclor 1232 and 1242. The correlation analysis showed the relatively good correlation among the PCB homologues and soil total organic carbon (TOC), suggesting important influence of soil TOC on PCBs contamination in soil matrix in Shanghai region. The toxic equivalency (TEQ) concentrations of these six dioxin-like PCBs detected in urban soil samples range from 2.71 to 24.9 pg kg⁻¹-PCDDeq with a mean 8.18 pg kg⁻¹-PCDDeq.     

Correlation of PCDD/F and PCB concentrations in soil samples from the Swiss soil monitoring network (NABO) to specific parameters of the observation sites

Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) and polychlorinated biphenyls (PCB) were determined in 23 soil samples collected at reference sites of the Swiss national soil monitoring network (NABO). Total PCDD/F and PCB concentrations are well correlated and proportional (R2=0.720). The total PCDD/F levels were between 72 and 703 ng/kg corresponding to 1.1-11 ng I-TEQ/kg, total PCB concentrations (sum of seven congeners IUPAC no. 28, 52, 101, 118, 138, 153, and 180) were from 1.1 to 12 microg/kg. In all samples, the PCDD/F and PCB concentrations were in the range of background levels for these contaminants in Central Europe. Ninteen samples revealed PCDD/F levels below the guide value of 5 ng I-TEQ/kg set by the Swiss ordinance relating to impacts on the soil (OIS); concentrations for the remaining four samples were below the trigger value (20 ng I-TEQ/kg). All PCB concentrations were below the guide value of 100 microg/kg. The elevated PCDD/F and PCB levels in some of the samples originating from forested sites could be attributed to the scavenging effect of forest canopies for semivolatile organic compounds. This interpretation could be substantiated by the observed distortion of the congener and homolog patterns of PCDD/F and PCB which is characteristic for forested sites.     

Digestibility, retention and incorporation of low-level dietary PCB contents in laying hens

Polychlorinated biphenyls (PCBs) are persistent and hazardous environmental contaminants, which tend to bioaccumulate in the food chain. In the present report the long-term effect of low-level dietary PCB concentrations was studied on performance, egg quality, apparent PCB digestibility, apparent PCB retention and PCB accumulation in laying hens that were fed experimental diets for 41 weeks. The tested dietary concentrations of supplemented PCBs, based on the sum of seven reference congeners, were 0, 1.5 and 6 ng/g. PCB ingestion did not significantly affect performance or egg quality parameters. The PCB concentration in egg yolk reached a nearly constant level after approximately 40 and 70 days of consumption of the diets containing 1.5 and 6 ng PCBs/g, respectively. Apparent faecal PCB digestibility and apparent retention were not influenced by dietary levels of added fat varying between 1.5% and 4.5%, but were significantly higher in hens fed diets containing added PCBs. Moreover, apparent PCB digestibility and retention increased significantly with age. Among the seven individual PCB congeners, no systematically significant differences with regard to apparent faecal digestibility were observed throughout the experiment. Accumulation of PCBs in the fat fraction of egg yolk, abdominal adipose tissue and thigh and breast muscle greatly depended upon PCB intake, but never exceeded the maximally allowed concentration of 200 ng/g. As PCBs 52 and 101 were hardly found in egg yolks and hen tissues, it was concluded that both congeners were greatly metabolised. Comparison of relative contents of individual PCB congeners revealed that PCBs 118, 138 and 153 were preferentially incorporated in yolk and body tissues.