Handling of dioxin measurement data in the presence of non-detectable values: overview of available methods and their application in the Seveso chloracne study

Exposure measurements of concentrations that are non-detectable or near the detection limit (DL) are common in environmental research. Proper statistical treatment of non-detects is critical to avoid bias and unnecessary loss of information. In the present work, we present an overview of possible statistical strategies for handling non-detectable values, including deletion, simple substitution, distributional methods, and distribution-based imputation. Simple substitution methods (e.g., substituting 0, DL/2, DL/ radical2, or DL for the non-detects) are the most commonly applied, even though the EPA Guidance for Data Quality Assessment discouraged their use when the percentage of non-detects is >15%. Distribution-based multiple imputation methods, also known as robust or "fill-in" procedures, may produce dependable results even when 50-70% of the observations are non-detects and can be performed using commonly available statistical software. Any statistical analysis can be conducted on the imputed datasets. Results properly reflect the presence of non-detectable values and produce valid statistical inference. We describe the use of distribution-based multiple imputation in a recent investigation conducted on subjects from the Seveso population exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in which 55.6% of plasma TCDD measurements were non-detects. We suggest that distribution-based multiple imputation be the preferred method to analyze environmental data when substantial proportions of observations are non-detects.     

The developmental neurotoxicity of legacy vs. contemporary polychlorinated biphenyls (PCBs): similarities and differences

Although banned from production for decades, PCBs remain a significant risk to human health. A primary target of concern is the developing brain. Epidemiological studies link PCB exposures in utero or during infancy to increased risk of neuropsychiatric deficits in children. Nonclinical studies of legacy congeners found in PCB mixtures synthesized prior to the ban on PCB production suggest that non-dioxin-like (NDL) congeners are predominantly responsible for the developmental neurotoxicity associated with PCB exposures. Mechanistic studies suggest that NDL PCBs alter neurodevelopment via ryanodine receptor-dependent effects on dendritic arborization. Lightly chlorinated congeners, which were not present in the industrial mixtures synthesized prior to the ban on PCB production, have emerged as contemporary environmental contaminants, but there is a paucity of data regarding their potential developmental neurotoxicity. PCB 11, a prevalent contemporary congener, is found in the serum of children and their mothers, as well as in the serum of pregnant women at increased risk for having a child diagnosed with a neurodevelopmental disorder (NDD). Recent data demonstrates that PCB 11 modulates neuronal morphogenesis via mechanisms that are convergent with and divergent from those implicated in the developmental neurotoxicity of legacy NDL PCBs. This review summarizes these data and discusses their relevance to adverse neurodevelopmental outcomes in humans.

     

Occurrence and distribution of PCB metabolites in blood and their potential health effects in humans: a review

In recent years, attention has been directed to chemicals with possible endocrine-disrupting properties. Polychlorinated biphenyls (PCBs) and their metabolites belong to one group of environmental contaminants that have been shown to interact with the endocrine system in mammals, including humans. Although recent developments have been made in terms of determination of PCB metabolites in blood samples, still limited number of studies have been able to elucidate their profiles and toxicological and health effects in humans. This review aims to evaluate and compare the levels of hydroxylated PCBs (OH-PCBs) and methyl sulfone PCBs (MeSO₂-PCBs) in blood and their relationship to parent compounds and also address the potential risks and adverse health effects in humans. Levels of OH-PCBs varied between 0.0002 and 1.6 ng g^?1 w/w in human serum/plasma from the selected literature, correlating well with ∑PCBs. In contrast, ∑OH-PCB/∑PCB ratio in animals did not show a significant correlation, which might suggest that the bioaccumulation plays an even more important role in the concentration of OH-PCBs compared to PCB metabolism. Highest levels of MeSO₂-PCBs were reported in marine mammals with high selectivity retention in the liver. Health effects of PCB metabolites included carcinogenicity, reproductive impairment, and developmental neurotoxicity, being more efficiently transferred to the brain and across the placenta from mother to fetus in comparison to the parent PCBs. Based on the lack of knowledge on the occurrence and distribution of lower chlorinated OH-PCBs in humans, further studies to identify and assess the risks associated to human exposure are essential.     

Statistical Methods and Pitfalls in Environmental Data Analysis

This paper reviews four commonly used statistical methods for environmental data analysis and discusses potential pitfalls associated with application of these methods through real case study data. The four statistical methods are percentile and confidence interval, correlation coefficient, regression analysis, and analysis of variance (ANOVA). The potential pitfall for estimation of percentile and confidence interval includes the automatic assumption of a normal distribution to environmental data, which so often show a log-normal distribution. The potential pitfall for correlation coefficient includes the use of a wide range of data points in which the maximum in value may trivialize other smaller data points and consequently skew the correlation coefficient. The potential pitfall for regression analysis includes the propagation of uncertainties of input variables to the regression model prediction, which may be even more uncertain. The potential pitfall for ANOVA includes the acceptance of a hypothesis as a weak argument to imply a strong conclusion. As demonstrated in this paper, we may draw very different conclusions based on statistical analysis if the pitfalls are not identified. Reminder and enlightenment obtained from the pitfalls are given at the end of this article.     

Statistical Methods and Pitfalls in Environmental Data Analysis

This paper reviews four commonly used statistical methods for environmental data analysis and discusses potential pitfalls associated with application of these methods through real case study data. The four statistical methods are percentile and confidence interval, correlation coefficient, regression analysis, and analysis of variance (ANOVA). The potential pitfall for estimation of percentile and confidence interval includes the automatic assumption of a normal distribution to environmental data, which so often show a log-normal distribution. The potential pitfall for correlation coefficient includes the use of a wide range of data points in which the maximum in value may trivialize other smaller data points and consequently skew the correlation coefficient. The potential pitfall for regression analysis includes the propagation of uncertainties of input variables to the regression model prediction, which may be even more uncertain. The potential pitfall for ANOVA includes the acceptance of a hypothesis as a weak argument to imply a strong conclusion. As demonstrated in this paper, we may draw very different conclusions based on statistical analysis if the pitfalls are not identified. Reminder and enlightenment obtained from the pitfalls are given at the end of this article.     

A Test Reference Year (TRY) approach to gas dispersion in the atmosphere

For environmental analysis such as the dispersion of pollutants in the atmosphere, it is essential to have meteorological data that are relevant for a long period. In this paper, we explore the possibility of using an environmental Test Reference Year (TRY), i.e., a set of real, contemporaneous and hourly meteorological variables, 'extracted' from a hourly series of at least 10 years, for modelling pollutant dispersion in the atmosphere. The classical approach, based on a statistical data set, implies the loss of important information such as the real correlation between the different meteorological variables, and this implies crude approximation in the simulation results. We compare the simulation results with the long hourly 10 years data set (which can be considered a 'brute force' approach, since it requires a huge amount of data and time processing, but it is here considered the most severe benchmark) and with the statistical data set commonly used. It is shown that the results obtained using the TRY have a good agreement with the ones obtained with the simulation of the 10 years and they are also much better than those obtained using the statistical data set.     

Polychlorinated biphenyls (PCBs) in the British environment: sinks, sources and temporal trends

This paper estimates the present UK environmental loading of polychlorinated biphenyls (PCBs). Of the estimated approximately 40,000 t SigmaPCB sold in the UK since 1954, only an estimated 1% (400 t) are now present in the UK environment. Comparisons of estimated production and current environmental loadings of congeners 28, 52, 101, 138, 153 and 180 suggest that PCB persistence broadly increases with increasing chlorination. Those PCBs that are not now present in the UK environment are considered to have been destroyed--by natural or anthropogenic mechanisms, to be still in use, to reside in landfills or to have undergone atmospheric and/or pelagic transport from the UK. The dramatic fall in PCB levels in archived UK soils and vegetation between the mid-1960s and the present is evidence that the latter mechanism is the most important and that a significant proportion of PCBs released into the UK environment in the 1960s have subsequently undergone environmental transport away from the UK. The bulk (93.1%) of the estimated contemporary UK environmental burden of SigmaPCBs is associated with soils, with the rest found in seawater (3.5%) and marine sediments (2.1%). Freshwater sediments, vegetation, humans and sewage sludge combined account for 1.4% of the present burden, whilst PCB loadings in air and freshwater are insignificant. Although consideration of individual congeners does not reveal any major deviations from the relative partitioning of Sigma PCBs, the importance of sinks other than soils is enhanced for individual congeners, particularly 138 and 180. In particular, around 2% of the total UK burden of congener 180 is present in humans, implying that biodata as a whole may constitute an important sink for the higher chlorinated congeners. The contemporary flux of SigmaPCBs to the UK surface is estimated at 19 t yr(-1), compared with an estimated annual flux to the atmosphere of 44-46 t. This implies that the major sources of PCBs to the UK atmosphere have been identified and that there is currently a net loss of these compounds from the UK. These sources are: volatilisation from soils (88.1%), leaks from large capacitors (8.5%), the production of refuse-derived fuel (RDF) (2.2%), leaks from transformers (0.6%), the recovery of contaminated scrap metal (0.5%) and volatilisation from sewage sludge-amended land (0.2%). Interestingly, whilst large excesses of estimated annual fluxes to the atmosphere over deposition fluxes for individual congeners exist for congeners 28, 52 and 101, estimates of fluxes in both directions across the soil-atmosphere interface agree closely for congeners 138, 153 and 180. This suggests that lower chlorinated congeners are more susceptible to both long-range environmental transport beyond the UK and to atmospheric degradation. Retrospective analysis of dated sediment cores, vegetation and soils indicates that environmental transport from North America and continental Europe introduced PCBs into the British environment well before the onset of their commercial production in the UK in 1954. Since that time, the input of PCBs to the UK environment has essentially reflected temporal trends in UK use. After peaking in the 1960s they declined rapidly through the 1970s following restrictions on PCB use. Recent evidence, however, is that the rate of decrease has diminished and that further significant reductions in fresh environmental input will take some time to occur. Such reductions will be especially slow for humans and other biota with long life-spans. This stems partly from cross-generational transfer from parents to offspring and also because the persistence of PCBs in biota means that present body burdens will reflect past as well as current exposure.     

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.     

PCBQ: Computerized quantification of total PCB and congeners in environmental samples

Computerized methodologies for the quantification of total PCBs, PCB in Aroclor mixtures and individual PCB congeners in environmental samples are presented. The method for total PCBs is based on a multiple-linear regression analysis using data from capillary gas chromatography of Arocolor standards. PCB congeners were identified and their weight percentages determined in Aroclor mixtures by GC/MS. PCB congeners and total PCBs were accurately quantified in predetermined test data and environmental samples.     

Evolution of Organic Analytical Methods in Environmental Forensic Chemistry

Over the past few decades the development of environmental regulations, advances in analytical chemistry and other scientific disciplines, and increased rigor in quality control procedures have created a new discipline, environmental forensics. The need for analytical methods that determine qualitatively and quantitatively organic compounds in the environment, especially in drinking waters, was recognized in the early 1950s. These methods were developed gradually by the early 1960s. The important tools of gas chromatography and mass spectroscopy that evolved in the 1970s provided the early environmental forensic chemist for the first time with the ability to produce scientifically sound data that was admissible in court. By the 1990s, multivariate statistical techniques became available and accepted, including principal component analysis (PCA) and polytopic vector analysis (PVA). These techniques, coupled with the advancing analytical methods, have enabled forensic investigator tools to evaluate and demonstrate unique attributes of a set of data. Analyses of marker compounds, PCBs, PCDD/Fs and petroleum hydrocarbons are all shown to be potentially valuable in deciphering the source and fate of contamination. This paper shows how advancements in environmental analytical chemistry provide the forensic chemist with tools to assess the source(s) of site contamination.     

Evolution of Organic Analytical Methods in Environmental Forensic Chemistry

Over the past few decades the development of environmental regulations, advances in analytical chemistry and other scientific disciplines, and increased rigor in quality control procedures have created a new discipline, environmental forensics. The need for analytical methods that determine qualitatively and quantitatively organic compounds in the environment, especially in drinking waters, was recognized in the early 1950s. These methods were developed gradually by the early 1960s. The important tools of gas chromatography and mass spectroscopy that evolved in the 1970s provided the early environmental forensic chemist for the first time with the ability to produce scientifically sound data that was admissible in court. By the 1990s, multivariate statistical techniques became available and accepted, including principal component analysis (PCA) and polytopic vector analysis (PVA). These techniques, coupled with the advancing analytical methods, have enabled forensic investigator tools to evaluate and demonstrate unique attributes of a set of data. Analyses of marker compounds, PCBs, PCDD/Fs and petroleum hydrocarbons are all shown to be potentially valuable in deciphering the source and fate of contamination. This paper shows how advancements in environmental analytical chemistry provide the forensic chemist with tools to assess the source(s) of site contamination.     

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.     

Sources of polychlorinated biphenyl blank contamination and their impact on fingerprinting

Abstract

The development of high-resolution mass spectrometry methods for the measurement of polychlorinated biphenyls (PCBs) in environmental samples has dramatically reduced detection limits, leading to problems obtaining clean blanks. When PCBs are detected in samples at concentrations similar to the blanks, blank contamination must be addressed before fingerprinting and source apportionment through positive matrix factorization (PMF) can be successful. We tested a variety of blank correction methods using data from a study of water column concentrations of PCBs in the Spokane River, where concentrations of Σ₂₀₉PCBs in whole water samples averaged 171?pg/L without blank correction and Σ₂₀₉PCBs in the blanks averaged 88?pg/L. The results suggest that subtracting blank masses from sample masses can lead to erroneous results. Instead, censoring at one times the batch-specific blank level is a better approach. The sources of PCBs in field and method blanks were investigated by examining their congener profiles via PMF. The results suggest that commercial PCB formulations (in the US, Aroclors) continue to be the primary source of PCBs in blanks forty years after PCB production and use were banned in the United States. Other sources of PCBs to blanks include PCB 11 from pigments; PCBs 44?+?47?+?65, 45?+?51, and 68 arising from polymers cured using bis(2,4-dichlorobenzoyl) peroxide; and PCBs 1, 2, 3, 4, 8, 15 and others arising from silicone products derived from phenylsiloxanes, such as silicone-based adhesives.     

Selected organochlorine pesticide and polychlorinated biphenyl residues in house dust in Singapore

Although the use of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) has been prohibited in Singapore since 1980, OCPs and PCBs still can be detected in the environment and represent a potential threat to public health. In this study, OCPs and PCBs were measured in house dust samples collected from 31 homes across the island-state of Singapore. Organochlorine pesticides, such as hexachlorocyclohexanes (HCHs), chlordanes and dichlorodiphenyltrichloroethanes (DDTs) were tested, with a range of 相似文献   

Evaluation of PCB sources and releases for identifying priorities to reduce PCBs in Washington State (USA)

Polychlorinated biphenyls (PCBs) are ubiquitously distributed in the environment and produce multiple adverse effects in humans and wildlife. As a result, the purpose of our study was to characterize PCB sources in anthropogenic materials and releases to the environment in Washington State (USA) in order to formulate recommendations to reduce PCB exposures. Methods included review of relevant publications (e.g., open literature, industry studies and reports, federal and state government databases), scaling of PCB sources from national or county estimates to state estimates, and communication with industry associations and private and public utilities. Recognizing high associated uncertainty due to incomplete data, we strived to provide central tendency estimates for PCB sources. In terms of mass (high to low), PCB sources include lamp ballasts, caulk, small capacitors, large capacitors, and transformers. For perspective, these sources (200,000–500,000 kg) overwhelm PCBs estimated to reside in the Puget Sound ecosystem (1500 kg). Annual releases of PCBs to the environment (high to low) are attributed to lamp ballasts (400–1500 kg), inadvertent generation by industrial processes (900 kg), caulk (160 kg), small capacitors (3–150 kg), large capacitors (10–80 kg), pigments and dyes (0.02–31 kg), and transformers (<2 kg). Recommendations to characterize the extent of PCB distribution and decrease exposures include assessment of PCBs in buildings (e.g., schools) and replacement of these materials, development of Best Management Practices (BMPs) to contain PCBs, reduction of inadvertent generation of PCBs in consumer products, expansion of environmental monitoring and public education, and research to identify specific PCB congener profiles in human tissues.     

Vapour pressures, aqueous solubilities, Henry's law constants, partition coefficients between gas/water (Kgw), n-octanol/water (Kow) and gas/n-octanol (Kgo) of 106 polychlorinated diphenyl ethers (PCDE)

Modelling the environmental fate of persistent organic pollutants like polychlorinated diphenyl ethers (PCDE) requires the knowledge of a number of fundamental physico-chemical properties of these compounds. We report here the physico-chemical properties of 106 PCDEs, which are over 50% of all possible congeners. Vapour pressures P(OL), water solubilities S(H2O), and n-octanol/water partition coefficients K(OW) were determined with chromatographic methods. With these experimental data the Henry's law constants H, gas/water K(GW) and gas/n-octanol K(GO) partition coefficients were calculated. Vapour pressures and water solubilities and n-octanol/water partition coefficients of the PCDEs are close to those of similar groups of organochlorine compounds like polychlorinated biphenyls (PCBs) and dibenzofurans (PCDFs). A similar environmental fate can be predicted and was partially already been observed.     

Modeling the influence of climate change on the mass balance of polychlorinated biphenyls in the Adriatic Sea

Climate forcing is forecasted to influence the Adriatic Sea region in a variety of ways, including increasing temperature, and affecting wind speeds, marine currents, precipitation and water salinity. The Adriatic Sea is intensively developed with agriculture, industry, and port activities that introduce pollutants to the environment. Here, we developed and applied a Level III fugacity model for the Adriatic Sea to estimate the current mass balance of polychlorinated biphenyls in the Sea, and to examine the effects of a climate change scenario on the distribution of these pollutants. The model’s performance was evaluated for three PCB congeners against measured concentrations in the region using environmental parameters estimated from the 20th century climate scenario described in the Special Report on Emission Scenarios (SRES) by the IPCC, and using Monte Carlo uncertainty analysis. We find that modeled fugacities of PCBs in air, water and sediment of the Adriatic are in good agreement with observations. The model indicates that PCBs in the Adriatic Sea are closely coupled with the atmosphere, which acts as a net source to the water column. We used model experiments to assess the influence of changes in temperature, wind speed, precipitation, marine currents, particulate organic carbon and air inflow concentrations forecast in the IPCC A1B climate change scenario on the mass balance of PCBs in the Sea. Assuming an identical PCBs’ emission profile (e.g. use pattern, treatment/disposal of stockpiles, mode of entry), modeled fugacities of PCBs in the Adriatic Sea under the A1B climate scenario are higher because higher temperatures reduce the fugacity capacity of air, water and sediments, and because diffusive sources to the air are stronger.     

Dioxin-like activity in environmental and human samples from Greenland and Denmark

Dioxins and dioxin-like (DL) compounds are some of the most toxic chemicals being highly persistent in the environment. The toxicological effects of dioxins are mediated via the aryl hydrocarbon receptor (AhR). Compounds of diverse structure and lipophility can bind and activate AhR. The AhR transactivation bioassay is utilized in an array of projects to study the AhR-mediated activities of individual chemicals and mixtures and for epidemiological purposes.This review summarizes a series of studies regarding the DL-activity of single compounds and complex compound mixtures in the environment and humans.We found that some pesticides, plasticizers and phytoestrogens can activate the AhR, and the combined effect of compounds with no or weak AhR potency cannot be ignored.The significant DL-activity in the wastewater effluent indicates the treatment is not sufficient to prevent contamination of surface waters with dioxins. Our results from human studies suggest that the serum DL-activity reflect the complex mixture of persistent organic pollutants (POPs). Greenlandic Inuit had lower serum DL-activity level compared to Europeans, probably due to long distance from the dioxin sources and UV degradation of the high potent dioxin and/or the inhibitory effect of the high level of non-DL POPs. Selective bioaccumulation of PCBs in the food chain may contribute to the negative correlation between serum POPs and DL-activity observed in Greenlandic Inuit.Hence the AhR transactivation bioassay provides a cost-effective and integrated screening tool for measurement of the DL-activity in human, environmental and commercial samples.     

In vitro approaches to assess bioavailability and human gastrointestinal mobilization of food-borne polychlorinated biphenyls (PCBs)

This study reports on the potential for gastrointestinal (GI) mobilization and bioavailability of food-borne PCBs in humans. The development and validation of a GI simulator and operational protocols, developed in compliance with the requirements of German DIN 19738 risk assessment test procedure, are presented. Food, naturally contaminated with PCBs, was homogenized with simulated saliva fluid and shaken in the GI simulator with simulated gastric fluids (containing pepsin, mucine) for 2 h at 37°C. Afterwards, the simulated intestinal fluids (containing pepsin, mucine, trypsin, pancreatin, bile) were added and the mixture shaken for a further 6 h prior to centrifugation and filtration using Buchner funnels to separate the undigested GI residues from GI fluids. PCBs were recovered from GI residues and fluids by Soxhlet and liquid-liquid extraction respectively, cleaned up using silica-SFE, and analyzed by gas chromatography mass spectrometry detection (GC-MSD). Detailed studies with fish indicate variations in mobilization and bioavailability of Σ PCBs (28, 52, 101, 118, 153, 138 and 180). For example, the bioavailable fractions (fractions mobilized) in mackerel, salmon, crab and prawn were 0.77, 0.60, 0.54, and 0.72 respectively of the Σ PCBs initially present in these food samples. The bioavailable fraction was dependent on the physicochemical characteristics of the PCBs. In mackerel bioavailable fractions for individual PCB congeners ranged from 0.47–0.82, from 0.30–0.70 in salmon, 0.44–0.64 in crab and in prawn from 0.47–0.77. Future studies will focus on understanding better, the variability in bioavailable fractions to be expected for different foodstuffs, in addition to tissue culture techniques using human gut cell lines to investigate a simultaneous mobilization and absorption of food-borne PCBs.     

In vitro approaches to assess bioavailability and human gastrointestinal mobilization of food-borne polychlorinated biphenyls (PCBs)

This study reports on the potential for gastrointestinal (GI) mobilization and bioavailability of food-borne PCBs in humans. The development and validation of a GI simulator and operational protocols, developed in compliance with the requirements of German DIN 19738 risk assessment test procedure, are presented. Food, naturally contaminated with PCBs, was homogenized with simulated saliva fluid and shaken in the GI simulator with simulated gastric fluids (containing pepsin, mucine) for 2 h at 37 degrees C. Afterwards, the simulated intestinal fluids (containing pepsin, mucine, trypsin, pancreatin, bile) were added and the mixture shaken for a further 6 h prior to centrifugation and filtration using Buchner funnels to separate the undigested GI residues from GI fluids. PCBs were recovered from GI residues and fluids by Soxhlet and liquid-liquid extraction respectively, cleaned up using silica-SFE, and analyzed by gas chromatography mass spectrometry detection (GC-MSD). Detailed studies with fish indicate variations in mobilization and bioavailability of Sigma PCBs (28, 52, 101, 118, 153, 138 and 180). For example, the bioavailable fractions (fractions mobilized) in mackerel, salmon, crab and prawn were 0.77, 0.60, 0.54, and 0.72 respectively of the Sigma PCBs initially present in these food samples. The bioavailable fraction was dependent on the physicochemical characteristics of the PCBs. In mackerel bioavailable fractions for individual PCB congeners ranged from 0.47-0.82, from 0.30-0.70 in salmon, 0.44-0.64 in crab and in prawn from 0.47-0.77. Future studies will focus on understanding better, the variability in bioavailable fractions to be expected for different foodstuffs, in addition to tissue culture techniques using human gut cell lines to investigate a simultaneous mobilization and absorption of food-borne PCBs.