Exposure of populations to dioxins and related compounds

The present situation with respect to the exposure of the general human population to PCDDs, PCDFs and (dioxin-like) PCBs and specific issues that should be taken into consideration for a risk assessment of these exposures have been summarized. The information is based on studies performed in The Netherlands and Germany in the last 10 years. Additional data have been collected through a literature search and through many contacts with researchers and national authorities. The most important route for human exposure to PCDDs, PCDFs and (dioxin-like) PCBs is food consumption contributing over 90% of total exposure, with products of animal origin and fish making the greatest contribution to this exposure. The dietary intake of PCDDs and PCDFs by the general population of industrialized countries is on average 1-3 picograms of (i)-TEQ per kilogram body weight per day. If the contribution of dioxin-like PCBs are also considered, the daily TEQ intake can be a factor of two to three higher. Special consumption habits and consumption of highly contaminated foodstuffs may lead to lower and higher TEQ intakes. In general, TEQ intake increases during childhood and stabilizes in adults of about 20 years of age. However, when normalized by body weight exposure is found to decrease with childhood age due to increasing body weight. Exposure has been shown to have fallen over time in all countries where data are available. Countries that started to implement measures to reduce dioxin emissions in the late 1980s, such as The Netherlands, United Kingdom and Germany, clearly show decreasing PCDD/PCDF and PCB levels in food and consequently a significantly lower dietary intake of these compounds by almost a factor of 2 within the past 7 years.     

Biota--sediment accumulation factors for polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans in southern Lake Michigan lake trout (Salvelinus namaycush)

A set of high-quality, age-specific biota-sediment accumulation factors (BSAFs) for polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs) have been determined from concentrations measured with high-resolution gas chromatography/high-resolution mass spectrometry, by use of the 13C isotopic dilution technique, in lake trout and surficial (0-2 cm) sediment samples from southern Lake Michigan. BSAFs ranged from <0.1 to 18 for PCBs and from <0.001 to 0.32 for PCDDs and PCDFs detected in the fish. PCBs with zero or one chlorine in an ortho position had smaller BSAFs than other PCBs. PCDDs and PCDFs with chlorines at the 2,3,7,8-positions had larger BSAFs than most other PCDDs and PCDFs. The fidelity of the relative bioaccumulation potential data between independent lake trout samples, within and among age classes, suggests that differences in slight rates of net metabolism in the food chain are important and contribute to the apparent differences in BSAFs, not only for PCDDs and PCDFs but also possibly for some PCBs. A complicating factor for non-ortho- and mono-ortho-PCBs is the uncertain contribution of enhanced affinity for black carbon (and possibly volatility) acting in concert with metabolism to reduce measured BSAFs for lake trout. On the basis of the association between chemicals with apparent slight rates of metabolism and measured dioxin-like toxicity, several PCDFs with similar measured BSAFs but unknown toxicity may be candidates for toxicity testing.     

Human risk assessment and TEFs

The concept of toxic equivalency factors (TEFs) has been developed to facilitate risk assessment and regulatory control of exposure to complex PCDD, PCDF and PCB mixtures. Recently the European Centre for Environment and Health of the World Health Organization (WHO-ECEH) and the International Programme on Chemical Safety (IPCS) jointly reevaluated the TEFs of PCDDs, PCDFs and dioxin-like PCBs for mammals and derived consensus TEFs for birds and fish (Stockholm, 1997). From a mechanistic point of view it can be concluded that, although the quantitative response will vary depending on the congener involved, the occurrence of a common mechanism (binding to the Ah receptor) legitimates the use of the TEF concept across species. But there also is criticism regarding the TEF concept. Pharmacokinetic differences between species can significantly influence the TEF value, and uncertainties due to additive or nonadditive interactions, to differences in species responsiveness and to differences in the shape of the dose response curve might hamper the derivation of consensus TEF values. In this context it should be noted, however, that using TCDD alone, as the only measure of exposure to dioxin-like PCDDs, PCDFs and PCBs, would severely underestimate the risk from exposure to these compounds. Therefore, it can be concluded that, for pragmatic reasons, the TEF concept remains the most feasible approach for risk assessment purposes, in spite of the uncertainties associated with its use.     

Polychlorinated biphenyls (PCBs), dioxins and furans (PCDD/Fs): Occurrence in fishery products and dietary intake

Concentrations and congener specific profiles of PCBs, PCDDs and PCDFs were determined in various edible fish from the Adriatic Sea. PCBs were the dominant chemicals (116–1980 ng g⁻¹ lipid wt), followed by PCDFs (ND-58.3 pg g⁻¹ lipid wt) and PCDDs (ND-20 pg g⁻¹ lipid wt). The levels of these contaminants varied among species. Benthic organisms possessed the highest concentrations, followed by demersal and pelagic fish species. PCB and PCDD/F accumulation pattern in the samples analysed showed a distribution typically reported for marine samples. The mean weekly intake of toxic equivalency (TEQ) was estimated to be 0.84 pg TEQs/kg bw/week. The dioxin-like PCBs accounted for more than 77% of this intake, followed by PCDDs (15.5%) and PCDFs (13.1%). In general, the samples analysed in this survey can be considered safe with regard to the levels obtained and the in-force legislation, nevertheless the consumption of some species may be of significance importance for consumer health.     

Quantitative source identification of dioxin-like PCBs in Yokohama, Japan, by temperature dependence of their atmospheric concentrations

The source and environmental behavior of dioxin-like polychlorinated biphenyls (PCBs) together with other PCBs and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) were evaluated based on analysis of variations in their atmospheric concentrations in Yokohama, Japan. Potential factors responsible for variations in the atmospheric concentrations of the congeners were investigated by principal component analysis and multiple regression analysis of the data. Two major variations were seen: one had strong temperature dependence, while the other had no significant temperature dependence. A possible explanation for this difference is that the former is related to congeners released by volatilization (e.g., volatilization from commercial PCB products and past polluted environments), while the latter is related to congeners emitted from thermal processes. The relative contributions of dioxin-like PCBs released by volatilization and those emitted from thermal processes were estimated based on the temperature dependence of the atmospheric concentrations. The results suggest that both dioxin-like PCBs emitted from thermal processes and those released by volatilization are significant sources of air pollution in this area in terms of the toxic equivalent (TEQ) for dioxin-like PCBs. We demonstrated that the present approach based on variations in atmospheric concentrations can be useful in providing a qualitative as well as quantitative understanding of source information.     

Polychlorinated dibenzo-p-dioxins, dibenzofurans, and polychlorinated biphenyls in human tissues, meat, fish, and wildlife samples from India

Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and non- and mono-ortho-substituted polychlorinated biphenyls (dioxin-like PCBs) were measured in tissues of humans, fishes, chicken, lamb, goat, predatory birds, and Ganges River dolphins collected from various locations in India. PCDDs/DFs were found in most of the samples analyzed with the liver of spotted owlet containing the highest concentration of 3,300 pg/g, fat wt. 2,3,7,8-Substituted PCDDs and PCDFs were found in human fattissues at concentrations ranging from 170 to 1,300 pg/g, fat wt. Concentrations of PCDDs were generally greaterthan those of PCDFs in human tissues, fishes, animal fat, and dolphin. Among fishes, meat, and wildlife samples analyzed, concentrations of PCDDs/DFs were found in the following order: country chicken < goat/lamb fat < fishes < river dolphins < predatory birds. Hepta-CDDs and OCDD were the major PCDD homologues found in humans, fishes, meat products, and dolphins. 2,3,7,8-Tetrachlorodibenzo-p-dioxin equivalents of PCDDs/DFs were greater than those of PCBs in selected fish, dolphin, and human samples. To our knowledge, this is the first report of PCDDs and PCDFs in human tissues, fishes, meat, and wildlife collected from India.     

Dietary exposure to dioxins and dioxin-like PCBs of Hong Kong adults: results of the first Hong Kong Total Diet Study

Dioxins and dioxin-like polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) covered by the Stockholm Convention on POPs. To assess the associated health risk of the Hong Kong population, the dietary exposure of the Hong Kong population and various age–gender subgroups to dioxins and dioxin-like PCBs was estimated in the first Hong Kong Total Diet Study (TDS), where food samples were collected and prepared “as consumed”. A total of 142 composite food samples, mainly foods of animal origin and their products and oily food, were analysed for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxin-like PCBs by the high-resolution gas chromatograph/high-resolution mass spectrometer (HRGC/HRMS) system. Dietary exposures were estimated by combining the analytical results with the food consumption data of Hong Kong adults. The mean and 95th percentile exposures to dioxins and dioxin-like PCBs of the Hong Kong population were 21.9 and 59.7 pg toxic equivalent (TEQ) kg^?1 body weight (bw) month^?1 respectively, which amounted to 31.3% and 85.2% of the provisional tolerable monthly intake (PTMI). The main dietary source of dioxins and dioxin-like PCBs was “Fish and seafood and their products” (61.9% of the total exposure), followed by “Meat, poultry and game and their products” (20.0%) and “Mixed dishes” (6.95%). The study findings suggest that the Hong Kong population is unlikely to experience the major undesirable health effects of dioxins and dioxin-like PCBs.     

Formation of PCDDs,PCDFs, and coplanar PCBs from incineration of various woods in the presence of chlorides

Exhaust gases from the combustion of woods (Japanese red pine, Japanese cedar, Siebold's beech, seawater-impregnated Japanese red pine and Japanese cedar, waste woods containing chlordane, and waste woods containing pentachlorophenol) were collected at the outlet of a combustion chamber. A small-scale incinerator with a stationary grate was used. The samples were analyzed for PCDDs, PCDFs, and coplanar PCBs by gas chromatography/ mass spectrometry (GC/MS). When the grate temperature of the combustion chamber was lower than 700 degrees C, the total amount of PCDDs, PCDFs, and coplanar PCBs formed was proportional to the chlorine content of the combustion samples. On the other hand, when the grate temperature of the combustion chamber was higher than 800 degrees C, there was only a slight formation of PCDDs, PCDFs, and coplanar PCBs regardless of the chlorine content of the combustion samples. When the grate temperature was low, nearly 90% of total PCDDs, PCDFs, and coplanar PCBs formed were PCDFs, whereas when the grate temperature was higher, 50-80% of total PCDDs, PCDFs, and coplanar PCBs formed was PCDFs. The total amount of PCDDs, PCDFs, and coplanar PCBs formed in a high-temperature condition was approximately 1/50 of that formed in a low-temperature condition. Coplanar PCBs tended to form less than PCDDs or PCDFs did. Mono-ortho-PCBs were formed several times more than nonortho-PCBs. PCDDs or PCDFs contributed significantly to the values of TEQ, while coplanar PCBs contributed only slightly.     

Surveillance of dioxins and polychlorinated biphenyls (PCBs) in food commercialized in Barcelona,Spain

This study explored the potential use of seven congeners of polychlorinated biphenyls (PCBs-7) as indicator compounds for the presence of dioxins and PCBs in food samples, as part of the routine surveillance programme of a public health agency. Samples of 24 foodstuffs with high fat content were collected (ten fresh fish, six dairy products, five meat and three eggs). Duplicate analyses were performed. A research laboratory tested samples for seven polychlorinated dibenzo-p-dioxin (PCDDs), ten dibenzofurans (PCDFs) and twelve dioxin-like PCBs, with limits of detection in the range of ng kg^?1 (ppt). The public health services official control laboratory tested samples for PCBs-7, with a limit of quantification of 5 µg kg^?1 (ppb). The research laboratory detected the presence of dioxins and dioxin-like PCBs in all samples; fish samples had the highest levels (0.04–10.3 pg WHO-TEQ g^?1). The public health service official control laboratory detected PCBs-7 only in five samples, which were all fish. Comparing the results in the two laboratories there seems to be an association between the detection of PCB-7 and the presence of higher levels of PCDD/Fs and dioxin-like PCBs. The use of PCB-7 as an indicator compound may be a practical surveillance strategy for those foodstuffs with higher concentrations of dioxin-like congeners.     

A Critical Review about Human Exposure to Polychlorinated Dibenzo-p-Dioxins (PCDDs), Polychlorinated Dibenzofurans (PCDFs) and Polychlorinated Biphenyls (PCBs) through Foods

Dioxins include polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and part of polychlorinated biphenyls (PCBs). Only the compounds that are chlorinated at the 2,3,7, and 8 positions have characteristic dioxin toxicity. PCDDs, PCDFs and PCBs accumulate in the food chain due to their high lipophilicity, high stability, and low vapor pressure. They are not metabolized easily; however their hydroxylated metabolites are detected in feces. They cause a wide range of endocrine disrupting effects in experimental animals, wildlife, and humans. Endocrine related effects of PCDDs, PCDFs and PCBs on thyroid hormones, neurodevelopment and reproductive development were referenced. In addition, some studies of contamination of foods, bioaccumulation, dietary exposure assessment, as well as challenges of scientific research in these compounds were reviewed.     

Congener-specific distribution of polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls in animal feed.

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) were extracted by accelerated solvent extraction from animal feed samples and analysed by high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). In all of the feed samples analysed, the concentrations of PCDD/Fs and PCBs were below the existing tolerance limit of 5 pg I-TEQ g(-1) and 200 ng g(-1) fat, respectively. The mean concentrations of the total PCDDs, total PCDFs and total PCBs were 1.73-11.50 pg g(-1), 0.23-11.91 pg g(-1) and 60.00-234.40 pg g(-1) feed, respectively. Investigation of the correlations among the concentrations of PCDDs, PCDFs and PCBs showed that samples containing increased amounts of PCDFs also contained higher concentrations of PCDDs, with an average ratio of PCDF:PCDD of about 1.23:1 (r(2)=0.72, p<0.05). The correlation between the concentrations of PCDD/Fs and PCBs was positive but not significant.     

Cleanup of food samples with pre-packed multi-layer silica gel column for the analysis of PCDDs,PCDFs and dioxin-like PCBs

The cleanup procedure for the determination of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (PCBs) in food samples using a disposable pre-packed multi-layer silica gel column (multi-layer dioxin tube; D-tube) was evaluated. The blank test showed the need for conditioning of the column with n-hexane. To compare the method with the D-tube and the conventional method for the analyses of actual food samples, seven food samples (spinach, komatsuna, rice, salmon, beef, egg and butter) were extracted by shaking with acetone-n-hexane or n-hexane after alkaline treatment, and then the extracts were cleaned up by use of the D-tube or the prepared conventional column, followed by several column chromatographic steps. Both cleanup procedures gave similar values at each isomeric concentration level and showed similar efficiency with favorable recoveries. The results suggest that the D-tube is applicable to cleanup for the analysis of PCDD/Fs and dioxin-like PCBs in foods.     

Approach to highly efficient dechlorination of PCDDs, PCDFs, and coplanar PCBs using metallic calcium in ethanol under atmospheric pressure at room temperature

Detoxification of highly toxic polychlorinated aromatic compounds such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and dioxin-like compounds such as coplanar polychlorinated biphenyls (co-PCBs) under mild conditions (atmospheric pressure and room temperature) was achieved by a simple stirring operation for 24 h using metallic calcium in ethanol, without any tedious decomposition procedures and harsh conditions such as high temperature and/or high pressure. Metallic calcium can be kept stable under atmospheric conditions for a long period as compared to metallic sodium since the surface is coated with CaCO3, which is formed in the contact with air. Moreover, ethanol, which is one of the safest solvents for humans, acts not only as a solvent but also as an accelerator due to its ablility to remove the carbonated coating. This decomposition method for PCDDs, PCDFs, and co-PCBs therefore is one of the most economical and environmentally friendly detoxification methods with respect to the input energy and safety of reagents used. Concentration for each isomer of PCDDs, PCDFs, and co-PCBs was reduced in 98.32-100% conversions by treatment in ethanol at room temperature. The toxicity equivalency quantity (TEQ), which was measured by the HRGC-HRMS analysis, for the total residues of isomers was reduced from 22,000 to 210 pg TEQ/mL of hexane (conversion: 99.05%) at room temperature. By refluxing over 24 h, the conversion increased up to 99.45%.     

Formation of PCDDs, PCDFs, and coplanar PCBs from polyvinyl chloride during combustion in an incinerator

Exhaust gases from the combustion of poly(vinyl chloride) (PVC), polyethylene (PE), polystyrene (PS), poly(ethylene terephthalate) (PET), and theirvarious mixtureswere analyzed for PCDDs, PCDFs, and coplanar PCBs by gas chromatography/mass spectrometry (GC/MS) in order to investigate the role of PVC in these chlorinated compounds. Total amounts of dioxins (PCDDs + PCDFs) found in the samples were 11.7 ng/g PE alone, 1.17 ng/g from PS alone, 25.3 ng/g from PET alone, 448 ng/g from PE with PVC, 140 ng/g from PS with PVC, 126 ng/g from PET with PVC, 824 ng/g from PVC alone under low-CO level, and 8,920 ng/g from PVC alone under high-CO level. CO level in high-CO level condition was 880 ppm which was 20 times greater than that in low-CO level condition. Formation of coplanar PCBs ranged from 0.095 ng/g (PE alone) to 77 ng/g (PVC alone under high-CO level). There is a clear correlation between dioxin formation and chloride content. PCDFs composed 80% (PET + PVC)--98% (PET alone) of the total dioxins formed in the exhaust gases. The results indicate that PVC contributes significantly to the formation of PCDDs, PCDFs, and coplanar PCBs from mixtures of plastics upon combustion.     

Dioxins,furans, and non-ortho PCBs in Canadian Arctic seabirds

This is the first account of PCDDs, PCDFs, and non-ortho PCBs in Canadian Arctic seabirds. Livers and eggs of thick-billed murres, northern fulmars, and black-legged kittiwakes were collected in 1975 and 1993 from Prince Leopold Island in Lancaster Sound, Canada. Detectable concentrations of PCDDs, PCDFs, and non-ortho PCBs were found in all the Arctic seabird samples analyzed. Of the PCDD congeners assayed, only 2,3,7,8-substituted PCDDs were detected in the samples, whereas non-2,3,7,8-substituted PCDFs were found in addition to 2,3,7,8-substituted PCDFs in some of the samples. The predominant PCDD/F congener found in the livers of all three species was 2,3,4,7,8-PnCDF, both in 1975 and 1993. Concentrations of most dioxins and furans decreased in the fulmars and kittiwakes between 1975 and 1993 but increased in the murres. Of the non-ortho PCBs measured, PCB-126 occurred in the highest concentrations and contributed the majority of the non-ortho PCB-TEQ in all three species in both years. The highest concentrations of dioxins and furans as well as the highest TEQ values were found in the northern fulmar livers in both 1975 and 1993. Concentrations of some of the PCDDs and PCDFs are among the highest reported for Canadian Arctic biota.     

Dioxin concentrations in the edible parts of Japanese common squid and saury

We examined the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) in muscle and gut tissues from Japanese common squid and saury. These body parts are often eaten in Japan, so it is important to measure their dioxin concentrations and evaluate the risks to consumers. The toxic equivalent (TEQ) concentrations in the squid gut samples (1.0 to 14 pg-TEQ/g fresh weight, n=3) were 50-fold larger than those in the muscle tissues (0.020 to 0.22 pg-TEQ/g fresh weight, n = 3) taken from the same samples. By contrast, the TEQ concentrations in the saury gut samples (0.35 to 0.63 pg-TEQ/g fresh weight, n=3) were only 1.1- to 1.7-fold greater than those in the muscle tissues (0.33 to 0.37 pg-TEQ/g fresh weight, n= 3) from the same samples. The TEQ contents in the squid gut tissues ranged from 60 to 990 pg-TEQ/squid, accounting for about 95% of the total dioxin content of the edible parts of the samples. By contrast, the TEQ contents in the saury gut tissues ranged from 4.4 to 12 pg-TEQ/saury, accounting for less than 25% of the total dioxin content of the edible parts of the samples. These tissues showed comparable PCDD/PCDF-congener and dioxin-like PCB-isomer profiles in both species. The results indicate that squid gut tissues occasionally contain high levels of dioxins, and consumption of this foodstuff could potentially significantly increase the dietary intake of dioxins.     

Statistical comparison of residential soil concentrations of PCDDs, PCDFs, and PCBs from two communities in Michigan

The University of Michigan dioxin exposure study was undertaken to address concerns that the industrial discharge of dioxin-like compounds in the Midland, MI area had resulted in contamination of soils in the Tittabawassee River floodplain and downwind of the incinerator. The study was designed in a rigorously statistical manner comprising soil measurements of 29 polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) from 766 residential properties, selected probabilistically, in the Midland area and in Jackson and Calhoun Counties (Michigan) as a background comparison. A statistical comparison determined that the geometric mean toxic equivalent (TEQ) levels in samples from the target populations were statistically significantly above background. In addition, the probabilities of being above the 75th and 95th percentiles of background were also greater. Congener contributions to the TEQ were dominated by 2,3,4,7,8-PeCDF and 2,3,7,8-TCDF in the floodplain and by 2,3,7,8-TCDD in the incinerator plume. However, PCB 126 was the top congener contributing to the background TEQ. On the basis of statistical inference to the total population, it was estimated that about 36% of the properties in the floodplain and incinerator plume have at least one soil sample over the Michigan Department of Environmental Quality's soil direct contact criterion of 90 pg/g TEQ.     

Comparison of sulfuric acid treatment and multi-layer silica gel column chromatography in cleanup methods for determination of PCDDs,PCDFs and dioxin-like PCBs in foods

Two typical cleanup methods, sulfuric acid treatment and multi-layer silica gel column chromatography, for the determination of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) in seventeen food samples were examined and compared. Vegetables, fruits, cereals, fish, meat and dairy foods were extracted by conventional methods (shaking with acetone/n-hexane or with n-hexane after alkaline treatment). The extracts were cleaned up by sulfuric acid treatment or multi-layer silica gel column chromatography, followed by several column chromatographic steps. Of the samples treated, the vegetable, fruit and cereal samples could be directly applied to the multi-layer silica gel column after extraction. However, the samples containing fats and oils such as fish, meat and dairy foods needed to be treated several times with concentrated sulfuric acid before multi-layer column chromatography, because these samples plugged the column with oily residues. Both cleanup methods gave similar values of isomeric concentrations and showed similar efficiency of purification, and the recoveries ranged from 40 to 120%. These results are considered to provide useful data for the efficient analysis of dioxins in foods which have wide-ranging compositions.     

Open dumping site in Asian developing countries: a potential source of polychlorinated dibenz-p-dioxins and polychlorinated dibenzofurans

Open landfill dumping areas for municipal wastes in Asian developing countries have recently received particular attention with regard to environmental pollution problems. Because of the uncontrolled burning of solid wastes, elevated contamination by various toxic chemicals including dioxins and related compounds in these dumping sites has been anticipated. In this study, concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (PCBs) were determined in soils from dumping sites in the Philippines, Cambodia, India, and Vietnam. Residue concentrations of PCDD/Fs and coplanar PCBs in dumping site soils were apparently greater than those in soils collected in agricultural or urban areas far from dumping sites, suggesting that dumping sites are potential sources of PCDD/Fs and related compounds. Observed PCDD/F concentrations in soils from dumping sites in the Philippines and Cambodia were comparable or higher than those reported for dioxin-contaminated locations in the world (e.g., near the municipal waste incinerators and open landfill dumping sites). Homologue profiles of PCDD/Fs in dumping site soils from the Philippines and, to a lesser extent, from Cambodia and India reflected patterns of samples representing typical emissions, while profiles of agricultural or urban soils were similar to those of typical environmental sinks. This result suggests recent formation of PCDD/Fs in dumping site areas and that open dumping sites are a potential source of dioxins in Asian developing countries. Uncontrolled combustions of solid wastes by waste pickers, generation of methane gas, and low-temperature burning can be major factors for the formation of dioxins in dumping sites. Elevated fluxes of PCDD/Fs to soils in dumping sites were encountered in the Philippines, Cambodia, India, and Vietnam-Hanoi, and these levels were higher than those reported for other countries. Considerable loading rates of PCDD/Fs in the dumping sites of these countries were observed, ranging from 20 to 3900 mg/yr (0.12-35 mg TEQ/yr). PCDD/F concentrations in some soil samples from the Philippines, Cambodia, India, and Vietnam-Hanoi exceeded environmental guideline values, suggesting potential health effects on humans and wildlife living near these dumping sites. The estimated intakes of dioxins via soil ingestion and dermal exposure for children were higher than those for adults, suggesting greater risk of dioxin exposure for children in dumping sites. To our knowledge, this is the first comprehensive study on PCDD/Fs contamination in open dumping sites of Asian developing countries. On the basis of the result of this study, we have addressed a new environmental issue that open dumping sites are potential sources of PCDD/Fs and related compounds, and dioxin contamination in dumping sites may become a key environmental problem in developing countries.     

A general indication of the Contemporary background levels of PCDDs, PCDFs, and coplanar PCBs in the ambient air over rural and remote areas of the United States

Long-term measurements of the atmospheric concentrations of PCDDs, PCDFs, and coplanar PCBs were taken in rural and remote areas of the United States by the National Dioxin Air Monitoring Network (NDAMN). A total of 21 quarterly sampling moments occurred from June, 1998 to December, 2002 at 34 locations geographically distributed throughout the United States. Sampling sites were located in rural and remote areas to obtain background air concentrations of dioxin-like compounds. Results were reported as the toxic equivalent (TEQ) of the mix of PCDDs/ PCDFs (TEQDF) and the mix of coplanar PCBs (TEQPCB). At the studied rural sites the mean annual TEQDF for each of the NDAMN sampling years was 10.43, 11.39, 10.40, and 10.47 fg m(-3) for 1999, 2000, 2001, and 2002, respectively. There was no statistically significant difference in the rural mean TEQDF air concentrations across the sampling years (at 0.05 level of significance), although the mean concentration in sampling year 2000 increased 10% relative to the other sampling years. The 95th percent confidence interval of TEQDF air concentrations in rural areas of the United States is from 6.4 to 15.4 fg m(-3), indicating there is a 95% probability that the true mean falls within this range. Mean annual atmospheric concentrations (TEQDF) at the remote sites were 1.41, 0.99, 0.7, and 1.07 fg m(-3) in 1999, 2000, 2001, and 2002, respectively, The 95th percent confidence interval of TEQDF air concentrations suggest that the true mean annual atmospheric TEQDF concentration in remote areas of the United States is between 0.1 and 3 fg m(-3). The remote sites have average air TEQDF concentrations that are approximately 10 times lower than those of the rural sites. For the rural sites, there was close agreement in the mean annual air concentrations of coplanar PCBs (TEQPCB) among the years 1999, 2000, 2001, and 2002 (i.e., 0.62, 0.69, 0.59, and 0.7 fg m(-3), respectively). However, as is the case with PCDDs/PCDFs, there was a marked increase (i.e., approximately equal to 13%) in the annual rural mean air concentration in 2000 as compared to the other sampling years. The confidence intervals across the NDAMN sampling years suggests a 95% probability that mean TEQPcB atmospheric concentrations in rural and remote areas of the United States are within the range of 0.5-0.9 fg m(-3) and 0.1-0.5 fg m(-3), respectively. The congener distributional patterns of PCDDs/PCDFs in air were relatively constant at all locations, and match the profile of urban air. We propose the hypothesis that urban areas are regional sources of PCDDs/PCDFs and are affecting atmospheric levels in rural and remote areas of the United States.