Characterizing the emissions of polybrominated dibenzo-p-dioxins and dibenzofurans from municipal and industrial waste incinerators

As yet, very little is known about the polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) characteristics in the stack flue gases of incinerators. In this study, nine large-scale continuous municipal solid waste incinerators (MSWIs), two small-scale batch MSWls, and nine industrial waste incinerators (IWIs) were investigated for 2,3,7,8-substituted PBDD/Fs. The elevated PBDD/F concentrations (18.2 pg/Nm3, 4.17 pg TEQ/Nm3) of the IWIs, which were eight times higher than those of MSWIs (2.28 pg/Nm3, 0.557 pg TEQ/Nm3), are accompanied by PCDD/ Fs that are in the same range as those measured from MSWIs (0.0171-1.98 ng I-TEQ/Nm3). The obtained TEQ ratios (in percentage) of the PBDD/F to the PCDD/F concentration in the stack flue gases of the MSWls (0.72%), batch MWIs (0.18%), and IWIs (5.4%) are useful for the future estimate of PBDD/F emission quantity based on the well-established PCDD/F inventory. In addition, a significantly high correlation was found between the PBDD/F and PCDD/F concentrations, and the PBDD/F and PCDD/F congener profiles of the same emission source were similar, indicating a similar formation and substitution mechanism of bromine and chlorine in the combustion system.     

Characterization of polybrominated dibenzo-p-dioxins and dibenzofurans in different atmospheric environments

Few studies have measured polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) in the atmosphere. In this study,four categories of atmospheric environments, including rural (Kengting national park, Taitung county, and Yilan county), urban (north Kaohsiung city and south Taichung city), industrial (Lin-hai industrial park), and science park (Hsinchu science park) areas were investigated for their characteristics of 2,3,7,8-substituted PBDD/F and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). The elevated PCDD/F I-TEQ concentrations and higher ratio of PCDFs to PCDDs in the industrial areas reveal that the metallurgical facilities, including sinter plants, electric arc furnaces, secondary aluminum smelters, and secondary copper smelters, significantly influence their surrounding atmospheric environments. The mean PBDD/F concentrations in the atmosphere of the rural, urban, industrial, and science park areas were 11, 24, 46, and 95 fg/Nm3, respectively, while the corresponding mean TEQ concentrations were 2.7, 6.4, 12, and 31 fg TEQ/Nm3, respectively. The significantly high correlation (r = 0.85, p = 0.034)found betweenthe PBDD/F and PCDD/F concentrations in the atmospheres of the industrial areas reveals that the metallurgical facilities are also the most likely PBDD/F emission sources in the industrial areas. The PBDD/F concentration in the science park area was approximately 2-fold higher than that in the industrial areas, whereas PCDD/F I-TEQ concentration in the area was only 23% of that in the industrial areas. The elevated PBDD/F concentrations in the science park areas may be attributed to the use of polybrominated diphenyl ethers as brominated flame retardants in the electrical and electronics industries, which contribute to direct PBDD/F emissions into the environment. PBDFs were all much more dominant than PBDDs in the atmosphere, and their mass fractions increase with PBDD/F concentrations.     

Evaluation of PCDD/F congener partition in vapor/solid phases of waste incinerator flue gases

Activated carbon injection (ACI) is commonly used to control PCDD/F (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) emissions from stationary sources. In this study, the characteristics of PCDD/Fs emitted from one municipal waste incinerator (MWI) and two industrial waste incinerators (IWI-1 and IWI-2) that apply activated carbon systems for controlling the emissions are investigated via intensive stack sampling. MWI and IWI-1 are equipped with ACI and bag filters (BF) while IWI-2 is equipped with a fixed activated carbon bed (FCB). Results indicate that most PCDD/Fs in flue gas downstream of ACI+BF exist in vapor phase (over 90%) while most PCDD/ Fs exist in solid phase (over 60%) downstream of FCB. For MWI and IWI-1, the removal efficiencies of vapor and solid-phase PCDD/Fs are 98.5-99.6% and 99.8-99.9%, respectively. In addition,the removal efficiencies of vapor- and solid-phase PCDD/Fs are 84.5% and -13.4% in IWI-2, respectively. The results also indicate that the partition of vapor/solid-phase PCDD/F is affected by the type of the air pollutant control devices (APCDs) applied upstream and the particulate matter concentration in flue gas. On the basis of the sampling results of waste incinerators, this study preliminarily establishes the equations for predicting vapor/solid-phase PCDD/F partition in flue gases downstream of various APCDs including cyclone (CY), electrostatic precipitator (EP), FCB, ACI+BF, and selective catalytic reduction system (SCR).     

Characterizing the emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from crematories and their impacts to the surrounding environment

This study was set out to characterize PCDD/F emissions from crematories and assess their impacts on the surrounding environment. Two crematories located in southern Taiwan were investigated, including the one (C1) with no air pollution control device installed and the other (C2) installed with a bag filter. Results show the mean PCDD/F emissions (11% oxygen) from the stacks of Cl and C2 were 2.36 and 0.322 ng I-TEQ Nm(-3), respectively. The mean emission factors for C1 and C2 were 13.6 and 6.11 microg I-TEQ body(-1), respectively. The removal efficiency of the bag filter on PCDD/Fs was 55.1%. The estimated PCDD/F emission rate for all crematories in Taiwan was 0.838 g I-TEG yr(-1) accounting for 227% and 112% of the annual emissions from all medical waste incinerators and municipal waste incinerators, respectively. The above results indicate that PCDD/F emissions from crematories were quite significant. To assess the impact of PCDD/F emissions from a crematory to the surrounding environment, ambient air samples were collected from the downwind site of C1 with the maximum ground concentration. We found the estimated maximum ground concentration at the downwind site of C1 (= 0.521 pg I-TEQ Nm(-3)) was much higherthan thatfound atthe background, rural area, residential area, urban area, and industrial area (= 0.006, 0.023, 0.052, 0.093, and 0.190 pg I-TEG Nm(-3), respectively). The above results suggestthat PCDD/F emissions from a crematory did significantly affect its surrounding environment. In conclusion, a proper control strategy should be taken immediately in order to eliminate PCDD/F emissions from crematories.     

Levels of dioxins in Japanese fruit in 1999 to 2002 and estimation of their intake

A total of 148 samples of nine species of fruit were collected between 1999 and 2002 and analyzed for PCDDs, PCDFs (PCDD/Fs) and Coplanar PCBs. Sampling points within about 1 km of operational municipal waste incinerators that were considered sources of dioxins were defined as "near-source" areas, and all other sampling points were defined as "general" areas. The TEQ of apples collected from near-source areas was significantly higher than that from general areas (p < 0.05). 3,3',4,4',5-PeCB (#126) was the main contributor to this difference in TEQs between apples collected from near-source areas and from general area. A principal component analysis performed to estimate the source of this congener revealed that not only the municipal waste incinerators, but also PCBs in the environment were associated with the high TEQ in apples collected from near-source areas. The daily intakes of PCDD/Fs and Coplanar PCBs from the fruits including skin were estimated to be 0.0082 pg-TEQ/kg b.w./day (ND = 0) and 0.072 pg-TEQ/ kg b.w./day (ND = 1/2 LOQ). Though these values are likely to be overestimates, they are far lower than the tolerable daily intake set in Japan for PCDD/Fs and Coplanar PCBs (4 pg-TEQ/kg b.w./day). It is thought that fruit intake is not an important pathway of human exposure to PCDD/Fs and Coplanar PCBs.     

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.     

Environmental impact and human health risks of polychlorinated dibenzo-p-dioxins and dibenzofurans in the vicinity of a new hazardous waste incinerator: a case study

The purpose of this study was to assess the environmental impact of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the vicinity of a new hazardous waste incinerator (HWI) 4 years after regular operation of the facility. A double approach was carried out. The PCDD/F congener profiles corresponding to environmental samples, soil and herbage, collected before the HWI (baseline) and 4 years after starting regular operations, as well as PCDD/F profiles of air emission samples, were compared. The potential health risks (carcinogenic and noncarcinogenic) due to PCDD/F exposure were assessed for adults and children living in the neighborhood of the facility. Human exposure to PCDD/Fs was mainly due to dietary food intake. Comparisons between the PCDD/F congener profiles corresponding to the baseline and current surveys, as well as data concerning the human health risk assessment, indicate that the HWI in question does not cause additional risks to the environment orto the population living in the vicinity of the facility.     

Secondary effects of catalytic diesel particulate filters: copper-induced formation of PCDD/Fs

Potential risks of a secondary formation of polychlorinated dibenzodioxins/furans (PCDD/Fs) were assessed for two cordierite-based, wall-through diesel particulate filters (DPFs) for which soot combustion was either catalyzed with an iron- or a copper-based fuel additive. A heavy duty diesel engine was used as test platform, applying the eight-stage ISO 8178/4 C1 cycle. DPF applications neither affected the engine performance, nor did they increase NO, NO2, CO, and CO2 emissions. The latter is a metric for fuel consumption. THC emissions decreased by about 40% when deploying DPFs. PCDD/F emissions, with a focus on tetra- to octachlorinated congeners, were compared under standard and worst case conditions (enhanced chlorine uptake). The iron-catalyzed DPF neither increased PCDD/F emissions, nor did it change the congener pattern, even when traces of chlorine became available. In case of copper, PCDD/F emissions increased by up to 3 orders of magnitude from 22 to 200 to 12 700 pg I-TEQ/L with fuels of < 2, 14, and 110 microg/g chlorine, respectively. Mainly lower chlorinated DD/Fs were formed. Based on these substantial effects on PCDD/F emissions, the copper-catalyzed DPF system was not approved for workplace applications, whereas the iron system fulfilled all the specifications of the Swiss procedures for DPF approval (VERT).     

Discrimination of aerial deposition sources of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran downwind from a pulp mill near Ketchikan, Alaska

Drinking water is supplied by individual roof-catchment systems for homes and businesses near a dissolving sulfite pulp mill (now closed) located just north of Ketchikan in southeast Alaska. This study was conducted to determine if polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) found in the sediments of the roof-catchment cisterns resulted from historical deposition of stack emissions from the pulp mill's multi-fuel power boilers. Fly ash from the power boilers had maximum total PCDD/F concentrations of 3.08 x 10(5)-3.10 x 10(6) ng/kg, which resulted from combustion of bleach plant wastewater sludge and saltwater-soaked wood waste. Cistern sediments had maximum total PCDD/F concentrations of 7.71 x 10(4) ng/kg. Potential sources of PCDDs/Fs in the cistern sediments were considered to be automobile exhaust, heating oil combustion, and private trash burning as well as pulp mill boiler emissions. Discriminant analysis was used to analyze differences between profiles of tetra through octa homologue classes of PCDDs/ Fs (defined as proportional contributions to total concentration) from different source terms. Homologue profiles of potential sources from Ketchikan included in this analysis were fly ash collected from the mill's power boilers and soils collected from background areas (areas with similar PCDD/F sources as the residences [e.g., auto exhaust and burn barrels] near the mill but beyond the zone of aerial deposition of emissions from the mill). Profiles for emissions from automobile exhaust, fertilizers, oil heating, residential trash burning, and residential wood heating were also included in the source "training" data set (for the discriminant analysis) using data from published literature. The classification rules developed from the discriminant analysis were applied to the following test media sampled at Ketchikan: roof-catchment cistern sediments and soils collected from areas in the vicinity of the mill's power boilers (i.e., nearby residential or commercial [developed] areas, on the mill property, and nearby forestlands). The homologue profiles of cistern sediment and nearby developed area soil samples were similar to background soils, whereas the profiles for the forestland soil samples (influenced by emissions from the mill but not other anthropogenic sources) closely matched the fly ash pattern. The homologue profiles of the emission sources from published data were more similar to one another than either background soils or fly ash. Soil samples from the mill property were classified as members of all source groups. On the basis of these analyses, the composition of PCDDs/Fs detected in the cistern sediments is typical of Ketchikan background conditions and not reflective of mill emissions.     

Assessment of chlorinated dibenzo-p-dioxin and dibenzofuran trends in sediment and crab hepatopancreas from pulp mill and harbor sites using multivariate- and index-based approaches

Mill process changes and source controls instituted in the late 1980s at pulp and paper mills along the British Columbia (BC) coast produced dramatic reductions in both the concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and the TEQ (2,3,7,8-TCDD toxic equivalents). Nevertheless, questions remained as to whether the sediments were acting as contaminant sources or sinks, whether crab uptake pathways have stayed the same since the mills ceased producing PCDD/Fs, and whether improvement was faster at some sites than others. To examine the processes governing the changes in PCDD/F composition, PCDD/F sources and compositional trends for the coastal BC sites were interpreted using sediment and crab PCA (principal components analysis) models and two indices based on the three main groups of PCDD/Fs that covary in all PCA models. One index measured the relative inputs of chlorine bleaching PCDFs and PCP (pentachlorophenol)-related PCDDs at each mill and harbor site whereas the other measured the relative inputs of PCP wood preservatives and pulp mill effluents. Results indicated that PCDFs produced during chlorine bleaching accumulate from sediments to crabs more readily than the PCDDs but that the chlorine bleaching TCDFs have generally decreased in importance at all mill sites. In the years just before 1995, little change was observed in either the proportion of toxic 2,3,7,8-chlorinated congeners or the PCDD/F concentrations, and the improvements seemed to have largely ceased by 1995. The lack of change in PCA composition for the harbors provided a further, disturbing indication that ecosystem recovery may have stalled. Results also implied that the main route of PCDD/Fs into crabs shifted from uptake via a pelagic food web incorporating effluent-borne PCDD/Fs associated with suspended particulate matter to uptake via a benthic food web.     

On-road emissions of PCDDs and PCDFs from heavy duty diesel vehicles

This work characterized emission factors of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) from on-road sampling of three heavy duty diesel vehicles (HDDVs) under experimental conditions of city and highway driving; idling operation; high (>400 ppm) and low (<5 ppm) sulfur (S) fuels; and high mileage and rebuilt engine testing. Emission factors, homologue profiles, and isomer patterns were compared to determine whether the experimental conditions had an impact on PCDD/F emissions, or whether these conditions were uninfluential in determining a fleet-representative emission factor. For a single HDDV tested under conditions of a high mileage engine, a newly rebuilt engine, and the newly rebuilt engine with low S diesel fuel, emission factors were 0.023 (+/- 0.022), 0.008 (+/- 0.002), and 0.016 (+/- 0.013) ng toxic equivalency (TEQ)/km, respectively. These results may infer some limited condition-specific differences in PCDD/F emissions, but these differences do not appear to have a significant effect on the HDDV emission factor. An older HDDV with mechanical fuel controls resulted in a single test value of 0.164 ng TEQ/km, significantly higher than all other results. Observed differences in emission factors, homologue profiles, and TEQ-related isomer patterns from this on-vehicle sampling and others' tunnel sampling suggest limitations in our present characterization of fleet PCDD/F emissions.     

Experimental study on the effect of SO2 on PCDD/F emissions: determination of the importance of gas-phase versus solid-phase reactions in PCDD/F formation

Cofiring coal in municipal solid waste incinerators (MSWls) has previously been reported to reduce polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) emissions due to increasing the flue gas SO2 concentration. The present study was focused on understanding the primary mechanism responsible for the suppressant effect of SO2 on total PCDD/F formation and toxic equivalent (TEQ) emissions. The addition of SO2, simulating the effect of coal addition on the flue gas composition, resulted in significant reductions in the TEQ emissions due to reactions involving SO2 in the postcombustion zone. However, emissions of total PCDDs/Fs, unlike the TEQ value, were dependent upon the Cl2 and SO2 injection temperatures due to increases in non-TEQ correlated isomers. The conversion of metal chlorides in the fly ash to sulfates, thus reducing the sites responsible for chlorination/oxidation reactions, was concluded to be the main suppressant mechanism; proposed reactions for copper and iron are presented. This mechanism was found to be independent of combustion conditions and could have prolonged effects on PCDD/F emissions from deposits formed with high flue gas S/Cl ratios.     

Formation of dioxins in the catalytic combustion of chlorobenzene and a micropollutant-like mixture on Pt/gamma-Al2O3

Catalytic combustion over a 2 wt % Pt/gamma-Al2O3 catalyst of chlorobenzene (PhCl) and of a micropollutant-like mixture representative for a primary combustion offgas has been investigated. Typical conditions were 1000-1500 ppm of organics in the inflow, contact times approximately 0.3 s, 16% O2 in nitrogen at approximately 1 bar, and temperature range 200-550 degrees C. PhCl reacts considerably slower than when processing Cl-free compounds such as heptane. At intermediate temperatures--and incomplete conversion--byproducts are formed, especially polychlorobenzenes (PhClx). These are accompanied by polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) at levels of about 10(-6) relative to PhClx. Additional HCI--made by co-reacting PhCl with tert-butylchloride--leads to much higher levels of PhClx and PCDD/Fs. Using the micropollutant-like mixture, the total chlorine input is reduced almost 20-fold, but it nevertheless leads to a 30-fold higher PCDD/F output. This is ascribed to reaction of the small amounts of (chloro)phenols in the mixture. The congener/isomer patterns of the PCDD/Fs for the mixture and with PhCl per se are quite comparable with those found in emissions from incinerators. As carbon is not present nor formed on the catalyst surface, de-novo formation therefrom cannot be involved. Rather condensation of phenolic entities or like precursors must have occurred. Consequences and options to ensure safe application are briefly discussed as well.     

Effect of 2,4-Dichlorophenoxyacetic Acid (2,4-D) on PCDD/F Emissions from Open Burning of Biomass

To understand the effect of leaf-surface pesticides on emissions of PCDD/F during biomass burns, nine combustion experiments simulating the open burning of biomass were conducted. Needles and branches of Pinus taeda (Loblolly pine) were sprayed with the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) at 1 and 10 times the manufacturer's recommended application concentration. The biomass was then dried overnight, burned in an open burn test facility, and emission samples were collected, analyzed, and compared against emission samples from burning untreated biomass. Blank tests and analysis of PCDD/F in the raw biomass were also performed. Emission results from burning a water-sprayed control show a ～20-fold increase in PCDD/F levels above that of the raw biomass alone, implicating combustive formation versus simple volatilization. Results from burns of pine branches sprayed with pesticide showed a statistically significant increase in the PCDD/F TEQ emissions when burning biomass at ten times the recommended pesticide concentration (from 0.22 to 1.14 ng TEQ/kg carbon burned (C(b)), both ND = 0). Similarly, a 150-fold increase in the total PCDD/F congener mass (tetra- to octa-chlorinated D/F) above that of the control was observed (from 52 to 7800 ng/kg C(b)), confirming combustive formation of PCDD/F from 2,4-D. More replicate testing is needed to evaluate effects at lower pesticide concentrations.     

Congener-specific tissue distribution and hepatic sequestration of PCDD/Fs in wild herring gulls from Bohai Bay, North China: comparison to coplanar PCBs

Tissue distribution is an important property of pharmacokinetic behaviors of dioxins to provide information for risk assessment to wild avian species. In this study, concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (coplanar PCBs) were determined in muscle, liver, spleen, kidney, brain, and adipose of wild herring gulls collected from Bohai Bay, North China. Tissue distribution results showed preferential accumulation of PCDD/Fs in liver and of co-PCBs in adipose. The congener patterns of coplanar PCBs were constant in different tissues, but the congener patterns for PCDD/F were tissue-specific. The liver/adipose concentration ratios for PCDD/ Fs were found to increase statistically significantly with log K(ow), providing the quantitative relationship of structure-activity for hepatic sequestration of PCDD/Fs for the first time. Furthermore, this relationship was compared with those developed on the basis of previous results reported in the literature showing that the wild herring gulls in Bohai Bay are still in the exposure period.     

Influence of an industrial waste incinerator as assessed by the levels and congener patterns of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans

To assess the spatial change in the influence of an industrial waste incinerator, a total of 47 soil samples (in continuous manner with distance) and 65 human blood samples (40 within 5 km and 20 at 7 and 12 km) were analyzed for polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs). The influence was not clearly observed both on the soil and blood levels of PCDD/Fs as the levels in the near zone (within 5 km) were not statistically different from those in the far zones at 7 and 12 km. Assessment was conducted on the congener patterns by using principal component analysis and by characterizing the congener fractions as a function of distance. In soil, the congener fractions of 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HxCDF, 1,2,3,6,7,8-HxCDF, 1,2,3,4,6,7,8-HpCDF, and OCDF decreased progressively with the distance. Blood was consistent with soil in that each congener fraction of these PCDFs (except OCDF) was statistically greater in the near zone than the far zones. The decreases in these PCDFs were balanced by OCDD in both soil and blood. It was concluded that although not obviously observed in the contamination levels, the influence of the incinerator was clearly shown by the congener patterns of PCDD/Fs in both soil and blood that changed with distance.     

Dioxin congener patterns in commercial catfish from the United States and the indication of mineral clays as the potential source

Since 1991 the US Department of Agriculture (USDA) has conducted annual surveys of pesticide residues in foods under the Agricultural Marketing Service's Pesticide Data Program (PDP). To assess chemical residues in domestically marketed catfish products, 1479 catfish samples were collected during the 2008–2010 PDPs. A subset of 202 samples was analysed for 17 toxic polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs). The average pattern of the individual PCDD/F congener concentrations in the catfish was rather unique in that it had almost no measurable amounts of polychlorinated dibenzofurans (PCDFs), but all PCDDs were present. This pattern was more dominant in the domestically produced catfish products than in the imported products (China/Taiwan). Comparison of the pattern to known sources of PCDD/Fs showed strong similarities to the pattern of PCDD/Fs found in kaolin clays which have often been used as anti-caking agents in animal feeds. To investigate whether catfish feeds may be the source of the PCDD/Fs found in the catfish, archived catfish feed data from a US Food and Drug Administration (USFDA) database were examined. In 61 out of 112 feed samples, the PCDD concentrations were 50 times higher than the PCDF concentrations and resembled the pattern found in the catfish products and in clays mined in the south-eastern United States. Although the source of PCDD/Fs in domestically marketed catfish products cannot be definitively established, mined clay products used in feeds should be considered a likely source and, given the wide concentration range of PCDD/Fs that has been found in clays, a critical control point for PCDD/Fs entrance to the food supply.     

Clay mediated route to natural formation of Polychlorodibenzo-p-dioxins

Recent studies have documented the ubiquitous occurrence of polychlorodibenzo-p-dioxins and dibenzofurans (PCDD/Fs) of unknown origin in soils and clay deposits. Interestingly, the PCDD/F congener profiles do not match any known natural or anthropogenic source, and global PCDD/F budgets fail to account for the observed levels in soils. To reconcile these observations, clay minerals had been hypothesized to play a central role in the natural in situ synthesis of PCDD/Fs. We recently demonstrated the clay-mediated formation of the most prevalent PCDD congener in soils, octachlorodibenzo-p-dioxin (OCDD), supporting this hypothesis. Here we report the formation of the direct precursors ("predioxins") of the most toxic PCDD congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), and of 1,2,4,7,8-pentachlorodizenzodioxin (1,2,4,7,8-PeCDD), and two additional dimers, from the reaction of 2,4,5-trichlorophenol (2,4,5-TCP) with Fe(III)-montmorillonite clay. We propose plausible reaction pathways, each initiated by single electron transfer from 2,4,5-TCP to Fe(III)-montmorillonite forming the 2,4,5-TCP radical cation. The operative reaction mechanisms, inferred from experimental results, are supported by quantum mechanical calculations. The key role of montmorillonite is apparently to stabilize the reactive radical cation intermediate. Fortuitously, PCDD formation reactions on clay surfaces are more facile for less toxic higher chlorinated congeners like OCDD, as predicted by the proposed reaction mechanism and consistent with the observed PCDD congener distributions in soils. Importantly, increasing the toxicity equivalency factor of OCDD would immediately cause many soils to exceed PCDD regulatory levels due to the predominance of this congener.     

Facilitated transport of dioxins in soil following unintentional release of pesticide-surfactant formulations

Colloids such as surfactant micelles can act as transport facilitators for highly lipophilic, generally immobile contaminants in soil. Following a fire at a pesticide facility, this study investigated vertical and lateral migration of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in heterogeneous soil beneath bunded ponds, where contaminated wastewater containing high surfactant loads was stored until remediation. Initially, surface and subsurface soil was obtained during excavation, and subsequently intact cores to 5.7 m were collected. ΣPCDD/F concentrations were elevated in the wastewater (15-81 ng/L) and correspondingly in pond surface soils (6.1-61 ng/g). Maximum ΣPCDD/F concentrations were, however, observed at 2-2.5 m depth (68-130 ng/g), far below their expected mobility range based on physicochemical properties. Congener specific analysis further indicated that PCDD/F mobility was reversed, with the least water-soluble congener migrating to the greatest extent. The presence of higher chlorinated PCDD/Fs throughout a core collected in the direction of groundwater flow indicated subsequent lateral transport. These results provide field evidence for rapid vertical migration (2.4 m in <4 months) of highly lipophilic PCDD/Fs and suggest surfactant facilitated transport as the dominant transport mechanism. Quantification and evaluation of such fundamental changes in contaminant transport and fate in the presence of surfactants is required to identify areas at risk of groundwater contamination.     

Associations of diet with body burden of dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (PCBs): observations on pregnant women from central Taiwan.

The aim of this study was to examine the relationship between placental polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/F) and polychlorinated biphenyls (PCBs) toxic equivalent (TEQ) levels and the consumption of various food types in pregnant women from central Taiwan. Placental PCDD/Fs and PCB congener TEQ levels were evaluated in 109 pregnant women and dietary information was obtained by questionnaire. TEQ levels of PCDD/Fs and PCBs were positively associated with age and annual family incomes (p < 0.05). PCDD/F TEQs were significantly associated with freshwater fish and dairy product consumption after adjustment for age and body mass index (BMI) (p < 0.05). For PCB TEQs, significant associations were detected for saltwater fish consumption (p < 0.05). In summary, positive correlations were found between freshwater fish and dairy product intake and PCDD/F levels, and a marginal correlation between saltwater fish intake and the body burden of PCBs in pregnant women from central Taiwan. Risk assessment of PCDD/Fs and PCB in fishery products is warranted in a future study to quantify the benefits of fish consumption during the perinatal period.