The absence and application of stable carbon isotopic fractionation during the reductive dechlorination of polychlorinated biphenyls

A bacterial enrichment culture (specific to doubly flanked chlorine removal) reductively dechlorinated 2,3,4,5-tetrachlorobiphenyl (2,3,4,5-CB) to 2,3,5-trichlorobiphenyl (2,3,5-CB) in aqueous media. Approximately 90% conversion to 2,3,5-CB occurred after 90 days, with no other products formed. The delta13C values of 2,3,4,5-CB and 2,3,5-CB were relatively constant over the course of the reaction, indicating a very small or no isotope effect. In addition, compound-specific delta13C analysis performed for every congener in three different lots of Aroclor 1268 showed an intrinsic isotopic trend of decreasing 13C abundance with increasing chlorine content, similar to observations in other commercial mixtures of polychlorinated biphenyls (PCBs). The results of this laboratory study suggest that microbial reductive dechlorination of PCBs in contaminated sediments will create congeners with more depleted delta13C values than native PCBs of similar chlorination. Such information may provide additional evidence for the occurrence of this process and aid in further understanding the biogeochemistry of these compounds.     

Using extrathermodynamic relationships to model the temperature dependence of Henry's law constants of 209 PCB congeners

Our previous measurements of the temperature dependencies of Henry's law constants of 26 polychlorinated biphenyls (PCBs) showed a well-defined linear relationship between the enthalpy and the entropy of phase change. Within a homologue group, the Henry's law constants converged to a common value at a specific isoequilibrium temperature. We use this relationship to model the temperature dependencies of the Henry's law constants of the remaining PCB congeners. By using experimentally measured Henry's law constants at 11 degrees C for 61 PCB congeners described in this paper combined with the isoequilibrium temperatures from our previous measurements of Henry's law constants of 26 PCB congeners, we have derived an empirical relationship between the enthalpies and the entropies of phase change for these additional PCB congeners. A systematic variation in the enthalpies and entropies of phase change was found to be partially dependent on the chlorine number and substitution patterns on the biphenyl rings, allowing further estimation of the temperature dependence of Henry's law constants for the remaining 122 PCB congeners. The enthalpies of phase change for all 209 PCB congeners ranged between 10 and 169 kJ mol(-1), where the enthalpies of phase change decreased as the number of ortho chlorine substitutions on the biphenyl rings increased within homologue groups. These data are used to predict the temperature dependence of Henry's law constants for all 209 PCB congeners.     

Polychlorinated naphthalenes, -biphenyls, -dibenzo-p-dioxins, and -dibenzofurans in double-crested cormorants and herring gulls from Michigan waters of the Great Lakes

Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), naphthalenes (PCNs), and biphenyls (PCBs) were measured in eggs of double-crested cormorants and herring gulls collected from Michigan waters of the Great Lakes. Concentrations of PCNs in eggs of double-crested cormorants and herring gulls were in the ranges of 380-2400 and 83-1300 pg/g, wet wt, respectively. Concentrations of 2,3,7,8-substituted PCDDs and PCDFs were 10-200 times less than those of PCNs in eggs whereas those of total PCBs (380-7900 ng/g, wet wt) were 3-4 orders of magnitude greater. While the profile of PCB isomers and congeners between double-crested cormorants and herring gulls was similar, the PCN isomer profile differed markedly between these two species. PCN congeners 66/67 (1,2,3,4,6,7/1,2,3,5,6,7) accounted for greater than 90% of the total PCN concentrations in herring gulls, whereas their contribution to total PCN concentrations in double-crested cormorants ranged from 18 to 40% (mean, 31%). The ratios of concentrations of PCDDs to PCDFs were greater in herring gulls than in double-crested cormorants collected from the same locations, suggesting the ability of the former to metabolize PCDF congeners relatively rapidly. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TEQs) contributed by PCNs in double-crested cormorant and herring gull eggs were 2-3% of the sum TEQs of PCBs, PCDDs, PCDFs, and PCNs. PCB congener 126 (3,3',4,4',5-PeCB) accounted for 57-72% of the total TEQs in double-crested cormorant and herring gull eggs.     

Abundances, depositional fluxes, and homologue patterns of polychlorinated biphenyls in dated sediment cores from the Pearl River Delta, China

Despite the recent efforts to investigate the distribution and fate of persistent organic pollutants in the tropical and subtropical regions of Asia, very little was known about the temporal change of polychlorinated biphenyls (PCBs) in the environmental ecosystem of China. In this study, three dated sediment cores collected from the Pearl River Delta of southern China were analyzed for a large suite of PCB congeners, from which the temporal profiles of PCB abundances, fluxes, and homologue patterns were constructed. The sedimentary inventories of total PCBs at the sampling sites ranged from 480 to 1310 ng/cm2, at the low end of the worldwide figures. Although production and use of PCBs have been banned or highly restricted in China since the early 1980s, the fluxes of total PCBs continued to increase in the Pearl River Delta sediments. There was a concurrent increase of PCB fluxes and gross domestic product per capita in the region from 1980 to 1997, and a decline of agricultural land use was evident at the same time. Apparently, large-scale land transform since the early 1980s as well as emissions from the PCB-containing electrical equipments were responsible for the sharp rise of PCB fluxes in the recent sediments. The difference in the PCB homologue patterns from 1940 to the mid-1970s was probably indicative of the different timelines of PCB usage in Macao/Hong Kong and mainland China and the differenttypes of technical PCBs commercially used. PCBs were detectable in sediments deposited well before the time frame when production of PCBs began (before 1930) and were relatively enriched in the less chlorinated homologue groups (3Cl and 4Cl PCBs), suggesting the downward mobility of lightly chlorinated PCB congeners in the sediment column.     

Long-term recovery of PCB-contaminated sediments at the Lake Hartwell superfund site: PCB dechlorination. 2. Rates and extent

This paper reports on extensive polychlorinated biphenyl (PCB) dechlorination measured in Lake Hartwell (Pickens County, SC) sediments. Vertical sediment cores were collected from 18 locations in Lake Hartwell (Pickens County, SC) and analyzed in 5-cm increments for PCB congeners. The preferential loss of meta and para chlorines with sediment depth demonstrated that PCBs in the sediments underwent reductive dechlorination after burial. Notably, ortho chlorines were highly conserved for more than 5 decades; since the first appearance of PCBs, ca. 1950-1955. These dechlorination characteristics resulted in the accumulation of lower chlorinated congeners dominated by ortho chlorine substituents. Dechlorination rates were determined by plotting the numbers of meta plus para chlorines per biphenyl molecule (mol of chlorine/mol of PCB) with sediment age. Regression analyses showed linear correlations between meta plus para chlorine concentrations with time. The average dechlorination rate was 0.094 +/- 0.063 mol of Cl/mol of PCB/yr. The rates measured using the 2001 cores were approximately twice those measured using the 2000 cores, most likely because the 2001 cores were collected only at transects O, L, and I, which had the highest rates measured in 2000. An inverse of the dechlorination rates indicated that 16.4 +/- 11.6 yr was required per meta plus para chlorine removal (ranging from 4.3 to 43.5 yr per chlorine removal). The rates determined from this study were 1-2 orders of magnitude lower than rates reported from laboratory microcosm studies using Hudson River and St. Lawrence River sediments, suggesting that dechlorination rates reported for laboratory experiments are much higher than those occurring in situ.     

Characterization of the PCB substrate range of microbial dechlorination process LP

We have characterized the substrate range of Process LP, a PCB dechlorination activity mediated by anaerobic bacteria, in Housatonic River sediment (Lenox, MA). Process LP has the rare ability to remove unflanked para chlorines from polychlorinated biphenyls (PCBs). We used 2,6-difluoro-4-chlorobiphenyl (DFCB) to activate Process LP in anoxic sediment microcosms and tested its ability to dechlorinate 34 potential PCB substrates, all of which are significant components of PCB mixtures found in contaminated sediments. We used gas chromatography-mass spectrometry to monitor the dechlorination of DFCB and PCBs and the appearance of products. The preferred substrates for Process LP were PCB congeners in which the target para chlorines were flanked by meta chlorines, such as those having 3,4- and 2,4,5-chlorophenyl rings. The unflanked para chlorines on PCBs with 2,4-, 2,4,6-, and sometimes 4-chlorophenyl rings, were also substrates. Furthermore, the data revealed that Process LP can also meta-dechlorinate 2,3-, 2,3,4-, and 2,3,5-chlorophenyl groups on some congeners. A single ortho chlorine on the unattacked ring generally enhanced dechlorination activity, but the presence of 3 or 4 ortho chlorines or a 4-chlorophenyl group decreased the dechlorination efficiency. PCBs with 2,4-, 2,4,6-, 2,3-, and 2,3,5-chlorophenyl rings are often terminal dechlorination products of other microbial dechlorination activities. Since these PCBs are substrates for Process LP, this dechlorination activity works especially well in tandem with other dechlorination activities and further reduces the toxicity and persistence of PCBs. The data presented here will facilitate the construction of accurate models to interpret in situ PCB dechlorination and predict PCB fate.     

Accumulation of atmospheric and sedimentary PCBs and toxaphene in a Lake Michigan food web

Seston, sediment, settling organic matter, and food web members were collected from Grand Traverse Bay, Lake Michigan, between April 1997 and September 1998 to examine PCB and toxaphene biomagnification. Stable isotopes of nitrogen and carbon were analyzed in samples and used to establish trophic structure of the food web and to determine the importance of atmospheric versus sedimentary sources in delivering PCBs to the food web. Nitrogen isotopes were confounded by multiple variables in this system, particularly seasonal variation, and did not display a simple pattern of enrichment among trophic levels. However, delta13C displayed little seasonal variation and was positively correlated with PCB concentrations among food web members (r2 = 0.69). Plots of delta13C vs PCBs separate food web members into three distinct groupings comprised of invertebrates, primary forage fish, and predatory fish. Stable isotope values of the primary organic sources indicate that the atmosphere, and not the sediment, is the most likely source of PCBs to the food web of Lake Michigan. Additionally, we suggest that seston may be important in delivering PCBs to pelagic food web members and species that receive a majority of their nutrition through pelagic sources. In contrast, settling particles are implicated in delivering PCBs to benthic organisms and Mysis relicta.     

Occurrence and biomagnification of polychlorinated naphthalenes and non- and mono-ortho PCBs in Lake Ontario sediment and biota

Biota and surface sediments collected from Lake Ontario were analyzed for polychlorinated naphthalenes (PCNs) and non- and mono-ortho-substituted polychlorinated biphenyls (n/ m-o-PCBs) to compare bioaccumulation behavior of these classes of dioxin-like chemicals in a food web from the Great Lakes. Mean sigmaPCN concentrations (tri-octaCN) ranged from 14 +/- 9 pg/g in plankton to 3500 +/- 3200 pg/g (wet weight) in lake trout while sediments contained from 21 to 38 ng/g (dry weight). Principal components analysis of PCN congener patterns indicated that chlorine substitution determined which congeners favored accumulation (e.g., CN-42, -52, -60, -66, -67, and -73), while others may be subject to metabolism. The bioaccumulative congeners exhibited similar trophic magnification factors (TMFs; 1.23-1.42) and biomagnification factors (BMFs; 5.5-8.6) to the n/m-o-PCBs for the trout/weighted diet relation, although BMFs for a benthic feeding relationship (slimy sculpin/Diporeia) indicated that the n/m-o-PCBs were more bioavailablethroughthe benthic pathway. PCNs contribute significantly to the burden of dioxin-like compounds in Lake Ontario biota, contributing between 12 and 22% of total PCN + PCB TEQ in lake trout and up to 69% in benthic organisms.     

Polychloronaphthalenes and other dioxin-like compounds in Arctic and Antarctic marine food webs

Here we report accumulation patterns of polychlorinated naphthalenes (PCNs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and pesticides (HCB, p,p'DDE) in polar organisms (polar bear from Alaskan Arctic and krill, sharp-spined notothen, crocodile icefish, Antarctic silverfish, Adélie penguin, South polar skua, and Weddell seal from the Ross Sea, Antarctica). PCNs, found in most of the samples, ranged from 1.5 pg/g in krill to 2550 pg/g in South polar skua on a wet weight basis. Lower chlorinated PCNs were the predominant congeners in organisms except skua and polar bear that showed similar PCN homologue patterns. PCDD/F concentrations were <90 pg/g wet wt in polar organisms; PCDD congeners showed peculiar accumulation patterns in different organisms. Correlation existed between PCN and PCB concentrations. PCB, HCF, and p,p'DDE levels were the highest in skua liver (11,150 ng/g wet wt, 345 ng/g wet wt, and 300 ng/g wet wt, respectively). Contribution of PCNs to 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQ) was negligible (<0.1%) because of the lack of most toxic congeners. The highest TEQ was found in South polar skua liver (45 pg/g, wet weight). This is the first study to document the occurrence of PCNs in Antarctic organisms. High levels of dioxin-like chemicals in skua suggest the importance of intake via diet and migration habits, thus POP detection can be useful to trace migration behavior. Moreover, POP concentrations in penguin and skua eggs prove their transfer from the mother to eggs.     

Atmospheric PCB concentrations at Terra Nova Bay, Antarctica

Concentrations of gas-phase polychlorobiphenyls (PCBs) were studied over an austral summer at a site in Terra Nova Bay, Antarctica. Gas-phase concentrations of individual PCB congeners in the atmosphere of Terra Nova Bay ranged from below the detection limit to 0.25 pg m(-3), with a mean concentration of sigmaPCB of 1.06 pg m(-3). The PCB profile was dominated by lower-chlorinated PCB congeners; in fact >78% of the total PCB content was due to congeners with 1-4 chlorine atoms and only about 10% with 5-7 chlorines, whereas higher-chlorinated PCB congeners were below detection limits. The mean sigmaPCB concentration obtained in this study were lower than those reported in previous Antarctic studies. Temporal concentration profiles of sigmaPCB do not correspond to seasonal temperature changes. In consideration of the low PCB concentrations observed, the studies with the wind roses, the regression between In P(PCB) and T(-1), and the distribution of congeners, we can hypothesize that PCB local source contributions are not very important, whereas long-distance transport is the prevalent factor bringing PCBs to Terra Nova Bay.     

Occurrence of polybrominated diphenyl ethers and polychlorinated biphenyls in shark liver oil supplements

Results are reported of a pilot survey of concentrations of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in shark liver oil supplements. Eleven brands of dietary supplements were analysed using an isotope dilution GC/MS method. Total concentrations of 10 PBDE congeners (BDE-28, -47, -49, -66, -99, -100, -153, -154, -155 and -183) ranged from 0.1 to 53 ng g^-1 oil weight and total concentrations of six PCB congeners (CB-28/31, -52, -118, -153 and -180) in the samples ranged from 16 to 340 ng g^-1 oil weight (undetected values are not included). Two brands of Japanese deep-sea shark liver oil contained the highest levels of PBDEs (49-53 ng g^-1 oil weight) and PCBs (290-340 ng g^-1 oil weight). These results indicate that PBDEs may have entered Japanese deep-sea waters.     

PCBs, PCDD/Fs, and organochlorine pesticides in farmed Atlantic salmon from Maine, eastern Canada, and Norway, and wild salmon from Alaska

Farmed Atlantic salmon (Salmo salar) from Maine and eastern Canada, wild Alaskan Chinook salmon (Oncorhynchus tshawytscha), and organically farmed Norwegian salmon samples were analyzed for the presence of polychlorinated biphenyls (PCBs), dioxin-like PCBs, polychlorinated dibenzo-p-dioxins (PCDDs), dibenzo-p-furans (PCDFs), and chlorinated pesticides. PCDD and PCDF congeners were not detected in > 80% of the samples analyzed. Total PCB concentrations (7.2-29.5 ng/g, wet weight, ww) in the farmed salmon were significantly higher than those in the wild Alaskan Chinook samples (3.9-8.1 ng/g, ww). Concentrations of PCBs, WHO PCB TEQs, and chlorinated pesticides varied significantly by region. PCB and WHO PCB TEQ concentrations in farmed salmon from eastern Canada were lower than those reported in samples collected two years earlier, possibly reflecting recent industry efforts to lower contaminant concentrations in feed. Organically farmed Norwegian salmon had the highest concentrations of PCBs (mean: 27 ng/g, ww) and WHO PCB TEQs (2.85 pg/g,ww); their TEQ values are in the higher range of those reported in farmed salmon from around the world. Removal of skin from salmon fillets resulted in highly variable reductions of lipids and contaminants, and in some skin-off samples, contaminant levels were higher, suggesting that skin removal does not protect the consumer from health risks associated with consumption of farmed salmon.     

A survey of extractable persistent organochlorine pollutants in Chinese commercial yogurt

Eighteen Chinese commercial brands of yogurt were collected from supermarkets from December 2002 to April 2003, for characterization of organochlorine pesticides (OCP) and polychlorinated biphenyls (PCB). Besides monitoring OCP and PCB by gas chromatography, the levels of extractable persistent organochlorine (EPOCl; i.e., sulfuric acid-resistant EPOCl) were also determined by instrumental neutron activation analysis. The results indicated that the contamination pattern of the selected OCP and PCB were in the order of dichlorodiphenyltrichloroethanes (DDT) approximately hexachlorocyclohexanes (HCH) > aldrin > or = chlordanes > or = heptachlor epoxide and 4-6 chlorinated biphenyls (CB) > 7-10 CB, respectively. Furthermore, beta-HCH, and 1,1-dichloro-2,2-bis (p-chlorophenyl) ethylene were the predominant isomers of HCH and DDT residues in yogurt, and PCB with 4,4'- and 2,3,5- substitution patterns were the predominant congeners of PCB residues. Also, the results indicated that the mean level of total chlorine in the identified organochlorine species was below 4% of EPOCl in yogurt, which implied that more than 96% of EPOCl measured in yogurt samples could not be accounted for by selected OCP and PCB.     

Congener-specific composition of polychlorinated naphthalenes, coplanar PCBs, dibenzo-p-dioxins, and dibenzofurans in the Halowax series

Concentrations and congener compositions of polychlorinated naphthalenes (PCNs), coplanar polychlorinated biphenyls (Co-PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs) were determined in seven Halowax (HW) preparations. In HW 1000 and 1031, low-chlorinated naphthalenes (CNs) and in HW 1051, highly chlorinated naphthalenes were dominant, whereas tri- through penta-CNs were major homologues in other Halowaxes. Concentrations of Co-PCBs were in the range of 2.0-2600 ng/g. CB 105 and 118 were dominant in all Halowaxes. Concentrations of PCDDs/DFs were in the range of 92-5900 ng/g. The 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) in Halowaxes calculated from the amounts of PCNs, Co-PCBs, and PCDDs/DFs were in the range of 2800-220,000 ng-TEQ/g. PCNs accounted for most of the total TEQs in Halowaxes, and the contribution of PCDDs/DFs and Co-PCBs to total TEQs was less than 1/1000 that of PCNs. Congeners that most significantly contributed to TEQs were CN 69, 73, 70, and 63. Total TEQs roughly estimated from the Japanese production of technical PCNs, 210 kg-TEQ, was about half from technical PCBs, 440 kg-TEQ on average.     

Current combustion-related sources contribute to polychlorinated naphthalene and dioxin-like polychlorinated biphenyl levels and profiles in air in Toronto,Canada

Polychlorinated naphthalenes (PCNs) and mono- and non-ortho substituted PCBs were analyzed in air from two sites in Toronto, Ontario, Canada to determine whether current combustion-related sources contribute to the levels and profiles of PCNs found in urban air. High-volume air samples were collected periodically at the University of Toronto (UT, a downtown site) and in north Toronto at the Meteorological Service of Canada (MSC). SigmaPCN concentrations ranged from 31 to 78 pg m(-3) at UT and from 7 to 84 pg m(-3) at MSC with concentrations lower at MSC than UT for paired samples. Ambient air congener profiles contrasted between the two sites with MSC profiles indicating inputs from combustion-related sources when compared to combustion fly ash and technical PCN and PCB mixture profiles. Combustion markers, including CN-44, -29, and -54, the more toxic CN-66 and -67 congeners, and non-ortho PCBs, were enriched in air at MSC on a mass percent basis in several samples. As a result, CN-66/67 contributed proportionally more to dioxin toxic equivalents at MSC than at UT. Downtown air PCN profiles resembled those of technical PCN and PCB mixtures, reflecting evaporative emissions from past uses, while PCN levels and profiles at MSC, a more industrialized location, are also influenced by current combustion sources, contributing as much as an estimated 54% of sigmaPCN in samples collected.     

Changes in enantiomeric fractions during microbial reductive dechlorination of PCB132, PCB149, and araclor 1254 in Lake Hartwell sediment microcosms

The enantioselectivity of microbial reductive dechlorination of chiral PCBs in sediments from Lake Hartwell, SC, was determined by microcosm studies and enantiomer-specific GC analysis. Sediments from two locations in the vicinity of the highest levels of PCB contamination were used as inocula. Dechlorination activity was monitored by concentration decreases in the spiked chiral PCBs and formation of dechlorination products using both achiral and chiral chromatography. Live microcosms spiked with PCB132 (234-236) exhibited dechlorination of PCB132 to PCB91 (236-24) and PCB51 (24-26). Meta dechlorination was the dominant mechanism. Microcosms spiked with PCB149 (245-236) exhibited preferential para dechlorination of PCB149 to PCB95 (236-25), followed by meta dechlorination to PCB53 (25-26) and subsequently PCB19 (26-2). Dechlorination of chiral PCB132 and PCB149 was not enantioselective. In Aroclor 1254-spiked microcosms, reductive dechlorination of PCB149 also was nonenantioselective. These results suggest that dechlorinating enzymes responsible for the dehalogenation of the chiral PCB132 and PCB149 congeners bind the two enantiomers equally. Reductive dechlorination of PCB91 and PCB95, however, occurred in an enantioselective manner, indicating that the dechlorinating enzymes for these PCBs are enantiomer-specific. The chlorine substitution pattern on the biphenyl ring appears to influence whether reductive dechlorination of chiral PCB congeners is enantioselective. Enantioselective PCB dechlorination by the microbial population of Lake Hartwell sediments occurs for select chiral PCBs; thus, certain chiral PCBs might be useful as markers for in situ reductive dechlorination.     

Distribution of phthalate esters in a marine aquatic food web: comparison to polychlorinated biphenyls

Dialkyl phthalate esters (DPEs) are widely used chemicals, with over 4 million tonnes being produced worldwide each year. On the basis of their octanol-water partition coefficients (Kow), which range from 10(1.61) for dimethyl phthalate to 10(9.46) for di-iso-decyl phthalate, certain phthalate esters have the potential to bioconcentrate and biomagnify in aquatic food webs. However, there are no reported field studies on the trophodynamics of phthalate ester in aquatic food webs. This study reports the distribution of 8 individual phthalate esters (i.e., dimethyl, diethyl, di-isobutyl, di-n-butyl, butylbenzyl, di(2-ethylhexyl), di-n-octyl, and di-n-nonyl) and 5 commercial isomeric mixtures (i.e., di-iso-hexyl (C6), di-iso-heptyl (C7), di-iso-octyl (C8), di-iso-nonyl (C9), and di-iso-decyl (C10)) in a marine aquatic food web. DPE concentrations were determined in 18 marine species, representing approximately 4 trophic levels. Co-analysis of DPEs and 6 PCB congeners (i.e., PCB-18, 99, 118, 180, 194, and 209) in all samples produced a direct comparison of the bioaccumulation behavior of PCBs and DPEs. Lipid equivalent concentrations of the PCBs increased with increasing trophic position and stable isotope ratios (delta15N). The Food-Web Magnification Factor (FWMF) of the PCB congeners ranged from 1.8 to 9.5. Lipid equivalent concentrations of low and intermediate molecular weight DPEs (i.e., C1-C7 DPEs: dimethyl, diethyl, di-iso-butyl, di-n-butyl, benzylbutyl, and C6 and C7 isomers) did not exhibit statistically significant trends with trophic position or stable nitrogen isotope ratios (delta15N) in the food web and FWMFs were not significantly different from 1. Lipid equivalent concentrations of the high-molecular-weight DPEs (i.e., C8-C10 DPEs: di(2-ethylhexyl), di-n-octyl, di-n-nonyl, C8, C9, and C10) declined significantly with increasing trophic position and stable isotope ratios (delta15N), producing FWMFs between 0.25 and 0.48. These results show that all DPEs tested did not biomagnify in the studied aquatic food web whereas PCBs did biomagnify.     

Stable carbon isotope ratio analysis of anhydrosugars in biomass burning aerosol particles from source samples

A new method for stable carbon isotope ratio analysis of anhydrosugars from biomass burning aerosol particle source filter samples was developed by employing Thermal Desorption--2 Dimensional Gas Chromatography--Isotope Ratio Mass Spectrometry (TD-2DGC-IRMS). Compound specific isotopic measurements of levoglucosan, mannosan, and galactosan performed by TD-2DGC-IRMS in a standard mixture show good agreement with isotopic measurements of the bulk anhydrosugars, carried out by Elemental Analyzer--Isotope Ratio Mass Spectrometry (EA-IRMS). The established method was applied to determine the isotope ratios of levoglucosan, mannosan, and galactosan from source samples collected during combustion of hard wood, softwood, and crop residues. δ(13)C values of levoglucosan were found to vary between -25.6 and -22.2‰, being higher in the case of softwood. Mannosan and galactosan were detected only in the softwood samples showing isotope ratios of -23.5‰ (mannosan) and -25.7‰ (galactosan). The isotopic composition of holocellulose in the plant material used for combustion experiments was determined with δ(13)C values between -28.5 and -23.7‰. The difference in δ(13)C of levoglucosan in biomass burning aerosol particles compared to the parent fuel holocellulose was found to be -1.89 (±0.37)‰ for the investigated biomass fuels. Compound specific δ(13)C measurements of anhydrosugars should contribute to an improved source apportionment.     

Degradation of PCBs in a marine sediment treated with ionizing and UV radiation

Radiolytic (electron beam) and photolytic (ultraviolet, UV) dechlorination of polychlorinated biphenyls (PCBs) in a marine sediment are described. Samples of a PCB-laden marine sediment, Standard Reference Material (SRM) 1944, NewYork/New Jersey Waterway Sediment, have been mixed with aqueous alcohol solutions and irradiated with an electron beam or photolyzed. Additives, such as alcohol, enhance the radiolytic yield and PCB dechlorination. In the electron beam irradiated samples, the concentrations of 29 PCB congeners decrease with irradiation dose. At the highest dose (500 kGy), the total concentration of PCBs is decreased by 83%. Photolysis leads to little dechlorination, but photolysis with added triethylamine leads to dechlorination (about 60%). It is likely that photolysis under optimal conditions (other additives, exposure time) may be as effective as electron beam radiolysis for the dechlorination of PCBs in sediment.     

Assessment of natural attenuation via in situ reductive dechlorination of polychlorinated biphenyls in sediments of the Twelve Mile Creek arm of Lake Hartwell, SC

Polychlorinated biphenyl (PCB)-contaminated sediment cores taken from five locations in Lake Hartwell, SC, with an increasing distance from the point source were evaluated for the presence of in situ reductive dechlorination of PCBs on the basis of a comparative congener-specific analysis of PCB distribution profiles between historical (1987) and current (1998) sediments from the same sites. A layer of 1998 sediment that was equivalent to 1987 sediment was determined by direct comparison of total PCB depth profiles after correction for any sedimentation that occurred at each location since 1987. Natural capping of contaminated sediments with the continued deposition of new sediments was observed in all locations except the one farthest from the source area. The residual PCB congeners accumulated in the field samples did not vary from site to site. Certain PCB congeners (e.g., 236-24 + 34-34, 245-25, and 23-4 CB) decreased with time and with depth along with an increase in lower chlorinated PCB congeners in all sampling locations. A similarity in distribution profiles between dechlorinated PCBs in laboratory microcosms and in the field samples was observed. These results provide supporting evidence that in situ reductive dechlorination has occurred in the Twelve Mile Creek arm of Lake Hartwell. Several sediment layers, particularlythe sites with highest PCB concentration, showed similar PCB distribution profiles between 1987 and 1998. An additional change in chlorine distribution between 1987 and 1998 at most "equivalent" depths was not observed. The ortho- and para-substituted congeners that accumulated during dechlorination of Aroclor 1254 after nearly 1 yr of incubation in the laboratory were the prominent residual products in all field samples. At a few locations and depths, evidence for dechlorination at surprisingly low concentrations (1-5 ppm) was observed. These results confirm that in situ reductive dechlorination of PCBs is operating at a very slow rate and may have been at a plateau since 1987 for certain depths and certain locations.