Field observation and modeling of dissolved fraction sediment-water exchange coefficients for PCBs in the Hudson River

Chemical fate and transport models that simulate sediment-water exchange of contaminants typically employ empirically determined sediment-water exchange coefficients for the dissolved fraction to describe the net effect of poorly understood mechanisms. This paper presents field-derived observations of the coefficient for 12 PCB congeners and two PCB mixtures in the Thompson Island Pool, Hudson River, and also presents an evaluation of a theoretical sediment-water exchange model. An extensive PCB data set was used to compute apparent coefficients for PCBs in the pool. Average exchange coefficients for the 12 congeners ranged from 2.6 to 18.8 cm/ day, and results showed a strong seasonal dependence. Peak coefficient values occurred in mid-May to early July, preceding peak water temperatures by 1 month and lagging the spring high-flow period. The coefficients increase with increasing partition coefficients, suggesting a dependence on congener properties. The large magnitude of the coefficients and the variation among the congeners is inconsistent with the pore-water molecular-diffusion transport process. A theory-based, mechanistic two-layer model reproduces the nonlinear relationship between the sediment-water exchange coefficients and partition coefficients. This model includes transfer through the mixed sediment layer by bioturbation and diffusion transfer through a water-side boundary layer governed by flow velocity. Results suggest that this algorithm can provide increased accuracyto future system-level fate and transport models for hydrophobic chemicals. The seasonal variation in the transfer coefficient appears to be a poorly understood interaction of physical and biological processes and merits further study.     

Addition of activated carbon to sediments to reduce PCB bioaccumulation by a polychaete (Neanthes arenaceodentata) and an amphipod (Leptocheirus plumulosus)

This work examines the effects of adding coke or activated carbon on the bioavailability of polychlorinated biphenyls (PCBs) in contaminated sedimentfrom South Basin at Hunters Point, San Francisco Bay. We show with 28-day sediment exposure tests that PCB bioaccumulation in a polychaete (Neanthes arenaceodentata) is reduced by 82% following 1-month contact of sediment with activated carbon and by 87% following 6-months contact of sediment with activated carbon. PCB bioaccumulation in an amphipod (Leptocheirus plumulosus) is reduced by 70% following 1-month contact of sediment with activated carbon and by 75% after 6-months contact of sediment with activated carbon. Adding coke had a negligible effect on reducing PCB bioaccumulation, probably because of the low specific surface area and the slow kinetics of PCB diffusion intothe solid coke particles. Reductions in congener bioaccumulation with activated carbon were inversely related to congener Kow, suggesting that the efficacy of activated carbon is controlled by the mass-transfer rate of PCBs from sediment and into activated carbon. We find that reductions in aqueous PCB concentrations in equilibrium with the sediment were similar to reductions in PCB bioaccumulation. While no lethality was observed following activated carbon addition, growth rates were reduced by activated carbon for the polychaete, but not for the amphipod, suggesting the need for further study of the potential impacts of activated carbon on exposed communities. The study suggests that treatment of the biologically active layer of contaminated sediments with activated carbon may be a promising in-situ technique for reducing the bioavailability of sediment-associated PCBs and other hydrophobic organic compounds.     

Source apportionment of polychlorinated biphenyls in the tidal Delaware River

The Delaware River, similar to many surface water bodies throughout the United States, is impaired due to polychlorinated biphenyl (PCB) concentrations that exceed the federal water quality standard. A total maximum daily load (TMDL) for PCBs in the Delaware was promulgated in 2003 after construction of a detailed water quality model that relied upon estimated PCB loadings from sources such as wastewater treatment plant effluents, contaminated sites, and tributaries. The purpose of this project was to corroborate this loading estimate by analyzing ambient water column data on PCB concentrations in the Delaware River via positive matrix factorization (PMF) in order to identify covarying congener patterns that are, in theory, associated with sources. The PMF program identified six factors (covarying congener patterns) that appear to be associated with sources, such as sediment resuspension, contaminated sites, and wastewater effluents and combined sewer overflows (CSOs). PCB 11 was found to be a useful tracer for CSO/ wastewater inputs despite the fact that no known dye manufacturers exist in the watershed. This analysis generally corroborates the PCB loading estimate used in the water quality model.     

Statistical method to evaluate the occurrence of PCB transformations in river sediments with application to Hudson River data

Polychlorinated biphenyls (PCBs) were produced in the mid 1900s for industrial use. The term PCBs refers to 209 theoretically possible chlorinated compounds of the biphenyl molecule (congeners). The number and location of the chlorines govern both the environmental fate and toxicity of each congener. Changes in the distribution of congeners in river sediments can result from congener transformation and/or preferential congener transport. This study exploits the distribution of PCB congeners, specifically congeners that maintain a constant ratio relationship in the commercially manufactured PCB mixtures (Aroclors), to quantify the likelihood of congener distribution shifts in river sediment. By using relative abundances, the influence of total PCB bias is eliminated. Correlated congeners (tracker pairs) maintain a constant relative proportion in sequentially more-highly chlorinated Aroclors, thus there is no need to know the source contaminating Aroclors a priori. Using the Frame et al. database of Aroclor congener distributions, 276 pairs of correlated congeners, constructed from 95 individual congeners, are identified. A comparison study of Aroclors and Hudson River sediments included 218 of the 276 tracker pairs. Conclusive evidence of a shift in the congener proportions is found in 120 of the 218 cases, a much greater number than expected if no change in congener distribution had occurred.     

Milwaukee, WI, as a source of atmospheric PCBs to Lake Michigan

A field study of atmospheric PCBs in Milwaukee, WI, U.S.A. was conducted on the shore of Lake Michigan. We believe this is the first report of atmospheric PCBs in Milwaukee, although PCBs are well-known to contaminate the sediments of the Milwaukee River and Outer Harbor. Concentrations of PCBs collected during the June 2001 study are similar to concentrations in other urban-industrial areas and higher than PCBs in background air. The average sigmaPCB (sum of 88 congener groups) gas-phase concentration in Milwaukee was 1.9 ng m(-3)+/-standard deviation 0.78 ng m(-3). The average and standard deviation for the particulate-associated PCBs are 0.05+/-0.02 ng m(-3). Particulate-phase PCBs account for less than 5% of the total atmospheric concentration. PCBs in Milwaukee air are a source of PCBs to Lake Michigan. Calculated net gas exchange fluxes predicted forthe Milwaukee sampling period ranged from -60 to -400 ng m(-2) d(-1), where net deposition is indicated by the negative sign. Calculated particle-associated PCB deposition ranged from 80 to 500 ng m(-2) d(-1). Most of the particle-phase deposition flux is a result of coarse particle deposition and decreases rapidly with distance from shore. Under typical meteorological conditions, particle-associated PCBs depositional flux to the lake surface decreases by 90% within 40 km. For net gas-exchange, the flux reaches zero at about the same distance. At greater distances, particle-phase PCB deposition is negligible, and PCBs are volatilizing at a higher rate than they are being deposited. We calculated that Milwaukee air contributes about 120 kg of PCBs to Lake Michigan each year. This is about 10 times larger than the discharge of PCBs from the Milwaukee River.     

Field-scale reduction of PCB bioavailability with activated carbon amendment to river sediments

Remediation of contaminated sediments remains a technological challenge because traditional approaches do not always achieve risk reduction goals for human health and ecosystem protection and can even be destructive for natural resources. Recent work has shown that uptake of persistent organic pollutants such as polychlorinated biphenyls (PCBs) in the food web is strongly influenced by the nature of contaminant binding, especially to black carbon surfaces in sediments. We demonstrate for the first time in a contaminated river that application of activated carbon to sediments in the field reduces biouptake of PCBs in benthic organisms. After treatment with activated carbon applied at a dose similar to the native organic carbon of sediment, bioaccumulation in freshwater oligochaete worms was reduced compared to preamendment conditions by 69 to 99%, and concentrations of PCBs in water at equilibrium with the sediment were reduced by greater than 93% at all treatment sites for up to three years of monitoring. By comparing measured reductions in bioaccumulation of tetra- and penta-chlorinated PCB congeners resulting from field application of activated carbon to a laboratory study where PCBs were preloaded onto activated carbon, it is evident that equilibrium sorption had not been achieved in the field. Although other remedies may be appropriate for some highly contaminated sites, we show through this pilot study that PCB exposure from moderately contaminated river sediments may be managed effectively through activated carbon amendment in sediments.     

Congener-specific survey for polychlorinated biphenlys in sediments of industrialized bays in Korea: regional characteristics and pollution sources

Areas of the Korean coastline with heavy industry and major harbors were investigated for polychlorinated biphenyl (PCB) pollution. This investigation paid attention to variations in the PCB congener patterns for a possible source of contamination. Surface sediments from 49 sites were sampled. Although the occurrence of PCBs in coastal marine environment correlates well with shipping and industrial activities, the contribution from shipping activities is considerable because of its enormous economical importance in Korea. The highest concentrations were found in harbors with heavy ship traffic and ship construction. Principal component analysis (PCA) of congener-specific composition of PCBs revealed distinct regional patterns, especially in a harbor and steel manufacturing area. PCB signatures with enhanced higher chlorinated congeners were typical for harbors with shipping activities and correlated well with commercial formulations that were formerly used in ship painting. Lower chlorinated congeners with up to five chlorines were significantly abundant in steel works zones which differed from harbor zones. This distinction was consistent with the congener patterns in the ambient air and the effluent of the steel works as well as in the nearby surface sediments. This study identified steel manufacturing as a recent and ongoing emission source of PCBs in Korea's coastal zone.     

Long-term recovery of PCB-contaminated surface sediments at the Sangamo-westonl Twelvemile Creek/lake Hartwell Superfund Site

Natural recovery of contaminated sediments relies on burial of contaminated sediments with increasingly clean sediments over time (i.e., natural capping). Natural capping reduces the risk of resuspension of contaminated surface sediments, and it reduces the potential for contaminant transport into the food chain by limiting bioturbation of contaminated surface or near-surface sediments. This study evaluated the natural recovery of surface sediments contaminated with polychlorinated biphenyls (PCBs) at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell Superfund Site (Lake Hartwell), Pickens County, SC. The primary focus was on sediment recovery resulting from natural capping processes. Total PCB (t-PCB), lead-210 (210Pb), and cesium-137 (137Cs) sediment core profiles were used to establish vertical t-PCB concentration profiles, age date sediments, and determine surface sedimentation and surface sediment recovery rates in 18 cores collected along 10 transects. Four upgradient transects in the headwaters of Lake Hartwell were impacted by historical sediment releases from three upgradient sediment impoundments. These transects were characterized by silt/ clay and sand layering. The highest PCB concentrations were associated with silt/clay layers (1.8-3.5% total organic carbon (TOC)), while sand layers (0.05-0.32% TOC) contained much lower PCB concentrations. The historical sediment releases resulted in substantial burial of PCB-contaminated sediment in the vicinity of these four cores; each core contained less than 1 mg/kg t-PCBs in the surface sand layers. Cores collected from six downgradient Lake Hartwell transects consisted primarily of silt and clay (0.91-5.1% TOC) and were less noticeably impacted by the release of sand from the impoundments. Vertical t-PCB concentration profiles in these cores began with relatively low PCB concentrations at the sediment-water interface and increased in concentration with depth until maximum PCB concentrations were measured at approximately 30-60 cm below the sediment-water interface, ca. 1960-1980. Maximum t-PCB concentrations were followed by progressively decreasing concentrations with depth until the t-PCB concentrations approached the detection limit, where sediments were likely deposited before the onset of PCB use at the Sangamo-Weston plant. The sediments containing the maximum PCB concentrations are associated with the period of maximum PCB release into the watershed. Sedimentation rates averaged 2.1 +/- 1.5 g/(cm2 yr) for 12 of 18 cores collected. The 1994 Record of Decision cleanup requirement is 1.0 mg/kg; two more goals (0.4 and 0.05 mg/kg t-PCBs) also were identified. Average surface sedimentation requirements to meet the three goals were 1.4 +/- 3.7, 11 +/- 4.2, and 33 +/- 11 cm, respectively. Using the age dating results, the average recovery dates to meet these goals were 2000.6 +/- 2.7, 2007.4 +/- 3.5, and 2022.7 +/- 11 yr, respectively. (The 95% prediction limits for these values also are provided.) Despite the reduction in surface sediment PCB concentrations, PCB concentrations measured in largemouth bass and hybrid bass filets continue to exceed the 2.0 mg/kg FDA fish tolerance level.     

Accumulation of PCB congeners in nestling tree swallows (Tachycineta bicolor) on the Hudson River, New York

Tree swallows (Tachycineta bicolor) were used as a sentinel species to monitor the contamination and bioavailability of polychlorinated biphenyls (PCBs) in the Hudson River watershed. Several tree swallow nest box colonies around and downstream from Hudson Falls, NY, were studied. Tree swallow eggs, adults, and 5-, 10-, and 15-day-old nestlings were collected and analyzed for 103 PCB congeners. Emergent insects collected by net (primarily Odonata) or as a food bolus (primarily Diptera) taken from the mouths of adult tree swallows returning to the nest were analyzed in the same manner. Total PCB concentrations (wet weight) in eggs from two contaminated sites ranged from 9000 to 25,000 ng/g and accumulated to 32,000 and 96,000 ng/g in 15-day-old nestling at two contaminated sites. The congener patterns of PCBs in eggs, nestlings, and adults were compared to those found in emergent insects (Odonata and Diptera) using principal components analysis. The PCB patterns of the biota differed from that of Aroclor technical mixtures. PCB patterns in adult tree swallows were similar to those in eggs, while the patterns in dietary insects were similar to nestling tree swallows. Uptake rate constants were determined for tree swallow nestlings and compared between the two contaminated sites. The estimated PCB congener uptake rate constants were 0.008-0.02 d(-1) based on uptake in nestlings until day 15 post-hatch. The rate constants were comparable between the two study areas and may be used to predict nestling contamination at other locations. Our studies confirm the utility of nestling tree swallows to evaluate localized PCB contamination.     

Temporal bioavailability of organochlorine pesticides and PCBs

Because PCBs and organochlorine pesticides continue to be of global concern, studies that address information gaps, such as factors and influences of spatial and temporal effects on contaminant bioavailability, are valuable. The present study focused on the spatial and temporal distribution of bioavailable organochlorine pesticides and PCBs in surface waters of a contaminated harbor. Passive sampling devices were intensively deployed adjacent to various land uses on the Willamette River, OR, including Portland Harbor and McCormick and Baxter Superfund sites, during summer and fall, extreme conditions, 2001-2004. An increase of bioavailable sigmaDDTs (sum of p,p'-DDT, p,p'-DDD, and p,p'-DDE) concentrations was strongly affected bythe local historic production of DDTs and temporal changes in river conditions. The increase of bioavailable p,p'-DDD and high DDD/DDE ratios observed during summer indicates conditions favoring anaerobic reductive processes. In contrast to sigmaDDTs, the bioavailable concentrations and daily loads of dieldrin and PCBs increased during fall, especially during episodic rainstorms. On the basis of the PCB congener profiles, PCB inputs from urban runoff /sewer overflows were considered likely current sources of bioavailable PCB into the Harbor. The exceedence of the U.S. national and Oregon water quality criteria was a function of the temporal variability of each bioavailable contaminant. This illustrates the impacts associated with temporal changes of bioavailable organochlorine distributions in surface waters and the significance of considering realistic temporal, bioavailability, and site-specific conditions in risk assessment and water quality management.     

Concentrations and fluxes of salmon-derived polychlorinated biphenyls (PCBs) in lake sediments

Fourteen sediment cores were collected from 10 lakes spanning a large gradient of sockeye salmon returns (0-40 000 spawners km(-2)) in Alaska and British Columbia in 1995-98 and 2002/03. The cores were analyzed for 210Pb to determine sedimentation rates and focusing factors. Polychlorinated biphenyl (PCBs) concentrations in the surface sediments (0-2 cm) were highly correlated with the number of sockeye salmon returns to each nursery lake. For 2002/03, the correlation between PCB concentration and number of salmon spawners was best with no correction factors applied, but decreased considerably when corrected for sedimentation rates, and was improved again by correcting for sediment focusing. Although sigmaPCB concentrations were similar in 1995-98 and 2002/03, the congener patterns varied. Because salmon are the dominant source of PCBs for most of these lakes, variation in sediment congener pattern likely derives from variation in congener patterns carried by the salmon. Overall, total PCB input by salmon has remained relatively constant since 1995. Unlike temperate Great Lakes contaminant studies, the North American west-coast lakes dominated by salmon bio-transport showed no sign of recent decrease in PCBs.     

Oil is a sedimentary supersorbent for polychlorinated biphenyls

The often-observed enhanced sorption of hydrophobic organic chemicals (HOCs) to sediments is frequently attributed to the presence of soot and soot-like materials. However, sediments may contain other hydrophobic phases, such as weathered oil residues. Previous experiments have shown that these residues can be efficient sorbents for certain PAHs. In this study we investigated sorption of PCBs to sediments contaminated with different concentrations and types of oils, and from that derived oil-water distribution coefficients (Koil). Sorption of PCBs to both fresh and weathered oils was proportional to sorbate hydrophobicity, and no effects of PCB planarity were observed. Furthermore, the experiments demonstrated that different oils sorbed PCBs similarly and extensively (Koil up to 108.3 for PCB 169), and that weathering caused an almost 2-fold increase in sorption of the lower chlorinated PCBs. Koil values indicated that at the PCB equilibrium concentrations tested (pg-ng/L range), for many congeners weathered oil is a stronger sorbent than pure soot and soot-like materials. Due to attenuation of adsorption to the latter materials in sediments (caused by competitive adsorption with organic matter), sedimentary weathered oil will therefore, if present as a separate phase, defeat sedimentary soot, coal, and charcoal as PCB sorbent in most cases. Consequently, weathered oil probably is the ultimate sedimentary sorbent for PCBs and should be included in HOC fate models.     

Sources and dechlorination of polychlorinated biphenyl congeners in the sediments of Fox River, Wisconsin

Polychlorinated biphenyl (PCB) congeners were analyzed in eight deep, dated sediment cores collected from the immediate upstream and downstream of DePere dam in Fox River, Wisconsin. The average time span of the cores is about 100 yr, except for one core (FR-9) which is influenced by mixing or covers a short time period (2 yr). The total PCB concentrations have a range of 0.2-6.8 ppm for the upstream and 0.3-17.6 ppm for the downstream cores. The PCB data obtained from the sampling were analyzed as upstream and downstream data, using a factor analysis (FA) model with nonnegative constraints to identify PCB sources and congener patterns. The factor loadings obtained from the FA model were interpreted in terms of the presence of possible environmental degradation mechanisms. In addition, a recently developed model, which is used to identify and quantify possible pathways of anaerobic dechlorination of PCBs in the sediments, was validated on the basis of in situ data from the literature, and then applied to the congener patterns obtained from the FA model. The major PCB source to the Fox River sediments is identified as Aroclor 1242, for both the upstream and the downstream sediments. Loss of di- and trichlorobiphenyls (e.g., 2-4, 25-2) from the sediments suggests desorption from the sediments. On the other hand, observation of elevated amounts of certain congeners such as 24-3 and 25-3 indicates the presence of anaerobic dechlorination activity. The anaerobic dechlorination model demonstrates significant similarities between the Aroclor 1242 profile altered according to dechlorination processes Q (upstream) and H' (downstream) and the dominant congener patterns obtained from the FA model.     

PCB congeners in Lake Michigan coho (Oncorhynchus kisutch) and chinook (Oncorhynchus tshawytscha) salmon

We determined PCB congener concentrations in coho and chinook salmon collected in two Lake Michigan tributaries during the fall of 1996. Chinook salmon were larger than coho salmon and contained higher concentrations of the 78 PCB congeners we detected. There were no differences between male and female chinook or coho salmon in size or their PCB concentrations. Among individual fish, we found little evidence for a relationship between congener concentrations and percent lipid; however, congener concentrations did show a generally positive relationship with salmon size. Fish and macroinvertebrate congener concentrations are clearly related, and PCB congeners biomagnify approximately 20-30-fold as they flow from macroinvertebrates, two trophic levels below salmon, to the salmon. Slopes of regressions of salmonid congener concentrations on macroinvertebrate congener concentrations within homologs indicated that the degree of biomagnification generally increased with the degree of congener chlorination, although this pattern was much stronger for Mysis than for Diporeia. Log Kow and categorical variables for coplanar and "toxic" PCBs were not significant additional model terms, indicating that bioaccumulation of PCB congeners was not statistically related to these physicochemical attributes of the PCBs. The distribution of homologue PCBs shifts from a distinct predominance of hexachlorobiphenyls in macroinvertebrates to pentachlorobiphenyls and hexachlorobiphenyls in the salmon.     

Sex, BMI and age in addition to dietary intakes influence blood concentrations and congener profiles of dioxins and PCBs

Scope: The aim of this study was to i) characterize dietary polychlorinated biphenyls (PCBs) and dioxin exposure in consumers of fish from the PCB contaminated Lake Mjøsa in Norway ii) examine the influence of demographic factors on blood concentrations and congener composition of dioxins and PCBs, iii) characterize dietary sources and possible exposures above tolerable intake. Methods and results: Blood samples were analysed for dioxin‐like (dl) compounds (PCDD/Fs and dl‐PCBs) and non‐dl‐PCBs (ndl‐PCBs). Dietary exposures were calculated using food frequency questionnaires (n=64). Men had higher median intake of dl‐compounds than women (1.2 and 0.85 pg TEQ/kg bw/day), but similar blood concentrations (23.3 and 25.8, pg TEQ/g lipid weight (lw)). For non‐dl‐PCBs, intakes (6.5 and 4.5 ng/kg bw/day) and blood concentrations (381 and 224 ng/g lw) were higher in men than in women. Blood concentrations correlated with dietary intakes in men only. Increasing BMI and age elevated blood concentrations mainly in women. Men and women had different blood congener profiles, with a higher share of PCB‐126 in women, despite similar dietary congener profiles. Eleven participants exceeded the tolerable intake for dl‐compounds. Fish from Lake Mjøsa was the main dietary source. Conclusion: The higher influence of BMI and age for women than for men may have implications for risk assessment.     

Polychlorinated biphenyls in salmon and salmon feed: global differences and bioaccumulation

Concentrations of 160 polychlorinated biphenyl (PCB) congeners or congener groups were determined in approximately 600 farmed Atlantic salmon from around the world and wild (ocean-caught) Pacific salmon from the Northeast Pacific. Concentrations and PCB congener profiles were analyzed to provide insight into the sources and uptake of PCBs in salmon as well as regional differences. Although total PCB concentrations in wild salmon appeared to be correlated to total lipid content, the increased proportion of total lipids in the farmed salmon could not account for the much greater PCB concentrations. We investigated the PCB congener patterns of hundreds of salmon samples using principal component analysis to further illuminate regional and species differences. Three major PCB patterns were observed, in most wild fish (except British Columbia and Oregon chinook), in farmed fish from the Atlantic, and in most farmed fish from the Pacific. The PCB congener profiles of farmed salmon often closely corresponded to a sample of commercial feed purchased in the same region, indicating that the feed is likely to be the major source of PCBs for farmed salmon. In such cases where PCB profiles in fish and feed were similar, a comparison of congener concentrations in fish and the feed showed that the majority of congeners, with some notable exceptions, were bioaccumulative to the same extent, irrespective of physical properties.     

PCB congeners and dechlorination in sediments of Lake Hartwell, South Carolina, determined from cores collected in 1987 and 1998

Four sediment cores were collected from Lake Hartwell, SC, in 1987 and 1998 and analyzed for polychlorinated biphenyl (PCB) congeners. Total PCBs ranged from -0 to 58 microg/ g. Positive matrix factorization (PMF) was applied to the data sets to determine PCB source profiles. Two factors were determined for each data set. One factor resembled the original estimated PCB mixture of 80% Aroclor 1016 and 20% Aroclor 1254 and the other factor was a dechlorinated version of the mixture. Evidence of a dechlorination plateau is apparent from the PMF loading solutions because the dechlorinated congener profiles do not change from 1987 to 1998, butthe contribution to the profile from the dechlorinated factor increases from 73% (1987) to 87% (1998). PMF source contributions and plots of PCB concentration versus congener for individual samples provide evidence of enhanced dechlorination at high concentrations. After source apportionment an anaerobic dechlorination model was applied to the dechlorinated source profiles to quantify possible dechlorination pathways. It was found that dechlorination process M, extended to target biphenyl rings with up to six chlorines, provided the best fit for an individual process, and M + Q provides the best fit for combined processes, although M + LP also provides a similarfit. Process LP targets the higher chlorinated congeners and appears to dechlorinate PCBs in the sediments initially.     

Long-term recovery of PCB-contaminated sediments at the Lake Hartwell superfund site: PCB dechlorination. 1. End-member characterization

Under anaerobic conditions, such as those typically found in buried sediments, the primary metabolic pathway for polychlorinated biphenyls (PCBs) is reductive dechlorination in which chlorine removal and substitution with hydrogen by bacteria result in a reduced organic compound with fewer chlorines. Vertical sediment cores were collected from Lake Hartwell (Pickens County, SC) and analyzed in 5-cm intervals for 107 PCB congeners in a total of more than 280 samples from 18 sediment cores and surface samples. This paper reports on extensive PCB dechlorination measured in Lake Hartwell sediments and the characterization of dechlorination end-member (EM) patterns using chemical forensic methods. PCB congener fingerprinting and a multivariate receptor modeling method, polytopic vector analysis (PVA), were used for identification and characterization of weathered and dechlorinated PCB congener patterns. Dechlorination resulted in a substantial shift in buried sediments from tetra- through decachlorobiphenyl congeners to mono- through trichlorobiphenyl congeners. Mono- through trichlorobiphenyls comprised approximately 80% of the PCBs in buried sediments that underwent maximum dechlorination as compared to approximately 20% in surface sediments. The major concentration decreases were seen in the tetra- through hexachlorobiphenyl homologues, which accounted for over 90% of the dechlorination. Octa- through decachlorobiphenyl congeners also were dechlorinated, but their overall contribution to dechlorination was relatively small due to their low initial concentrations (< 5%). The net accumulation of 2-CB, 2,2'/2,6-DCBs, 2,4'-DCB, 2,2',4-TCB, and 2,2',6-TCB at Lake Hartwell matched characteristic PCB dechlorination products reported in the literature, such as those for Processes M, Q, and C; and the persistence of tetrachlorobiphenyls (TeCBs) that contained 24- and 25-congener groups resembled dechlorination Processes H or H'. Although dechlorination tended to be very extensive in most of the cores, it was not always consistent from core to core or at various depth intervals within a single core. The reason for this variability in dechlorination extent could not be determined from the existing data and did not appear to correlate with such factors as PCB concentration, total organic carbon, or age. The authors used fingerprinting analysis and a PVA multivariate receptor model as exploratory data analysis tools to characterize PCB sources and their alteration patterns. Dominant sources and alteration patterns were determined in this large data set by comparing PVA EM patterns with known source patterns (i.e., Aroclors or Aroclor mixtures) and literature-reported alteration patterns. PVA also afforded an opportunity to characterize the vertical and lateral distributions of the weathered and unweathered PCB source patterns and dechlorination patterns, a task that would have been much more difficult to accomplish through comparison of chromatograms alone.     

Latitudinal fractionation of polychlorinated biphenyls in surface seawater along a 62 degrees N-89 degrees N transect from the southern Norwegian Sea to the North Pole area

Surface seawater concentrations of PCBs, relative congener abundance, and possible effects of cold condensation were studied along a transect from the southern Norwegian Sea to the central Arctic Ocean (62 degrees N-89 degrees N). Large volume samples were collected from an ice breaker using a stainless steel surface seawater intake connected online to an ultra-clean laboratory. Concentrations of all studied PCB congeners, except for trichlorinated PCB 18, decreased with latitude. For instance, PCB 52 decreased from 470 fg L(-1) at 62 degrees N to 110 fg L(-1) at 89 degrees N and PCB 180 from 110 to 12 fg L(-1). Concentrations in the central Arctic Ocean were on the order of 10-100 fg L(-1) for the most abundant congeners. The relative contribution oftrichlorinated PCBs to the total PCB concentration increased with latitude, the tetrachlorinated contribution to the total PCBs did not show any correlation to latitude, and the relative contribution of heavier congeners decreased with latitude. This study establishes the occurrence at very low abundances of PCBs in seawater in the central Arctic Ocean and demonstrates a northward concentration decrease. The latitudinal shift in congener pattern is reflecting the relative propensity of the PCB congeners to undergo long-range transport in the Arctic and is consistent with their relative vapor pressures.     

Bioenergetics-based modeling of individual PCB congeners in nestling tree swallows from two contaminated sites on the upper Hudson River, New York

A bioenergetics-based model was used to simulate the accumulation of total PCBs and 20 PCB congeners by nestling tree swallows at two contaminated sites on the Upper Hudson River, New York. PCB concentrations in birds were calculated as the sum of inherited residues and those acquired through consumption of contaminated insects. Close agreement between simulations and measured residues in 5-, 10-, and 15-day-old nestlings was obtained when PCB concentrations in the diet were set equal to those in food boli taken from adult birds. These simulations were further optimized by fitting the value of a dietary assimilation efficiency constant. Fitted constants for both sites were similar and averaged about 0.7. An evaluation of model performance for individual congeners provided no evidence of metabolic biotransformation. The results of this study are consistent with a companion effort in which principal components analysis was used to compare PCB congener patterns in insects and in tree swallow eggs, nestlings, and adults. Together, these studies establish a quantitative linkage between nestling tree swallows and the insects that they consume and provide strong support for the use of nestling swallows as a biomonitoring species for exposure assessment.