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Anomalous Concentrations and Chlorination of Polychlorinated Biphenyls in Sediment Downwind of Lake Ontario
J. Great Lakes Res. 28(4):674–687 Internat. Assoc. Great Lakes Res., 2002
Anomalous Concentrations and Chlorination of Polychlorinated Biphenyls in Sediment Downwind of Lake Ontario Jeffrey Chiarenzelli1,*, Clark Alexander2, Ronald Scrudato3, James Pagano3, Lauren Falanga3, Benjamin Connor3, and Michael Milligan4 1Department
of Geology SUNY Potsdam Potsdam, New York 13676 2Skidaway
Institute of Oceanography 10 Ocean Science Circle Savannah, Georgia 31411
3Environmental
Research Center SUNY Oswego Oswego, New York 13126
4Department
of Chemistry SUNY Fredonia Fredonia, New York 14063 ABSTRACT. Relatively high concentrations (up to 98.5 ng/g dry wt) of polychlorinated biphenyls (PCBs) have been found in two cores penetrating fluvial sands east of Lake Ontario. One core was taken from the upper Salmon River reservoir on the Tug Hill Plateau and the other from Rice Creek near the lake at Oswego. In both instances, portions of the cores containing PCBs and other organochlorines (OCs) lack excess radiogenic 210Pb and 137Cs, implying depositional ages predating widespread OC commercial production, use, and release. Within each core there is little vertical variation in PCB composition and highly chlorinated congeners dominate the pattern. In addition, the PCB signature is analytically indistinguishable between cores despite collection over 50 km apart. This argues against local sources, and implies deposition and accumulation by processes operating over a substantial area and time period. Transport and introduction of a residual fraction of colloidal-bound PCBs to the sands via tannin-rich riverine waters is proposed. The PCB congener-specific pattern of air samples collected during the spring and summer of 1999 downwind of the lake at two locations (Rice Creek and Sterling) are similar to the sediments and display anomalous concentrations and chlorination with respect to other air sampling localities in the Great Lakes. A link between the residual fraction of PCBs observed in the sediment and air patterns via volatilization from the terrestrial surface is proposed. Elevated PCB concentrations and chlorination in non-radiogenic fluvial sands and air may reflect regional accumulation and weathering processes operating over many decades and/or enhancement of contaminant deposition and partitioning downwind of the lake related to lake-effect precipitation. INDEX WORDS:
Organochlorides, radionuclides, sediment core, Lake Ontario, Tug Hill Plateau.
INTRODUCTION Over two decades of research has enhanced the understanding of the mass balance of organic conta-
*Corresponding
minants in Great Lake’s environmental media (Anderson et al. 1999, Eisenreich et al. 1981, Green et al. 2000, Hillery et al. 1997, Hornbuckle et al. 1993). This work has been particularly relevant in predicting future trends in contaminant levels, and devising appropriate strategies for continued moni-
author. E-mail: [email protected]
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Polychlorinated Biphenyls Downwind of Lake Ontario toring and improvements in environmental quality. In addition to the concentrations of contaminants in environmental media, temporal trends in their composition must also be considered. The fractionation of contaminants related to their physicochemical properties has been widely documented (Blais et al. 1998, Rappe 1974, Wania and MacKay 1996) and suggests temporal changes in contaminant compositions in various environmental media are inevitable, particularly within a group of related isomers. Because of their capacity to store enormous amounts of heat, large water bodies influence the meteorology of bounding landmasses. The Great Lakes have a significant moderating effect along their shores and one meteorological phenomenon is copious amounts of precipitation downwind of the lakes. The scavenging effect of precipitation, especially snowfall, relative to organic carbon compounds (OCs) is widely recognized (Blais et al. 1998; Franz and Eisenreich 1998, 2000). It is hypothesized that “lake-effect” precipitation may result in enhanced contaminant deposition and fractionation in the Great Lakes ecosystem. Located downwind of Lake Ontario, the Tug Hill Plateau (Fig. 1) receives enhanced rain and snowfall, often forming discrete bands extending from the lake inland as much as 80 km or more. One such “lake-effect” snowstorm resulted in the deposition of 241 cm of snow in Montague, NY (11 and 12 January 1997). It is suspected that the Tug Hill Plateau may have received relatively high fluxes of OCs in the past and, if so, these trends may be reflected by their concentration and composition in environmental media. In addition, because lakeeffect precipitation largely occurs, and is recaptured, within Lake Ontario’s drainage basin, regional processes, related to meteorological factors, may further enhance OC partitioning during complex cycling of contaminants within the drainage basin. A preliminary investigation of OCs in air and sediment was begun in 1999. The results of the air sampling program has been previously summarized (Chiarenzelli et al. 2001b) and suggest a significant seasonal enhancement in both PCB chlorination and concentration downwind of Lake Ontario relative to other Great Lakes sample sites (Hillery et al. 1997). Reported here is the signature of PCBs found in sediment cores collected near the lake and 50 km away on the Tug Hill Plateau, both areas of considerable lake-effect precipitation. The signature of the sediment will be compared with that of airborne PCBs in the same area to evaluate the hypothesis
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FIG. 1. Diagram showing the study area, geographic place names, locations of core and air samples discussed, and major water bodies. that volatilization from the terrestrial surface controls the composition and concentration of airborne PCBs. The heavily chlorinated nature of the PCB patterns in both media may be a reflection of temporal trends and local meteorological factors, such as lake-effect precipitation, which may enhance deposition and fractionation of OC contaminants. EXPERIMENTAL SECTION Sampling Locations Core samples were taken from fluvial sands in the upper Salmon River reservoir (SR) near Redfield, New York, and Rice Creek near Oswego, New York, adjacent to Lake Ontario (Fig. 1). Data from the Rice Creek core have been reported elsewhere (Chiarenzelli et al. 2001a) and further discussion of this sample will be limited to comparison with SR samples to avoid unnecessary duplication. The SR receives drainage from a large (~464 km2), remote, forested region of the Tug Hill Plateau whose center is 50 km east of Lake Ontario. The Salmon River core was collected from a shallow (1-m depth), marshy area adjacent to the entry of the North Branch of the Salmon River into the eastern end of the reservoir at an elevation of 286 m, 1 kilometer from the hamlet of Redfield (pop. 564; U.S. Census Bureau 1990). The upper SR reservoir was built in 1914, and dams at the upper and lower reservoirs and the intervening
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Salmon River Falls prevent the access of migrating salmonids and their body burden of contaminants (Scrudato and McDowell 1989). Sampling Procedures The SR core samples were taken on 5 August 1999 utilizing pre-cleaned Plexiglas tubes driven into the sediment. Samples were collected from a relatively quiet, shallow water site (N43°31′48″ W75°48′47″) located where deltaic sediments of the North Branch of the Salmon River are prograding into the reservoir. A carpet of well established aquatic vegetation indicated little, if any, recent reworking of the sampling site. Due to seasonal lowering of water levels during operation of the hydroelectric facilities, the site is periodically emergent during the winter months. Several cores containing 40 to 50 cm of sediment were recovered; only one was utilized for analysis. Sediment samples varied from moderately to weakly stratified and consisted of homogeneous, fine silty sands of dark brown to gray brown color with sparse organic fragments. The preservation of stratification suggested that bioturbation was minimal. Cores were immediately returned to the laboratory and opened by successive longitudinal scoring with a Dremel tool and carpet knife. Care was taken to minimize disturbance of the core. Once exposed, the core was rapidly sectioned into 2-cm intervals with stainless steel tools and placed in pre-cleaned glass jars. The jars were stored in the dark in the refrigerator at 4°C until analyzed. Analyses were completed within 3 months of sampling. Before analysis each core interval was homogenized manually. The sub samples were never allowed to dry or otherwise exposed to ambient air for periods in excess of several minutes (Chiarenzelli et al. 1996). Organochlorines Complete analytical details are presented in recently published work (Chiarenzelli et al. 2001a). Sediment samples were extracted by steam distillation (Veith and Kiwus 1977, Swackhamer and Armstrong 1986) to minimize the extraction of organic compounds with the potential for chromatographic co-elution with PCBs (Mudroch et al. 1992). Five to ten grams of sediment (wet weight) was boiled in 300 mL of water for 24 hours and the condensate continuously refluxed through 10 mL of hexane. After extraction the hexane layer was drained and transferred for Florisil clean up. Before extraction,
recovery surrogates consisting of IUPAC congeners 14, 65, 166, and 209 were added to the sediment. Cleanup consisted of acid digestion (HNO 3) and sulfur removal (tetrabutylammonium sulfate) followed by elution through deactivated (4%) Florisil columns. After clean up, samples were condensed to 1 mL using a Kuderna-Danish apparatus and steam bath for GC-ECD analysis. Analysis included 93 peaks representing 130 PCB congeners, p,p′DDE, HCB, and mirex. A program incorporating method, apparatus, and reagent blanks, surrogate spikes, matrix spikes, and duplicate samples monitored quality assurance. All blanks were < 5 pg/µL injection PCBs and > 90% were at sub-picogram level. The mass of PCBs in core sample extracts ranged from 20 to 264 pg/µL with an average of 65.4 pg/µL, indicating a favorable sample to blank ratio. Recovery of IUPAC congeners 14, 65, 166, and 209 during extraction and analysis averaged (± 1SD) 83 ± 15, 90 ± 15, 118 ± 24 and 103 ± 30 percent. Congener-specific PCB analyses and select pesticides utilized capillary column procedures after Frame et al. (1996). The calibration standard was composed of a nine set mixture of all 209 PCB congeners, and HCB (5 pg/µL), DDE (10 pg/µL), and mirex (10 pg/µL) obtained from the EPA Pesticide Repository. This standard was run every sixth sample and used to calibrate the gas chromatograph. Congener assignments and weight percent distributions for the calibration standard were confirmed with a Hewlett Packard Model 5890 II gas chromatograph with an electron capture detector (Pagano et al. 1999). Samples were analyzed utilizing a HP Ultra II 25 meter DB-5 capillary column with 0.22 mm ID and 0.33 µm film thickness on a Hewlett Packard Model 5890 II gas chromatograph equipped with an auto sampler and electron capture detector ( 63N i ). Helium and P5 (argon/methane) were used as carrier and makeup gases, respectively. After 2 minutes, the system was incrementally heated from 100 to 160°C over 6 minutes and then at a rate of 3°C/min to 270°C and held for 16 minutes. The injector port and detector were maintained at 270°C and 330°C, respectively. Major and Trace Element Analysis The core was composed predominantly of fine to very fine sand (~75 to 86%), a small amount of silt (~14 to 24%), and only minor amounts of claysized material (0.3 to 1.4%). Organic carbon varied from 0.90 to 3.95%. Core interval sub samples were
Polychlorinated Biphenyls Downwind of Lake Ontario sieved to provide < 62.5µ fraction for major and trace element analysis. Because of the scarcity of fine material, each sub sample represented 4-cm intervals of core in contrast to the 2-cm interval utilized for all other analyses. Acme Analytical Laboratories, Ltd. in Vancouver, Canada, conducted major and trace element analyses. Sub samples (0.2 g dry weight) were fused with 1.5 g of LiBO2 and dissolved in 100 mL of 5% HNO3 before x-ray fluorescence analysis. Splits for trace element analysis where gently ground by mortar and pestle and sieved. Sub samples (5.0 g) were digested with a 30 mL HCl-HNO3-H2O (1:1:1) solution at 90°C for 1 hour and brought up to 100 mL in water and directly analyzed. Metals of anthropogenic interest (Mo, Cu, Zn, Ag, As, Cd, Sb, Hg, and Se) are further extracted with methyl isobutyl ketone and then analyzed by ICP-MS. Quality control was monitored through replicate samples and standards. Aside from Ni and Zr, concentrations of all elements were replicated to within 90%. Core Dating Sediment age was inferred from radiochemical analysis of naturally occurring and manmade radionuclides. Lead-210 (210Pb), a naturally occurring radionuclide with a 22.3-year half-life, has been used for decades to characterize sedimentary processes on 100-y time scales (Krishnaswami et al. 1971, Koide et al. 1972, Nittrouer et al. 1979, Oldfield and Appleby 1984, DeMaster et al. 1985, Alexander et al. 1991, 1993). There are two components to the total 210Pb signal: 1) supported 210Pb activity, that provided by in situ decay of the effective parent, 226Ra, in the sediment column; and 2) excess 210Pb activity, that amount above the supported levels provided by particulate scavenging of 210Pb in the atmosphere and water column. Excess 210 Pb decays below detectable limits in approximately five half-lives and thus is observed in sediments representing the past ~112 y. If no excess 210 Pb is present, sediments are interpreted to be non-accumulating or erosional and older than 100 years in age. Cesium-137 (137Cs), a bomb-produced impulse tracer with a 30.1 y half-life was first introduced into the environment through atmospheric weapons testing in 1954. Since the cessation of atmospheric weapons testing, the atmospheric flux of 137Cs has decreased to 10% of its 1964 peak value. Activities of radionuclides within each sample were determined concurrently using a low-background germanium detector following the tech-
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niques described in Alexander et al. (1999). Sediments were dried, ground with a porcelain mortar and pestle, and sealed in 30-mL polypropylene jars. Samples were allowed to equilibrate for 20 days to assure equilibrium between 226Ra and intermediate daughter products. Total 210Pb activity was directly determined by gamma-spectroscopic measurement of its 46.5-KeV gamma peak (Appleby et al. 1986). Correction for sediment self-absorption was performed following the method of Cutshall et al. (1983). Supported levels of 210Pb were determined for each depth interval by concurrently measuring the gamma activity of 214Pb and 214Bi, the shortlived granddaughters of 226Ra, at 295, 352, and 609 KeV. The activity of 137Cs was directly determined by gamma spectroscopic measurement of its 661.6KeV peak (Robbins 1978). RESULTS Radiochemistry Excess 210Pb activity was measured within the core down to the 36 to 38 cm interval. The lack of excess 210Pb activity below the 36 to 38 cm interval documents that sediments below this level in the core are older than ~100 years. Lead-210 activity is relatively constant from the surface down to 24 to 26 cm and decreases exponentially from 25 to 37 cm (Fig. 2). Statistically significant amounts of
FIG. 2. Trends in radionuclide activities measured in the upper Salmon River reservoir core. Note that 226Ra is an estimate of supported 210Pb and 210PbTotal = 210Pbexcess + 200Pbsupported.
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FIG. 3. Trends in organochlorine concentrations measured in the upper Salmon River reservoir core.
137Cs
activity occur in the core down to 32 to 34 cm interval. The values are relatively constant and low from the top of the core to the 14 to 16 cm interval, peak in the 24 to 26 cm interval, and decrease sharply with a linear trend thereafter.
Organochlorines Polychlorinated biphenyls were found throughout the core in measurable concentrations (Fig. 3). Dry weight concentrations ranged from a high of 98.5 ng/g (20–22 cm) to ca. 3 ng/g near both the top and bottom of the core. No clear vertical trends were apparent, with variable concentrations occurring throughout the core. However, a general decrease in PCB concentration occurs from 20 to 22 cm upwards, while below 22 cm the concentration fluctuates significantly. A concentration of 70 ng/g was measured in the lowermost interval (48 to 50 cm), at odds with depositional trends and production records (Eisenreich et al. 1989, Oliver et al.1989). The concentrations of p,p′-DDE and HCB show similar trends and their concentrations were the best correlated (r = .73), even though p,p′-DDE is approximately ten times more abundant. The occurrence of both compounds was low below 34 to 36 cm with both compounds being sporadically nondetectable. Both compounds showed a gradual increase with broad maxima occurring from about 8 to 32 cm (Fig. 3). Maximum concentrations of p,p′DDE occurred at 26 to 28 cm (1,005 pg/g) and that of HCB at 20 to 22 cm (84.7 pg/g). The profiles observed are similar to, but do not necessarily reflect,
commercial production trends of DDT and chlorobenzene in the U.S. and deposition records in the Lake Ontario cores (Eisenreich et al. 1989, Oliver et al. 1989). Mirex, first commercially manufactured in 1959, was absent from the bottom 20 cm of the core (Fig. 3). Above the 28–30 cm interval Mirex was detected in all but three intervals (2 to 4, 10 to 12, 12 to 14 cm). Maximum concentrations occurred in both the 22 to 24 cm interval (78.6 pg/g) and again at 8 to 10 cm (82.3 pg/g). The profile is not consistent with sediment profiles from Lake Ontario or production records (Eisenreich et al. 1989, Oliver et al. 1989), suggesting an alternative explanation for its sporadic occurrence and concentration pattern. Porosity A clear shift in porosity values is also noted in the core between the 22 to 24 and 24 to 26 cm intervals (Fig. 4). Below 22 to 24 cm the porosity is relatively low, ranging from ~47 to 60%. In the upper half of the core, however, values range from ~60 to 75%, with the exception of the two uppermost intervals which are distinctly lower (41.7 and 49.9%).
FIG. 4. Trends in porosity, and select major and trace element chemistry measured in the upper Salmon River reservoir core. The dashed line represents the proposed break in sedimentation at ~24 cm.
Polychlorinated Biphenyls Downwind of Lake Ontario Major Elements The lower half of the core contained significantly more SiO2 (Fig. 4), reflecting a greater percentage of detrital quartz. In contrast, the upper half of the core contained significantly higher amounts of Fe 2O 3, CaO, MnO, and C, and lost more weight upon ignition (LOI). Other major elements, that were also more abundant in the upper half of the core, include Al2O3, MgO, K2O, and P2O5. However, these differences were not statistically significant. No trends in major element chemistry were noted in either half of the core. The data support a distinct break in major element chemistry in the core between the 22 to 24 and 24 to 26 cm intervals. Trace Elements While virtually all trace element concentrations were elevated in the upper half of the core, differences in Cd, Cu, Hg, Mn, Pb, and Zn were statistically significant at the two sigma confidence levels (Fig. 4). As with the major elements, no clear vertical trends were found in trace element composition. Trace element concentrations also support a significant change in sediment composition at ~24 cm, probably reflecting the greater percentage of fine sediment in the upper half of the core. DISCUSSION Interpretation of the Salmon River Core Fluvial sands are subject to substantial reworking and extended periods of little or no sediment accumulation and are unlikely to accurately record uninterrupted depositional trends; this study is no exception. A significant observation, prompting this study, is that the core has elevated OC concentrations throughout its 50-cm length and despite its grain-size. Further, intervals below 36 to 38 cm lack excess radiogenic 210 Pb activity and were therefore were deposited over ~100 years ago. The occurrence of OC compounds implies their introduction after deposition, which has also been documented in the Rice Creek core taken 50 kilometers away near the lakeshore (Chiarenzelli et al. 2001a). The vertical concentration trends of PCBs and mirex concentrations in the core do not match depositional trends recorded in Lake Ontario or commercial production records (Eisenreich et al. 1989, Oliver et al. 1989), requiring an alternative explanation. Taken together, the radiochemical data presented
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above indicates a significant change in sediment and radionuclide accumulation history at ~24 cm and that sediment deposition or mixing was rapid in the upper half of the core relative to a time scale of 22 years (210Pb half-life). A distinct break at 24 cm is also supported by changes major and trace element chemistry and porosity values. Precipitation records indicate that after a relatively dry spring and summer, over 59 cm of precipitation fell on the Tug Hill Plateau during the fall of 1965 (Highmarket Station—Northeast Regional Climatic Center). Runoff in response to this precipitation would have resulted in substantial reworking of the bed of the Salmon River. Other scenarios, including a thick (24 cm) zone of mixing, are also possible. However, maximum 137Cs activities were measured in the core at 24 to 26 cm and likely correspond to peak atmospheric levels of 137Cs at ca. 1964, and if so, provide a time-marker just prior to the proposed reworking event. Thus a plausible explanation for the non-accumulative nature of both 210 Pb and 137Cs above 24 cm is the rapid deposition of sediment in response to reworking of the riverbed during the unusually wet fall of 1965. Regional Accumulation Processes A sediment core was also taken from fluvial sands of Rice Creek nearly 50 kilometers from the Salmon River sampling site (Fig. 1). The Rice Creek core was collected within a kilometer of Lake Ontario near Oswego and its drainage basin has several substantial differences with that of the remote, entirely forested upper Salmon River drainage basin. Differences include population density, size, land-use, and elevation, among others (Chiarenzelli et al. 2001a). Despite these differences, PCB congener-specific patterns (Fig. 5) and the mean PCB concentration found in both cores are statistically identical. In addition, neither site shows significant vertical trends in the PCB congener pattern and chemistry (Fig. 6). Similar to the Salmon River core, the Rice Creek core was found to lack 137Cs and excess 210Pb, and the sediment was inferred to be older than ~100 years despite significant concentrations of OCs (Chiarenzelli et al. 2001a). The correspondence of PCB patterns despite differences in geographic location (50 km), drainage basin characteristics, and stratigraphic position suggests regional processes, rather than local sources, are responsible for the deposition of contaminants in the area east of Lake Ontario and that
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FIG. 5. Comparison of the average congener specific PCB pattern of fluvial sands from upper Salmon River (n = 25) reservoir and Rice Creek (n = 22) by mole fraction percentage. The correlation coefficient (r2) between the average patterns is 0.97; comparisons between individual samples are as high as 0.99. Note the slight enrichment in higher chlorinated congeners in the Rice Creek pattern relative to the Salmon River core.
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FIG. 6. Vertical trends in PCB chemistry observed in the Salmon River (n = 25) and Rice Creek (n = 22) cores (average chlorines per biphenyl, sum of penta- through hepta-homolog groups, and ortho-chlorine mole fraction percentage). The chlorine per biphenyl ratio of Aroclor 1254 has been added for reference as a dashed line. The penta-hepta homologs have been grouped to point out relative proportions of highly chlorinated (~60-70%) versus di-tetra chlorinated (~10-20%) congeners (not shown).
these processes have selectively concentrated the same PCB congeners over many decades. The PCB congener pattern in both cores is dominated by congeners with five to seven chlorines (Fig. 6) which generally comprise 60 to 70% of the total. These include IUPAC congeners (89+101, 77+110, 123+149, 118, 153, 138+163+164, 187, 174, 180, and 170+190), interpreted as a residual fraction of atmospherically deposited PCBs remaining in the drainage basin after partitioning and weathering in the environment (Chiarenzelli et al. 2001a). Perhaps even more striking is the lack of lower chlorinated PCBs in samples from both cores. With one exception (the sporadic occurrence of IUPAC # 15+17), congeners with two, three, or four chlorines that typically dominate the pattern of air and water samples are nearly absent, comprising at most a percent or two of the total (Fig. 5). This is taken as evidence of considerable fractionation in
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an area (Tug Hill Plateau), which receives its entire PCB load by atmospheric deposition. How this fraction of highly chlorinated congeners was introduced into sediment deposited before the widespread production and use of PCBs is an intriguing problem. Considerable amounts of PCBs can be found and transported in water; however, the composition of aqueous phase PCBs is dominated by lower chlorinated congeners with relatively high solubilities (Achman et al. 1993, Anderson et al. 1999, Bush et al. 1985, Crane and Sonzogni 1992, Datta et al. 1998), thus making introduction by direct adsorption from riverine or ground waters improbable. Particulate phase PCBs in water are generally higher chlorinated, however, particulate phase PCBs pattern in Lake Ontario (Anderson et al. 1999) is significantly less chlorinated than that found in the core samples in this study. Lower portions of the core also lack excess 210Pb and 137Cs that would also be introduced adhered to fine particles. The length of both cores (~44 and 50 cm), and the lack of vertical compositional trends, suggest introduction by diffusionrelated processes is also unlikely. In other core studies in which PCBs are found in horizons dating before their production, lower chlorinated congeners are enriched (Gevao et al. 1997, Yamashita et al. 2000), unlike the consistently heavily chlorinated pattern found in this study. Proposed is an accumulation mechanism whereby residual PCBs are introduced into fluvial sands by tannin-rich riverine waters in colloidal suspension and/or adhered to dissolved organic matter (Chiarenzelli et al. 2001a). If so, permeability may be the primary factor controlling which stratigraphic intervals accumulate large amounts of OCs and thus likely bear no relevance to the historical deposition in the drainage basin. Some areas of the core, particularly zones of enhanced permeability, may represent the accumulation of PCBs over several decades or the location of introduced contaminants may shift with time as water levels fluctuate in the drainage basin or reservoir. Such a scenario may explain the composition of the PCB fraction in the fluvial sands (intense weathering and removal of the lower chlorinated congeners resulting in a highly chlorinated residual) and their enhanced concentrations (decades of and/or preferential accumulation). Further, the discovery of identical congener-specific patterns in fluvial sands at widely separated (50 km) locations argues that PCB accumulation occurred by processes operating over a wide area downwind of the lake.
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Chiarenzelli et al. in sediments of Lake Michigan (Swackhamer and Armstrong 1986, Golden et al. 1993) that received direct PCB discharge from urban areas including Chicago and are significantly elevated above those in other rural and remote areas. The sporadic occurrence of other OCs may be a reflection of numerous factors, including their low initial concentrations in air samples relative to PCBs, detection limits, biological or physical alteration in the drainage basins, extended, complex, multi-stage partitioning processes, and solubility and volatility considerations.
FIG. 7. Comparison of PCB concentrations measured in sediment core studies in the literature. References: Lake Ontario—Eisenreich et al. (1989) and Oliver et al. (1989); Tokyo Bay— Yamashita et al. (2000); Urban reservoirs—Van Metre et al. (1997); Lake Michigan—Swackhamer and Armstrong (1986) and Golden et al. (1993); Salmon River—this study; Rice Creek—Chiarenzelli et al. (2001); Wisconsin Lakes—Swackhamer and Armstrong (1986); Rural English Lakes— Gevao et al. (1997); Lake Winnipeg—Rawn et al. (2000); Rural Reservoirs—Van Metre et al. (1997); Lake Superior—Golden et al. (1993); Baltic Proper—Kjeller and Rappe (1995); Great Slave Lake—Mudroch et al. (1992); Subarctic Finland—(Vartianien et al. 1997).
One long-term consequence of this process may be the relatively high concentrations of PCBs in the cores examined. Figure 7 shows the mean concentrations of the Salmon River and Rice Creek cores relative to other studies in the literature. However, in contrast to the other studies relatively clean sands were analyzed rather than clay and organicrich, deeper water muds. Despite this, the concentrations measured in both cores are similar to those
Links to Anomalously Chlorinated Airborne PCB Signature Downwind of the Lake? The discovery of a highly chlorinated fraction of PCBs in fluvial sands downwind of the lake may have other important implications. Previous air sampling in the same area has documented an increase in PCB chlorination and concentration as the land surface warms (Chiarenzelli et al. 2001b). Both the concentrations and chlorination of airborne PCBs downwind of the lake are anomalous with respect to other sampling sites (Hillery et al. 1997) in the Great Lakes basin (Fig. 8). Urban areas could conceivably provide higher concentrations and more chlorinated PCB patterns (Currado and Harrad 2000) and indeed, the data from the Rice Creek air sampling station is similar to that of Chicago collected in the summers of 1994 and 1995 (Green et al. 2000). Plumes containing elevated concentrations of airborne PCBs have been traced for maximum distances of 40 km east of the city (Green et al. 2000). However, no large, urban center exists within several hundred kilometers upwind of the Tug Hill Plateau and volatilization of PCBs directly from the lake (Achman et al. 1993, Hornbuckle et al. 1993, Jeremiason et al. 1994, McConnell et al. 1998) cannot explain the highly chlorinated air pattern observed. A more likely scenario is that the PCB signature observed in fluvial sands from two locations downwind of the lake is representative of regional processes across the Tug Hill Plateau in concert with global atmospheric trends. As PCBs concentrations have dropped globally workers have concluded that fugacity considerations (Harner et al. 1995) now facilitate the release of previously sequestered PCBs from terrestrial repositories (Alcock et al. 1993, Lee and Jones 1999, Sweetman and Jones 2000). Thus it is likely that the air concentrations and patterns recently measured down-
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would minimize the chlorination of air samples relative to the sediment pattern.
FIG. 8. A comparison of Integrated Atmospheric Deposition Network (IADN) airborne PCB concentrations and chlorination (Hillery et al. 1997) with those east of Lakes Erie and Ontario (Chiarenzelli et al. 2001a). The area in black surrounding the Great Lakes is the drainage basin. White ovals contain mean spring and summer airborne PCB concentrations in picograms per cubic meter, black ovals give the mean chlorine per biphenyl ratio. Note that IADN samples were collected during 1994 to 1996, while those of Chiarenzelli et al. (2001b) were collected in 1999. wind of the lake in the summer are the direct result of volatilization from the terrestrial surface. This is consistent with seasonal increase in PCB concentration and chlorination observed in air samples taken downwind of the lake from the late winter to summer (Chiarenzelli et al. 2001b) and along the St. Lawrence River (Chiarenzelli et al. 2000). Airborne PCBs from the same area show many similarities (r2 = 0.78) to the pattern recovered from the fluvial sand cores with many of the same highly chlorinated congeners dominating the pattern (Fig. 9). However, as observed in volatilization experiments with PCB Aroclors (Chiarenzelli et al. 1997), the air pattern is somewhat less chlorinated than the sediment pattern, reflecting the preferential volatilization of available congeners with fewer chlorines. The admixture of lower chlorinated congeners from atmospheric background (Panshin and Hites 1994) or derived from volatilization from the lake (Achman et al. 1993, Hornbuckle et al., 1993, Jeremiason et al. 1994, McConnell et al. 1998)
Regional Considerations and the Potential Role of Lake-effect Precipitation? The scavenging effect of precipitation, both rain and snow, is widely recognized (Blais et al. 1998; Franz and Eisenreich 1998, 2000; Simcik et al. 2000) and likely leads to the enhanced deposition of PCBs and other OCs in areas effected by lakeeffect precipitation. The cold temperatures of high altitude and latitude regions maximize the deposition of lower chlorinated congeners via cold condensation processes (Blais et al. 1998, Rappe 1974, Wania and MacKay 1996). In contrast, the climatic conditions near Lake Ontario would maximize the potential for the residual accumulation of highly chlorinated congeners derived from the snow pack, as lower chlorinated congeners were lost through volatilization or runoff when warming occurs. Concentrations of PCBs measured in sands from cores at Rice Creek and the upper Salmon River record the deposition and retention of highly chlorinated congeners. The sporadic occurrence of lower chlorinated congeners in core samples and air near the lake documents their preferential removal from the system via the “grass hopper” effect and/or thermally driven volatilization. Lake-effect precipitation may play a critical role in contaminant deposition and fractionation, particularly in the removal of fine particulates from fartraveled air masses. This is not unprecedented, as air masses originating in Asia have deposited considerable amounts of OCs and fine particulates in so-called “brown” snow events in the Canadian Arctic (Welch et al. 1991) and much recent work has also focused on the trans-oceanic transport of particulates. The areas south and east of Lake Ontario receive considerable amounts of lake-effect precipitation from prevailing southwesterly to northwesterly winds. In particular, elevated areas of the Tug Hill Plateau and western Adirondacks receive localized precipitation, often in the form of bands, resulting from the evaporation of lake water and deposition over the frozen land. Precipitation records for the past 40 years indicate a mean of 135.7 cm on the Tug Hill Plateau at Highmarket and 105 cm at Oswego on the lake (Northeast Regional Climate Center, Cornell University). In these areas annual snowfall totals can exceed 500 cm per year. If the scenario described above has merit, one
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FIG. 9. Comparison of average (n = 22) sediment PCB signatures at Rice Creek with airborne (summer 1999) patterns just east of Lake Ontario near Oswego, New York, by mole fraction percentage. The correlation coefficient (r2) for the comparison is 0.78. Note the similarity in the abundance of highly chlorinated congeners and the preferential enrichment of the heaviest congeners in the sediment relative to the air. The lower chlorinated congeners in the air samples cannot be derived from the sediment but may reflect volatilization from the lake or the atmospheric background signature.
Polychlorinated Biphenyls Downwind of Lake Ontario could legitimately ask why other areas impacted by lake-effect snow in the Great Lakes basin do not show similar phenomena? For instance, work at the Stockton air sampling site east of Lake Erie (Fig. 8) has found only slightly elevated PCB concentrations relative to other sites (IADN sites, Hillery et al. 1997) despite its location in Lake Erie’s snow shadow. However, the Stockton PCB signature is more chlorinated than any of the other air sampling sites, except those east of Lake Ontario. The Tug Hill Plateau is uniquely situated with respect to a number of distant, downwind urban centers including Rochester, Buffalo-Niagara Falls, Toronto-Hamilton Harbour, and the more distant metropolitan areas in the mid-west. Urban areas, particularly those associated with manufacturing and the chemical industry, are typically sources of organic contaminants. For example, despite the ban of PCBs in 1977, Chicago continues to serve as a source of PCBs forming plumes that extend for tens of kilometers or more under certain meteorological conditions (Green et al. 2000). Urban areas are also generally associated with more highly chlorinated PCB air patterns (Currado and Harrad 2000). It is suggested that a large percentage of the highly chlorinated PCBs and other contaminants found in fluvial sands east of Lake Ontario probably originated in urban and/or industrial centers to the south and west. Over the last six or seven decades, lake-effect precipitation associated with Lake Ontario’s meteorological influence has provided an effective mechanism for removing these contaminants from regional air masses and depositing them in remote areas far from other sources. Weathering processes in the drainage basin, including volatilization and solubilization, have led to the removal of most lower chlorinated PCBs, retaining a residual fraction of highly chlorinated congeners and other similar OCs (Chiarenzelli et al. 2001a, 2001b). Transportation of semi-volatile contaminants within drainage basins in colloidal suspension and/or adsorbed to humic and fulvic acids has resulted in their introduction into fluvial sands deposited more than 100 years ago. Falling fugacities for PCB congeners (Harner et al. 1995) have resulted in the near equilibrium release of higher chlorinated congeners from local terrestrial repositories (Currado and Harrad 2000) and these now dominate the air pattern over the region (Chiarenzelli et al. 2001b). A similar chlorination enrichment mechanism has been proposed by Commoner et al. (1999) for airborne PCB signature found at localities in the New York City watershed despite the
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low chlorinated signature of PCBs volatilized from the suspected source (Hudson River). Finally, if lake-effect precipitation on the Tug Hill Plateau is an effective scavenger of highly chlorinated particulate-bound contaminants then one would expect to see a change in the PCB signature downwind of the area effected by lake-effect precipitation. Air sampling at Potsdam (Chiarenzelli et al. 2001a) and ten miles to the west at Canton (Chiarenzelli et al. 2000) northwest of the Tug Hill Plateau, and well outside of the area generally impacted by lake-effect storms, has documented a less chlorinated PCB pattern, consistent with the pattern from other sampling sites in the Great Lakes basin (Fig. 8). However, the Potsdam site has elevated concentrations of PCBs, similar to those measured at sites near the lake. This may reflect the ongoing migration of a continuous pulse of lower chlorinated PCBs downwind of Lake Ontario similar to the seasonal hopping proposed in the “coldcondensation” or “grasshopper” hypothesis (Rappe 1974, Wania and MacKay 1996). Note also that the average PCB signature of the Rice Creek core contains a greater proportion of the most chlorinated congeners than the Salmon River core (Fig. 5), perhaps because of its proximity to the lake (2 km). Confirmation of these proposed trends using soil or sediment transects from the lake eastward are planned for the near future. ACKNOWLEDGMENTS The authors wish to acknowledge funding from the Great Lakes Protection Fund and Great Lakes Research Consortium. Tom Holsen, Tom Young, and Phil Hopke of Clarkson University are thanked for their input on related studies. Three anonymous reviewers are thanked for their excellent suggestions on how to improve the manuscript. REFERENCES Achman, D., Hornbuckle, K., and Eisenreich, S., 1993. Volatilization of polychlorinated biphenyls from Green Bay, Lake Michigan. Environ. Sci. Technol. 27:75–86. Alcock, R., Johnston, A., McGrath, S., Berrow, M., and Jones, K., 1993. Long-term changes in the polychlorinated biphenyl content of United Kingdom soils. Environ. Sci. Technol. 27:1918–1923. Alexander, C., DeMaster, D., and Nittrouer, C. 1991. Sediment accumulation in a modern epicontinentalshelf setting. Marine Geology 98:51–72. ——— , Smith, R., Schropp, S., Calder, S., and Windom,
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H. 1993. The historical record of metal enrichment in two Florida estuaries. Estuaries 16: 627–637. Anderson, D., Bloem, T., Blankenbaker, R., and Stanko, T. 1999. Concentrations of polychlorinated biphenyls in the water column of the Laurentian Great Lakes. J. Great Lakes Res. 25:160–170. Appleby, P., Nolan, P., Gifford, D., Godfrey, M., Oldfield, F., Anderson, N., and Battarbee, R. 1986. Pb210 dating by lowbackground gamma counting. Hydrobiologia 143: 21–27. Blais, J., Schindler, D., Muir, D., Kimpe, L., Donald, D., and Rosenberg, B. 1998. Accumulation of persistent organochlorine compounds in mountains of western Canada. Nature 395:585–588. Bush, B., Simpson, K., Shane, L., and Koblintz, R., 1985. PCB congener analysis of water and caddisfly larvae in the Upper Hudson River by glass capillary column. Bull. Environ. Contam. Toxicol. 34:96–105. Chiarenzelli, J., Scrudato, R., Arnold, G., Wunderlich, M., and Rafferty, D. 1996. Volatilization of polychlorinated biphenyls from sediment during drying at ambient temperatures. Chemosphere 33:899–911. ——— , Scrudato, R., and Wunderlich, M. 1997. Volatile loss of PCB Aroclors from subaqueous sand. Environ. Sci. Technol. 31:597–602. ——— , Bush, B., Casey, A., Barnard, E., Smith, B., O’Keefe, P., Gilligan, E., and Johnson, G. 2000. Defining the sources of airborne polychlorinated biphenyls: evidence for the influence of microbially dechlorinated congeners from river sediment? Can. J. Fish. Aquat. Sci. 57:86–94. ——— , Alexander, C., Isley, A., Scrudato, R., Pagano, J., and Ramirez, W. 2001a. Polychlorinated biphenyls in nonaccumulating, century-old sediments: sources, signatures, and mechanism of introduction. Environ. Sci. Technol. 35:2903–2908. ——— , Pagano, J., Scrudato, R., Falanga, L., Migdal, K., Hartwell, A., Milligan, M., Battalagia, T., Holsen, T., Hsu, Y-K., and Hopke, P. 2001b. Enhanced airborne polychlorinated biphenyl (PCB) concentrations and chlorination downwind of Lake Ontario. Environ. Sci. Technol. 35:3280–3285. Commoner, B., Bush, B., Barlett, P., Couchot, K., and Eisl, H. 1999. The exposure of New York City Watershed to PCBs emitted from the Hudson River. Final Report for the Center for the Biology of Natural Systems, Queens College, Flushing, New York. Crane, J., and Sonzogni, W. 1992. Temporal distribution and fractionation of polychlorinated biphenyl congeners in a contaminated Wisconsin Lake. Chemosphere 24:1921–1941. Currado, G., and Harrad, S. 2000. Factors influencing atmospheric concentrations of polychlorinated biphenyls in Birmingham, U.K.. Environ. Sci. Technol. 34:78–82. Cutshall, N., Larsen, I., and Olsen, C. 1983. Direct analysis of 210Pb in sediment samples: self-absorption
corrections. Nuclear Instruments and Methods 206:309–312. Datta, S., McConnell, L., Baker, J., Lenoir, J., and Seiber, J., 1998. Evidence for atmospheric transport and deposition of polychlorinated biphenyls to the Lake Tahoe Basin, California-Nevada. Environ. Sci. Technol. 32:1378–1385. DeMaster, D., McKee, B., Nittrouer, C., Qian, J., and Cheng, G. 1985. Rates of sediment accumulation and particle reworking based on radiochemical measurements from continental shelf deposits in the East China Sea. Cont. Shelf Res. 4:143–158. Eisenreich, S., Looney, B., and Thornton, J.R. 1981. Airborne organic contaminants in the Great lakes ecosystem. Environ. Sci. Technol. 15:30–38. ——— , Capel, P., Robbins, J., and Bourbonniere, R. 1989. Accumulation and diagenesis of chlorinated hydrocarbons in lacustrine sediments. Environ. Sci. Technol. 23:1116–1126. Frame, G., Wagner, R., Carnahan, J., Brown, J., May, R., Smullen, L., and Bedard, D. 1996. Comprehensive, quantitative, congener-specific analyses of eight aroclors and complete congener assignments on DB-1 capillary GC columns. Chemosphere 33:603–623. Franz, T., and Eisenreich, S. 1998. Snow scavenging of polychlorinated biphenyls and polycyclic aromatic hydrocarbons in Minnesota. Environ. Sci. Technol. 32:1771–1778. ——— , and Eisenreich, S. 2000. Accumulation of polychlorinated biphenyls and polycyclic aromatic hydrocarbons in the snowpack of Minnesota and Lake Superior. J. Great Lakes Res. 26:220–234. Gevao, B., Hamilton-Taylor, J., Murdoch, C., Jones, K., Kelly, M., and Tabner, B. 1997. Depositional time trends and remobilization of PCBs in lake sediments. Environ. Sci. Technol. 31:3274–3280. Golden, K., Wong, C., Jeremiason, J., Eisenreich, S., Sanders, G., Hallgren, J., Swackhamer, D., Engstrom, D., and Long, D. 1993. Accumulation and preliminary inventory of organochlorines in Great Lakes sediments. Wat. Sci. Tech. 28:19–31. Green, M., DePinto, J., Sweet, C., and Hornbuckle, K. 2000. Regional spatial and temporal interpolation of atmospheric PCBs: interpretation of Lake Michigan mass balance data. Environ. Sci. Technol. 34:1833–1841. Harner, T., MacKay, D., and Jones, K. 1995. Model of the long-term exchange of PCBs between soil and the atmosphere in the southern U.K.. Environ. Sci. Technol. 29:1200–1209. Hillery, B., Basu, I., Sweet, C., and Hites, R. 1997. Temporal and spatial trends in a long term study of gasphase PCB concentrations near the Great Lakes. Environ. Sci. Technol. 31:1811–1816. Hornbuckle, K.C., Achman, D., and Eisenreich, S. 1993. Over-water and over-land polychlorinated biphenyls
Polychlorinated Biphenyls Downwind of Lake Ontario in Green Bay, Lake Michigan. Environ. Sci. Technol. 27:87–98. Jeremiason, J., Hornbuckle, K., and Eisenreich, S., 1994. PCBs in Lake Superior, 1978–1992: Decreases in water concentrations reflect loss by volatilization. Environ. Sci. Technol. 28:903–914. Kjeller, L-O., and Rappe, C. 1995. Time trends in levels, patterns, and profiles for polychlorinated dibenzo-pdioxins, dibenzofurans, and biphenyls in a sediment core from the Baltic Proper. Environ. Sci. Technol. 29:346–355. Koide, M., Soutar, A., and Goldberg, E. 1972. Marine geochronology with Pb-210. Earth Planet. Sci. Lett. 14:442–446. Krishnaswami, S., Lal, D., Martin, J., and Meybeck, M. 1971. Geochronology of lake sediments. Earth Planet. Sci. Lett. 11:407–414. Lee, R., and Jones, K. 1999. The influence of meteorology and air masses on daily atmospheric PCB and PAH concentrations at a UK location. Environ. Sci. Technol. 33:705–712. McConnell, L., Bidleman, T., Cotham, W., and Walla, M. 1998. Air concentrations of organochlorine insecticides and polychlorinated biphenyls over Green Bay, WI, and the four lower Great Lakes. Environ. Poll. 101:391–399. Mudroch, A., Allan, R., and Joshi, S. 1992. Geochemistry and organic contaminants in the sediments of Great Slave Lake, Northwest Territories, Canada. Arctic 45:10–19. Nittrouer, C., Sternberg, R., Carpenter, R., and Bennett, J. 1979. The use of Pb-210 geochronology as a sedimentological tool. Marine Geology 31:297–316. Oldfield, F., and Appleby, P. 1984. Empirical testing of Pb-210 dating models. In Lake Sediments and Environmental History, eds. E. Haworth and J. Lund, pp. 93–124. Minneapolis, MN: Univ. Minn. Press. Oliver, B., Charlton, M., and Durham, R. 1989. Distribution, redistribution, and geochronology of polychlorinated biphenyl congeners and other chlorinated hydrocarbons in Lake Ontario sediments. Environ. Sci. Technol. 23:200–208. Pagano, J., Rosenbaum, P., Roberts, R., Sumner, G., and Williamson, L. 1999. Assessment of maternal contaminant burden by analysis of snapping turtle eggs. J. Great Lakes Res. 25:950–961. Panshin, S., and Hites, R. 1994. Atmospheric concentrations of polychlorinated biphenyls at Bermuda. Environ. Sci. Technol. 28:2001–2007. Rappe, C. 1974. Ecological Problems of the Circumpolar Area, eds. E. Bylund, H. Linderholm, and O. Rune; pp. 29–32. Luleå, Sweden: Norbottem Museum. Rawn, D., Muir, D., Savoie, D., Rosenberg, G., Lock-
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hart, W., and Wilkinson, P. 2000. Historical deposition of PCBs and organochlorine pesticides to Lake Winnipeg (Canada). J. Great Lakes Res. 26:3–17. Robbins, J. 1978. Geochemical and geophysical applications of radioactivity. In The Biogeochemistry of Lead in the Environment, ed. J. Nriagu, pp. 285–393. Amsterdam, Netherlands: Elsevier. Scrudato, R., and McDowell, W., 1989. Upstream transport of mirex by migrating salmonids. Can. J. Fish. Aquat. Sci. 46:1484–1488. Simcik, M., Hoff, R., Strachan, W., Sweet, C., Basu, I., And Hites, R. 2000. Temporal trends of semivolatile organic contaminants in Great Lakes precipitation. Environ. Sci. Technol. 34:361–367. Swackhamer, D., and Armstrong, D. 1986. Estimation of the atmospheric and nonatmospheric contributions and losses of polychlorinated biphenyls for Lake Michigan on the basis of sediment records of remote lakes. Environ. Sci. Technol. 20:879–883. Sweetman, A., and Jones, K. 2000. Declining PCB concentrations in the U.K. atmosphere: evidence and possible causes. Environ. Sci. Technol. 34:863–869. U.S. Census Bureau. 1980. http://www.census.gov/ cgi-bin/gazetteer?city+Redfield&state=NY&zip= Van Metre, P., Callender, E., and Fuller, C. 1997. Historical trends in OCs in river basins identified using sediment cores from reservoirs. Environ. Sci. Technol. 31:2339–2344. Vartiainien, T., Mannio, J., Kinnunen, K., and Strandman, T. 1997. Levels of PCDD, PCDF and PCB in dated lake sediments in subarctic Finland. Chemosphere 34:1341–1350. Veith, G., and Kiwus, L. 1977. An exhaustive steam-distillation and solvent extraction unit for pesticides and industrial chemicals. Bull. Environ. Contam. Toxicol. 17:631–636. Wania, F., and MacKay, D. 1996. Tracking the distribution of persistent organic pollutants. Environ. Sci. Technol. 30:390A–396A. Welch, H., Muir, D., Billeck, B., Lockhart, L., Burnskill, G., Kling, H., Olson, M., and Lemoine, R. 1991. Brown snow: A long-range transport event in the Canadian Arctic. Environ. Sci. Technol. 25:280–286. Yamashita, N., Kannan, K., Imagawa, T., Villeneuve, D., Hashimoto, S., Miyazaki, A., and Giesy, J. 2000. Vertical profile of polychlorinated dibenzo-p-dioxoins, dibenzofurans, naphthalenes, biphenyls, polycyclic aromatic hydrocarbons, and alkylphenols in a sediment core from Tokyo Bay, Japan. Environ. Sci. Technol. 34:3560–3567. Submitted: 9 February 2002 Accepted: 22 July 2002 Editorial handling: Keri C. Hornbuckle
Anomalous Concentrations and Chlorination of Polychlorinated Biphenyls in Sediment Downwind of Lake Ontario Jeffrey Chiarenzelli1,*, Clark Alexander2, Ronald Scrudato3, James Pagano3, Lauren Falanga3, Benjamin Connor3, and Michael Milligan4 1Department
of Geology SUNY Potsdam Potsdam, New York 13676 2Skidaway
Institute of Oceanography 10 Ocean Science Circle Savannah, Georgia 31411
3Environmental
Research Center SUNY Oswego Oswego, New York 13126
4Department
of Chemistry SUNY Fredonia Fredonia, New York 14063 ABSTRACT. Relatively high concentrations (up to 98.5 ng/g dry wt) of polychlorinated biphenyls (PCBs) have been found in two cores penetrating fluvial sands east of Lake Ontario. One core was taken from the upper Salmon River reservoir on the Tug Hill Plateau and the other from Rice Creek near the lake at Oswego. In both instances, portions of the cores containing PCBs and other organochlorines (OCs) lack excess radiogenic 210Pb and 137Cs, implying depositional ages predating widespread OC commercial production, use, and release. Within each core there is little vertical variation in PCB composition and highly chlorinated congeners dominate the pattern. In addition, the PCB signature is analytically indistinguishable between cores despite collection over 50 km apart. This argues against local sources, and implies deposition and accumulation by processes operating over a substantial area and time period. Transport and introduction of a residual fraction of colloidal-bound PCBs to the sands via tannin-rich riverine waters is proposed. The PCB congener-specific pattern of air samples collected during the spring and summer of 1999 downwind of the lake at two locations (Rice Creek and Sterling) are similar to the sediments and display anomalous concentrations and chlorination with respect to other air sampling localities in the Great Lakes. A link between the residual fraction of PCBs observed in the sediment and air patterns via volatilization from the terrestrial surface is proposed. Elevated PCB concentrations and chlorination in non-radiogenic fluvial sands and air may reflect regional accumulation and weathering processes operating over many decades and/or enhancement of contaminant deposition and partitioning downwind of the lake related to lake-effect precipitation. INDEX WORDS:
Organochlorides, radionuclides, sediment core, Lake Ontario, Tug Hill Plateau.
INTRODUCTION Over two decades of research has enhanced the understanding of the mass balance of organic conta-
*Corresponding
minants in Great Lake’s environmental media (Anderson et al. 1999, Eisenreich et al. 1981, Green et al. 2000, Hillery et al. 1997, Hornbuckle et al. 1993). This work has been particularly relevant in predicting future trends in contaminant levels, and devising appropriate strategies for continued moni-
author. E-mail: [email protected]
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Polychlorinated Biphenyls Downwind of Lake Ontario toring and improvements in environmental quality. In addition to the concentrations of contaminants in environmental media, temporal trends in their composition must also be considered. The fractionation of contaminants related to their physicochemical properties has been widely documented (Blais et al. 1998, Rappe 1974, Wania and MacKay 1996) and suggests temporal changes in contaminant compositions in various environmental media are inevitable, particularly within a group of related isomers. Because of their capacity to store enormous amounts of heat, large water bodies influence the meteorology of bounding landmasses. The Great Lakes have a significant moderating effect along their shores and one meteorological phenomenon is copious amounts of precipitation downwind of the lakes. The scavenging effect of precipitation, especially snowfall, relative to organic carbon compounds (OCs) is widely recognized (Blais et al. 1998; Franz and Eisenreich 1998, 2000). It is hypothesized that “lake-effect” precipitation may result in enhanced contaminant deposition and fractionation in the Great Lakes ecosystem. Located downwind of Lake Ontario, the Tug Hill Plateau (Fig. 1) receives enhanced rain and snowfall, often forming discrete bands extending from the lake inland as much as 80 km or more. One such “lake-effect” snowstorm resulted in the deposition of 241 cm of snow in Montague, NY (11 and 12 January 1997). It is suspected that the Tug Hill Plateau may have received relatively high fluxes of OCs in the past and, if so, these trends may be reflected by their concentration and composition in environmental media. In addition, because lakeeffect precipitation largely occurs, and is recaptured, within Lake Ontario’s drainage basin, regional processes, related to meteorological factors, may further enhance OC partitioning during complex cycling of contaminants within the drainage basin. A preliminary investigation of OCs in air and sediment was begun in 1999. The results of the air sampling program has been previously summarized (Chiarenzelli et al. 2001b) and suggest a significant seasonal enhancement in both PCB chlorination and concentration downwind of Lake Ontario relative to other Great Lakes sample sites (Hillery et al. 1997). Reported here is the signature of PCBs found in sediment cores collected near the lake and 50 km away on the Tug Hill Plateau, both areas of considerable lake-effect precipitation. The signature of the sediment will be compared with that of airborne PCBs in the same area to evaluate the hypothesis
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FIG. 1. Diagram showing the study area, geographic place names, locations of core and air samples discussed, and major water bodies. that volatilization from the terrestrial surface controls the composition and concentration of airborne PCBs. The heavily chlorinated nature of the PCB patterns in both media may be a reflection of temporal trends and local meteorological factors, such as lake-effect precipitation, which may enhance deposition and fractionation of OC contaminants. EXPERIMENTAL SECTION Sampling Locations Core samples were taken from fluvial sands in the upper Salmon River reservoir (SR) near Redfield, New York, and Rice Creek near Oswego, New York, adjacent to Lake Ontario (Fig. 1). Data from the Rice Creek core have been reported elsewhere (Chiarenzelli et al. 2001a) and further discussion of this sample will be limited to comparison with SR samples to avoid unnecessary duplication. The SR receives drainage from a large (~464 km2), remote, forested region of the Tug Hill Plateau whose center is 50 km east of Lake Ontario. The Salmon River core was collected from a shallow (1-m depth), marshy area adjacent to the entry of the North Branch of the Salmon River into the eastern end of the reservoir at an elevation of 286 m, 1 kilometer from the hamlet of Redfield (pop. 564; U.S. Census Bureau 1990). The upper SR reservoir was built in 1914, and dams at the upper and lower reservoirs and the intervening
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Salmon River Falls prevent the access of migrating salmonids and their body burden of contaminants (Scrudato and McDowell 1989). Sampling Procedures The SR core samples were taken on 5 August 1999 utilizing pre-cleaned Plexiglas tubes driven into the sediment. Samples were collected from a relatively quiet, shallow water site (N43°31′48″ W75°48′47″) located where deltaic sediments of the North Branch of the Salmon River are prograding into the reservoir. A carpet of well established aquatic vegetation indicated little, if any, recent reworking of the sampling site. Due to seasonal lowering of water levels during operation of the hydroelectric facilities, the site is periodically emergent during the winter months. Several cores containing 40 to 50 cm of sediment were recovered; only one was utilized for analysis. Sediment samples varied from moderately to weakly stratified and consisted of homogeneous, fine silty sands of dark brown to gray brown color with sparse organic fragments. The preservation of stratification suggested that bioturbation was minimal. Cores were immediately returned to the laboratory and opened by successive longitudinal scoring with a Dremel tool and carpet knife. Care was taken to minimize disturbance of the core. Once exposed, the core was rapidly sectioned into 2-cm intervals with stainless steel tools and placed in pre-cleaned glass jars. The jars were stored in the dark in the refrigerator at 4°C until analyzed. Analyses were completed within 3 months of sampling. Before analysis each core interval was homogenized manually. The sub samples were never allowed to dry or otherwise exposed to ambient air for periods in excess of several minutes (Chiarenzelli et al. 1996). Organochlorines Complete analytical details are presented in recently published work (Chiarenzelli et al. 2001a). Sediment samples were extracted by steam distillation (Veith and Kiwus 1977, Swackhamer and Armstrong 1986) to minimize the extraction of organic compounds with the potential for chromatographic co-elution with PCBs (Mudroch et al. 1992). Five to ten grams of sediment (wet weight) was boiled in 300 mL of water for 24 hours and the condensate continuously refluxed through 10 mL of hexane. After extraction the hexane layer was drained and transferred for Florisil clean up. Before extraction,
recovery surrogates consisting of IUPAC congeners 14, 65, 166, and 209 were added to the sediment. Cleanup consisted of acid digestion (HNO 3) and sulfur removal (tetrabutylammonium sulfate) followed by elution through deactivated (4%) Florisil columns. After clean up, samples were condensed to 1 mL using a Kuderna-Danish apparatus and steam bath for GC-ECD analysis. Analysis included 93 peaks representing 130 PCB congeners, p,p′DDE, HCB, and mirex. A program incorporating method, apparatus, and reagent blanks, surrogate spikes, matrix spikes, and duplicate samples monitored quality assurance. All blanks were < 5 pg/µL injection PCBs and > 90% were at sub-picogram level. The mass of PCBs in core sample extracts ranged from 20 to 264 pg/µL with an average of 65.4 pg/µL, indicating a favorable sample to blank ratio. Recovery of IUPAC congeners 14, 65, 166, and 209 during extraction and analysis averaged (± 1SD) 83 ± 15, 90 ± 15, 118 ± 24 and 103 ± 30 percent. Congener-specific PCB analyses and select pesticides utilized capillary column procedures after Frame et al. (1996). The calibration standard was composed of a nine set mixture of all 209 PCB congeners, and HCB (5 pg/µL), DDE (10 pg/µL), and mirex (10 pg/µL) obtained from the EPA Pesticide Repository. This standard was run every sixth sample and used to calibrate the gas chromatograph. Congener assignments and weight percent distributions for the calibration standard were confirmed with a Hewlett Packard Model 5890 II gas chromatograph with an electron capture detector (Pagano et al. 1999). Samples were analyzed utilizing a HP Ultra II 25 meter DB-5 capillary column with 0.22 mm ID and 0.33 µm film thickness on a Hewlett Packard Model 5890 II gas chromatograph equipped with an auto sampler and electron capture detector ( 63N i ). Helium and P5 (argon/methane) were used as carrier and makeup gases, respectively. After 2 minutes, the system was incrementally heated from 100 to 160°C over 6 minutes and then at a rate of 3°C/min to 270°C and held for 16 minutes. The injector port and detector were maintained at 270°C and 330°C, respectively. Major and Trace Element Analysis The core was composed predominantly of fine to very fine sand (~75 to 86%), a small amount of silt (~14 to 24%), and only minor amounts of claysized material (0.3 to 1.4%). Organic carbon varied from 0.90 to 3.95%. Core interval sub samples were
Polychlorinated Biphenyls Downwind of Lake Ontario sieved to provide < 62.5µ fraction for major and trace element analysis. Because of the scarcity of fine material, each sub sample represented 4-cm intervals of core in contrast to the 2-cm interval utilized for all other analyses. Acme Analytical Laboratories, Ltd. in Vancouver, Canada, conducted major and trace element analyses. Sub samples (0.2 g dry weight) were fused with 1.5 g of LiBO2 and dissolved in 100 mL of 5% HNO3 before x-ray fluorescence analysis. Splits for trace element analysis where gently ground by mortar and pestle and sieved. Sub samples (5.0 g) were digested with a 30 mL HCl-HNO3-H2O (1:1:1) solution at 90°C for 1 hour and brought up to 100 mL in water and directly analyzed. Metals of anthropogenic interest (Mo, Cu, Zn, Ag, As, Cd, Sb, Hg, and Se) are further extracted with methyl isobutyl ketone and then analyzed by ICP-MS. Quality control was monitored through replicate samples and standards. Aside from Ni and Zr, concentrations of all elements were replicated to within 90%. Core Dating Sediment age was inferred from radiochemical analysis of naturally occurring and manmade radionuclides. Lead-210 (210Pb), a naturally occurring radionuclide with a 22.3-year half-life, has been used for decades to characterize sedimentary processes on 100-y time scales (Krishnaswami et al. 1971, Koide et al. 1972, Nittrouer et al. 1979, Oldfield and Appleby 1984, DeMaster et al. 1985, Alexander et al. 1991, 1993). There are two components to the total 210Pb signal: 1) supported 210Pb activity, that provided by in situ decay of the effective parent, 226Ra, in the sediment column; and 2) excess 210Pb activity, that amount above the supported levels provided by particulate scavenging of 210Pb in the atmosphere and water column. Excess 210 Pb decays below detectable limits in approximately five half-lives and thus is observed in sediments representing the past ~112 y. If no excess 210 Pb is present, sediments are interpreted to be non-accumulating or erosional and older than 100 years in age. Cesium-137 (137Cs), a bomb-produced impulse tracer with a 30.1 y half-life was first introduced into the environment through atmospheric weapons testing in 1954. Since the cessation of atmospheric weapons testing, the atmospheric flux of 137Cs has decreased to 10% of its 1964 peak value. Activities of radionuclides within each sample were determined concurrently using a low-background germanium detector following the tech-
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niques described in Alexander et al. (1999). Sediments were dried, ground with a porcelain mortar and pestle, and sealed in 30-mL polypropylene jars. Samples were allowed to equilibrate for 20 days to assure equilibrium between 226Ra and intermediate daughter products. Total 210Pb activity was directly determined by gamma-spectroscopic measurement of its 46.5-KeV gamma peak (Appleby et al. 1986). Correction for sediment self-absorption was performed following the method of Cutshall et al. (1983). Supported levels of 210Pb were determined for each depth interval by concurrently measuring the gamma activity of 214Pb and 214Bi, the shortlived granddaughters of 226Ra, at 295, 352, and 609 KeV. The activity of 137Cs was directly determined by gamma spectroscopic measurement of its 661.6KeV peak (Robbins 1978). RESULTS Radiochemistry Excess 210Pb activity was measured within the core down to the 36 to 38 cm interval. The lack of excess 210Pb activity below the 36 to 38 cm interval documents that sediments below this level in the core are older than ~100 years. Lead-210 activity is relatively constant from the surface down to 24 to 26 cm and decreases exponentially from 25 to 37 cm (Fig. 2). Statistically significant amounts of
FIG. 2. Trends in radionuclide activities measured in the upper Salmon River reservoir core. Note that 226Ra is an estimate of supported 210Pb and 210PbTotal = 210Pbexcess + 200Pbsupported.
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FIG. 3. Trends in organochlorine concentrations measured in the upper Salmon River reservoir core.
137Cs
activity occur in the core down to 32 to 34 cm interval. The values are relatively constant and low from the top of the core to the 14 to 16 cm interval, peak in the 24 to 26 cm interval, and decrease sharply with a linear trend thereafter.
Organochlorines Polychlorinated biphenyls were found throughout the core in measurable concentrations (Fig. 3). Dry weight concentrations ranged from a high of 98.5 ng/g (20–22 cm) to ca. 3 ng/g near both the top and bottom of the core. No clear vertical trends were apparent, with variable concentrations occurring throughout the core. However, a general decrease in PCB concentration occurs from 20 to 22 cm upwards, while below 22 cm the concentration fluctuates significantly. A concentration of 70 ng/g was measured in the lowermost interval (48 to 50 cm), at odds with depositional trends and production records (Eisenreich et al. 1989, Oliver et al.1989). The concentrations of p,p′-DDE and HCB show similar trends and their concentrations were the best correlated (r = .73), even though p,p′-DDE is approximately ten times more abundant. The occurrence of both compounds was low below 34 to 36 cm with both compounds being sporadically nondetectable. Both compounds showed a gradual increase with broad maxima occurring from about 8 to 32 cm (Fig. 3). Maximum concentrations of p,p′DDE occurred at 26 to 28 cm (1,005 pg/g) and that of HCB at 20 to 22 cm (84.7 pg/g). The profiles observed are similar to, but do not necessarily reflect,
commercial production trends of DDT and chlorobenzene in the U.S. and deposition records in the Lake Ontario cores (Eisenreich et al. 1989, Oliver et al. 1989). Mirex, first commercially manufactured in 1959, was absent from the bottom 20 cm of the core (Fig. 3). Above the 28–30 cm interval Mirex was detected in all but three intervals (2 to 4, 10 to 12, 12 to 14 cm). Maximum concentrations occurred in both the 22 to 24 cm interval (78.6 pg/g) and again at 8 to 10 cm (82.3 pg/g). The profile is not consistent with sediment profiles from Lake Ontario or production records (Eisenreich et al. 1989, Oliver et al. 1989), suggesting an alternative explanation for its sporadic occurrence and concentration pattern. Porosity A clear shift in porosity values is also noted in the core between the 22 to 24 and 24 to 26 cm intervals (Fig. 4). Below 22 to 24 cm the porosity is relatively low, ranging from ~47 to 60%. In the upper half of the core, however, values range from ~60 to 75%, with the exception of the two uppermost intervals which are distinctly lower (41.7 and 49.9%).
FIG. 4. Trends in porosity, and select major and trace element chemistry measured in the upper Salmon River reservoir core. The dashed line represents the proposed break in sedimentation at ~24 cm.
Polychlorinated Biphenyls Downwind of Lake Ontario Major Elements The lower half of the core contained significantly more SiO2 (Fig. 4), reflecting a greater percentage of detrital quartz. In contrast, the upper half of the core contained significantly higher amounts of Fe 2O 3, CaO, MnO, and C, and lost more weight upon ignition (LOI). Other major elements, that were also more abundant in the upper half of the core, include Al2O3, MgO, K2O, and P2O5. However, these differences were not statistically significant. No trends in major element chemistry were noted in either half of the core. The data support a distinct break in major element chemistry in the core between the 22 to 24 and 24 to 26 cm intervals. Trace Elements While virtually all trace element concentrations were elevated in the upper half of the core, differences in Cd, Cu, Hg, Mn, Pb, and Zn were statistically significant at the two sigma confidence levels (Fig. 4). As with the major elements, no clear vertical trends were found in trace element composition. Trace element concentrations also support a significant change in sediment composition at ~24 cm, probably reflecting the greater percentage of fine sediment in the upper half of the core. DISCUSSION Interpretation of the Salmon River Core Fluvial sands are subject to substantial reworking and extended periods of little or no sediment accumulation and are unlikely to accurately record uninterrupted depositional trends; this study is no exception. A significant observation, prompting this study, is that the core has elevated OC concentrations throughout its 50-cm length and despite its grain-size. Further, intervals below 36 to 38 cm lack excess radiogenic 210 Pb activity and were therefore were deposited over ~100 years ago. The occurrence of OC compounds implies their introduction after deposition, which has also been documented in the Rice Creek core taken 50 kilometers away near the lakeshore (Chiarenzelli et al. 2001a). The vertical concentration trends of PCBs and mirex concentrations in the core do not match depositional trends recorded in Lake Ontario or commercial production records (Eisenreich et al. 1989, Oliver et al. 1989), requiring an alternative explanation. Taken together, the radiochemical data presented
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above indicates a significant change in sediment and radionuclide accumulation history at ~24 cm and that sediment deposition or mixing was rapid in the upper half of the core relative to a time scale of 22 years (210Pb half-life). A distinct break at 24 cm is also supported by changes major and trace element chemistry and porosity values. Precipitation records indicate that after a relatively dry spring and summer, over 59 cm of precipitation fell on the Tug Hill Plateau during the fall of 1965 (Highmarket Station—Northeast Regional Climatic Center). Runoff in response to this precipitation would have resulted in substantial reworking of the bed of the Salmon River. Other scenarios, including a thick (24 cm) zone of mixing, are also possible. However, maximum 137Cs activities were measured in the core at 24 to 26 cm and likely correspond to peak atmospheric levels of 137Cs at ca. 1964, and if so, provide a time-marker just prior to the proposed reworking event. Thus a plausible explanation for the non-accumulative nature of both 210 Pb and 137Cs above 24 cm is the rapid deposition of sediment in response to reworking of the riverbed during the unusually wet fall of 1965. Regional Accumulation Processes A sediment core was also taken from fluvial sands of Rice Creek nearly 50 kilometers from the Salmon River sampling site (Fig. 1). The Rice Creek core was collected within a kilometer of Lake Ontario near Oswego and its drainage basin has several substantial differences with that of the remote, entirely forested upper Salmon River drainage basin. Differences include population density, size, land-use, and elevation, among others (Chiarenzelli et al. 2001a). Despite these differences, PCB congener-specific patterns (Fig. 5) and the mean PCB concentration found in both cores are statistically identical. In addition, neither site shows significant vertical trends in the PCB congener pattern and chemistry (Fig. 6). Similar to the Salmon River core, the Rice Creek core was found to lack 137Cs and excess 210Pb, and the sediment was inferred to be older than ~100 years despite significant concentrations of OCs (Chiarenzelli et al. 2001a). The correspondence of PCB patterns despite differences in geographic location (50 km), drainage basin characteristics, and stratigraphic position suggests regional processes, rather than local sources, are responsible for the deposition of contaminants in the area east of Lake Ontario and that
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FIG. 5. Comparison of the average congener specific PCB pattern of fluvial sands from upper Salmon River (n = 25) reservoir and Rice Creek (n = 22) by mole fraction percentage. The correlation coefficient (r2) between the average patterns is 0.97; comparisons between individual samples are as high as 0.99. Note the slight enrichment in higher chlorinated congeners in the Rice Creek pattern relative to the Salmon River core.
Polychlorinated Biphenyls Downwind of Lake Ontario
FIG. 6. Vertical trends in PCB chemistry observed in the Salmon River (n = 25) and Rice Creek (n = 22) cores (average chlorines per biphenyl, sum of penta- through hepta-homolog groups, and ortho-chlorine mole fraction percentage). The chlorine per biphenyl ratio of Aroclor 1254 has been added for reference as a dashed line. The penta-hepta homologs have been grouped to point out relative proportions of highly chlorinated (~60-70%) versus di-tetra chlorinated (~10-20%) congeners (not shown).
these processes have selectively concentrated the same PCB congeners over many decades. The PCB congener pattern in both cores is dominated by congeners with five to seven chlorines (Fig. 6) which generally comprise 60 to 70% of the total. These include IUPAC congeners (89+101, 77+110, 123+149, 118, 153, 138+163+164, 187, 174, 180, and 170+190), interpreted as a residual fraction of atmospherically deposited PCBs remaining in the drainage basin after partitioning and weathering in the environment (Chiarenzelli et al. 2001a). Perhaps even more striking is the lack of lower chlorinated PCBs in samples from both cores. With one exception (the sporadic occurrence of IUPAC # 15+17), congeners with two, three, or four chlorines that typically dominate the pattern of air and water samples are nearly absent, comprising at most a percent or two of the total (Fig. 5). This is taken as evidence of considerable fractionation in
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an area (Tug Hill Plateau), which receives its entire PCB load by atmospheric deposition. How this fraction of highly chlorinated congeners was introduced into sediment deposited before the widespread production and use of PCBs is an intriguing problem. Considerable amounts of PCBs can be found and transported in water; however, the composition of aqueous phase PCBs is dominated by lower chlorinated congeners with relatively high solubilities (Achman et al. 1993, Anderson et al. 1999, Bush et al. 1985, Crane and Sonzogni 1992, Datta et al. 1998), thus making introduction by direct adsorption from riverine or ground waters improbable. Particulate phase PCBs in water are generally higher chlorinated, however, particulate phase PCBs pattern in Lake Ontario (Anderson et al. 1999) is significantly less chlorinated than that found in the core samples in this study. Lower portions of the core also lack excess 210Pb and 137Cs that would also be introduced adhered to fine particles. The length of both cores (~44 and 50 cm), and the lack of vertical compositional trends, suggest introduction by diffusionrelated processes is also unlikely. In other core studies in which PCBs are found in horizons dating before their production, lower chlorinated congeners are enriched (Gevao et al. 1997, Yamashita et al. 2000), unlike the consistently heavily chlorinated pattern found in this study. Proposed is an accumulation mechanism whereby residual PCBs are introduced into fluvial sands by tannin-rich riverine waters in colloidal suspension and/or adhered to dissolved organic matter (Chiarenzelli et al. 2001a). If so, permeability may be the primary factor controlling which stratigraphic intervals accumulate large amounts of OCs and thus likely bear no relevance to the historical deposition in the drainage basin. Some areas of the core, particularly zones of enhanced permeability, may represent the accumulation of PCBs over several decades or the location of introduced contaminants may shift with time as water levels fluctuate in the drainage basin or reservoir. Such a scenario may explain the composition of the PCB fraction in the fluvial sands (intense weathering and removal of the lower chlorinated congeners resulting in a highly chlorinated residual) and their enhanced concentrations (decades of and/or preferential accumulation). Further, the discovery of identical congener-specific patterns in fluvial sands at widely separated (50 km) locations argues that PCB accumulation occurred by processes operating over a wide area downwind of the lake.
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Chiarenzelli et al. in sediments of Lake Michigan (Swackhamer and Armstrong 1986, Golden et al. 1993) that received direct PCB discharge from urban areas including Chicago and are significantly elevated above those in other rural and remote areas. The sporadic occurrence of other OCs may be a reflection of numerous factors, including their low initial concentrations in air samples relative to PCBs, detection limits, biological or physical alteration in the drainage basins, extended, complex, multi-stage partitioning processes, and solubility and volatility considerations.
FIG. 7. Comparison of PCB concentrations measured in sediment core studies in the literature. References: Lake Ontario—Eisenreich et al. (1989) and Oliver et al. (1989); Tokyo Bay— Yamashita et al. (2000); Urban reservoirs—Van Metre et al. (1997); Lake Michigan—Swackhamer and Armstrong (1986) and Golden et al. (1993); Salmon River—this study; Rice Creek—Chiarenzelli et al. (2001); Wisconsin Lakes—Swackhamer and Armstrong (1986); Rural English Lakes— Gevao et al. (1997); Lake Winnipeg—Rawn et al. (2000); Rural Reservoirs—Van Metre et al. (1997); Lake Superior—Golden et al. (1993); Baltic Proper—Kjeller and Rappe (1995); Great Slave Lake—Mudroch et al. (1992); Subarctic Finland—(Vartianien et al. 1997).
One long-term consequence of this process may be the relatively high concentrations of PCBs in the cores examined. Figure 7 shows the mean concentrations of the Salmon River and Rice Creek cores relative to other studies in the literature. However, in contrast to the other studies relatively clean sands were analyzed rather than clay and organicrich, deeper water muds. Despite this, the concentrations measured in both cores are similar to those
Links to Anomalously Chlorinated Airborne PCB Signature Downwind of the Lake? The discovery of a highly chlorinated fraction of PCBs in fluvial sands downwind of the lake may have other important implications. Previous air sampling in the same area has documented an increase in PCB chlorination and concentration as the land surface warms (Chiarenzelli et al. 2001b). Both the concentrations and chlorination of airborne PCBs downwind of the lake are anomalous with respect to other sampling sites (Hillery et al. 1997) in the Great Lakes basin (Fig. 8). Urban areas could conceivably provide higher concentrations and more chlorinated PCB patterns (Currado and Harrad 2000) and indeed, the data from the Rice Creek air sampling station is similar to that of Chicago collected in the summers of 1994 and 1995 (Green et al. 2000). Plumes containing elevated concentrations of airborne PCBs have been traced for maximum distances of 40 km east of the city (Green et al. 2000). However, no large, urban center exists within several hundred kilometers upwind of the Tug Hill Plateau and volatilization of PCBs directly from the lake (Achman et al. 1993, Hornbuckle et al. 1993, Jeremiason et al. 1994, McConnell et al. 1998) cannot explain the highly chlorinated air pattern observed. A more likely scenario is that the PCB signature observed in fluvial sands from two locations downwind of the lake is representative of regional processes across the Tug Hill Plateau in concert with global atmospheric trends. As PCBs concentrations have dropped globally workers have concluded that fugacity considerations (Harner et al. 1995) now facilitate the release of previously sequestered PCBs from terrestrial repositories (Alcock et al. 1993, Lee and Jones 1999, Sweetman and Jones 2000). Thus it is likely that the air concentrations and patterns recently measured down-
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would minimize the chlorination of air samples relative to the sediment pattern.
FIG. 8. A comparison of Integrated Atmospheric Deposition Network (IADN) airborne PCB concentrations and chlorination (Hillery et al. 1997) with those east of Lakes Erie and Ontario (Chiarenzelli et al. 2001a). The area in black surrounding the Great Lakes is the drainage basin. White ovals contain mean spring and summer airborne PCB concentrations in picograms per cubic meter, black ovals give the mean chlorine per biphenyl ratio. Note that IADN samples were collected during 1994 to 1996, while those of Chiarenzelli et al. (2001b) were collected in 1999. wind of the lake in the summer are the direct result of volatilization from the terrestrial surface. This is consistent with seasonal increase in PCB concentration and chlorination observed in air samples taken downwind of the lake from the late winter to summer (Chiarenzelli et al. 2001b) and along the St. Lawrence River (Chiarenzelli et al. 2000). Airborne PCBs from the same area show many similarities (r2 = 0.78) to the pattern recovered from the fluvial sand cores with many of the same highly chlorinated congeners dominating the pattern (Fig. 9). However, as observed in volatilization experiments with PCB Aroclors (Chiarenzelli et al. 1997), the air pattern is somewhat less chlorinated than the sediment pattern, reflecting the preferential volatilization of available congeners with fewer chlorines. The admixture of lower chlorinated congeners from atmospheric background (Panshin and Hites 1994) or derived from volatilization from the lake (Achman et al. 1993, Hornbuckle et al., 1993, Jeremiason et al. 1994, McConnell et al. 1998)
Regional Considerations and the Potential Role of Lake-effect Precipitation? The scavenging effect of precipitation, both rain and snow, is widely recognized (Blais et al. 1998; Franz and Eisenreich 1998, 2000; Simcik et al. 2000) and likely leads to the enhanced deposition of PCBs and other OCs in areas effected by lakeeffect precipitation. The cold temperatures of high altitude and latitude regions maximize the deposition of lower chlorinated congeners via cold condensation processes (Blais et al. 1998, Rappe 1974, Wania and MacKay 1996). In contrast, the climatic conditions near Lake Ontario would maximize the potential for the residual accumulation of highly chlorinated congeners derived from the snow pack, as lower chlorinated congeners were lost through volatilization or runoff when warming occurs. Concentrations of PCBs measured in sands from cores at Rice Creek and the upper Salmon River record the deposition and retention of highly chlorinated congeners. The sporadic occurrence of lower chlorinated congeners in core samples and air near the lake documents their preferential removal from the system via the “grass hopper” effect and/or thermally driven volatilization. Lake-effect precipitation may play a critical role in contaminant deposition and fractionation, particularly in the removal of fine particulates from fartraveled air masses. This is not unprecedented, as air masses originating in Asia have deposited considerable amounts of OCs and fine particulates in so-called “brown” snow events in the Canadian Arctic (Welch et al. 1991) and much recent work has also focused on the trans-oceanic transport of particulates. The areas south and east of Lake Ontario receive considerable amounts of lake-effect precipitation from prevailing southwesterly to northwesterly winds. In particular, elevated areas of the Tug Hill Plateau and western Adirondacks receive localized precipitation, often in the form of bands, resulting from the evaporation of lake water and deposition over the frozen land. Precipitation records for the past 40 years indicate a mean of 135.7 cm on the Tug Hill Plateau at Highmarket and 105 cm at Oswego on the lake (Northeast Regional Climate Center, Cornell University). In these areas annual snowfall totals can exceed 500 cm per year. If the scenario described above has merit, one
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FIG. 9. Comparison of average (n = 22) sediment PCB signatures at Rice Creek with airborne (summer 1999) patterns just east of Lake Ontario near Oswego, New York, by mole fraction percentage. The correlation coefficient (r2) for the comparison is 0.78. Note the similarity in the abundance of highly chlorinated congeners and the preferential enrichment of the heaviest congeners in the sediment relative to the air. The lower chlorinated congeners in the air samples cannot be derived from the sediment but may reflect volatilization from the lake or the atmospheric background signature.
Polychlorinated Biphenyls Downwind of Lake Ontario could legitimately ask why other areas impacted by lake-effect snow in the Great Lakes basin do not show similar phenomena? For instance, work at the Stockton air sampling site east of Lake Erie (Fig. 8) has found only slightly elevated PCB concentrations relative to other sites (IADN sites, Hillery et al. 1997) despite its location in Lake Erie’s snow shadow. However, the Stockton PCB signature is more chlorinated than any of the other air sampling sites, except those east of Lake Ontario. The Tug Hill Plateau is uniquely situated with respect to a number of distant, downwind urban centers including Rochester, Buffalo-Niagara Falls, Toronto-Hamilton Harbour, and the more distant metropolitan areas in the mid-west. Urban areas, particularly those associated with manufacturing and the chemical industry, are typically sources of organic contaminants. For example, despite the ban of PCBs in 1977, Chicago continues to serve as a source of PCBs forming plumes that extend for tens of kilometers or more under certain meteorological conditions (Green et al. 2000). Urban areas are also generally associated with more highly chlorinated PCB air patterns (Currado and Harrad 2000). It is suggested that a large percentage of the highly chlorinated PCBs and other contaminants found in fluvial sands east of Lake Ontario probably originated in urban and/or industrial centers to the south and west. Over the last six or seven decades, lake-effect precipitation associated with Lake Ontario’s meteorological influence has provided an effective mechanism for removing these contaminants from regional air masses and depositing them in remote areas far from other sources. Weathering processes in the drainage basin, including volatilization and solubilization, have led to the removal of most lower chlorinated PCBs, retaining a residual fraction of highly chlorinated congeners and other similar OCs (Chiarenzelli et al. 2001a, 2001b). Transportation of semi-volatile contaminants within drainage basins in colloidal suspension and/or adsorbed to humic and fulvic acids has resulted in their introduction into fluvial sands deposited more than 100 years ago. Falling fugacities for PCB congeners (Harner et al. 1995) have resulted in the near equilibrium release of higher chlorinated congeners from local terrestrial repositories (Currado and Harrad 2000) and these now dominate the air pattern over the region (Chiarenzelli et al. 2001b). A similar chlorination enrichment mechanism has been proposed by Commoner et al. (1999) for airborne PCB signature found at localities in the New York City watershed despite the
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low chlorinated signature of PCBs volatilized from the suspected source (Hudson River). Finally, if lake-effect precipitation on the Tug Hill Plateau is an effective scavenger of highly chlorinated particulate-bound contaminants then one would expect to see a change in the PCB signature downwind of the area effected by lake-effect precipitation. Air sampling at Potsdam (Chiarenzelli et al. 2001a) and ten miles to the west at Canton (Chiarenzelli et al. 2000) northwest of the Tug Hill Plateau, and well outside of the area generally impacted by lake-effect storms, has documented a less chlorinated PCB pattern, consistent with the pattern from other sampling sites in the Great Lakes basin (Fig. 8). However, the Potsdam site has elevated concentrations of PCBs, similar to those measured at sites near the lake. This may reflect the ongoing migration of a continuous pulse of lower chlorinated PCBs downwind of Lake Ontario similar to the seasonal hopping proposed in the “coldcondensation” or “grasshopper” hypothesis (Rappe 1974, Wania and MacKay 1996). Note also that the average PCB signature of the Rice Creek core contains a greater proportion of the most chlorinated congeners than the Salmon River core (Fig. 5), perhaps because of its proximity to the lake (2 km). Confirmation of these proposed trends using soil or sediment transects from the lake eastward are planned for the near future. ACKNOWLEDGMENTS The authors wish to acknowledge funding from the Great Lakes Protection Fund and Great Lakes Research Consortium. Tom Holsen, Tom Young, and Phil Hopke of Clarkson University are thanked for their input on related studies. Three anonymous reviewers are thanked for their excellent suggestions on how to improve the manuscript. REFERENCES Achman, D., Hornbuckle, K., and Eisenreich, S., 1993. Volatilization of polychlorinated biphenyls from Green Bay, Lake Michigan. Environ. Sci. Technol. 27:75–86. Alcock, R., Johnston, A., McGrath, S., Berrow, M., and Jones, K., 1993. Long-term changes in the polychlorinated biphenyl content of United Kingdom soils. Environ. Sci. Technol. 27:1918–1923. Alexander, C., DeMaster, D., and Nittrouer, C. 1991. Sediment accumulation in a modern epicontinentalshelf setting. Marine Geology 98:51–72. ——— , Smith, R., Schropp, S., Calder, S., and Windom,
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