Enrichment of PCBs in Lake Michigan Surface Films

The processes of exchange of PCBs and related organics at the surface of large bodies of water such as the Great Lakes are unavoidably linked to the unique properties of surface films. We have observed a 3 to 8 fold enrichment of PCB over underlying water in surface film samples taken from Lake Michigan with a Garrett screen sampler. The particle association of the PCBs was highest in the microlayer, averaging 50% compared to 20% on particles in the subsurface water and less than 5% in the air. The PCBs in the samples were identified as Aroclor 1254 and Aroclor 1242. The percentage composition of the two Aroclors varied between the air and the water as follows: the air was 30.2% Aroclor 1254 and the water (microlayer plus subsurface) was 57.6% Aroclor 1254.     

Historical Changes in PCB Patterns in Lake Ontario and Green Bay,Lake Michigan, 1971 to 1982, from Herring Gull Egg Monitoring Data

Patterns of PCB congener bioaccumulation were examined in archived herring gull (Larus argentatus) eggs collected from Big Sister Island in Green Bay, Lake Michigan, and Scotch Bonnet Island in Lake Ontario from 1971 to 1982 as part of the Canadian Wildlife Service's Great Lakes Herring Gull Monitoring Program. Concentrations of 97 PCB congeners were measured. From 1971 to 1982, ecological half-lives of most congeners, particularly the tri- through hexachlorobiphenyls, were greater in eggs from Green Bay than Lake Ontario. Comparing sum PCB levels in eggs collected in 1971 and 1982, concentrations declined 80% at Scotch Bonnet Island and 74% at Big Sister Island. PCB congener patterns were different in eggs from the two colonies. Principal components analysis showed that inter-site differences in congener patterns became more apparent after 1976. This indicated that regional PCB sources were the most influential in determining patterns of biologically-available PCBs during the 1971 to 1982 period in these two lakes, via recycling of historical PCBs from sediments or gradually decreasing loading. Trend analysis of selected congeners specific to Aroclors 1242, 1254, and 1260 revealed that the rapid decline of less chlorinated congeners, observed from 1971 to 1976 in Lake Ontario, was explained by a decrease in loading of Aroclor 1242 to the lake. At both colonies, ecological half life of the congeners was significantly (p < 0.001) correlated with log K_ow and with –log HLC. Changes in PCB composition, after 1976 in Lake Ontario and from 1971 to 1982 in Green Bay, could be explained by differences in the physical behavior of individual congeners affecting removal by volatilization and sedimentation.     

PCB Congeners and Dechlorination in Sediments of Upper Sheboygan River,Wisconsin

Nine hand-collected sediment cores were obtained for PCB concentration analysis and dating from the Upper Sheboygan River, Wisconsin, USA. The primary PCB Aroclors in the Upper Sheboygan River were 1248 (50%) and 1254 (50%). The total PCB concentrations in the sediments ranged from 0.1–104 ppm (based on dry weight). The PCB data obtained from the sampling were analyzed using a factor analysis (FA) model with non-negative constraints in order to identify PCB sources and congener patterns. The factor loadings obtained from the FA model represent a general dechlorination profile common to most of the higher concentration samples and another associated with contamination from upstream dredging during 1989–1991. Anaerobic dechlorination is occurring in Upper Sheboygan River sediments and is most significant at high concentrations (≥ 20 ppm). Observation of elevated amounts of lower chlorinated congeners such as congeners 4 (2-2), 8 (2-4), 25 (24-3), and 26 (25-3) indicates the presence of anaerobic dechlorination activities. Based on the data from the FA model, anaerobic dechlorination was occurring according to dechlorination activities M and P. All possible dechlorination pathways involving marker congeners were considered. A significant improvement (86–91%) in similarity between the original Aroclor profile and the altered ones was found.     

Residues of PCB in a Cladophora Community Along the Lake Huron Shoreline

PCB residues were measured in samples of Cladophora, Ulothrix, net plankton, water, and fish collected in the Harbor Beach area of Lake Huron. The average concentrations of total PCB in each of the sample groups were as follows: water - 0.154 ng/g; Cladophora - 92 ng/g; Ulothrix - 126 ng/g; net plankton - 1,651 ng/g; and fish - 40 to 4,400 ng/g. The PCB patterns in the samples were found to match a mixture of Aroclo6r 1242 and 1254. Aroclor 1242 represented about 60% of the mixture in all the samples except the fish, where Aroclor 1254 represented about 75% of the total PCB measured. The accumulation factors observed in the progression from Cladophora to net plankton to fish were 1:15:30; these were similar to the concentration factors (1:14:44) developed on these ecosystem compartments in Lake Ontario during the 1972 IFYGL program.     

Sedimentary records of non-Aroclor and Aroclor PCB mixtures in the Great Lakes

Three sediment cores from Lake Ontario, Lake Erie and Indiana Harbor Ship Canal were collected, segmented and analyzed for Aroclor and non-Aroclor polychlorinated biphenyl congeners (PCBs). PCBs associated with the commercially produced Aroclor mixtures 1248 and 1254 dominate the sediment signal and the sum of all congeners (∑ PCB) peaks in concentration and accumulation around 1970 in the Great Lakes. This trend is very similar to Aroclor production history. In the Indiana Harbor Ship Canal, PCBs appear around 1935 and remain at very high levels between 1940 and 1980, probably reflecting the history of use at the nearby steel mill. In contrast, the non-Aroclor PCBs in the Lake Ontario and IHSC sediment cores, including PCB11 and heavily chlorinated congeners PCB206, 207, 208 and 209 reach a peak in the 1950s, decline and peak again in the 1970s or in the early 1980s. All five congeners have been previously measured in commercial paint pigment. PCB11 was found to peak about 5 years later than ∑ PCBs, and is probably associated with the production or use history of diarylide yellow pigments. The temporal distribution profiles of these non-Aroclor PCBs are well correlated with the production history of paint pigments and dyes. Although it is well known that the production of Aroclor PCBs is preserved in Great Lakes sediments, this study is the first to show that production of non-Aroclors are also preserved in the sediments as a record of long term trends in environmental exposure.     

Horizontal and Vertical Distribution of PCBs in Southern Lake Michigan Sediments and the Effect of Waukegan Harbor as a Point Source

The spatial distribution of PCBs in southern Lake Michigan sediments was obtained from the analysis of 66 box cores and 8 grab samples. PCB concentrations in surficial sediments were closely related to sedimentation zone and to the oxidizable organic matter content of the sediments. Average surficial sediment concentrations ranged from 81 ng/g in depositional zones to 7.2 ng/g in non-depositional zones. The vertical distribution of PCBs was determined at several sites and was used to estimate the areal burden and flux of PCBs in each of the southern sedimentation zones. The total sediment PCB burden in the southern portion of the lake was estimated to be 5,900 kg. Southern Lake Michigan has received PCBs since approximately 1930 at an average flux of 7.1 μg/m² yr.The effect of Waukegan Harbor as a point source of PCBs to Lake Michigan was evaluated by comparing the PCB distribution and Aroclor composition of harbor sediments to those of sediments of decreasing distances from the harbor. Significant differences in total PCB concentration between non-depositional zones near the harbor and those in other areas of the basin indicate that Waukegan Harbor has influenced the PCB burden of Lake Michigan.     

Comparison of PCB congener profiles in the embryos and principal prey of a breeding colony of black-crowned night-herons

We compared polychlorinated biphenyl (PCB) congener profiles of embryos of black-crowned night-herons (Nycticorax nycticorax) nesting in an urban-industrialized area of Chicago, Illinois, USA, with those of regurgitated food boluses from nestlings and their primary prey. Consistent with previous studies of piscivorous birds, the PCB burden of embryos was shifted towards more heavily chlorinated congeners (those with 6, 7, and 8 chlorines), when compared to prey. The PCB congener profiles for measured and homolog concentrations in alewife (Alosa pseudoharengus) collected from Lake Michigan at the Chicago, Illinois, waterfront, closely resembled that of regurgitated food boluses collected from nestlings at the Lake Calumet colony. Also, alewife from Illinois and regurgitates were not clearly differentiated by the discriminant analyses for measured, proportional, and homolog concentrations. Congener profiles in alewife from the highly contaminated Indiana Ship Canal, which had a much higher PCB burden (geometric average = 1061.7 ng/g ww [95% CI = 648.6−1061.7 ng/g ww]) than did alewife from Illinois (158.1 [135.8−184.5] ng/g ww) and regurgitates (212.3 [177.0−254.7] ng/g ww), reflected a less-chlorinated mixture (i.e., Aroclor 1242). These results are consistent with our observations, which indicated that many of the adults of this colony were foraging along the Chicago waterfront, where alewife had lower PCB burdens. Because the congener patterns of the prey differ, the PCB congener profiles can be used to elucidate foraging patterns of colonial piscivorous birds and determine relative risks to exposed populations.     

PCBs in Great Lakes sediments, determined by positive matrix factorization

Previously determined PCB concentrations in 10 dated sediment cores from Lakes Michigan, Huron, Erie, and Ontario are analyzed by positive matrix factorization in order to find characteristic congener patterns including signs of anaerobic dechlorination. Three or four factors are sufficient to describe the PCB data for each lake. All four lakes are dominated by Aroclors 1248A, 1248G, 1254A, and 1254G. Aroclor 1260 is only a significant factor in Lake Michigan prior to 1975, reflecting in part a usage patterns of heavy chlorinated Aroclors early and less chlorinated Aroclors in the phase-out years in the 1970s. Dated records of factors or sources indicate clear PCB concentration maxima for Lakes Erie (1981) and Ontario(1968), while redistribution of PCBs in the less contaminated Lakes Michigan and Huron has occurred after 1980. Using a single data matrix for all four lakes provides a common basis and possibility to examine low degrees of dechlorination, while individual data matrices for each lake provide more accurate results and better separation of factors. Lakes Ontario, Michigan, and Huron undergo dechlorination via reactions such as 66(24-34) → 25(24-3) and 18(25-2) → 4(2-2) consistent with reactions H' + M, while Lake Erie appears to be dominated by 18(25-2) → 4(2-2) and 53(25-26) → 19(26-2) that are typical for processes M + Q.     

Distribution of Contaminants in Clams and Sediments from the Huron-Erie Corridor. I–PCBs and Octachlorostyrene

Samples of surficial sediments and the clam species Lampsilis radiata siliquoidea were collected from 102 sites covering all of Lake St. Clair and the Canadian shoreline of the St. Clair and Detroit rivers. The distribution patterns of both octachlorostyrene (OCS) and PCBs were mapped throughout this area. The mean level of PCBs in sediments of 3.9 μg kg^?1 (Aroclor 1254) was much lower than values for “total PCBs” reported in studies carried out in the early 1970s. This reduction does not appear to reflect a real decrease in PCB levels in the environment, but rather changes that have been made in sampling procedures and analytical techniques. Highest levels of PCBs in both sample types were found along the western shore of Lake St. Clair. Mean levels of OCS in whole clam tissue and surficial sediment (0–10 cm) were 43.0 and 5.1 μg kg^?1, respectively. The distribution pattern of OCS in the Huron-Erie corridor in both clams and sediments suggests that the primary source is in the St. Clair River. The mean chemical concentration factor was 59 for OCS, indicating considerable bioaccumulation in the biota of Huron-Erie corridor.     

Polychlorinated Biphenyl Contamination in Surficial Sediments of Northeastern Lake Michigan

The results of this study indicate that the polychlorinated biphenyl contamination in northeastern Lake Michigan surficial sediments is relatively low. Concentration ranges from 1.6 to 6.7 μg/L PCB (Aroclor 1254) were found. The concentration of PCBs in these sediment samples was also found to be highly correlated with % organic carbon (r=0.93) and the % silt-clay fraction (r=0.98). The % organic carbon and % silt-clay fraction were also highly correlated (r=0.93).     

Chlorinated Contaminants in Surficial Sediments of Lakes Huron,St. Clair,and Erie: Implications Regarding Sources Along the St. Clair and Detroit Rivers

Surficial sediments from southern Lake Huron, Lake St. Clair, and Lake Erie have been analyzed for a broad spectrum of chlorinated organics including PCBs, chlorobenzenes, and several pesticides. The differences between sediment contaminant concentrations in Lake Huron and Lake St. Clair indicated sources of hexachlorobenzene, hexachlorobutadiene, octachlorostyrene, and several other chlorinated benzenes along the St. Clair River. Similar differences between sediment PCB concentrations in Lakes Huron/St. Clair and Lake Erie indicated major PCB sources along the Detroit River. Specific PCB congener analysis revealed that PCBs discharged to the Detroit River contained especially high concentrations of highly chlorinated hexa-, hepta-, and octachloro-biphenyls which are major constituents of the industrial mixture Aroclor 1260. The analysis of individual PCB congeners made it possible to trace PCBs of Detroit River origin to the central and eastern basins of Lake Erie, and to estimate the contribution of the Detroit River to the PCB burden in sediments of these basins.     

Temporal evolution of urban wet weather pollution: analysis of PCB and PAH in sediment cores from Lake Bourget, France.

In order to evaluate the historical impact of urban stormwater runoff on a lacustrine environment, eight sediment cores were collected in October 2006 in Lake Bourget (Savoie, France). Sediment samples were analysed for polycyclic aromatic hydrocarbons (PAH) and polychlorobyphenyls (PCB) in order to correlate the vertical profiles of contamination and the evolution of the urbanisation on the watershed for the last 100 years. Overall, we observe that vertical profiles of PCB and PAH concentrations in Lake Bourget are showing a downward trend, probably resulting from the pollution control measures. Concentrations of PCB and PAH measured in surface sediments are approximately 5-10 fold less than maximal concentrations found in the cores. Maximal PAH concentrations were found at the bottom of the cores ( approximately 40 cm) which approximately correspond to the beginning of the 20th century. Maximal PCB concentrations measured in cores L5 and L6 are respectively 850 and 790 microg/g dw (dryweight). The peak of PCB corresponds to the maximum of PCB production and consumption in the 1970s. In surface sediments total PCB concentrations range between 47 and 79 microg/kg dw. Those concentrations are particularly high compared to other values measured in lake sediments and highlight the problem of a local source of PCB contamination in the watershed. General trends were observed, yet the part of urban stormwater runoff in the total contamination could not be determined.     

Modeling PCB Bioaccumulation by the Zebra Mussel (Dreissena polymorpha) in Saginaw Bay,Lake Huron

Zebra mussels were collected from navigation buoys in Saginaw Bay and the lower Saginaw River and analyzed for PCBs. Total PCB concentrations ranged from 0.076 to 1.2 μg/g, with the highest values for zebra mussels collected near the mouth of the Saginaw River. These data were combined with PCB concentration measurements in water and suspended solids to calculate congener-specific partition coefficients and bioaccumulation factors. Lipid-normalized bioaccumulation factors for PCB congeners ranged from 10^5.6 to 10^7.0. A model based on three-phase equilibrium partitioning and a bioaccumulation mass balance were applied to simulate the concentration ratios. Model results provided an unbiased best fit of the observed partition coefficients and bioaccumulation factors, as well as optimum parameter estimates. PCB fluxes mediated by zebra mussels were calculated from the model. Transfer across the gut was found to be the predominant route of PCB uptake for zebra mussels. Egestion and fecal excretion were estimated to generate a PCB flux of 1 to 30 μg/m²/d at zebra mussel densities reported for the Great Lakes. This flux exceeds the gross settling flux of PCBs to inner Saginaw Bay, demonstrating the potential of zebra mussels to alter particle and contaminant fluxes in the Great Lakes ecosystem. Zebra mussels may contain as much PCBs as the surficial sediments in Saginaw Bay.     

Relationships Between Chlorinated Hydrocarbon Concentrations and Rearing Mortality of Chinook Salmon (Oncorhynchus Tshawytscha) Eggs from Lake Michigan

A study was conducted to investigate a possible correlation between chlorinated hydrocarbon concentrations and rearing mortality of chinook salmon. Eggs, collected from adult Lake Michigan chinook salmon in October, 1982, were analyzed for chlorinated hydrocarbon concentrations and rearing mortality. Polychlorinated biphenyls, toxaphene, and fifteen other chlorinated hydrocarbons were quantified. Also, concentrations of individual PCB congeners were quantified. We found 78 quantifiable PCB congeners, only three of which were non-ortho substituted. Mean concentrations of Arocloi^® 1242, 1254 and 1260 were 1.7, 5.4, and 1.1 μg/g, respectively. The concentration of toxaphene-like material was 3.3 μg/g, and the mean concentration of the total DDT complex was 1.0 μg/g. Concentrations of chlorinated hydrocarbons ranged approximately 10-fold among individual fish. An analysis of variance components demonstrated that this variability represented among-fish variation and was not due to errors in sampling or quantification. Duplicate studies of egg viability and fry mortality, conducted at 10, 11, and 15°C, correlated with residue concentrations. While some residue concentrations were significantly negatively correlated with egg viability and survival of fry, others were positively correlated. Thus, we observed no consistent trends in Pearson, pairwise-correlations between either egg viability or survival of fry to swim-up stage and individual residue concentrations. When the residues were classified into four principal components, two of the principal components which contained primarily the toxaphene and PCB concentrations were negatively correlated with survival of fry to the swim-up stage.     

Organochlorine Insecticides and PCB in Surficial Sediments (1968) and Sediment Cores (1976) from Lake Ontario

Surficial sediments were collected in 1968 and core sediments in 1976 from Lake Ontario. These were analysed for organochlorine insecticides and PCB. Residues of organochlorine compounds were higher in the three Ontario depositional basins than in sediment in the non-depositional zones. PCB was present at the highest concentration, with mean levels of 57 ppb for the whole lake. Residues of PCB in the three basins exhibited only minimal differences.ΣDDT was the second most frequently found contaminant. Both parent DDT and its two metabolites were present in sediment, giving a mean residue of 42.8 ppb for the whole lake. Differences in residues for the three basins were again minimal. DDT was present in sediments estimated to be deposited between 1958 and 1976. HEOD was present in only 40% of sediments and the mean residue for the whole lake was 0.6 ppb. The Niagara basin contained mean residues (1.4 ppm) of HEOD much above the other basins.Chlordane was virtually absent from the lake in the sediments collected in 1968 but appeared in cores between 1964-1976. Endosulfan appeared in lake sediments as a spill of deck cargo at a location in the Niagara basin. This spill dispersed with the current down the south shore to deposit in the Rochester basin.     

Record of mercury pollution in sediments of lakes Nakaumi and Shinji in Japan

Two sediment core profiles from lakes Shinji and Nakaumi were studied in order to understand the level of mercury (Hg) pollution in lakes in northwestern Japan. The sedimentation rates were established on the basis of the activity of [²¹⁰Pb] and [¹³¹Cs] in the sediments. In Lake Shinji, the highest level of Hg (130 ng g^–1) in the sediment was found at a depth of 20–22 cm, while 195 ng g^–1 was found at a depth of 10–12 cm in the core profiles from Lake Nakaumi. The relative increase in Hg concentration in lake sediments started after 1960 and significant contamination events occurred in the early 1960s. Mercury profiles in lake sediments from lakes Shinji and Nakaumi are found to reflect the anthropogenic Hg released into the environment in the 1950s and 1960s. A pronounced maximun concentration of Hg is found in both lakes, where sediment accumulation rates differ.     

Spatiotemporal trends of polychlorinated biphenyls (PCBs) in surface and suspended sediments from the Lake Ontario Canadian nearshore 1994–2018: A fish consumption advisory perspective

Spatiotemporal trends for polychlorinated biphenyls (PCBs) were examined in surface and suspended sediments collected between 1994 and 2018 from over twenty nearshore stations on the Canadian side of Lake Ontario and the St. Lawrence River. In 2018, PCB concentrations ranged over an order-of-magnitude in surface (<10 ng/g?357 ng/g) and suspended sediments (<10 ng/g–330 ng/g), illustrating the presence of legacy hotspots as well as diffuse urban inputs. PCB concentrations in both surface and suspended sediments were consistently highest in Hamilton Harbour, but were also elevated at other stations around the perimeter of the Niagara basin as well as near Trenton and Kingston, Ontario. Generally, higher PCB concentrations were found in surface sediment relative to paired suspended sediment samples suggesting temporal improvements in nearshore sediment quality. However, many stations demonstrated temporal variability in PCB concentrations, a likely factor in the lack of an overall nearshore declining trend. Given that PCBs are listed as a consumption-limiting contaminant for all fish sampling blocks in the Canadian waters of Lake Ontario and are responsible for 78% of restricted advisories, sediment quality benchmarks that account for bioaccumulation potential should be considered over toxicologically-derived guidelines to gauge severity of PCB contamination of nearshore sediments. Relatively higher TOC-normalized PCB concentrations in the western end of Lake Ontario suggests additional research on PCB bioavailability from nearshore sediment would be beneficial in understanding basinwide trends of PCBs in fish, and that an adaptive approach to sediment management may be needed in the context of consumption advisories.     

Mobility of 2,2’,5,5’-Tetrachlorobiphenyl in Model Systems Containing Bottom Sediments and Water from the Lower Fox River,Wisconsin

Sediment-water partitioning and diffusive transport of 2,2’,5,5’-tetrachlorobiphenyl, PCB congener IUPAC #52 (TCB52) were examined in laboratory experiments with sediments from two sites in the lower Fox River, Wisconsin. Native water was pumped at controlled flow rates through cells containing sediments amended with a known activity of carbon-14-labeled TCB52. Concentrations of TCB52 in water and sediments were determined by liquid scintillation measurements of carbon-14 activity. Sediment-water partitioning was independent of flow rate for rates up to 8 m/d. Distribution coefficients (K_d) and soil-sorption coefficients (K_oc) were found to be at maximum levels 5–10 cm below the surface, despite an absence of significant variation in the fraction of organic carbon (f_oc) through the same profile. Other factors, such as the effects of colloids and microbial activity in the sediments, are likely to be important in controlling the PCB distribution. Log K_d and log K_oc ranges were 4.1–4.9 and 5.3–6.1, respectively, and calculated effective diffusivities at the sediment-water interface ranged from 3 to 8 × 10⁻¹⁰ cm²/s. Gradual increases with time in TCB52 concentrations in the water phase, possibly due to effects of microbial activity, were observed. Diffusion experiments and models showed that the TCB52 migration rate within the sediment column is 8-9 mm/yr.     

Gender difference in walleye PCB concentrations persists following remedial dredging

Eleven male walleyes (Sander vitreus) and 10 female walleyes from the Saginaw Bay (Lake Huron) population were caught during the spawning run at Dow Dam (Midland, Michigan) in the Tittabawassee River during April 1996, and individual whole-fish polychlorinated biphenyl (PCB) determinations were made. Total PCB concentrations averaged 7.95 and 3.17 mg/kg for males and females, respectively. As part of the Natural Resource Damage Assessment remediation process, contaminated sediments from the Saginaw River, the main tributary to Saginaw Bay, were removed during 2000 and 2001. Total PCB concentrations of 10 male and 10 female walleyes caught at Dow Dam during April 2007 averaged 1.58 and 0.55 mg/kg, respectively. Thus, dredging of the Saginaw River appeared to be effective in reducing PCB concentrations of Saginaw Bay adult walleyes, as both males and females decreased in PCB concentration by more than 80% between 1996 and 2007. However, the ratio of male PCB concentration to female PCB concentration did not decline between 1996 and 2007. This persistent gender difference in PCB concentrations was apparently due to a gender difference in habitat utilization coupled with a persistent spatial gradient in prey fish PCB concentrations from the Saginaw River to Lake Huron.     

Anomalous Concentrations and Chlorination of Polychlorinated Biphenyls in Sediment Downwind of Lake Ontario

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.