Air-Water Exchange of Legacy and Emerging Organic Pollutants across the Great Lakes

Abstract:

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are transported to great water bodies via long-range atmospheric transport and released from the surface water as air concentrations continue to diminish. As the largest fresh water bodies in North America, the Great Lakes have both the potential to accumulate and serve as a secondary source of persistent bioaccumulative toxins. OCP and PCB concentrations were sampled at 30+ sites across Lake Superior, Ontario and Erie in the summer of 2011. Polyethylene passive samplers (PEs) were simultaneously deployed in surface water and near surface atmosphere to determine air-water gaseous exchange of OCPs and PCBs. In Lake Superior, surface water and atmospheric concentrations were dominated by α-HCH (average 250 pg/L and 4.2 pg/m³, respectively), followed by HCB (average 17 pg/L and 89 pg/m³, respectively). Air-water exchange varied greatly between sites and individual OCPs, however α-endosulfan was consistently deposited into the surface water (average 19 pg/m²/day). PCBs in the air and water were characterized by penta- and hexachlorobiphenyls with distribution along the coast correlated with proximity to developed areas. Air-water exchange gradients generally yielded net volatilization of PCBs out of Lake Superior. Gaseous concentrations of hexachlorobenzene, dieldrin and chlordanes were significantly higher (p < 0.05) at Lake Erie than Lake Ontario. A multiple linear regression that incorporated meteorological, landuse and population data was used to explain variability in the atmospheric concentrations. Results indicated that landuse (urban and/or cropland) greatly explained the variability in the data. Freely dissolved concentrations of OCPs (<LOD-114 pg/L) were lower than previously detected concentrations. Nonetheless, concentrations of p,p'-DDE and chlordanes were higher than water quality guidelines for the protection of human health from the consumption of fish. Spatial distributions of freely dissolved OCPs in Lakes Erie and Ontario were influenced by loadings from areas of concern and the water circulation patterns. Air-water exchange calculations indicated that the majority of OCPs were volatilizing from the water; therefore the lower Great Lakes were acting as a secondary source to the atmosphere.