Endosulfan and γ-HCH in the Arctic: An Assessment of Surface Seawater Concentrations and Air - Sea Exchange

摘要

Arctic seawater concentrations of two currently used pesticides, endosulfan and γ-HCH, were collated from a variety of cruises undertaken throughout the 1990s up to 2000 for different regions of the Arctic Ocean. Surface seawater concentrations for α-and β-endosulfan ranged from < 0.1 -8.8 (mean 2.3) pg/L and 0.1 -7.8 (mean 1.5) pg/L, while γ-HCH concentrations were ～ 100 fold higher than α-endosulfan, ranging between < 0.70 and 894 (mean 250) pg/L. Geographical distributions for α-endosulfan revealed the highest concentrations in the western Arctic, specifically in the Bering and Chukchi Seas with lowest levels toward the central Arctic Ocean. In contrast, γ-HCH revealed higher concentrations toward the central Arctic Ocean, with additional high concentrations in the coastal regions near Barrow, Alaska and the White Sea in northwest Russia, respectively. A fugacity approach was employed to assess the net direction of air-water transfer of these two pesticides, using coupled seawater and air concentrations. For α-endosulfan, water - air fugacity ratios (FR) were all < 1 indicating net deposition to all regions of the Arctic Ocean, with the lowest values (0.1-0.2) evident in the Canadian Archipelago. Given the uncertainty in the temperature-adjusted Henry's Law constant (factor ～ 10), it is plausible that equilibrium may have been reached for this compound in the western fringes of the Arctic Ocean where the highest water concentrations were observed. Similarly, FR values for γ-HCH were generally < 1 and in agreement with other separate studies, although, like α-endosulfan, netdeposition predominated over the Canadian Archipelago. In the central and eastern regions of the Arctic Ocean, as well as in the two coastal areas of this study, the fugacity ratios for γ-HCH where ～ 1 indicating conditions approaching equilibrium. The elevated water concentrations and higher FRs in these coastal areas support the assessment that riverine/coastal sources are important for this chemical, but less so for α-endosulfan for which air to water transfer during the ice-free summer months is likely to be the major contemporary source to the Arctic. It is recommended that archived extracts of river water be reanalyzed for α-endosulfan to confirm this.