Air-water gas exchange of hexachlorocyclohexanes (HCHs) and the enantiomers of alpha-HCH in arctic regions

In the summers of 1993 and 1994, air and water samples were taken in the Bering and Chukchi Seas and on a transect across the polar cap to the Greenland Sea to measure the air-sea gas exchange of hexachlorocyclohexanes (HCHs) and the enantiomers of alpha-HCH. Atmospheric concentrations of alpha- and gamma-HCH have decreased threefold or more since the mid-1980s, whereas concentrations in surface water have shown little change. The saturation state of surface water (water/air fugacity ratio) was determined from the air and water concentrations of HCHs and their Henry's law constants as a function of temperature. Fugacity ratios >1.0 indicated net volatilization of alpha-HCH in all regions except the Greenland Sea, where concentrations in air and water were close to equilibrium. Net deposition of gamma-HCH in the Chukchi Sea was indicated by fugacity ratios <1.0. In other regions, gamma-HCH was volatilizing or near air-water equilibrium. Enantioselective degradation of (-)alpha-HCH was found in surface water of the Bering and Chukchi Seas. The ER was reversed in the Canada Basin and Greenland Sea, where (+)alpha-HCH was preferentially lost. The same order of enantioselective degradation was seen in air within the marine boundary layer of these regions, which provides direct evidence for sea-to-air transfer of alpha-HCH.