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 t he Bering and Chukchi Seas and on a transect across the polar cap to t he Greenland Sea to measure the air-sea gas exchange of hexachlorocycl ohexanes (HCHs) and the enantiomers of alpha-HCH. Atmospheric concentr ations of alpha- and gamma-HCH have decreased threefold or more since the mid-1980s, whereas concentrations in surface water have shown litt le change. The saturation state of surface water (water/air fugacity r atio) was determined from the air and water concentrations of HCHs and their Henry's law constants as a function of temperature. Fugacity ra tios >1.0 indicated net volatilization of alpha-HCH in all regions exc ept the Greenland Sea, where concentrations in air and water were clos e to equilibrium. Net deposition of gamma-HCH in the Chukchi Sea was i ndicated by fugacity ratios <1.0. In other regions, gamma-HCH was vola tilizing or near air-water equilibrium. Enantioselective degradation o f (-)alpha-HCH was found in surface water of the Bering and Chukchi Se as. The ER was reversed in the Canada Basin and Greenland Sea, where ( +)alpha-HCH was preferentially lost. The same order of enantioselectiv e degradation was seen in air within the marine boundary layer of thes e regions, which provides direct evidence for sea-to-air transfer of a lpha-HCH.