DECLINE OF HEXACHLOROCYCLOHEXANE IN THE ARCTIC ATMOSPHERE AND REVERSAL OF AIR-SEA GAS-EXCHANGE

Hexachlorocyclohexanes (HCHs) are the most abundant organochlorine pes ticides in the arctic atmosphere and ocean surface water. A compilatio n of measurements made between 1979-93 from stations in the Canadian a nd Norwegian Arctic and from cruises in the Bering and Chukchi seas in dicates that atmospheric concentrations of alpha-HCH have declined sig nificantly (p < 0.01), with a time for 50% decrease of about 4 y in su mmer-fall and 6 y in winter-spring. The 1992-93 levels of about 100 pg m(-3) are 2-4 fold lower than values in the mid-1980s. The trend in g amma-HCH is less pronounced, but a decrease is also suggested from mea surements in the Canadian Arctic and the Bering-Chukchi seas. HCHs in ocean surface water have remained relatively constant since the early 1980s. The decline in atmospheric or-HCH has reversed the net directio n of air-sea gas exchange to the point where some northern waters are now sources of the pesticide to the atmosphere instead of sinks.