Removal of alpha- and gamma-hexachlorocyclohexane and enantiomers of alpha-hexachlorocyclohexane in the eastern Arctic Ocean

Atmospheric concentrations of hexachlorocyclohexanes (HCHs) have declined o ver the last two decades, and the Arctic Ocean is now eliminating HCHs thro ugh degradation, volatilization, and advective outflow. Air and water sampl es were collected on a cruise of the eastern Arctic Ocean in July-September 1996 for HCHs and enantiomers of alpha-HCH. Mean concentrations of alpha- and gamma-HCH in air were 37 and 17 pg\m(-3). Back trajectories indicated t hat the concentration and proportion of gamma-HCH increased when air parcel s passed over Eurasia where lindane (gamma-HCH) is currently used. Mean con centrations in surface water (910 pg L-1 alpha-HCH; 270 mu g L-1 gamma-HCH) were lower than those in the western Arctic. The enantiomer ratio, ER = ()-alpha-HCH /(-)-alpha-HCH, averaged 0.87 +/- 0.06 (n = 21) in surface wate r and decreased with depth. Microbial degradation rates of HCHs were estima ted using vertical profiles of ER and concentration, surface water data fro m 1979 (21), and the "ventilation" age of water at a particular depth (22). Microbial rate constants were 3-10 times greater than those for hydrolysis . Half-lives for (+)-alpha- HCH, (-)-alpha-HCH, and gamma-HCH were 5.9, 23. 1, and 18.8 years, respectively. Water-air fugacity ratios (f(w)/f(a)) indi cated that alpha-HCH was near steady state, while gamma-HCH was undergoing deposition to the ocean. ERs of alpha-HCH in air (0.95 +/- 0.03, n = 16) we re slightly less th a n racemic, showing the contribution of volatilization to the boundary layer.