Removal of α- and γ-Hexachlorocyclohexane and Enantiomers of α-Hexachlorocyclohexane in the Eastern Arctic Ocean

Abstract

Atmospheric concentrations of hexachlorocyclohexanes (HCHs) have declined over the last two decades, and the Arctic Ocean is now eliminating HCHs through degradation, volatilization, and advective outflow. Air and water samples were collected on a cruise of the eastern Arctic Ocean in July−September 1996 for HCHs and enantiomers of α-HCH. Mean concentrations of α- and γ-HCH in air were 37 and 17 pg m - 3 . Back trajectories indicated that the concentration and proportion of γ-HCH increased when air parcels passed over Eurasia where lindane (γ-HCH) is currently used. Mean concentrations in surface water (910 pg L - 1 α-HCH; 270 pg L - 1 γ-HCH) were lower than those in the western Arctic. The enantiomer ratio, ER = (+)-α-HCH /(−)-α-HCH, averaged 0.87 ± 0.06 ( n = 21) in surface water and decreased with depth. Microbial degradation rates of HCHs were estimated using vertical profiles of ER and concentration, surface water data from 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 (+)-α-HCH, (−)-α-HCH, and γ-HCH were 5.9, 23.1, and 18.8 years, respectively. Water−air fugacity ratios ( f w / f a ) indicated that α-HCH was near steady state, while γ-HCH was undergoing deposition to the ocean. ERs of α-HCH in air (0.95 ± 0.03, n = 16) were slightly less than racemic, showing the contribution of volatilization to the boundary layer.