Air-water gas exchange and evidence for metabolism of hexachlorocyclohexanes in Resolute Bay, N.W.T

Abstract

Paired air and water samples were collected at Resolute Bay (74 degrees N, 95 degrees W) in summer 1992 to estimate the direction of gas exchange of hexachlorocyclohexanes (HCHs) and investigate possible loss processes in the water column. Average concentrations of alpha-HCH and gamma-HCH in ocean surface water were 4.7 +/- 0.9 and 0.44 +/- 0.11 ng/l, respectively. These alpha- and gamma-HCH levels are approximately 66-104% and 54-72% of values reported for the central Arctic Ocean at the Canadian Ice Island in 1986. Mean atmospheric concentrations of alpha-HCH and gamma-HCH (114 +/- 16 and 9.8 +/- 1.3 pg/m3) were 2-3 times lower than summer Arctic levels in the 1980s. The ocean surface water (-1.4 degrees C) was approximately within Henry's Law equilibrium with respect to atmospheric gamma-HCH levels. Water/air fugacity ratios were 1.03 for gamma-HCH and 1.57 for alpha-HCH, indicating a slight potential for volatilization of alpha-HCH. The two alpha-HCH enantiomers in air and water were separated by chromatography on a gamma-cyclodextrin capillary column. The enantiomeric ratio (ER = ratio of (+)alpha-HCH/(-)alpha-HCH) in air was 1.00 +/- 0.04. This agrees excellently with ER = 1.00 +/- 0.01 found for a racemic alpha-HCH standard. The (+) enantiomer was depleted in seawater, resulting in ER = 0.93 +/- 0.06 in Resolute Bay. ERs of samples from Amituk Lake on Cornwallis Island ranged from 0.65 to 0.99, depending on location, date and relative contributions of fresh snowmelt and older lake water. These results suggest that microbial degradation of HCHs is taking place in Arctic lakes and near-shore marine waters.