Degradation as a Loss Mechanism in the Fate of α-Hexachlorocyclohexane in Arctic Watersheds

Water extracts of samples collected from Amituk Lake in July−August, 1994 and samples collected at Char and Meretta Lakes in July 1997 were analyzed for enantiomers and concentrations of α-HCH to estimate the extent of biodegradation in watersheds in the Canadian High Arctic. (+)/(−)-α-HCH enantiomer ratios (ERs) in three streams entering Amituk Lake ranged from racemic values of 1.01 in snow to 0.36 in meltwater. Lower ERs were promoted by warmer temperatures and increased contact with stream substrates during low streamflows, especially biologically productive substrates. Most α-HCH degradation occurred during peak runoff when ERs were 0.95−0.80, rather than later in summer when ERs reached their minimum. Approximately 7% of α-HCH in the Amituk Lake basin was enantioselectively degraded prior to entering the lake. ERs within Amituk Lake are controlled by meltwater inputs rather than within lake degradation and clearly illustrate the riverine-like nature of high arctic lakes. Differences in lake α-HCH inventory from end of summer 1993 to spring 1994 indicate that from 33 to 61% of α-HCH within the lake may have been lost via nonenantioselective microbial degradation at a rate ranging from 0.48 to 1.13 y - 1 .