Degradation as a loss mechanism in the fate of alpha-hexachlorocyelohexanein arctic watersheds

Water extracts of samples collected from Amituk Lake in July-August, 1994 a nd samples collected at Char and Meretta Lakes in July 1997 were analyzed f or enantiomers and concentrations of alpha-HCH to estimate the extent of bi odegradation in watersheds in the Canadian High Arctic. (+)/(-)-alpha-HCH e nantiomer ratios (ERs) in three streams entering Amituk Lake ranged from ra cemic 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 alpha- 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 a lpha-HCH in the Amituk Lake basin was enantioselectively degraded prior to entering the lake. ERs within Amituk Lake are controlled by meltwater input s rather than within lake degradation and dearly illustrate the riverine-li ke nature of high arctic lakes. Differences in lake alpha-HCH inventory fro m end of summer 1993 to spring 1994 indicate that from 33 to 61% of alpha-H CH within the lake may have been lost via nonenantioselective microbial deg radation at a rate ranging from 0.48 to 1.13 y(-1).