ENANTIOSELECTIVE BREAKDOWN OF ALPHA-HEXACHLOROCYCLOHEXANE IN A SMALL ARCTIC LAKE AND ITS WATERSHED

Water and snow samples were collected at Amituk Lake on Cornwallis Isl and to investigate the enantioselective degradation of alpha-hexachlor ocyclohexane (alpha-HCH) in the Arctic. The two enantiomers were separ ated by gas chromatography on permethylated cyclodextrin capillary col umns. The enantio- meric ratio (ER = (+)alpha-HCH/(-)alpha-HCH) for an alpha-HCH standard was 1.00 +/- 0.005, which is in excellent agreemen t with a theoretical ER of 1.00 for unmetabolized alpha-HCH. ERs of sn ow samples were racemic (0.98 +/- 0.03). Degradation was found in Amit uk Lake at 15-21 m where ERs were 0.77 +/- 0.004; however, stream runo ff and lake outflow ERs varied considerably during the study. ERs of t he outflow traced the meltwater running over the surface of the lake, being close to streamwater values during peak runoff and returning to deep lake water values during low flow. Streamwater ERs decreased with in a few weeks of snowmelt and showed a large variability (0.97-0.62), which may be due to the differences in temperature and amount of susp ended sediments. The rapid enantioselective breakdown of alpha-HCH sug gests that the ability of arctic microbial systems to degrade organic contaminants is greater than commonly thought.