Enantioselective breakdown of a-HCH in a small Arctic lake and its watershed

Air, water and snow samples were collected at Resolute Bay and Amituk Lake on Cornwallis Island to investigate the enantioselective degradation of a-hexachlorocyclohexane (a-HCH) in the Arctic. The two enantiomers were separated by gas chromatography on permethylated cyclodextrin capillary columns. The enantiomeric ratio (ER = (+)a-HCH/({minus})a-HCH) in air was 1.00 {+-} 0.04, which agrees excellently with a theoretical ER = 1.00 for unmetabolized a-HCH and ER = 0.996 {+-} 0.005 found for a standard. ERs of snow samples were slightly, but significantly less than 1.00. Seawater samples showed a 10--15% degradation of the (+) enantiomer. More extensive degradation was found in Amituk Lake at 20 m where ERs were 0.769 {+-} 0.003, however stream runoff and lake outflow ERs varied considerably during the study. ERs of the outflow traced the meltwater running over the surface of the lake, being close to stream water values during peak runoff and returning to deep lake water values during low flow. Stream water ERs decreased within a few weeks of snowmelt and showed a large variability (0.946--0.620) which may be due to the differences in temperature and amount of suspended sediments. The rapid enantioselective breakdown of a-HCH suggests that the ability of arctic microbialmore » systems to degrade organic contaminants is greater than commonly thought.« less