ENANTIOMERS OF ALPHA-HEXACHLOROCYCLOHEXANE AS TRACERS OF AIR-WATER GAS-EXCHANGE IN LAKE-ONTARIO

The technique of chiral phase capillary gas chromatography was applied to investigate the degradation and transport of the persistent chiral pesticide alpha-hexachlorocyclohexane (alpha-HCH) in the Lake Ontario environment Chiral analysis gave the enantiomeric ratios (ERs) of alp ha-HCH in samples taken May-October 1993 from the lake and its atmosph ere. ERs of (+)alpha-HCH/(-)alpha-HCH for Lake Ontario surface and dee p water samples were similar and averaged 0.85 +/- 0.02 as compared wi th a value of 1.00 for the alpha-HCH standard. Higher ERs were observe d in water samples from the Niagara River (0.91 +/- 0.02) and from pre cipitation (1.00 +/- 0.01). Air samples of alpha-HCH measured at 10 m above the lake show a seasonal variability with values near 1.00 in sp ring and fall and minimum values in individual samples near 0.90 in su mmer. A simple air-water gas transfer model demonstrates that enantiom eric ratios <1.0 in air are derived from equilibration of the air with the water during transport of the air mass over the lake. Based on th e measured ERs, it is calculated that as much as 60% of the alpha-HCH in air above Lake Ontario was derived from the lake itself. These resu lts strongly support the need for overwater air measurements to provid e better estimates of air-water gas transfer fluxes of persistent orga nic pollutants.