Enantiomers of α-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 α-hexachlorocyclohexane (α-HCH) in the Lake Ontario environment. Chiral analysis gave the enantiomeric ratios (ERs) of α-HCH in samples taken May−October 1993 from the lake and its atmosphere. ERs of (+)α-HCH/(−)α-HCH for Lake Ontario surface and deep water samples were similar and averaged 0.85 ± 0.02 as compared with a value of 1.00 for the α-HCH standard. Higher ERs were observed in water samples from the Niagara River (0.91 ± 0.02) and from precipitation (1.00 ± 0.01). Air samples of α-HCH measured at 10 m above the lake show a seasonal variability with values near 1.00 in spring and fall and minimum values in individual samples near 0.90 in summer. A simple air−water gas transfer model demonstrates that enantiomeric 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 the m...