Air samples were collected in Alabama in January−October 1996 and in May 1997, to determine the seasonal variations of toxaphene and other OC pesticides (chlordanes, DDTs, dieldrin, and HCHs). Log partial pressure versus 1/T plots for γ-HCH, dieldrin, chlordanes, and their metabolites showed significant relationships, whereas those for toxaphene, heptachlor, and p,p‘-DDE did not. The chromatographic profile of toxaphene congeners in air and soil showed depletion of certain labile congeners, notably B8-531 and B8-806/809; other persistent congeners (B8-1412 and B9-1679) were enriched in air samples. Concentrations of toxaphene in Alabama air were 6−40 times higher than in the Great Lakes region, and chlordane in Alabama air exceeded Great Lakes concentrations by 3−9-fold. This suggests that transport from the southern U.S. is a continuing source of toxaphene and chlordane to the Great Lakes. Levels of HCHs and dieldrin in Alabama were similar to those in the Great Lakes region. Patterns of 8-chlorinated bornanes in air more closely resemble residues in soil than the technical toxaphene standard. Enantiomer ratios of chlordanes in air were nearly racemic, indicating that their source is probably evaporation from termiticide usage rather than from soils, which contain nonracemic chlordanes.

No abstract

The chiral pesticide heptachlor can undergo photolysis to yield the racemic products heptachlor-exo-epoxide (HEPX) and photoheptachlor. Heptachlor is also metabolized to nonracemic HEPX in biological systems and soils. HEPX in ambient air samples from the southern United States and Lakes Ontario and Superior was nonracemic and enriched in the (+) enantiomer. Average enantiomer ratios (ER ) areas of (+)/(-) HEPX) in these locations ranged from 1.51 to 2.02, and were similar to ER values of HEPX reported for agricultural soils. Airborne heptachlor was racemic, with ERs of 0.98-1.02. These results suggest that the main source of HEPX in ambient air is not photolysis of heptachlor, but rather metabolism of heptachlor in soils followed by volatilization of HEPX. The study exemplifies the use of chiral analysis for investigating the environmental fate of pesticides.