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Past research has shown that selective enzymatic degradation of enantiomers by microorganisms does occur. This work was done to determine concentrations and enantiomeric ratios of several chiral organochlorine pesticides in soils from the Corn Belt region. Quantitative analysis was done by gas chromatography with electron capture detection using a DB-5 column. Concentrations were determined for 11 compounds (o,p‘-DDT, p,p‘-DDT, p,p‘-DDD, p,p‘-DDE, cis-chlordane, trans-chlordane, heptachlor, heptachlor epoxide, dieldrin, α-hexachlorocyclohexane, and trans-nonachlor) in 38 agricultural soils and two garden soils. Residues were log-normally distributed, and geometric mean values (ng/g dry wt) were ∑DDT = 9.6, ∑chlordane = 1.4, dieldrin = 1.0, and HEPX = 0.58. HEPT and α-HCH were found infrequently. Concentrations in two garden soils were similar to those for agricultural soils. Enantioselective analysis was done by gas chromatography−mass spectrometry with chiral-phase capillary columns. Evidence of enantioselective degradation of OCs was found in 30 soils. o,p‘-DDT and OXY showed differing enantiomeric patterns in different soils, while (+)TC, (−)CC, and (−)HEPX were in excess in all soils with nonracemic compositions. The two garden soils showed similar patterns of degradation. No correlations were found between ER and pesticide concentration or ER and % TOC for any of the compounds.

Chiral organochlorine pesticides were examined in soils collected in 1989 from six farms in the Fraser Valley, British Columbia. Concentrations of pesticide residues were 1-2 orders of magnitude higher in muck soils (27-56% organic matter) than in silt loams (3-7% organic matter). Enantiomeric composition of R-hexachlorocyclohexane residues in muck soils indicated preferential breakdown of the (-) enantiomer, whereas R-hexachlorocyclohexane in the silt loams was racemic. Five of the soils contained racemic o,p′-DDT, but the (+) enantiomer was selectively lost in one silt loam soil. No enantioselective breakdown of cis-or trans-chlordane was found in any of the soils, but nonracemic traces of oxychlordane were found in one silt loam and three muck soils. Enantiomeric composition of heptachlor and heptachlor exo-epoxide in muck soils indicated loss of (-)-heptachlor and production of (+)-heptachlor exo-epoxide, suggesting that the metabolism of these two compounds in soil may be more complex than a simple conversion of heptachlor to heptachlor exo-epoxide.

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