Concentrations and Enantiomeric Ratios of Organochlorine Pesticides in Soils from the U.S. Corn Belt

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.