CONCENTRATIONS AND ENANTIOMERIC RATIOS OF ORGANOCHLORINE PESTICIDES IN SOIL FROM THE US CORN-BELT

Past research has shown that selective enzymatic degradation of enanti omers by microorganisms does occur. This work was done to determine co ncentrations and enantiomeric ratios of several chiral organochlorine pesticides in soils from the Corn Belt region. Quantitative analysis w as 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, heptac hlor, heptachlor epoxide, dieldrin, alpha-hexachlorocyclohexane, and t rans-nonachlor) in 38 agricultural soils and two garden soils. Residue s were log-normally distributed, and geometric mean values (ng/g dry w t) were Sigma DDT = 9.6, Sigma chlordane = 1.4, dieldrin = 1.0, and HE PX = 0.58. HEPT and alpha-HCH were found infrequently. Concentrations in two garden soils were similar to those for agricultural soils. Enan tioselective analysis was done by gas chromatography-mass spectrometry with chiral-phase capillary columns. Evidence of enantioselective deg radation of OCs was found in 30 soils, o,p'-DDT and OXY showed differi ng enantiomeric patterns in different soils, while (+)TC, (-)CC, and ( -)HEPX were in excess in all soils with nonracemic compositions. The t wo garden soils showed similar patterns of degradation. No correlation s were found between ER and pesticide concentration or ER and % TOC fo r any of the compounds.