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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