Chiral Pesticides in Soils of the Fraser Valley, British Columbia

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 α-hexachlorocyclohexane residues in muck soils indicated preferential breakdown of the (−) enantiomer, whereas α-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.