Environmental Behavior of Acetamide Pesticide Sterepisomers. 2. Stereo- and Enantioselective Degradation in Sewage Sludge and Soil

摘要

The degradation of five acetamide pesticides (alachlor, acetochlor, metalaxyl, metolachlor and dimethenamid) with different types of stereoisomerism (axial-and/or C-chirality) was studied in soil and sewage sludge using chiral high-resolution gas chromatography/ mass spectrometry (HRGC/MS). Overall degradation rates in both media were in the order of alachlor > acetochlor > dimethenamid > metolachlor > metalaxyl. The results indicated the degradation of metalaxyl, metolachlor, and dimethenamid to be stereo- and/ or enantioselective, particularity with respect to C-chirality. For acetochlor (axial-chiral), the results were inconclusive due to interference in the detection of this compound. Metalaxyl showed different enan-tioselectivity in the two media with the 1′ S-(+)-enantiomer faster degraded in sewage sludge and the fungicidal more active 1′ R-(-)-enantiomer faster degraded in soil. α-Hexachlorocyclohexane (α-HCH) and its enantioselective degradation were used as an internal control to confirm biotic action in the sewage sludge. Surface water (lakes, drainage canal) and rain contained detectable quantities (2-120 ng/L) of some of these pesticides. The peak area ratios in all but one sample (drainage canal) were close to those of the technical products, indicating little if any biological degradation.