Md. Muller et Hr. Buser, ENVIRONMENTAL BEHAVIOR OF ACETAMIDE PESTICIDE STEREOISOMERS .2. STEREOSELECTIVE AND ENANTIOSELECTIVE DEGRADATION IN SEWAGE-SLUDGE AND SOIL, Environmental science & technology, 29(8), 1995, pp. 2031-2037
The degradation of five acetamide pesticides (alachlor, acetochlor, me
talaxyl, metolachlor and dimethenamid) with different types of stereoi
somerism (axial- and/or C-chirality) was studied in soil and sewage sl
udge 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 dime
thenamid to be stereo- and/or enantioselective, particularily with res
pect to C-chirality. For acetochlor (axial-chiral), the results were i
nconclusive due to interference in the detection of this compound. Met
alaxyl showed different enantioselectivity 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. alpha-Hexachl
orocyclohexane (alpha-HCH) and its enantioselective degradation were u
sed as an internal control to confirm biotic action in the sewage slud
ge. Surface water (lakes, drainage canal) and rain contained detectabl
e quantities (2-120 ng/L) of some of these pesticides. The peak area r
atios in all but one sample (drainage canal) were close to those of th
e technical products, indicating little if any biological degradation.