Environmental Behavior of the Chiral Acetamide Pesticide Metalaxyl: Enantioselective Degradation and Chiral Stability in Soil

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• 作者：Hans-Rudolf Buser ; Markus D. Mü ; ller ; Thomas Poiger ; and Marianne E. Balmer
• 刊名：Environmental Science & Technology
• 出版年：2002
• 出版时间：January 15, 2002
• 年：2002
• 卷：36
• 期：2
• 页码：221 - 226
• 全文大小：104K
• 年卷期：v.36,no.2(January 15, 2002)
• ISSN：1520-5851

文摘

Racemic metalaxyl is currently being replaced in manycountries by metalaxyl-M, the fungicide enantiomericallyenriched with the biologically active R-enantiomer. This "chiralswitch" is expected to reduce the amount of pesticidereleased into the environment as well as potential side-effects on nontarget organisms. Detailed knowledge ofthe environmental behavior of such chiral compounds shouldinclude information on the chiral stability (interconversionof enantiomers). In the present study, the degradation/dissipation of metalaxyl and its primary carboxylic acidmetabolite (MX-acid) in soil was investigated under laboratoryconditions using enantioselective gas chromatography-mass spectrometry (GC-MS). Racemic and the enantiopureR- and S-compounds were incubated in separateexperiments. The degradation of metalaxyl was shown tobe enantioselective with the fungicidally active R-enantio-mer being faster degraded than the inactive S-enantiomer,resulting in residues enriched with S-metalaxyl when theracemic compound was incubated. The relatively highenantioselectivity suggests that degradation/dissipationwas largely biological. The data indicated a conversion of40-50% of metalaxyl to MX-acid, and the remainingmetalaxyl being degraded via other pathways. The degradationof MX-acid was also enantioselective. Metalaxyl and MX-acid were both configurationally stable in soil, showingno interconversion of R- to S-enantiomers, and vice-versa.Furthermore, the conversion of metalaxyl to MX-acidproceeded with retention of configuration. Degradationfollowed approximate first-order kinetics but showedsignificant lag phases.