Influence of pH on the Stereoselective Degradation of the Fungicides Epoxiconazole and Cyproconazole in Soils
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- 作者：Ignaz J. Buerge ; Thomas Poiger ; Markus D. Mü ; ller ; Hans-Rudolf Buser
- 刊名：Environmental Science & Technology
- 出版年：2006
- 出版时间：September 1, 2006
- 年：2006
- 卷：40
- 期：17
- 页码：5443 - 5450
- 全文大小：184K
- 年卷期：v.40,no.17(September 1, 2006)
- ISSN：1520-5851
文摘
Many pesticides are chiral and consist of two or moreenantiomers/stereoisomers, which may differ in biologicalactivity, toxicity, effects on nontarget organisms, and environmental fate. In the last few years, several racemic compounds have been substituted by enantiomer-enrichedor single-isomer compounds ("chiral switch"). In this context,the stereoselective degradation in soils is an importantpart of a benefit-risk evaluation, but the understanding ofthe environmental factors affecting the chiral preferencesis limited. In this study, the stereoselective degradationof the fungicides epoxiconazole and cyproconazole wasinvestigated in different soils, selected to cover a wide rangeof soil properties. The fungicides were incubated underlaboratory conditions and the degradation and configurationalstability of the stereoisomers were followed over timeusing enantioselective GC-MS with a 
-cyclodextrinderivative as chiral selector. In alkaline and slightly acidicsoils, the degradation of epoxiconazole was clearly enantioselective, whereas in more acidic soils, both enantiomerswere degraded at similar rates (overall half-lives 78-184 d).The enantioselectivity, expressed as ES = (ki - kj)/(ki + kj), ranged from -0.4 in alkaline soils (faster degradationof enantiomer j) to ~0 in acidic soils (non-enantioselective),and showed a reasonably linear correlation with thesoil pH. The four stereoisomers of cyproconazole (overall half-lives 5-223 d) were also degraded at different rates inthe various soils, but only the stereoselectivities betweenepimers showed some correlations with pH, whereasenantioselectivities did not. Both fungicides wereconfigurationally stable in soils, i.e., no enantiomerizationor epimerization was observed. Correlations between pH andES have previously been reported for other pesticides(metalaxyl, dichlorprop, mecoprop), but the presence orabsence of such correlations is not obviously linked to thepathways of degradation. It can be assumed that differentmicroorganisms and enzymes are involved in the primarydegradation of these compounds, but on which level soil pHhas an influence on ES remains to be investigated.
-cyclodextrinderivative as chiral selector. In alkaline and slightly acidicsoils, the degradation of epoxiconazole was clearly enantioselective, whereas in more acidic soils, both enantiomerswere degraded at similar rates (overall half-lives 78-184 d).The enantioselectivity, expressed as ES = (ki - kj)/(ki + kj), ranged from -0.4 in alkaline soils (faster degradationof enantiomer j) to ~0 in acidic soils (non-enantioselective),and showed a reasonably linear correlation with thesoil pH. The four stereoisomers of cyproconazole (overall half-lives 5-223 d) were also degraded at different rates inthe various soils, but only the stereoselectivities betweenepimers showed some correlations with pH, whereasenantioselectivities did not. Both fungicides wereconfigurationally stable in soils, i.e., no enantiomerizationor epimerization was observed. Correlations between pH andES have previously been reported for other pesticides(metalaxyl, dichlorprop, mecoprop), but the presence orabsence of such correlations is not obviously linked to thepathways of degradation. It can be assumed that differentmicroorganisms and enzymes are involved in the primarydegradation of these compounds, but on which level soil pHhas an influence on ES remains to be investigated.