Abstract: We studied the dissipation of chiral triazole fungicide myclobutanil in four tea orchard soils with different cultivating ages by enantiomeric fractionation analysis(EFA) and compound-specific isotope analysis(CSIA). The dissipation of myclobutanil in soils followed first order kinetics with half-lives ranging from 28.4 to 70.5 days. Enantioselective degradation occurred in all tea orchard soils where(+)myclobutanil was preferentially degraded. The dissipation half-life and enantiomer fraction of myclobutanil were significantly lower in 50year than in 100, 20, and 2year tea orchard soils (P<0.05), while degradation half-life and enatioselectivity were significantly correlated with sand and silt contents (P<0.05), respectively. We used the logarithmic forms of the Rayleigh equation in evaluating the carbon isotope enrichment factors for various soils and established the biodegradation assessment model. The biodegradation rates of myclobutanil evaluated by both enantiomeric and isotopic fractionation analysis were consistent with the observed degradation rates.

Key words: myclobutanil, enantioselective degradation, compound-specific isotope analysis(CSIA), enantiomeric fractionation analysis(EFA), isotope fractionation