Enantioselective Degradation of Dufulin in Four Types of Soil

In this study, enantioselective degradation of dufulin in four types of soil (Guiyang silty loam, Nanning silty clay, Hefei silty clay, and Harbin silty clay) was investigated under sterile and nonsterile conditions. Pesticide residues in soil samples were extracted with acetonitrile. <i>S</i>-(+)-Dufulin and <i>R</i>-(−)-dufulin were separated and determined on an amylose tris­(3,5-dimethylphenylcarbamate) (Chiralpak IA) chiral column by normal phase high-performance liquid chromatography (HPLC). The absolute configurations of dufulin enantiomers were determined by obtaining experimental and computed circular dichroism spectra. Dufulin enantiomers were found to be configurationally stable in the selected soils, and no interconversion was observed during the incubation of enantiopure <i>S</i>-(+)- or <i>R</i>-(−)-dufulin under nonsterile conditions. Compared to the half-life (<i>t</i>_1/2) of dufulin in sterile soils, the degradation rate was higher in nonsterile soils, which suggests that dufulin degradation can be attributed primarily to microbial activity in soils used for agricultural cultivation. Furthermore, enantiopure <i>S</i>-(+)-dufulin degraded more rapidly than its antipode. This suggests that use of enantiopure <i>S</i>-(+)-dufulin could exert less disturbance to soil bioactivity and contribute less to environmental pollution

Comparative Study of the Selective Degradations of Two Enantiomers in the Racemate and an Enriched Concentration of Indoxacarb in Soils

In this study, selective degradations of the two enantiomers of indoxacarb in the concentrate (2.33S/1R) and racemate (1S/1R) are examined. The absolute configurations of indoxacarb enantiomers were determined using X-ray diffraction. The results showed that in two alkaline soils, the <i>S</i>-(+)-indoxacarb was preferentially degraded in both the concentrate and racemate. In one acid soil, the two enantiomers degraded no-selectivity. In another acid soil and one neutral soil, the <i>R</i>-(−)-indoxacarb was preferentially degraded in both the concentrate and racemate. Indoxacarb enantiomers were configurationally stable in the five soils, and no interconversion was observed during the incubation. Because no significant difference in degradation was observed after samples were sterilized, the observed enantioselectivity may be attributed primarily to microbial activity in soils. The results indicate that the selective degradation behavior was the same for both formulations that were tested