Enantioselective environmental behavior of the chiral fungicide mandipropamid in four types of Chinese soil

Abstract

AbstractEnantioselective degradation behavior of mandipropamid, and factors affecting its degradation and metabolites in four types of Chinese soil were investigated in this work. The results showed that the enantiomeric selectivity values ranged from 0.025 to 0.170, indicating that enantioselectivity was found in the degradation process of the racemate in all of the soil samples and that the R‐(−)‐enantiomer was preferentially degraded. The degradation compounds formed faster in native alkaline soils (half‐lives = 35.5–39.80 d) than in native acidic soils (half‐lives = 51.3–77.90 d). The half‐lives of the R‐(−)‐enantiomer and S‐(+)‐enantiomer were 35.5–73.7 and 37.5–77.9 d, 66.6–97.6 and 70.0–103.5 d, and 52.5–110.0 and 66.0–144.4 d in the four types of soil under native, sterilized, and organic matter‐removed conditions, respectively, which indicated that mandipropamid degradation can be attributed to microbial activity and the organic matter content in the soil. Furthermore, the half‐lives of the R‐(−)‐enantiomer and S‐(+)‐enantiomer decreased 1.07–1.95 and 1.08–1.79 times with each 10 °C increase in incubation temperature, and the half‐lives of the R‐(−)‐enantiomer and S‐(+)‐enantiomer decreased 1.09–1.43 and 1.06–1.50 times with increasing moisture content. However, the incubation temperature and soil moisture did not change the enantioselectivity. Mandipropamid enantiomers were observed to be configurationally stable in the selected soil, and no interconversion was found during the incubation of enantiopure R‐(−)‐mandipropamid or S‐(+)‐mandipropamid in native or sterilized soil. During the degradation process, four major metabolites were detected. In comprehensive consideration of the environmental behavior, the enantioselective degradation results should be considered to more accurately assess the risk of this chiral pesticide in a real environment.