Chiral fungicide penconazole: Absolute configuration, bioactivity, toxicity, and stereoselective degradation in apples.

Abstract Traditional evaluation of chiral pesticides can lead to inaccurate results, as their enantiomers may show different properties. Penconazole, a chiral triazole fungicide with two enantiomers, is widely applied to protect against phytopathogens. In this study, its absolute configuration, bioactivity, ecotoxicity, and stereoselective degradation were investigated at the enantiomeric level in detail. The absolute configuration of the two enantiomers (R-(+)-penconazole and S-(−)-penconazole) was first confirmed by electronic circular dichroism (ECD), and their enantioseparation method was developed and optimized using UPLC–MS/MS. S-(−)-penconazole showed high bioactivity, as its fungicidal activity against four target phytopathogens (Alternaria alternate f. sp. mali, Botryosphaeria berengeriana f. sp. piricola, Colletotrichum gloeosporioides, and Fusarium oxysporum) was 1.8–4.4 times higher than that of R-(+)-penconazole. The results of an acute toxicity test showed that the LC50 values of S-(−)-penconazole against Daphnia magna were 32.5 times higher than those of R-(+)-penconazole at 24 h during the test period. Stereoselective degradation behaviors were found in nonbagging and bagging Fuji apples collected from three major apple-producing regions in China, with half-lives of 23.5–51.6 d (nonbagging treatment) and 23.0–57.5 d (bagging treatment) for R-(+)-penconazole and 41.1–60.9 d (nonbagging treatment) and 52.5–91.2 d (bagging treatment) for S-(+)-penconazole, respectively. This study provided new insights into the bioactivity, ecotoxicity, and stereoselective degradation of penconazole enantiomers. The above results also emphasized the importance of risk assessments of chiral pesticides at the enantiomeric level.