Stereoselective bioaccumulation and dissipation of pyrisoxazole in earthworm-soil microcosm

Pyrisoxazole is a chiral fungicide with high sterilizing activity to the plant pathogenic bacteria. It has two chiral C atoms, which bring four stereoisomers. The present work was the first time to explore the stereoselective bioaccumulation behavior of pyrisoxazole in earthworms by chiral liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS). The absolute configurations of pyrisoxazole stereoisomers were confirmed by circular dichroism (CD) coupled with calculated electronic circular dichroism (ECD) method, and the elution order in Lux Cellulose-3 column was as follows: (-)-3S, 5R-pyrisoxazole, (+)-3R, 5S-pyrisoxazole, (+)-3S, 5S-pyrisoxazole and (-)-3R, 5R-pyrisoxazole. The recoveries of pyrisoxazole stereoisomers in earthworm and soil samples ranged from 80.8 % to 101 % with the RSD lower than 6.3 %. In bioaccumulation progress, (+)-3R, 5S-pyrisoxazole was accumulated preferentially in earthworms, and the bioaccumulation concentrations of high-activity (-)-3S, 5R-pyrisoxazole were the lowest. There were no stereoselective bioaccumulation between (+)-3S, 5S-pyrisoxazole and (-)-3R, 5R-pyrisoxazole, while there was diastereoselectivity between Z-pyrisoxazole and E-pyrisoxazole with higher E-pyrisoxazole concentrations. In the whole bioaccumulation process, the BAF values of (+)-3R, 5S-pyrisoxazole were significantly higher than (-)-3S, 5R-pyrisoxazole, and the BAF values of (-)-3S, 5R-pyrisoxazole were the lowest. The dissipation of pyrisoxazole stereoisomers in the artificial soil was very slow and had no stereoselectivity, and the existence of earthworms had little effects on the dissipation of pyrisoxazole stereoisomers, which indicated that the stereoselective behaviors of pyrisoxazole in earthworms were caused by the stereoselective enrichment and dissipation of earthworms themselves. Taken together, (-)-3S, 5R-pyrisoxazole was recommend as a commercial product. This study played a positive role in guiding the development of environmentally friendly pesticides and provided database for the environmental and biological risk assessment of pyrisoxazole.