Identification and ecotoxicity prediction of pyrisoxazole transformation products formed in soil and water using an effective HRMS workflow

Pyrisoxazole, an isoxazoline-class fungicide, has been registered and used for approximately 19 years. However, its environmental transformation products (TPs) and corresponding ecotoxicological effects remain ambiguous. In this study, the photolysis, hydrolysis, and soil transformation behavior of pyrisoxazole were systematically investigated by indoor simulation experiments and analyzed by liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS) and UNIFI software. Transformation products in different environemnts were effectively identfied by a proposed workflow, which organically combined suspect and non-target screening strategies. In total, 17 TPs were screened out. Eight TPs were confirmed using the corresponding reference standards. Structures of another 9 compounds were tentatively proposed based on diagnostic evidence. Among them, 14 products were reported for the first time. The transformation pathways of pyrisoxazole in soil and water were proposed. Pathway analysis demonstrated that the different pH of aqueous solutions had little effect on the pathways, while the influence of different soil types and oxygen conditions was evident. Finally, the toxicity of the proposed TPs to fish and daphnids was predicted using ECOSAR software. These proposed TPs in soil and water, transformation pathways, and predicted ecotoxicity information could provide systematic insight into the fate and environmental risks of pyrisoxazole.