Pesticides remaining in water of environmental systems are usually degraded by hydrolysis and photolysis, and may form a series of toxic transformation products. Isopyrazam is a novel succinate dehydrogenase inhibitor fungicide (SDHI), whose degradation pathway and products in aqueous have not been studied. This work focused on the hydrolysis and photolysis behavior of isopyrazam in water, and investigated the contribution of light sources, pH and natural photosensitizers to the degradation kinetics, pathways and metabolite species of isopyrazam. In addition, the transformation products were identified by HPLC-QTOF-MS and toxicity of them were predicated. Results suggested that isopyrazam in water was hydrolytically stable under dark conditions when the pH of solution changed from 4.0 to 9.0. Under ultraviolet and simulated natural light, isopyrazam degraded with half-lives of 30.12 min and 53.32 h, respectively. The acidity of the solution had an effect on the rate of photolysis, but with little change in the type of products. The contribution of natural photosensitizers to photolysis is not prominent. Evlen products were screened by high resolution mass spectrometry, and the possible pathway of isopyrazam were proposed to include photohydrolysis, hydroxylation, nitration, demethylation, dehydrofluorination, photoisomerization, where the theories of computational chemistry were used to corroborate the inference. The predicted results of acute and chronic toxicity to aquatic organisms showed that TP4 and TP11 had a higher toxicity to fish, daphnid and green algae than the parent. These findings will offer valuable information for understanding the fate and ecological risk of isopyrazam.

Degradation of isopyrazam in water: Kinetics, pathways, transformation products identification and toxicity prediction

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ACS Fall 2022

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