Dimethoate, a systemic insecticide, has been used extensively in vegetable production. Insecticide residues in treated vegetables, however, pose a potential risk to consumers. Photocatalytic degradation is a new alternative to managing pesticide residues. In this study, the degradation of dimethoate in Bok choy was investigated under the field conditions using cerium-doped nano titanium dioxide (TiO2/Ce) hydrosol as a photocatalyst. The results show that TiO2/Ce hydrosol can accelerate the degradation of dimethoate in Bok choy. Specifically, the application of TiO2/Ce hydrosol significantly increased the reactive oxygen species (ROS) contents in the treated Bok choy, which speeds up the degradation of dimethoate. Ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) analysis detected three major degradation products, including omethoate, O,O,S-trimethyl thiophosphorothioate, and 1,2-Bis (acetyl-N-methyl-) methane disulfide. Two potential photodegradation pathways have been proposed based on the intermediate products. To understand the relationship between photodegradation and the molecular structure of target insecticides, we investigated the bond length, Mulliken atomic charge and frontier electron density of dimethoate using ab initio quantum analysis. These results suggest the P = S, P-S and S-C of dimethoate are the initiation sites for the photocatalytic reaction in Bok choy, which is consistent with our empirical data.

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Published in PLOS ONE, v. 13, no. 5, e0197560, p. 1-16.

© 2018 Liu et al.

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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This work was supported by a grant from the National Natural Science Foundation of China (Award #: 31672043, 21003042), the Special Fund for Agro-scientific Research in the Public Interest, P.R. China (Award #: 201303031), China Postdoctoral Science Foundation funded project (Award #: 2015M582329), Natural Science Funds of Hunan Province (Award #: 2018JJ2165), China Scholarship Council (File No. 201608430210), Shen-Nong Visiting Scholar Funding Program of Hunan Agricultural University, and Collaborative Innovation Center for Field Weeds Control (ZCFKP20141203).