Residue dissipation and dietary intake risk assessment of thiophanate-methyl and its metabolite carbendazim in watercress under Chinese field conditions

In this study,the QuEChERSand high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS)was applied to determine thiophanate-methyl and its metabolite carbendazim residue in watercress. The average recoveries of both analytes in watercress ranged from 96.2% to 102.9% with relative standard deviation (RSD) less than 8.2%. The limit of quantification (LOQ)of method for both analytes was 0.01 mg/kg. The field trials were carried out in 2018 to monitor the residues of thiophanate-methyl and its metabolite in six main cultivation areas inwatercressof China. Thiophanate-methylrapidly dissipated and transformed to carbendazim under watercress field conditions with half-lives less than 2.12 d.Carbendazim also rapidly dissipated with half-lives of 2.76 and 3.77d at two experiment sites. The terminal residue of thiophanate-methyl,carbendazim and total thiophanate-methyl were lower than 14.5 mg/kg, 5.26 mg/kg and 13.3 mg/kg, respectively. In order to ensure the safety, the acute and chronic dietary intake risks were evaluated. The ADI%of thiophanate-methyl, carbendazim and total thiophanate-methyl ranged from 21.1% to 84.9% and their%ARfDranged from 2.1% to 19.2%, which suggested that thiophanate-methyl and carbendazim has a low risk for Chinese populations caused by application of thiophanate-methyl.