Residue and safety evaluation of thiophanate-methyl and its metabolite carbendazim in kiwi fruit

To evaluate the safety of thiophanate-methyl in kiwi fruit, the QuEChERS-ultra high performance liquid chromatography-tandem mass spectrometry (QuEChERS-UPLC-MS/MS) analysis method was used to analyze the residues of thiophanate-methyl and its metabolite carbendazim in kiwi fruit. The kinetic equation and half-life of thiophanate-methyl residues in kiwi fruit were calculated. The dietary intake risk assessment was conducted. The maximum residue limit (MRL) of thiophanate-methyl in kiwi fruit was recommended and the safety of its metabolite carbendazim was evaluated. The results showed that the recovery rates of thiophanate-methyl and carbendazim were 85%-102% and 86%-101%, respectively, and their relative standard deviations (RSD) were 1.0%-7.1% and 2.1%-5.2%, respectively, at the spiked levels of 0.01, 0.1 and 1.0 mg/kg. The limits of quantitation (LOQ) of two pesticides on kiwi fruit were both 0.01 mg/kg. The regulation of thiophanate-methyl residues in kiwi fruit conformed to the first-order reaction kinetic equation, with the half-life of 10.1-10.5 d. When the recommended dosage and 1.5 times of the recommended dosage (875 mg/kg, 1 166.7 mg/kg) of thiophanate-methyl (70% WP) were sprayed for 3-4 times and the harvest interval was 21 days, the dietary risk quotient (RQ) was calculated as 78.7%. The result was acceptable to the general population and a MRL valaue of 5 mg/kg was recommended. The metabolite carbendazim had a greater risk of exceeding the standard of 0.5 mg/kg according to GB 2763. The MRL valaue of thiophanate-methyl should be established in kiwi fruit, while the MRL value of carbendazim should be reevaluated.