Degradationregularityoffourfield-incurredinsecticidesinriceduringprocessing

It is crucial to develop practical procedures for the control and reduction of pesticide residues in rice grain. In this study, dissipation of insecticides (triazophos, chlorpyrifos, carbosulfan and chlorantraniliprole) in rice grain from farm to dining table were studied to reveal the relationship among spraying stages, application dosage, harvest interval and pesticide residues. In addition, more efficient processing techniques were applied to assess harvest residual before dietary exposure. Field experiments were performed following the guideline on pesticide residue trials. Residues of the four insecticides in the samples processed via different treatments were determined using HPLC-MS/MS. The results showed that hulling and polishing processes can significantly reduce pesticide residues, and P_F values of all the tested pesticides were less 0.5. Washing twice followed by high-pressure cooking is able to further reduce the insecticide residues in the polished rice with the P_F < 0.2, which can further lower the risk of exposure. The variety of pesticide, application dosage and harvest interval were connected with the security of rice grain. The highest concentrations of carbosulfan and chlorantraniliprole were observed in the hull and bran of rice, which accounted for nearly 85% of total contents in rice grain. Therefore, those two insecticides were not detected even if they were sprayed once in dough stage at a pre-harvest interval of 21 days. However, triazophos and chlorpyrifos were detected in the polished rice, and their concentration were 0.032-0.043 mg/kg and 0.053-0.073 mg/kg, respectively. The residue of triazophos in the polished rice reduced at first then increased along with harvest interval, and the final residue was beyond the national standard of maximum residue limit in food (0.05 mg/kg) for all treatments. This is important to extend harvest interval to reduce residue level. Although higher residues in the polished rice were observed after the application of insecticide at the milky stage, the residue levels dropped to below MRL values after washing twice followed by high-pressure cooking. This study demonstrated that washing twice followed by high-pressure cooking can significantly reduce the pesticide residues, and it is safe for all the consumers.