Dissipation dynamic and risk assessment of thiamethoxam in rice

To evaluate the application safety of thiamethoxam 20% SC,the terminal residue and dissipation dynamic of thiamethoxam in rice plant,rice straw,rice hulls and brown rice in Anhui and Jilin provinces were investigated and the samples were analyzed by HPLC-UVD.The results showed that the established methanol-methylene chloride mixture(1∶1,v∶v) had good elution effect;the dissipation curves of thiamethoxam in rice plant fitted to the first-order kinetics;the half-life of thiamethoxam was 2.1 d and 5.6 d in rice plant in Anhui and Jilin provinces respectively.When the formulation was sprayed at the recommended dosage,the final residues of thiamethoxam in brown rice was up to 1.0 mg·kg-1.By calculating,the daily average intakes of thiamethoxam from rice was only 0.4 mg per person and the risk quotient(RQ) was 0.32,so the application was safe.