Dissipation and Risk Evaluation of Nitenpyram and Tolfenpxrad Residues in Tea and Soil

  Objective  Dissipation of two new insecticides and risk of the residues in tea and soil were studied.

  Method  A gas chromatographic method was applied for analyzing nitenpyram and tolfenpxrad residues in tea and soil specimens to determine the dissipation and transfer of the insecticides after application.

  Result  The insecticide residues in tea and soil decreased exponentially with time after application in a first-order kinetic function. The half-lives of nitenpyram at the recommended dosage were 6.08–6.54 d in tea and 1.52–1.68 d in soil. It took 0.91–3.33 d for the residue to degrade below the maximum allowable residue limit (MRL) in tea. For tolfenpxrad at the recommended usage level, the residue half-lives were 4.47–4.74 d in tea and 1.87–1.89 d in soil. It took 5.10–8.18 d for the pesticide residue to dissipate below MRL in tea.

  Conclusion  Both nitenpyram and tolfenpxrad were found to degrade to below the MRLs in tea for safe consumption as well as in soil for environmental protection.