Dissipation and dietary exposure risk assessment of spinosad, thiocyclam, and its metabolite nereistoxin in cucumber and groundwater for different population groups

A QuEChERS (quick, easy, cheap, effective, rugged, and safe) technique using ultrahigh-performance liquid chromatography with tandem mass spectrometry for the analysis of spinosad (spinosyn A + spinosyn D), thiocyclam, and nereistoxin in cucumber was developed with mean recoveries of 93-104%, relative standard deviations of ≤9%, and limits of quantification of 0.01 mg/kg. Field trials of spinosad and thiocyclam were performed in 12 representative cultivating areas in China. Field trial results indicate that spinosyn A and spinosyn D easily dissipated in cucumber with half-lives of 2.48-6.24 and <3 days, respectively. Nereistoxin was produced after thiocyclam application and was more persistent than its parent. The terminal residues of spinosad were all below the maximum residue limits (0.2 mg/kg) in China, whereas the terminal concentration of nereistoxin (calculated as the stoichiometric equivalent of thiocyclam), which was much higher than that of thiocyclam, was far beyond the maximum residue limits of thiocyclam in cucumber (0.01 mg/kg) established by the European Union. The predicted no-effect concentrations of spinosyn A, spinosyn D, thiocyclam, and nereistoxin leaching into groundwater were estimated using China-PEARL (Pesticide Emission Assessment at Regional and Local scales) models after application. However, the dietary (food and water) exposure risk quotient for different populations was below 1 with a preharvest interval set at 5 days after the last application, indicating that the application of spinosad and thiocyclam in cucumber was unlikely to pose unacceptable risk for human health. This study provides data for the safe use of spinosad and thiocyclam in cucumber ecosystem.