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

Abstract

A QuEChERS technique via UPLC-MS/MS for analysis of spinosad (spinosyn A+spinosyn D), thiocyclam and nereistoxin in cucumber was established with mean recoveries of 93-104%, relative standard deviations of ≤9% and limits of quantifications of 0.01 mg/kg. Field trials of spinosad and thiocyclam were performed in twelve representative cultivating areas in China. Field trial results indicates that spinosyn A and spinosyn D easily dissipated in cucumber with half-lives of 2.48-6.24 days and <3 days, respectively. Nereistoxin produced after thiocyclam application and was more persistent than its parent. The terminal residues of spinosad were all below MRLs (0.2 mg/kg) in China, while the terminal concentration of nereistoxin (calculated as the stoichiometric equivalent of thiocyclam), which was much higher than those of thiocyclam, was far beyond MRLs of thiocyclam in cucumber (0.01 mg/kg) established by EU. PNECs of spinosyn A, spinosyn D, thiocyclam and nereistoxin leaching to groundwater were estimated using China-PEARL Models after application. However, the dietary (food and water) exposure risk quotient for different populations was below 1 with Pre-Harvest Interval set at 5 days after the last application, indicating 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.