Dissipation, processing factors, and dietary exposure of imidacloprid and thiamethoxam in sweet potato stems.

Abstract

Residues of two applied parent insecticides, imidacloprid and thiamethoxam, in sweet potato stems (Ipomoea batatas L.) were investigated during field dissipation, household processing, and dietary exposure assessment. Residues were determined using a QuEChERS-LC-MS/MS method validated in raw and processed matrices. The LOQ was 0.01 mg/kg, matrix-matched calibration showed R2 > 0.999, and recoveries ranged from 77.8 to 104.1%. Field dissipation followed first-order kinetics, with DT50 values of 2.5 days for imidacloprid and 1.8 days for thiamethoxam. Boiling gave the lowest processing factors (0.24 and 0.32), mainly through transfer into boiling water. Microwaving increased fresh-weight concentrations because of moisture loss, although dry-weight reduction factors remained below 1. Age-specific, commodity-specific, chronic dietary exposure estimates for sweet potato stems were low for all sample types and age groups, with %ADI values of 0-0.244% for imidacloprid and 0-0.143% for thiamethoxam. These results provide processing-factor and residue redistribution data that can support chronic dietary exposure assessment for processed sweet potato stems.