Estimation of thiamethoxam and its metabolites in wheat using QuEChERS methodology combined with LC-MS/MS

Abstract

ABSTRACT Thiamethoxam, a systemic neonicotinoid insecticide, is widely accepted for use against various chewing and sucking insect pests. In this particular study, the authors examined the dissipation kinetics and metabolism of thiamethoxam in wheat using quick, easy, cheap, effective, rugged and safe (QuEChERS) methodology combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) over two years during the same cropping season. Residues of thiamethoxam and its metabolites in wheat plants were investigated following foliar spray of thiamethoxam at recommended dose (12.5 g a.i. ha−1) and four times the recommended dose (50.0 g a.i. ha−1) at earhead formation stage. Total residues of thiamethoxam and its metabolites in leaves at 0 day (2 h after spray) ranged from 3.69 to 14.36 mg kg−1 for the two doses over the two years. Clothianidin was the only metabolite detected in leaves at 0 day (2 h after spray); however at 7 days after spray nitroguanidine, N-desmethyl-thiamethoxam and 1-methyl-3-nitroguanidine were also detected. Total residues of thiamethoxam and its metabolites in soil at 0 day (2 h after spray) ranged from 0.23 to 0.84 mg kg−1. Thiamethoxam residue in leaves and soil followed first order kinetics with half-life ranging from 9.04 to 15.50 days for the two doses over the two study years. Residues of thiamethoxam and its metabolites in leaves, straw and grain at harvest time for both the doses were below their limit of quantification (0.01 mg kg−1). This information could be helpful for evaluating both regulatory and food safety decisions regarding use of neonicotinoids.