Magnitude of thiamethoxam and its metabolite residues in okra following open field application: an arid ecosystem pilot study

This study evaluates the dissipation kinetics, terminal residues, and dietary risk of thiamethoxam and its metabolite clothianidin in okra under field conditions, using an optimized and validated dispersive solid phase extraction and liquid chromatography-tandem mass spectrometry method. The method demonstrated high selectivity and linearity (R² > 0.999) for both analytes, with recoveries ranging from 88.8 to 101.2% across different spiking levels. Method optimization included adjustments to hydration levels and adsorbent combinations, which minimized matrix suppression (reduced matrix effects to − 8.91% for thiamethoxam and − 10.4% for clothianidin). Validation confirmed low limits of detection (0.15 µg/kg for thiamethoxam and 0.73 µg/kg for clothianidin) and quantification (1 µg/kg and 2.5 µg/kg, respectively), with acceptable precision [intra- and inter-day relative standard deviations values below 12.5%]. Residue dissipation of thiamethoxam in okra followed first-order kinetics, with a half-life of 1.72 days and a pre-harvest interval of 8.11 days based on a maximum residue limit (MRL) of 0.01 mg/kg, while clothianidin fell below MRL by day 10. Chronic dietary risk assessments confirmed negligible risk to adult consumers when thiamethoxam was applied at twice the recommended field dose (40 g a.i./ha). The findings highlight the rapid dissipation of thiamethoxam in okra, driven by its tender surface and high environmental exposure, ensuring safe pesticide use and regulatory compliance.