Technological Substitution in Pesticide Application Reduces Occupational Risk but Fails to Mitigate Dietary Residue Burden: Field Evidence from UAV versus Manual Spraying in Paddy Rice

Abstract UAV spraying has been widely promoted as superior to manual application in Asian rice production, yet its combined implications for food safety and occupational exposure have never been evaluated within a single integrated framework. Here, we report a full-season field trial comparing UAV and manual imidacloprid (IMI) application in paddy rice, simultaneously tracking grain residue dynamics and occupational exposure in 29 applicators through to harvest. Grain IMI concentrations at harvest were comparable between regimes (86−115 μg/kg) and exceeded the EU maximum residue limit (MRL, 10 μg/kg) in both groups. More critically, on an LC-HRMS-derived relative-concentration basis, parent IMI accounted for 30.4% of the detected IMI-related profile in grain, whereas transformation products collectively accounted for 69.6%. Among these, 6-hydroxynicotinic acid was the single highest-abundance compound, surpassing parent IMI itself, yet none of the detected transformation products are included in China’s residue definition for imidacloprid in plant-derived foods. Regarding occupational exposure, urinary IMI rose approximately 9-fold from pre-exposure baseline in UAV operators compared with 17-fold in manual applicators. Manual application also induced markedly greater lipid peroxidation stress, with median baseline-normalized MDA fold changes of approximately 3.8- and 2.6-fold in the manual and UAV groups, respectively (p = 0.001). These findings establish that application technology substitution effectively reduces occupational exposure risk but confers no advantage at the food safety end point. Current parent-compound-centered residue surveillance frameworks systematically underestimate the true IMI-related burden in harvested grain, and expansion of regulatory monitoring beyond the parent compound is warranted.