Comparative Residue and Dietary Risk Assessment of Four Acaricides in Citrus Following Knapsack Versus UAV Spraying Using UHPLC-MS/MS

A sensitive and reliable analytical method based on ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) was developed and validated for the simultaneous determination of bifenazate, cyflumetofen, etoxazole, and abamectin B1a in citrus leaves, whole fruit, peel, and pulp. The method exhibited good linearity (0.0001–0.1 mg/L, R2 > 0.999), a limit of quantification (LOQ) of 0.001 mg/kg, mean recoveries of 77.3–110.5%, and relative standard deviations of 3.1–19.8%. This method was applied to compare the dissipation dynamics and dietary risks of the four acaricides following knapsack spraying versus unmanned aerial vehicle (UAV) spraying. Compared to knapsack application, UAV spraying resulted in 2.2- to 4.1-fold higher initial deposits on citrus leaves and shorter dissipation half-lives. After 21 days, all terminal residues were below the maximum residue limits (MRLs) established by China, the Codex Alimentarius Commission, the United States, Australia, Korea, the European Union, and Japan. Chronic dietary risk assessment revealed risk quotients below 1% for cyflumetofen and etoxazole, and approximately 47% for bifenazate and 93% for abamectin B1a. Although all values were below the acceptable threshold of 100%, the risk for abamectin B1a approached this limit, indicating that its cumulative dietary risk should not be overlooked. This study provides scientific evidence for residue monitoring of acaricides in citrus and for the safety evaluation of UAV-based pesticide application.