Integrated Assessment of Clothianidin Residues and Antioxidant Response in Sweet Pepper: Dissipation Kinetics, Pre-Harvest Interval, Washing Effects, and Dietary Risk Evaluation

A green, water-based extraction method was validated for quantifying clothianidin residues in greenhouse-grown sweet peppers (Capsicum annuum) using LC–MS/MS. The method showed excellent linearity (R2 = 0.9947), precision (RSDr = 10.66%, RSDR = 14.31%), recoveries of 86.1–91.6%, and a limit of quantification (LOQ) of 0.002 mg/kg. Clothianidin dissipation followed first-order kinetics, with half-lives of 2.91 days at the recommended dose and 2.61 days at double the dose. Preharvest intervals (PHIs) estimated from the kinetic model were 8.2–9.5 days at the EU MRL of 0.04 mg/kg and 14.0–14.7 days at the EU default MRL of 0.01 mg/kg. Dietary exposure based on terminal residues was negligible (maximum HQc = 0.006%). Postharvest washing (10 min, ∼25 °C) reduced residues; 1% NaHCO3 removed ≈ 60%, while vinegar and the NaHCO3–vinegar mixture had intermediate effects, and tap water was the least effective. Vinegar, NaHCO3, and their mixture also lowered total antioxidant capacity (TAC), consistent with losses of water-soluble phenolics. 1% NaHCO3 washing is supported as a practical household step to reduce residues, and reporting PHIs at both 0.01 and 0.04 mg/kg facilitates current compliance and historical comparability.