Acetamiprid in Rizhao green tea: Residue dynamics, degradation pathways, and ecological risks via integrated...

This study assesses the environmental persistence, processing effects, and toxicity mechanisms of acetamiprid in Rizhao green tea. Uniquely, we integrate season-resolved field trials, full-scale factory processing and atomistic DFT-docking analyses to deliver the first "field-to-cup" mass-balance for any neonicotinoid in tea. Field trials demonstrated concentration-dependent dissipation kinetics, with half-lives decreasing from 5.54 days (spring, RD) to 4.36 days (autumn, 3 ×RD). Seasonal variations, driven by higher autumn temperatures (18.2 °C vs. 12.5 °C) and light intensity (PAR: 1451 vs. 982 μmol/m²/s), significantly accelerated acetamiprid degradation. During tea processing, fixation reduced residues (PF<1), while drying caused significant accumulation (PF 2.63-2.99) due to high vapor pressure. GC-MS identified six degradation products, two of which-6-chloronicotinaldehyde and methyl 6-chloronicotinate-showed chronic toxicity to aquatic organisms (EC₅₀: 45.2-62.7 mg/L), though acute toxicity was absent. Density functional theory (DFT) revealed reactive sites in acetamiprid's side chain, aligning with hydrolysis/oxidation pathways. Molecular docking and dynamics simulations elucidated acetamiprid's neurotoxic mechanism: stable binding to nAChRs via hydrogen bonds with Trp-86 (-12.5 ± 0.8 kcal/mol contribution) and Lys-10, yielding a spontaneous binding energy of -5.5 kcal/mol. Seasonal harvesting adjustments (prolonged spring intervals) and optimized drying protocols are proposed to minimize residues. The study underscores the ecological risks of acetamiprid's environmental persistence (soil half-life: 6.3-9.5 days) and transformation products, advocating for integrated agronomic practices to safeguard tea quality and aquatic ecosystems.