Dissipation and Residue of Acephate and Its Metabolite Metamidophos in Peach and Pear Under Field Conditions

Study on the dissipation of the pesticide and its metabolite in commodity is an important task to evaluate their environmental behavior and toxicity. In this study, dissipation and residue of acephate and its metabolite methamidophos were investigated on nectarine, juicy peach, and pear fruits under three treatments, including direct spray, bagged spray and root-irrigation. The residues in fruit samples were determined by ultra-performance liquid chromatography tandem mass spectrometry. The dissipation of acephate under direct spray treatments was found to follow the first-order kinetics with half-lives of 4.1–5.5 days for nectarine and juicy peach, and 8.5 days for pear, respectively. Additionally, degradation of acephate to methamidophos was presented along with the occurrence of acephate in the three fruits under different treatments. The concentrations of acephate and methamidophos under bagged spray and root-irrigation treatments were generally lower than those obtained from direct spray. At 20 days after acephate application, the concentrations of the two compounds in the three fruits were reduced below the maximum residue limits (500 μg/kg for acephate, and 50 μg/kg for methamidophos) set by China, suggesting the safe use of acephate on peach and pear fruits. The results would be helpful for reducing the residues as well as potential risk of acephate and methamidophos for humans.