Study of the Removal Chlorpyrifos in Apples and the Degradation Pathway

Objective: Through experiments and analysis of the degradation effect of chlorpyrifos on the surface of apples by acidic electrolyzed oxidizing water (EOW) under different conditions, a degradation pathway of chlorpyrifos was proposed to provide theoretical support for apple producing and processing industries. Methods: The specific experimental method used in this research was to use chlorpyrifos to simulate the pollution of the surface of apples at first, then to degrade the chlorpyrifos by soaking and shaking the apples in EOW with different ACC (10, 50, 100 mg/L) and pH (2.80, 5.80). The experiment used gas chromatography and GC-MS to analyze the residual amount of chlorpyrifos and degradation pathway. Results: The experimental results showed that the degradation efficiency of chlorpyrifos on the surface of apples was directly related to the reaction time and the concentration of available chlorine (ACC) when it was treated by strong acid electrolyzed oxidizing water (AcEW). As reaction time increased or the ACC increased, the degradation efficiency also increased. When the available chlorine concentration reached 50 mg/L with the immersion time reached 15 min, the degradation rate of chlorpyrifos reached more than 55%, which significantly differed with the control group in which apple was immersed in tap water (P<0.01). When the ACC was 100 mg/L, the degradation rate of chlorpyrifos exceeds 70%. Under same conditions, there was no significant difference between the AcEW and the slightly acidic electrolyzed water (SAEW) in the degradation effect of chlorpyrifos (P>0.05), and there was no significant difference between the immersion treatment and shaking treatment as it showed in experimental results (P>0.05). The surface treated with EOW had no effect on the main quality indicators of the apple itself (P>0.05). According to GC-MS analysis, the degradation products produced by the degradation of chlorpyrifosbys AcEW included chlorpyrifos oxide (CPO) and 3, 5, 6-trichloropyridin-2-ol (TCP). The possible degradation pathway, as we propose, is chlorpyrifos→CPO→TCP→small molecule organic matter→inorganic matter. Conclusion: This results may provide a new method for the apple processing industries in eliminating pesticide residues.