Removal of six pesticide residues from vegetables by the coupled ultrasonic-ozonation process

Abstract

The presence of pesticide residues in vegetables is a worldwide issue regarding food safety. This study explores the efficacy of a novel advanced oxidation process (AOP), namely the coupled ultrasonic-ozonation (US/O₃) process, for removing six commonly found pesticides from vegetables. The US/O₃ process demonstrated remarkable pesticide removal rates ranging from 79.1% to 92.2%, which were much higher than the separate US (40.4%–62.4%) and O₃ (32.3%–69.6%) processes. This high efficiency was achieved by the oxidation of pesticides in both the vegetables and the water, facilitated by the free radicals generated during the process. The surface area and structure of vegetables had a great impact on the removal of pesticide residues by US/O₃. Notably, a significant improvement in pesticide removal rate was observed when the ultrasonic frequency was increased from 20 to 40 kHz. The intermediates formed during the degradation of chlorpyrifos were identified by GC/MS and possible mineralization pathways were proposed. The degradation of chlorpyrifos by US/O₃ was found to occur through three routes, including oxidation of the SP bond, substitution of the chlorine atom and cleavage of the phosphoester bond. Although the US/O₃ process resulted in a slight decrease (6%) in the total chlorophyll content of spinach, this was deemed acceptable given the high efficacy of the US/O₃ process for pesticide removal. Overall, the coupled US/O₃ process shows great promise as a safe and effective method for removing pesticide residues from vegetables.