Reduction of Pesticide Clothianidin, Thiamethoxam, and Propoxur Residues via Plasma-Activated Water Generated by a Pin-Hole Air Plasma Jet

Abstract

This study explores the efficacy of plasma-activated water (PAW), produced using a laboratory-made pin-hole air plasma jet, in the reduction of pesticide residues, including clothianidin, thiamethoxam, and propoxur. The physicochemical analysis indicated that PAW’s pH decreased significantly with longer discharge times, while oxidation–reduction potential (ORP) and electrical conductivity (EC) increased. Nitrogen and oxygen species in the plasma state were confirmed using optical emission spectroscopy. These results reflected the formation of rich reactive oxygen and nitrogen species (ROS and RNS), including hydroxyl radicals, hydrogen peroxide, and nitrate, contributing to its strong oxidative properties. The optimal PAW parameters for pesticide degradation were determined, and pesticide reduction was assessed using high-performance liquid chromatography (HPLC) and liquid chromatography–mass spectrometry (LC-MS). After 25 min of treatment, maximum reduction rates of 65%, 93%, and 88% were achieved for clothianidin, thiamethoxam, and propoxur, respectively. Only clothianidin yielded a single degradation product which is suggested to be formed by cyclic rearrangement following the loss of Cl and NO<inf>2</inf>, while those of thiamethoxam and propoxur were not detected. PAW produced by atmospheric pin-hole air plasma jet demonstrated superior degradation efficiency with minimal toxic by-product formation. The findings contribute valuable insights into sustainable practices for environmental detoxification.