Gamma radiation induced degradation of the phenoxy acid herbicide diclofop-methyl in aqueous solutions

Abstract

Gamma radiation of diclofop methyl (DM) an herbicide deriving from aryloxy-propionic acid was investigated. DM aqueous solutions was irradiated at different doses from 1 kGy to 8 kGy. The effects of radiation doses on UV-visible spectroscopy, pH, total inorganic carbon (TOC) and kinetic study have been studied. It was found that absorption bands decrease with increasing radiation dose. The TOC removal efficiency was 97% at 8 kGy. Several degradation by-products such as 4-(2,4-dichlorophenoxy) phenol, 2-hydroxy-propanoic acid methyl ester, 2,4-dichlorophenol, 1,4-hydroquinone, quinone, 2-chloro-1,4-hydroquinone and 1,2,4-benzenetriol were identified by gas chromatography-mass spectrometry (GC/MS) evidencing that radiation process starting with the fragmentation of the molecule involving the hydroxyl radical, which is generated by the radiolysis of water. Based on the identification intermediates, a plausible DM mineralization pathway has been proposed. Finally, a kinetic study was effected and showed that the DM degradation process is a pseudo-first order.

Keywords: Diclofop methyl; GC/MS; Gamma radiation; Hydroxyl radicals; Total organic carbon.