Degradation of 2,4-dichlorophenoxyacetic acid by ionizing radiation: influence of oxygen concentration

Ionizing radiation has been proved as a promising method for the degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The gamma-radiolytic decomposition and chloride formation follows an apparent first order kinetic, kde/kCl = 3. For complete removal of 500 microM 2,4-D, a dose of 4 kGy is required. Phenolic intermediates (2,4-dichlorophenol, the isomers 2-chloro-4-hydroxy- and 4-chloro-2-hydroxy phenoxyacetic acid and three hydroxylation products of 2,4-D) are formed. Using oxygen saturation during irradiation, they are removed again with a dose of 4 kGy. For the formation of the main organic product acetic acid a reaction mechanism is discussed. Oxygen concentration enhances strongly fragmentation and mineralization. A reduction of 36% TOC could be achieved.