Oxidation of 2,4-dichlorophenoxyacetic acid by ionizing radiation: degradation, detoxification and mineralization

The gamma-radiation-induced degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in aerated (A) and in during irradiation air saturated (AS) solutions. Whereas the decomposition rates were not influenced by AS, chloride elimination, detoxification as well as mineralization were significantly enhanced. In the range 50–500 μmol dm −3 2,4-D, degradation showed proportionality to concentration, while chloride formation was successively retarded. The ratios of the pseudo first-order rate constants for degradation and chloride formation, k de/ k Cl, increase in AS solutions from 1.4 (50 μmol dm −3) to 2.7 (500 μmol dm −3) and in A solutions from 1.4 to 3.3. In AS for total chloride release 0.7 kGy (50 μmol dm −3) to 10 kGy (500 μmol dm −3) were required, the reduction of organic carbon at 10 kGy was 95% (50 μmol dm −3) and 50% (500 μmol dm −3). Increase and decrease of toxicity during irradiation correlated well with formation and degradation of intermediate phenolic products. The doses for detoxification corresponded to those of total dehalogenation. The oxygen uptake was ∼1.1 ppm 100 Gy −1. The presence of the inorganic components of Vienna drinking water affect the degradation parameters insignificantly.