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 mumol 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 mumol dm(-3)) to 2.7 (500 mumol dm(-3)) and in A solutions from 1.4 to 3.3. In AS for total chloride release 0.7 kGy (50 mumol dm(-3)) to 10 kGy (500 mumol dm(-3)) were required, the reduction of organic carbon at 10 kGy was 95% (50 mumol dm(-3)) and 50% (500 mumol 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 similar to 1.1 ppm 100 Gy(-1). The presence of the inorganic components of Vienna drinking water affect the degradation parameters insignificantly. (C) 2003 Elsevier Science Ltd. All rights reserved.