PHOTOLYSIS RATES OF (2,4,5-TRICHLOROPHENOXY)ACETIC ACID AND 4-AMINO-3,5,6-TRICHLOROPICOLINIC ACID IN NATURAL-WATERS
Skurlatov, YI; Zepp, RG; Baughman, GL
Photoreactions of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) and 4-amino-3,5,6-trichloropicolinic acid (picloram) were studied in distilled water, natural water samples, fulvic acid solutions, and solutions containing iron (III) and/or hydrogen peroxide to determine the effects of dissolved natural substances on the photolysis rates of these herbicides. Most of the experiments were conducted with sunlight as the light souree and with dilute solutions of 3,4-dichloroaniline (DCA) as an outdoor actinometer. When reaction quantum yields determined in this study were used, near-surface half-lives for direct photolysis were computed to be 15 days for 2,4,5-T and 2.2 days for picloram during late summrr at latitude 40° N, in close agreement with observed values. Humic substances in natural water samples and a commercial fulvic acid enhanced near-surface photolysis rate constants of 2,4,5-T with similar efficiencies, as indicated by the linear dependence of the rate constants on the UV absorbance of the waters. 2,4,5-Trichlorophenol was a major product of the humic-induced photoreactions. Humic substances, even at the highest concentrations usually observed in natural waters, had only a minor enhancing effect on the photolysis rate of picloram. Preliminary studies indicated that photocatalytic processes involving iron species and peroxides may contribute to the sunlight-induced reaction of 2,4,5-T in acidic, weakly absorbing natural waters. © 1983, American Chemical Society. All rights reserved.