Tolfenamic acid degradation by direct photolysis and the UV-ABC/HO process: factorial design, kinetics, identification of intermediates, and toxicity evaluation.

This study employed direct UV-ABC photolysis and the UV-ABC/HO process to investigate the degradation of tolfenamic acid (TA), a common anti-inflammatory drug used in both human and veterinary medicine. A 2 factorial design with added center point was used to evaluate the effect of three independent variables-namely, HO concentration ([HO]), TA concentration ([TA]), and experiment time (time)-on TA degradation and HO photolysis during UV-ABC/HO treatment using a high-pressure mercury vapor lamp (photon flux of 2.6307 × 10 J s) as the UV irradiation source. The responses yielded similar values, revealing a linear behavior, with correlation coefficients R = 0.9968 and R = 0.9921 for TA degradation and R = 0.9828 and R = 0.9570 for HO photolysis. The most efficient combination of variables was [HO] = 255 mg L and [TA] = 25 mg L, resulting in 100% TA degradation and 98.87% HO photolysis by 90 min of treatment. Additionally, the second-order kinetic constant of the reaction between TA and HO was determined using a competitive kinetic model, employing 2,4-dichlorophenoxyacetic acid (2,4D) as the reference compound. The kinetic constant was 1.9 × 10 M s in alkaline medium. TA degradation by direct photolysis generated quinone imines as by-products, responsible for the formation of a dark red "internal filter" that increased the value of acute toxicity to Artemia salina. The UV-ABC/HO process did not promote formation of quinone imines by 90 min of treatment and therefore did not increase acute toxicity values. Several by-products generated during TA degradation were identified and possible degradation pathways for the UV-ABC and UV-ABC/HO processes were proposed.