51. Tolfenamic acid degradation by direct photolysis and the UV-ABC/H 2 O 2 process: factorial design, kinetics, identification of intermediates, and toxicity evaluation.
- Author
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de Melo da Silva L, Pereira Cavalcante R, Fabbro Cunha R, Gozzi F, Falcao Dantas R, de Oliveira SC, and Machulek A Junior
- Subjects
- Animals, Artemia drug effects, Artemia radiation effects, Kinetics, Lethal Dose 50, Models, Theoretical, Molecular Structure, Oxidation-Reduction, Photolysis, Research Design, Toxicity Tests, Acute, Water Pollutants, Chemical chemistry, Water Pollutants, Chemical radiation effects, Water Pollutants, Chemical toxicity, ortho-Aminobenzoates chemistry, ortho-Aminobenzoates radiation effects, ortho-Aminobenzoates toxicity, Hydrogen Peroxide chemistry, Ultraviolet Rays, Water Pollutants, Chemical analysis, Water Purification methods, ortho-Aminobenzoates analysis
- Abstract
This study employed direct UV-ABC photolysis and the UV-ABC/H
2 O2 process to investigate the degradation of tolfenamic acid (TA), a common anti-inflammatory drug used in both human and veterinary medicine. A 23 factorial design with added center point was used to evaluate the effect of three independent variables-namely, H2 O2 concentration ([H2 O2 ]), TA concentration ([TA]), and experiment time (time)-on TA degradation and H2 O2 photolysis during UV-ABC/H2 O2 treatment using a high-pressure mercury vapor lamp (photon flux of 2.6307 × 104 J s-1 ) as the UV irradiation source. The responses yielded similar values, revealing a linear behavior, with correlation coefficients R = 0.9968 and Radj = 0.9921 for TA degradation and R = 0.9828 and Radj = 0.9570 for H2 O2 photolysis. The most efficient combination of variables was [H2 O2 ] = 255 mg L-1 and [TA] = 25 mg L-1 , resulting in 100% TA degradation and 98.87% H2 O2 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 × 1010 M-1 s-1 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/H2 O2 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/H2 O2 processes were proposed., (Copyright © 2016 Elsevier B.V. All rights reserved.)- Published
- 2016
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