Oxidation of MCPA and 2,4-D by UV radiation, ozone, and the combinations UV/H2O2 and O3/H2O2

• Published in: Journal of environmental science and health. Part B, Pesticides, food contaminants, and agricultural wastes Vol. 39; no. 3; pp. 393 - 409
• Main Authors: Benitez, F.J, Acero, J.L, Real, F.J, Roman, S
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA Taylor & Francis Group 2004; Taylor & Francis
• Subjects: 2,4-D; 2,4-Dichlorophenoxyacetic Acid - chemistry; 2-Methyl-4-chlorophenoxyacetic Acid - chemistry; Agronomy. Soil science and plant productions; Biodegradation, Environmental; Biological and medical sciences; chemical degradation; Fundamental and applied biological sciences. Psychology; Herbicides - chemistry; hydrogen peroxide; Hydrogen Peroxide - chemistry; Hydrogen Peroxide - pharmacology; Hydrogen-Ion Concentration; Hydroxyl Radical - chemistry; Hydroxyl radicals; Kinetics; MCPA; MCPA (herbicide); oxidants; Oxidants, Photochemical - chemistry; oxidation; Oxidation-Reduction; Ozone; Ozone - chemistry; Phenoxyalkyl acid derivative herbicides; photolysis; Photolysis - drug effects; Photolysis - radiation effects; pollution control; Quantum yields; Rate constants; reaction kinetics; Soil and water pollution; Soil science; ultraviolet radiation; Ultraviolet Rays; UV radiation; water pollution; Quantum yields; MCPA; Rate constants; 2,4-D; Pesticides; Ozone; Hydrogen Peroxides; Herbicide; UV radiation; Pollutant; Ultraviolet irradiation; Aqueous medium; Phenoxyalkyl acid derivative herbicides; Hydroxyl radicals; Oxidation; Phytohormone; Photochemical degradation
• ISSN: 0360-1234; 1532-4109
• DOI: 10.1081/PFC-120035925

The phenoxyalkyl acid derivative herbicides MCPA (4-chloro 2-methylphenoxyacetic acid) and 2,4-d (2,4-dichlorophenoxyacetic acid) were oxidized in ultrapure water by means of a monochromatic UV irradiation and by ozone, as well as by the combinations UV/H 2 O 2 and O 3 /H 2 O 2 . In the direct photolysis of MCPA, the quantum yield at 20°C was directly evaluated and a value of 0.150 mol Eins −1 was obtained in the pH range 5-9, while a lower value of 0.41 × 10 −2  mol Eins −1 was determined at pH = 3. Similarly, for 2,4-d a value of 0.81 × 10 −2 mol Eins −1 was deduced, independent of the pH of work. The influence of the additional presence of hydrogen peroxide was established in the combined process UV/H 2 O 2 , and the specific contribution of the radical pathway to the global photo-degradation was evaluated. The oxidation by ozone and by the combination O 3 /H 2 O 2 was also studied, with the determination of the rate constants for the reactions of both herbicides with ozone and hydroxyl radicals at 20°C. These rate constants for the direct reactions with ozone were 47.7 and 21.9 M −1  s −1 for MCPA and 2,4-d respectively, while the found values for the rate constants corresponding to the radical reactions were 6.6 × 10 9 and 5.1 × 10 9  M −1  s −1 .