Degradation of selected pesticide active ingredients and commercial formulations in water by the photo-assisted Fenton reaction

The destruction of pesticide active ingredients (AI) and commercial formulations in acidic aqueous solution with the catalytic photo-Fenton, Fe(III)/H2O2/UV, advanced oxidation process has been studied. The AI are alachlor, aldicarb, atrazine, azinphos-methyl, captan, carbofuran, dicamba, disulfoton, glyphosate, malathion, methoxylchlor, metolachlor, picloram and simazine. Complete loss of pure AI occurred in most cases in < 30 min under the following conditions: 5.0 x 10(-5) M Fe(III), 1.0 x 10(-2) M H2O2, T = 25.0 degrees C, pH 2.8 and 1.2 x 10(19) quanta l(-1) s(-1) with fluorescent blacklight UV irradiation (300-400 nm). Considerable mineralization over 120 min occurred in most cases as evidenced by the appearance of inorganic ions and the decline in total organic carbon (TOC) of the solution. Intermediate products such as formate, acetate and oxalate appeared in early stages of degradation in some cases. Observed rate constants calculated from initial rates varied by a factor of <similar to 3. The commercial products, Furadan (AI, carbofuran), Lasso 4EC (AI, alachlor) and Lasso Microtech (AI, alachlor) were also tested. The "inert ingredients" (adjuvants) present in these products had no effect (Furadan), a slight effect (Lasso 4EC), or a strong effect (Lasso Microtech) on the rate of degradation of the AI. Lasso Microtech, in which the AI is micro-encapsulated in a polymeric shell wall microsphere, required slightly elevated temperatures to effect removal of alachlor in a timely manner. The results show that many pesticides and their commercial formulations in dilute aqueous solution are amenable to photo-Fenton treatment. (C) 1999 Elsevier Science Ltd. All rights reserved.