Degradation of Chloroacetanilide Herbicides by Anodic Fenton Treatment CAREY L. FRIEDMAN,ANN T. LEMLEY,* AND ANTHONY HAY Graduate Field of Environmental Toxicology, TXA, MVR Hall, Cornell University, Ithaca, New York 14853-4401 Anodic Fenton treatment (AFT) is an electrochemical treatment employing the Fenton reaction for the generation of hydroxyl radicals, strong oxidants that can degrade organic compounds via hydrogen abstraction. AFT has potential use for the remediation of aqueous pesticide waste. The degradation rates of chloroacetanilides by AFT were investigated in this work, which demonstrates that AFT can be used to rapidly and completely remove chloroacetanilide herbicides from aqueous solutions. Acetochlor, alachlor, butachlor, metolachlor, and propachlor were treated by AFT, and parent compound concentrations were analyzed over the course of the treatment time. Degradation curves were plotted and fitted by the AFT kinetic model for each herbicide, and AFT model kinetic parameters were used to calculate degradation rate constants. The reactivity order of these five active ingredients toward hydroxyl radical was acetochlor ≈ metolachlor > butachlor ≈ alachlor > propachlor. Treatment of the chloroacetanilides by AFT removed the parent compounds but did not completely mineralize them. However, AFT did result in an increase in the biodegradability of chloroacetanilide aqueous solutions, as evidenced by an increase in the 5-day biochemical oxygen demand to chemical oxygen demand ratio (BOD 5 /COD) to >0.3, indicating completely biodegradable solutions. Several degradation products were formed and subsequently degraded, although not always completely. Some of these were identified by mass spectral analyses. Among the products, isomers of phenolic and carbonyl derivatives of parent compounds were common to each of the herbicides analyzed. More extensively oxidized products were not detected. Degradation pathways are proposed for each of the parent compounds and identified products. KEYWORDS: Chloroacetanilide; herbicide; degradation; Fenton; wastewater treatment; anodic; aceto- chlor; alachlor; butachlor; metolachlor; propachlor INTRODUCTION Pesticide contamination of water resources has become a concern in the United States, especially in regions dominated by farmland. Monitoring of groundwater and surface waters such as lakes and rivers for pesticide parent compounds and metabolites has repeatedly resulted in the detection of chloro- acetanilide herbicides and their ethanesulfonic and oxanilic acid metabolites (1, 2). Chloroacetanilide herbicides are some of the most widely used herbicides in the United States. The U.S. EPA reports that in 2001 acetochlor, metolachlor, and alachlor were the 4th, 10th, and 16th most widely used pesticide active ingredients in the United States, with 30-35 million, 15-22 million, and 6-9 million lb applied, respectively (3). Several chloroacetanilide herbicides have been identified as possible or probable human carcinogens (4), and there is concern about the effects of parent compounds and metabolites on aquatic ecosystems (5). These reports have led to an effort to reduce the use of at least one of the chloroacetanilides and to remediate already contaminated water resources. The development of anodic Fenton treatment (AFT), an advanced oxidation treatment process that generates highly reactive hydroxyl radicals via the Fenton reaction provides an opportunity to control several sources of chloro- acetanilide contamination. AFT was developed with the goal of creating a cost-effective and user-friendly treatment method for the remediation of low-volume, high-concentration pesticide wastes, such as applicator rinse water or unused stocked commercial mixes (6). AFT is an improvement on other Fenton processes, such as classic Fenton treatment (CFT) and electro- chemical Fenton treatment (EFT), in that the system is divided into anodic and cathodic half-cells separated by an ion-exchange membrane, allowing for treatment and the Fenton reaction to occur in an optimal pH environment (pH ∼2-3) in the anodic half-cell (see ref 7 for diagram). AFT also has greater potential to be used on-site, eliminating the need for transportation of * Author to whom correspondence should be addressed [telephone (607) 255-3151; fax (607) 255-1093; e-mail ATL2@cornell.edu]. Fe 2+ + H 2 O 2 f Fe 3+ + OH - + • OH (1) 2640 J. Agric. Food Chem. 2006, 54, 2640-2651 10.1021/jf0523317 CCC: $33.50 © 2006 American Chemical Society Published on Web 03/08/2006