Ferric Complexes as Catalysts for “Fenton” Degradation of 2,4‐D and Metolachlor in Soil

Abstract

AbstractFenton‐type reactions of hydrogen peroxide with Fe compounds generate hydroxyl radical (OH‐) or other reactive species and are potentially useful for degrading organic contaminants in soil. The use of simple Fe salts is limited, however. This study investigated certain pH 6‐soluble Fe(III) complexes (Fe‐L, where L is an organic ligand) as catalysts for degradation of herbicides 2,4‐dichlorophenoxyacetic acid (2,4‐D) and metolachor (2‐chloro‐N‐[2‐ethyl‐6‐methylphenyl]‐N‐[2‐methoxy‐1‐methylethyl]acetamide). Reactions were carried out in 1:1 aqueous suspensions of a topsoil (15.7 g kg−1 organic C) at the natural pH of 5.7 with herbicides at concentrations representative of a spill (2–3 g kg−1, about 0.01 mol kg−1). The two herbicides had contrasting sorption behavior in that 2,4‐D was mostly in solution, whereas metolachlor was mostly sorbed. The best results were obtained using Fe‐nitrilotriacetate (NTA) or Fehydroxyethyleniminodiacetate (HEIDA) at 0.01 mol kg−1 and [H2O2] ≥ 0.5 mol kg−1. The gallic acid complex was less effective. In 3 h, 14C‐labeled 2,4‐D was quantitatively dechlorinated and partially (15–30%) converted to 14CO2: metolachlor was 93% transformed and 29% dechlorinated. Controls using free ligand plus peroxide or peroxide alone gave little or no reaction. Fe‐L + H2O2 was superior to the Fenton reagent itself (Fe2+ + H2O2). The results of this study demonstrate that relatively mild chemical oxidation can be effective for remediation of certain contaminants in soil.