Reduction of Oxamyl and Related Pesticides by Fe^II:  Influence of Organic Ligands and Natural Organic Matter

Abstract

The reduction of oxamyl and related oxime carbamate pesticides (OCPs; methomyl and aldicarb) by FeII is an important pathway for the degradation of these compounds in soil and groundwater. A series of batch kinetic experiments was carried out to assess the effects that selected carboxylate and aminocarboxylate ligands have on these reactions. In the absence of FeII, no OCP reduction by the ligands is observed. In the presence of FeII, the rate of OCP reduction varies by several orders of magnitude and can be described by the expression k(red) = [FeII]sigma(i)k(i)alpha(i) where k(red) is the observed pseudo-first-order rate constant for OCP reduction, [FeII] is the total FeII concentration, alpha(i) is the fraction of each FeII species in solution, and k(i) is the second-order rate constant for OCP reduction by each FeII species. The reactivity of individual FeII species is dependent upon the standard one-electron reduction potential of the corresponding FeIII/FeII redox couple (E(H)o) and the availability of inner-sphere FeII coordination sites for bonding with Lewis base donor groups within the OCP structure. A linear free energy relationship is proposed. Kinetic measurements demonstrate that natural organic matter from the Great Dismal Swamp facilitates OCP reduction by FeII in the same manner as the individual organic ligands. Results from this study improve our understanding of the pathways and rates of pesticide degradation in reducing subsurface environments, especially those rich in organic matter.

Enhanced inhibition of bromate formation in catalytic ozonation of organic pollutants over Fe–Al LDH/Al2O3

“…BrO 3 À is also a strong oxidant that can be reduced to Br À in water by reduced iron species (Fe 2+ or Fe 0 ) [8]. Moreover, our and other studies have verified that more Fe(II) could be generated from the reaction of Fe(III) and HO 2 ÅÀ /O 2 ÅÀ due to the complexation of Fe(III) with the oxygen functional groups (-OH and -COOH) of intermediates [20,21] [22,23]. Thus, it is necessary to investigate the degradation process of organic compounds with different structure and its influence on the minimization of BrO 3 À formation in catalytic ozonation.…”

Enhanced Fenton-like degradation of refractory organic compounds by surface complex formation of LaFeO3 and H2O2

“…The chemical environment of iron element in LaFeO 3 was changed [33], and the O O bond in H 2 O 2 was significantly weakened [14] due to the formation of LaFeO 3 -H 2 O 2 complex. Moreover, the complexed Fe 3+ /Fe 2+ could decrease the Fe 3+ /Fe 2+ redox potential significantly [34]. Hence, the Fe 3+ /Fe 2+ cycle was greatly accelerated and more reactive oxygen species such as • OH and O 2…”

Reduction of Substituted p-Benzoquinones by FeII Near Neutral pH

“…The standard approach toward addressing the energetics of Fe III /Fe II interconversion is to compare reduction potentials (e.g. Strathmann and Stone 2002). According to the Franck-Condon principle (IUPAC 1997), protons and other nuclei are stationary during electron transfer.…”

“…Chelating agents with higher logKs for complex formation with Fe III than for Fe II accelerate Fe II oxidation (Buerge et al 1998;King and Farlow 2000;Wehrli et al 1989;Wehrli 1990;Strathmann and Stone 2002). The effect is explained by evoking stabilization of the transition state, which has some Fe III product character (Purcell and Kotz 1977).…”