Redox Reactivity of Organically Complexed Iron(Ⅱ) Species with Aquatic Contaminants

摘要

Extracellular organic ligands and ligand functional groups within macromolecular natural organic matter can significantly influence the speciation and kinetic redox reactivity of Fe(Ⅱ) with aquatic contaminants. Fe(Ⅱ) complcxation by Fe(Ⅲ)-stabilizing ligands (e.g., carboxylate, catccholate, thiol) leads to formation of Fe(Ⅱ) species with low standard reduction potentials (E_H~0) and enhanced reactivity with reducible contaminants (e.g., nitroaromatics and halogenated alkanes). Rates of contaminant reduction by Fe(Ⅱ) are highly variable and dependent upon the identity and concentration of specific organic ligands as well as environmental conditions that affect the extent of complex formation. Linear free energy relationships have been developed to predict the aqueous reactivity of individual Fe(Ⅱ) species with contaminants. Studies on the reactivity of Fe(Ⅱ) complexes with model ligands also provide mechanistic insights into the potential mechanisms responsible for contaminant transformations observed in more complex aquatic systems where Fe(Ⅱ) co-accumulates with more poorly defined natural organic matter.