Transformation of chlorinated hydrocarbons using aquocobalamin or coenzymeF-430 in combination with zero-valent iron

More effective methods are necessary for the remediation of soils, sediment s, and ground waters contaminated with halogenated organic compounds. Our o bjective was to determine the feasibility and utility of using a tetrapyrro le-Fe(0) mixture for reductive dehalogenation of synthetic organic contamin ants. Aquoeobalamin or coenzyme F-430 was combined with Fe(0) in aqueous sy stems containing either a single chlorinated compound or mixtures of chlori nated compounds, and substrate disappearance was monitored using gas chroma tography-mass spectrometry (GC-MS). Zero-valent iron effectively dehalogena ted CCl4 at low to neutral pH values, while increases in CCl4 dehalogenatio n resulting from inclusion of tetrapyrrole catalysts along with Fe(0) occur red only at basic pH values. Rates of CCl4 disappearance increased with add itional aquocobalamin, but reached a maximum and decreased at higher aquoco balamin concentrations. Overall dehalogenation rates may thus be a function of Fe(0)'s limited reactive surface area. There was a trend for both tetra pyrrole catalysts to promote the disappearance of halogenated compounds in a mixed substrate containing 20 compounds. Studies with five individual sub strates likewise showed trends for increased substrate removal with F-430 b eyond that for Fe(0) alone. This increase is most important for compounds s uch as 1,2-dichloroethane and 1,4-dichlorobenzene that are not readily deha logenated by Fe(0). Chloride concentrations in the reaction mixtures indica ted that reductive dehalogenation was the dominant process responsible for substrate disappearance. Use of a combination of aquocobalamin or coenzyme F-430 and Fe(0) may effectively promote dehalogenation, thus producing fewe r products and more complete dehalogenation of the target substrates than c an be achieved using only one of the abiotic reductants alone.