Reductive dehalogenation of trichloroethene mediated by wetland dog-transition metal complexes

Natural attenuation of chlorinated solvents, such as trichloroethene (TCE), within aquifers is often slow, leading to long contaminant plumes which can reach surface water discharge points such as wetlands. Though suboxic environments, such as high organic carbon wetland sediments, are often sufficiently reducing to make reductive dechlorination reactions thermodynamically favorable, the transfer of electrons from reduced species to a chlorinated solvent is often kinetically constrained. The reduction rate may be enhanced in the presence of compounds capable of facilitating the transfer of electrons from a bulk reductant to the chlorinated solvent of interest. Ni and Cu complexes with dissolved organic carbon (DOC) in wetland sediment porewaters and surface water were able to mediate the reductive dehalogenation of TCE using Ti(III) citrate as the bulk reductant. The reactions were pseuo-first-order with half lives typically less than 2 h. Reaction rates were comparable for systems containing Ni or Cu Aldrich humic acid complexes. Dechlorination was complete, with the dominant products being ethene and ethane. The mass balance was near 100% and chlorinated intermediates were either absent or at extremely low concentrations.