New insights into reductive detoxification of chlorinated solvents and radionuclides

Abstract

Naturally occurring bacterial populations are capable of detoxifying chlorinated compounds and immobilizing the radionuclide uranium via reductive processes. This study addressed the following three knowledge gaps in the fields of chlorinated solvent and uranium bioremediation, 1) the risks and benefits of coupling bioremediation with thermal treatment for clean-up of chlorinated ethene-contaminated sites, 2) the accuracy of available techniques for the monitoring of chlorinated solvent bioremediation, and 3) the role of gram positive Desulfitobacterium spp. in uranium immobilization. Experiments demonstrated that thermal treatment increases electron donor availability, but the increased electron donor was not used to fuel reductive dechlorination and was actually consumed for methanogenesis. Two approaches for monitoring chlorinated solvent bioremediation were investigated, molecular techniques and compound-specific isotope analysis (CSIA). Results demonstrated that while Dehalococcoides (Dhc) gene expression was up-regulated under conditions inhibitory to dechlorination, the isotope effects associated with dechlorination reactions catalayzed by Dhc populations in consortia and in pure cultures were similar. U(VI) reduction by multiple Desulfitobacterium isolates was demonstrated. Interestingly, while almost all U(VI)-reducing populations have been reported to produce uraninite (UO2), the product of U(VI) reduction by Desulfitobacterium isolates was a unique form of insoluble mononuclear U(IV).