Stimulating Bacteria to Immobilize Chromium in Groundwater
Hexavalent chromium is a major contaminant in numerous soil and groundwater systems worldwide, in particular at Department of Energy sites due to former weapons production and reprocessing activities and wastes from electroplating processes, and from industrial efforts to reduce corrosion in steel pipes. Although hexavalent chromium is readily transported in groundwater, reduction to a less mobile form involves the interaction of hexavalent chromium with certain minerals and microorganisms. Specifically, iron-reducing bacteria can convert the oxidized form of iron in clay minerals (ferric iron) into the reduced form of iron (ferrous iron) that can then reduce hexavalent chromium to much less mobile trivalent chromium. Efforts to understand the specific details of this process were recently reported by a team of scientists from Miami University and the Environmental Molecular Sciences Laboratory (EMSL), using EMSL’s ultra-sensitive microscopy and spectroscopy capabilities. Starting with the iron-reducing bacterium Geobacter sulfurreducens and ferric iron-containing clay minerals, the team found that they could provide a specific nutrient to the bacteria that would significantly stimulate the bacteria to reduce ferric to ferrous iron. The resulting ferrous iron was able to reduce hexavalent chromium, and it reduced the chromium even faster as the temperature of the system was increased. In addition to demonstrating a possible way to reduce the transport of hexavalent chromium in groundwater, the team also determined the kinetics of these reactions. These kinetic parameters can now be incorporated into models to improve predictions of the transport of hexavalent chromium in subsurface environments.
Bishop, M. E., P. Glasser, H. Dong, B. Arey, and L. Kovarik. 2014. “Reduction and Immobilization of Hexavalent Chromium by Microbially Reduced Fe-bearing Clay Minerals,” Geochimica et Cosmochimica Acta 133, 186-203. DOI: 10.1016/j.gca.2014.02.040.