BERKELEY, CA -- Seventy-five meters beneath the surface of a site in Idaho where high-level radioactive waste has been stored for more than 40 years, microorganisms living in the pores and crevices of dry basaltic rock are able to reduce a toxic form of chromium to a much less toxic form -- and they do so faster in the presence of volatile organic wastes.
Hoi-Ying Holman and her colleagues Dale Perry, Michael Martin, Wayne McKinney, and Jennie Hunter-Cevera of the Department of Energy's Lawrence Berkeley National Laboratory made the discovery by examining core samples from beneath the Radioactive Waste Management Complex at DOE's Idaho National Engineering and Environmental Laboratory. By using infrared spectromicroscopy at Berkeley Lab's Advanced Light Source (ALS), they were able to follow the reduction of toxic metals among populations of living organisms on minerals for the first time. The researchers will discuss their findings in the forthcoming October/November issue of Geomicrobiology Journal.
"We have shown that organic vapor may accelerate the transformation of mobile, toxic chromium pollutants into less mobile, less toxic, stable compounds," says Holman, a chemist and engineer with Berkeley Lab's Earth Sciences Division and the Center for Environmental Biotechnology (CEB). "This should help in the design and implementation of new, environmentally benign remediation techniques for cleaning up mixed waste sites."
The Idaho site is polluted with mixtures of hexavalent chromium and other inorganic ions, radionuclides, petroleum hydrocarbons, and volatile organic compounds. Hexavalent chromium (Cr6+) is carcinogenic, mutagenic, and highly toxic to living organisms because it occurs in soluble chromates that readily cross cell membranes. Once inside the cell, these ions are reduced (electrons are added) first to pentavalent chromium (Cr5+), then to trivalent chromium (Cr3+), which disrupts DNA replication.