Heavy Metals and Microorganisms: The Story of Chromium. Erin Field MB433. Outline. Chromium Sources Speciation Remediation Strategies Metal-Microbe Interaction Case Study: Hanford Site. Questions to be Answered. Why is chromium contamination such a problem?
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Heavy Metals and Microorganisms: The Story of Chromium
Erin Field MB433
Estimated $360 billion in the United States for cleanup and prevention of metal contamination as of 2005 (Atlas and Philip 2005).
As of 2005, over 50% of the 170 DOE sites are contaminated with Chromium (Atlas and Philip 2005).
Chemical Approaches (often changing pH with reducing agents)
Expensive to Apply
Lack specificity to contaminant
“Pump and Treat”: remove metals from a site in the aqueous phase and treated ex situ
Expensive, inefficient, contaminants often higher than EPA standards
“Dig and Dump”: dig up contaminated soil and dump it somewhere else
Expensive, impractical for large sites
Metabolism-independent sorption including both adsorption and absorption by live or dead cells. Ligands involved include carboxyl, amine, hydroxyl, phosphate, and sulfhydryl groups.
Molecular biologists are working on modifying the binding ligand to increase sorption of a specific metal. For instance, ZnO-binding peptides fused to fimbrae on the surface of E.coli.
Negative influence on metal mobility. Organic acids (such as those produced through fermentation) can create a metal-chelate complex increasing the metal’s solubility and thus its mobility.
Enzyme-mediated transformation of toxic metals to their less toxic forms usually through the use of these metals as electron acceptors. A cheap and less invasive method of bioremediation.
Metals precipitate with enzymatically produced ligands such as sulfides and phosphates. For example, Citrobacter often creates phosphate-metal minerals. Exciting area for future research.
Cr(VI) Reducing Microorganisms
30 lbs 13C-labled HRC
Redox potential and dissolved oxygen data also suggest that the microorganisms were stimulated and reducing conditions occurred.
Atlas, R.M., and Philip, J. (ed) Bioremediation: Applied Microbial Solutions for Real-World Environmental Cleanup. Washington,D.C.: ASM Press, 2005.
Chen, J.M and Hao, O.J. (1998) Microbial Cr(VI) reduction. Critical Reviews in Env Sci and Tech 28(3):219-251.
Department of Energy Hanford Site (visited 2006) www.hanford.gov.
Field Investigations of Lactate-Stimulated Bioreduction of Cr(VI) to Cr(III) at Hanford 100H (visited 2006) http://www.esd.lbl.gov/ERT/hanford100h/index.html.
Lloyd, J.R. and Lovley, D.R. (2001) Microbial detoxification of metals and radionuclides. Current Opinion in Biotechnology 12:248-253.
Palmer, C.D. and Wittbrodt, P.R. (1991) Processes affecting the remediation of chromium-contaminated sites. Environ Health Perspect 92:25-40.
Riley, R.G. and Zachara, J.M. (1992) Chemical contaminants on DOE lands and selection of contaminant mixtures for subsurface science research. Technical Report.