Basic Research Needs for Geosciences - Energetics Meetings and ...

PRIORITY RESEARCH DIRECTION:BIOGEOCHEMISTRY IN EXTREME SUBSURFACE ENVIRONMENTSoccur in microscopic regions surrounding them as a result of extracellular metabolic fluxes. Newmicrobe-mediated phenomena of potentially broad application and significance may bediscovered. For radioactive waste isolation specifically, the research will provide knowledgeunderpinnings to evaluate microbiologic influences on waste form stability through corrosionand similar processes, and down-gradient migration of radionuclides through bio-influencedspeciation changes, precipitation, and surface chemical processes.SUMMARY OF RESEARCH DIRECTIONResearch is needed at different scales using laboratory model systems, field-derived geologicmaterials, microorganisms isolated from relevant environments, and in-field observations atanalogue or real sites. Pervading the research is an emphasis on the extreme characteristics andsystem variables of the target deep subsurface environments that motivate and distinguish thistopic. Integration of experimental studies and measurements with state-of-the-art or newlydeveloped models of different types is essential to unravel and understand the complex linkageof geochemical and biologic processes at the fundamental level required.SCIENTIFIC CHALLENGESResearch over the past ten years has shown that microorganisms can strongly influence thevalence, solubility, mineral association, and migration potential of actinides and other importantradionuclides (e.g., 99 Tc, U) and inorganic chemical contaminants (Cr). Often, microorganismsconcentrate soluble metals or radionuclides through biosorption or bioprecipitation reactions onthe organism surface (see Figure 46) or within the cell envelope’s periphery where metabolicproducts and biostructures create a unique and unexplored chemical environment. These sameorganism types can also nucleate and form unique, high surface area, major element biomineralFigure 46. Two forms of microbiologic radionuclide precipitates generated under reducing conditions. Left:Extracellular uraninite (UO 2 ) produced by Shewanella resulting from the reaction of U(VI) with externalizedcytochromes on exopolysaccharide. Right: TcO 2 . nH 2 O precipitated within the periplasm (P) and on the outermembrane (OM) of Anaeromyxobacter (Marshall et al. 2006, 2007).146 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems