Resolving the Impact of Biological Processes on DNAPL Transport in Unsaturated Porous Media through Nuclear Magnetic Resonance Relaxation Time Measurements

This research leads to a better understanding of how physical and biological properties of porous media influence water and dense non-aqueous phase liquid (DNAPL) distribution under saturated and unsaturated conditions. This project exploits the capability of low-field nuclear magnetic resonance (NMR) proton relaxation decay-rate measurements for determining environmental properties affecting DNAPL solvent flow in the subsurface, including determining if DNAPL exist in water-wet or solvent-wet environments, the pore-size distribution of the soils containing DNAPLs, and the impact of biological processes on their transport mechanisms in porous media. Knowledge of the in-situ flow properties and pore distributions of organic contaminants are critical to understanding where and when these fluids will enter subsurface aquifers

Microbially Promoted Solubilization of Steel Corrosion Products and Fate of Associated Actinides

The ultimate goal of this project was to demonstrate that metal-reducing bacteria could be used to remove heavy metal and radionuclide contaminants from the surfaces of corroding steel surfaces. Toward this end, fundamental scientific issues regarding (1) factors influencing the adhesion and colonization of DIB on mineral surfaces, (2) the enzymatic activity of cells once they have adhered to mineral surfaces, (3) and (4) methods for recovering bacteria and attendant radionuclides following release from mineral surfaces were addressed. The fate of radionuclides (plutonium) contaminants following reduction by DIRB

A sensitive chromatographic method for the detection of pyruvyl groups in microbial polymers from sediments

A method was developed for the quantitation of pyruvyl groups in microbial polymers using mild acid hydrolysis, o-phenylenediamine labeling, reversed-phase high-performance liquid chromatography (RP-HPLC), and fluorescence detection. The method was used to determine the pyruvate content of various microbial exopolysaccharides and to estimate the abundance of polymeric pyruvate in freshwater sediments. The results of this method were compared with those of several other pyruvate assays. The detection limit of the method was 1.6 nmol pyruvate. As little as 3.7 μg of the bacterial polysaccharide xanthan gum, or from 5 to 22 mg of sediment (depending on polymeric pyruvate content), were needed for detection and quantitation of polymeric pyruvate. The results should be useful in determining the contribution of polymeric pyruvate to total metal-binding ligands in sediments.</p

Microbially Promoted Solubilization of Steel Corrosion Products and Fate of Associated Actinides

This project will probe fundamental scientific issues regarding a microbial process with potential for decontaminating corroding metal surfaces. We hypothesize that dissimilatory iron-reducing bacteria (DIRB), via anaerobic respiration, can quantitatively dissolve amorphous and crystalline iron oxides and thereby release oxide-associated radionuclide contaminants. Associated actinides will be sorbed by cell surfaces or precipitated within biofilms that can be removed and recovered by enzymatic digestion of microbial attachment factors. This environmentally benign, enzymatic process avoids the use of hazardous or toxic chemicals, minimizes the volume and toxicity of secondary wastes, and could be applied in situ. Although an increasing body of scientific literature supports this working hypothesis, a basic understanding is needed of the biological and chemical processes that impact (1) attachment and detachment of iron reducing bacteria to oxide surfaces; (2) the rate, extent, and products of iron reduction; and (3) the fate of radionuclides following enzymatic reduction of corroding steel (which is needed to evaluate and develop effective biological approaches for decontamination of aging metallic structures and piping). The goal of this project is to provide the scientific underpinnings for the development of biologically based approaches for the removal of contaminants from corroding steel surfaces. Specifically, this research will accomplish the following: (1) determine the role of oxide structure, topology, and composition on bacterial attachment and subsequent reductive dissolution of Fe(III) oxide corrosion products that form on stainless and mild steels; (2) identify how soluble electron ''shuttles'' can facilitate the rate and extent of microbial reductive dissolution of iron oxide corrosion products, including surface features and pores inaccessible to bacteria; (3) determine the distributions of radionuclides released during reductive dissolution of oxide films on metal surfaces as a function of aqueous geochemical composition. This project uniquely couples PNNL's expertise in microbial metal reduction and biogeochemistry with Montana State University's Center for Biofilm Engineering's expertise and capabilities in biofilm analysis, engineering, and corrosion. In addition, this research project will take advantage of the capabilities and expertise at PNNL in actinide chemistry and advanced instrumentation for probing the distribution and chemical nature of surface-associated radionuclides and metals associated with the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL)