Quantifying Bacteria-Metal-Mineral Adsorption: Wet Chemistry and Advanced Photon Source Approaches

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Fein9905704The proposed research will use bulk adsorption and EXAFS experiments to calibrate a surface complexation approach to quantifying bacterial adsorption of aqueous metals in groundwater systems. In order to remediate dissolved heavy metal contamination in groundwater, we must understand the chemical controls on contaminant mobilities. Bacteria are ubiquitous in low-temperature water-rock, and depending on conditions, they can either enhance or retard contaminant transport through adsorption reactions. With our current knowledge, it is impossible to predict if bacterial adsorption effects occur given a set of conditions, or to predict the magnitude of such effects. The primary questions we will answer with the proposed research are as follows: (1) Does a reversible equilibrium state exist for metal-bacteria adsorption reactions, or do kinetics, inorganic metal precipitation, or cell metabolic processes prevent equilibrium from being attained?; (2) Do the reaction stoichiometries that we obtain from bulk adsorption experiments agree with direct observations of the metal-bacteria surface complexes that we will make using XAFS studies on the Advanced Photon Source at Argonne National Laboratory?; and, (3) Can we expand the surface complexation equilibrium thermodynamic approach to describe bacteria-mineral adsorption reactions? We will conduct bulk adsorption and desorption experiments, examining both isolated metal-bacteria and bacteria-mineral systems, to rigorously test the reversibility of the metal-bacteria-mineral adsorption reactions. Furthermore, we will quantify the importance of adsorption/desorption kinetics, surface precipitation, and metabolism on metal uptake by the cell. Coupling the direct observations of the surface complex that are possible with the Advanced Photon Source with the laboratory adsorption/desorption experiments is a powerful technique to unequivocally determine both the reaction stoichiometry and the equilibrium constants for the important adsorption/desorption reactions.This proposal was submitted in response to the Environmental Geochemistry and Biogeochemistry solicitation NSF 99-9, and is being funded jointly by the Divisions of Chemistry, Earth Sciences, Ocean Sciences, and MPS Office of Multidisciplinary Activities.