<p> The legacy of disposal practices for radioactive and other heavy metals has resulted in highly contaminated soils at the INL facility in Idaho Falls. Microbial effects on the mobility of a suite of metals (U, As, Cr, Co and Zn) within INL vadose sediments were assessed over a range of solution metal concentrations and biological activity through batch experiments. Sediment associated metals in the bulk sample as well as individual soil compartments increased as a function of total solution metal concentration. System specific trends in partitioning coefficients emerged, reflecting complex interrelations among biological activity, solution metal concentration and the specific metals involved. </p> <p> Results of this study clearly show that cyclic linkages between metal concentration and biological activity play a role in metal sediment biogeochemical behaviour. Differential impacts of biological activity on metal solid retention as a function of solution metal concentration were observed. This result may reflect feedback of metals on the microbial population such that the extent and/or nature of microbial activity is concentration dependent. Typically biological activity has a stronger effect with increased concentration, changing from a beneficial/neutral impact to an increasingly negative effect across the concentration range. The degree of this effect, and whether positive or negative on soil metal retention was however, element specific and dependent on the degree of biological activity. </p> <p> This is one of the first studies to evaluate the relative affinities of a suite of metals for the solid vs. solution phases over varying metal cocktail concentrations and levels of biological activity. My results indicate that differing affinities occur across this suite of metals, and that their relative affinities are non-linearly dependent on both the levels of metal and biological activity present. These results indicate that successful prediction of metal behaviour in complex natural systems, based on mono-metal laboratory experiments is likely limited. </p> / Thesis / Master of Science (MSc)