Superfund Research Program
Environmental Controls on Bioavailability of Arsenic and Toxic Metals
- Project Summary
The research team narrowed the selection of representative mine waste sits to test the hypothesis that climate controls the depth dependent trends in concentration, molecular speciation, and bioaccessibility of toxic elements, such as lead and arsenic. Climate-driven oxidative weathering of the initially deposited sulfidic material results in the release of iron and arsenic that, under toxic conditions, can precipitate as iron hydroxysulfates and oxyhydroxides, thereby attenuating arsenic mobility. The depth and structure of this redox gradient is hypothesized to be controlled by climate, and the site selection was based on broad and comprehensive climate coverage. Mini-column experiments were conducted to test the effects of natural organic matter and model labile carbon substrates on the microbial reduction and mobilization of iron and arsenic. The team also focused on understanding flow dynamics in saturated and unsaturated conditions to enhance modeling of fluid-surface interactions across a wider spatial scale. To accomplish this goal, they established methods to facilitate the validation of reactive transport flow modeling, including work with the PFLOTRAN code and micro-analysis of surface roughness and air-water-grain distributions in connected pore space with X-ray micro tomography. In support of the broader University of Arizona SRP Center, the team is developing analytical chemistry methods for quantification of methylated-thiolate arsenic species. The synthesis of pure arsenic compounds is a critical prerequisite to characterizing the molecular form of dissolved arsenic species in vitro and in vivo.