Assessing the transport, fate, and effects of metals and metalloids in surface water and sediment

The sources of metals to the atmosphere, surface water, groundwater, and sediment are both natural and anthropogenic. In aquatic systems trace metals play a dual role as toxicants and essential nutrients. A major challenge in metal risk assessments is quantification of the diverse and complex processes that affect metal transport, fate, and bioavailability. These include chemical speciation (including redox chemistry), adsorption/desorption, precipitation/dissolution, biological uptake mechanisms. It is therefore critical that continual effort be directed toward increasing our understanding of these processes and refining the tools used to describe them in mechanistic terms.;This work summarizes a number of separate efforts directed at this common goal. An arsenic redox model, based upon an iron(II)-catalyzed arsenic(III) oxidation mechanism, was developed to describe arsenic oxidation in sediments. A comparison of model results to experimental observations from sand column experiments suggests that this mechanism is capable of explaining the oxidation of arsenic(III) in iron-rich sediment systems. The chemical speciation model WHAM6 was tested against field data from rivers and estuaries. This work highlights the influence competition can have on WHAM6 results. A robust probabilistic framework was applied to metal risk assessments in rivers and streams. Applications to field data highlight the importance of including cross-correlations and indicate the utility of probabilistic models in planning remediation efforts. Finally, to address the need to expand our understanding of metal speciation, an analysis was made that details the theoretical underpinnings of an electrochemical method for estimating metal complex stability constants.