One of the important long-term environmental issues that our society faces is the management of toxic trace metals and other harmful inorganic constituents in the environment.  Elevated levels of these substances are often the result of human activities but can also be naturally occurring.  My main research interests are to elucidate the processes that control the mobility and fate of harmful inorganic constituents such as heavy metals in aquatic and soil environments.   These processes include the formation of metal-containing solid phases, the formation of aqueous metal complexes, the adsorption of metals to soils and sediments and to aquatic particles, and reduction and oxidation reactions. 

Understanding these processes is crucial for the evaluation of human health risks and ecosystem effects of inorganic contaminants and for the development of rational and cost-effective remediation strategies for contaminated sites.  The scope of these research efforts ranges from spectroscopic investigations at the molecular level to bench scale experiments with natural materials and model systems to field investigations and numerical modeling. 

Two specific areas of research in this field are described below:

Chromium-containing precipitates can affect the mobility of toxic Cr(VI) in the subsurface, control its concentration in groundwater, limit its bioavailability, and impede remediation of chromium contaminated sites.  These precipitates can be pure phases such as KFe₃(CrO₄)₂(OH)₆, the chromate-analog of the common sulfate mineral jarosite, or solid-solutions where chromate partially substitutes for another ion such as sulfate (e.g. Ba(S_xCr_1-xO₄)).  In my research, we are measuring the thermodynamic properties of these solids.  These thermodynamic properties are the basis for determining the conditions under which these solids form and remain stable, as well as the chromium concentrations in water equilibrated with them. In addition to the practical applications, the thermodynamics of inorganic solid solutions is also one of the remaining theoretical frontiers in inorganic geochemistry. (e.g. Baron and Palmer, 2002; Drouet et al., 2003; Drouet et al., 2004).

We recently acquired 45 m of core from the Soda Lake basin in the Carrizo Plain National Monument of San Luis Obispo County, California. Initial analyses demonstrate that they contain a likely nonmarine counterpart to the well-known record of millennial-scale climate change from offshore Santa Barbara Basin. The Santa Barbara Basin record remains one of the most convincing pieces of evidence that the high-frequency, high-amplitude climate events shown in the ice core records are at least hemispheric in scale. Because the Soda Lake coring site is close to the Santa Barbara Basin locality and because the level of Soda Lake, a closed basin lake, should be very sensitive to changes in climate, the Soda Lake core should provide critical information on the impact of global climate change on nonmarine settings (e.g. Negrini et al., 2007). 

This work has been funded by the National Science Foundation.