Collaborative Research: Chemical Hydrogeologic Investigations of Tungsten: Field, Laboratory, and Modeling Studies of an Emerging Environmental Contaminant

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Childhood leukemia clusters in e.g. Fallon, NV have been tentatively linked to the proximity to tungsten (W)-bearing ore deposits and ore-processing operations. Because residents of Fallon were shown to have high body-burdens of W in their systems, it has been suggested that W may be responsible for the high incidence of childhood leukemia. Studies have since shown that W can be toxic and may be carcinogenic. The need to understand W in the environment is also important due to its increasing use as a replacement for lead in ammunition and in fishing weights. Here, the use of W was originally thought to be a non-toxic, inert metal of low environmental mobility, it was thus a manner in which to limit the addition of toxic Pb to the environment. However, W is readily mobilized in the environment following oxidation and very little is actually known about its biogeochemistry in the environment, and in particular, its mobility and transport in real groundwater flow systems. This project will investigate the biogeochemistry of W reaction and transport in the environment. Specifically, the project will evaluate how W concentrations evolve along groundwater flow paths as biogeochemical reactions between groundwaters, aquifer minerals, organic matter, and in situ microbial communities, modify the groundwater solution composition and redox conditions. To conduct the study, the project will: 1) measure W concentrations along flow paths in well characterized aquifers along with redox sensitive parameters [e.g., Fe species, S(-II)], and other geochemical constituents to determine how changing solution composition and redox conditions affect W in aquifers; 2) examine solid-phase W speciation in aquifer sediments (e.g., XANES, EXAFS, sequential extractions); 3) measure stability constants for thiotungstate complexes in sulfidic aqueous solutions to develop a solution complexation model that will allow prediction of W speciation in aerobic and anaerobic groundwaters; and 4) assemble a conceptual, biogeochemical model that incorporates the stability constants for thiotungstate complexes along with the currently available thermodynamic data for the tungstate oxyanion to probe the biogeochemical behavior of W along groundwater flow paths. The project focus on pristine aquifers that are important drinking water sources to investigate the natural geochemical cycling of W in aquifers. The resulting 'baseline' data and conceptual model will provide an important resource for other investigators studying the effects of anthropogenic sourced W in the environment.