The toxicological effects of prolonged exposure to elevated levels of arsenic are apparent in populations worldwide. Arsenic is now widely recognized as a global environmental contaminant and dissemination of arsenic in soils, sediments, surface and ground waters has been repeatedly documented. Intensive efforts have been put forth to determine the controls, regulation and pathways affecting the distribution of arsenic in subsurface aquifers. Fewer investigations have been initiated regarding controls on arsenic mobility and transport in geothermal fluids. Because geothermal fluids are one of the primary means of surface water arsenic contamination, it is imperative to understand controls on arsenic speciation and mobility in geothermal environments. The proposed project is a first step towards understanding the biological controls on arsenic speciation and mobility in geothermal fluids of springs within the Alvord Basin, OR. The goal of the proposed project is to investigate the geochemical and biological processes effecting arsenic speciation of surface-expressed geothermal fluids. We propose to show that rapid oxidation of arsenite to arsenate is primarily due to microbial processes, and that over their observed range the pH, temperature and oxygenation status of the fluids has a minor impact on arsenite oxidation within springs in which arsenite oxidation is occurring. Furthermore, we will use molecular tools to determine if microbial populations within arsenite oxidizing zones of spring outflow channels are consistent from spring to spring when geochemical parameters of pH, temperature and dissolved oxygen are equivalent. Finally, we will enrich for and isolate thermophilic arsenite oxidizing microorganisms presiding in springs in which rapid arsenite oxidation is occurring. It is anticipated that these basic studies will set the groundwork for future research investigating the controls on arsenic speciation in surface geothermal waters, the biogeochemical cycling of arsenic in geothermal waters, and the metabolic mechanisms employed by microorganisms utilizing arsenic as an energy source. Intellectual Merit. The completion of the proposed studies will have an immediate impact on the earth science and life science disciplines. It is recognized that arsenic mobility in geothermal environments is partly controlled by temperature and the oxidation potential of fluids, yet the principles defining arsenic solubility in geothermal fluids have been elusive. Thus it is critical to understand the role of microorganisms in regulating arsenic solubility for accurate geochemical models to be developed. Furthermore, the recognition that microorganisms actively participate in arsenic oxidation-reduction reactions is relatively recent, thus there is a demand for further studies investigating the types of interactions occurring between microorganisms and arsenic compounds. Broader Impacts. One of the primary goals of the PI's program is to expose students in the Environmental Sciences and Geology programs to microbiology. The incorporation of field investigations into an established interdisciplinary field class in collaboration with faculty in the Geological Sciences is a direct means of achieving that goal. Furthermore, continued collaborations among the PI, co-PI and faculty within the PI's home department will provide the infrastructure necessary for the development of a strong interdisciplinary biogeosciences program.
