Collaborative Research: Selenium redox reactions and isotope ratios: The role of microbial and abiotic Selenium oxidation

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Selenium (Se) is an essential micronutrient, a potential environmental contaminant, and an indicator of chemical reactions involving oxidation and reduction, in both present and past environmental systems. Chemical and biological processes control the mobility and environmental impact of Se. Although Se oxidation is an important Se-mobilizing process, our understanding of this process is limited. Additionally, although measurements of variations in Se stable isotope abundances (82Se/76Se ratios) provide a powerful new way to study key chemical reactions involving Se in modern and ancient environments, poor understanding of Se stable isotope shifts caused by Se oxidation limits interpretation of Se isotope data. Therefore, this project will investigate stable Se isotope variation caused by oxidation as a means to achieve a robust understanding of Se oxidation in the environment. Investigators will train one postdoctoral fellow, two doctoral students, and 6-8 undergraduate students per year through programs that target underrepresented students. The societal benefits of this project include communications with the concerned governmental agencies to enable better assessments of Se fate linked to human nutritional adequacy, toxic thresholds and the fundamental understanding of Se in the earth system.The scope of the project is to integrate stable isotope geochemistry and microbiology to gain an improved understanding of biotic and abiotic Se oxidation. The specific objectives are to (1) demonstrate that microbial Se oxidation supports chemoautotrophic growth, (2) determine the magnitude of Se isotopic fractionation caused by microbial and abiotic oxidation of reduced Se-species, and (3) examine oxidation of Se in natural soil/sediment matrices to determine how the laboratory-derived fractionation factors will apply in natural environments. Controlled laboratory experiments will be conducted to determine reaction rates and Se isotope fractionation during microbial and abiotic Se oxidation. Slurry experiments with soils and sediments of two different field sites will provide complementary understanding of Se oxidation in natural samples under well-defined conditions. By establishing a link between Se oxidation and Se isotope fractionation, the results will open new avenues for studies of Se cycling and the fate of Se as a micronutrient and contaminant.