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

硒（Se）是一种必需的微量营养素，是一种潜在的环境污染物，也是现在和过去环境系统中涉及氧化和还原的化学反应的指标。化学和生物过程控制硒的流动性和对环境的影响。虽然硒氧化是一个重要的硒动员过程，但我们对这一过程的了解有限。此外，尽管测量硒稳定同位素丰度（82Se/76Se比值）的变化为研究现代和古代环境中涉及硒的关键化学反应提供了强有力的新方法，但由于对硒氧化引起的硒稳定同位素变化的了解不足，限制了对硒同位素数据的解释。因此，本项目将研究氧化引起的稳定硒同位素变化，作为对环境中硒氧化的有力理解的一种手段。研究人员将通过针对代表性不足的学生的项目，每年培养一名博士后、两名博士生和6-8名本科生。该项目的社会效益包括与有关政府机构进行沟通，以便更好地评估与人类营养充足性、毒性阈值和对地球系统中硒的基本认识有关的硒命运。该项目的范围是整合稳定同位素地球化学和微生物学，以提高对生物和非生物硒氧化的理解。具体目标是：(1)证明微生物硒氧化支持化学自养生长，(2)确定微生物和非生物氧化还原硒物种引起的硒同位素分异的大小，以及(3)检查天然土壤/沉积物基质中硒的氧化，以确定实验室衍生的分异因子如何应用于自然环境。将进行受控的实验室实验，以确定微生物和非生物硒氧化过程中的反应速率和硒同位素分馏。两个不同地点的土壤和沉积物的泥浆实验将在明确的条件下提供对自然样品中硒氧化的补充理解。通过建立硒氧化与硒同位素分异之间的联系，该结果将为研究硒循环以及硒作为微量营养素和污染物的命运开辟新的途径。

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.