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，也是氧化还原化学反应的指示剂。化学和生物过程控制硒的流动性和环境影响。虽然硒氧化是一个重要的硒动员过程，我们对这个过程的理解是有限的。此外，虽然硒稳定同位素丰度（82硒/76硒比）的变化的测量提供了一个强大的新方法来研究关键的化学反应，涉及硒在现代和古代环境中，硒氧化引起的硒稳定同位素位移的认识不足限制了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，作为一种手段，以实现对环境中硒氧化的强大理解。研究人员将通过针对代表性不足的学生的计划，每年培训一名博士后研究员，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的沟通，使更好地评估硒的命运与人类营养充足性，毒性阈值和硒在地球系统中的基本认识，该项目的范围是整合稳定同位素地球化学和微生物学，以获得生物和非生物硒氧化的更好的理解。具体目标是（1）证明微生物硒氧化支持化能自养生长，（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馏的大小，（3）检查自然土壤/沉积物基质中硒的氧化，以确定实验室衍生的分馏因子如何应用于自然环境。控制实验室实验将进行，以确定在微生物和非生物硒氧化的反应速率和硒同位素分馏。泥浆实验与土壤和沉积物的两个不同的领域网站将提供互补的理解硒氧化天然样品在明确的条件下。通过建立硒氧化和硒同位素分馏之间的联系，结果将开辟新的途径，硒循环和命运的硒作为微量营养素和污染物的研究。

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.