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

在现在和过去的环境系统中，硒是一种必需的微量营养素，是一种潜在的环境污染物，也是涉及氧化和还原的化学反应的指示剂。化学和生物过程控制着Se的迁移和对环境的影响。尽管Se氧化是一个重要的Se动员过程，但我们对这一过程的了解有限。此外，尽管对Se稳定同位素丰度(82Se/76Se比值)变化的测量为研究现代和古代环境中涉及Se的关键化学反应提供了一种强有力的新方法，但对Se氧化引起的Se稳定同位素位移的缺乏限制了对Se同位素数据的解释。因此，该项目将研究氧化引起的稳定的Se同位素变化，作为一种手段，以实现对环境中Se氧化的强有力的了解。调查人员将通过针对代表性不足的学生的项目，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相关政府机构的沟通，以便能够更好地评估与人类营养充分性、毒性阈值和对地球系统中Se的基本了解有关的Se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，以更好地了解生物和非生物Se的氧化。具体目标是(1)证明微生物Se氧化支持化学自养生长，(2)确定还原Se物种的微生物和非生物氧化引起的Se同位素分馏的程度，以及(3)研究自然土壤/沉积物基质中Se的氧化，以确定实验室得出的分馏系数如何应用于自然环境。将进行受控实验室实验，以确定微生物和非生物Se氧化过程中的反应速率和Se同位素分馏。对两个不同场地的土壤和沉积物进行的泥浆实验将提供对明确条件下天然样品中Se氧化的补充理解。通过建立Se氧化和Se同位素分馏之间的联系，这一结果将为研究Se的循环以及Se作为微量营养素和污染物的去向开辟新的途径。

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.