Collaborative Research: Investigation of the Effects of Organic Matter and Sulfur in the Environmental Fate of Mercury

合作研究：调查有机物和硫对汞环境归宿的影响

• 批准号: 1629698
• 负责人: Joseph Ryan
• 金额: $ 28.82万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1629698&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigation; Effects; Organic

Mercury is responsible for more than 80% of the fish consumption advisories in fresh waters of the United States. Most of this mercury is released by the combustion of coal and is deposited from the atmosphere near and far from the sources. Once deposited, the threat of mercury to food webs depends on the extent to which ionic mercury is converted to (1) methylmercury, the form of mercury that is accumulated from plankton to fish and ultimately to humans, and (2) elemental mercury, the form of mercury that is removed from aquatic systems by volatilization. Mercury is converted to methylmercury mainly by sulfate-reducing bacteria that thrive in aquatic environments deprived of oxygen. The ability of these bacteria to methylate mercury depends on the form of the ionic mercury -- whether or not its availability to sulfate-reducing bacteria is limited by its association with organic matter or its precipitation as mercuric sulfide minerals. Mercury is converted to elemental mercury by reduction by a variety of processes for which the influence of organic matter association and precipitation as mercuric sulfide is not well known. The goal of this research is to assess the role of organic matter and sulfur in influencing the conversion of ionic mercury to methylmercury, the first step in making mercury available to aquatic organisms.The focus of this proposal is to improve understanding of the interactions between mercury, sulfur, and organic matter. The research is driven by two main hypotheses that investigate the role of sulfur cycling and redox conditions on the reactivity of organic matter to mercury. The first hypothesis examines the abiotic incorporation of sulfide into organic matter as a function of organic matter composition, and the role of metals on the stability of the newly-incorporated organic sulfur to oxidation. The second hypothesis addresses the effects of the composition and redox state of organic matter on the reduction of mercury from Hg(II) to Hg(0), and inhibition of the reduction of Hg(II) by complexation to reduced sulfur groups in organic matter and inorganic sulfide. The hypotheses will be tested by (1) examining sulfide incorporation into organic matter and reduction of Hg(II) to Hg(0) by organic matter using laboratory experiments and field studies at sites in the Florida Everglades and interior Alaska that represent a range of sulfur and organic matter conditions and (2) characterizing sulfur and mercury in these materials by X-ray absorption near-edge structure (XANES) spectroscopy. These efforts will be enhanced by the use of electrochemistry to study coupled metal-organic matter redox reactions and high energy-resolution XANES spectroscopy to resolve sulfur functionality. The research goals will be complemented by a high-school teacher training program focusing on the laboratory research and participation in ongoing and new science, technology, engineering, and mathematics (STEM) education efforts.

汞是美国淡水沃茨中80%以上的鱼类消费量的来源。 这些汞大部分是由煤炭燃烧释放出来的，并从大气中沉积在靠近和远离源头的地方。 一旦沉积，汞对食物网的威胁取决于离子汞转化为（1）甲基汞的程度，甲基汞是从浮游生物积累到鱼类并最终到达人类的汞形式，以及（2）元素汞，汞通过挥发从水生系统中去除的形式。 汞主要通过硫酸盐还原菌转化为甲基汞，而硫酸盐还原菌在缺氧的水生环境中大量繁殖。 这些细菌使汞甲基化的能力取决于汞离子的形式-无论其对硫酸盐还原菌的可用性是否受到其与有机物的结合或其作为硫化汞矿物沉淀的限制。 汞通过各种还原过程转化为元素汞，其中有机物缔合和以硫化汞形式沉淀的影响尚不清楚。 本研究的目的是评估有机物和硫在影响汞离子向甲基汞转化中的作用，这是使汞可用于水生生物的第一步，本提案的重点是提高对汞、硫和有机物之间相互作用的理解。 这项研究是由两个主要的假设，调查硫循环和氧化还原条件对有机物的反应性汞的作用。 第一个假设检查非生物纳入有机物的硫化物作为有机物组成的函数，和金属的作用，对新纳入的有机硫氧化的稳定性。 第二个假设涉及有机物的组成和氧化还原状态对汞从Hg（II）还原为Hg（0）的影响，以及通过与有机物和无机硫化物中还原硫基团络合来抑制Hg（II）还原。 将通过以下方式检验假设：（1）在代表一系列硫和有机物条件的佛罗里达大沼泽地和阿拉斯加内陆地区，利用实验室实验和实地研究，检查硫化物掺入有机物和有机物将Hg（II）还原为Hg（0）的情况;（2）通过X射线吸收近边结构（XANES）光谱法，表征这些材料中的硫和汞。 这些努力将通过使用电化学来研究耦合的金属-有机物氧化还原反应和高能量分辨率XANES光谱来解决硫功能来加强。 研究目标将由高中教师培训计划补充，重点是实验室研究和参与正在进行的和新的科学，技术，工程和数学（STEM）教育工作。