Measurement and Determination of the Importance of Total Sulfhydryl Binding Site Concentrations in a Wide Range of Environmental Samples: A Novel UHPLC-MS Approach

地表水和地下水系统的重金属污染影响着整个工业化世界的水质，重金属在这些水中的存在形式控制着这些元素的环境命运和生物可利用性。许多金属污染物的水形态是通过与细菌和溶解有机物上的硫基结合位点结合来控制的。尽管这些硫基结合位点很重要，但由于测量这些位点类型的浓度存在分析困难，人们对天然水域中这些位点的丰度或影响其丰度的过程知之甚少。在这项研究中，我们将使用我们开发的一种分析方法来测量来自各种环境的水和沉积物样品中的硫基结合位点。通过提供基线信息，该研究将具有变革性，可用于评估硫基站点在控制自然和人为影响的水系统中金属形态和行为方面的重要性。此外，在我们的新方法的敏感性下，能够测量水样品和环境固相表面中硫基结合位点的浓度，使研究人员能够测试关于这些重要位点在地表和近地表水-岩石系统中的作用的几个假设。赞助的研究项目将涉及与印第安纳州南本德学校当地高中科学研究项目的外展和协调。地球微生物学/环境化学模块将在这些高中科学研究项目中创建并教授（一个由3-4个讲座和演示组成的短期课程），每年将招募2-3名高中生进行一些样本分析。具有巯基金属结合位点的有机化合物在天然和工程地表水、地下水和土壤环境中普遍存在，但由于难以测量其在水和固体样品中的浓度，人们对它们在控制环境行为和金属命运方面所起的作用知之甚少。虽然其他结合位点类型通常更丰富，但巯基位点可能控制亲铜元素在环境中的命运、运输和生物利用度，因为与其他结合位点类型相比，这些元素与巯基位点具有更高的结合亲和力。确定有机巯基结合位点在控制自然系统中金属形态和生物利用度方面的作用的第一步是测量这些位点类型在地表水和地下水以及环境表面中的总浓度。天然水中的总巯基浓度通常在nM到μM范围内，但目前的方法无法直接检测到这些浓度的巯基位点。在这项研究中，研究人员将使用一种新的超高性能液相色谱-质谱（UHPLC-MS）分析方法，他们已经开发并测试了用于测量水相和固相样品中总巯基位点浓度的方法，并在广泛的环境中进行巯基位点浓度的调查。与以前的分析方法相比，UHPLC-MS方法大大降低了检测限，通过测量暴露于巯基位点时分子的浓度变化，间接测量样品中的总巯基位点浓度，该分子与水分子或固相表面上的巯基位点特异性且基本上不可逆地结合。由于使用UHPLC-MS可以非常精确地确定巯基结合分子的浓度，因此该分析方法有可能将总巯基位点浓度测量的检测限降低2-3个数量级，并获得约10 nM的检测限。研究小组将使用这种方法来测试关于巯基位点在湖泊系统、土壤、微生物和根系中的作用和发生的几个假设。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Heavy metal contamination of surface waters and groundwater systems affects water quality across the industrialized world, and the form in which heavy metals are present in these waters controls the environmental fate and bioavailability of these elements. The aqueous speciation of many metal contaminants is controlled by binding onto sulfur-based binding sites on bacteria and on dissolved organic matter. Despite the importance of these sulfur-based binding sites, very little is known about the abundance of the sites in natural waters or the processes that affect their abundance primarily due to analytical difficulties in measuring the concentration of these site types. In this study, we will use an analytical approach that we have developed for measuring sulfur-based binding sites both in water and sediment samples from a wide range of environments. The research will be transformative by providing baseline information that can be used to assess the importance of sulfur-based sites in controlling metal speciation and behavior in natural and human-impacted water systems. Furthermore, the ability to measure the sulfur-based binding site concentrations in aqueous samples and on environmental solid-phase surfaces at the sensitivity of our new approach enables the investigators to test several hypotheses about the role of these important sites in surface and near-surface water-rock systems. The sponsored research project will involve outreach and coordination with local high school science research programs in South Bend, Indiana schools. A geomicrobiology/environmental chemistry module will be created and taught in these high school science research programs (a short-course of 3-4 lectures and demonstrations), and 2-3 high school students will be recruited each year to conduct some of the sample analyses. Organic compounds with sulfhydryl metal-binding sites are ubiquitous in natural and engineered surface water, groundwater, and soil settings, yet the role that they play in controlling the environmental behavior and fate of metals is poorly understood due to the difficulty of measuring their concentrations in aqueous and solid samples. Although other binding site types are typically more abundant, sulfhydryl sites likely control the fate, transport, and bioavailability of chalcophile elements in the environment due to the much higher binding affinities that these elements have with sulfhydryl sites compared to with other binding site types. A first step in determining the role of organo-sulfhydryl binding sites in controlling metal speciation and bioavailability in natural systems is to measure the total concentration of these site types in surface and groundwaters and on environmental surfaces. Total sulfhydryl site concentrations in natural waters are likely to be, typically, in the nM to μM range, but sulfhydryl sites at these concentrations are not directly detectable using current approaches. In this study, the investigators will use a novel ultra-high performance liquid chromatography – mass spectrometry (UHPLC-MS) analytical approach that they have developed and tested for measuring total sulfhydryl site concentrations in aqueous and solid-phase samples, and conduct a survey of sulfhydryl site concentrations in a wide range of environments. The UHPLC-MS approach dramatically lowers the detection limit relative to previous analytical methods, measuring the total sulfhydryl site concentration in a sample indirectly by measuring the change in concentration, upon exposure to sulfhydryl sites, of a molecule that binds specifically and essentially irreversibly to sulfhydryl sites on aqueous molecules or solid phase surfaces. Because the concentration of the sulfhydryl-binding molecule can be determined very precisely using UHPLC-MS, the analytical approach has the potential to lower the detection limit for total sulfhydryl site concentration measurements by 2-3 orders of magnitude over current state-of-the-art techniques and to obtain detection limits of approximately 10 nM. The research team will use this approach to test several hypotheses about the role and occurrence of sulfhydryl sites in lake systems and on soil, microbiological, and root systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.