Collaborative Research: An Integrated Study of the Fractionation of Natural Dissolved Organic Matter Upon Sorption to Mineral Surfaces

9628166中国天然有机物(NOM)是土壤、溪流、湖泊、地下水和河口水的重要组成部分，在矿物生长和溶解、痕量金属循环以及全球生物地球化学碳收支等多种环境现象中发挥着关键作用。也许最重要的是，NOM在有机和无机污染物通过多孔介质的传输过程中发挥着关键的、尽管复杂的作用。一方面，结合在矿物表面的NOM可以去除水体中的痕量金属、非极性有机化合物(NOCs)和其他污染物。另一方面，在水体中保持自由或胶体状态的NOM可能会增加污染物的流动性。因此，理解和量化NOM在固相和溶解相之间的整体分配是研究广泛的污染物迁移现象的基础。此外，由于NOM由各种结构、功能和反应活性不同的疏水和亲水分子组成，我们不仅需要了解NOM是如何分配的，而且还需要了解它在吸附到矿物表面时是如何分级的。例如，疏水性较强的组分的优先吸附可能会增加NOC在多孔介质中的滞留。大量的野外和实验室研究表明，NOM在吸附时发生分馏，并为分馏过程提供了线索。然而，NOM组成、溶液特性、矿物表面性质和动力学因素对分馏的影响仍然存在许多问题。此外，对矿物溶解、金属络合和NOM凝聚对表观分馏的影响知之甚少。最后，我们目前对分馏的大部分理解主要是基于间接证据。例如，尽管一些人将观察到的分馏动力学效应归因于吸附的NOM分子构象的变化，但这一假说并未得到直接验证。为了更好地了解NOM的分馏过程，我们提出了一项为期3年的跨学科研究工作，将精心挑选的淡水湿地分水岭新泽西州的麦当劳分支盆地的现场采样与新开发的分子水平方法相结合，以比以前更直接的方式研究NOM的吸附和分馏。NOM样本将从地表水、土壤以及详细记录的补给区和排泄区的浅层和深层地下水中采集。McDonalds Branch和标准NOM样品的吸附分级将通过在吸附之前和之后对溶液进行表征来量化，使用的分析技术组合包括：13CNMR和1HNMR；UV-VIS、荧光和衰减傅立叶变换红外(ATR-FTIR)光谱；高压尺寸排除色谱(HPSEC)；总有机碳分析(TOC)；蒸汽压渗透法；电位滴定；和元素分析。扫描隧道和原子力显微镜(STM和AFM)，包括新的敲击模式AFM，将被用来确定吸附的有机分子的结构，以及结构变化在吸附和分级中的作用。高压液相色谱(HPLC)和原子吸收光谱(AA)将用于研究氧化物的溶解和非金属结合现象。表面FTIR将有助于阻止吸附机制，以及它们如何影响分馏。我们相信，这一项目对水质研究的许多领域都是至关重要的，我们选择了一个真正的终端成员天然实验室分水岭来进行现场调查。上面列出的最先进的实验室技术的组合将使我们能够以比以前更定量、更机械化的方式来解决这个问题。在这项研究过程中，将改进金属络合分析的新技术，进一步发展吸附有机分子的STM/AFM成像新方法，并将形成一种将NOM结构、组成和反应性的实验室和现场研究相结合的新途径。拟议的研究将为广泛的其他研究奠定坚实的基础。例如，该方法可以扩展到包括具有不同NOM特征的更多样化的流域类型的采样。我们预计，这项研究将使未来能够广泛研究NOM的分馏如何影响疏水和亲水污染物的传输。最后，鉴于淡水湿地的重要性，以及它们从我们的景观中迅速消失的速度，我们认为，涉及湿地NOM演变的调查对于加深我们对这种复杂但脆弱的生态系统的理解至关重要。

9628166 Chin Natural organic matter (NOM) is an important component of soils, streams, lakes, ground waters, and estuarine waters, and it plays a key role in such diverse environmental phenomena as mineral growth and dissolution, cycling of trace metals, and the global biogeochemical C budget. Perhaps most importantly, NOM plays a crucial, though complex, role in the transport of organic and inorganic pollutants through porous media. On the one hand, NOM that is bound to mineral surfaces may remove trace metals, nonpolar organic compounds (NOCs ) and other pollutants from the water column. On the other hand, NOM that remains free or in colloidal form within the water column may increase the mobility of pollutants. Hence, understanding and quantifying the bulk partitioning of NOM between solid and dissolved phases is fundamental to a wide range of pollutant transport phenomena. Moreover, because NOM consists of a variety of hydrophobic and hydrophilic molecules with variable structure, functionality, and reactivity, we need to understand not only how NOM partitions but also how it fractionates upon sorption to mineral surfaces. For example, preferential sorption of the more hydrophobic components may increase the retardation of NOCs through porous media. Numerous field and laboratory studies have suggested that NOM fractionates upon sorption, and provided clues to fractionation processes. Nevertheless, many questions remain regarding the effects of NOM composition, solution characteristics, mineral surface properties and kinetic considerations on fractionation. Additionally, little is known about the effects of mineral dissolution, metal complexation, and NOM coagulation on apparent fractionation. Finally, much of our current understanding of fractionation is based on largely indirect evidence. For example, although observed kinetic effects on fractionation have been attributed by some to changes in conformations of sorbed NOM molecules, this hypothesis has not been tes ted directly. To better understand NOM fractionation processes, we propose a 3-year interdisciplinary research effort combining field sampling at a carefully chosen freshwater wetland watershed, McDonalds Branch basin in the New Jersey Pinelands, with newly developed molecular-level methodologies, to study NOM sorption and fractionation in a far more direct manner than previously has been possible. NOM samples will be collected from surface waters, soils, and shallow and deep ground waters in carefully documented recharge and discharge zones. Fractionation on sorption of McDonalds Branch and standard NOM samples will be quantified by characterizing solutions prior to and following adsorption, using a combination of analytical techniques, including: 13C NMR and 1H NMR; UV-Vis, fluorescence, and attenuated fourier transform infra-red (ATR-FTIR) spectroscopies; high pressure size exclusion chromatography (HPSEC); total organic carbon analysis (TOC); vapor pressure osmometry; potentiometric titration's; and elemental analysis. Scanning-tunneling and atomic-force microscopy (STM and AFM), including the new tapping mode AFM, will be used to determine the structure of sorbed organic molecules, and the role of structural changes in sorption and fractionation. High pressure liquid chromatogrphy (HPLC) and AA will be used to study oxide dissolution and NOM-metal binding phenomena. Surface FTIR will assist in deterring sorption mechanisms, and how they influence fractionation. We believe that this project is fundamental to many areas of water quality research, and that we have chosen a true end-member natural laboratory watershed to conduct the field investigation. The combination of state-of-the-art laboratory techniques listed above will allow us to tackle this problem in a far more quantitative, mechanistric manner than previously has been possible. Over the course of this research, new techniques of metal-complexation analysis will be refined, new methods of STM/AFM imaging of sorbed organic molecules will be furthered, and a new approach to integrating laboratory and field investigations of NOM structure, composition, and reactivity will be fostered. The proposed research will lay a strong foundation for a broad spectrum of additional research. For example, the approach may be expanded to encompass sampling at a greater diversity of watershed types, with different NOM characteristics. We anticipate that this research will enable a wide range of future studies of how NOM fractionation influences the transport of hydrophobic and hydrophilic pollutants. Finally, given the importance of freshwater wetlands, and the rapidity with which they are disappearing from our landscape, we feel that investigations involving NOM evolution in wetlands are crucial to further our understanding of such complex but fragile ecosystems.