Silver: Concentrations, Sources, Processes in Fresh Water

9406373伯努瓦银是水环境中毒性最强的金属之一，然而，由于过去的污染文物，目前没有关于其在淡水中的浓度、迁移和去向的可靠数据。根据模拟河口条件的实验室实验，中等水平的银会直接对浮游生物和无脊椎动物产生毒性，而低水平的银会影响河口的群落结构，降低双壳类的生长速度。与河口相比，淡水中银的来源更多，氯化物的络合作用更少，因此银的毒性问题可能会更严重。银的天然低丰度意味着它可能几乎完全来自人为来源，并且可以作为一种不可降解的污染示踪剂，不受自然背景浓度变化的影响。研究银的另一个同样重要的原因是，它是为数不多的纯B类金属之一，因此，它的研究可以帮助描绘出金属行为总范围的一端。目前，人们对银的水化学知之甚少。由于几乎完全缺乏关于淡水银的可靠信息，这项提议旨在作为一种侦察，以探索银循环的生物地球化学背景，并使研究人员为未来对具体过程进行更详细的研究做好准备。这项研究包括三个主要部分：1)开始建立淡水中银的基准水平，2)确定和量化自然和人为来源，3)具体说明并开始调查控制银的运输、生物有效性和命运的过程和机制。这项研究将使用超清洁方法，以避免污染文物，这些文物一直困扰着之前几乎所有关于淡水中痕量金属的研究。一个重要的目标是促进使用这些方法的更多淡水研究。调查将沿着曾经高度工业化的昆尼皮亚克河全长进行，包括一个中游湖泊。将使用质量平衡法，提供机会来比较自然、点和非点来源的银，并量化去除速率。根据初步测量，昆尼皮亚克河的源头非常干净，而下游河流受到严重污染。另外两条河流，诺加塔克河和康涅狄格州，将进行不那么深入的研究，以便在有限的预算限制下增加研究结果的普遍性。在这两个国家中，诺加塔克有严重的金属污染历史，而康涅狄格州则没有。将使用的技术包括：1)常规膜过滤(分离颗粒物和非颗粒物)，2)超滤(胶体形式)，3)阳极溶出伏安法(评估银-有机物络合物)，4)热力学计算(估计溶解离子形态)，5)孔隙水测量(评估沉积物的扩散通量)，以及6)沉积物的银浓度和210Pb年代学(评估再悬浮通量和记录污染历史)。

9406373 Benoit Silver is one of the most toxic metals in the aquatic environment, yet, because of past contamination artifacts, there are currently no reliable data on its concentration, transport, and fate in fresh waters. Based on lab experiments that simulate estuarine conditions, silver at moderate levels can be directly toxic to plankton and invertebrates while low levels can influence estuarine community structure and reduce bivalve growth rates. Fresh waters, having more silver sources and less complexation by chloride than do estuaries, are likely to have an even greater problem with silver toxicity. Silver's naturally low abundance means that it may derive almost entirely from anthropogenic sources, and can serve as a non-degradable tracer of pollution, free from obfuscation by natural background concentration variations. An equally important reason to study silver is that it is one of the few pure class B metals, and as such, its study can help to delineate one end of the total range of metal behavior. At present the aquatic chemistry of silver is poorly understood. Because of the almost complete lack of reliable information on freshwater silver, this proposal is designed as a reconnaissance to explore the biogeochemical context of silver cycling and to position researchers for more detailed studies of specific processes in the future. The research comprises three main components: 1) to initiate establishment of benchmark Ag levels in freshwater, 2) to identify and quantify natural and anthropogenic sources, and 3) to specify and begin to investigate processes and mechanisms that control silver's transport, bioavailability, and fate. The research will use ultra-clean methods to avoid contamination artifacts that have plagued nearly all previous studies on trace metals in fresh waters. An important goal is to prompt additional freshwater studies that use these methods. The investigation will be conducted along the entire length of the once highly- industrialized Quinnipiac River, including a mid-stream lake. A mass balance approach will be used, providing the opportunity to compare natural, point, and nonpoint sources of silver, and to quantify removal rates. Based on preliminary measurements, headwaters of the Quinnipiac are extremely clean, while the lower river is badly contaminated. Two other rivers, the Naugatuck and Connecticut, will be studied in less depth in order to increase the generality of the findings within the constraints of a modest budget. Of these two, the Naugatuck has a history of severe metal pollution, while the Connecticut does not. Techniques that will be used are: 1) conventional membrane filtration (to separate particulate and non-particulate fractions), 2) ultrafiltration (for colloidal forms), 3) anodic stripping voltammetry (to appraise silver -organic matter complexes), 4) thermodynamic calculations (to estimate dissolved ion speciation), 5) measurement of pore water (to evaluate diffusive flux from sediments), and 6) Ag concentration and 210Pb geochronology of sediments (to assess resuspension fluxes and document contamination history).