Dissolved Metal Sulfides in Fully Oxygenated River Waters: Sources, Distribution, Composition and Bioavailability

9909278简介：这项建议是为了研究重金属(铜、镉、锌、铅、银)在完全含氧的地表水中被溶解的还原硫化合物络合的研究。该项目将是首次对含氧淡水环境中溶解的还原硫化物进行系统研究。初步研究表明，金属-硫化物络合物可能是河流中许多金属的主要形态。然而，对于在这种环境中溶解的还原硫化合物和金属硫化物络合物的身份、分布、来源和循环几乎一无所知。虽然这项研究建立在海洋领域已知的基础上，但淡水构成了一个不同的、可能更复杂的生物地球化学系统，其中包含地下水、缺氧沉积物、湿地和污染。研究概述：人们对硫化物及其与含氧淡水中金属的相互作用知之甚少。因此，研究策略分两个不同的阶段进行，首先是基础阶段，然后是更多地以过程为导向。在第一阶段，将使用广泛的现场采样来记录硫化物的空间和时间变化，并将在实验室开发新的分析方法。在第二阶段，将对从两个精心挑选的地点收集的样品应用改进的分析技术，以阐明硫化物及其金属络合物在这一新环境中的生物地球化学循环。目标是确定来源，阐明组成，并更好地了解控制溶解的还原硫化合物的行为、运输和命运的过程，以及它们与新鲜含氧地表水体中的重金属形成的络合物。将实现以下目标：(1)确定含氧淡水中溶解还原硫相互转化的池和途径，(2)评价硫化物与其他配体，特别是DOM的络合作用的相对大小，(3)评价溶解还原硫源的性质和大小，(4)评价20条河流和湖泊中涵盖广泛生物地球化学特征的溶解硫化物总水平，方法：采用多种分析方法对几类硫化物进行可靠的鉴定和定量，包括：(1)五种硫化物和单独的金属硫化物络合物(伏安法)；(2)游离硫化物、前驱体挥发性还原硫化物和溶解的酸挥发性金属硫化物(气相色谱)；(3)DOM(高效液相色谱-极谱/光谱联合检测)；(4)总溶解硫化物(预浓集和亚甲蓝分光光度法)。在样品采集、前处理和分析的所有阶段都将使用清洁技术，以避免污染人工制品。意义：络合作用可以极大地降低金属的反应活性，从而降低它们的生物利用率和作为微量营养素或毒素的倾向。在许多河流和湖泊中，溶解的硫化物可能会主导金属的形态，甚至比DOM起到更大的作用。

9909278BenoitIntroduction: This proposal is for research to investigate complexation of heavy metals (Cu, Cd, Zn, Pb, Ag) by dissolved, reduced sulfur compounds in fully oxygenated surface waters. This project will be the first systematic investigation of dissolved reduced sulfides in oxic freshwater environments. Preliminary research suggests that metal-sulfide complexes may be the dominant form of many metals in rivers. Yet, almost nothing is known about the identity, distribution, sources, and cycling of dissolved reduced sulfur compounds and metal-sulfide complexes in this environment. While the research builds on what is known about in the marine realm, fresh waters constitute a different, and possibly more complex, biogeochemical system containing groundwater, anoxic sediments, wetlands, and pollution. Research Overview: Little is known about sulfides and their interaction with metals in oxic fresh waters. Consequently, the research strategy proceeds in two distinct stages, first, basic, then, more process oriented. In the first stage, extensive field sampling will be used to document the spatial and temporal variability of sulfides, and new analytical methods will be developed in the laboratory. In the second stage, the refined analytical techniques will be applied to samples collected from two carefully selected sites, to clarify the biogeochemical cycle of sulfides and their metal complexes in this new environment. Goals are to identify sources, elucidate composition, and better understand processes that control the behavior, transport, and fate of the dissolved reduced sulfur compounds and the complexes that they form with heavy metals in fresh oxic surface waters. The following objectives will be achieved: (1) identification of pools and pathways of interconversion of dissolved reduced sulfur in oxic fresh waters, (2) evaluation of the relative magnitude of sulfide complexation compared to other ligands, especially DOM, (3) appraisal of the nature and magnitude of dissolved reduced sulfur sources, (4) assessment of levels of total dissolved sulfides in 20 rivers and lakes covering a broad range of biogeochemical characteristics, and (5) development and refinement of analytical techniques to identify and quantify a spectrum of reduced sulfur and sulfide-metal species.Methods: Multiple analytical methods will be used to provide reliable identification and quantification of several classes of sulfur compounds, including: (1) five sulfides and individual metal-sulfide complexes (voltammetry), (2) free sulfides, precursor volatile reduced sulfur species, and dissolved acid-volatile metal sulfides (gas chromatography), (3) dissolved reduced sulfur associated with DOM (HPLC with combined polarographic/spectroscopic detection), and (4) total dissolved sulfides (preconcentration and methylene blue spectrophotometry). Clean techniques will be used at all stages of sample collection, pretreatment, and analysis to avoid contamination artifacts.Significance: Complexation can greatly reduce the reactivity of metals, thereby decreasing their bioavailability and tendency to function as micronutrients or toxins. Dissolved sulfides may dominate metal speciation in many rivers and lakes, playing a greater role than even DOM.