Organic matter variability and implications for metal bioavailability in urban watersheds

水是加拿大的一项重要资源，但城市环境中点源和非点源排放的金属可能对水生生物群产生有害影响。这些负面影响可以通过金属与溶解有机物（DOM）的结合来减少。DOM存在于所有水生环境中，是由自然过程形成的。高浓度时，它会使水呈“茶”色。金属与DOM的结合可以通过确定金属形态来量化。金属形态是一套实验技术，用于测量和/或预测总金属在其可能的化学形式的某些子集中的分布。某些形式的金属比其他形式的金属更具生物可利用性；因此，正在利用计算机模型在环境立法中考虑到金属的形态。毒性预测的一个主要输入变量是溶解有机碳（DOC）浓度，作为DOM的近似度量，但DOM的时空变异性以及毒性预测/调节模型是否需要考虑有机碳的质量和数量，这是一个悬而未决的问题。质量可以被认为是与有机物的分子性质成正比的某种度量。在这里提出的方案中，将对有机质变异性进行“从摇篮到坟墓”的分析。安大略省南部的格兰德河将被用作一个模型系统。这条河从农村地区的一个大型湿地源头（路德沼泽）开始，通过日益增长的城市化流向伊利湖。在对有机物转化和质量变异性的全面调查中，包括水处理过程的影响是很重要的。格兰德河沿岸的大多数城市向上游输送饮用水，向下游排放经过处理的污水。下游的下一个城市将含有这种污水衍生有机物的水用于饮用水处理等等。在这个研究项目中需要解决的重要问题是：(1)有机物的不断加工和再加工对其质量有什么影响？(2)对金属生物利用度的影响是什么？

Water is a vital resource in Canada, but the discharge of metals from point and non-point sources in urban environments can have a detrimental affect on aquatic biota. The negative impacts can be reduced by binding of metals to dissolved organic matter (DOM). DOM occurs in all aquatic environments and is formed by natural processes. At high concentrations, it gives water a "tea''-like colour. Metal binding to DOM can be quantified by metal speciation determinations. Metal speciation is a set of experimental techniques used to measure and/or predict the distribution of total metal among some subset of its possible chemical forms. Some forms of metal are more bioavailable than other forms; thus, metal speciation is being taken into account in environmental legislation using computer models. A major input variable to toxicity prediction is dissolved organic carbon (DOC) concentration as an approximate measure of DOM but there is an open question of the temporal and spatial variability of DOM and if toxicity prediction/regulatory models need to consider quality as well as quantity of organic carbon. Quality can be considered as some measure proportional to the molecular nature of the organic matter. In the program proposed here a "cradle to grave" analysis of organic matter variability will be performed. The Grand River in Southern Ontario will be used as a model system. This river starts from a large wetland headwater (Luther Marsh) in a rural area and moves through increasing urbanization towards Lake Erie. In a complete survey of organic matter transformation and quality variability it is important to include the impacts of water treatment processes. Most of the cities along the Grand River bring in drinking water upstream and discharge treated sewage effluent downstream. The next city downstream takes in the water containing this sewage derived organic matter for their drinking water treatment and so on. The significant questions to be addressed in this research program are (1) what does this constant processing and reprocessing of organic matter do to its quality? and (2) what are the implications for metal bioavailability?