The physical and chemical nature of elemental selenium in the environment

在北美，硒(Se)是一种非常重要的无机污染物。一些主要工业过程，包括燃煤发电厂、炼油厂和各种类型的采矿作业(如煤、金和铀)，会意外地排放到水环境中。在一些接收环境中，人们担心Se排放产生的生态毒理效应，这可能导致Se在水生生物中的生物积累，以及对水鸟和捕食性鱼类的繁殖影响，最终可能危及整个当地人口的生存。美国环境保护局和加拿大环境局正在重新评估并(最有可能)降低他们目前的环境Se水质标准。因此，大多数工业企业目前都在评估或安装除硒系统。细菌还原反应器是目前考虑/安装的最流行的处理系统，它模拟了当Se被移到沉积物中时在周围水体中发生的过程。这些系统被认为是将可溶的Se化合物转化为不溶的元素Se，然后从水中去除并与固体残留物一起处理。虽然这些处理系统在降低工艺水中的总Se浓度方面通常非常有效，但一小部分Se通过这些系统，仍然可能引起生态毒理方面的担忧。特别令人感兴趣的是释放出的Se的化学性质，初步研究表明，其中一些Se可能以悬浮胶体元素Se的形式存在，颗粒尺寸很小。然而，目前还没有可用的分析方法来测量胶体元素Se，或从分子组成或颗粒大小来表征其性质。在拟议的研究计划中，我们将开发这样的方法，然后在实验室研究中，以及后来在天然水-沉积物系统中，以及在工业除硒工厂中，对生物还原和化学过程产生的元素Se进行量化和表征。我们的研究结果将首次确定胶体元素Se是否以及以何种确切形式在这些过程中发挥作用。这将为评估从工业处理作业中排放到周围水域的元素Se的去向奠定基础，因为元素Se可能对生物体不可用，会迅速沉积，但也可能在水柱中转化回可溶的Se物种。对于工业利益相关者，我们的研究将提供部分评估，从长远来看，生物减少是否是正确的处理技术，而对于加拿大公众，它将有助于确定此类处理过程中持续的低水平Se排放是否对水生生物构成危险。

Selenium (Se) is an inorganic contaminant of high current importance in North America. It is discharged accidentally into the aquatic environment from some major industrial processes, including coal-fired power plants, petroleum refineries and various types of mining operations (e.g. coal, gold and uranium). In some receiving environments, there is concern about ecotoxicological effects arising from Se discharges, which may lead to Se bioaccumulation in aquatic organisms, and to reproductive effects in aquatic birds and predatory fish that can ultimately endanger the survival of entire local populations.The US Environmental Protection Agency and Environment Canada are in the process of re-evaluating and (most likely) lowering their current ambient Se water quality criteria. Consequently, most industrial operations are currently evaluating or installing Se removal systems. Bacterial reduction reactors, which mimic the processes occurring in ambient water bodies when Se is removed to the sediments, are currently the most popular type of treatment system considered/installed. These systems are supposed to convert soluble Se compounds into insoluble elemental Se, which is removed from the water and disposed of with solid residues. While these treatment systems are often very effective at lowering the total Se concentration in the process waters, a small fraction of Se passes through these systems, and may still raise ecotoxicological concerns. Of particular interest is the chemical nature of the released Se, and preliminary studies suggest that some of this Se might be present in the form of suspended colloidal elemental Se with very small particle size. However, there are currently no analytical methods available to measure colloidal elemental Se, or characterize its properties with respect to molecular composition or particle size.In the proposed research program, we will develop such methods, and then quantify and characterize elemental Se generated by biological reduction, as well as chemical processes, in laboratory studies, and later on in natural water-sediment systems, as well as in industrial Se removal plants. The results of our studies will determine for the first time if, and in what exact form, colloidal elemental Se plays a role in these processes. This will lay the foundation for assessing the fate of elemental Se discharged from industrial treatment operations into ambient waters, since it is possible that elemental Se is unavailable to organisms and will sediment rapidly, but may also be able to convert back into soluble Se species in the water column. For the industrial stakeholders, our research will provide part of the assessment whether biological reduction is the right treatment technique in the long term, while for the Canadian public, it will help determine if continued low-level Se emissions from such treatment processes pose danger to aquatic organisms.