The physical and chemical nature of elemental selenium in the environment

硒（Se）是一种无机污染物，目前在北美具有很高的重要性。一些主要的工业过程，包括燃煤电厂、炼油厂和各种类型的采矿作业（如煤、金和铀），会意外地排放到水生环境中。在一些接收环境中，人们担心硒排放产生的生态毒理学效应，这可能导致硒在水生生物中的生物积累，并对水鸟和掠食性鱼类的生殖产生影响，最终危及整个当地种群的生存。******美国环境保护署和加拿大环境部正在重新评估和（极有可能）降低他们目前的环境硒水质量标准。因此，目前大多数工业作业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类型，它模拟了环境水体中硒被去除到沉积物中的过程。这些系统应该将可溶性硒化合物转化为不溶性元素硒，将其从水中去除并与固体残留物一起处理。虽然这些处理系统通常非常有效地降低了工艺水中的总硒浓度，但仍有一小部分硒通过这些系统，这仍可能引起生态毒理学问题。特别令人感兴趣的是释放的硒的化学性质，初步研究表明，其中一些硒可能以悬浮的胶体元素硒的形式存在，颗粒尺寸非常小。然而，目前还没有可用的分析方法来测量胶体元素硒，或表征其分子组成或粒度的性质。******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，以及在自然水-沉积物系统中，以及在工业除硒厂中，量化和表征生物还原和化学过程产生的元素硒。我们的研究结果将首次确定胶体元素硒是否以及以何种确切形式在这些过程中起作用。这将为评估从工业处理操作中排放到环境水中的元素硒的命运奠定基础，因为元素硒有可能对生物来说是不可用的，并且会迅速沉积，但也可能能够在水柱中转化回可溶的硒。对于工业利益相关者来说，我们的研究将提供部分评估，从长远来看，生物还原是否是正确的处理技术，而对于加拿大公众来说，它将有助于确定这种处理过程中持续的低水平硒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.