Speciation is important to the environmental effects of selenium, isoelectronic to sulfur, and consideration of the particular speciation under environmental conditions allows for identification of beneficial and more toxic forms. The most common forms of Se in the aquatic environment are the oxidized forms selenate (Se(VI)) and selenite (Se(IV)). These forms of Se enter the water as a result of oxidation and weathering of substrate minerals. Recent evidence indicates that the presence of salts and nitrates can change the forms of Se present in natural waters in a way that makes current Pourbaix diagrams inaccurate when working with low Se concentrations present in rivers1. This inaccuracy requires Se species to be measured by LC-ICPMS and may be used to determine the toxicity of these forms in natural water ecosystems1. Se is a dietary requirement for all animals and humans and can be toxic if present in high concentrations. The EPA has listed the chronic exposure limits for fish tissue as 15.8 mg Se/Kg for egg/ovary, 8.0 mg Se/Kg whole body. The new chronic water exposure limit is under agency review and may be lowered to 1.2 mg Se/L. The Fountain Creek Watershed has segments of Fountain Creek where Se water levels exceed the current EPA limits of 5 mg/L. The source of this Se is the Se rich Pierre Shale. According to Pourbaix diagrams, the Se species present should be hydrogen selenite. However our results indicate that the Se present is the less toxic selenate. The high levels of Se present in the creek and the native bryophytes would predict negative trends in the health and the diversity of fish present at sites with high Se. The results of our analysis show that fish diversity is unaffected by the Se levels in the Fountain Creek. This result indicates that other factors may be involved in the availability of Se to aquatic organisms in Fountain Creek.

Selenium speciation in the Fountain Creek water and effects on fish species diversity

253rd National Meeting (2017)

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