Selenium speciation in the Fountain Creek Watershed and its effects on fish diversity

Abstract

Se is an environmental concern as it can be toxic if present in high concentrations even though it is a dietary requirement for all animals. Se levels are a special concern in the Fountain Creek Watershed located in southeastern Colorado whose geological source is the Se-rich Pierre Shale. Segments of Fountain Creek have Se water levels that exceed the current EPA limit of 5 µg/l. In the studies described here, the effects of river water containing selenium were examined on fish populations at different sites along the Fountain Creek Watershed. Based on the hypothesis that high levels of Se present in the Creek and resident bryophytes should be an indicator of diversity in the river fish we explored the possibility that the low toxicity of the selenium could be due to speciation. A speciation analysis was conducted to determine the selenium(IV) and selenium(VI). Our results show that sites with higher ratios of the more toxic Se(IV) relative to total selenium exhibit lower fish diversity and number of fish. Our results indicate that factors, other than total Se, such as Se speciation may be involved in controlling the bioavailability and toxicity of this element to aquatic organisms in Fountain Creek.

Selenium Speciation in the Fountain Creek Watershed (Colorado, USA) Correlates with Water Hardness, Ca and Mg Levels

“…While Se toxicity is linked to particular species [ 5 , 12 , 13 , 14 , 16 , 20 ] and the presence of selenite (SeO 3 2− ) [ 21 , 22 ], many environmental studies only measure and report the total amount of elemental Se. When analyzing and investigating Se speciation, a better understanding of the interaction of Se species in a natural environment is gained [ 5 , 7 , 21 , 23 , 24 , 25 , 26 , 27 , 28 ]. Recent studies of fish in the Fountain Creek Watershed demonstrated that high numbers of fish species can be observed at sites with high levels of Se [ 21 ].…”

“…When analyzing and investigating Se speciation, a better understanding of the interaction of Se species in a natural environment is gained [ 5 , 7 , 21 , 23 , 24 , 25 , 26 , 27 , 28 ]. Recent studies of fish in the Fountain Creek Watershed demonstrated that high numbers of fish species can be observed at sites with high levels of Se [ 21 ]. This work led to the hypothesis that the toxicity is dependent on the presence of toxic Se species and not the total Se level [ 21 ] and support the need for additional studies that consider the effects of Se species on different types of fish.…”

“…Recent studies of fish in the Fountain Creek Watershed demonstrated that high numbers of fish species can be observed at sites with high levels of Se [ 21 ]. This work led to the hypothesis that the toxicity is dependent on the presence of toxic Se species and not the total Se level [ 21 ] and support the need for additional studies that consider the effects of Se species on different types of fish. The following manuscript analyzes the chemistry of Se speciation in these waters and that of two major cations, Ca 2+ and Mg 2+ , using the thermodynamic parameters.…”

“…The less soluble and reduced form of Se, Se 2− , exists complexed in the earth’s crust, and may also be found at low levels in reducing water environments [ 8 ]. Pourbaix diagrams are important to describe the speciation of Se in idealized systems [ 8 , 15 , 21 , 34 , 35 ]. However, considering that the Pourbaix diagrams are calculated assuming specific conditions, for example, where the concentration and ionic strength do not affect the speciation; such representations are at best, a first approximation [ 15 , 21 , 34 , 35 ].…”

“…Above pH 5.0 selenate (SeO 4 2− ) is the most favored Se species. Using this information, it follows that in less aerated waters (pE ≈ 13.5) at pH values between 3 and 8, hydrogen selenite, HSeO 3 − is the favored species [ 21 , 34 ]. However, recently we demonstrated that for Fountain Creek the Se was about 90% Se(VI) and 10% Se(IV) even through the Pourbaix diagrams predicted more Se(IV) [ 21 ].…”