Selenium speciation determined by ICPMS: effects on fish diversity, solubility, and bioavailability to the bryophyte Hygrohypnum ochraceum in Fountain Creek, Colorado
Date
2019
Authors
Carsella, James S., author
Crans, Debbie C., advisor
Bonetti, Sandra J., committee member
Laybourn, Paul J., committee member
Ryan, Elizabeth P., committee member
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Abstract
Selenium (Se) is a micronutrient that can be present in high levels in aquatic environments which may result in toxic effects observed in aquatic wildlife. The levels in Fountain Creek Colorado are of special concern as these levels are above the EPA limit of 5 µg/L. The high Se levels are a result of the exposure of the water to Pierre Shale deposits that underlie parts of the creek. The effects of this creek water on fish diversity were examined at different locations along the creek. The hypothesis tested was that high Se present in the water and bryophytes should be an indicator of fish species diversity. In addition, the possibility of low toxicity resulting from Se species was explored. The speciation analysis determined the levels of Se(IV) and SE(VI) at 12 sites and the statistical results show that sites with higher Se(IV)/Se total exhibit lower fish diversity and fish number than the other sites. There is a statistically significant difference in Ca, Mg, and Se levels in each of the 3 main tributaries in the Fountain Creek Watershed. The tributaries are Monument Creek and Upper Fountain Creek, which join at a confluence near Eighth Street in the city of Colorado Springs, Colorado, to form the Lower Fountain Creek which empties into the Arkansas River in eastern Pueblo, Colorado. The following factors were considered in determining the forms of Se that could exist: Ca2+, Mg2+, SeO42-, SeO32-, and carbonates in addition to the reported thermodynamic relationships. There is a correlation that exists between water hardness and Se level. This correlation can be described in terms of the formation of a soluble CaSeO4. The formation of CaSeO4 is assisted by the increase in Ca2+ by the presence of Mg2+ regardless of the equilibria with the Ca2+ level reducing carbonate. The bryophyte Hygrohypnum ochraceum has been shown to accumulate zinc, cadmium, and lead is often found growing near acid mine drainages. This natural ability to accumulate metals makes H. ochraceum an good organism to use in the study of heavy metals and metalloids in the environment. In a previous work the bryophytes were shown to differentially uptake Se based on season. In this study the seasonality of the uptake of Se was examined and it is suggested to be related to an Iron (Fe) cofactor. The H. ochraceum cultures were placed in the creek for 10 days, harvested, dried and digested according to EPA Method 3052. The resulting digestates were analyzed using EPA Method 6020a for ICPMS metal determination. The results show that Fe and Se uptake are correlated. The hypothesis that was developed from these results is that Fe is needed by the plant for Se uptake from the creek water. Indeed H. ochraceum demonstrated statistically significant log-linear uptake of Se in the presence of dissolved Fe (R2=0.8488, p=0.002). Se uptake was negatively sloped in the fall compared to the linear relationship in the spring. It was determined that the Fe in the water went from a soluble form to an insoluble form. We failed to reject the null hypothesis that Fe is not required in a soluble form for the bryophyte H. ochraceum to uptake Se. Further examination did show that a significantly different slope exists between the Se(IV) uptake and the Se(VI) uptake. There was not a significant difference between the total dissolved Se and Se(VI). In the future directions, this work could be extended to look at specific markers for Se induced stress in the fish populations that may aid in determining the cause for a lack of diversity in some areas as the habitat along the reaches is similar for that reach. Targeted research of water chemistry could investigate the interesting solubility phenomenon giving rise to the seasonal variation of the Fe in Fountain Creek. Finally, the use of plants as bioremediation in the high Se areas could be further investigated with the knowledge that plant nutritional needs must be accounted for when using plants such as H. ochraceum as biological indicators or biological remediators.
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Subject
fresh water contamination
speciation
toxicology
selenium
bryophyte
thermodynamics