Uptake of waterborne selenite, and its toxic effects, in the water flea (Daphnia magna), Westslope cutthroat trout (Oncorhynchus clarkii lewisi) and rainbow trout (Oncorhynchus mykiss)
Creators: Klaczek, Chantelle E
Publisher: name: University of Alberta Library
Year: 2024

<p>Selenium is an essential element, playing an important role in many physiological processes. However, it possesses a narrow margin between essentiality and toxicity. In aquatic systems, selenium is increasingly identified as a trace element of major concern with levels exceeding regulatory guidelines detected. The major sources of anthropogenic selenium are the coal mining and agricultural industries. Selenium exposure in aquatic biota results in bioaccumulation and is associated with toxic effects such as teratogenesis, tissue pathologies, oxidative stress, ionoregulatory and enzymatic disruption, reproductive alterations and even death. Although the diet is the main route of selenium exposure to higher organisms, aqueous exposures can still contribute to accumulation and subsequent toxicity. There is, however, little mechanistic understanding of how waterborne selenium is taken up and accumulated in aquatic organisms. There are also limited data regarding how water chemistry can affect these processes, and how accumulation relates to toxic effects. The relationship between accumulation and toxicity is an important consideration for the environmental risk assessment of selenium. The overall aim of this thesis is to advance our mechanistic understanding of waterborne selenite uptake and how water chemistry may affect accumulation in aquatic species. <br>
To assess uptake mechanisms of waterborne selenite in a primary consumer, Daphnia magna were exposed to increasing aqueous selenite concentrations with varied water chemistries. At concentrations found in heavily contaminated areas, selenite uptake was mediated by a phosphate transporter while at higher, less environmentally-relevant concentrations, selenite uptake was likely mediated by a bicarbonate transporter. <br>
To investigate selenite handling in fish, and to determine if patterns of selenite accumulation are conserved in fishes, Westslope cutthroat trout (Oncorhynchus clarkii lewisi) and rainbow trout (Oncorhynchus mykiss) were exposed to increasing aqueous selenite with varied water chemistries as per the D. magna study. Increasing phosphate in the water mediated an inhibition of selenite accumulation in the gills and liver of Westslope cutthroat trout, an outcome that contrasted with the lack of effect of phosphate in rainbow trout. <br>
The sensitivity of Westslope cutthroat trout to selenium was assessed via exposure to a graded concentration series of waterborne selenite. A median lethal (LC50) value of 15.55 mg L-1 was determined. Sub-lethal biochemical effects were also examined. Protein carbonylation, a marker of oxidative damage, was significantly reduced in the gill and liver indicating an improved oxidative status associated with sub-lethal selenium exposure. This effect was not mediated by changes in glutathione peroxidase, as activity of this important antioxidant enzyme remained unchanged in gill and liver. Activities of the key ionoregulatory enzymes Na+/K+-ATPase and H+-ATPase activity were upregulated in the gills, but there was no effect of waterborne selenite on lactate dehydrogenase, a key marker of metabolic status. <br>
Uptake and accumulation of waterborne selenite in D. magna and O. clarkii lewisi were consistent with the original hypothesis of anionic-mediated transport. However, accumulation in O. mykiss was not consistent with anion-dependence. Furthermore, the relative sensitivity of Westslope cutthroat trout was lower than expected. However, sub-lethal toxic endpoints were still altered, suggesting aqueous exposures may still be of relevance and concern to this species. <br>
Overall, this thesis contributes to the knowledge of the mechanisms of uptake and accumulation of waterborne selenite in aquatic species and provides a better understanding of the sensitivity of a previously unstudied fish species to a prominent, ubiquitous contaminant. The findings of this research suggest that specific water chemistries could alter the toxicological impacts of selenite in contaminated waters. Furthermore, this thesis provides support that waterborne exposure results in significant accumulation and this remains a concern for the health of local aquatic species. These results also provide insight into potential protective measures and can help inform water quality management plans to help conserve water bodies susceptible to selenium contamination. </p>