Date of Award

5-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Toxicology

Advisor

Klaine, Stephen J

Committee Member

van den Hurk , Peter

Committee Member

Brumaghim , Julia

Abstract

Total Dissolved Solids, commonly referred to as TDS, is a measure of all organic and inorganic substances that pass through a 2-um filter and are naturally found in aquatic environments. Anthropogenic activities such as agricultural irrigation, road salt runoff, hydraulic fracturing, and coal-fired power plant effluents can increase TDS concentrations of freshwater ecosystems ultimately increasing salinity. Aquatic organisms actively manage the ion balance between their external and internal environments. Freshwater organisms use energy to pump sodium in from the environment, while losing it through passive diffusion. If the external ion concentration changes significantly, these organisms must allocate more energy towards ionoregulation, reducing energy for other important functions such as reproduction. Eight-day static renewal exposures were conducted to characterize the chronic effects of chloride, sulfate and bicarbonate as single anions and in binary mixtures to Ceriodaphnia dubia. The results of the individual anion toxicity tests were used to design binary mixture bioassays. Two experimental approaches were used to test the hypothesis that binary anion mixtures were additive in their combined toxic effects: Dose Addition and Slope Analysis. Reproductive effects (EC50s) indicated that the relative toxicity of single anions was SO42- (0.0108M) > HCO3- (0.0136M) > Cl- (0.0163M). The slope of the overall concentration-response relationship for each anion identified a similar trend, with SO42- and HCO3- having similar slopes (-4776,-4884 respectively) while Cl- was significantly less (-3074). The Dose Addition approach utilized binary mixtures expected to result in an EC50 and then tested if the results were significantly different from expected. This experimental design identified mixtures containing chloride as additive and the bicarbonate/sulfate mixture as greater-than-additive. The Slope Analysis approach compares the slope of the single contaminant concentration-response relationship with the slope of the concentration-response relationship for that contaminant in the presence of a constant background concentration of the second contaminant. This approach identified most ion combinations as being greater-than-additive. In general, the Slope Analysis experimental design was a more efficient and straight-forward approach.

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