Influence of calcium proportion on the toxicity of a saline solution to Ephemeroptera, Austrophlebioides sp. AV11

Nanjappa, Vinitha (2015). Influence of calcium proportion on the toxicity of a saline solution to Ephemeroptera, Austrophlebioides sp. AV11 MPhil Thesis, Centre for Water in the Minerals Industry, The University of Queensland. doi:10.14264/uql.2015.851

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Author Nanjappa, Vinitha
Thesis Title Influence of calcium proportion on the toxicity of a saline solution to Ephemeroptera, Austrophlebioides sp. AV11
Formatted title
Influence of calcium proportion on the toxicity of a saline solution to Ephemeroptera, Austrophlebioides sp. AV11
School, Centre or Institute Centre for Water in the Minerals Industry
Institution The University of Queensland
DOI 10.14264/uql.2015.851
Publication date 2015-09-14
Thesis type MPhil Thesis
Supervisor Sue Vink
Jason Dunlop
Matthew Krosch
Total pages 92
Total colour pages 10
Total black and white pages 82
Language eng
Subjects 0502 Environmental Science and Management
0606 Physiology
0302 Inorganic Chemistry
Formatted abstract
Anthropogenic activities such as coal mining, oil and gas production, application of salts on roads for de-icing and agricultural practices can result in saline discharges to aquatic ecosystems. Salts are components of all natural waters. Salinity is a measure of inorganic ions or salts. It is mainly comprised of major cations (calcium–Ca, potassium–K, magnesium–Mg, sodium–Na) and major anions (chloride–Cl, sulfate–SO4, bicarbonateHCO3). The ionic composition of mine waters can have varying proportions of major cations and anions. Saline discharges to freshwater ecosystems can increase salinity as well as change the ionic composition. Major ions are also essential for the normal functioning of the organisms. Change in salinity or ionic composition of the surrounding water can have a detrimental effect on organisms. While increased calcium concentration is presumed to decrease the toxicity of saline solutions, the effect of calcium proportion of a mine water ionic composition is not well understood. The aim of this study was to investigate the influence of calcium proportion on the toxicity of a saline solution to Ephemeroptera, Austrophlebioides sp. AV11. The hypothesis tested was that increased calcium proportion decreases the toxicity of a saline solution to Austrophlebioides sp. AV11. The effect of calcium proportion was tested in presence of all the major cations, potassium, magnesium and sodium and the major anions, chloride, sulfate and bicarbonate.

The aim of the study was evaluated using static non – renewal 96 h acute toxicity tests. The saline solution used in the present study was based on the ionic composition of mine water from the study of Prasad et al. (2012) and named as artificial mine water (AMW). The term calcium proportion used here refers to the proportion of calcium in relation to all the major ions measured in milliequivalents (% meq). Solutions with increased calcium proportion were prepared using calcium chloride and calcium sulfate salts together. Calcium proportion was increased above that of AMW two fold (Ca Cl.SO4(2)), four fold (Ca-Cl.SO4(4)) and eight fold (Ca Cl.SO4(8)). Additional tests were conducting using calcium chloride and calcium sulfate salts separately to assess the effect of calcium in isolation of the associated anions. Calcium proportion was increased as two fold and four fold designated Ca-Cl(2), Ca-Cl(4) and Ca-SO4(2) and Ca SO4(4).

For the experiments with calcium chloride and calcium sulfate together, there was a statistically significant reduction in toxicity for Ca-Cl.SO4(2) and Ca-Cl.SO4(4) solutions compared with AMW, but no difference between Ca-Cl.SO4(8) and AMW. The 96 h LC50 values were: AMW  6.0 mS/cm, Ca-Cl.SO4(2) – 6.9 mS/cm, Ca-Cl.SO4(4) – 8.1 mS/cm and Ca-Cl.SO4(8) – 6.2 mS/cm. These results show that both two fold and four fold increase in calcium reduced toxicity by 15 % and 35 % respectively but that an eight fold increase in calcium did not affect toxicity.

The finding of this thesis suggests that calcium concentration beyond 7.5 mM (300 mg/L) has no ameliorative effect or may contribute to increased toxicity to organisms. The observed toxicity associated for solutions Ca-Cl.SO4(2) and Ca-Cl.SO4(4) and Ca Cl.SO4(8) could be due to the influence of calcium on the permeability of ions and water across the cell membranes. The concentration of calcium has been found to influence the sodium influx in aquatic organisms. Increase in calcium can alter the Ca:Na ratio, which has been found to influence the physiological mechanism.

For experiments which used calcium chloride or calcium sulfate separately, the chloride solutions were more toxic than AMW, while the sulfate solutions showed similar toxicity to the AMW. The 96 h LC50 values were: AMW – 6.0 mS/cm, Ca-Cl(2) – 4.5 mS/cm and Ca-Cl(4) – 5.4 mS/cm, Ca SO4(2) – 5.2 mS/cm and Ca-SO4(4) – 6.1 mS/cm. These solutions did not show a similar effect as observed for solutions with increased calcium proportion using calcium chloride and calcium sulfate together. This can be due to the change in anion ratio that could have interfered in ion exchange mechanisms across cell membranes. It also suggests solutions with both calcium chloride and sulfate together probably had more balanced anions and were less toxic.

The findings of this study will assist in evaluating the toxicity of waters with ionic compositions with a similar relative proportion of calcium. The results suggest that a potential ameliorative effect of calcium should be considered when assessing potential impacts of saline discharges and developing discharge criteria. While this thesis provides the effect of calcium proportion on a complex ionic composition, further research on the effect of Ca:Na ratio and the ratios of other ions on toxicity is needed. This thesis focussed on an Ephemeroptera species; however, the effect of calcium proportion can vary for laboratory cultured organisms that are widely used to evaluate effluent toxicity. The potential for variation in the observed toxicity between laboratory and field collected species needs further investigation.
Keyword Salinity
Ionic composition
Calcium
Ephemeroptera

Document type: Thesis
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Created: Mon, 07 Sep 2015, 01:07:07 EST by Vinitha Nanjappa on behalf of Scholarly Communication and Digitisation Service