Copper toxicity to Paratya australiensis: II. Influence of bicarbonate and ionic strength

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Abstract
The acute toxicity of copper to the Australian freshwater shrimp, Paratya australiensis, was shown to decrease in solutions of increasing alkalinity brought about by the addition of NaHCO3. This effect could not be explained merely in terms of changes in copper speciation in the solutions. Estimates of the free copper(II) ion concentration of the LC50 values were made using both copper ion selective electrodes measurements and chemical equilibrium computer calculations. Whereas there were discrepancies between the estimates obtained using these two methods, both indicated an apparent increase in tolerance of P. australiensis to the free copper(II) ion in more alkaline waters. An additional set of experiments, in which NaCl was added to test waters in place of NaHCO3, demonstrated that the increased tolerance of P. australiensis to copper in higher alkalinity waters was caused by a combination of physiological effects associated with increased ionic strength of the test waters and, to a lesser extent, changes in metal speciation in test waters. Further study of the reason for the discrepancy between estimates of copper(II) concentrations derived from ion selective electrode measurements and computer calculations is required.