Influence of calcium on the toxicity of saline solutions to the mayfly, Austrophlebioides sp. AV11

Context Although calcium may provide a means to reduce toxicity of saline waters, the relationship between them is not well understood. Aim To investigate whether increasing calcium may result in a proportional reduction in toxicity. Methods Acute toxicity tests were conducted using an artificial mine-affected water (AMW) and the same AMW with increased calcium on the mayfly species, Austrophlebioides sp. AV11. Results Results demonstrated that there was a reduction in toxicity when calcium concentration (added as both calcium chloride and calcium sulfate together) was increased by both two-fold (+143 mg L-1) and four-fold (+272 mg L-1) compared with the AMW test solution (161 mg L-1). A further increase by up to eight-fold (+718 mg L-1) did not substantially change the toxicity of the AMW solution. Conclusion The toxicity did not reduce when calcium chloride and calcium sulfate salts were used independently. This study suggests that adding calcium (as calcium chloride and calcium sulfate) to a saline solution reduces toxicity upto a maximum threshold, beyond which no further benefit is achieved. Implications Increased calcium can have diminishing effect on toxicity or reach a maximum threshold beyond which no further reduction in toxicity is achieved. Improved understanding of this relationship is needed to inform the management of saline mine waters.