Bioavailability and toxicity of metals in mine and metallurgical effluents

Symposium Rouyn-Noranda 2002
Abstract To protect aquatic life, the current water quality criteria for metals are based on total concentrations. However, complexation (association of these metals with ligands in solution) can significantly reduce the toxicity of metals for aquatic organisms. In order to evaluate the importance of complexation in lowering the toxicity of metals in mine and metallurgical effluents, we studied the speciation of metals and the chronic toxicity of various mine and metallurgical effluents. The dissolved phase of the effluents was sampled using in situ dialysis and copper, zinc and cadmium speciation were calculated with the WHAM chemical equilibrium model. Concentrations of free metals were also measured by an ion exchange technique. Free metal concentrations calculated and measured indicate that complexation is important in mine effluents especially for Cu. To link metal speciation and chronic toxicity, we measured, in parallel, the growth inhibition of the algae Selenastrum capricornutum and the larvae of the fish Pimephales promelas and the reproduction inhibition of the water flea Ceriodaphnia dubia (chronic toxicity tests included in the monitoring program for environmental effects of the federal regulation concerning metal mine effluents). In the absence of thiosalts, no mortality was observed for the tests as a whole and also, there was no growth inhibition of the P. promelas fish larvae. Growth inhibition of the S. Capricornutum algae is not linked to trace metal concentrations but rather to calcium concentrations. Reproduction inhibition of the C. dubia water flea is linked to dissolved and free metal concentrations and not to total metal concentrations, showing the significance of chemical speciation on metal toxicity. Our results show that growth inhibition of the S. capricornutum algae is due to the high concentrations of calcium found in mine effluents and that the total metal concentrations cannot be used to predict the chronic toxicity for the C. dubia water flea.
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