Environmental context. The release of mining effluents exposes natural waters to excess metals and thereby threatens both human and environmental health. The present study explores the toxicity of aqueous mining effluents collected from a mining area in Sudbury (Ontario, Canada), using two different methods for determination of metal speciation, and an algal toxicity study. The results show reasonable correlation between metal speciation and the observed toxicity and suggest the importance of taking into account other factors related to water quality criteria such as nutrient concentrations, diluent water and presence of other toxic metals that can greatly influence the toxicological result.

Abstract. The present study explores the toxicity of aqueous mining and municipal effluents from the Sudbury area (Canada) using equilibrium- and kinetics-based estimates of metal speciation and chronic toxicity studies using algae (Pseudokirchneriella subcapitata). Free metal ion concentration was determined by the Ion Exchange Technique (IET) and a computer speciation code, Windermere Humic Aqueous Model (WHAM) VI. Labile metal concentration was determined using the Competing Ligand Exchange Method. In general, no correlation was found between the observed IC₂₅ (concentration of test substance that inhibits growth of organism by 25%) and the [Ni]_labile, [Ni²⁺]_IET or [Ni²⁺]_WHAM, probably because of contributions by other metals such as Cu and Zn being also significant. Reasonable correlation (r² = 0.7575) was found when the observed toxicity was compared with the sum of free metal ions of Cu, Ni, and Zn predicted by WHAM. The results of the present study reveal the importance of taking into account other factors related to water quality criteria such as nutrient concentrations, diluent water, and the presence of other toxic metals, which greatly influence the toxicological result in complex, multi-metal contaminated waters.