W5 PM Toxicity of Complex Mixtures
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 321-323

(SCH-1118-074979) Understanding mine effluent toxicity: beyond the usual suspects.

Schwartz, M¹, Vigneault, B¹, Gosselin, I¹, Beyak, J¹, McGeer, J¹, ¹ Mining and Mineral Sciences Laboratories, Natural Resources Canada, Ottawa, Ontario, Canada

ABSTRACT- While wastewater discharge is usually regulated for a limited number of chemical parameters, there are increasing requirements related to whole-effluent toxicity. An example is the Canadian Metal Mine Effluent Regulations (MMER) which require that mines asses both acute toxicity (rainbow trout and Daphnia magna) and sublethal toxicity (Fathead minnows, Ceriodaphnia dubia, Lemna minor and Selenastrum capricornutum). Previously we have reported on the toxicology of metals in effluents and the extension of biotic ligand modeling to predict acute and chronic impacts. The development of these prediction models is complicated by the fact that mine effluents are complex mixtures. As well, although metals are generally considered as the primary source of potential toxicity, in some cases the observed toxicity cannot be explained by metals alone. There is little toxicological information about other effluent constituents such as process reagents, by-products and wastewater treatment chemicals. Effluent components we have tested include xanthates, sulfur oxyanions (thiosalts), flocculants and elevated hardness. Focusing on MMER test species, we found that organisms respond very differently to such substances, for example algae growth is quite tolerant of thiosalts but sensitive to flocculants while invertebrate reproduction is sensitive to both. Elevated calcium concentrations, due to liming, while not lethal to Ceriodaphnia dubia, dramatically inhibit reproduction. Despite high dosages used or elevated discharge concentrations, most of the substances tested have lethal or inhibition concentrations in the low mg/L range for at least one of the species used. Finally, risk assessment for the discharge of these substances is often limited by the lack of analytical methods to measure concentrations in waste and receiving waters.

Key words: mine effluents, chronic toxicity, aquatic invertebrates