PARENT SESSION
MA2 - Aquatic Toxicology
Chair: Spehar, Bob¹, ¹ U.S. EPA, Duluth, MN
Co-chair: Henry, Mary², ² U.S. Fish and Wildlife Service, Arlington, VA
8:00 AM to 12:00 PM - Monday, 18 November 2002
Room Ballroom J

(173) Is the biotic ligand model approach applicable to mining effluents ?

Vigneault, Bernard^*,1, McGeer, Jim², Prairie, Robert¹, ¹ Noranda Inc., Technology Centre, Pointe-Claire, Quebec, Canada² Natural Resources Canada, CANMET, Ottawa, Ontario, Canada

ABSTRACT- Several models based on chemical speciation have been proposed to predict acute toxicity to different aquatic organisms. We evaluated the applicability to mining effluents of current modelling approaches using geochemical and toxicological data collected on effluents from different mining sites. First, the use of the BLM approach would require to refine existing model for chronic toxicity since none of the studied mining effluents where acutely lethal. In addition, competitive cations such as calcium and magnesium can be found in mine effluents at concentrations much higher than the ranges studied to develop BLM models. As a result, there is uncertainty regarding the extrapolation of the modelled toxicity reductions at such high levels of calcium and magnesium, which furthermore were proved to be responsible for some of the chronic toxicity responses observed. Finally, the chemical speciation computer code used in BLM models may significantly overestimate free metal concentrations since they do not account for complexation by ligands derived from milling processes that are likely to be also present in addition to natural organic matter in mining effluents. Therefore, current BLM formulations can not be directly apply to mining effluents, but it appears possible to develop refined models that will be account for the important trace metal complexation and elevated major cations concentrations found in mining effluents.

Key words: mining effluent, chronic toxicity, complexation, BLM