THE TOXICITY OF BINARY METAL MIXTURES TO CERIODAPHNIA DUBIA IN MINING INFLUENCED WATERS

摘要

Revisions to current EPA regulations for surface waters containing metals, such as mining influenced waters (MIW), are under consideration. It is proposed to substitute a calculation using the Biotic Ligand Model (BLM) for the current hardness-based criteria. This approach may more accurately account for the influence of varying surface water chemistry on metal toxicity. Although the revision may be a great improvement from the traditional toxicity determination, metals are only considered individually. Most effluents from mining disturbed lands contain multiple toxic metals. Currently the approach used in this situation is to assume that metal toxicity is additive. There are reasons to believe that not all metals form additive combinations. The biotic ligand model was used to determine the LC50 values for copper, cadmium, nickel, and zinc individually for Ceriodaphnia dubia in a MIW. Binary-metal acute toxicity tests on C. dubia using the four metals were then conducted. Both the BLM calculations and the experiments were performed using stream water collected upstream of a mining-impacted reach of North Fork Clear Creek, Colorado. Experiments were performed in order to determine if additivity was occurring. In fact, antagonistic (less than additive) effects were seen for most binary combinations. Results indicate that, for the metal combinations tested, the proposed BLM-based regulations could be sufficiently protective if non-additive effects are accounted for in describing the toxicity of metal mixtures.