Potential Toxicity of Multiple Metals Associated with PGE Deposits

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Water quality and aquatic life standards that are set by Federal and state regulatory agencies are used to evaluate the quality of our nation’s water and the health of aquatic ecosystems. These standards currently are based on hardness of the water and are determined for single metals, not for mixtures of metals that are typically found in natural systems. Metal mixtures can potentially be more or less toxic, or have the same toxicity as single metals to aquatic organisms.  However, models that predict the toxicity of metal mixtures to aquatic organisms are in their infancy. In this study we will conduct a series of mesocosm studies to examine the toxicity of cobalt, copper, nickle, and zinc to natural communities of invertebrates. 

A mesocosm study is labor intensive, requires comprehensive chemical and biological analyses, and involves:

  • deployment of well-washed rocks in a pristine stream for 40 days to allow colonization of macro invertebrates;
  • retrieval of those rocks that are then placed in 36 flow-thru “streams” at the Aquatic Experimental Lab (USGS-Fort Collins);
  • manipulation of metal concentrations in the “streams;"
  • daily collection of emergent adults during the 30-day experiment;
  • multiple measurements of water quality (temperature, pH, dissolved major and minor ions, and DOC) during the experiment; and, at its conclusion,
  • (6) identification and counting of larval invertebrates in each stream. Each experiment simultaneously considers impacts of individual metals and binary metal mixtures on the health of the invertebrate communities.

Using Zn as a reference point and the experimental design of our previous Cd-Zn experiment, our plan is to conduct an experiment with Cd, Cu, Zn, Cu+Zn, and Cd+Cu+Zn in year 1; Cu, Ni, Zn, Ni+Zn, Cu+Ni+Zn in year 2, and Co, Cu, Ni, Zn, Co+Zn, Co+Cu+Ni+Zn in year 3. Results and interpretation of the experiments will be presented at national meetings and in journal articles.

See also: Impacts of Metal Mixtures in Mineralized Rock Drainage

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