ADVANCES IN SIMPLE METHODS OF ASSESSING THE TOXICITY OF MINE WASTES

Three years ago, we developed a system for assessing the environmental impact of mining wastes. Key features of this are a well-tested plan to secure a composite sample, the use of simple leach tests, and the development of a decision tree for assessment. Since then, progress has occurred in a number of areas. Independent sampling of mine waste piles and comparison of leachate tests between CSM and USGS have found the sampling, leaching, and analytical techniques to be robust. At marginally impacted sites, simple microbial enzyme bioassays tests, such as MetPLATE™ have been developed to replace traditional in-vitro aquatic toxicity tests. These tests do give accurate and reproducible results for lab and field samples. There is a good correlation between MetPLATE™ and traditional toxicity tests. However, the EC50 for Cu by MetPLATE™ is about 10 times higher than the LC50 using C. dubia. For Zn, the toxicity results match well. Finally, we have been using the Biotic Ligand Model for determining aquatic toxicity to correlate our toxicity measurements with established stream standards and traditional toxicity measurements for the purpose of testing the model over time and chemistry changes. Once the model has been reasonably calibrated, we can begin to predict how different treatment methods that add alkalinity, hardness and organic matter to the water affect the metal toxicity of the water.