Toxicity of Mine Drainage to Embryonic and Larval Boreal Toads (Bufonidae: Bufo Boreas)

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Abstract
Chemical analyses and bioassays of mine drainage were made to determine if it could be a factor accounting for the absence of amphibians from Clear Creek County, Colorado [USA]. The concentrations of H+, Fe, Cu and Zn in the drainage were all individually much greater than the tolerance levels of premetamorphic toads. The lethality of the drainage was of such a magnitude that it required diluting approximately 1000 times before larvae could survive in it. Boreal toad (B. boreas) larvae are more resistant to acidity than most fish but are very similar to other anuran larvae and salmonids in their sensitivity to Cu and Zn.