Another even more serious problem is the fact
that gold is now rarely found as nuggets, but rather is extracted
chemically from the ore by using a cyanide leaching process. Though this
process is designed to be a closed system, with leach heaps and
contaminated tailings isolated from their surroundings, their long
timeframes and the extensiveness of the operations usually lead to
cyanide and other toxics eventually getting into the surrounding land,
surface water, and groundwater.
In some cases, acid mine drainage—in which the
sulfides in the now-exposed rock waste combine with water to form
sulfuric acid—turns groundwater more toxic than battery acid. As for
cyanide, an amount of it equivalent in size to a grain of rice will kill
a human, and very low concentrations of cyanide in surface water will
kill fish.
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