Brazil Gold Mining and Environment

 The actual dispute is over the effects of the gold mining
process on the Amazon, specifically the mercury used to isolate
the gold from the surrounding sediment.  The amount of mercury
entering the environment from gold mining activities is estimated
to be 200 tons last year alone.  Mercury enters the environment
during each of the two steps involved in acquiring the gold.

http://www1.american.edu/ted/bragold.htm