Gold Mining and the Environment

From as early as the 16^th century, mercury has been used extensively for gold mining. It is estimated that between 1550 and 1880, nearly 200,000 tons of mercury were released in South America alone. Today, mercury poisoning is a global problem. Approximately 1,000 tons of mercury are released each year into the environment from informal or small-scale gold mining. Gold mining accounts for at least 30-40% of man made mercury pollution.

As much as two grams of mercury can be released into the environment for every gram of gold recovered. The mercury often enters river basins, spreading the mercury across national borders and into larger bodies of water. It is estimated that the Amazon basin receives 40 tons of mercury a year, while mining in Indonesia adds 150 tons to the Java Sea annually.
http://www.brilliantearth.com/gold-mining-environment/