Cyanide

• Gold is usually found in small concentrations in rock. In order to dissolve the rock and obtain the pure gold, the rock has to be dissolved. Cyanide is one of the most effective chemicals for this use. However, cyanide is highly toxic to humans, and the large quantities of cyanide necessary to extract gold often end up in the environment. Cyanide is highly toxic to humans and wildlife, with amounts smaller than a grain of rice being enough to kill a human.
  
  

Mercury

• Mercury is used for the same purpose cyanide is, to extract gold from the minerals it is encased in. With this method, mercury is combined with gravel and mud to make an abrasive liquid that separates the gold and rock. Mercury is easily absorbed by the soil surrounding a gold mine, meaning a large portion of the massive amounts of mercury used to extract gold ends up in the environment. Although no longer common, mercury was once used widely in gold mines, and the mercury from these mines continues to have harmful effects on the ecosystem. The National Institute of Environmental Health Sciences estimates that gold mining in the Sierra Nevada mountain range in California introduced up to 8 million pounds of mercury after just three decades of operation, ending in 1888. Mercury levels remain high in that region.
  
  

Air Pollution

• Gold mining produces substantial air pollution. Many gold mines are open-air pits. Dust is produced during excavation, which can be harmful to people living in the vicinity. Fumes from the toxic chemicals used in the extraction process mix with vehicle exhaust from the cars and heavy machinery at the site, producing an area of dense, polluted air. Off-site, most gold is sent to a processing plant to undergo smelting, a process by which the gold is melted down to eliminate impurities. These smelting facilities can produce massive amounts of air pollution.
  
  

Acid Mine Drainage

• Acid mine drainage occurs when water, either from rain or underground springs, washes through a mine. This water drains into the ecosystem, bringing along whatever toxic chemicals were dormant in the mine. The National Institute for Environmental Health Science notes that this can occur even if the mine has been closed for more than 100 years. An study conducted by the EPA shows that as much as 40 percent of all watershed areas in the western United States have been affected by acid mine drainage. Acid mine drainage can have a number of long-lasting effects on the environment, from killing off fish and other wildlife to poisoning drinking water for humans.
  
  

Future

• Although gold mining has historically been an environmentally damaging enterprise, recent advancements in technology and industry standards are helping to mitigate the damage. Smelting plants, as is the case with many factories in the United States, are becoming cleaner and holding to higher emissions standards. Measures are being taken by mining companies to prevent acid mine drainage, such as checking the levels of dangerous minerals in the ground before drilling. Cyanide is still the industry standard for extraction because an effective replacement hasn't been found.