Chemical reactions in the atmosphere and bacteria in water transform the mercury at varying rates. It drops from the sky onto land and in waterways, then rain and runoff carry the mercury into lakes and rivers.
• How do Nevada's gold mines compare with other industrial sources of mercury?
One mine in 1998 was emitting 9,400 pounds of mercury a year, while another emitted more than 2,200 pounds. Coal-fired power plants are the national focus of mercury pollution, but each plant emits only an average of 250 pounds of mercury annually.
• How have the mines reduced their mercury emissions?
Cinnebar, the natural source of mercury, is mixed in with the gold ore. When the ore is roasted, mercury is released and some is collected, some is left in the waste rock while some goes up the stack. The mines have added scrubbers to their smokestacks that remove the mercury from their pollution plume. The miners also have changed their processing so they can collect more mercury or leave more in the waste rock.