According to a July 2002 report by the Environmental Protection Agency (EPA), hard-rock mining companies and coal-burning power plants are responsible for nearly two-thirds of the poisonous contaminants in the nation's air and water. In its most comprehensive inventory of pollution and its sources, the EPA said mining of gold, silver, uranium, copper, lead, zinc, and molybdenum was responsible for 3.4 billion pounds of toxic pollutants in 2000. Coal-burning electric generating plants were responsible for another 1.2 billion pounds. There are numerous techniques of hard rock mining. Lead, aluminum, copper, silver, and gold are not generally found in pure form. They are mixed with rock and are usually found as mineral compounds. Separation of the ore by gravity methods, froth flotation, hydro metallurgical techniques are a large part of modern mining. Cyanide heap leach technology is currently the main method for extraction of gold from ore as displayed in the following web site. www.ac.wwu.edu/~gmyers/esssa/cyanideleach.html. Additional information on cyanide heap leach mining can be found at the following Fish and Wildlife Service link. http://news.fws.gov/issues/cyanide3.html. Until the 1890's, milling operations used mercury in an amalgamation process to extract precious metals from ores. Some loss of mercury occurred in this process and was released into the environment through discarded mill tailings. Mercury has become widely distributed in the lower Carson River basin where elevated concentrations have been identified in water, sediment, and biological tissues. Once in the environment, mercury in the food chain poses a poison threat to wildlife. Piscivorous birds, migratory waterfowl, four federally listed species (endangered bull trout, threatened Lahontan cutthroat trout, threatened bald eagle, and proposed mountain plover), and one candidate species (Northern spotted frog) may potentially be harmed by mercury exposure.