Mercury hazards traditionally have been associated with the gold mining industry in the United States and continue to pose hazards to present day miners. In her 1925 book Industrial Poisons of the United States, Dr. Alice Hamilton recognized the severe hazards of mercury in mining. 1 In 1997, mercury continues to present risks to miners.
Mercury is a cumulative poison which can affect the brain, the central nervous system and the reproductive system. It can be absorbed by inhalation, ingestion and through the skin. 2 3 If proper care is not taken at the worksite, miners can carry contaminants home and expose their families.4 Because it has no warning properties, individuals often underestimate the hazard of exposure to mercury.
The amount of gold produced in the United States has increased tenfold since 1980; employment in gold mining has increased greatly in the same period. In the past six years, the Mine Safety and Health Administration (MSHA) has found many overexposures involving mercury. Because of these overexposures and their corresponding serious potential risks for miners, MSHA has developed this document which discusses mercury hazards and current “Best Practices” to reduce exposure in the gold and silver mining industries. The “Best Practices” section recommends procedures and activities that a mine operator or health and safety professional can use to ensure the miner a healthful worksite.Mercury contamination of the environment from historical and ongoing mining practices that rely on mercury amalgamation for gold extraction is widespread. Contamination was particularly severe in the immediate vicinity of gold extraction and refining operations; however, mercury, especially in the form of water-soluble methylmercury, may be transported to pristine areas by rainwater, water currents, deforestation, volatilization, and other vectors. Examples of gold mining-associated mercury pollution have been shown for Canada, the U.S., Africa, China, the Philippines, Siberia, and South America. In parts of Brazil, for example, mercury concentrations in all abiotic materials, plants, and animals, including endangered species of mammals and reptiles, collected near ongoing mercury amalgamation gold mining sites were far in excess of allowable mercury levels promulgated by regulatory agencies for the protection of human health and natural resources. Although health authorities in Brazil are unable to detect conclusive evidence of human mercury intoxication, the potential exists in the absence of mitigation for epidemic mercury poisoning of the mining population and environs. In the U.S., environmental mercury contamination is mostly from historical gold mining practices, and portions of Nevada remain sufficiently mercury contaminated to pose a hazard to reproduction of carnivorous fishes and fish-eating birds. Concentrations of total mercury lethal to sensitive representative natural resources range from 0.1 to 2.0 microg/L of medium for aquatic organisms; from 2,200 to 31,000 microg/kg BW (acute oral) and from 4,000 to 40,000 microg/kg (dietary) for birds; and from 100 to 500 microg/kg BW (daily dose) and from 1,000 to 5,000 microg/kg diet for mammals. Significant adverse sublethal effects were observed among selected aquatic species at water concentrations of 0.03-0.1 microg Hg/L. For some birds, adverse effects, mainly on reproduction, have been associated with total mercury concentrations (microg/kg FW) of 5,000 in feathers, 900 in eggs, and 50-100 in diet, and with daily intakes of 640 microg/kg BW. Sensitive nonhuman mammals showed significant adverse effects of mercury when daily intakes were 250 microg/kg BW, when dietary levels were 1,100 microg/kg, or when tissue concentrations exceeded 1,100 microg/kg. Proposed mercury criteria for protection of aquatic life range from 0.012 microg/L for freshwater life to 0.025 microg/L for marine life; for birds, less than 100 microg/kg diet FW; and for small mammals, less than 1,100 microg/kg FW diet. All these proposed criteria provide, at best, minimal protection.
