Mercury is a toxic metal that exists as a trace element in the earth's crust. Mercury is mined as cinnabar ore, which contains mercuric sulfide. The metallic form of mercury, or elemental mercury, is refined by heating the cinnabar ore to temperatures above 1000F, vaporizing the mercury in the ore. The vapors are then cooled to form liquid elemental mercury. The primary countries that mined for cinnabar ore between 1995 and 1998 were: Russia, Canada, Kyrgyzstan, and Spain. The total amount of mercury produced from mining in 1998 was 2,320 tons.

According to the United States Geological Survey (USGS), in the United States, the primary source of mercury is from the recovery of mercury from obsolete or wornout items, including batteries, chlor-alkali wastewater sludges, dental amalgams, electrical apparatus, fluorescent light tubes, and measuring instruments. The USGS estimated this amount at 400 tons in 1998. In addition, a very small quantity of mercury was produced in 1998 as a byproduct from approximately 10 gold mining operations in California, Nevada and Utah. Also in 1998, the USGS estimated that approximately 35% of the mercury consumed in the United States was used in the manufacture of chlorine and caustic soda, 35% for applications such as measuring and control instruments and dental amalgams, and 30% for electrical and electronic applications.

Mercury can be released to the atmosphere by human (anthropogenic) and natural activities. The 1997 "Mercury Study: Report to Congress" by the U.S. Environmental Protection Agency (EPA) reports that between 50 and 75 percent of the total annual mercury input to the atmosphere from all sources is the result of human activities.

The major human contributions of mercury to the environment occur when:

• fossil fuels are burned, (estimated 54% of total human contribution)
• wastes that contain mercury are burned or landfilled, (estimated 34%)
• mercury is emitted from manufacturing or recycling facilities, laboratories, hospitals or dental offices, (estimated 11%)
• products that contain mercury (e.g., fluorescent bulbs and mercury fever thermometers) are broken, (estimated 1%)
(These figures do not include estimates of releases from mining operations.)

Natural activities that can release mercury into the environment include the following:

• volcano eruptions
• weathering of rocks
• forest fires
• emissions of previously deposited mercury by biologic processes (e.g., vaporization of mercury from water bodies after biologic conversion to methylmercury)

Note: Percentages were obtained from Table 3-1 of the U.S. Environmental Protection Agency "Mercury Study: Report to Congress, Volume I, Executive Summary," 1997.

Additional source of information: U.S. Geological Survey, "Mineral Commodity Summaries: Mercury," February 2000.