21.3 SOURCES
Mercury is emitted to the atmosphere by “degassing” of the earth’s surface and by resuspension
of mercury-containing particles previously deposited. Emissions from volcanoes and other
natural sources are estimated to constitute about 1000 tons per year (UNEP, 2002). An
additional annual emission of about 2500 tons comes from anthropogenic sources, the major
source being energy production from fossil fuels, especially coals with high mercury contents
(UNEP, 2002). Mercury is produced by the mining and smelting of cinnabar ore. It has been
extensively used in chloralkali plants (producing chlorine and sodiumhydroxide), butmodern
plant designs have now made large stores of mercury unnecessary. A myriad of mercurycontaining
products have been in use, including compounds in paints as preservatives or
pigments, in electrical switching equipment and batteries, inmeasuring and control equipment
(thermometers and othermedical equipment), inmercury vacuuminstruments, as a catalyst in
chemical processes, inmercury quartz and luminescent lamps, in the production and use of high
explosives usingmercury fulminate, in copper/silver amalgams in dental restorationmaterials,
andas fungicides in agriculture (especially as seed dressings).Many of these uses are nowbeing
banned or phased out.According to data fromtheU.S. EPA, these efforts have been beneficial,
as overall mercury emissions from industrial use in the United States have dropped 45%since
1990, and are still decreasing.