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Methylmercury Contamination in Fish and Shellfish
(Released February 2007)

 
  by Laura Griesbauer  

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Mercury and Its Sources

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Human exposure to mercury begins with the production of many useful products. As the only metal on Earth that can be found in a liquid form at room temperature, mercury and mercury compounds have many uses. Due to its special properties, including high density and high rate of thermal expansion, mercury is often used in barometers and thermometers. It can also be combined with other metals to create special alloys called amalgams. Gold and silver amalgams have been used in dentistry for fillings and tin amalgams are used to make mirrors. Mercury can be found in many different lamps, including "black lights," and is used in the industrial production of chloride and sodium hydroxide (Environment Canada, 2004). Some mercury compounds are used as ingredients in skin creams, antiseptics, diuretics, fungicides, insecticides, and as a preservative in vaccines. Mercury compounds were even once used in the treatment of syphilis (Clarkson & Magos, 2006).

industrial area
View of the Electrochemical factory at Skoghall, Sweden. The chloralkali, chlorine condensation and lye evaporation section are visibile

chart
Mercury Emissions
While some of these compounds are fairly inert, many mercury compounds are extremely toxic. In the U.S., some products containing mercury have been banned, have usage limits, or have special disposal requirements. These include dental fillings, vaccines, non-industrial thermometers, lamps, car starters, and electronics. There are also many regulations regarding the disposal of mercury wastes (EPA, 2006).

One form of mercury that is toxic and very harmful is elemental mercury. It is highly volatile and can easily be converted to mercury vapor, exposure to which can damage the nervous system, lungs, and kidneys. This type of exposure generally only happens to industrial workers directly handling mercury compounds. They are exposed either by inhaling mercury vapor or through chronic contact with volatile inorganic mercury compounds. For most people, exposure to mercury occurs when they eat fish or shellfish contaminated with methylmercury, an organic mercury compound. This compound is found in nearly all freshwater and marine fish (EPA, 2006). Methylmercury has the ability to be absorbed by the digestive tract and enter the blood stream, which, over time, can result in damage to the nervous system.

products that have mercury
Mercury vapor is emitted to the atmosphere through both natural and anthropogenic sources. Natural sources of mercury vapor include volcanoes, as well as rocks, soils and water surfaces. Mercury is also found naturally in cinnabar, the major ore for the production of mercury. Anthropogenic sources of mercury vapor include emissions from coal-burning power plants, municipal incinerators, and through the recycling of automobiles (Clarkson & Magos, 2006). It is estimated that 50 to 70 percent of the total emission of mercury to the environment is a result of human activity. About 1,000 tons of mercury per year is emitted to the atmosphere by natural sources, while more than twice as much, about 2,600 tons, is emitted from anthropogenic sources (Honda et al., 2006). Mercury emitted from all these sources is then cycled through the ecosystem.

Go To Mercury in the Environment

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