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Why Is Mercury Important?

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What Is Mercury?

Mercury, also known as quicksilver because it is a silver-colored liquid at room temperature, is an element that does not break down. It occurs naturally and is found in very small amounts in oceans, rocks and soils. It becomes airborne when rocks erode, volcanoes erupt and soil decomposes. It then circulates in the atmosphere and is redistributed throughout the environment. Large amounts of mercury also become airborne when coal, oil or natural gas is burned as fuel or mercury-containing garbage is incinerated. Once in the air, mercury can fall to the ground with rain and snow, landing on soils or water bodies, causing contamination.

Mercury Cycle

Lakes and rivers are also contaminated when there is a direct discharge of mercury-laden industrial waste or municipal sewage. Once present in these water bodies, mercury accumulates in fish and may ultimately reach the dinner table.

Although mercury has been a very useful element, due to its unique properties, it poses a very real health risk-from direct exposure to mercury, as well as from eating contaminated fish. We can minimize this risk by reducing our use of mercury-containing products and properly disposing of mercury-containing waste.

How Is Mercury Released from Human Activities?

Mercury has been used for hundreds, if not thousands, of years for a wide variety of purposes. Historical uses, which are no longer prevalent, include: preparing felt for hats, controlling mildew in paints, killing weeds as a component of herbicides, and various medical uses-teething powder, antiseptic ointments and syphilis treatment. Its toxic effects on workers in hat factories in the late 1800's led to the term "mad as a hatter." Mercury is still used for folk medicine and ceremonial purposes in several cultures.

Today, mercury is released to the environment from many sources. It is still used in household and commercial products, as well as industrial processes. Coal-fired power plants, incinerators, some manufacturing plants, hospitals, dental offices, schools and even homes have all been found to release mercury. In the home, mercury can be found in fluorescent lights, thermostats, thermometers, and even some children's toys. At school, mercury may be in science and chemistry classrooms, the nurse's office and electrical systems.

Click here to see a demonstration on how mercury is vaporized.

Mercury Health Issues

Two different forms of mercury are of greatest human health concern. Elemental mercury, which is most toxic in its vapor form, slowly vaporizes at room temperature and more quickly when heated. Breathing the invisible vapor from mercury spilled in carpeting, furniture or other surfaces can seriously poison children playing with or near elemental mercury.

Mercury easily enters the body through several routes, but it may take many months for the body to purge itself of the poisonous metal. Mercury vapors can be breathed - among the most hazardous exposures to elemental mercury. Handling the liquid metal also allows mercury to enter the body through pores of the skin. Mercury leaves the body mostly through the urinary and digestive tracts.

Elemental and inorganic mercury salts can be transformed into organic mercury by the bacteria in the bottom mud in water bodies. Unlike elemental mercury, organic mercury (often referred to as "methylmercury") can be readily absorbed in humans. The most likely source of methylmercury is eating contaminated fish. Human exposure to methylmercury can result in long-lasting health effects, especially on fetal development during pregnancy. In addition, mercury poisoning has been linked to nervous system, kidney and liver damage and impaired childhood development. Nervous system disorders include impaired vision, speech, hearing and coordination.

Symptoms of Mercury Poisoning:
  • Impairment of the peripheral vision
  • Disturbances in sensations ("pins and needles" feelings, numbness) usually in the hands feet and sometimes around the mouth
  • Lack of coordination of movements, such as writing
  • Impairment of speech, hearing, walking;
  • Muscle weakness
  • Skin rashes
  • Mood swing
  • Memory loss
  • Mental disturbance

Mercury in the Environment

Mercury is an environmental problem around the world. States with many lakes are especially aware of this because one of the most serious ways people are exposed to mercury is through eating contaminated fish.

Organic mercury tends to increase up the food chain, particularly in lakes. The mud at the bottom of a lake may have 100 or 1000 times the amount of mercury than is in the water. Worms and insects in the mud extract and concentrate the organic mercury. Small fish that eat these critters further concentrate the mercury in their bodies. This concentration process, known as "bioaccumulation", continues as larger fish eat smaller fish until the top predator fish in the lake have methylmercury levels in their tissues that are up to 1,000,000 times the level in the water in which they live.


Over 40 states in the U.S. and several Canadian provinces advise anglers and their families to reduce their consumption of certain types of fish taken from various lakes and streams due to their high mercury content. Certain types of store bought fish also have elevated mercury levels, including swordfish and tuna.


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Last revised: July 15, 2004