Mercury is a naturally occurring element that is found in air, water and soil. It exists in several forms: elemental or metallic mercury, inorganic mercury compounds, and organic mercury compounds. Elemental or metallic mercury is a shiny, silver-white metal and is liquid at room temperature. It is used in thermometers, fluorescent light bulbs and some electrical switches. When dropped, elemental mercury breaks into smaller droplets which can go through small cracks or become strongly attached to certain materials. At room temperature, exposed elemental mercury can evaporate to become an invisible, odorless toxic vapor. People can be exposed to elemental mercury vapor when products that contain mercury break and expose mercury to the air, particularly in poorly-ventilated spaces.
Inorganic mercury compounds take the form of mercury salts and are generally white powder or crystals, with the exception of mercuric sulfide (cinnabar) which is red. Inorganic mercury compounds have been included in products such as fungicides, antiseptics or disinfectants. Some skin lightening and freckle creams, as well as some traditional medicines, can contain mercury compounds.
Organic mercury compounds, such as methylmercury, are formed when mercury combines with carbon. Microscopic organisms convert inorganic mercury into methylmercury, which is the most common organic mercury compound found in the environment. Methylmercury accumulates up the food chain.
Mercury can be released in the environment from natural sources, such as volcanic and geothermal activity, marine environments or forest fires, or it can be released from anthropogenic (man-made) sources like coal-fired power plants and other industrial activities. Recent studies suggest that human activity contributes 50-70% of the mercury in the environment globally (EPA Office of Air Quality and Standards Report to Congress, 1997). Once mercury enters the environment, it circulates in and out of the atmosphere until it ends up in the bottoms of lakes and oceans. Mercury is among a group of pollutants called persistent bioaccumulative toxins or PBTs. These pollutants "persist" in the environment, meaning that they do not break down or go away. Mercury cannot be destroyed, it cannot be combusted, and it does not degrade. Mercury also "bioacccumulates" in the environment, meaning it builds up in the food chain over time.
- Get more information from the ATSDR Web site.
When mercury is deposited in waterways, bacteria convert it to methylmercury. Methylmercury builds up in the tissue of fish, which may then be eaten by wildlife (e.g., eagles, osprey, common loons, river otters, minks) and by people. Because mercury is tightly bound to the fish muscle tissue, there is no method of cooking or preparation that will remove or reduce mercury once it is in fish. This doesn't mean that you should stop eating fish. It is a good source of protein and is low in saturated fat. You can still get the benefits of eating fish by using moderation in how much you eat. The two organ systems most likely affected by methylmercury are the central nervous system and the kidneys. The groups most vulnerable to the effects of mercury toxicity include women who are pregnant or may become pregnant, nursing mothers, and young children. The most significant concerns regarding chronic exposure to low concentrations of methylmercury in fish are for neurological effects in the developing fetus and children.
Although human exposure to mercury occurs most frequently through eating contaminated fish, other human exposures to mercury can occur. People have been exposed to mercury from inhaling mercury vapors from broken fluorescent lamps, gas regulators, or even home fever thermometers. There have been cases of mercury exposures from accidental swallowing, but these cases are rare.
- Get more information from the ATSDR Web site.
Mercury (Hg) is a naturally occurring metal found throughout the environment. It is a liquid at room temperature, combines easily with other metals and expands and contracts evenly with temperature changes. Because of these properties, mercury has been used in many household, medical and industrial products. Although mercury performs many useful functions in our workplaces and homes, it is toxic and can impair our health. Mercury is a potent neurotoxin, meaning that it interferes with the way nerve cells function. Mercury poisoning causes a decreased ability to see, hear, talk and walk. It can cause personality changes, depression, irritability, nervousness, and the inability to concentrate. It can also cause damage to the brain, kidneys, and lungs. Mercury is a particularly serious problem for pregnant women and children. Fetuses and young children suffer the greatest risk because their nervous systems are still developing. They are four to five times more sensitive to mercury than adults.
- ATSDR Web Site
- Fish Species and Waterbodies Affected by this Contaminant
- Frequently Asked Questions about Mercury (from the EPA Web site)
- Mercury Advisory for Pregnant Women and Small Children
- Three Safety Tips for Selecting and Eating Fish or Shellfish