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Frequently Asked Questions about Mercury and Thimerosal
What is mercury? Metallic mercury is a shiny, silver-white metal that is a liquid at room temperature. Metallic mercury is the elemental or pure form of mercury (i.e., it is not combined with other elements). Metallic mercury metal is the familiar liquid metal used in thermometers and some electrical switches. At room temperature, some of the metallic mercury will evaporate and form mercury vapors. Mercury vapors are colorless and odorless. The higher the temperature, the more vapors will be released from liquid metallic mercury. Some people who have breathed mercury vapors report a metallic taste in their mouths. Metallic mercury has been found at 714 hazardous waste sites nationwide. Inorganic mercury compounds occur when mercury combines with elements such as chlorine, sulfur, or oxygen. These mercury compounds are also called mercury salts. Most inorganic mercury compounds are white powders or crystals, except for mercuric sulfide (also known as cinnabar) which is red and turns black after exposure to light. When mercury combines with carbon, the compounds formed are called "organic" mercury compounds or organomercurials. By far the most common organic mercury compound in the environment is methylmercury. Methylmercury is of particular concern because it can build up in certain edible freshwater and saltwater fish and marine mammals to levels that are many times greater than levels in the surrounding water. Thimerosal is an organic mercury compound that is metabolized to ethylmercury and thiosalicylate (Institute of Medicine, 2001). For more information, visit the Agency for Toxic Substances and Disease Registry's Public Health Statement for Mercury. How are recommended limits for mercury exposure established? Recommended limits on methylmercury exposure are not “set lines” below which there is safety and above which adverse health effects will occur immediately (Mahaffey, 1999). A significant safety margin is incorporated into all acceptable mercury exposure limits. Such guidelines are meant to be starting points for evaluation of mercury exposure, and should not be viewed as absolute levels above which harm can be expected to occur. What happens if your exposure exceeds the recommended levels? It is important to keep in mind that being exposed to more than the recommended mercury limits does not necessarily mean you will experience adverse health effects. A significant safety margin is incorporated into all acceptable mercury exposure limits; they should not be viewed as absolute levels above which harm can be expected to occur. Who is most vulnerable to mercury? How can mercury affect children? If a pregnant woman ingests mercury at high levels, harmful effects that may be passed from the mother to the developing fetus include brain damage, mental retardation, lack of coordination, blindness, seizures, and an inability to speak. Children poisoned by mercury may develop nervous and digestive system problems and kidney damage. What is thimerosal? Today, according to the U.S. Food and Drug Administration, the only vaccines routinely recommended for children 6 years of age and younger that contain thimerosal are: one vaccine for DTaP, and three vaccines for influenza (flu). These four vaccines contain only trace amounts of thimerosal. Is the mercury in thimerosal the same as the kind found in certain fish? References Please see References for a list of data sources for this information.
Page last reviewed: September 24, 2008
Page last updated: October 22, 2007 Content source: Immunization Safety Office | ![]() |
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