Releases of Elemental Mercury
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Mercury is a highly toxic element that is found both naturally and as a contaminant that is introduced to the environment. Forms of mercury include elemental or metallic mercury , organic mercury, and inorganic mercury.

Elemental (or metallic) mercury, which is contained in items including thermometers and barometers, is a silver-gray metal that is a liquid at room temperature. Due to its high surface tension, it forms small compact spherical droplets when released. These droplets are stable, but the high vapor pressure of mercury results in volatilization into mercury vapors. In addition to thermometers and barometers, elemental mercury is or has been found in thermostats, sphygmomanometers, dental amalgams, batteries, fluorescent lights and electrical switches. It was also commonly found in household latex paint prior to the early 1990s (Illinois Department of Health).

The risk of mercury to human health is determined by the route of exposure, the form of mercury, and the geochemical and ecological factors that influence how mercury moves and changes form in the environment. If elemental mercury is ingested, it is absorbed relatively slowly and may pass through the digestive system with a minimal amount of absorption, making toxicity from this route of exposure rare. Inhalation of elemental mercury is the most common route of exposure.

Several federal governmental agencies have established limits for various types of exposures to mercury, including those that deal with the chronic exposure of workers in industries that use mercury or mercury-containing devices, and effects of acute exposure such as those associated with a mercury spill. Inhalation exposure limit standards, guidelines, and action levels have been established by various agencies. Although no standards exist for residential exposures and no standards exist for exposures in environments such as schools, the Agency for Toxic Substances and Disease Registry (ATSDR) typically considers mercury vapor concentrations of 1,000 nanograms per cubic meter (ng/m3) (and lower) to satisfy the safety requirements for airborne mercury exposure for long-term exposures as would likely occur in a residence or other places where people would tend to spend a significant amount of time (ATSDR, 1999).