Mercury Background

Mercury is a naturally occurring element. Its distribution in the environment is the result of both natural and man-made processes. People don’t usually come in contact with all forms of mercury. There are two general categories of mercury:

1. Inorganic mercury  - This is an ionized form of mercury that combines with other chemical elements to create salt forms. These salts have been used in medicines and cosmetics as well as industrial applications.
   • Elemental mercury vapor (Hg0) from metallic mercury or liquid mercury is the elemental or pure form of mercury; i.e., it is not combined with other elements. It is the primary form of mercury released into the air by natural processes, such as volcanic activity. It is used to measure pressure and temperature, as well as in electric switches. Elemental mercury is used in a number of industries, including the chloralkali and formaldehyde synthesis processes. It is generally the form of mercury that falls from the atmosphere and is turned into methylmercury by microorganisms.
2. Organic mercury - Microorganisms in the environment can convert inorganic mercury to organic forms, most commonly methylmercury.
   • Methylmercury is the form of mercury that the general population is most likely to encounter. This form can build up in the environment and accumulate in certain freshwater and saltwater fish, and marine mammals. Fish eating birds also accumulate methylmercury primarily, and are another way that people can come in contact with mercury.
   • Ethylmercury is an organic form of mercury found in some medical preservatives. Also used in some parts of the world as an antifungal agent in grains. 

For more information about mercury exposure, please visit the Toxic Substance Portal page on Mercury and the Mercury and Your Health website.