Mercury is a naturally occurring element. Its distribution in the environment is the result of both natural and man-made processes. There are three categories of mercury with unique characteristics and unique potential health effects:
- Elemental or metallic mercury
- Organic mercury compounds
- Inorganic mercury compounds
Not all forms are encountered by the general public. The forms most likely encountered by the general public are:
- Elemental mercury vapor (Hg0) from metallic mercury or liquid mercury - This 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.
- Methylmercury - Microorganisms in the environment can convert inorganic mercury to the organic form methylmercury. This form can build up in the environment and accumulate in certain freshwater and saltwater fish, and marine mammals. Methylmercury is the form of mercury that is most likely to cause adverse health effects in the general population.
- Ethylmercury - This 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.
- Inorganic mercury (mercuric salts) - This is an oxidized mercury that combines with other chemical elements to create salt forms.
For more information about mercury exposure, please visit the Chemical Agent Briefing Sheet on Mercury page.