revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY
1. PUBLIC HEALTH STATEMENT
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. There is a potentially large number of organic mercury
compounds; however, by far the most common organic mercury compound in the environment is
methylmercury (also known as monomethylmercury). In the past, an organic mercury compound
called phenylmercury was used in some commercial products. Another organic mercury
compound called dimethylmercury is also used in small amounts as a reference standard for some
chemical tests. Dimethylmercury is the only organic mercury compound that has been identified
at hazardous waste sites. It was only found in extremely small amounts at two hazardous waste
sites nationwide, but it is very harmful to people and animals. Like the inorganic mercury
compounds, both methylmercury and phenylmercury exist as "salts" (for example, methylmercuric
chloride or phenylmercuric acetate). When pure, most forms of methylmercury and
phenylmercury are white crystalline solids. Dimethylmercury, however, is a colorless liquid.
Several forms of mercury occur naturally in the environment. The most common natural forms of
mercury found in the environment are metallic mercury, mercuric sulfide (cinnabar ore), mercuric
chloride, and methylmercury. Some microorganisms (bacteria and fungi) and natural processes
can change the mercury in the environment from one form to another. The most common organic
mercury compound that microorganisms and natural processes generate from other forms is
methylmercury. Methylmercury is of particular concern because it can build up in certain edible
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