Mercury, a nerve poison, is a major ingredient in many products - from thermometers and fluorescent bulbs to batteries and old latex paint. Although even mercury in its elemental form is toxic, its most poisonous embodiment is methyl mercury, the result of a chemical modification by bacteria.

Methyl mercury comes in two forms: mono- and dimethyl-mercury, with the latter being the more toxic.

Mercury is found naturally in the environment in several forms. In its elemental form, mercury is a shiny, silver-white, liquid metal used in thermometers and some electrical switches. It can be combined with other elements to form inorganic compounds.

Mercury can evaporate to form colorless, odorless mercury vapors. It can combine with organic material to form organic compounds such as methyl mercury, which is produced primarily by bacteria and is the form which poses the greatest concern for environmental exposure.

1. Elemental (metallic) Mercury: The shiny, silver, odorless liquid used in thermometers. It is absorbed by the body through vapors.

2. Organic Mercury: Mercury combined with carbon. Methyl mercury is a common form of organic mercury. These forms of mercury are soluble in lipids and cross the blood brain barrier and placenta easily. Organic mercury is absorbed through the digestive tract and also through vapors.

3. Inorganic Mercury: Mercury combined with non-carbon substances. Mercury salts are one kind of inorganic mercury. Inorganic mercury is usually a white powder or crystals. This form of mercury has been used in medicines.

Did you know? Mercuric nitrate was used by the felt-hat industry to cure felt. People in the felt-hat industry sometimes showed neurological symptoms of mercury poisoning, then named "Mad-Hatter" syndrome. This is where the phrase "mad as a hatter" originated and was the basis for the "Mad Hatter" character in Lewis Carroll's book Alice in Wonderland.


Handling liquid mercury for a very short period of time usually does not result in any problems. An allergic rash is possible, though. Mercury is not well absorbed across the skin so skin contact is not likely to cause mercury poisoning, especially with a brief one-time exposure. Even if a person has cuts in their skin, mercury is too heavy to be contained by a cut. Merely washing the wound well will wash the mercury out of the wound.

Modes of Exposure
Inhalation of mercury fumes.

Absorption of mercury through the skin. (A common route of skin exposure is when one cleans up broken glass thermometers containing mercury without taking safety precautions)

Consumption of objects that contain, or have been contaminated by mercury. Broken high power lights and long fluorescent tubes can also contain mercury. Small amounts of mercury from these sources may be ingested accidentally.

Consumption of food (especially fish) or drink water that has been contaminated by mercury. Mercury is absorbed by fish through their gills. It also makes its way up the food chain when fish eat plankton or smaller fish that are already contaminated. Fish that are commonly found with high levels of mercury include shark, swordfish and large tuna. The U.S. Food and Drug Administration has set a limit on the amount of mercury (1 part per million) that cannot be exceeded in fish intended for human consumption.

Mercury Exposure : The World’s Toxic Time Bomb

Mercury : Tiny Drops that Kill; Toxics Link Factsheet