Mercury Information

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What is Mercury?

Mercury is a naturally-occurring chemical element found in rock in the earth's crust, including in deposits of coal.  On the periodic table, it has the symbol "Hg" and its atomic number is 80.   It exists in several forms:

  • methylmercury and other organic compounds,
  • elemental (metallic) mercury, and
  • inorganic mercury compounds.

Methylmercury and other organic mercury compounds are formed when mercury combines with carbon. Microscopic organisms convert mercury into methylmercury, which is the most common organic mercury compound found in the environment. 

Elemental or metallic mercury is a shiny, silver-white metal and is liquid at room temperature. It is used in older thermometers, fluorescent light bulbs and some electrical switches. When dropped, elemental mercury breaks into smaller droplets which can go through small cracks or become strongly attached to certain materials. At room temperature, exposed elemental mercury can evaporate to become an invisible, odorless toxic vapor. If heated, it is a colorless, odorless gas.  

Elemental mercury is an element that has not reacted with another substance. When mercury reacts with another substance, it forms a compound.

Inorganic mercury compounds take the form of mercury salts and are generally white powder or crystals, with the exception of mercuric sulfide (cinnabar) which is red. Most uses of inorganic compounds have been discontinued.


Health Effects Associated with Exposures to Mercury

  • Mercury exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages.
  • High levels of methylmercury in the bloodstream of babies developing in the womb and young children may harm their developing nervous systems, affecting their ability to think and learn.


Ecological Effects of Mercury Exposure

Birds and mammals that eat fish are have more exposures to methylmercury than other animals in water ecosystems. Predators that eat these birds and mammals are also at risk. Methylmercury has been found in eagles, otters, and endangered Florida panthers. At high levels of exposure, methylmercury's harmful effects on these animals include:

  • death,
  • reduced reproduction,
  • slower growth and development, and
  • abnormal behavior. 


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