Dec 20, 2004: Why is elemental mercury not toxic when ingested, but potentially toxic when spilled?

Mercury is a naturally occurring metal that is mined chiefly as cinnabar ore.  It is converted into elemental mercury, inorganic mercury salts, and organic mercury.  This discussion will address the ingestion and inhalation of elemental mercury.  The other forms will be addressed in a later question.

Elemental mercury is part of the earth’s crust and is released into the environment thru mining and industrial discharge.  Thermometers contain elemental mercury.  When ingested, elemental mercury is poorly absorbed from the intact GI tract.  (Therefore, low toxicity) 

Due to a very low vapor pressure, metallic mercury can evaporate slowly at room temperature or rapidly when heated.  A small spill in an enclosed space can produce high levels of mercury in the air.  When inhaled, most of the mercury vapor crosses the alveolar membrane and is absorbed into the circulation.  The absorbed elemental mercury vapor diffuses into the RBCs and tissues, undergoes oxidation to the mercuric ion, and binds to ligands in the RBC.  A certain amount persists in the plasma, crosses the blood-brain barrier, becomes oxidized to the mercuric ion and is trapped in the CNS.

CNS and pulmonary system are the primary target organs systems of inhaled elemental l mercury. Mercury vapor acts as an airway irritant and cellular poison.  Alveolar and interstitial pneumonitis , emphysema, and pneumatocele formation may occur.  In the CNS, mercuric ion has an affinity to bind to cellular proteins causing pathologic alteration of cellular membranes.  Chronic intoxication from inhalation causes gingivostomatitis, tremor, and neuropsychiatric disturbances such as insomnia, anorexia, memory dysfunction, mood change, irritability, timidity and paranoia.

One of the main concerns of toxicity is when the mercury in thermometers is spilled in a bedroom and then vacuumed.  Each time the mercury is vacuumed, mercury vapor will be released in the air, and eventually cause CNS toxicity.  The mercury should be pushed onto cardboard and discarded appropriately (all the public health dept for locations).  If all the mercury cannot be removed, or the carpet is shag or has a deep nap,  the carpet should be removed.  The Public Health Department can arrange for mercury concentrations of the air, if necessary.

(A couple of years ago,  teens were placing elemental mercury into a hot frying pan to watch it bounce.  This is not a good idea-they were inhaling the mercury vapor as they leaned over the frying pan to watch it.  Significant toxicity can occur as a result of such endeavors.)


Thanks to Dr. Preston Stein for the question about the differing toxicity of mercury.

I am also attaching the “Holiday Hazard” question from last year.


As always, if there are any questions, call the Tennessee Poison Center at 1-800-222-1222.


I am interested in any questions that you would like answered in “Question of the Week.”  Please email me with any suggestions at


Donna Seger, M.D.

Medical Director, Tennessee Poison Center