Mercury can cause acute or chronic poisoning. Metallic mercury is not dangerously poisonous in very small doses: The child who bites through a clinical thermometer and swallows a few drops of the metal will probably come to no harm. However, mercuric chloride ingestion, either intentional or accidental, results in acute poisoning. The initial symptoms are nausea, vomiting, diarrhea, and abdominal pain. Cardiovascular collapse may occur after several hours.

Chronic mercury poisoning is most often due to occupational exposure or to industrial pollution of the environment. Depending on the amount and length of exposure and the age of the victim, symptoms include weakness, tremors, progressive incoordination, and paralysis. Numbness in the fingers and toes is an early sign of poisoning. Mental changes include lethargy and intellectual dullness.

Mass outbreaks of chronic mercury poisoning have occurred in the past few decades: Minamata disease in Japan was due to contamination of fish by industrial effluent. More recently, industrial contamination of fishing lakes in northern Quebec caused an epidemic of mercury poisoning, and in several countries there have been epidemics of mercury poisoning resulting from the human consumption of chemically treated wheat seed.

A metallic pool sat in the palm of my hand, glittering silver. A slow waterfall of heavy silver ball bearings tumbled from the crease in my palm, bouncing and rolling crazily across my black desktop.

When I later found out how poisonous the metal named for the speedy Roman messenger god is, I was horrified. I'd played with the stuff, bouncing tiny beads of it between my fingertips.

Mercury's huge atoms can cause tremendous damage to living tissues, especially in the nervous system—hanging around for a long time like a particularly tenacious bull in a china shop.

Luckily for me, mercury is not terribly dangerous in its typical, metallic form. This is principally because, at body temperature, mercury is fairly stable. Metallic mercury does not thus readily absorb through skin or digestive system (although it is not 100% safe to ingest, as some minute quantities will likely enter the bloodstream).

Mercury salts or mercury vapor, on the other hand, are quite dangerous. In salts, mercury quickly absorbs into the body and in gaseous form the metal will enter the bloodstream with incredible speed. Mercury salts, such as acetate, sulfate and mercuric chloride, are common in certain industries and may sometimes enter food animals and plants through industrial pollution. The mercury ions thus present in the circulatory system are thus free to wreak havok wherever they may land. Mercury is a cumulative toxin, with very long residency time in the bloodstream and tissues, so that repeated exposure to even minute quantities can cause damage in the long term.

Historically, this was a big problem for hat makers, alchemists, metal smelters (particularly those who worked with lead and/or silver, two metals often found with mercury) and chemists.

Reworked and revised: 9/6/07
Dr. Joseph F. Smith Medical Library online -
Taber's Cyclopedic Medical Dictionary, 19th edition (FA Davis, Philadelphia, 1997).

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