Mercury or "quicksilver," is a shiny liquid metal that is a widespread environmental contaminant. It is fairly toxic, though the metallic mercury is less so. Especially a problem is methyl or ethyl mercury, or mercuric chloride, which is very poisonous.
Modern humans have much higher body levels of mercury than did our ancestors, because of its greater use in recent times. It has been used for more than 2,000 years. Nowadays, mercury is employed daily by medical and dental practices in thermometers, drugs (more so in the past), and amalgam for fillings; by agriculture in fungicides and pesticides; and by the cosmetics industry. Mercury in industrial waste has polluted our waters and contaminated our fresh- and salt-water plants and fish.
In the 1950s, Minamata Bay in Japan was poisoned with industrial mercury; it was measured in the waters at between 5 and 15 ppm, about 20 times normal. Many people experienced serious nervous system symptoms, staggering, and even comas and death before the pollution was discovered. In the early 1970s, the "mercury in the fish" scare spread across the United States. Swordfish, tuna, and other large fish were the subjects of concern, and, in some areas, were measured with higher than acceptable levels of mercury. Caused by industrial contamination, the problem was not as widespread as the concern. Currently, most fish do not contain toxic or problematic levels of mercury, though further contamination could certainly raise the possibility.
Today, the average person's body contains about 10-15 mg. of mercury. We obtain some daily from food, air, and water. Mercury is poorly absorbed from the intestinal tract, about 5-10 percent. Inhaled mercury fumes go into the blood, as mercury is soluble and passes through the lungs. Some mercury is retained in body tissues, mainly in the kidneys, which store about 50 percent of the body mercury. The blood, bones, liver, spleen, brain, and fat tissue also hold mercury. This potentially toxic metal does get into the brain and nerve tissue, so central nervous system symptoms may develop. Mercury can also get into a growing fetus and into breast milk. But mercury is also eliminated daily through the urine and feces. Hair tissue analysis is the best way to measure body stores of mercury, while urine levels will show whether the body is actively working to eliminate it.
Sources: Mercury is widely used in industry, agriculture, and health care. Even though hat makers are safer and saner these days since the mercury used for the felt linings of hats was reduced, there are still people walking about "mad as a hatter" from mercury. Common uses of mercury include:
Fungicides and pesticides. These are a large source, used worldwide to treat grains and seeds. Methyl mercury is the most common form here.
Cosmetics. Mercury is added to decrease bacterial growth.
Dental fillings. Mercury is widely used, though many dentists no longer employ the silver-mercury amalgam, as they feel that it leads to a variety of problems. The American Dental Association, however, still claims that there is no proven mercury toxicity due to dental amalgams.
Medicines. Organic mercurial diuretics have been the most common, though these are less used these days. Mercury-containing cathartics, anthelminetics, and teething powders were also employed in the past. Broken thermometers can increase mercury exposure, and mecurochrome also contains mercury.