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.

Coal burning. This releases mercury into the atmosphere.

Fish. Fish may contain varying amounts of mercury. Ocean bacteria, algae, and small fish may all contain some; mercury concentrations usually increase with the size of the fish. An excessive intake of fish foods may lead to increased body levels of mercury.

Other sources of mercury are mirrors, latex paints, fabric softeners, felt, floor waxes and polishes, sewage sludge, laxatives containing calomel, cinnabar jewelry, tatoo dyes, and many others. Most of these are not specifically mercury toxic, as they do not give off high amounts of volatile mercury. Fungicides are the most widely used and probably the most potentially toxic.

Methods of toxicity: Mercury has no known essential functions, though it was at one time used to treat syphilis, with some success. Mercury probably affects the inherent protein structure which may interfere with functions relating to protein production. Mercury has a strong affinity for sulfhydryl, amine, phosphoryl, and carboxyl groups, and inactivates a wide range of enzyme systems, as well as causing injury to cell membranes. However, none of mercury’s specific body interactions are clearly defined, though the main problems seem to result from its attack on the nervous system. Mercury may also interfere with some functions of selenium, and can be an immunosuppressant.

Symptoms of toxicity: There are many processes and symptoms of mercury toxicity. Poisoning can come from four categories of mercury: metallic or elemental mercury, which is relatively mild; inorganic mercury, such as mercury chlorides, which primarily affect the kidneys; organo-mercurials, such as mercury salts in diuretics or fungicides, which convert to inorganic mercury; and short chain alkyl mercury compounds, of which methyl mercury is the most toxic, more so than ethyl or diethyl mercury.

Acute symptoms are caused mainly by mercuric chloride or methyl mercury exposure. Chronic, lower level exposure may lead to specific acute symptoms or to subtle renal and nervous system problems. Inhaled mercury has a different effect differently than ingested mercury, for which most symptoms are related to the gastrointestinal tract and the nervous system. Inhaling high levels of metallic mercury (in an industrial setting or a dentist’s office) can cause acute symptoms, such as fever, chills, coughing, and chest pain. With low, long-term exposure, more subtle symptoms such as fatigue, headache, insomnia, nervousness, impaired judgment and coordination, emotional liability, and loss of sex drive, may be experienced. Ingested mercury may cause stomatitis and gastrointestinal inflammation, with nausea, vomiting, abdominal pain, and bloody diarrhea, progressing to neurological problems. These symptoms, which are often confused with psychogenic causes, are referred to as “micromercurialism.”

Mild or early symptoms of mercury intoxication include fatigue, insomnia, irritability, anorexia, loss of sex drive, headache, and forgetfulness or poor memory. This may lead to other nervous system symptoms, such as dizziness, tremors, incoordination, and depression; then progress to numbness and tingling, most commonly of the hands, feet, or lips; and to further weakness, worse memory and coordination, reduced hearing and speech, paralysis, and psychosis. Mercury toxicity may be a factor in multiple sclerosis. Other problems of severe mercury intoxication are kidney and brain damage, as well as birth defects in pregnant women. Luckily, these extreme symptoms are unusual. However, the subtle and nervous system symptoms from low-level chronic exposure may be more common than we realize.

Amounts leading to toxicity: The average intake of mercury varies with location and diet. It may range from 10 mcg. to more than 500 mcg., mainly depending on air contamination. Industrial cities and heavily sprayed farmland have the highest levels. The average overall daily intake is probably about 30-50 mcg. Most humans can process at least that much daily without any problems.

Blood levels of mercury should be below .02 ppm, while hair levels may be higher, up to about 3-5 ppm. More than 5 ppm becomes a concern. When these levels are exceeded, we should look for the sources of increased exposure and work toward avoiding or eliminating them.

Who is susceptible? Anyone working with mercury, especially methyl or ethyl mercury or mercuric chloride, is more likely to have problems of mercury toxicity. Farmers using mercury products should be very careful with them and should be aware of mercury toxicity symptoms or have mercury levels checked every couple of years.

Treatment of toxicity: Drinking milk helps reduce the acute effects of mercury, as the mercury will act on the protein in the milk instead of on the stomach and intestinal lining. This may prevent the acute symptoms of gastrointestinal tissue irritation, such as vomiting and bleeding.

Penicillamine is a chelating drug that can pull mercury out of the circulation. It works best when given soon after exposure, rather than after tissue storage occurs. Penicillamine itself, however, is potentially toxic. Dimercaprol (BAL) has also been used. EDTA,

Occupations with Potential Mercury Exposure

Barometer and thermometer makers
Ink makers
Dentists and dental workers
Paint makers
Dental amalgam makers
Neon light makers
Mirror makers
Paper makers
Insecticide makers
Dye makers
Pesticide workers
Explosives and fireworks makers
Wood preservative workers

a stronger chelating agent, can also be used to pull out body mercury. It usually has fewer side effects than penicillamine. Vitamin C, selenium, and the fibers pectin and algin may also reduce mercury levels and toxicity, though usually only in cases of less severity.

Prevention: Avoidance of mercury contamination is foremost in preventing mercury toxicity. Staying clear of mercury fungicides and avoiding fungicide-treated foods or eating only organically grown grains and produce may be helpful. Many health-oriented dentists now avoid mercury-containing amalgam to prevent further mercury exposure. Silver-mercury fillings during pregnancy, I believe, should be avoided.

Pectin and algin can decrease absorption of mercury, especially inorganic mercury. Selenium binds both inorganic and methyl mercury; mercury selenide is formed and excreted in fecal matter. Selenium is, for many reasons, an important nutrient for all of us, and in an amount of at least 100-200 mcg., it does seem to protect against heavy metal toxicity.

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Elson M. Haas MD Written by Elson M. Haas MD

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