Mercury is a naturally occurring metal in the Earth's crust. It has been used in products including auto parts, fluorescent light bulbs, agricultural fungicides, paints, batteries, thermometers, dental amalgams and as a vaccine preservative. Many uses of mercury, including as a vaccine preservative, have declined or have been completely phased out in the United States. Acute and chronic mercury toxicity affects multiple organ systems and the symptoms are dependent on the severity of exposure and the chemical form of mercury.
Forms of Mercury
Mercury occurs in three forms: elemental, inorganic compounds and organic compounds. Elemental mercury may be found in liquid or vapor form. Exposure to elemental mercury is primarily by inhalation because it easily vaporizes, and it is not easily absorbed in the gastrointestinal tract. Because of extensive regulations in the United States and other countries, occupational exposure to elemental mercury is rare. Inorganic mercuric salts are found mainly in batteries and can be absorbed orally or through the skin. Exposure to organic mercurial compounds most often occurs from eating fish that have accumulated them in fatty tissues. Organic mercury compounds, in contrast to the other mercurial forms, are extensively absorbed from the gastrointestinal tract.
Mercury Toxicity
Inhalation of elemental mercury can cause severe, irreversible damage to the respiratory and central nervous systems. Inorganic mercurial salts do not cause appreciable systemic toxicity because they are not very soluble; however, they will accumulate in the kidneys, where they can cause significant damage. They are also corrosive and can cause severe burns and ulcers. An article in the eMedicine Clinical Knowledge Base reports that although inorganic mercurial compounds are poorly soluble, repeated exposure can lead to a buildup of mercury in brain tissue causing toxicity. Acute ingestion of organic mercury compounds may cause visual disturbances, loss of motor control, mental deterioration, tremors, paralysis and potentially death. Chronic exposure to all forms of mercury causes kidney toxicity, dementia, insomnia, loss of motor control, anorexia and other behavioral disorders.
Acute Emergency Care
If elemental mercury is inhaled and symptoms of acute respiratory distress are evident, patients are treated with oxygen and mercury may be sucked out of the lungs. If mercury has been ingested, patients are treated by stomach pumping or activated charcoal, which binds mercury in the gastrointestinal tract and prevents absorption. Also, in the case of acute oral exposure to inorganic mercurial salts, people are intravenously loaded with fluids because of the caustic properties of these compounds.
Chelating Agents
Chelating agents, such as dimercaptosuccinic acid, are used to remove mercury once it has been absorbed. These agents bind to mercury in the blood and then are excreted, preventing the accumulation of mercury in tissues. An article in the eMedicine Clinical Knowledge Base reports that the nonabsorbable resin polythiol may be used to chelate organic mercury once it has been absorbed into the blood. Mercury bound to polythiol is excreted in bile.
Antioxidants
Some reports say certain antioxidants, such as alpha lipoic acid, glutathione and selenium, may reverse toxicity caused by mercury. An article in the journal Alternative Medicine Review notes that mercury causes toxicity by increasing oxidative stress in cells and that alpha lipoic acid and glutathione can enter cells and remove mercury. No clinical studies have evaluated the efficacy of antioxidants in treating acute or chronic mercury toxicity; however, this review mentions several animal studies that demonstrated antioxidants remove mercury from cells and prevent cellular damage.
