This article includes discussion of mercury neuropathy, metallic mercury intoxication, elemental mercury, inorganic mercury poisoning, and organic mercury compounds. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Mercury neuropathy is a recognized sequela of occupational or environmental exposure to one of the various forms of the heavy metal. In this article, the author discusses common exposure sources, biological exposure indices, and clinical manifestations of mercury toxicity while focusing on mercury neuropathy for elemental, inorganic, and organic mercury. The author has updated this article to reflect the current literature regarding peripheral nervous system disease and this commonly encountered metal.
• Peripheral neuropathy from mercury exposure most commonly involves distal latency sensory slowing for short-term exposures, followed by motor slowing for more long-term exposures.
• Inorganic and elemental mercury exposures are more likely to cause peripheral nervous system complaints and findings.
• Central nervous system effects are more common with organic mercury exposures.
• Twenty-four-hour urine mercury best assess exposures to inorganic or elemental mercury. Blood mercury is most appropriate for short-term exposures.
Historical note and terminology
Inorganic mercury is historically associated with environmental epidemics in Iraq and Japan, illness in occupational settings, and bizarre poisonings that have led to detective investigations.
Mercury has been known to cause illness in artists, gilders, gold refiners, and workers using metals in dyes, cosmetics, and unguents since Roman times. Later, occupational hazards of mining metallic mercury were associated with a slow death. Mercury and its salts were used as salves for syphilitics until the mid-20th century. Teething powders and antihelminthics are now rarely made with mercury (78; 83).
Today, dental amalgams, eye ointments, dermatological antiseptics, and hemorrhoidal sclerotics are still common medical sources of mercury. Calomel, a type of inorganic mercury salt also known as “sweet mercury,” was used in laxatives and teething powders, the latter leading to outbreaks of “pink disease” or acrodynia, a hypersensitivity syndrome to elemental mercury that can occur in children (83; 40). Occasional cases are still reported today.
Mercury is extracted from ore called cinnabar (HgS) by a roasting process. Elemental mercury, also called quicksilver or liquid silver, is a liquid at room temperature. Mercury exists in 3 oxidative states and also forms univalent (mercurous) and bivalent (mercuric) compounds. Mercuric chloride is readily dissolved, ionized, and absorbed and is more toxic than the less soluble mercurous chloride. Phenylic mercury compounds are less toxic than alkyl mercury compounds. Toxicity of these and other organic compounds have only been recognized in this century.
Elemental mercury is used in barometers, thermometers, and gauges. Mercuric salts are used in gold, silver, and bronze plating processes. Mercury is also found in electronic equipment, such as batteries, switches, rectifiers, compact fluorescent light bulbs, and mercury vapor lamps. Inorganic mercury is used in photography, antiseptics, tanning processes, embalming, felt manufacturing, and wood preservation methods.
Mercury poisoning in hat makers resulted from prolonged exposure to mercury vapors in poorly ventilated factories. Lewis Carroll’s Mad Hatter from the children’s tale Alice in Wonderland is literature’s most famous victim of mercury toxicity. A ban in the United States on the use of mercurous nitrate in the hat making industry was finally instituted in 1941.
Exposure to elemental mercury vapor occurs in the chloralkali industry during the manufacturing of chlorine. Natural gas from certain sites has been reported to contain elemental mercury, and this exposure can occur in inspectors and maintenance or equipment workers at these sites. Metallic mercury is used in dental amalgams. There has been literature discussing this as a possible low-level hazard in the dental workplace. In 1994, the Agency for Toxic Substances and Disease Registry (ATSDR) estimated 70,000 workers were exposed to mercury in the United States; 10% to 20% were estimated to experience intoxication. Some mercurochromes have been used as preservatives and antibacterials; thimerosal, which contains less than 2% mercury, has been suspected but not proven to affect autism rates.