Mercury is a naturally occurring metal that is widely toxic to multiple organ systems. Whereas elemental mercury produces pulmonary toxicity, inorganic mercury initially causes gastrointestinal (GI) symptoms followed by nephrotoxicity. A nearly pure neurologic toxicity results from organic (methylmercury) exposure.
The toxicologic manifestations of mercury are well known as a result of thousands of years of medicinal applications, industrial use, and environmental disasters.58,92 Mercury occurs naturally in small amounts as the elemental silver-colored liquid (quicksilver); as inorganic salts such as mercuric sulfide (cinnabar), mercurous chloride (calomel), mercuric chloride (corrosive sublimate), and mercuric oxide; and as organic compounds (methylmercury and dimethylmercury). In recent centuries, mercury preparations were widely used to treat both syphilis and constipation. The musician Paganini was one of several famous persons whose gingivitis, dental decay, ptyalism (excessive salivation), and erethism (pathologic shyness) were attributed to mercury therapy.67 In the 1800s, the United States witnessed an epidemic of "hatters' shakes" or "Danbury shakes" and "mercurial salivation" in hat industry workers.103 Danbury, CT, was a U.S. center of felt hat manufacturing where mercuric nitrate was used to mat animal furs to make felt.92,103
In the early 1900s, acrodynia, or "pink disease," was described in children who received calomel for ascariasis or teething discomfort.12 Vividly described in a series of 41 children, the development of acrodynia was more common in younger children, did not seem to correlate with mercury dose, and was not necessarily related to urine concentrations of mercury.102
One of the most devastating epidemics of mercury poisoning occurred as the result of a decade of contamination of Minamata Bay in Japan by a nearby vinyl chloride plant during the 1940s. Methylmercury accumulated in the bay's marine life and poisoned the inhabitants of the local fishing community. Although officially only 121 victims were initially counted, thousands more are believed to have been affected by what has subsequently been named Minamata disease.72,94 The largest outbreak of methylmercury poisoning to date occurred in Iraq in late 1971. Approximately 95,000 tons of seed grain intended for planting and treated with methylmercury as a fungicide were baked into bread for direct consumption, resulting in widespread neurologic symptoms, 6530 hospital admissions, and more than 400 deaths.4,18,77
In 1990, the Environmental Protection Agency (EPA) banned mercury-containing compounds from interior paints.2 However, mercury-containing paints manufactured before that ruling may still be on interior walls, and mercury-containing paint can still be sold for outdoor use. In 1997, a scientist succumbed to delayed, progressive neurologic deterioration after dermal exposure to a minute quantity of dimethylmercury.64
Contemporary exposures occur in the form of mercury-tainted seafood and mercury-based preservatives (thimerosal). However, a once widely feared source of potential poisoning, mercury-containing dental amalgam, does not result in clinically important poisoning. Occasionally, exposure to mercury from broken thermometers leads to poisoning in the home.