When you think of mercury, what comes to mind? Do you think about the small, hot planet in our solar system nearest the sun? Perhaps the Roman god with winged feet?
I know some people who would surely think about the car. But how about heavy metal?
No, not rock music; the transition metal with the atomic number 80. Mercury is one of only five elements that is a liquid at room temperature.1 The periodic table symbol for mercury, Hg, comes from the Greek name hydrargyrum, a combination of the words for water (hydro) and silver (argyros) forming a word meaning “watery silver.’’ It’s an apt physical description of elemental mercury. The other common name for mercury is quicksilver.
Mercury, an element with a storied past, still presents dangers hospitalists must be aware of.
Organic compounds of mercury especially are toxic at even low levels. Human exposure must be limited when possible. Many elements and heavy metals are used by living organisms in trace amounts. Not mercury. Mercury is a toxin at any dose. Pure elemental mercury is less toxic than the organic compounds and salts. Exposed to water, mercury is quickly converted to the more toxic form, methylmercury. Because of its volatility, any open container of mercury is a biohazard and presents a risk of poisoning from mercury vapor. Inhaled vaporized mercury is readily absorbed through the alveoli.2
Mankind has used mercury-containing products for a long time. Some of the red color in ancient cave drawings is cinnabar, or mercury sulfide (HgS). Cinnabar has also been used as the red pigment in tattoos. When I was in the Navy, we were told any skin rash that spared the red color in a tattoo was sure to be syphilis; according to the information we were given, the red pigment in a tattoo was created by mercury. Actually, tattoo parlors use several forms of red pigment, but mercury sulfide is certainly one of the choices.
Historically, many cultures used mercury in a variety of ways. More than two millennia ago, Greeks used mercury in medicines; Romans incorporated the element in their cosmetics.3 Medicinal uses of mercury have included the treatment of syphilis and use as a diuretic, antiseptic, and laxative.4 In the mid-20th century, mercury-containing compounds were popular as a remedy for infant-teething pain.
From the 17th to 19th centuries, mercury was used in the process of making felt for hats; hat makers were subjected to excessive exposure to the element. Mercury toxicity manifested as psychiatric illness and was widely recognized as an occupational hazard of hat-making.4,5 Reflecting this observation, “mad as a hatter” became a figure of speech and even found its way into the famous book “Through the Looking Glass (And What Alice Found There)’’ by Lewis Carroll.
Gold mining presents another occupational exposure to mercury. During 19th-century gold mining in California, mercury was used to extract gold from ore. Today, much controversy and ecological protest is focused on the South American gold mining industry, particularly in Brazil. In the past 20 years or so, it is estimated that 2,000 tons of mercury have been released into the environment in the Brazilian Amazon.6 Watchdog groups have been sounding the alarm for people who live in the villages along the Amazon River and consume a diet of fish caught from the river. Hair samples of those villagers revealed high levels of mercury.7 To date, clinical disease has not been reported there.