mercury
Meaning of mercury: Three chemical forms with three different hazards, which is why an exposure cannot be judged from the word mercury alone.
Definition of mercury
Mercury is a dense silver-white metal, the only one that is liquid at ordinary room temperature. It once filled thermometers and blood pressure devices, still binds the alloy of dental amalgam fillings, and lends its name to the millimeters of mercury used to report pressure. It is also a poison, in forms that differ sharply in how they act.
What are the three forms?
| Form | How exposure happens | What it mainly affects |
|---|---|---|
| Elemental, the liquid metal | Breathing vapor from a spill or an industrial process; barely absorbed if swallowed | Nervous system, and the lungs at high vapor concentrations |
| Inorganic salts | Swallowed or absorbed from certain products | Corrosive to the gut lining, then the kidneys |
| Organic, chiefly methylmercury | Eating fish that have concentrated it up the food chain | Nervous system, and the developing brain before birth |
The differences are large enough that the three behave almost as separate poisons. Swallowed liquid metal passes through largely unabsorbed, while the same metal as vapor crosses from the lungs into the blood readily, which is why a broken thermometer is treated as an air problem rather than a swallowing one. Methylmercury is the form that accumulates, rising in concentration through the food chain so that long-lived predatory fish carry the most.
Where is exposure met now?
Fish is the main route for most people. Occupational exposure occurs in chlorine and electrical manufacturing, in laboratories, in dentistry and, on a large scale, in small-scale gold mining where mercury is used to bind gold. Some skin-lightening creams and traditional remedies contain mercury compounds, and antiseptics such as merbromin, once an ordinary over-the-counter product, have been withdrawn in many countries. Thermometers and blood pressure devices containing mercury have been replaced in most healthcare settings, which is part of a broader retreat from the metal now that it is recognized as toxic and internationally regulated.
What about fillings and vaccines?
Dental amalgam binds elemental mercury into an alloy with silver, tin and copper. The set filling releases very small amounts of vapor, particularly during placement and removal, and reviews of the evidence have not identified harm from fillings in place, though several countries have restricted their use in children and pregnancy on precautionary and environmental grounds. Thimerosal is a different compound entirely, an ethylmercury preservative used to keep multi-dose vials sterile. It was removed from most childhood vaccines, remains in some multi-dose influenza vials, and has been examined in large studies that found no evidence of harm at the amounts used. Ethylmercury is cleared from the body considerably faster than the methylmercury found in fish.
Also known as
Used in a sentence
The patient's occupational history included a period of regular exposure to mercury vapor.
Good to know
The health effects of mercury exposure depend on its chemical form, since elemental mercury vapor, inorganic mercury salts and organic forms such as methylmercury are absorbed, distributed and cleared by the body differently.
Word origin
Where “mercury” comes from
Named for the Roman god and the planet Mercury; the chemical symbol Hg comes from Greek hydrargyros, formed from hydor, water, and argyros, silver.