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Mercury is used in its liquid metal form as an amalgam with other metals or in chemical compounds. It is used in the manufacture of chlorine, caustic soda and dry cell batteries and as an industrial catalyst. Dry cell batteries contain no added mercury but it may be present as a contaminant. The metal is used in thermometers and barometers and some dental fillings consist of an amalgam (mixture) of mercury, silver and tin. It is present in circuit boards and computer monitors. Organic mercury compounds are used in dyes (e.g. mercurochrome) and as fungicides in wood, paints, plastics, seed dressing and paper.

Health effects
Organic mercury compounds are much more strongly absorbed when ingested than inorganic mercury compounds or the metal. Mercury vapour is readily absorbed in the lungs.

Mercurous nitrate was used in making felt and caused body tremors in hat workers (hence 'mad as a hatter'). Mercury compounds were also used to treat syphilis until 1896 and were used in babies' teething powder until 1950.

Absorbed mercury accumulates in the brain. First symptoms of poisoning include depression, fatigue, headaches, loosening of the teeth and blueness of hands and feet in children. Severe and chronic symptoms include crippling, brain damage, blindness and premature aging. Dental workers, hospital workers, unborn babies, small children and people eating a lot of fish, shellfish, grain or eggs from a contaminated site are those most at risk. Abraham Lincoln was treated with a remedy containing mercury for depression and outbursts of rage. Ironically, the mercury was responsible for the problem, which abated after he took the Presidency and stopped taking the pills because 'they made him cross'.

Mercury in dental fillings dissolves very slowly in saliva but this small amount is believed to be readily eliminated by the body, though there is some debate about that.

Environmental effects
Broken thermometers, leaking batteries, dental fillings, blood pressure units in hospitals and industrial processes all inject mercury into the environment. All dental surgeries must have mercury traps to catch the amalgam from their effluent. Cremation of bodies with teeth containing mercury amalgam fillings has been identified as a major source of atmospheric mercury in Sweden.

Inorganic mercury can be converted to organic mercury by bacteria and can thus enter the food chain. Shellfish can concentrate mercury 100,000-fold and in oysters the concentration can reach five ppm. In 1953 people living around Japan's Minimata Bay, whose diet included a lot of shellfish, developed a nerve disorder ('Minimata disease') caused by mercury discharged from a nearby plastics factory.

Alternatives
Where possible, use alcohol thermometers, non-mercury fungicides and mercury-free batteries. Acrylic-polymers are now available for use as dental fillings.

 
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