THURSDAY MARCH 22 2001

medical briefing

Mercury poisoning

DR THOMAS STUTTAFORD

Mercury is back in the news. Historians investigating the graves of the early Tsars have found evidence of mercury poisoning, and the journal NUTRI News has expressed concern about the safety of mercury amalgams as dental fillings.

If this were not enough there is also alarm about the potential risk of eating fish from areas where the sea may be contaminated by mercury from industry.

No one seems to be proposing that Ivan the Terrible’s female relatives were poisoned by mercury accidentally. Even so, this has been the most common cause of mercury poisoning since Roman times, when Pliny described it. Since then goldsmiths (who used a gold amalgam for gilding), mirror-makers and hatters have all become accidental victims of mercury poisoning.

Mercury is the only pure metal which is liquid at room temperature, and most other metals will dissolve in it to form an amalgam. Workers in many other industrial processes have also been accidentally poisoned, and it is still used in the manufacture of scientific apparatus, in the electrical industry, as a fungicide and to prevent barnacles clinging to the bottoms of ships.

Even the police were not exempt from mercury poisoning. As late as 1949 one in four of the Lancashire police force, which regularly used mercury powder when dusting for fingerprints, suffered mercury poisoning. The most famous example of the symptoms of mercury poisoning in literature will always remain the exuberant insanity of Lewis Carroll’s Mad Hatter in Alice in Wonderland.

Ivan, the first Tsar, reputedly became “the Terrible” because he became paranoid and saw treachery everywhere after his closest female relatives died from what he believed was poisoning. His fears were dismissed as paranoid delusions, but historians have recently analysed the sludge at the bottom of the exhumed coffins of his kin and found that his suspicion of poisoning may be supported by mercury traces found during the investigation.

Most doctors who qualified half a century ago are familiar with mercury poisoning since we regularly poisoned our infant patients with calomel laxatives: these were made from mercurous salts. We were taught that mercurous chloride was relatively safe, whereas mercuric salts, such as mercuric chloride, were acute poisons giving rise to a fatal gastro-enteritis with diarrhoea and shock.

We were wrong. At about that time a well-known children’s disease known as Pink disease was shown to be the result of poisoning from mercury purgatives. These same mercury compounds were used in teething powders for babies and as a constituent of various mercury creams and ointments for all ages. Children purged with mercury, or quietened by mercury teething powders, became listless, cross and disliked the light. Their extremities, including their hands, were pink and swollen — hence the name Pink disease or acrodynia.

Mercury poisoning is now more insidious. Those in contact with mercury, or breathing its vapour, may develop inflamed gums and dribble excessively. They develop a tremor, which is made worse if they take alcohol, giving rise to the classic shaky handwriting of someone who is suffering from chronic mercury poisoning.

The mad hatters of Lewis Carroll’s time — the mercury poisoned felt-hat makers — were appropriately named. One of the symptoms of low-grade mercury poisoning is depression, loss of memory and a labile mood. With larger doses of mercury the patient is psychotic, suffers hallucinations and delusions and, like Alice’s Mad Hatter, becomes demented.

Heavy doses of mercury cause a generalised physical disruption of the central nervous system so that patients become unsteady on their feet, their talking becomes slurred and they find it difficult to eat or drink effectively, let alone neatly. Little wonder that Ivan the Terrible noticed that something was wrong with his mother and feared that she was being poisoned.

Whatever the fears of the general public, even those with heavy amalgam fillings in their mouth are not going to become mad hatters. Dental experts deny any risk from the leaking of mercury or its vapours from amalgam fillings. They deny that it would even make patients depressed and listless, let alone cause ME.

Those who are worried despite this reassurance can always ask their dentists for mercury-free fillings.

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