It is well known that the phrase “as mad as a hatter” originated because the people who made hats often appeared mad as a result of the mercury used in their manufacture. The fur of small animals was treated with a solution of mercury (II) nitrate, and then heated in an oven. This process was known as ‘carroting’ because the fur turned orange. The process caused the fur to also shrink, so it was easy to remove and press into felt.
The mercury accumulated in the hatters bodies and led to mercury poisoning. The symptoms included a tremor together with other behavioural changes such as irritability, depression and shyness. In extreme cases delirium was experienced – as illustrated so well by the character of the mad hatter in Lewis Carroll’s Alice’s Adventures in Wonderland.
However, it wasn’t just hatters who suffered from metal poisoning. In the Bronze Age, arsenic was often added to copper to strengthen it when tin was not available. This meant the smiths of the Bronze Age often suffered with chronic arsenic poisoning. Hephaestus, the Greek god of blacksmiths, metallurgy, fire and volcanoes is depicted with crippled and misshaped feet probably as a result of arsenic poisoning. Arsenic has a very dubious history, to quote John Emsley: “Arsenic has a long and disreputable pedigree: its very name seems to condemn it as something unspeakable.”
The reason why it was chosen by the great poisoners was that it is a cumulative poison (harmless in small doses), and since its oxide is colourless, odourless and tasteless and dissolves in water, it was easy to dose your victim. Finally there weren’t any good tests for detecting arsenic until the nineteenth century and so you could readily get away with it.
Famous poisoners include Marie-Madeleine-Marguerite d’Aubray, Marquise de Brinvilliers who used arsenic, among other things, to murder members of her family to inherit property, and Madeleine Smith who allegedly murdered her lover in Glasgow in the 1850s.
Famous victims of arsenic poisoning include:
- King George III whose hair was found to contain large amounts of arsenic.
- Napoleon Bonaparte who may have been poisoned by the copper arsenite in his wallpaper.
- George Wythe Sweeney, a friend of Thomas Jefferson and a co-signer of the Declaration of Independence.
However, it should not be forgotten that arsenic was also used in a range of medicines, for example salvasan to treat syphilis.
More recently, thallium has become a metal of choice. In fiction, the crime writers Ngaio Marsh, Agatha Christie and Nigel Williams (in The Wimbledon Poisoner) all wrote about the use of thallium in foul play.
It is worth pausing to consider what is meant by toxicity with regard to a compound. The German physician Paracelsus explored the relationship between dose and response. To paraphrase his conclusion: All things are poison and nothing without poison.
Solely the dose determines that a thing is not a poison. The toxicity of a chemical is often stated in a way that relates the dose to the subject, such as an animal or human, and the time of exposure. For example, the compound lithium carbonate has a median lethal dose (LD50 or toxic to 50% of the subjects) in rats of 525mg/kg when administered orally.
However, it may be safely prescribed to humans at a therapeutic dose to treat, for instance, depression, but the levels of toxicity mean it has to be prescribed and taken carefully to avoid an overdose. Unfortunately, it has been reported to contribute to fatal overdoses when taken in excess, particularly in combination with other prescribed drugs.
There are also examples of poisoning that arise due to environmental pollution with perhaps one of the most famous occurring in 1956 at Minamata in Japan. This was one of the worst known cases of environmental contamination from mercury. It was caused by the discharge of methyl mercury into the sea from nearby industry. Over a 35-year period, many tonnes of mercury were released into the bay in the industrial waste waters. The mercury bioaccumulated in the shellfish and fish in the bay, and many thousands of the local population were poisoned from eating the contaminated seafood.
In 2013 the United Nations Environment Programme introduced the Minamata Convention to curb mercury pollution by a series of measures limiting the use and industrial discharges of the metallic element and its compounds. However, mercury poisoning still remains a problem in many areas worldwide where poorly regulated or illegal gold mining takes place.
Antidotes have also been developed by chemists to treat poisoning - be it intended or accidental. For example, Lewisite is a poison gas derived from arsenic developed at the end of the First World War which Sir Rudolph Peters developed British anti-Lewisite (BAL) or dimercaprol to counter. His design criteria for BAL were simply that it should be non-toxic itself and that it should form a stable and water-soluble compound with the arsenic that could then be readily excreted from the body. BAL is an example of chelation therapy and is also able to treat poisoning by other heavy metals, such as mercury.