Thallium - the poisoner's poison

Exiled Russian security agent Alexander Litvinenko - who is fighting for his life in a London hospital - is believed to have been poisoned with thallium, a highly-toxic heavy metal.

Derivatives of the chemical are used legally in objects as diverse as optical lenses, low temperature thermometers, green-coloured fireworks and jewellery.

It was used in some rat poisons up until the mid-1970s, but authorities now strictly control its sale because of its deadly potential.

Salts of thallium are colourless, odourless, tasteless and soluble in water, making them an ideal weapon for the poisoner.

The chemical attacks the nervous system, lung, heart, liver, and kidneys. Hair loss, vomiting, and diarrhoea are symptoms.

Death can occur after exposure to doses as small as one gramme.

Thallium has been the poison of choice for murderers and secret service agents for many years.

South African agents are said to have once plotted to use it against Nelson Mandela while he was in prison on Robben Island. Plans were drawn up to add tiny doses of the chemical to his medication to disable him, the South African Truth Commission heard.

In a bizarre scheme, the CIA once plotted to use thallium salts to make Cuban dictator Fidel Castro’s beard fall out.

According to declassified military documents from the 1960s, the idea was to dust the powder into Castro’s shoes when they were put out at night to be shined during a visit to New York.

The poison would cause his hair to fall out, thus destroying his image.

Earlier this year a 17-year-old Japanese girl, described as a promising chemistry student, attempted to kill her mother with the poison.

She had apparently been inspired by Graham Young, who was convicted of killing three people and poisoning dozens of others in the 1960s and 1970s.

Serial killer and great grandmother Caroline Grills earned the tabloid nickname “Aunt Thally” after killing four distant relatives with the chemical.

The Australian put thallium sulphate, taken from rat killer, in to their food, killing them all in 1953.

In 2004, up to 25 Russian soldiers became seriously ill after discovering a tin of thallium powder dumped at their camp in Siberia.

The servicemen became seriously ill after apparently adding it to their cigarette tobacco, dusting it on their feet as talcum powder and even snorting it.