In 1978, Bulgarian dissident writer, Georgi Markov, was assassinated in London at the age of 49. In a plot that could have been lifted from a Cold War spy novel, Markov died when a poison-tipped umbrella, designed by the KGB, delivered a deadly dose of ricin to the back of his leg.

Ricin is a poison derived from castor beans; it is extremely toxic. Just one mere milligram is lethal if inhaled or ingested, and only 500 micrograms – an amount the size of the head of a pin – is fatal if injected, according to the CDC.

In the 1940s the U.S. military experimented with using ricin as a possible warfare agent, and some reports suggest that ricin may have been used as a warfare agent in the 1980s in Iraq and more recently by terrorists. It has been sporadically found in letters destined for the Senate and White House, but fortunately, mail screening detected it before delivery to its intended targets.

Of the two toxins found in the castor bean plant, Ricinus communis, the main toxic protein, ricin, is considered both a chemical and biological weapon. It is explicitly prohibited by the Biological and Toxin Weapons Convention and Schedule 1 of the Chemical Weapons Convention. 

Ricin can be produced from the common waste remaining after the processing of castor beans, but it’s most lethal only after having been purified in a technically complex process. As well, it’s very difficult to produce ricin that retains the physical properties that make it easy to inhale.

The poison works by invading the body’s cells and destroying ribosomes, the small parts of the cell that produce proteins. Without these proteins, the cells die.

Its lethality depends on the dose, purity, length of exposure, and whether it was inhaled, ingested, or injected.  Initial symptoms occur from four to 12 hours after exposure and differ varying upon route of exposure: Ingestion leads to gastrointestinal symptoms; inhalation leads to respiratory symptoms. Death from ricin poisoning takes place between 36 to 72 hours after exposure.

There is no specific test for exposure to ricin. And since there is also no antidote, be on the lookout for shady spies bearing umbrellas.

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What is ricin?
The poison derived from common castor beans is extremely lethal.