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From beans to weapon: The discovery of ricin

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Castor beans are used to make castor oil, but they leave a biproduct of deadly ricin. (Photo: Steve Hurst USDA-NRCS PLANTS Database)

In a recent article in Science, the biological mechanism behind the health benefits of castor oil was examined. But one cannot look at a derivative of the castor bean without also recalling that another byproduct creates one of the most toxic substances known to man: ricin.

Ricin is a naturally occurring protein that is part of the leftover "waste mash" created when beans from the castor plant (Ricinus communis) are processed to make castor oil. Exposure occurs if the bean seeds are eaten; otherwise, exposure must be deliberate. The substance can be made into a powder, mist, or pellet as a biological agent for warfare, exposing people through food, water, or air. There is no antidote.  

Castor beans grow in warm climates and over a million tons are processed worldwide, so they are readily available. Separating out the protein requires only someone skilled in chromatography, so it is not that difficult to manufacture. In December 2002, six terrorist suspects were arrested in Manchester, England when it was discovered that the group, led by a 27-year-old chemist, was using an apartment as a ricin laboratory.

The toxic properties of ricin have likely been known since the plant was discovered and its beans eaten for food; it wasn't until German scientist Peter Hermann Stillmark extracted the toxin in 1888 that its use as a biological weapon became a possibility.

Interestingly, as a result of his observation of ricin's highly agglutinating properties, Stillmark is the first person to have described lectin, a protein that binds sugar, which he described in his doctoral thesis the year of his discovery.

The United States looked at using ricin as a weapon in World War I, either using it to coat bullets, or creating a dust cloud of the toxin that would be inhaled by the enemy. However, ricin's sensitivity to heat made its use on bullets problematic, and the dust cloud idea was dismissed until an antitoxin could be found.

In World War II, British, French, Canadian, and American scientists all studied the possibility of using ricin as a weapon, and the U.S. conducted tests at the Dugway Proving Ground in Utah in 1944; however, it was not used in World War II, and it was set aside while more deadly toxins such as botulinum toxin A were favored as a biological weapon.

Because of its limitations, ricin seemed more appropriate for small-scale or personal attacks; hence becoming a weapon for terrorists rather than wide-scale biological warfare.

On September 7, 1978 in London, outspoken Bulgarian dissident Georgi Markov was stabbed in the leg with an umbrella by an unknown foreign man. Within three days he was dead. It was found that the tip of the umbrella had held a miniscule metal sphere containing a pellet of ricin that remained in the wound and killed him.

Since then, there have been several attempted uses of ricin as a terrorist weapon.

In 1991, four people were arrested in Minnesota for planning to kill a U.S. marshal by mixing ricin with DMSO (dimethyl sulfoxide, a commercial solvent), which they planned to coat on the door handles of his vehicle. The plan probably would not have worked, since the poison likely would not have been absorbed through the skin.

In 2003, an apartment raid near London foiled a plot by Chechen separatists to use ricin to attack the Russian embassy. The raid revealed 22 castor seeds and recipes for making ricin.

In October of 2003, ricin was discovered in a post office in Greenville, South Carolina, with a letter threatening to poison water supplies. One month later, ricin was discovered in the White House mailroom. Only three months later, in February 2004, ricin was found in Senate Majority Leader Bill Frist's mailrooms, and the U.S. Senate building was closed. No one was injured in these incidents.

On November 1, 2011, four men were arrested in Georgia for plotting to disperse ricin in Atlanta among other places in the U.S.

When Stillwater discovered how to extract ricin, one wonders if he foresaw the sinister use to which it would eventually be put. However, there are some benefits to ricin. It is being developed for use as a cancer-killing agent by targeting specific cells, and it is being used to develop a vaccine against ricin exposure.

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Castor beans are used to make castor oil, but they leave a biproduct of deadly ricin. (Photo: Steve Hurst USDA-NRCS PLANTS Database)
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Susan Borowski