Ricin has a long history of use in espionage and warfare. Economic surveys have shown that there are over 1 million tons of castor beans produced in the world annually. Ricin toxin can constitute up to 5 percent of the total protein of the bean. The global commercial production has the potential to yield approximately 50,000 tons of pure ricin. The fate of much of this ricin in countries outside of the US is unknown.
Ricin is highly stable at room temperature and difficult to inactivate by conventional methods. Because of the high content of ricin in castor beans, ricin toxin can be extracted from the mash produced as a by-product of castor oil production by several simple enrichment steps, and is therefore easy to stockpile.
While ricin is second in toxicity only to botulinum toxin, it is far easier to obtain, prepare, and use. Before the 1990 war, the Iraqi military had attempted to devise ways to disseminate ricin as an explosive bomb. These attempts were forestalled by the war and ensuing events.
Ricin has also been detected in a powder form sent in a letter addressed to Senator Bill Frist in 2004, and several other similar but less publicized incidents. More recently, there have been sporadic reports of ricin stockpiles and attempted use of ricin in the US and Europe.
Once exposed to lethal doses of ricin, the effects are essentially irreversible. The current expectation that drives vaccine development is that ricin is most likely to be distributed as an aerosol form, since it is highly lethal by this route.