Ricin toxin--the toxin from the castor bean plant Ricin communis--is "one of the most poisonous naturally occuring substances known." 
The Arizona Department of Health Services Ricin Fact Sheet says that 
- "Ricin has been used as biological weapon for assassinations in the past. It is toxic by numerous exposure routes, however, its use by bioterrorists might involve poisoning of water or foodstuffs, inoculation via ricin-laced projectiles, or aerosolization of liquid ricin or lyophilized powder. Waste from the commercial production of castor oil contains 5% ricin, making it easy for such a substance to fall into the hands of bioterrorists."
- "When inhaled as a small particle aerosol, ricin would likely produce symptoms within 8 hours. Fever, cough, difficulty breathing, nausea, and chest tightness are followed by profuse sweating, skin turning blue, low blood pressure, and finally respiratory failure and circulatory collapse. Time to death would likely be 36-72 hours, depending on the dose received."
According to the Wisconsin Department of Health & Human Services' Fact Sheet on Ricin Poisoning: 
- "Ricin is a stable toxin easily made from the mash that remains after processing Castor beans (Ricinus communis) for oil. Castor Oil was once used as an oral laxative, but is now used mainly as an industrial lubricant and for preparing leather products. Castor beans are grown agriculturally worldwide and the plants grow wildly in arid parts of the United States. Castor beans are slightly larger than pinto beans, darkly colored with light mottling, and have a small light-brown cap at one end. They have been described as looking like blood-engorged ticks. The beans are not normally used as food. Poisoning can occur following inhalation, ingestion, or injection of ricin toxin from Castor beans."
- Project BioSense
- Project BioShield
- Project BioWatch
- weapons of mass destruction suspected terrorists
- Terrorism Project: CDI Fact Sheet: Ricin, Center for Defense Information, February 7, 2003.
- Tim Radford, Terror weapon from a humble bean. The background: Ricin, Guardian/UK, February 8, 2003.