What is ricin?
(CNN) -- Ricin is a natural highly toxic compound that comes from castor beans, used to make castor oil.
About one million tonnes of these beans are processed every year. When they are boiled down, the residue is ricin.
Less than a pinpoint can kill a human if ingested, injected or inhaled and there is no known cure.
Ricin can kill someone within five days but it is not always fatal. Children are more at risk than adults.
If inhaled, ricin can cause death within 36 to 48 hours from failure of the respiratory and circulatory systems.
If injected, ricin causes immediate death of the muscles and lymph nodes near the site of the injection. Failure of the major organs and death usually follows.
One molecule inside a cell will kill it.
If ingested, it causes nausea, vomiting and internal bleeding of the stomach and intestines, followed by failure of the liver, spleen and kidneys, and death by collapse of the circulatory system.
If the seed is swallowed whole without damage to the seed coat, it will probably pass harmlessly through the system. But if the coat is chewed or broken, then swallowed, the poison will enter the body.
Medical experts point out that ricin is nowhere near as powerful a killer as anthrax.
To equal one kilogramme of anthrax, four metric tons of ricin would be needed. On the other hand, anthrax can be treated, if caught early enough.
Ricin was used in the 1978 assassination of Bulgarian dissident Georgi Markov. The author, who had defected nine years earlier, was jabbed by the tip of an umbrella while waiting for a bus in London and died four days later.
A post mortem showed ricin poisoning was the cause of death. The lethal dose, estimated at 450 micrograms, was delivered in a pinhead-sized hollow pellet, found during the examination. (Full story)
Ricin can be produced easily and cheaply but analysts say as a weapon it is most effective on individuals. It is thought a large amount would be needed to make it a weapon of mass destruction -- about four tonnes of spray to kill half the people in an area of 100 square kilometres.