A suspected al-Qaeda operative has been convicted of plotting to spread ricin and other poisons in Britain. The BBC News website examines the deadly potential of ricin.
What is ricin?
Ricin is a toxic material which can be fatal when inhaled, ingested or - most dangerously - injected.
It can damage the organs, and a combination of pulmonary, liver, renal and immunological failure can lead to death, although people can recover from exposure.
How is it made?
The jury in the Old Bailey trial of Kamel Bourgass and others heard detailed evidence of how ricin could be made.
For obvious reasons the authorities are not keen for the full details to be widely disseminated.
Suffice to say that it is easily produced, and can be extracted from the beans of the castor oil plant.
Several recipes were found which, the prosecution claimed, suggested the defendants were aware of how to make ricin.
How does it get into the body?
It can be delivered through the air in an aerosol spray, or it can be injected or swallowed.
One to three castor beans chewed by a child, or just eight seeds chewed by an adult can be fatal.
How potent is it?
Just a tiny amount of ricin is enough to kill - it is 6,000 times more poisonous than cyanide.
Seventy micrograms or two millionths of an ounce, roughly equivalent to the weight of a single grain of salt, is enough to kill an adult.
But terror expert Professor Paul Wilkinson told the BBC it was not possible to cause huge numbers of casualties by simply spraying the substance into the air.
Ricin is estimated to be lethal at 70 micrograms for a person weighing 160lb if injected into the bloodstream.
Experts say using ricin to cause mass casualties would require either it being used in aerosol form or as an additive to food or drink.
Such methods would require extensive prior research, development, operational planning, and testing, and are beyond the means of most terror groups.
Is there any treatment?
There is currently no antidote to the poison, though scientists are working on a vaccine.
If someone is affected, doctors can only treat their symptoms.
In January 2003 Deputy Chief Medical Officer Dr Pat Troop told the BBC the public health system had been alerted.
Doctors and the telephone helpline NHS Direct were briefed so they could answer questions from patients.
How would someone know they were affected?
The first symptoms depend on how the person has been exposed to ricin but can include fever, stomach upsets and coughing.
If someone breathes the poison in, they could suffer serious lung damage, eventually leading to heart failure.
Ricin is a deadly poison which can be extracted from castor beans
If ricin gets into the digestive system, it can lead to irritation of the gut, gastroenteritis, bloody diarrhoea and vomiting.
It can also affect the central nervous system, and cause seizures.
These effects may not become evident until 24 hours after the person has been exposed to the poison. It could be several days before the most serious problems develop.
Has it been used elsewhere?
Traces of ricin have been found in caves in Afghanistan.
The poison was also used during the Cold War to kill Bulgarian dissident Georgi Markov in London.
A specially-equipped umbrella was used to inject a pellet coated with 450 micrograms of ricin into his leg in an infamous attack on Waterloo Bridge in 1978.
Does ricin have any positive benefits?
Ricin is being studied to see if it could form the basis of cancer treatments because it can kill cells easily.