Under the Microscope / Prof William Reville: Readers will periodically hear about ricin in the news, usually in the context of bioterrorism. It is a deadly natural poison that can be extracted from the beans of the castor oil plant Ricinus communis.
In January 2003, four people were charged with producing ricin at a London flat and in November 2003 a letter containing ricin was sent to the White House. The most famous case of ricin poisoning was in 1978 when Bulgarian dissident Georgi Markov was killed by a ricin-laden pellet injected into his thigh in London. Ricin is cheap, easy to produce and doesn't have to be highly purified to be effective. Undoubtedly we have not heard the last of it.
Plant seeds are responsible for future growth of the plant and, because of this, many seeds are endowed with a defence against predators so that at least some of them will survive to germinate. Seeds can reduce the probability of being eaten and destroyed with structural defences such as thorns or stinging hairs. Many also contain toxic chemicals that are unpalatable, or interfere with digestion. Ricin is one such chemical. It is very toxic and when it enters the cells of predators it rapidly inactivates the protein-making machinery of those cells.
India, China and Brazil are the principal countries growing castor beans, but the plant is found everywhere around the world. Annually 460,000 tons of castor oil are produced and used in industries such as paints, cosmetics and textiles. After the oil is squeezed from the bean, a wet mash (550,000 tons annually) remains, and 5 per cent of this wet mash is ricin.
In its pure form, 70 micrograms (the weight of a grain of salt) can kill an adult. Ricin is more than 1,000 times more poisonous than cyanide. The castor bean plant is not native to Ireland but can be found in gardens. Castor bean plants should not be allowed to flower and seed.
Ricin is soluble in water, forming a colourless and tasteless solution. As a poison weapon, it can be delivered through the air as an aerosol spray or it can be swallowed or injected. It is quite stable, so long-term storage is feasible and it isn't volatile, so transporting and handling it is relatively safe. Although scientists are working on a vaccine, there is currently no antidote to the poison and doctors can only treat the symptoms.
Symptoms of human poisoning set in within a few hours of ingestion - pain in the abdomen, vomiting and diarrhoea. Within several days severe dehydration and a decrease in blood pressure is established. If the victim doesn't die within five days, he/she usually recovers. Ricin is particularly toxic to children because they dehydrate much more easily them adults. If you chew castor beans you will be poisoned and, it is said, chewing even one bean can kill a child. Castor beans swallowed without chewing will probably pass through the gut without releasing ricin and cause no harm. It is not easy to identify ricin poisoning because the symptoms mimic the symptoms produced by several natural diseases. One tell-tale signal of ricin poisoning is a greatly elevated white blood cell count in the victim.
Georgi Markov was a Bulgarian communist dissident and worked in London for the BBC World Service. He wrote satirical plays and heavily criticised the rule of the communist leader Todor Zhivkov. Markov's broadcasts encouraged the dissident movement in Bulgaria and he survived two assassination attempts before he was finally killed.
Markov was waiting at a bus stop in London on his way home from work. He felt a sharp jab in his thigh and saw a man picking up an umbrella. Some believe that the umbrella was modified into a weapon that fired or injected a ricin-bearing pellet into Markov's leg. Others think the attacker used a needle to inject Markov as he bent down to pick up the umbrella. Markov went home, developed a high fever and died three days later.
A post-mortem carried out on Markov, with the help of the UK germ-warfare centre at Porton Down, showed that he had been killed by a tiny pellet bearing 0.2 milligrams of ricin. Nobody was ever charged with the murder but it is widely assumed that the KGB and Bulgarian secret service were responsible. The case remains open.
Law enforcement agencies say that are the international terrorist groups have manuals detailing methods of ricin production and use and that militant groups in America have also considered using ricin. There is no risk that newspaper articles such as this will tell those groups anything they don't already know.
The potential use of ricin by terrorists would be in small-scale events such as contamination of a building or shopping centre by pumping aerosolised ricin into the ventilation system, or into an underground train station.
The main intent would be to cause terror and chaos in the target population, much like the intent of the suicide bomber who blows up a restaurant full of people at lunch hour. The relative number of people killed is small (10-20) but the terror caused by such an event can paralyse an entire city. My topic today is a depressing one, but even worse than the thought of terrorist poison attacks are the reports of parents in some parts of the world killing unwanted children with ricin.
William Reville is associate professor of biochemistry and public awareness of science Officer at UCC. http://understandingscience.ucc.ie