The FBI is warning local police about ricin and offering tips for recognizing and handling the deadly toxin.
A bulletin was sent to local agencies nationwide Thursday following the arrests earlier this week in London of seven men allegedly connected with an Algerian extremist group. Police say the men were plotting to kill a small number of people with ricin in an attempt to terrify the London population.
FBI officials stress there is no evidence of any planned attack in the United States using ricin, which is made from beans of the common castor plant. The purpose is to provide police and emergency personnel with a primer on the potent poison's hazards and handling, an FBI spokesman said Friday.
The FBI notes that ricin can be made in liquid, crystal or dry powder form and that in low doses, it has a laxative rather than lethal effect. But if it is inhaled or ingested, the FBI says, serious symptoms such as fever, cough, shortness of breath, chest tightness and low blood pressure can occur with in eight hours. Death can come between 36 and 72 hours after exposure.
"It is estimated that one milligram of ingested ricin can kill an adult," the bulletin said.
The toxin could be used in ventilation systems, drinking water or food supplies, the FBI says. But it would be most effective as a poison through individual injection or as a food contaminant.
Use of ricin in an attempted mass attack in water supplies, the FBI added, "would require the processing of an extremely large amount of castor beans."
Some groups in the United States in the past have attempted to use ricin in attacks. For example, four men were convicted following a 1991 scheme in which a group called the Patriot's Council of Minnesota made ricin from castor beans and plotted using it against law enforcement officials.
The FBI said the amount of ricin manufactured in that case could have killed up to 100 people.