Castor beans contain ricin.(Photo: Wikimedia Commons)
Dan Vergano, USA TODAY
As poisons go, ricin has humble origins, produced in the waste "mash" left over in making castor oil. Letters sent to President Obama and several senators have raised new fears about a poison favored in the past by spies, soldiers and domestic terrorists.
Ricin stops cells in the body from producing the proteins that keep us alive, killing people within 36 to 72 hours. It can kill after being eaten, inhaled or injected, as happened in 1978 to a Bulgarian writer, Georgi Markov, assassinated with a poison-tipped umbrella. More recently, letters containing ricin were sent in 2003 and 2004 to the White House, by someone unhappy about trucking safety regulations. No one was injured.
The poison is described as very toxic by the federal Centers for Disease Control and Prevention, "several times deadlier than cobra venom." That explains the concern about letters containing the poison. As little as three milligrams of the stuff could be deadly if inhaled by someone opening an envelope containing "aerosolized" ricin. Creating such a powder would require a great deal of expertise, according to the CDC. Just touching ricin would only cause irritation to the eyes or skin, but not kill.
Ricin is not contagious. The symptoms of ricin poisoning depend on how it is delivered: difficulty breathing, fever and coughing as soon as four hours afterward if inhaled, and bloody diarrhea within 10 hours of being eaten. There is no cure for the poison, only treatment to alleviate the symptoms.