Monday, lawmakers said a letter sent to Sen. Roger Wicker, R-Miss., tested positive for the poison ricin, which is derived from the castor oil plant and is lethal at very small doses. According to the FBI, a second letter addressed to President Barack Obama "containing a granular substance that preliminarily tested positive for ricin" was discovered Tuesday.
The U.S. Department of Health and Human Services lists ricin as one of 49 "regulated agents" and toxins that could be used in a bioterrorism attack.
Ricin has been on the radar of the Centers for Disease Control and the National Institutes of Health for some time – researchers at Sandia National Laboratories have been using a $4 million National Institute of Allergy and Infectious Diseases grant to develop a portable device that can detect ricin, anthrax and other toxins in the event of a terrorist attack.
Here's a primer on what the poison is and its bioterrorism history.
What is it?
According to the Centers for Disease Control, ricin is a poison that is naturally found in castor beans. Eating castor beans can release the poison and can cause injury. Prepared ricin can be disseminated as a powder, as it apparently was in the letter addressed to Wicker. It can also be dissolved in water, used as a mist or formed into a pellet.
The CDC says that it would take a "deliberate act" to become exposed to poison. They warn it could be used as a poisonous agent "through the air, food, or water."
How does it kill?
Ricin is a fairly slow-acting poison. Sometimes, symptoms, which include difficulty breathing, chest tightness and eventual low blood pressure and respiratory failure can lead to death. The poison can take up to 72 hours to kill, depending on how it's delivered. It acts fastest if injected.
There is no known antidote for ricin, but some of the symptoms can be treated if exposed to only a small amount, people can survive a ricin poisoning.
Why have I heard of it before?
Everyone's favorite fictional chemist, Walter White of AMC's "Breaking Bad," prepares ricin in order to kill a rival drug dealer named Tuco. White mixes the poison with a packet of crystal meth, hoping Tuco will snort it. Unfortunately for White, Tuco refuses to snort it. White then sprinkles it on Tuco's food but he was foiled again. Tuco dies in a shootout with police instead.
Ricin was famously used to kill Georgi Markov, a Bulgarian writer. A hitman in London used a modified umbrella to inject Markov with a pellet containing ricin. He died soon after.
Who has used it?
According to the U.S. Air Force, ricin was first identified in 1889. During World War I, the military considered using the poison to coat bullets and creating a "dust cloud" of ricin that could be dropped from planes onto the battlefield.
According to a technical report prepared by the military in 1918, "easily prepared preparations of ricin can be made to adhere to shrapnel bullets … it is not unreasonable to suppose that every wound inflicted by a shrapnel bullet coated with ricin would produce a serious casualty … many wounds which would otherwise be trivial would be fatal."
But the means of dissemination weren't perfected before the end of the war, and ricin wasn't used during the conflict by the U.S. military. The U.S. military also considered using ricin during the 1940s. The CDC says there have been reports of ricin being used as a warfare agent in the 1980s.