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Ricin: Technical Background And Potential Role In Terrorism


By Dana A. Shea and Frank Gottron for CRS

On December 20, 2010, CBS News reported that the Department of Homeland Security had uncovered a credible threat of attacks using poisons, such as ricin, in salad bars and buffets.1 Ricin is often mentioned as a potential bioterror weapon. This report describes what ricin is, how it is made, its effects, examples of its use, its potential for use as a bioterror weapon, and how its possession is currently regulated.

What Is Ricin?

Castor Beans
Castor Beans

Ricin is a potent plant toxin found in the seeds of the castor plant (Ricinus communis). It works by blocking cell protein synthesis, which results in cell death. This cell death can lead to organ failure and death.2

How Is Ricin Obtained?

Ricin can be isolated from castor beans by several well-known processes. During the industrial production of castor oil, bean mash with approximately 5% ricin content is produced. Several recipes for extracting ricin from castor beans are available on the Internet and from commercial bookstores. The quality of these directions varies. Some directions would produce only crude preparations while others would produce nearly pure ricin.3 Even the crude preparations have been considered deadly.4

Effects of Ricin

Persons exposed to ricin exhibit different symptoms depending on the route of exposure. Ingestion of ricin causes nausea, vomiting, diarrhea, gastric hemorrhaging, and shock. With a sufficient dose, death occurs within three to five days. Injection of ricin produces severe internal bleeding and tissue death, which can result in the collapse of major organ systems. Death often follows such a collapse. Inhalation of ricin irritates the lung linings and airways, leading to weakness and fever. Lesions may occur in the lungs causing tissue swelling and further damage.5

The lethal dosage of ricin depends on the route of exposure. Inhaled or injected doses as low as 3 to 5 micrograms per kilogram body weight may be lethal.6 This dose equals 240 to 400 micrograms for a 175-pound individual.7 Because ricin is less well absorbed in the gastrointestinal tract, the lethal dosage for ingestion is higher. Ricin is not active upon contact with intact skin.

Detection and Treatment

Several methods are currently available to detect the release of ricin. Potential field detectors include automated air samplers that could detect the release of aerosolized ricin and swab-type tests that could signal the presence of ricin on surfaces. Highly sensitive laboratory-based tests can be performed on samples gathered on site. Since these detectors are generally not widely implemented in civilian settings, health care workers diagnosing ricin poisoning may be the first to detect a covert ricin attack. Both military and civilian sectors are developing faster, more sensitive detectors.

Pre-exposure Treatment

No ricin vaccine is currently available for use by the general public. The Department of Defense has investigated vaccines in animal studies and submitted an Investigational New Drug (IND) application to the Food and Drug Administration for human safety testing. Research continues in the academic and private sectors to develop new vaccines. Additionally, animal studies suggest that passive prophylaxis, (i.e., injecting animals with antibodies obtained from other immunized animals), is effective against injected and ingested ricin. For inhaled ricin, the most effective prophylaxis appears to be through vaccination.8

Post-exposure Treatment

No medicine has been approved specifically to treat ricin exposure. The progressive nature of the toxin’s effects requires hospitalization and continual supportive care. In cases of ingestion, the recommended treatment of activated charcoal limits the ricin exposure. Stomach pumping may be considered if it can be performed within an hour of ingestion.9 Researchers continue to attempt to find new, more effective treatments for ricin exposure.10

Examples of Ricin’s Use

Ricin has been considered for use as a weapon since at least the 1940s, when military programs investigated the feasibility of bomb-dissemination of aerosolized ricin. Such a weapon was reportedly developed by the United States and the United Kingdom, but never used.11 Iraq reportedly attempted to weaponize ricin in the 1980s.12

In 1978, ricin was used to assassinate Bulgarian dissident Georgi Markov in London. A novel, umbrella-based weapon was used to inject a pellet containing ricin into Markov. Shortly after this episode, a similar pellet was discovered to be the source of illness of another Bulgarian exile, Vladimir Kostov.

Some individuals attempting to possess ricin, generally through its manufacture in makeshift laboratories, have been arrested and subsequently convicted of violations of the Biological Weapons Anti-Terrorism Act (P.L. 101-298).13 For example, in 2008, a man in Las Vegas poisoned himself manufacturing ricin in a hotel room. He survived the poisoning and was subsequently convicted of possession of a biological toxin.14 In other cases, unidentified individuals have sent ricin to government officials. In November 2003, the U.S. Secret Service reportedly intercepted an envelope containing ricin addressed to the White House.15 In February 2004, ricin was detected in the Dirksen Senate Office Building in the mailroom of Senator Frist.16 Additionally, trace amounts of ricin have been reportedly found in various locales in Afghanistan,17 and an insurgent group in Iraq reportedly attempted to acquire ricin.18

Ricin as a Weapon of Terror Rather than Mass Destruction

Many experts believe that ricin would be difficult to use as a weapon of mass destruction. Ricin needs to be injected, ingested, or inhaled by the victim to injure.19 Biological weapons experts estimate that 8 metric tons would be required to cover a 100 km2 area with enough toxin to kill 50% of the people. Thus, using ricin to cause mass casualties becomes logistically impractical even for a well-funded terrorist organization.20 Furthermore, some experts have stated that the required preparatory steps to use ricin as a mass casualty weapon also pose significant technical barriers that may preclude such use by non-state actors.21

Although causing mass casualties would be difficult, many experts agree that ricin could be a formidable weapon if used in small-scale attacks.22 The Centers for Disease Control and Prevention have listed ricin as a Category B Agent because it would be moderately easy to disseminate and result in moderate morbidity rates and low mortality rates.23 Although a string of attacks targeting dozens of victims at a time may not produce mass devastation, they might instill terror in the population, causing local economic disruption.

Current Regulation

Ricin is on the Department of Health and Human Services’ Select Agent list (42 CFR 73), and possession, transfer, and use of ricin is restricted under the Public Health Security and Bioterrorism Preparedness Act of 2002 (P.L. 107-188).24 Access to stores of ricin is limited to select bona fide researchers under the USA PATRIOT Act (P.L. 107-56). It is not illegal to possess or transfer castor beans, nor castor bean plants, because agents on the select agent list are exempt if they are in their natural state and no effort has been made to isolate the active agent (18 USC 175). Both castor beans and castor bean plants are openly sold within the United States, and castor bean plants grow naturally in the southwest.

The United States is a party to both the Biological Weapons Convention and the Chemical Weapons Convention. Ricin is a prohibited substance under both of these conventions. The Biological Weapons Convention bans the development, production, and stockpiling of biological agents or toxins for non-peaceful purposes. The Chemical Weapons Convention bans the development, production, stockpiling, transfer, and use of chemical weapons. The United States has entered into multilateral agreements to prevent the development of both chemical and biological weapons by other nations and terrorist groups.25


Dana A. Shea
Specialist in Science and Technology Policy
[email protected], 7-6844

Frank Gottron
Specialist in Science and Technology Policy
[email protected], 7-5854


This article, Ricin: Technical Background and Potential Role in Terrorism, first appeared as a December 21, 2010 Congressional Research Service report


1 Armen Keteyian, “Latest Terror Threat in US Aimed to Poison Food,”, December 20, 2010.
2 Jennifer Audi, et al., “Ricin Poisoning: A Comprehensive Review,” Journal of the American Medical Association,
2005, Vol. 294, pp. 2342-2351.
3 The effectiveness of two well publicized methods was examined in René Pita, et al., “Extraction of Ricin by
Procedures Featured on Paramilitary Publications and Manuals Related to the Al Qaeda Terrorist Network,” Medicina
Militar (España), Vol. 60, 2004, pp. 172-175.
4 In 1997, Thomas Leahy was convicted for possessing 0.7 grams of a powder that was approximately 4 percent ricin.
Department of Justice officials stated that this was equal to 125 lethal doses of ricin. See W. Seth Carus, Bioterrorism
and Biocrimes: The Illicit Use of Biological Agents Since 1900, (Washington, DC: Center for Counterproliferation
Research, National Defense University) 2001, pp. 97-98.
5 See David R. Franz and Nancy K. Jaax, “Ricin Toxin,” Medical Aspects of Chemical and Biological Warfare,
(Washington, DC: Borden Institute, Walter Reed Army Medical Center) 1997, Chapter 32, pp. 631-642 and Jennifer Audi, et al., op cit.
6 A microgram is equal to a millionth of a gram.
7 David R. Franz and Nancy K. Jaax, op cit.
8 David R. Franz and Nancy K. Jaax, op cit.
9 Jennifer Audi, et al., op cit.
10 See, for example, Sophie Rovner, “A Shield Against Ricin,” Chemical and Engineering News, Volume 88, Number
16, April 19, 2010.
11 David R. Franz and Nancy K. Jaax, op cit.
12 Raymond Zilinskas, “Iraq’s Biological Weapons: the Past as Future?” Journal of the American Medical Association,
1997, Vol. 278, pp. 418-424.
13 Examples of such cases can be found in Special Report on Ricin, James Martin Center for Nonproliferation Studies,
February 29, 2008, and in Toxic Terror: Assessing Terrorist Use of Chemical and Biological Weapons, Jonathan B.
Tucker, Ed. (Cambridge, MA: MIT Press) 2000.
14 United States Attorney, District of Nevada, U.S. Department of Justice, “Man Who Possessed Ricin and
Unregistered Firearm Silencers in Las Vegas Hotel Room Sentenced to 3 ½ Years in Prison,” News Release, November
17, 2008.
15 Dan Eggen, “Letter With Ricin Vial Sent to White House,” Washington Post, February 4, 2004.
16 “Frist: Ricin Confirmed, but No Illness Reported,”, February 4, 2004.
17 Jonathan Weisman, “Possible Anthrax Lab Unearthed Near Kandahar,” USA Today, March 25, 2002.
18 Charles Duelfer, Special Advisor to the Director of Central Intelligence, Comprehensive Revised Report with
Addendums on Iraq’s Weapons of Mass Destruction, (Washington, DC: Government Printing Office, September 2004),
Vol. 1, p. 5.
19 Some have suggested that ricin may be converted into a contact poison when combined with a solvent that can
penetrate the skin. Reportedly, the Minnesota Patriots Council planned to use this delivery method. See Jonathan B. Tucker and Jason Pate, op cit.
20 Mark Kortepeter and Gerald Parker, “Potential Biological Weapons Threats,” Emerging Infectious Diseases, Vol. 5,
No. 4, July-August 1999, pp. 523-527.
21 Office of Technology Assessment, Technologies Underlying Weapons of Mass Destruction, OTA-BP-ISC-115,
(Washington, DC: Government Printing Office, December 1993), p. 82.
22 Ibid. For more on small-scale chemical and biological terrorist attacks, see CRS Report RL32391, Small-scale
Terrorist Attacks Using Chemical and Biological Agents: An Assessment Framework and Preliminary Comparisons, by
Dana A. Shea and Frank Gottron.
23 See Lisa Rotz, et al., “Public Health Assessment of Potential Biological Terrorism Agents,” Emerging Infectious
Disease, Vol. 8, February 2002, pp. 225-230.
24 For more information on laws and regulations related to potential biological terrorism agents, see CRS Report
RL32220, Biological and Chemical Weapons: Criminal Sanctions and Federal Regulations, by Michael John Garcia.
25 For more information on this topic, see CRS Report RL31559, Proliferation Control Regimes: Background and
Status, coordinated by Mary Beth Nikitin.

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