Ricin: Technical Background and Potential Role in Terrorism [Updated April 19, 2013] [open pdf - 852KB]
From the Summary: "In April 2013, envelopes sent to President Obama and a U.S. Senator tested positive for ricin, a deadly toxin derived from castor beans. Ricin has been identified as a potential bioweapon. Ricin is extremely toxic by ingestion, inhalation, and injection. No treatment or prophylaxis currently exists, though research into new therapies and vaccines against ricin exposure continues. Additionally, research to improve ricin detection is ongoing. Although governments have investigated ricin's potential use as a military weapon, individuals have used ricin in small quantities. Most experts believe that ricin would be difficult to use as a weapon of mass destruction, but do not discount its potential as a weapon of terror. Ricin is a select agent, and its possession, transfer, or use is regulated under domestic and international law. This report will not be updated."
CRS Report for Congress, RS21383
Congressional Research Service: https://crsreports.congress.gov/