Data
Many studies have been conducted to determine the toxicity of ricin using several different animals. It is estimated that the toxin is approximately 1,000 times less effective when administered orally than when injected. Below is a table outlining the the median lethal dose of ricin for several different animals. Values for toxicity in humans were estimated using case studies of accidental ingestion or intentional injection of the toxin.
Most studies focusing on the toxicity of ricin are concerned with the possibility of its use as a weapon of bioterrorism. While it is most effective when administered by injection, this method is not a practical mode of delivery for bioterrorism purposes. This leaves ingestion and inhalation as the only two viable delivery methods. Experts speculate that inhalation would be the most effective route of administration for this specific cause. Some research has investigated the weaponization of ricin, but further research is needed to determine whether development of such weapons is a significant nationall security threat. It is currently not known how much ricin must be inhaled to prove lethal. It is also challenging to determine effective doses for inhaled ricin because the delivery into the lungs depends on particle size, the solvent used, and several other factors.
There is no reported NOAEL for ricin. Physical symptoms include nausea, vomiting, diarrhea, dyspnea, vertigo, muscular pain, emesis, dehydration, circulatory collapse, and eventually death. Muscular pain and circulatory collapse are most commonly observed in cases of injected ricin. Additionally, ingestion of ricin can lead to significant erosion of the intestinal mucosa and, in extreme cases, leads to fatal hypovolemic shock.
The majority of hard data concerning the effects of ricin on humans is derived from case reports of accidental ingestion of the toxin or parenteral administration with a malicious or suicidal intent. Below is a table detailing multiple case studies of parenteral administration of ricin (Beasley et. al., 2009):
Death from oral consumption of the ricin-containing castor bean (Ricinus communis) is much less common than by injection of ricin extract. Most fatalities after ingesting the beans occurred in the pre-modern medicine era. The following table outlines several recent cases of Ricinus communis ingestion and the following outcomes (Avondet et al., 2011):