Castor Beans and Conspiracies: The Profile of a Toxin

Ricin is a white powder that is easily made from castor beans and highly lethal. It is amongst the most poisonous of known substances. The lowest published lethal concentration is 300µg/kg. It is deadly through ingestion or inhalation. The effect is violent purging which leads to collapse and death. It either causes severe dehydration, or the destruction of red blood cells. It has molecular weights of 60,000 and 120,000 and is a by-product of making castor oil, which does not contain this toxin.

When the castor oil seeds are pressed, the oil cake residue left over is mainly protein and is the source of the toxin, which is a toxalbumin that can comprise up to 3% of the total weight of a castor seed. Toxalbumins are very toxic plant derivatives that combine carbohydrate and protein components. Ricin is water soluble, which is why castor oil will not contain it, if correctly produced.

The castor bean is native to Africa but is planted throughout the US. It is commercially grown in California, Illinois, Kansas, Missouri, Oklahoma, and Oregon. In the South it grows as a weed and is most often found near stream beds, dumping grounds, barnyards or along roadsides. Castor bean is used also as an ornamental shrub, occasionally planted indoors or outdoors.

Ricin is a powerful neurotoxin, that is at least 10 times as potent as potassium cyanide. Its toxic properties are said to be at least equivalent to those of tetanus or botulism. Humans as well as cattle, dogs, goats, horses, poultry, rabbits, insects, sheep, and swine have been poisoned by eating castor seeds. The ricin content is highest in the seeds, but also present in the leaves. Swallowing a seed without chewing reduces the risk of poisoning because of the hard seed cover. Chewing, though, allows the release of the water-soluble chemical so that poisoning occurs.

One of the variations of ricin, is actually ricinus communis agglutinin (RCA), a different protein. It is this protein that causes the hemaglutonating activity and coagulation of red blood cells, leading to blood poisoning and eventually death. There is a wide variation of sensitivity to this toxin, from species to species. A lethal dose by injection can be as small as two-millionths of total body weight. Ricin is a potent cytotoxin but a weak hemagglutinin, whereas RCA is a weak cytotoxin and a powerful hemagglutinin. Poisoning by ingestion of the castor bean is caused by Ricin, not by RCA. RCA does not penetrate the intestinal wall; it cannot attack red blood cells unless it is in the bloodstream. Once in the blood stream, it will cause the red blood cells to agglutinate and burst by hemolysis.

The symptoms of poisoning by ingestion begin within a few hours and start with abdominal pain, vomiting, and (occasionally bloody) diarrhea. Within several days it progresses to severe dehydration, causing a decrease in urine and blood pressure. If death does not occur within five days, the victim usually recovers. It is said that just one seed can kill a child, as children are more affected by fluid loss from vomiting and diarrhea, and can more quickly become severely dehydrated.

The castor plant is used to make paints, varnishes, lacquers, oils such as hydraulic brake fluid and aviation fuel, certain types of laundry detergent, as a plasticizer, for wire coating, and for fertilizer. If not produced properly, it is possible that all of these could have some amounts of ricin present. It is because of this wide usage of castor products (and other factors such as personal experience) that some have hypothesized that ricin might be an environmental cause of Lou Gehrig's Disease.

One example of the use of ricin for specifically lethal purposes was in the famous Umbrella Murder of Georgi Markov. It is estimated that only 450µg were used to kill this Bulgarian dissident, in 1978.

Besides this real life case, ricin has also appeared in fiction. "The House of Lurking Death" by Agatha Christie, features two deaths caused by ricin mixed with fig paste.