Toxin in Castor Beans

Overview

The mottled seeds of the castor bean plant may look about as harmless as the pinto bean they resemble, but they contain one of the world's most deadliest toxins. Though the valuable oil pressed from the seeds does not contain the toxin, the flesh of the seed itself contains a dose of ricin that would be lethal to most young children.

Description

The castor bean plant (Ricinus communis) is a member of the Spurge plant family that originated in Ethiopia but is now distributed through many parts of the world. It is present both as a cultivated ornamental and escaped wild plant in at least 27 states, and is reviled as a pest weed in Australia. Also known as the umbrella plant, the castor bean can grow 15 feet tall and features large, deeply palmate leaves. In spring, pink and white flowers give way to spiky seed heads that mature to reveal several smooth, spotted seeds. Though the plant's notorious toxins are found in small quantities in most parts of the plant, the highest concentrations are in the seeds.

Ricin

Gram for gram, ricin is among the most potent poisons in existence, 6,000 times more toxic than cyanide and 12,000 times more poisonous than rattlesnake venom. The toxic compounds in castor beans are soluble in water, meaning they are not present in oils pressed from the seed. However, when ingested, the alkaloid toxin ricinine and protein toxin ricin are easily absorbed through the lining of the stomach and intestines; seeds with unbroken coats may pass through the digestive tract without harm. Ricin is a potent cytotoxin, a type of poison that destroys cells. In the case of the castor bean, the responsible toxin halts the protein synthesis process of red blood cells, which leads to cell death. Ricin also causes blood cells to agglutinate, or clump together.

Symptoms of Poisoning

One castor bean contains enough ricin to kill a child, while the ricin in several seeds---roughly 0.5 milligrams---is enough to kill an adult. The first symptoms of ricin poisoning may show up within 12 hours or as long as 48 hours after ingestion. Early symptoms include stomach irritation, nausea and vomiting and bloody diarrhea. Later symptoms include increased heart rate and copious sweating, collapse, seizures and, finally, death within several days. Victims who survive past five days generally make a full recovery.

Toxicity in Animals

Many animals are susceptible to ricin poisoning, especially if they are housed in an area where the plant is growing and seeds are accidentally ingested. Though larger animals are somewhat more tolerant of higher doses, dogs, pigs and ducks display the highest resistance to poisoning. Though six ingested beans may kill an ox or a horse, a dog may not suffer symptoms until it has eaten 11 beans, and a lethal dose for a duck is around 80 seeds. Animals display many of the same poisoning symptoms as humans, but also include violent vomiting, lethargy, trembling or convulsions, and premature molting in birds. Dehydration is a serious risk for animals poisoned by ricin.

Treatment

No specific antidote is available to treat ricin poisoning. However, if symptoms are recognized right away, the United States Centers for Disease Control recommends immediate administration of intravenous fluids and vasopressor drugs to increase blood pressure. If a person or animal ingests ricin or castor beans but is not yet vomiting, a single dose of activated charcoal should be administered. Stomach pumping is an alternative treatment.

Uses

The oil pressed from the castor bean seed has many uses in commerce. Castor oil is a main ingredient in many synthetic motor oils; dehydrated, the oil is used widely as a component in quick-drying paints and varnishes. It is one of the main ingredients used in the production of nylon, and the oil's chemical structure makes it invaluable for producing artificial fruit flavors and in the production of soaps, inks, plastics and insecticides. Seed meal leftover from the oil-pressing process is cooked to deactivate the ricin toxins and is used in many types of animal feed.

Keywords: castor bean toxins, castor bean toxicity, castor plant poisons

About this Author

Michelle Z. Donahue lives in Washington, D.C., and has worked there as a journalist since 2001, when she graduated from Vanderbilt University with a B.A. in English. She first covered politics as a reporter for the weekly Fairfax Times newspaper, then for the daily newswire Canadian Economic Press, where she reported from the U.S. Treasury. Donahue is currently a freelance writer.