The castor plant is a beautiful, large semi-woody shrub that can grow to 40-feet tall in the right environment. The star-shaped leaves can grow more than 2.5 feet across. Each lobed leaf has serrated edges and prominent central veins that vary in color from green to red to white. Many species have glossy green leaves; others can be purplish, dark red, or maroon. The stems are often a striking red color.
The female flower develops a bundle of seed capsules, each about the size of a large walnut, which are covered with soft flexible spines after pollination. They have notable colors of coral pink or red that fade to brown with maturity.
To protect and defend themselves from herbivores, some plants develop innate immune systems. These defense mechanisms include lectins and proteins that act to make the threatening animals ill after ingestion, resulting in future plant avoidance.
The castor plant has been recognized for thousands of years as having properties that can be used for health benefit but may also be harmful. The two major components are castor oil and ricin.
Ricin: The Poison
Ricin is a poison found naturally in castor beans. A nonmalicious exposure might occur if a castor bean is chewed and swallowed. Mastication releases ricin and causes injury.
Ricin is a natural product that is created from waste material when processing castor beans. It is a heat-labile powder, dissolvable in water or weak acid.
Ricin is a toxalbumin (protein toxin) that is composed of two chains, A and B (the “killer” and the “key”). As a group, they are referred to as ribosome-inactivating proteins (RIPs).
The B chain (key) is a lectin that binds to cell membrane surface glycoproteins and glycolipids, which causes endocytosis and allows ricin to access the cell. Once inside, the A chain (killer) irreversibly inactivates RNA, stopping protein synthesis, leading to cell death.
Ricin is estimated to be 6,000 times more poisonous than cyanide and 12,000 times more poisonous than rattlesnake venom.
One milligram of ricin can kill an adult. The symptoms of human poisoning begin within a few hours of ingestion.
After ingestion, nonspecific symptoms—including nausea, vomiting, diarrhea, and abdominal pain—develop after approximately 12 hours. Ultimately, this progresses to hypotension, liver failure, renal dysfunction, and may progress to death due to multiple organ failure or cardiovascular collapse. After inhalation, symptoms develop within eight hours and include cough, dyspnea, arthralgias, and fever, which may progress to respiratory distress and death, without other organ system manifestations.