Irritant Plant Poisons — Abrus Precatorius, Ricinus, Croton, Calotropis, Semecarpus and Capsicum

Forensic toxicology groups poisons by their main action. Irritant poisons cause local inflammation — vomiting, purging and gastrointestinal bleeding when swallowed, and burning, blisters or keratitis on skin and eyes. Among plants, six are classically examined: Abrus precatorius, Ricinus communis, Croton tiglium, Calotropis, Semecarpus anacardium and Capsicum.

Abrus precatorius (rosary pea, jequirity pea; gunja in Ayurveda) has seeds that are commonly bright red with a black spot, though red, black, orange and white varieties exist. The toxin abrin is a toxalbumin with a reported fatal dose of 0.1–1 µg/kg in humans; boiling is reported to render the seed harmless.

• Whole seeds are relatively harmless when swallowed because the hard outer shell resists digestion; crushed or chewed seeds are the most poisonous.
• Usual fatal dose quoted: 90–120 mg (1–3 seeds); a single chewed seed may be fatal in an adult or child.
• Symptoms: nausea, severe vomiting, abdominal pain, diarrhoea (may appear 3–4 days after ingestion and can be profuse) and gastrointestinal bleeding; less often encephalopathy, arrhythmias and renal failure from volume loss.
• In a JIPMER series of 112 patients, most were women aged 13–30, crushed seeds were the usual form, diarrhoea was the commonest symptom (66%), and mortality was 5.35%.
• Rare neurological sequels reported: acute disseminated encephalomyelitis and central pontine myelinolysis.
• Treatment: no antidote; supportive care with aggressive fluid replacement.

Mechanism of abrin: it has two chains. The B chain binds galactose-containing receptors on the cell surface and lets the A chain enter. The A chain is an RNA N-glycosidase that removes an adenine from the 28S rRNA, so elongation factors cannot bind and protein translation stops completely — the same mechanism as ricin. The classic clinical result is bloody diarrhoea from capillary leak and direct injury to the intestinal mucosa; in the JIPMER series 29% had bloody stools, and all six deaths followed a handful of crushed seeds with profuse bloody diarrhoea within 12 hours.

Ricinus communis (castor bean) seeds contain ricin, a type II ribosome-inactivating protein (A and B chains linked by a disulphide bond), and the alkaloid ricinine. Ricin and ricinine are not transferred into castor oil during pressing — they remain in the seed cake, which is why medicinal castor oil is safe.

• Whole beans can pass intact through the gut; chewing releases ricin, and seeds may act as a 'timed-release capsule' in the lower bowel.
• Estimated fatal oral dose of ricin: 1–20 mg/kg, roughly 5–10 beans.
• Features: vomiting, diarrhoea, abdominal pain, massive fluid and electrolyte loss, haematemesis or melaena, then hypovolaemic shock and multi-organ failure involving liver, spleen and kidney.
• In animals, ricin given by injection or inhalation is about 1000 times more toxic than by mouth, because oral ricin is partly destroyed in the gut; there is a delay of hours before death even at high doses.
• Ricin has been used in biocrime because castor beans are easy to obtain.

Croton tiglium seeds contain an irritating oil, a toxic protein called crotin (made of crotonglobulin and crotonalbumin), and strong purgative principles — phorbol esters and crotonic acid. The plant is used in Ayurveda for constipation only after a purification process (Śodhana), which has been shown to reduce the phorbol content and remove crotonic acid.

Calotropis (C. gigantea and C. procera; milkweed; jilledu in parts of South India) exudes a copious milky latex. Its toxic principles — calotropin, uscharin, calotoxin and calactin — are cardenolide glycosides that inhibit the Na⁺/K⁺-ATPase, with digoxin-like effects.

Marking nut or bhilawa is the fruit of Semecarpus anacardium (family Anacardiaceae, related to cashew and to the poison-ivy group). The pericarp contains a tarry oil of anacardic acid (about 90%) and cardol (about 10%), together with bhilawanols (urushiols), semecarpol and anacardol. Bhilawanol and anacardic acid cause irritation, blisters and contact dermatitis.

• Exposure causes an irritant or allergic contact dermatitis with vesicles and blisters.
• It can be applied deliberately to produce factitious dermatitis (dermatitis artefacta) — the medico-legal point: self-made lesions that can be mistaken for disease or injury.
• Ayurvedic processing (Śodhana) of the fruit can itself cause dermatitis; workers apply coconut oil to exposed skin to reduce it.

The irritant in chilli is capsaicin, which activates the TRPV1 (transient receptor potential vanilloid 1) pain receptor. Concentrated oleoresin capsicum is the active agent of pepper spray. By contrast, tear gases such as CS activate TRPA1. StatPearls notes that capsicum exposures cause more intense burning and inflammation than CS, which tends to resolve faster.

• Eyes: intense burning and inflammation; corneal abrasions and keratitis, rarely vision loss.
• Skin: burning and inflammation. Airways: respiratory symptoms, usually self-limited.
• Management: remove contaminated clothing and irrigate copiously with water — the first-line treatment; fluorescein examination if eye symptoms persist.
• Warning signs: confined-space exposure, symptoms beyond 30–60 minutes, hypoxia or vision changes. Activated charcoal and gastric decontamination are not indicated.

1. Identify the plant and the form taken — whole versus crushed or chewed seeds matters for abrus and castor, because intact seeds may pass through unchanged. Intact and crushed seeds may be found in vomitus and stool.
2. Look for the dominant syndrome — gastroenteritis with fluid loss (abrus, ricinus, croton), cardiac toxicity (Calotropis), or local skin and eye injury (Calotropis latex, marking nut, capsicum).
3. Resuscitate — fluids and electrolytes; most abrus diarrhoea settles with fluid support. Watch for hypovolaemic shock and renal failure.
4. Monitor the heart after Calotropis ingestion, as its cardenolides act like digoxin.
5. Decontaminate the surface — wash skin and irrigate eyes with water for latex, marking-nut juice or pepper spray; refer persistent eye symptoms for slit-lamp and fluorescein examination.
6. Record medico-legal findings — intent (suicidal, accidental, homicidal, cattle poisoning) and any lesion that could be self-made.