Plant poisons are the toxic substances possessed by the plants and known as phytotoxins and the study of poisoning by plants is called phytotoxicology. Most of the plant poisons are organic irritant poisons and are considered as vegetable poisons. However, there are certain species of toxic plants which act as neurotoxic, spinal, and cardiac poisons.
The toxins of plants are usually biologically active substances known as alkaloids, which are characterized by the presence of nitrogen and their ability to combine with acids to form salts. It has been estimated that about 10 percent of the plant species contain some type of alkaloid. Only a few of the 5,000 alkaloids characterized thus far do not produce any biological activity; most cause a strong physiological reaction when administered to an animal or human being.
Apart from the alkaloids there are certain other biomolecules which are responsible for the toxicity of the plant. They can be polypeptides, glycosides, resins, toxalbumins, oxalate, amines, etc.
Under certain ecological conditions plants may become poisonous as a result of the accumulation of toxic inorganic minerals such as copper, lead, cadmium, fluorine, manganese, nitrates, or selenium. Ingestion of poisonous plants by animals is called photosensitization, which causes toxic effects in such animals.
There is a wide variety of plants present in nature and hence the number of poisonous plants is quite vast which is beyond the limit of this article. Therefore only a few famous plants are mentioned here.
Organic Irritant Plant Poisons
1. Abrus Precatorius
- Common Name– Jequirity bean, ratti
- Active Principle– Abrin
- Poisonous Part– Seeds
- Symptoms– Painful swelling at the puncture site, ecchymosis, necrosis, cardiac arrhythmia, convulsions and death. If ingested then nausea, vomiting, diarrhea and collapse is common.
- Fatal Dose and Fatal Period– 1-2 seeds by ingestion and 90-120mg abrin by injection. Fatal period is 3-5 days.
- Postmortem Appearances– local signs of inflammation, congested internal organs and haemorrhagic patches under mucosal membrane.
- Medicolegal Aspects- Used as an arrow poison to kill cattles usually, but homicidal poisoning of humans is also common.
2. Calotropis sp.
- Common Name– Madar. Akdo
- Active Principle– Calactin, Calotoxin, Calotropin, Gigantin, Uscharin
- Poisonous Part- The serum or the acrid milky juice yielded from the crushed leaves and stems.
- Symptoms– Redness and vesicles on the skin contacted with the juice. If the juice is instilled in the eyes, it causes conjunctivitis and may result in permanent vision impairment. If ingested, then it may cause burning sensation in the throat and stomach, nausea, vomiting and diarrhoea. If the powdered roots are snuffed, death ensues instantly.
- Fatal Dose and Fatal Period-The dose is uncertain and the period is about 12 hours.
- Postmortem Appearances– Dilated pupils, stomatitis, acute inflammation in the alimentary canal, congested viscera.
- Medicolegal Aspects– the whole plant is used in Indian medicine to cure various ailments. It can be used as infanticide, arrow poison, etc.
3. Claviceps Purpurea (fungus)
- Common Name– Ergot
- Active Principle– Ergotoxine, Ergotamine, Ergometrine
- Symptoms– Irritation in throat, nausea, vomiting, diarrhoea, muscle cramps, dizziness, bleeding from nose, etc.
- Fatal Dose and Fatal Period– 1 gm of ergot can cause death within 24 hours.
- Postmortem Appearances– congested viscera, gangrene of fingers and toes.
- Medicolegal Aspect– accidental poisoning is most common
4. Citrullus Colocynthis
- Common Name- Bitter apple, Indrayani
- Active Principle– Colocynthin
- Poisonous Part– Pulp of the fruit which is freed from seeds
- Symptoms– Severe abdominal pain, yellow vomit and yellow watery stools, collapse and death.
- Fatal Dose & Fatal Period– 1-2 gm of fruit pulp can cause death within 24 hours to a few days.
- Postmortem Appearances– Inflamed gastrointestinal tract, kidneys and urinary bladder.
- Medicolegal Aspects- Can be used as abortifacient. Suicidal and accidental deaths are common.
5. Croton Tiglium
- Common Name– Jamalgota, Nepala
- Active Principle– Crotin
- Poisonous Part– Seeds and oil obtained from seeds.
- Symptoms– Oil causes irritation and blistering on the skin. Powerful purging and burning pain at anus. Collapse and death.
- Fatal Dose & Fatal Period– 4 seeds or 20 drops of oil can cause death within 4-6 hours or may be delayed for 3-6 days.
- Postmortem Appearances– Inflamed bowel, occasional erosions and congested organs.
- Medicolegal Aspect– Used as an arrow poison by the tribes. Homicidal and accidental poisoning is common.
6. Ricinus Communis
- Common Name– Arandi, Castor oil plant
- Active Principle– Ricin
- Poisonous Part– Whole plant especially the seeds
- Symptoms– burning throat, salivation, nausea, painful vomiting, bloody purging, dehydration cramps, coma, convulsions and death.
- Fatal Dose & Fatal Period– 10 seeds(6 gm) can cause death within several days.
- Postmortem Appearances– Inflammation and congestion of gastrointestinal tract.
- Medicolegal Aspect– Homicidal and accidental poisoning is common.
7. Semecarpus Anacardium
- Common Name– Marking nut, Bhilawan
- Active Principle– Bhilawanol, Semecarpol
- Poisonous Part– Seeds and the oily acrid juice.
- Symptoms– Redness and painful blisters on the skin if juice is applied. On ingesting the seeds, blisters are observed in the mouth, throat and gastroenteritis, dyspnea, cyanosis, coma and death.
- Fatal Dose & Fatal Period– 5-10 gm of seeds can cause death within 12-24 hours.
- Postmortem Appearances– Black blisters on the skin, inflamed and congested viscera.
- Medicolegal Aspect– Juice is used a s an abortifacient and can be used to cause artificial bruises. Homicidal and accidental poisoning is common.
Other Poisonous Plants
There are other species of plant poisons which are organ specific and they are as follows:
1. Central Nervous System Poison
a) Papaver Somniferum
- Common Name– Poppy plant, Afim
- Active Principle– Morphine, Narcotine, Papaverine, Thebane, etc.
- Poisonous Part– Latex obtained from the unripe fruit
- Effect– It acts as a depressant.
b) Datura Alba
- Common Name– Datura
- Active Principle– Hyoscine, Scopolamine and Laevo Hyoscyamine
- Poisonous Part– Whole plant but the seeds and fruit are more poisonous
- Effect– It acts as a deliriant poison.
c) Cannabis Sativa
- Common Name– Marijuana, Hemp
- Active Principle– Cannabinol
- Poisonous Part– Whole plant especially the leaves
- Effect– It acts as a stimulant as well as hallucinating poison
2. Peripheral Nervous System Poison
a) Strychnos Curare
- Common Name– Curare
- Active Principle– Curine, Curarina
- Poisonous Part– Bark and wood
- Effect– Paralyses the voluntary muscles
b) Conium Maculatum
- Common Name– Spotted hemlock
- Active Principle– Coniine
- Poisonous Part– Whole plant
- Effect– Paralyses the motor nerve terminals of muscles and motor cells of spinal cord and brain.
3. Spinal Poison
a) Strychnos Nux Vomica
- Common Name– Kuchila
- Active Principle– Strychnine, Brucine, Loganin
- Poisonous Part– Seeds, bark, wood and leaves
- Effect– Stimulates the brain and spinal cord leading to increased reflexes of excitability which causes convulsions and opisthotonos.
4. Cardiac Poison
a) Digitalis Purpurea
- Common Name– Foxglove
- Active Principle– Digitalin, Digitoxin, Digitalein
- Poisonous Part– Roots, Leaves and Seeds
- Effect– Heart block and ventricular defibrillation.
b) Nerium Odorum
- Common Name– Oleander, Kaner
- Active Principle– Nerin
- Poisonous Part– Whole plant
- Effect– Heart failure and tetanic spasm.
c) Nicotiana Tobaccum
- Common Name– Tobacco plant
- Active Principle– Nicotine
- Poisonous Part– Leaves
- Effect– Acts as stimulant, then depresses the central nervous system and finally paralyses the ganglia. Heart failure.
The above mentioned plants are found commonly and are in easy reach of human beings. Some of them have medicinal values, ornamental values while some have religious values.
They are commonly encountered in accidental poisoning. However, homicidal poisoning cases are not rare either. But the suicidal poisoning cases are less in number. Usually the vegetable poisons are used by the tribal people who inhabitat in the forests.
In urban areas the use of such plants in causing homicide is not that common as compared to rural areas.