Poisons and toxins
Poisons are substances that cause harm to organisms when sufficient quantities are absorbed, inhaled or ingested. Some poisons make an organism sick, others may cause it to die and yet others may lead to subtle changes in health that may not be noticed for years. Toxicology is the science of poisons. It is the study of harmful effects of chemicals on living organisms.
Some people associate the word ‘chemical’ with manufactured poisons. However, a chemical is not harmful just because it’s manufactured nor is it harmless just because it’s natural. Potentially poisonous chemicals can be synthetic (manufactured) or natural. For example, dioxins, some pesticides and nerve gases are poisonous manufactured chemicals, whereas, belladonna, botulinum and tetrodotoxin are poisonous naturally produced chemicals. There are also poisonous substances that occur naturally in the ground, such as asbestos and lead.
The seven most deadly (to humans) chemical substances are:
- botulinum toxin A (from bacteria – Clostridium botulinum)
- tetanus toxin A (from bacteria – Clostridium tetani)
- diphtheria toxin (from bacteria – Corynebacterium diphtheriae)
- dioxin (manufactured)
- muscarine (from mushrooms – Amanita muscaria)
- bufotoxin (from the common toad – genus Bufo)
- sarin (manufactured).
In science, a toxin is often considered a specific type of poison – a poisonous substance produced within living cells or organisms. Some scientists, though, refer to toxins as they would any poison and call those toxins that have a living source ‘biotoxins’ or ‘natural toxins’. Venoms are toxins that are injected by a bite (for example, from a spider) or sting (for example, from a wasp) to cause their effect.
Five of the seven most deadly known compounds have their source in nature (see list above). Toxins may be classified as exotoxins (those excreted by an organism, for example, bufotoxin) or endotoxins (toxins that are structurally part of bacteria, for example, botulinum).
The most toxic compound is the toxin botulinum. It is a million times more deadly than the most deadly manufactured compound – dioxin. One teaspoon of botulinum could kill a quarter of the world’s population! Botulinum is the compound that is used in Botox® – a popular method of reducing wrinkles from the skin. The toxin blocks nerve impulses and temporarily paralyses the muscles that cause wrinkles, giving the skin a smoother appearance. Botulinum is also used for medical procedures such as the treatment of muscle spasms.
Toxins cause harm to organisms when the toxic compound comes in contact with or is absorbed by body tissues. These compounds interact with parts of the body. Toxins vary greatly in the severity of their affect, ranging from minor but acute (bee stings) to almost immediately deadly (botulinum).
They can be classified according to the location of the body where their effects are most notable:
- Hemotoxins (for example, found in some snakes) destroy red blood cells and cause general tissue damage.
- Phototoxins (for example, alpha-terthienyl found in marigold plants) cause allergic reactions in susceptible individuals.
- Necrotoxins (for example, necrotising fasciitis – flesh-eating bacteria) destroy cells they encounter and cause general tissue damage.
- Neurotoxins (for example, tetrodotoxin found in pufferfish and some grey side-gilled sea slugs) affect the nervous system of organisms
The function of toxins
Toxins in nature have two primary functions:
- Predation – killing a potential meal (for example, spiders, jellyfish, wasps and sea anemones).
- Defence – discouraging the predator (for example, honey bees, ants and monarch butterflies, and plants such as broccoli produce a toxin to discourage insects from eating them).
Antidotes or cures for particular toxins are produced using the toxin itself. Small doses of the toxin are injected into an animal to stimulate the animal’s immune system to produce antibodies to destroy the toxin. Serum (containing the antibodies) is harvested from the animal’s blood, and this serum with the antibodies becomes the antidote for that particular toxin. Some toxins have no known antidote, such as highly poisonous aconitine – a toxin derived from the aconite plant species. However, this toxin can be given in small doses as a calming medicine!