Toxin

Universal warning symbol used to indicate toxic substances or environments

A toxin (Greek: τοξικόν, toxikon, lit. (poison) for use on arrows) is a poisonous substance produced by living cells or organisms^[1] that is active at very low concentrations. Toxins can be small molecules, peptides, or proteins and are capable of causing disease on contact with or absorption by body tissues by interacting with biological macromolecules such as enzymes or cellular receptors. Toxins vary greatly in their severity, ranging from usually minor and acute (as in a bee sting) to almost immediately deadly (as in botulinum toxin).

Toxins are often distinguished from other chemical agents by its method of production- the word toxin does not specify method of delivery (compare with venom and (the narrower meaning) of poison). It simply means it is a biologically produced poison. There was an ongoing dispute between NATO and the Warsaw Pact over whether to call a toxin a biological or chemical agent, in which the former opted for the latter, and vice versa.

Biotoxins vary greatly in purpose and mechanism, and can be highly complex (the venom of the cone snail contains dozens of small proteins, each targeting a specific nerve channel or receptor), or relatively small protein.

Biotoxins

Biotoxins in nature have two primary functions:

• Predation (spider, snake, scorpion, jellyfish, wasp)
• Defense (bee, poison dart frog, honeybee, wasp)

Some of the more well known types of biotoxins include:

• Cyanotoxins, produced by cyanobacteria
• Hemotoxins target and destroy red blood cells, and are transmitted through the bloodstream. Organisms that produce hemotoxins include:
  • Pit vipers, such as rattlesnakes
• Necrotoxins cause necrosis (i.e., death) in the cells they encounter and destroy all types of tissue. Necrotoxins spread through the bloodstream. In humans, skin and muscle tissues are most sensitive to necrotoxins. Organisms that possess necrotoxins include:
  • The brown recluse or "fiddle back" spider
  • The "Puff Adder" - Bitis arietans
  • Necrotizing fasciitis (the "flesh eating" bacteria)
• Neurotoxins primarily affect the nervous systems of animals. Organisms that possess neurotoxins include:
  • The Black Widow and other widow spiders
  • Most scorpions
  • The box jellyfish
  • Elapid snakes
  • The Cone Snail
• Cytotoxins are toxic at the level of individual cells, either in a non-specific fashion or only in certain types of living cells:
  • Ricin is a plant toxin found in the castor bean plant

Environmental toxins

Non-technical usage

When used non-technically, the term "toxin" is often applied to any toxic substances. Toxic substances not of biological origin are more properly termed poisons. Many non-technical and lifestyle journalists also follow this usage to refer to toxic substances in general, though some specialist journalists at publishers such as the BBC and The Guardian maintain the distinction that toxins are only those produced by living organisms.

In the context of alternative medicine the term is often used non-specifically to refer to any substance claimed to cause ill health, ranging anywhere from trace amounts of pesticides to common food items like refined sugar or additives like artificial sweeteners and MSG.

See also

• Apitoxin
• Exotoxin
• Hemotoxin
• Mycotoxin
• Neurotoxin
• Phototoxin
• Cardiotoxin III
• Toxicophore
• Toxoid
• Venom
• List of fictional toxins

References

External links

• Society of Toxicology
• The Journal of Venomous Animals and Toxins including Tropical Diseases
• Cycad toxicity
• Corrections and clarifications, The Guardian, 30 May, 2005.
• Special Issue on "Marine Toxins"