Toxin

Universal warning symbol used to indicate toxic substances or environments

A toxin (Greek: τοξικόν, toxikon) is a poisonous substance produced by living cells or organisms^[1][2] (although humans are technically living organisms, man-made substances created by artificial processes usually are not considered toxins by this definition). It was the organic chemist Ludwig Brieger (1849-1919) who first used the term 'toxin'. ^[3]

For a toxic substance not produced by living organisms, "toxicant" is the more appropriate term, and "toxics" is an acceptable plural .

Toxins can be small molecules, peptides, or proteins that are capable of causing disease on contact with or absorption by body tissues 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).

Terminology

Toxins are often distinguished from other chemical agents by their 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.

According to a International Committee of the Red Cross review of the Biological Weapons Convention, "Toxins are poisonous products of organisms; unlike biological agents, they are inanimate and not capable of reproducing themselves." and "Since the signing of the Convention, there have been no disputes among the parties regarding the definition of biological agents or toxins..."^[4]

According to Title 18 of the United States Code, "...the term "toxin" means the toxic material or product of plants, animals, microorganisms (including, but not limited to, bacteria, viruses, fungi, rickettsiae or protozoa), or infectious substances, or a recombinant or synthesized molecule, whatever their origin and method of production..."^[5]

A rather informal terminology of individual toxins relate them to the anatomical location where their effects are most notable:

• Hemotoxin, causes destruction of red blood cells (hemolysis)
• Phototoxin, causes dangerous photosensitivity

On a broader scale, toxins may be classified as either exotoxins, being excreted by an organism, and endotoxins, that are released mainly when bacteria are lysed.

Related terms are:

• Toxoid, weakened or suppressed toxin
• Venom, toxins in the sense of use by certain types of animals

Biotoxins

The term "biotoxin" is sometimes used to explicitly confirm the biological origin.^[6][7]

Toxins produced by microorganisms are important virulence determinants responsible for microbial pathogenicity and/or evasion of the host immune response.^[8]

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 in nature have two primary functions:

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

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
• Apitoxin, the honey bee venom
• Mycotoxins are toxins produced by fungi. They are a common source of toxins in grains and other foods.

Environmental toxins

The term "environmental toxin" is often used.^[9][10][11]

In these contexts, it can sometimes explicitly include contaminants that are man-made,^[12] which contradicts most formal definitions of the term "toxin". Because of this, when encountering the word "toxin" outside of microbiological contexts, it is important to confirm what the researcher means by the use of the term. The toxins from food chains which maybe dangerous to human health include:

• Paralytic shellfish poisoning (PSP) ^{[13], [14], [15]}
• Amnesic shellfish poisoning (ASP) ^{[16], [17]}
• Diarrheal shellfish poisoning (DSP) ^{[18], [19]}
• Neurotoxic shellfish poisoning (NSP) ^{[20], [21], [22]}

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 Guardian^[23] maintain the distinction that toxins are only those produced by living organisms.

In the context of alternative medicine the term is often used non-scientifically 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 such as monosodium glutamate (MSG).^[24]

See also

• Brevetoxin
• Insect toxins
• List of fictional toxins
• List of highly toxic gases
• Mycotoxin
• Microbial toxins
• Toxicophore, feature or group within a chemical structure that is thought to be responsible for the toxic property

References

External links

• Toxin-target database
• ATDB: A animal toxin database
• Society of Toxicology
• The Journal of Venomous Animals and Toxins including Tropical Diseases