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Poison

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In the context of biology, poisons are substances that cause injury, illness, or death to organisms, usually by chemical reaction or other activity on the molecular scale. Some poisons are also toxins, and a distinction between the two terms is not always observed, even among scientists. The derivative forms "toxic" and "poisonous" are synonomous. Within chemistry and physics, a poison is a substance that obstructs or inhibits a reaction, for example by binding to a catalyst.

Biological poisoning

Contact or absorption of poisons can cause rapid death or impairment. Agents that act on the nervous system can paralyze in seconds or less, and include both biologically derived neurotoxins and so-called nerve gases, which may be synthesized for warfare or industry. Inhaled or ingested cyanide almost instantly starves the body of energy by poisoning mitochondria and the synthesis of ATP. Intravenous injection of an unnaturally high concentration of potassium chloride, such as in the execution of prisoners in parts of the United States, quickly stops the heart by eliminating the cell potential necessary for muscle contraction. Such rapid reactions are often called acute poisoning.

A poison may also act slowly. This is known as chronic poisoning and is most common for poisons that bioaccumulate. Examples of these types of poisons are mercury, lead, and asbestos.

Many substances regarded as poisons are toxic only indirectly. An example is "wood alcohol" or methanol, which is not poisonous itself, but is chemically converted to toxic formaldehyde in the liver. Many drug molecules are made toxic in the liver, and the genetic variability of certain liver enzymes makes the toxicity of many compounds differ between one individual and the next.

Milkweeds (Asclepias sp.) produce glycosides which are toxic to most organisms. (It is unlikely that any organism will eat much because of the extremely bitter taste.) Monarch butterfly larvae, however, are not susceptible to the toxin; in fact they accumulate it in their bodies as they eat the leaves of their host plant. Any predator who wishes to make a meal of an adult monarch will tend to be dissuaded by the bitter taste, and learn to leave the brightly colored insects alone. This gives considerable protection for monarchs from birds and other predators.

The study of the symptoms, mechanisms, treatment and diagnosis of biological poisoning is known as toxicology.

Exposure to radioactive substances can produce radiation poisoning, an unrelated phenomenon.

Classification of biological poisons by mechanism

Corrosives

Corrosives mechanically damage biological systems on contact. Both the sensation and injury caused by contact with a corrosive resembles burn injury.

Acids

Strong inorganic acids, such as concentrated sulfuric acid, nitric acid or hydrochloric acid, destroy any biological tissue they come in contact with within seconds.

Bases

Strong inorganic bases, such as lye, gradually dissolve skin on contact but can cause serious damage to eyes or mucous membranes much more rapidly. Ammonia is a far weaker base than lye, but has the distinction of being a gas and thus may more easily come into contact with the sensitive mucous membranes of the respiratory system.

Oxidizers

Poisons of this class are generally not very harmful to higher life forms such as humans, but lethal to microorganisms such as bacteria. Typical examples are ozone and chlorine, either of which is added nearly every municipal water supply in order to to kill any harmful microorganisms present.

Reducing agents

Metabolic poisons (energy)

Specific biochemical inhibitors

Heavy metals

A common trait shared by heavy metals is the chronic nature of their toxicity. Low levels of heavy metal salts ingested over time accumulate in the body until toxic levels are reached.

Notable examples:


Neurotoxins

Neurotoxins interfere with nervous system functions and often lead to near-instant paralysis followed by rapid death. They include most spider and snake venoms, as well as many modern chemical weapons.

Anticholinesterases

Acetylcholine Antagonists

Cell Membrane Disrupters

Teratogens (birth defects)

Mutagens (DNA damage)

Carcinogens (cancer)

Examples of biological poisons by source

Note: Items below should be added as examples under the appropriate poison class above.

Non-radioactive inorganic poisons

Organic poisons

Naturally produced posions and toxins


Famous poisonings

Poisons in crime fiction

This is of course an inexhaustive list. You may wish to add other novels and/or specify the poisons used.

Novels:

Films:

See Also venom --toxicity -- Antidote -- Mithridates VI of Pontus -- Pollutant -- Lethal injection --Toxicity rating -- biosecurity -- Lead poisoning--skull and crossbones.

Poison is also the name of a US rock band active in the 1980s and 1990s. For more information, see Poison.

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