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In the context of biology, poisons are substances that can cause damage, illness, or death to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism. Paracelsus, the father of toxicology, once wrote: "Everything is poison, there is poison in everything. Only the dose makes a thing not a poison."
In medicine (particularly veterinary) and in zoology, a poison is often distinguished from a toxin and a venom. Toxins are poisons produced via some biological function in nature, and venoms are usually defined as biologic toxins that are injected by a bite or sting to cause their effect, while other poisons are generally defined as substances which are absorbed through epithelial linings such as the skin or gut.
Some poisons are also toxins, usually referring to naturally produced substances, such as the bacterial proteins that cause tetanus and botulism. A distinction between the two terms is not always observed, even among scientists.
Animal toxins that are delivered subcutaneously (e.g. by sting or bite) are also called venom. In normal usage, a poisonous organism is one that is harmful to consume, but a venomous organism uses poison to defend itself while still alive. A single organism can be both venomous and poisonous.
The derivative forms "toxic" and "poisonous" are synonymous.
Within chemistry and physics, a poison is a substance that obstructs or inhibits a reaction, for example by binding to a catalyst. For example, see nuclear poison.
The phrase "poison" is often used colloquially to describe any harmful substance, particularly corrosive substances, carcinogens, mutagens, teratogens and harmful pollutants, and to exaggerate the dangers of chemicals. The legal definition of "poison" is stricter.
Uses of poison
Poisons are usually not used for their toxicity, but may be used for their other properties. The property of toxicity itself has limited applications: mainly for controlling pests and weeds, and for preserving building materials and food stuffs. Where possible, specific agents which are less poisonous to humans have come to be preferred, but exceptions such as phosphine continue in use.
Throughout human history, intentional application of poison has been used as a method of assassination, murder, suicide and execution.  As a method of execution, poison has been ingested, as the ancient Athenians did (see Socrates), inhaled, as with carbon monoxide or hydrogen cyanide (see gas chamber), or injected (see lethal injection). Many languages describe lethal injection with their corresponding words for "poison shot". Poison was also employed in gunpowder warfare. For example, the 14th century Chinese text of the Huo Long Jing written by Jiao Yu outlined the use of a poisonous gunpowder mixture to fill cast iron grenade bombs.
Poisonous materials are often used for their chemical or physical properties other than being poisonous. The most effective, easiest, safest, or cheapest option for use in a chemical synthesis may be a poisonous material. Particularly in experimental laboratory syntheses a specific reactivity is used, despite the toxicity of the reagent. Chromic acid is an example of such a "simple to use" reagent. Many technical applications call for some specific physical properties; a toxic substance may possess these properties and therefore be superior. Reactivity, in particular, is important. Hydrogen fluoride, for example, is poisonous and extremely corrosive. However, it has a high affinity for silicon, which is exploited by using HF to etch glass or to manufacture silicon semiconductor chips.
Acute poisoning is exposure to a poison on one occasion or during a short period of time. Symptoms develop in close relation to the exposure. Absorption of a poison is necessary for systemic poisoning. In contrast, substances that destroy tissue but do not absorb, such as lye, are classified as corrosives rather than poisons.
Chronic poisoning is long-term repeated or continuous exposure to a poison where symptoms do not occur immediately or after each exposure. The patient gradually becomes ill, or becomes ill after a long latent period. Chronic poisoning most commonly occurs following exposure to poisons that bioaccumulate such as mercury and lead.
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 as used as method of execution on US gas chambers almost instantly starves the body of energy by inhibiting the enzymes in mitochondria that make 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.
Most (but not all) biocides, including pesticides, are created to act as poisons to target organisms, although acute or less observable chronic poisoning can also occur in non-target organism, including the humans who apply the biocides and other beneficial organisms. For example, the herbicide 2,4-D imitates the action of a plant hormone, to the effect that the lethal toxicity is specific to plants. Indeed, 2,4-D is not a poison, but classified as "harmful" (EU).
Many substances regarded as poisons are toxic only indirectly, by toxication. An example is "wood alcohol" or methanol, which is not poisonous itself, but is chemically converted to toxic formaldehyde and formic acid 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 individuals.
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.
Initial medical management
Some poisons have specific antidotes:
Types of poisons
The majority of this section is sorted by ICD-10 code, which classifies poisons based upon the nature of the poison itself. However, it is also possible to classify poisons based upon the effect the poison has (for example, "Metabolic poisons" such as Antimycin, Malonate, and 2,4-Dinitrophenol act by adversely disrupting the normal metabolism of an organism.)
(T36-T50) Poisoning by drugs, medicaments and biological substances
(T44.) Poisoning by drugs primarily affecting the autonomic nervous system 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. One class of toxins of interest to neurochemical researchers are the various cone snail toxins known as conotoxins.
Cell membrane disrupters Others
(T45.) Poisoning by primarily systemic and haematological agents, not elsewhere classified
(T46.) Poisoning by agents primarily affecting the cardiovascular system
(T50.) Poisoning by diuretics and other unspecified drugs, medicaments and biological substances
(T51-T65) Toxic effects of substances chiefly nonmedicinal as to source
(T51.) Toxic effect of alcohol
(T52.) Toxic effect of organic solvents
(T53.) Toxic effect of halogen derivatives of aliphatic and aromatic hydrocarbons
Acids (T54.2) Strong inorganic acids, such as concentrated sulfuric acid, nitric acid or hydrochloric acid, destroy any biological tissue with which they come in contact within seconds.
Bases (T54.3) 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. Quicklime, which has household uses, is a particularly common cause of poisoning. Some of the light metals, if handled carelessly, can not only cause thermal burns, but also produce very strongly basic solutions in sweat.
(T55.) Toxic effect of soaps and detergents
(T56.) Toxic effect of metals A common trait shared by toxic metals is the chronic nature of their toxicity (a notable exception would be bismuth, which is considered entirely non-toxic). Low levels of toxic metal salts ingested over time accumulate in the body until toxic levels are reached. Toxic metals are often inaccurately referred to as "heavy metals", although not all heavy metals are necessarily harmful and not all toxic metals are heavy metals.
Toxic metals are generally far more toxic when ingested in the form of soluble salts than in elemental form. For example, metallic mercury passes through the human digestive tract without interaction and is commonly used in dental fillings—even though mercury salts and inhaled mercury vapor are highly toxic.
(T57.) Toxic effect of other inorganic substances
(T59.) Toxic effect of other gases, fumes and vapours
Oxidizers Poisons of this class are generally not very harmful to higher life forms such as humans (for whom the outer layer of cells are more or less disposable), but lethal to microorganisms such as bacteria. Typical examples are ozone and chlorine (T59.4), either of which is added to nearly every municipal water supply in order to kill any harmful microorganisms present.
All halogens are strong oxidizing agents, fluorine (T59.5) being the strongest of all.
(T60.) Toxic effect of pesticides
(T61.) Toxic effect of noxious substances eaten as seafood
(T62.) Toxic effect of other noxious substances eaten as food
(T65.) Toxic effect of other and unspecified substances
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Poison". A list of authors is available in Wikipedia.|