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Encyclopedia > Poisons
This article is about the dangerous substance. For the band see Poison.
The skull and crossbones symbol traditionally used to label a poisonous substance.

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, usually referring to naturally produced substances that kill rapidly in small quantities, 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. Poisons have been known to be symbolized by the skull and crossbones (shown beside), although since this attracts children (being linked to pirates) it is gradually being replaced by Mr. Yuk.


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 and lead.

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.

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


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.


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.


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 kill any harmful microorganisms present. All halogens are strong oxidizing agents, fluorine being the strongest of all.

See also: Free radical

Reducing agents

The most notable substance in this class is phosphorus.

Metabolic poisons (energy)

Metabolic poisons act by adversely disrupting the normal metabolism of an organism.

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.

Heavy 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.

Notable examples:

  • beryllium (a highly but subtly toxic light metal)


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.


  • Fasciculin

Acetylcholine antagonists

Cell membrane disrupters


  • Nicotine - not strictly a neurotoxin, but capable in large doses of causing heart attack

Teratogens (birth defects)

Mutagens (DNA damage)

Carcinogens (cancer)

A carcinogen is a chemical substance which is believed to cause cancer. There are an enormous variety of possible carcinogens. Some of the better known or more controversial examples are listed below.

  • Some artificial sweeteners (e.g. Aspartame and Saccharin) have been alleged to be carcinogenic or neurotoxic (however these research behind these claims is highly controversial and inconclusive; the FDA believes aspartame is safe for humans in dietary doses).
  • Asbestos - a widely used insulating material that causes mesothelioma and other cancers especially in the respiratory tract.
  • Benzene (lab solvent, used in various chemical reactions).
  • Carbon tetrachloride (formerly used in fire extinguishers).
  • Dioxin - actually a group of many chemicals - has carcinogenic and other toxic effects.

Examples of biological poisons by source

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

Non-radioactive inorganic poisons

  • Arsenic compounds
    • arsenic trioxide
    • Fowler's solution
  • Acids and bases, corrosives
    • ammonia
    • The 6 strong acids are all listed above (besides HBr and HI, which are debatably important)
    • Lye
    • Lime, Quicklime, various light metal oxides, hydroxides, superoxides
    • Bleach, some pool chemicals, other hypochlorates (acidic and oxydizing effect)
    • hydrofluoric acid

Organic poisons

Naturally produced poisons and toxins

Famous poisonings

See also victims of poisoning

Confirmed poisonings

Viktor Yushchenko as he appeared in July 2004 (left) and as he appeared in November 2004 (right) after dioxin poisoning
Viktor Yushchenko as he appeared in July 2004 (left) and as he appeared in November 2004 (right) after dioxin poisoning
  • Bhopal Disaster — An accidental release of poisonous gas from a pesticide plant in India that killed over 2,000 people and injured many more.
  • Jonestown inhabitants — died from a poisoned drink in a mass suicide/murder: see Jonestown mass suicide
  • Love Canal — Buried toxic waste was covered and used as a building site for housing and school in Niagara Falls, New York, resulting in claims of chronic poisoning and a massive environmental cleanup.
  • Clare Boothe Luce — Fell ill but did not die; arsenic poisoning
  • Georgi Markov — Assassinated in London with ricin
  • Socrates — According to Plato, killed by drinking Hemlock (water hemlock, not hemlock the evergreen tree)
  • Alan Turing — Apparently committed suicide by painting an apple with Cyanide and taking a bite.
  • Viktor Yushchenko — poisoned with dioxin during the Ukrainan elections.

Suspected or rumoured poisonings

  • Yasser Arafat — Arafat reputedly died from liver cirrhosis, which may be a consequence of chronic alcohol use or poisoning. Some Arafat supporters feel it is extremely unlikely that Arafat habitually used alcohol, and so suspect poisoning, possibly by the Mossad. (Note that cirrhosis is not necessarily caused by alcohol use, or indeed any poison.)
  • Napoleon Bonaparte — some claim he was killed by someone on his staff with arsenic.
  • Charles Darwin — possibly died due to self-medication with Fowler's solution, one percent potassium arsenite
  • Jamestown colonists — Standard historical accounts claim deaths by starvation, but the possibility of arsenic poisoning by rat poison (or of death by Bubonic plague) has also been reported (see here (http://www.pbs.org/wnet/secrets2/case3_clues.html))
  • Joseph Stalin — Officially cerebral hemorrhage; homewer, according to Vyacheslav Molotov's memoirs, Lavrenty Beria claimed to have poisoned Stalin.

Poisons in crime fiction

This list is incomplete, given that poisoning is a frequent plot twist in crime fiction.



  • D.O.A. (1950 movie)
  • Arsenic and Old Lace (movie)

See also

  Results from FactBites:
MedlinePlus: Poisoning (334 words)
A poison is any substance that is harmful to your body.
The dangers of poisoning range from short-term illness to brain damage, coma and death.
To prevent poisoning it is important to use and store products exactly as their labels say.
Poisoning (1943 words)
The type of poison, the amount and time of exposure, and the age, size, and health of the victim are all factors which determine the severity of symptoms and the chances for recovery.
Symptoms of plant poisoning range from irritation of the skin or mucous membranes of the mouth and throat to nausea, vomiting, convulsions, irregular heartbeat, and even death.
The outcome of poisoning varies from complete recovery to death, and depends on the type and amount of the poison, the health of the victim, and the speed with which medical care is obtained.
  More results at FactBites »



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