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A cyanide is any chemical compound that contains the group CN, with the carbon atom triple bonded to the nitrogen atom. Inorganic cyanides contain the highly toxic cyanide ion CN- and are the salts of the acid hydrogen cyanide (HCNCN). Organic cyanides contain the CN group single-bonded to another carbon atom and are also known as nitriles.

Table of contents
1 Appearance
2 Occurrence and use
3 Effects on the human body
4 Mechanism of toxicity and treatment
5 Use as a poison
6 Mining
7 Fishing


Hydrogen cyanide is a colorless gas with a faint, bitter, almond-like odor. Some people are unable to smell cyanide at all, due to a genetic trait. Sodium cyanide (NaCNCN) and potassium cyanide (KCNCN) are both white solids with a bitter, almond-like odor in damp air.

Occurrence and use

Cyanides can be produced by certain bacteria, fungi, and algae, and are found in a number of foods and plants. Cyanide occurs naturally in cassava roots, which are potato-like tubers of cassava plants grown in tropical countries; these must be processed prior to consumption. Fruits which have a pit, such as cherries or apricots, often contain some cyanides in the pit. Bitter almonds from which almond oil and flavoring is made also contain cyanide.

Hydrogen cyanide is contained in vehicle exhaust and in tobacco smoke. The smoke of burning plastics contains hydrogen cyanide, and house fires often result in cyanide poisonings. A deep blue pigment called Prussian Blue, used in the making of blueprints, also contains hydrogen cyanide.

Cyanides and hydrogen cyanide are used in electroplating, metallurgy, production of chemicals, photographic development, making plastics, fumigating ships, and some mining processes.

Effects on the human body

To deal with the cyanides contained in many foods, the body has an enzyme (rhodanide synthetase) which can convert small amounts of cyanides to the harmless sulfur containing thiocyanate (SCNCN). Cyanides also combine with a chemical to form vitamin B12.

In larger amounts, cyanides are harmful to people. Symptoms of moderate poisoning include vomiting, convulsions, deep breathing, shortness of breath and anxiety; more serious cases result in convulsions, loss of consciousness, and death after apnea and heart arrest.

Exposure to lower levels of cyanide over a long period (e.g. after use of cassava roots as a primary food source in tropical Africa) results in increased blood cyanide levels. These may result in weakness of the fingers and toes, difficulty walking, dimness of vision, deafness, and decreased thyroid gland function, but chemicals other than cyanide may have contributed to these effects. Skin contact with cyanide can produce irritation and sores.

It is not known whether cyanides can directly cause birth defects in people. Birth defects were seen in rats that ate diets of cassava roots. Effects on the reproductive system were seen in rats and mice that drank water containing sodium cyanide.

There are medical tests to measure blood and urine levels of cyanide; however, small amounts of cyanide are not always detectable in blood and urine. Tissue levels of cyanide can be measured if cyanide poisoning is suspected, but cyanide is rapidly cleared from the body, so the tests must be done soon after the exposure. An almond-like odor in the breath may alert a doctor that a person was exposed to cyanide.

Mechanism of toxicity and treatment

Cyanide ion kills all aerobic organisms by shutting down the respiration in cells. It interrupts the electron transport chain in the inner membrane of the mitochondrion because it binds more strongly than oxygen to the Fe+3 in cytochrome a3, preventing this cytochrome from combining electrons with oxygen.

Contrary to popular belief, cyanide does not bind well to ferrous hemoproteins, such as hemoglobin, the mechanism which makes carbon monoxide toxic. One of the therapies for cyanide poisoning is to convert part of the hemoglobin of the blood from ferrous hemoglobin to ferric; this creates a pool of binding potential that can divert cyanide from the cytochromes it poisons. This is done with the compound 4-Dimethylaminophenyl.

Use as a poison

The cyanide ion, if used as poison, is generally delivered in the form of gaseous hydrogen cyanide or in the form of potassium cyanide (KCN) or sodium cyanide (NaCN).

Zyklon B, the poison gas used in Nazi gas chambers during the Holocaust, works by delivering hydrogen cyanide gas. Cyanide is also the compound used in US execution chambers.

The cyanide salts are fast acting "suicide pills". When they reach the stomach acids, cyanide ions are released; therefore they work faster on an empty stomach. Famous cyanide salt suicides include:

Poisoning by cyanide also figures prominently in crime fiction, for example Agatha Christie's Sparkling Cyanide; cyanide is the instrument of one murder in The Big Sleep by Raymond Chandler.

Cyanides were stockpiled in both the Soviet and the United States chemical weapons arsenals in the 1950s and 1960s. During the Cold War, the Soviet Union was thought to be planning to use hydrogen cyanide as a "blitzkrieg" weapon to clear a path through the opposing front line, knowing that the harmful gas itself would evaporate and allow unprotected access to the captured zone.


Cyanide salts are used in silver and gold mining, called the cyanide process. The ore is finely ground and mixed or sprayed with cyanide solution. The precious metal cations bind to the cyanide anions and form a soluble cyanide. The left-over dirt is discarded and the metal is recovered from the clear solution with zinc. This process can result in environmental and health problems.


Cyanides are used to capture live fish near coral reefs for the aquarium and seafood market. In this method, a diver uses a large needleless syringe to squirt a cyanide solution into areas where the fish are hiding, stunning them so that they can be easily gathered. Environmental organizations decry the practice.