Many<unk> s are highly toxic. The<unk>  anion is an inhibitor of the enzyme cytochrome c oxidase (also known as aa3), the fourth complex of the electron transport chain found in the inner membrane of the mitochondria of eukaryotic cells. It attaches to the iron within this protein. The binding of<unk>  to this enzyme prevents transport of electrons from cytochrome c to oxygen. As a result, the electron transport chain is disrupted, meaning that the cell can no longer aerobically produce ATP for energy. Tissues that depend highly on aerobic respiration, such as the central nervous system and the heart, are particularly affected. This is an example of histotoxic hypoxia. The most hazardous compound is hydrogen<unk> , which is a gas and kills by inhalation. For this reason, an air respirator supplied by an external oxygen source must be worn when working with hydrogen<unk> . Hydrogen<unk>  is produced by adding acid to a solution containing a<unk>  salt. Alkaline solutions of<unk>  are safer to use because they do not evolve hydrogen<unk>  gas. Hydrogen<unk>  may be produced in the combustion of polyurethanes; for this reason, polyurethanes are not recommended for use in domestic and aircraft furniture. Oral ingestion of a small quantity of solid<unk>  or a<unk>  solution of as little as 200 mg, or exposure to airborne<unk>  of 270 ppm, is sufficient to cause death within minutes. Organic nitriles do not readily release<unk>  ions, and so have low toxicities. By contrast, compounds such as trimethylsilyl<unk>  (CH3)3SiCN readily release HCN or the<unk>  ion upon contact with water. Antidote Hydroxocobalamin reacts with<unk>  to form cyanocobalamin, which can be safely eliminated by the kidneys. This method has the advantage of avoiding the formation of methemoglobin (see below). This antidote kit is sold under the brand name Cyanokit and was approved by the U.S. FDA in 2006. An older<unk>  antidote kit included administration of three substances: amyl nitrite pearls (administered by inhalation), sodium nitrite, and sodium thiosulfate. The goal of the antidote was to generate a large pool of ferric iron (Fe3+) to compete for<unk>  with cytochrome a3 (so that<unk>  will bind to the antidote rather than the enzyme). The nitrites oxidize hemoglobin to methemoglobin, which competes with cytochrome oxidase for the<unk>  ion. Cyanmethemoglobin is formed and the cytochrome oxidase enzyme is restored. The major mechanism to remove the<unk>  from the body is by enzymatic conversion to thiocyanate by the mitochondrial enzyme rhodanese. Thiocyanate is a relatively non-toxic molecule and is excreted by the kidneys. To accelerate this detoxification, sodium thiosulfate is administered to provide a sulfur donor for rhodanese, needed in order to produce thiocyanate. Sensitivity Minimum risk levels (MRLs) may not protect for delayed health effects or health effects acquired following repeated sublethal exposure, such as hypersensitivity, asthma, or bronchitis. MRLs may be revised after sufficient data accumulates.
Cyanide
Lewisite
Bromide
Hydrogen fluoride
Carbonated water
Carbon monoxide
Isothiocyanate
Metaldehyde