Sodium nitrite, with chemical formula NaNO2, is used as a color fixative and preservative in meats and fish. When pure, it is a white to slight yellowish crystalline powder. It is very soluble in water and is hygroscopic. It is also slowly oxidized by oxygen in the air to sodium nitrate, NaNO3. The compound is a strong oxidizing agent.
It is also used in manufacturing diazo dyes, nitroso compounds, and other organic compounds; in dyeing and printing textile fabrics and bleaching fibers; in photography; as a laboratory reagent and a corrosion inhibitor; in metal coatings for phosphatizing and detinning; and in the manufacture of rubber chemicals. Sodium nitrite also has been used in human and veterinary medicine as a vasodilator, a bronchodilator, and an antidote for cyanide poisoning.
While this chemical will prevent the growth of bacteria, it can be toxic for mammals. (LD50 in rats is 180 mg/kg.) For this reason, sodium nitrite sold as a food additive is dyed bright pink to avoid mistaking it for something else. Cooks and makers of charcuterie often simply refer to sodium nitrite as "pink salt".
Various dangers of using this as a food additive have been suggested and researched by scientists. A principal concern is the formation of carcinogenic N-nitrosamines by the reaction of sodium nitrite with amino acids in the presence of heat in an acidic environment. Its usage is carefully regulated in the production of cured products; in the United States, the concentration in finished products is limited to 200 ppm, and is usually lower. In about 1970, it was found that the addition of ascorbic acid inhibited nitrosamine production. U.S. manufacturing of cured meats now requires the addition of 500 ppm of ascorbic acid or erythorbic acid, a cheaper isomer. Sodium nitrite has also been linked to triggering migraines.
Recent studies have found a link between high processed meat consumption and colon cancer, possibly due to preservatives such as sodium nitrite.
In the laboratory, sodium nitrite is also used to destroy excess sodium azide.