Sodium nitrite

Sodium nitrite is an inorganic compound with the chemical formula. It is a white to slightly yellowish crystalline powder that is very soluble in water and is hygroscopic. From an industrial perspective, it is the most important nitrite salt. It is a precursor to a variety of organic compounds, such as pharmaceuticals, dyes, and pesticides, but it is probably best known as a food additive used in processed meats and in fish products.

Uses

Industrial chemistry

The main use of sodium nitrite is for the industrial production of organonitrogen compounds. It is a reagent for conversion of amines into diazo compounds, which are key precursors to many dyes, such as diazo dyes. Nitroso compounds are produced from nitrites. These are used in the rubber industry.
It is used in a variety of metallurgical applications, for phosphatizing and detinning.
Sodium nitrite is an effective corrosion inhibitor and is used as an additive in industrial greases, as an aqueous solution in closed loop cooling systems, and in a molten state as a heat transfer medium.

Food additive and preservative

Sodium nitrite is used to speed up the curing of meat, inhibit the germination of Clostridium botulinum spores, and also impart an attractive pink color. Nitrite reacts with the meat myoglobin to cause color changes, first converting to nitrosomyoglobin, then, on heating, to nitrosohemochrome.
Historically, salt has been used for the preservation of meat. The salt-preserved meat product was usually brownish-gray in color. When sodium nitrite is added with the salt, the meat develops a red, then pink color, which is associated with cured meats such as ham, bacon, hot dogs, and bologna.
In the early 1900s, irregular curing was commonplace. This led to further research surrounding the use of sodium nitrite as an additive in food, standardizing the amount present in foods to minimize the amount needed while maximizing its food additive role. Through this research, sodium nitrite has been found to give taste and color to the meat and inhibit lipid oxidation that leads to rancidity, with varying degrees of effectiveness for controlling growth of disease-causing microorganisms. The ability of sodium nitrite to address the above-mentioned issues has led to production of meat with extended storage life and has improved desirable color and taste. According to scientists working for the meat industry, nitrite has improved food safety. This view is disputed in the light of the possible carcinogenic effects caused by adding nitrites to meat.
Nitrite has the E number E250. Potassium nitrite is used in the same way. It is approved for usage in the European Union, USA, and Australia and New Zealand.
In meat processing, sodium nitrite is never used in a pure state but always mixed with common salt. This mixture is known as nitrited salt, curing salt or nitrited curing salt. In Europe, nitrited curing salt contains between 99.1% and 99.5% common salt and between 0.5% and 0.9% nitrite. In the US, nitrited curing salt is dosed at 6.25% and must be remixed with salt before use.

Color and taste

The appearance and taste of meat is an important component of consumer acceptance. Sodium nitrite is responsible for the desirable red color of meat. Very little nitrite is needed to induce this change. It has been reported that as little as 2 to 14 parts per million is needed to induce this desirable color change. However, to extend the lifespan of this color change, significantly higher levels are needed. The mechanism responsible for this color change is the formation of nitrosylating agents by nitrite, which has the ability to transfer nitric oxide that subsequently reacts with myoglobin to produce the cured meat color. The unique taste associated with cured meat is also affected by the addition of sodium nitrite. However, the mechanism underlying this change in taste is still not fully understood.

Inhibition of microbial pathogens

In conjunction with salt and pH levels, sodium nitrite reduces the ability of Clostridium botulinum spores to grow to the point of producing toxin. Some dry-cured meat products are manufactured without nitrites. For example, Parma ham, which has been produced without nitrite since 1993, was reported in 2018 to have caused no cases of botulism. This is because the interior of the muscle is sterile and the surface is exposed to oxygen. Other manufacture processes do not assure these conditions, and reduction of nitrite results in toxin production.
Sodium nitrite has shown varying degrees of effectiveness for controlling growth of other spoilage or disease causing microorganisms. Although the inhibitory mechanisms are not well known, its effectiveness depends on several factors including residual nitrite level, pH, salt concentration, reductants present and iron content. The type of bacteria also affects sodium nitrite's effectiveness. It is generally agreed that sodium nitrite is not effective for controlling Gram-negative enteric pathogens such as Salmonella and Escherichia coli.
Other food additives provide similar protection against bacteria, but do not provide the desired pink color.

Inhibition of lipid peroxidation

Sodium nitrite is also able to effectively delay the development of oxidative rancidity. Lipid peroxidation is considered to be a major reason for the deterioration of quality of meat products. Sodium nitrite acts as an antioxidant in a mechanism similar to the one responsible for the coloring effect. Nitrite reacts with heme proteins and metal ions, neutralizing free radicals by nitric oxide. Neutralization of these free radicals terminates the cycle of lipid oxidation that leads to rancidity.

Medication

Sodium nitrite is used as a medication together with sodium thiosulfate to treat cyanide poisoning. It is recommended only in severe cases of cyanide poisoning and has largely been replaced by use of hydroxocobalamin, a form of vitamin B12, but given in much higher doses than needed nutritionally.
In those who have both cyanide poisoning and carbon monoxide poisoning sodium thiosulfate by itself is usually recommended if the facility does not have sufficient hydroxycobalamin. It is given by slow injection into a vein.
side effects are chiefly related to creation of methemoglobinemia and vasodilation. Side effects can include low blood pressure, headache, shortness of breath, loss of consciousness, and vomiting. Greater care should be taken in people with underlying heart disease. The patient's levels of methemoglobin should be regularly checked during treatment. While not well studied during pregnancy, there is some evidence of potential harm to the baby. Sodium nitrite works by creating methemoglobin, where the iron atom at the center of the heme group is in the oxidized ferric state, which binds with cyanide with greater affinity than its binding to the cytochrome C oxidase, and thus removes it from blocking the metabolic function of mitochondria.
Sodium nitrite came into medical use in the 1920s and 1930s. It is on the World Health Organization's List of Essential Medicines.

Suicide

Several academic publications in 2020 and 2021 discussed the toxicity of sodium nitrite, and an apparent recent increase in suicides using sodium nitrite which had been ordered online. The usage of sodium nitrite as a suicide method has been heavily discussed on suicide forums, primarily Sanctioned Suicide.
Sodium nitrite was also the focal-point of the McCarthy et al. v Amazon lawsuit alleging that Amazon knowingly assisted in the deaths of healthy children by selling them "suicide kits" as Amazon's "frequently bought together" feature recommended buying sodium nitrite, an antiemetic, and a suicide instruction book together. This lawsuit was dismissed in June 2023. The online marketplace eBay has globally prohibited the sale of sodium nitrite since 2019. Kenneth Law, a Canadian distributor of sodium nitrite was prosecuted in 2023 for assisting suicide. That same year, legislation was introduced in the United States with the aim of deeming sodium nitrite products with a sodium nitrite concentration of greater than 10% by volume to be banned consumer products under the Consumer Product Safety Act.
In cases of suspected suicide involving sodium nitrite, it is critical that responding individuals administer immediate intravenous methylene blue. Methylene blue is the antidote to the methemoglobinemia caused by intentional ingestion of sodium nitrite as a suicide agent.

Toxicity

Sodium nitrite is toxic. The LD₅₀ in rats is 180 mg/kg and in humans LD_Lo is 71 mg/kg. The mechanism by which sodium nitrite causes death is methemoglobinemia. The oftentimes severe methemoglobinemia found in sodium nitrite poisoning cases results in systemic hypoxia, metabolic acidosis, and cyanosis. The reported signs of sodium nitrite poisoning are as follows:
With prompt action, sodium nitrite poisoning is reversible using an antidote, methylene blue. It has been reported that sodium nitrite poisoning can also be detected post-mortem:
Death by sodium nitrite ingestion can happen at lower doses than the previously known LD_Lo. Sodium nitrite has been used for homicide and suicide. To prevent accidental intoxication, sodium nitrite sold as a food additive in the US is dyed bright pink to avoid mistaking it for plain salt or sugar. In other countries, nitrited curing salt is not dyed but is strictly regulated.

Occurrence in vegetables

Nitrites do not occur naturally in vegetables in significant quantities, but deliberate fermentation of celery juice, for instance, with a naturally high level of nitrates, can produce nitrite levels sufficient for commercial meat curing. Boiling vegetables does not affect nitrite levels.
The presence of nitrite in animal tissue is a consequence of metabolism of nitric oxide, an important neurotransmitter. Nitric oxide can be created de novo from nitric oxide synthase utilizing arginine or from ingested nitrite.