Sodium nitrite is an inorganic compound used as a food additive to prevent botulism. It inhibits the growth of bacteria and gives taste and color to meat. While it prevents spoilage, sodium nitrite is also toxic in high amounts and has been linked to cancer due to the formation of nitrosamines when meat is cooked. It is regulated as a food additive and manufacturers must add antioxidants like vitamin C to inhibit nitrosamine production when curing meats.

1. Sodium nitrite
Not to be confused with sodium nitrate, sodium nitride,
or nitratine.
“E250” redirects here. For the mobile phone, see
Samsung SGH-E250.
Sodium nitrite is the inorganic compound with the
chemical formula NaNO2. It is a white to slightly yellow-
ish crystalline powder that is very soluble in water and
is hygroscopic. It is a useful precursor to a variety of
organic compounds, such as pharmaceuticals, dyes, and
pesticides, but it is probably best known as a food addi-
tive to prevent botulism.
It is on the World Health Organization’s List of Essential
Medicines, the most important medications needed in a
basic health system.[2]
1 Uses
1.1 Industrial chemistry
The main use of sodium nitrite is for the industrial pro-
duction 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.[3]
Other applications include uses in photography. It may
also be used as an electrolyte in electrochemical grinding
manufacturing processes, typically diluted to about 10%
concentration in water. It is used in a variety of metallur-
gical applications, for phosphatizing and detinning.
Sodium nitrite is an effective corrosion inhibitor and is
used as an additive in industrial greases,[4]
as an aqueous
solution in closed loop cooling systems, and in a molten
state as a heat transfer medium.[5]
1.2 Medicine
Main article: Sodium nitrite (medical use)
Sodium nitrite is used together with sodium thiosulfate to
treat cyanide poisoning.[6]
It is in the section "antidotes and other substances used
in poisonings" of the World Health Organization’s List
of Essential Medicines, the most important medications
needed in a basic health system.[2]
1.3 Food additive
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.[7]
Through this re-
search, sodium nitrite has been found to inhibit growth
of disease-causing microorganisms; give taste and color
to the meat; and inhibit lipid oxidation that leads to
rancidity.[7]
The ability of sodium nitrite to address the
above-mentioned issues has led to production of meat
with improved food safety, extended storage life and im-
proving desirable color/taste.[7]
It has the E number E250.
Potassium nitrite (E249) is used in the same way. It is
approved for usage in the EU,[8][9]
USA[10]
and Australia
and New Zealand.[11]
1.3.1 Inhibition of microbial growth
Sodium nitrite is well known for its role in inhibiting
the growth of Clostridium botulinum spores in refriger-
ated meats.[12]
The mechanism for this activity results
from the inhibition of iron-sulfur clusters essential to en-
ergy metabolism of Clostridium botulinum.[12]
However,
sodium nitrite has had varying degrees of effectiveness
for controlling growth of other spoilage or disease caus-
ing microorganisms.[7]
Even though the inhibitory mech-
anisms for sodium nitrite are not well known, its effec-
tiveness depends on several factors including residual ni-
trite level, pH, salt concentration, reductants present and
iron content.[13]
Furthermore, the type of bacteria also
affects sodium nitrites effectiveness.[13]
It is generally
agreed upon that sodium nitrite is not considered effec-
tive for controlling gram-negative enteric pathogens such
as Salmonella and Escherichia coli.[13]
1.3.2 Taste and color
The appearance and taste of meat is an important com-
ponent of consumer acceptance.[7]
Sodium nitrite is re-
sponsible for the desirable red color (or shaded pink)
of meat.[7]
Very little nitrite is needed to induce this
change.[7]
It has been reported that as little as 2 to 14
parts per million (ppm) is needed to induce this desirable
color change.[13]
However, to extend the lifespan of this
1

2. 2 2 TOXICITY
color change, significantly higher levels are needed.[13]
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 re-
acts with myoglobin to produce the cured meat color.[13]
The unique taste associated with cured meat is also af-
fected by the addition of sodium nitrite.[7]
However, the
mechanism underlying this change in taste is still not fully
understood.[13]
1.3.3 Inhibition of lipid oxidation
Sodium nitrite is also able to effectively delay the de-
velopment of oxidative rancidity.[13]
Lipid oxidation is
considered to be a major reason for the deterioration
of quality of meat products (rancidity and unappetiz-
ing flavors).[13]
Sodium nitrite acts as an antioxidant in
a mechanism similar to the one responsible for the col-
oring affect.[13]
Nitrite reacts with heme proteins and
metal ions, neutralizing free radicals by nitric oxide (one
of its byproducts).[13]
Neutralization of these free radi-
cals terminates the cycle of lipid oxidation that leads to
rancidity.[13]
2 Toxicity
While this chemical will prevent the growth of bacteria,
it can be toxic in high amounts for animals and humans.
Sodium nitrite’s LD50 in rats is 180 mg/kg and its human
LDLₒ is 71 mg/kg, meaning a 65 kg person would likely
have to consume at least 4.6 g to result in death.[14]
To
prevent toxicity, sodium nitrite (blended with salt) sold
as a food additive is dyed bright pink to avoid mistak-
ing it for plain salt or sugar. Nitrites are not naturally
occurring in vegetables in significant quantities.[15]
How-
ever, nitrates are found in commercially available veg-
etables and a study in an intensive agricultural area in
northern Portugal found residual nitrate levels in 34 veg-
etable samples, including different varieties of cabbage,
lettuce, spinach, parsley and turnips ranged between 54
and 2440 mg/kg, e.g. curly kale (302.0 mg/kg) and green
cauliflower (64 mg/kg).[16][17]
Boiling vegetables lowers
nitrate but not nitrite.[16]
Fresh meat contains 0.4–0.5
mg/kg nitrite and 4–7 mg/kg of nitrate (10–30 mg/kg ni-
trate in cured meats).[15]
The presence of nitrite in animal
tissue is a consequence of metabolism of nitric oxide, an
important neurotransmitter.[18]
Nitric oxide can be cre-
ated de novo from nitric oxide synthase utilizing arginine
or from ingested nitrate or nitrite.[19]
2.1 Humane toxin for feral hog/wild boar
control
Because of sodium nitrite’s high level of toxicity to swine
(Sus scrofa) it is now being developed in Australia to con-
trol feral pigs and wild boar.[20][21]
The sodium nitrite in-
duces methemoglobinemia in swine, i.e., it reduces the
amount of oxygen that is released from hemoglobin, so
the animal will feel faint and pass out, and then die in a hu-
mane manner after first being rendered unconscious.[22]
The Texas Parks and Wildlife Department operates a re-
search facility at Kerr Wildlife Management Area, where
they examine feral pig feeding preferences and bait tac-
tics to administer sodium nitrite.[23]
2.2 Nitrosamines
A principal concern about sodium nitrite is the formation
of carcinogenic nitrosamines in meats containing sodium
nitrite when meat is charred or overcooked. Such car-
cinogenic nitrosamines can also be formed from the re-
action of nitrite with secondary amines under acidic con-
ditions (such as occurs in the human stomach) as well as
during the curing process used to preserve meats. Di-
etary sources of nitrosamines include US cured meats
preserved with sodium nitrite as well as the dried salted
fish eaten in Japan. In the 1920s, a significant change in
US meat curing practices resulted in a 69% decrease in
average nitrite content. This event preceded the begin-
ning of a dramatic decline in gastric cancer mortality.[24]
About 1970, it was found that ascorbic acid (vitamin C),
an antioxidant, inhibits nitrosamine formation.[25]
Con-
sequently, the addition of at least 550 ppm of ascor-
bic acid is required in meats manufactured in the United
States. Manufacturers sometimes instead use erythorbic
acid, a cheaper but equally effective isomer of ascor-
bic acid. Additionally, manufacturers may include α-
tocopherol (vitamin E) to further inhibit nitrosamine pro-
duction. α-Tocopherol, ascorbic acid, and erythorbic
acid all inhibit nitrosamine production by their oxidation-
reduction properties. Ascorbic acid, for example, forms
dehydroascorbic acid when oxidized, which when in
the presence of nitrosonium, a potent nitrosating agent
formed from sodium nitrite, reduces the nitrosonium into
nitric oxide.[26]
The nitrosonium ion formed in acidic ni-
trite solutions is commonly[27][28]
mislabeled nitrous an-
hydride, an unstable nitrogen oxide that cannot exist in
vitro.[29]
Nitrate or nitrite (ingested) under conditions that result
in endogenous nitrosation has been classified as “proba-
bly carcinogenic to humans” by International Agency for
Research on Cancer (IARC).[30][31]
Sodium nitrite consumption has also been linked to the
triggering of migraines in individuals who already suffer
from them.[32]
One study has found a correlation between highly fre-
quent ingestion of meats cured with pink salt and the
COPD form of lung disease. The study’s researchers sug-
gest that the high amount of nitrites in the meats was re-
sponsible; however, the team did not prove the nitrite the-
ory. Additionally, the study does not prove that nitrites or

3. 3
cured meat caused higher rates of COPD, merely a link.
The researchers did adjust for many of COPD’s risk fac-
tors, but they commented they cannot rule out all possible
unmeasurable causes or risks for COPD.[33][34]
3 Mechanism of action
Carcinogenic nitrosamines are formed when amines that
occur naturally in food react with sodium nitrite found in
cured meat products.
R2NH (amines) + NaNO2 (sodium nitrite) → R2N–N=O
(nitrosamine)
In the presence of acid (such as in the stomach) or heat
(such as via cooking), nitrosamines are converted to
diazonium ions.
R2N–N=O (nitrosamine) + (acid or heat) → R–N+
2 (diazonium ion)
Certain nitrosamines such as N-nitrosodimethylamine[35]
and N-nitrosopyrrolidine[36]
form carbocations that react
with biological nucleophiles (such as DNA or an enzyme)
in the cell.
R–N+
2 (diazonium ion) → R+
(carbocation) + N2 (leaving
group) + Nu (biological nucleophiles) → R–Nu
If this nucleophilic substitution reaction occurs at a cru-
cial site in a biomolecule, it can disrupt normal cell func-
tions, leading to cancer or cell death.
4 Production
The salt is prepared by treating sodium hydroxide with
mixtures of nitrogen dioxide and nitric oxide:
2 NaOH + NO2 + NO → 2 NaNO2 + H2O
The conversion is sensitive to the presence of oxygen,
which can lead to varying amounts of sodium nitrate.
In former times, sodium nitrite was prepared by reduction
of sodium nitrate with various metals.[3][37]
5 Chemical reactions
In the laboratory, sodium nitrite can be used to destroy
excess sodium azide.[38][39]
2 NaN3 + 2 NaNO2 + 2 H+
→ 3 N2 + 2 NO + 2 Na+
+
2 H2O
Above 330 °C sodium nitrite decomposes (in air) to
sodium oxide, nitric oxide and nitrogen dioxide.[40]
2 NaNO2 → Na2O + NO + NO2
Sodium nitrite can also be used in the production of
nitrous acid via sulfuric acid. This reaction first yields
nitrous acid and sodium sulfate:
2 NaNO
2 + H
2SO
4 → 2 HNO
2 + Na
2SO
4
The nitrous acid then, under normal conditions, decom-
poses:
2 HNO
2 → NO
2 + NO + H
2O
The nitrogen dioxide of the prior decomposition is then
routed through a condensor or fractional distillation ap-
paratus to react with water and yield nitric acid:
2 NO
2 + H
2O → HNO
3 + HNO
2
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[1] Zumdahl, Steven S. (2009). Chemical Principles (6th ed.).
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[2] “WHO Model List of EssentialMedicines” (PDF). World
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[3] Wolfgang Laue, Michael Thiemann, Erich Scheibler, Karl
Wilhelm Wiegand “Nitrates and Nitrites” in Ullmann’s
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[4] Krakhmalev, S. I.; Vorotnikova, V. A.; Ten, N. V.;
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[5] “Sodium Nitrite”. General Chemical. Retrieved 2012-09-
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[13] Sindelar, Jeffrey; Milkowski, Andrew (November 2011).
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[14] http://msds.chem.ox.ac.uk/SO/sodium_nitrite.html
[15] Dennis, M. J.; Wilson, L. A. (2003). “Nitrates and
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[16] Leszczyńska, Teresa; Filipiak-Florkiewicz, Agnieszka;
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Missing or empty |title= (help)
[28] Nollet, Toldra, D (2015). Handbook of Food Analysis
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[29] Williams, D (2004). “Reagents effecting nitrosation”. Ni-
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[31] “VOLUME 94 - Ingested Nitrate and Nitrite, and
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[32] “Heading Off Migraine Pain”. FDA Consumer magazine.
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[33] Hitti, Miranda (17 April 2007). “Study: Cured Meats,
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[35] Najm, Issam; Trussell, R. Rhodes (February 2001).
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[36] Bills, Donald D.; Hildrum, Kjell I.; Scanlan, Richard
A.; Libbey, Leonard M. (May 1973). “Potential pre-
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doi:10.1021/jf60189a029. PMID 4739004.
[37] Hao, Zhi-wei; Xu, Xin-hua; Wang, Da-hui (March 2005).
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7 External links
• ATSDR – Case Studies in Environmental Medicine
– Nitrate/Nitrite Toxicity U.S. Department of
Health and Human Services (public domain)
• International Chemical Safety Card 1120.
• National Center for Home Food Preservation Ni-
trates and Nitrites.
• TR-495: Toxicology and Carcinogenesis Studies
of Sodium Nitrite (CAS NO. 7632-00-0) Drinking
Water Studies in F344/N Rats and B6C3F1 Mice.
• Nitrite in Meat

6. 6 8 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES
8 Text and image sources, contributors, and licenses
8.1 Text
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