Sodium nitrite

Sodium nitrite
Identifiers
CAS number	7632-00-0 Y
PubChem	23668193
EC number	231-555-9
UN number	1500
RTECS number	RA1225000
Properties
Molecular formula	NaNO2
Molar mass	68.9953 g/mol
Appearance	white solid
Density	2.168 g/cm3
Melting point	271 °C decomp.
Solubility in water	82 g/100 ml (20 °C)
Structure
Crystal structure	Trigonal
Hazards
MSDS	External MSDS
EU Index	007-010-00-4
EU classification	Oxidant (O) Toxic (T) Dangerous for the environment (N)
R-phrases	R8, R25, R50
S-phrases	(S1/2), S45, S61
NFPA 704	3 3 1 OX
Autoignition temperature	489 °C
LD50	85 mg/kg
Related compounds
Other anions	Lithium nitrite Sodium nitrate
Other cations	Potassium nitrite Ammonium nitrite
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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. It may also be used as an electrolyte in electrochemical grinding manufacturing processes, typically diluted to about 10% concentration in water. Sodium nitrite also has been used in human and veterinary medicine as a vasodilator, a bronchodilator, and an antidote for cyanide poisoning.

Uses

Food additive

As a food additive, it serves a dual purpose in the food industry since it both alters the color of preserved fish and meats and also prevents growth of Clostridium botulinum, the bacteria which causes botulism. In the European Union it may be used only as a mixture with salt containing at most 0.6% sodium nitrite. It has the E number E250. Potassium nitrite (E249) is used in the same way.

While this chemical will prevent the growth of bacteria, it can be toxic in high amounts for animals, including humans. Sodium nitrite's LD₅₀ in rats is 180 mg/kg and its human LD_Lo is 71 mg/kg, meaning a 65 kg person would likely have to consume at least 4.615 g to result in toxicity.^[1] To prevent toxicity, sodium nitrite sold as a food additive is dyed bright pink to avoid mistaking it for something else.

A principal concern of sodium nitrite is the formation of carcinogenic nitrosamines in meats containing sodium nitrite when exposed to high temperatures. Sodium nitrite's usage is carefully regulated in the production of cured products in the United States as the concentration in finished products is limited to 200 ppm, and is usually lower. In about 1970, it was found that ascorbic acid (vitamin C), an antioxidant, inhibits nitrosamine formation.^[2] Consequently, the addition of at least 550 ppm of ascorbic acid is required in meats manufactured in the United States. Manufacturers sometimes instead use erythorbic acid, a cheaper but equally effective isomer of ascorbic acid. Additionally, manufactures may include alpha-tocopherol (vitamin E) to further inhibit nitrosamine production. Alpha-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 nitrous anhydride, a potent nitrosating agent formed from sodium nitrate, reduces the nitrous anhydride into the nitric oxide gas.^[3]

Sodium nitrite consumption has also been linked to triggering migraines in individuals who already suffer from them.^[4]

A recent study has found a link between frequent ingestion of cured meats and the COPD form of lung disease. The study's researchers suggest that the high amount of nitrites in the meats was responsible; however, the team did not prove the nitrite theory. Additionally, the study doesn't prove that nitrites or cured meat caused higher rates of COPD, merely a link. The researchers did adjust for many of COPD's risk factors, but they commented they cannot rule out all possible unmeasurable causes or risks for COPD.^[5][6]

Disease treatment

Recently, sodium nitrite has been found to be an effective means to increase blood flow by dilating blood vessels, acting as a vasodilator. Research is ongoing to investigate its applicability towards treatments for sickle cell anemia, cyanide poisoning, heart attacks, brain aneurysms, and pulmonary hypertension in infants.^[7][8]

Synthetic reagent

Sodium nitrite is used to convert amines into diazo compounds. The synthetic utility of such a reaction is to render the amino group labile for nucleophilic substitution, as the N₂ group is a better leaving group.

In the laboratory, sodium nitrite is also used to destroy excess sodium azide.^[9][10]

NaNO₂ + H₂SO₄ → HNO₂ + NaHSO₄

2 NaN₃ + 2 HNO₂ → 3 N₂ + 2 NO + 2 NaOH

Health Concerns

Sodium nitrite is commonly added to bacon, ham, hot dogs, luncheon meats, smoked fish, and corned beef to stabilize the red color and add flavor. The preservative prevents growth of bacteria, but studies have linked eating it to various types of cancer. "This would be at the top of my list of additives to cut from my diet," says Christine Gerbstadt, M.D., M.P.H., R.D., L.D.N., a spokesperson for the American Dietetic Association. "Under certain high-temperature cooking conditions such as grilling, it transforms into a reactive compound that has been shown to promote cancer."^[11]

"[Sodium nitrite] is used to cure and preserve meats but can be toxic in large quantities, due to its property of removing oxygen from the blood. Sodium nitrite is also suspected of playing a role in the development of colon cancer, migraines and chronic obstructive lung disease."^[12]

"The cured meat industry made substantial changes to the manufacturing process in the past 20 years to address some of the concerns about nitrite in cured meats. It has stopped using sodium nitrate (except for some specialty meats) in major meat processes and reduced the use of nitrite in the processing of cured meats. Residual levels of nitrite found in nitrite-cured meats have decreased in the past 20 years and now average one-tenth of what the regulations actually allow. The industry also has increased the use of two other substances – ascorbate and erythorbate – in the curing process, which are known to deplete residual nitrite and inhibit the production of N-nitrosamines." ^[13]

"There...were a number of studies during the 1970s that linked the consumption of nitrite with cancer in laboratory animals or associated the consumption of cured meats with illnesses in children. As a result of some lingering concerns about nitrite safety, the FDA and the USDA commissioned a comprehensive review of sodium nitrite's role as a food additive. The results were two scientific reports from the National Academy of Sciences (issued in 1981 and 1982). The 1981 report stated that nitrate does not cause cancer, although some population studies have found an association between high exposure to nitrate levels and certain cancers. Also, nitrite does not act directly as a cancer-causing agent in animals. The NAS recommended that both these issues be researched further. The NAS also recommended that people's exposure to both nitrates and nitrites be reduced as much as possible without jeopardizing the protection against botulism." ^[14]

"Two important actions in the year 2000 have reinforced the message that the use of sodium nitrite in cured meats is safe and is not associated with cancer risk in humans. The first is a thorough review of the results of sodium nitrite studies by the National Toxicology Program, which undertook the review at the request of the FDA. After carefully considering all the evidence presented, the NTP Board of Scientific Counselors voted unanimously in May 2000 that the evidence showed that sodium nitrite does not cause cancer in male rats, male mice or female rats. While they found "equivocal evidence" in the forestomachs of female mice, the scientists have determined that the finding is not relevant to human health because humans do not have forestomachs. This comprehensive review by NTP shows that sodium nitrite does not cause cancer in laboratory animals, even when they are fed massive doses throughout the animals' lifetime. The second action occurred in the state of California, where a panel of independent expert toxicologists reviewing almost 100 scientific publications about sodium nitrite voted that the evidence does not show that sodium nitrite causes developmental or reproductive toxicity. If found by the DART committee to be harmful, sodium nitrite would have been listed under the state's Proposition 65 law, which was enacted to protect citizens against known cancer-causing agents and reproductive toxicants. ^[15]

As of June 2004, the American Medical Association concludes that: "Data are irrefutable that when ingested in high concentrations nitrites can cause methemoglobinemia. Additionally, certain populations such as infants may be particularly vulnerable. However, the human body can tolerate fairly high levels of methemoglobin before toxemia sets in. Thus, there have been no reports of methemoglobinemia caused by nitrites added intentionally to food, although disease caused by contamination of water and food by sodium nitrite has been reported. USDA regulations do not permit nitrites and nitrates in baby, junior, or toddler foods. The scientific evidence is clear that NOCs have carcinogenic effects in animal models. Thus, it must be assumed that at the right concentrations, NOCs are likely to be carcinogenic in humans as well. The primary source of NOCs in the human diet is the nitrosation of secondary amines and amides by nitrites present in food. However, epidemiological studies cannot confirm the link between the presence of nitrites (or nitrates) in food and the formation of NOCs and the causation of human cancer. In fact, studies that suggest a link between nitrites in food and cancer have largely been disputed due to these studies’ inability to exclude confounding factors, such as recall bias. Regardless, the use of nitrites in the preparation and preservation of meats and poultry has been substantially reduced from the time when these studies were first performed. Additionally, the use of erythorbate and/or ascorbate with nitrites has been shown to inhibit the formation of NOCs. Accordingly, given the current FDA and USDA regulations on the use of nitrites, the risk of developing cancer as a result of consumption of nitrites-containing foods is negligible.^[16]

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⁺-N=O (diazonium ion)

Certain nitrosamines such as N-nitrosodimethylamine^[17] and N-nitrosopyrrolidine^[18] form carbocations that react with biological nucleophiles (such as DNA or an enzyme) in the cell.

R-N⁺-N=O (diazonium ion) → R⁺ (carbocation) + N₂ (leaving group) + :Nu (biological nucleophiles) → R-Nu

If this nucleophilic substitution reaction occurs at a crucial site in a biomolecule, it can disrupt normal cell functioning leading to cancer or cell death.

References

1. ^ http://msds.chem.ox.ac.uk/SO/sodium_nitrite.html
2. ^ http://carcin.oxfordjournals.org/cgi/content/abstract/10/2/397 The inhibition of bacterially mediated N-nitrosation by vitamin C: relevance to the inhibition of endogenous N-nitrosation in the achlorhydric stomach. Carcinogenesis 1989; 10(2) 397-399.
3. ^ http://lpi.oregonstate.edu/f-w00/nitrosamine.html Nitrosamines and Cancer by Richard A. Scanlan, Ph.D.
4. ^ "Heading Off Migraine Pain". FDA Consumer magazine. U.S. Food and Drug Administration. 1998. http://www.fda.gov/FDAC/features/1998/398_pain.html. 
5. ^ Miranda Hitti (17 April 2007). "Study: Cured Meats, COPD May Be Linked". WebMD Medical News. http://www.webmd.com/news/20070417/study-copd-cured-meats-may-be-linked. 
6. ^ http://ajrccm.atsjournals.org/cgi/content/abstract/175/8/798 Cured Meat Consumption, Lung Function, and Chronic Obstructive Pulmonary Disease among United States Adults - Jiang et al. 175 (8): 798 - American Journal of Respiratory and Critical Care Medicine
7. ^ Associated Press (9/5/2005). "Hot dog preservative could be disease cure". http://www.usatoday.com/news/health/2005-09-05-hot-dog-drug_x.htm. 
8. ^ Roxanne Khamsi (27 January 2006). "Food preservative fights cystic fibrosis complication". NewScientist.com. http://www.newscientist.com/article.ns?id=dn8643. 
9. ^ "Sodium Azide". Hazardous Waste Management. Northeastern University. March 2003. http://www.ehs.neu.edu/hazardous_waste/fact_sheets/sodium_azide/. 
10. ^ Committee on Prudent Practices for Handling, Storage, and Disposal of Chemicals in Laboratories, Board on Chemical Sciences and Technology, Commission on Physical Sciences, Mathematics, and Applications, National Research Council. (1995). Prudent practices in the laboratory: handling and disposal of chemicals. National Academy Press. ISBN 0309052297. http://books.nap.edu/openbook.php?record_id=4911&page=165. 
11. ^ http://health.msn.com/nutrition/slideshow.aspx?cp-documentid=100204508
12. ^ http://www.NaturalNews.com/023873_sodium_meat_sodium_nitrite.html
13. ^ http://www.medem.com/?q=medlib/article/ZZZ80XEN0IC
14. ^ http://www.medem.com/?q=medlib/article/ZZZ80XEN0IC
15. ^ http://www.medem.com/?q=medlib/article/ZZZ80XEN0IC
16. ^ http://www.ama-assn.org/ama/no-index/about-ama/13661.shtml
17. ^ Najm, Issam; Trussell, R. Rhodes (February 2001). "NDMA Formation in Water and Wastewater". Journal AWWA 93 (2): 92–99. 
18. ^ Donald D. Bills, Kjell I. Hildrum, Richard A. Scanlan, Leonard M. Libbey (May 1973). "Potential precursors of N-nitrosopyrrolidine in bacon and other fried foods". J. Agric. Food Chem. 21 (5): 876–877. doi:10.1021/jf60189a029. PMID 4739004. 

External links

• Organic Consumers Association: Why Processed Meats Are Dangerous to Your Health
• ATSDR - Case Studies in Environmental Medicine - Nitrate/Nitrite Toxicity U.S. Department of Health and Human Services (public domain)
• International Chemical Safety Card 1120.
• European Chemicals Bureau.
• National Center for Home Food Preservation Nitrates 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.
• FOX news article concerning carcinogicity and hot dogs