To prevent accidental intoxication, sodium nitrite (blended with salt) 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 are not naturally occurring in vegetables in significant quantities. 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. Pigs
Because of sodium nitrites high level of toxicity to swine (Sus scrofa) it is now being developed in Australia to control feral pigs and wild boar. The sodium nitrite induces 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 humane manner after first being rendered unconscious. The Texas Parks and Wildlife Department operates a research facility at Kerr Wildlife Management Area, where they examine feral pig feeding preferences and bait tactics to administer sodium nitrite.
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, manufacturers may include α-tocopherol (vitamin E) to further inhibit nitrosamine production. 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. The nitrosonium ion formed in acidic nitrite solutions is commonly mislabeled nitrous anhydride, an unstable nitrogen oxide that cannot exist in vitro.Ingesting nitrite under conditions that result in endogenous nitrosation has been classified as "probably carcinogenic to humans" by International Agency for Research on Cancer (IARC).Sodium nitrite consumption has also been linked to the triggering of migraines in individuals who already experience them.One study has found a correlation between highly frequent ingestion of meats cured with pink salt and the COPD form of lung disease. The studys 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 does not prove that nitrites or cured meat caused higher rates of COPD, merely a link. The researchers did adjust for many of COPDs risk factors, but they commented they cannot rule out all possible unmeasurable causes or risks for COPD.