Nitrite

Nitrite refers to the nitrite ion, NO2−, the conjugate base of nitrous acid (HNO2). It is an inorganic anion that forms salts such as sodium nitrite (NaNO2) and potassium nitrite (KNO2). In solution, nitrite exists mainly as NO2−; under acidic conditions HNO2 can form and decompose to nitric oxide (NO) and nitrogen dioxide (NO2).

Biogeochemically, nitrite is an intermediate species in the nitrogen cycle. It is produced by the oxidation of ammonium (nitrification) by bacteria such as Nitrosomonas, and is subsequently oxidized to nitrate (NO3−) by Nitrobacter. Nitrite can accumulate temporarily in soils and receiving waters, particularly after fertilizer application or during rapid microbial shifts.

Industrial and agricultural uses include as a preservative in cured meats and as an antioxidant and color fixative, and in chemical synthesis. In food, nitrite helps inhibit microbial growth and preserves red color, but nitrosamines can form when nitrite reacts with secondary amines under certain cooking conditions, raising cancer risk concerns. Consequently regulatory agencies limit nitrite levels in foods and drinking water and encourage proper processing.

Health effects: ingestion of high nitrite doses can cause methemoglobinemia, reducing the blood's oxygen-carrying capacity, especially dangerous for infants. Lower-level exposure is monitored due to nitrite's role in nitrosamine formation and potential links to cancer risk. Drinking-water and meat products are subject to safety limits in many jurisdictions.

Environmental and treatment considerations: nitrite can enter water through agricultural runoff and wastewater. It is toxic to aquatic life at sufficient concentrations. In water treatment, nitrite is removed via biological denitrification, ion exchange, or reverse osmosis; management aims to prevent nitrite accumulation and formation of nitrosamines.