At a glance
| Chemical family | Inorganic nitrogen oxyanion (NO₂⁻), the reduced partner of nitrate (NO₃⁻) in the nitrogen cycle. Soluble and mobile; interconverts with nitrate biologically and chemically. |
| CAS number | 14797-65-0 (nitrite ion) |
| Classification | Acutely toxic via methemoglobinemia (blue-baby syndrome) — more potent than nitrate for this effect. Nitrite can also react with amines to form nitrosamines (a nitrosation, cancer-relevant, pathway). EPA MCL 1 mg/L as N; combined nitrate+nitrite MCL 10 mg/L as N. |
| Where you encounter it | Farm-country water (fertilizer, manure, septic) alongside nitrate; and distinctively, formed inside distribution systems by nitrification — especially in chloramine-disinfected systems, in warm water and dead-end mains. |
| Sleep micro environment relevance | Indirect — an ingestion exposure via drinking water, on the Atlas as part of the agricultural and infant-safety tap-water picture the water hub anchors, paired with nitrate. |
| Activated carbon capture | Not removed by standard carbon. Removal uses reverse osmosis, anion exchange, or distillation. Inferred from standard nitrate/nitrite water-treatment engineering; the nitrite oxyanion is not adsorbed by ordinary carbon |
Regulatory & certification status
Nitrite is regulated both on its own and jointly with nitrate, reflecting that the two interconvert and share the blue-baby endpoint. The rows below give the standards.
| United States | EPA enforceable Maximum Contaminant Level of 1 mg/L (as nitrogen) for nitrite — ten times stricter than the 10 mg/L nitrate limit, reflecting nitrite's greater acute potency — plus a combined nitrate-plus-nitrite MCL of 10 mg/L as N. Regulatory — US EPA |
| World Health Organization | WHO sets a short-term guideline value of 3 mg/L for nitrite (and a long-term value), keyed to the methemoglobinemia endpoint. Regulatory — WHO |
| Toxicological basis | The ATSDR Toxicological Profile for Nitrate and Nitrite identifies methemoglobinemia in infants as the critical acute effect, and notes the nitrosation (nitrosamine-formation) pathway. Regulatory — ATSDR |
| The 72-hour test window | Not applicable. Nitrite is a waterborne ingestion exposure measured by a specialized water-lab test, unrelated to the VOC-emission chamber tests used for mattresses and foam. Inferred — from the ingestion-via-water route versus the material/VOC focus of product emissions testing |
What it is
Nitrite is a nitrogen-oxygen ion, the partly-reduced middle step between ammonia and nitrate in the nitrogen cycle. In water it usually sits in the background behind the far more abundant nitrate — but it matters out of proportion to its concentration because it is the more directly toxic form. Where nitrate must first be converted to nitrite (in the gut, especially in infants) to do its harm, nitrite is already the active agent.
Its signature effect is methemoglobinemia: nitrite oxidizes hemoglobin into methemoglobin, which cannot carry oxygen, so the blood's oxygen delivery drops. In infants under six months this becomes "blue-baby syndrome," visible as a bluish skin tint. Beyond the acute effect, nitrite is also the reactive partner in nitrosation — it can combine with amines to form nitrosamines, which is the cancer-relevant chemistry that connects nitrite (and nitrate) to the colorectal-cancer discussion on our nitrate page.
What makes nitrite distinctive among water contaminants is that it has a source inside the system. In utilities that disinfect with chloramine — which carries ammonia — bacteria in the pipes can oxidize that ammonia to nitrite, a process called nitrification. So nitrite can arrive both from the farmland that feeds the source water and from the treated water's own chemistry, particularly in warm weather and slow-moving parts of the network.
Where you encounter it
Agricultural sources (with nitrate)
The same fertilizer, manure, and septic inputs that drive nitrate also supply nitrite, since the two interconvert. Private wells in farm country are the classic setting, and nitrite is part of the same "test your well" panel as nitrate — especially before using well water for infant formula.
Nitrification inside the pipes
The distinctive route. In chloraminated distribution systems, ammonia-oxidizing bacteria can generate nitrite within the mains, particularly in warm water, storage tanks, and dead-end sections. This is a recognized operational challenge for utilities using chloramine, and it means nitrite can appear even where source-water nitrogen is low. Inferred from distribution-system nitrification chemistry in chloraminated systems
What the research says
The infant methemoglobinemia endpoint
The critical, well-established effect is methemoglobinemia in young infants, which anchors the strict 1 mg/L nitrite limit and the combined nitrate-plus-nitrite standard. Regulatory — ATSDR / EPA Infants under six months are the sensitive group because they both generate methemoglobin more readily and clear it more slowly.
The nitrosation pathway
Nitrite's ability to form nitrosamines links it to the broader, still-evolving question about nitrogen compounds and cancer — the same thread running through the nitrate literature (including the colorectal-cancer signal). Inferred from the shared nitrosation chemistry underlying the nitrate cancer discussion This is a chronic, lower-certainty concern layered on top of the clear acute one.
What helps
Test wells for nitrite and nitrate together — before formula. If you have an infant and a private well, confirm both are under the limits before using the water to mix formula.
Remove it with reverse osmosis or ion exchange. Point-of-use RO at the kitchen sink removes nitrite for drinking and formula water; anion exchange handles it at higher flow. See water filters compared.
On chloraminated water, be aware of nitrification. If your utility reports nitrite excursions, it's usually managing distribution-system nitrification; RO at the tap protects the most sensitive uses. Inferred from utility nitrification-management practice
What does NOT help
- Boiling. Boiling does not remove nitrite and concentrates it as water evaporates — the same dangerous mistake as with nitrate.
- Standard carbon pitcher filters. They don't remove nitrite's oxyanion form. Use RO, ion exchange, or distillation.
- Assuming low nitrate means no nitrite. Nitrification can produce nitrite inside chloraminated systems even where source nitrate is low — so it's worth checking on its own.
- Using unfiltered high-nitrite well water for formula. This is the specific scenario the limit exists to prevent; filter or use an alternative source for infants.
Open questions
- The chronic significance of the nitrite-driven nitrosation pathway relative to the well-established acute infant risk. Speculation re: chronic nitrosamine risk; the acute methemoglobinemia endpoint is established
- How often distribution-system nitrification in chloraminated networks produces nitrite excursions at the tap, and the best operational controls. Inferred from ongoing utility nitrification research
Where you meet Nitrite across your home
The same compound turns up in more than one place you live. Here's where it shows up in Embr — each links to the full breakdown for that part of your home.
Citations
- US Environmental Protection Agency. National Primary Drinking Water Regulations — nitrite MCL 1 mg/L (as N); combined nitrate+nitrite 10 mg/L (as N). epa.gov Regulatory
- Agency for Toxic Substances and Disease Registry (2017). Toxicological Profile for Nitrate and Nitrite. atsdr.cdc.gov Regulatory
- World Health Organization. Nitrate and nitrite in drinking-water — guideline values. who.int Regulatory
Frequently asked questions
What is the difference between nitrate and nitrite in water?
They are chemically related nitrogen compounds, but nitrite (NO2-) is more acutely toxic than nitrate (NO3-). Nitrate is the common one in farm-country water; it becomes dangerous partly because the body can convert some of it to nitrite. Nitrite is the form that directly interferes with the blood's ability to carry oxygen, which is why its drinking-water limit is ten times stricter — 1 mg/L as nitrogen, versus 10 mg/L for nitrate. In most water, nitrate is far more abundant, but when nitrite is present it is the more immediately hazardous of the two, especially for infants.
Why is nitrite dangerous for babies?
Nitrite causes methemoglobinemia, or "blue-baby syndrome": it converts hemoglobin into a form that can't carry oxygen, so the blood delivers less oxygen to the body. Infants under six months are uniquely vulnerable — their immature systems both convert nitrate to nitrite more readily and are less able to reverse the effect — and formula made with high-nitrite or high-nitrate well water is the classic cause. Symptoms include a bluish tint to the skin. This is why nitrate and nitrite testing matters most for households mixing infant formula with private-well water.
Where does nitrite in water come from?
Two main routes. First, the same agricultural sources as nitrate — fertilizer, manure, and septic systems — since nitrite and nitrate interconvert in the nitrogen cycle. Second, and distinctively, nitrite can form inside the distribution system through nitrification: in systems disinfected with chloramine (which contains ammonia), bacteria can convert that ammonia to nitrite in the pipes, especially in warm water or dead-end mains. So nitrite can appear both from the source water and from the treatment chemistry itself.
How do I remove nitrite from water?
Nitrite (like nitrate) is removed by reverse osmosis, ion exchange (anion resin), and distillation. A standard activated-carbon filter does not remove it, and — critically — boiling makes it worse by concentrating it as water evaporates. For a private well over the limit, point-of-use reverse osmosis at the kitchen sink is the common fix for drinking and formula water. If you have an infant and a private well, test for both nitrate and nitrite before using the water for formula.
Related compounds
Embr researches the chemistry of where you live — including the nitrogen compounds in farm-country and treated water. See the methodology page for how this Atlas tags claims by evidence strength, the tap-water hub for the other things in your water, and water filters compared for how to remove nitrite.
Last reviewed 2026-07-13. If you find a factual error, contact us.