Ammonium nitrate is moderately toxic. It won’t poison you on brief casual contact, but swallowing it, breathing its dust, or being exposed over long periods can cause real harm. The primary danger comes from its ability to interfere with your blood’s capacity to carry oxygen, a condition called methemoglobinemia. It also releases highly toxic gases when it decomposes at high temperatures.
How Toxic Is It if Swallowed?
In animal studies, the lethal dose for 50% of test subjects (a standard toxicity benchmark) is about 2,217 mg per kilogram of body weight in rats. That places ammonium nitrate in a relatively low acute toxicity category, meaning a small accidental taste is unlikely to be fatal. But ingesting a significant amount is dangerous for a different reason than straightforward poisoning: it disrupts how your blood delivers oxygen.
Once inside the body, ammonium nitrate converts to nitrite. Nitrite changes the iron in your hemoglobin from a form that can grab and release oxygen to a form that cannot. The result is hemoglobin that is functionally useless. Your blood is still flowing, but it’s carrying less and less oxygen to your tissues. This is methemoglobinemia, and it produces symptoms ranging from a bluish tint to the skin and lips at mild levels, to confusion, seizures, and death when a large fraction of hemoglobin is affected.
Infants are especially vulnerable because their digestive systems more readily convert nitrate to nitrite, and their hemoglobin is more susceptible to oxidation. Contaminated well water with high nitrate levels has historically caused outbreaks of “blue baby syndrome” for exactly this reason.
Breathing Ammonium Nitrate Dust
Inhaling ammonium nitrate dust irritates the nose, throat, and lungs. Workers in fertilizer plants or anyone near large quantities of the granular material can be exposed when it becomes airite. Symptoms of short-term inhalation are similar to breathing any irritant dust: coughing, sore throat, and a burning sensation in the nasal passages.
There is no substance-specific occupational exposure limit set by OSHA for ammonium nitrate. Instead, it falls under the general category of “particulates not otherwise regulated,” which caps workplace air concentrations at 15 mg per cubic meter for total dust and 5 mg per cubic meter for the respirable fraction over an eight-hour shift.
Skin and Eye Contact
Ammonium nitrate is classified as a Category 2 skin irritant and a Category 2A eye irritant under the Globally Harmonized System. In practical terms, this means it can cause redness and discomfort on skin contact and noticeable eye irritation, but it is not corrosive. Washing the area with soap and water typically resolves skin exposure. Eye contact calls for thorough rinsing with water for at least 15 minutes.
Long-Term Exposure Risks
Chronic occupational exposure raises more serious concerns. Repeated contact with ammonium nitrate over years has been linked to kidney inflammation. A case study published in the Indian Journal of Occupational and Environmental Medicine described a worker who spent 25 years in an ammonium nitrate factory and developed a type of kidney disease called membranoproliferative glomerulonephritis, with no other identifiable cause beyond his prolonged chemical exposure.
The underlying mechanism for long-term damage is the same nitrate-to-nitrite conversion that causes acute problems. Sustained low-level exposure means the body is continuously producing small amounts of nitrite, which places ongoing oxidative stress on the blood and kidneys. Over decades, this can contribute to tissue damage that a single exposure would never cause.
Toxic Gases From Decomposition
Ammonium nitrate begins to break down at around 210°C (410°F), initially producing nitrous oxide and water. At higher temperatures, or when heated rapidly, it releases highly toxic nitrogen oxide fumes. These gases are dangerous in their own right: nitrogen dioxide, for example, can cause severe lung injury even at relatively low concentrations. This secondary toxicity is a major concern during fires, industrial accidents, and explosions involving stored ammonium nitrate, where the immediate blast is only one part of the hazard. The toxic cloud that follows can affect people well beyond the blast zone.
How Ammonium Nitrate Poisoning Is Treated
Most cases of mild methemoglobinemia from nitrate exposure resolve once the source is removed and the body’s natural enzyme systems gradually restore hemoglobin to its normal state. Not every patient needs specific treatment.
When methemoglobin levels climb above roughly 20% in someone showing symptoms, or above 30% even without symptoms, hospital treatment becomes necessary. The standard antidote is methylene blue, given intravenously. It works by boosting the activity of an enzyme that converts methemoglobin back to functional hemoglobin, and it typically brings levels down significantly within an hour. People with preexisting heart disease, lung conditions, or anemia may need treatment at much lower thresholds, since their oxygen delivery is already compromised.
For infants, whose poisoning often involves contaminated water and accompanying dehydration, correcting fluid balance and blood acidity can improve symptoms alongside the standard antidote when needed.