In a recent study published in Science, researchers have identified a previously unknown disinfection by-product in chloraminated tap water systems across the United States.
The compound, known as chloronitramide anion (Cl-N-NO₂⁻), is not yet regulated or fully understood, but its widespread presence and potential health effects are raising new questions about water treatment safety (Fairey et al., 2024).
Chloramine, a disinfectant made by combining chlorine and ammonia, is widely used in American water systems because it produces fewer of the regulated by-products that chlorine alone creates. Over 113 million Americans are estimated to drink water disinfected with chloramines. But unlike chlorine, which has been extensively studied, the decomposition pathways of chloramines are still not fully mapped out.
And this is where things start to get complicated.
The story of chloronitramide anion begins decades ago, when water chemists noticed an unidentified chemical forming during chloramine breakdown. It absorbed ultraviolet light but eluded detection by conventional methods. Over the years, this substance was found again and again, but its structure remained unknown.
Scientists recreated chloramine breakdown reactions in the lab. They used advanced ion chromatography and high-resolution mass spectrometry to confirm the compound’s chemical formula as ClN₂O₂⁻. It is formed when chloramines decompose in the presence of natural organic matter and oxygen, which is common in water systems (Fairey et al., 2024).
Now that the researchers knew what to look for, they found the chloronitramide anion in 40 drinking water samples collected from ten U.S. cities.
Concentrations varied widely, ranging from 1.3 to 120 micrograms per liter, with a median of 23 micrograms per liter. That is a level comparable to or higher than some currently regulated by-products like trihalomethanes and haloacetic acids.
And while the health impacts of chloronitramide anion are not yet fully known, predictive toxicology modeling suggests it may pose risks in categories like chronic toxicity, reproductive toxicity, and developmental toxicity.
This isn’t just a question for chemists. Because chloronitramide anion is stable and persistent in treated water, it may travel from treatment plants to homes and businesses across the country. The compound has not been found in water systems that use non-chlorine disinfectants, such as those in Switzerland, further confirming that its presence is linked specifically to chloramination.
One of the most concerning aspects of this discovery is how the chemical has remained hidden for so long. Traditional methods of concentrating water samples for toxicity tests often fail to detect polar, inorganic compounds like chloronitramide anion. As a result, previous toxicological studies likely missed it entirely.
What can be done?
There is a call for more careful monitoring of chloramine stability in water systems.
When chloramines degrade, especially in the presence of natural organic matter, they can create a cascade of reactions that lead to unintended by-products. Understanding and controlling these conditions could help reduce the formation of chloronitramide anion and similar compounds.
One pathway forward is the use of activated carbon filtration, which has shown the ability to break down chloronitramide anion through chemical reaction. Such filters are common in many household water filter/purification systems (such as reverse osmosis, pitchers or fridge filters) and can be an immediate mitigation option as research on the contaminant continues.
This new finding doesn’t mean Americans should stop drinking tap water. On the contrary, tap water remains one of the safest and most monitored resources in the country. But it does highlight the need for ongoing scrutiny and innovation in water treatment science.
Chloronitramide anion does not yet have a Chemical Abstracts Service number. It is, in effect, a ghost in the system. Chloronitramide anions are present, detectable, but unregulated.
Journal source:
Fairey, J.L., Laszakovits, J.R., Pham, H.T., Do, T.D., Hodges, S.D., McNeill, K. and Wahman, D.G., 2024. Chloronitramide anion is a decomposition product of inorganic chloramines. Science, 386(6724), pp.882-887. <DOI: 10.1126/science.adk6749>