Mystery chemical in US drinking water could be risk to hundreds of millions

Millions of Americans may be exposed to an unregulated and potentially hazardous chemical in their drinking water, according to a new study.
Researchers have identified chloronitramide anion, a previously unknown by-product of chloramine disinfection, in tap water systems across the United States.
The compound, detected at levels exceeding regulatory limits for similar contaminants, raises urgent questions about its toxicity and the safety of chloraminated water supplies.
“I just want to note that its toxicity is currently unknown,” David Wahman, co-author of the study, said during a press conference on Tuesday.
But he added, “It has similarity to other toxic molecules. Therefore, future research[…]is needed to understand the potential implications of it in drinking water.”
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Chloramines, widely used as an alternative to chlorine for disinfecting drinking water, are a cornerstone of U.S. public health, with nearly one-third of Americans relying on chloraminated water today.
However, their decomposition products have remained poorly understood, with chemists aware for decades of unidentified nitrogen-containing by-products.
The newly characterized chloronitramide anion appears to fill a long-standing gap in understanding chloramine chemistry.
A team led by Julian Fairey of the University of Arkansas used advanced techniques to isolate and identify the compound.
Fairey’s study detected chloronitramide anion at concentrations up to 100 micrograms per liter (μg/L) in chloraminated water—a level surpassing the typical limits for regulated disinfection by-products, which range from 60 to 80 μg/L.
Although the compound’s toxicity has yet to be assessed directly, computational models suggest it may pose health risks. This has spurred calls for immediate toxicological evaluations and monitoring of chloronitramide anion in water systems.
“Regardless of whether chloronitramide anion is found to be toxic or not, its discovery warrants a moment of reflection for water researchers and engineers,” wrote Daniel McCurry, a researcher who provided commentary on the findings in the journal Science.
This discovery could reignite debate over the widespread use of chloramines in water treatment. Chloramination became widely adopted in the U.S. from the 1970s onward as an alternative to chlorine, following the discovery of harmful chlorinated by-products in treated drinking water.
“The switch to chloramination was an easy fix for a thorny problem,” McCurry wrote. But it introduced new, unintended risks, including increased lead release from pipes and the formation of other toxic nitrogen-containing by-products such as nitrosamines.
In contrast, Europe has largely avoided chloramination, favoring additional water treatment steps and more rigorous maintenance of distribution systems.
The study underscores the need for improved oversight and collaboration between researchers and policymakers to address emerging water contaminants.
Chloronitramide anion’s discovery highlights the gaps in knowledge about chloramine by-products and their health impacts.
“This reckoning is arguably overdue,” McCurry wrote, calling for a reevaluation of the long-term safety of chloramination in public water supplies.
In response to a question from Newsweek during Tuesday’s press conference, the authors of the study suggested that BRITA filters could be useful for those wishing to treat their water themselves while toxicity of the compound is assessed.
But, while Wahman noted that activated carbon filters have been shown to remove chloronitramide anion, he also said that “there probably needs to be a little more work done to figure out what it’s being broken down into.”
For now, the authors acknowledged that they just don’t know what the impacts are on users. But, as Fairey put it, it “looks concerning,” and health effect studies are warranted based on these new findings.
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Reference
Fairey, J. L., Laszakovits, J. R., Pham, H. T., Do, T. D., Hodges, S. D., McNeill, K., & Wahman, D. G. (2024). Chloronitramide anion is a decomposition product of inorganic chloramines. Science. 10.1126/science.adk6749