A survey of municipal drinking water in the U.S. has revealed the pervasive presence of a little-understood contaminant, chloronitramide anion, which shares a concerning structural similarity to other toxic molecules.  

The study was funded by the U.S. National Science Foundation (NSF) and was authored by researchers at the University of Arkansas, Fayetteville; the Institute of Biogeochemistry and Pollutant Dynamics in Switzerland; and the U.S. Environmental Protection Agency (EPA).

Chloronitramide anion is a byproduct of chloramines, chemicals that are often used as disinfectants in chlorinated water. Its presence was first noted in chlorinated water in the 1980s, but little is known about its toxicity, and until the present study, the extent of its presence in water was not understood. Municipal water supplies treated with chloramines serve more than 113 million people in the U.S. alone.

For the study, the researchers tested 40 drinking water samples from ten U.S. drinking water systems that use chloramines. Chloronitramide anion was found in all 40 samples, with a median concentration of 23 micrograms per liter (μg/L). Some samples showed chloronitramide anion at levels close to 100 μg/L.

The U.S. water samples were compared against tap water samples from Switzerland, where chloramines are not commonly used to treat drinking water. Unlike the U.S., Swiss water samples were devoid of chloronitramide anion.

Because so little is known about chloronitramide anion and it is so prevalent in chloraminated water, the researchers call for urgent research into its toxicity—especially considering its structural similarity to other toxic compounds.