Approximately one-third of Americans may be exposed to a newly discovered by-product resulting from certain chlorine-based water treatments. Although the toxicity of this electrically charged molecule remains uncertain, preliminary analyses indicate potential adverse health effects. This is particularly concerning as some water systems exhibit concentrations of this chemical above the permissible limits for other harmful by-products, as reported by researchers on November 21 in Science.
"This paper is likely to generate significant attention," comments Daniel McCurry, an environmental engineer at the University of Southern California in Los Angeles, who, although not involved in the research, authored a perspective on the study for the same issue of Science. Most U.S. water systems use chlorine for disinfection; while effective in killing germs, it can react with other water components to form hundreds of by-products, some of which are harmful. Consequently, several municipalities switched to chloramines, chemicals that combine nitrogen and chlorine, for water treatment, explains Julian Fairey, an environmental engineer at the University of Arkansas in Fayetteville.
About 113 million Americans receive their drinking water from systems that employ chloramines. These compounds also produce by-products, though typically at lower rates than chlorine. While many chloramine by-products in drinking water are identifiable, one has remained elusive for decades. Laboratory experiments have suggested the presence of an additional by-product containing nitrogen and absorbing specific wavelengths of light, but researchers were unable to isolate it for identification. Using advanced analytical techniques, Fairey and colleagues successfully identified this mysterious substance: a negatively charged molecule named chloronitramide, which, due to its small size—comprising only five atoms—had eluded detection.
Field studies revealed that chloronitramide was not detected in Swiss water treatment systems that do not use chlorine or chloramine disinfectants. However, in 10 U.S. systems using chloramines, 40 samples averaged 23 micrograms per liter, with the highest concentration reaching 120 μg/l. For context, the U.S. Environmental Protection Agency sets a limit of 80 μg/l for some harmful by-products. The potential health impacts of chloronitramide are yet to be thoroughly investigated, and it is currently unregulated. A preliminary assessment using a web app suggests numerous potential concerns, including toxicity and adverse effects during prenatal development.
"Many chemicals formed through chlorination and fluorination processes are difficult to link directly to diseases," notes Beate Escher, a toxicologist at the Helmholtz Centre for Environmental Research in Leipzig, Germany, who was not involved in the study. Detailed laboratory studies are essential to determine whether chloronitramide poses a health risk. While the overall population health risks may warrant concern due to the large numbers affected, individual risks are likely minimal, according to McCurry. "I drink tap water at home and everywhere else I go," he says. "The potential risks from chloronitramide are not significant enough to deter me from drinking tap water."
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