Scientists identify a long-sought by-product of some drinking water treatments

Roughly one-third of Americans could be exposed to a long-sought, newly identified breakdown product of some chlorine-based water treatments.

Although the toxicity of the by-product, an electrically charged molecule, is yet to be determined, analyses suggest the substance could have several detrimental health effects. That’s a concern because in some water systems the chemical appears in concentrations above the threshold allowed for other harmful breakdown products, researchers report November 21 in Science.

“This paper’s going to cause quite a stir,” says Daniel McCurry, an environmental engineer at the University of Southern California in Los Angeles who was not involved in the research but did write a perspective on the study for the same issue of Science.

Most water systems in the United States disinfect water with chlorine; the dissolved gas effectively kills germs but can react with other substances in the water to create hundreds of by-products, some of them harmful. As a result, some municipalities decades ago switched to treating their water with chemicals called chloramines, says Julian Fairey, an environmental engineer at the University of Arkansas in Fayetteville.

Nationwide, about 113 million people get their drinking water from systems that use chloramines as a disinfectant. These nitrogen-chlorine compounds also create breakdown products, but generally do so at much lower rates than chlorine. Many chloramine by-products in drinking water are readily identified, but one has remained elusive for decades.

Lab experiments to date have hinted at the presence of one more by-product — something that contained nitrogen and absorbed particular wavelengths of light — but researchers could not isolate it from other by-products to identify it. Using a combination of analytical techniques, Fairey and colleagues finally identified the enigmatic substance: a negatively charged molecule dubbed chloronitramide. Its small size —only five atoms — among other factors helped it remain hidden among other breakdown products, Fairey says.

Chloronitramide was not detected in Swiss water treatment systems that don’t use chlorine or chloramine disinfectants, the team’s field studies show. But in 10 systems in the United States that use chloramines to treat their water, 40 samples contained an average of 23 micrograms per liter, with the highest concentration measuring a whopping 120 μg/l. For comparison, the U.S. Environmental Protection Agency regulates the concentrations of some breakdown products known to be harmful to be no higher than 80 μg/l.

Potential health effects of chloronitramine haven’t been studied in detail yet, the team notes. As such, the substance isn’t regulated. But using a web app to do a preliminary assessment of the newly identified substance suggests that there could be dozens of issues of concern, including toxicity and detrimental effects occurring during prenatal development.

“Many, many chemicals are formed by chlorination and fluorination processes, and it’s tough to tell which ones are causative” of disease, says Beate Escher, a toxicologist at the Helmholtz Centre for Environmental Research in Leipzig, Germany, who was not involved in the new study. Detailed lab studies are needed to figure out whether chloronitramide may be harmful, she notes.

While health risks may be worth worrying about across the population at large, due to the large numbers involved, they’re probably not worth worrying about on an individual basis, McCurry says. “I drink tap water at home and everywhere else I go,” he says. The potential risks from chloronitramide, he says, “are not enough to make me stop drinking tap water.”