The “mystery” chemical found in the tap water of millions of Americans may be toxic: “Good reason to investigate”

Researchers say they have identified a previously unknown, potentially toxic chemical in the treated drinking water consumed by millions of Americans.

The chloronitramide anion is a byproduct of the decomposition of chloramine, which is used by treatment plants to disinfect drinking water and kill diseases such as cholera and typhoid fever.

After eluding them for years, researchers reported in the journal Science this week that they detected the “mystery” anion in 40 drinking water samples from 10 US systems that use chloramine. More than 113 million Americans drink chlorinated water.

“It’s a very stable chemical with a low molecular weight,” explained Julian Fairey, an associate professor of civil engineering at the University of Arkansas and co-first author of the new paper. “It’s a very difficult chemical to find. The hardest part was identifying it and proving it was the structure we were saying it was.”

The team observed concentrations of up to 100 micrograms per liter, exceeding typical regulatory limits for most disinfection byproducts.

The compound was not detected in ultrapure water or drinking water untreated with chlorine-based disinfectants.

Fairey synthesized the anion in the lab for the first time, but could not immediately determine whether it was associated with any cancer or other adverse health risks. He told reporters there are “good reasons to investigate the toxicity” of the compound.

“It is well known that when we disinfect drinking water, some toxicity is created. Chronic toxicity, really,” Fairey said.

“A certain number of people can get cancer from drinking water over several decades. But we haven’t identified which chemicals are driving that toxicity. A major goal of our work is to identify these chemicals and the reaction pathways through which they are formed.”

Chlorine is used to kill harmful bacteria, viruses and other microorganisms that can cause disease. Chlorine is allowed in drinking water, but the US Environmental Protection Agency limits the amount.

Some studies have linked long-term exposure to chlorinated water to an increased risk of certain cancers, especially bladder cancer, and concerns about birth defects and respiratory problems due to the byproducts produced when chlorine reacts with organic matter in the water.

Many municipal water supplies have switched from chlorine to chloramine—a compound created by mixing chlorine and ammonia—because chloramine is more stable, lasts longer, and typically generates fewer disinfection byproducts.

But the water expert Dr. David Sedlak told CNN this week that “in the last 30 years we’ve seen a little bit of buyer’s remorse about this switch from free chlorine to chloramine because we keep finding these byproducts of chloramine disinfection.”

“The challenge is that we don’t really know about the health impacts, because unlike free chlorine disinfection byproducts, there just hasn’t been as much toxicology done on these compounds,” added Sedlak, vice president for graduate studies and Plato. Malozemoff Professor of Environmental Engineering at UC Berkeley, who was not involved in the new study.

While research continues, the study authors suggest using a carbon-based filter like a British filter if you’re concerned about what’s in the water you’re drinking.