A group of chemical compounds used to disinfect water for one-third of the US population and millions of others globally produces a potentially toxic byproduct, according to new research published Thursday, sparking calls for an “immediate” investigation into possible health impacts.

Inorganic chloramines have been used for decades to remove pathogens from public water supplies.

Though chlorine remains the most widely used disinfectant in the US and globally, chloramines have increasingly replaced it in many systems to reduce certain byproducts linked to bladder and colon cancer, low birth weight, and miscarriage.

Today, more than 113 million Americans rely on chloraminated drinking water, with the compound also in use across Canada, Asia and Europe.

“However, chloramines themselves decompose into products that are poorly characterized,” said Julian Fairey, lead author of the study published in the journal Science, during a press briefing.

One such product, identified more than 40 years ago but left chemically unresolved, was simply dubbed the “unidentified product.”

Fairey and his team have finally cracked the mystery.

Using a combination of traditional chemistry methods and modern tools like high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy, they identified the compound as “chloronitramide anion.”