Over the span of more than four decades, a perplexing chemical compound has been detected in the treated drinking water consumed by millions across the United States. However, the precise identity of this substance remained elusive until recently. Researchers have now identified it as chloronitramide anion, a byproduct resulting from the decomposition of chloramine, a chemical widely utilized in water treatment facilities to ensure potable water.

According to a study published in the esteemed journal Science, approximately 113 million individuals are potentially exposed to this compound through their tap water. The health implications of chloronitramide anion are yet to be fully understood, but the researchers note that it shares characteristics with other regulated toxic molecules. Historically, there have been instances where chemicals employed to purify drinking water have produced byproducts that the US Environmental Protection Agency (EPA) had to regulate due to their carcinogenic potential.

In the early 20th century, the adoption of low-level chlorine in public water systems marked a significant advancement in public health by eliminating waterborne diseases such as cholera and typhoid. However, this practice also introduced new health risks. Epidemiological studies indicated that prolonged consumption of chlorinated water could increase the risk of colon and bladder cancers. For pregnant individuals, there was a potential link to miscarriages and the birth of infants with low birth weights.

While chlorine is safe for consumption at low concentrations, it was discovered that toxic byproducts were formed when it interacted with naturally occurring elements in water. The EPA now monitors and limits these byproducts to ensure water safety for human consumption. Some water systems have transitioned to chloramine, a compound formed by combining chlorine and ammonia, which was believed to have fewer hazardous byproducts and greater stability.

More recently, scientists observed that chloramine also produced byproducts, one of which remained unidentified. This unknown compound has been a subject of intrigue for Dr. Julian Fairey and Dr. David Wahman for many years. After their graduate studies, Fairey and Wahman, who studied at the University of Texas, dedicated their careers to understanding chloramine chemistry, with Wahman at the EPA and Fairey at the University of Arkansas. Their quest to identify the mysterious compound that had been present in research for approximately four decades was initially thought to be straightforward but ultimately took them 15 years to resolve.

Dr. Juliana Laszakovits, a mass spectrometry expert, was one of the first they consulted for assistance. Mass spectrometry is an analytical technique that can measure the mass-to-charge ratio, thereby determining a substance's exact molecular weight. Laszakovits suggested using a mass spectrometer to determine the compound's accurate mass and chemical formula. However, she quickly encountered the challenges that had kept the substance a mystery for so long. The water samples containing the compound had an unusually high salinity, much greater than that of seawater, making it difficult to isolate the compound using mass spectrometry alone.

Laszakovits had to employ a more innovative approach, utilizing ion chromatography in conjunction with mass spectrometry. Ion chromatography is a technique that separates and analyzes ions and polar molecules. This combination of techniques, not commonly used in environmental studies, was successful in isolating the compound and determining its mass and chemical formula. Dr. Kristopher McNeill, a co-author of the study and a professor of environmental chemistry at ETH Zurich, confirmed the structure of the compound, and Fairey recreated it using a different method to demonstrate its similarity.

To establish the compound as a byproduct of decomposing chloramines, Wahman searched for it in drinking water systems across the United States that used chloramine and compared them with systems in Switzerland that did not. He discovered the presence of chloronitramide anions in water with chloramines but not in the Swiss systems. Although the team gained significant insights into chloronitramide anions, they were unable to ascertain its impact on human health. Fairey stated, "Its toxicity is currently unknown. Its presence is expected in all chlorinated drinking waters to some extent because of the chemistry, and it has similarity to other toxic molecules. Therefore, future research on chloronitramide anion is needed to understand its potential implications in drinking water."

Dr. David Sedlak, a water expert, described the research as a "fascinating story and a very nice piece of science." He noted that chloramines produce their own families of disinfection byproducts, and there has been some regret over the switch from free chlorine to chloramines due to the continuous discovery of these byproducts. Sedlak, who is the vice chair for graduate studies and the Plato Malozemoff Professor of Environmental Engineering at UC Berkeley, emphasized the need for more toxicological research on these compounds, stating, "The challenge is, we don’t really know about the health impacts, because unlike the free chlorine disinfection byproducts, there just hasn’t been as much toxicology done on these compounds." He also pointed out that local water systems lack the funding to investigate the health effects of these byproducts, suggesting that the federal government should take on this responsibility.

Oliver Jones, a professor of chemistry at RMIT University in Melbourne, praised the study for its elegant chemistry and was convinced by the analytical evidence identifying the unknown compound as chloronitramide anion. While he agreed that a toxicological investigation would be beneficial now that the compound's identity is known, he expressed little concern about tap water, stating, "The compound in question is not newly discovered, just newly defined. We should remember that the presence of a compound does not automatically mean it is causing harm." He raised the question of whether the compound is toxic at the levels people are exposed to, suggesting that it is probably not.

The study's authors suggest that for those concerned about their drinking water, using a simple filter, such as a carbon-based filter, might be a logical step, although they cannot guarantee its effectiveness. Wahman recommended, "I think a Brita filter or something like that is probably logical, in terms of any kind of carbon-based filter that you have in your refrigerator would probably remove it if someone was concerned."