### Unraveling a Four-Decade Enigma: The Discovery of Chloronitramide in Chloraminated Drinking Water
In an extraordinary investigation, scholars from the United States and Switzerland have shed light on a riddle that has persisted for almost forty years: the nature of a mysterious compound present in chloraminated drinking water. This revelation, which identifies the molecule known as chloronitramide, brings to the forefront pressing concerns regarding its potential health implications and reassesses the wider consequences of using chloramines for water sanitation.
#### A Persistent Enigma Comes to Light
The foundation of this inquiry traces back to the early 1980s, when environmental engineer Richard Valentine at the University of Iowa detected an unknown molecular ion in chloraminated water via ultraviolet (UV) spectroscopy. At that time, Valentine and his team noted that this compound arose naturally as monochloramine—a widely employed disinfectant—decomposed in the water. Remarkably, the UV absorbance spectrum of this compound was nearly indistinguishable from that of monochloramine itself, making it difficult to clarify its distinct structure.
Valentine likened the challenge to “searching for a needle in a haystack where all the strands of hay are needles.” After many years of advancements in technology, researchers spearheaded by Julian Fairey at the University of Arkansas, alongside analytical chemists at ETH Zurich including Juliana Laszakovits, revisited this issue with advanced tools, ultimately piecing the puzzle together.
#### Innovations in Analytical Methods
The research team utilized modern techniques that were unavailable in the 1980s, such as ion chromatography combined with electrospray ionization mass spectrometry (IC-ESI-MS). This powerful method excelled at isolating anions, enabling previously hidden molecular signatures to come to light. Additional techniques like nuclear magnetic resonance (NMR) and infrared spectroscopy further clarified the true identity of chloronitramide.
The molecule, discerned through isotopically labeled mass spectrometry, consists of two oxygen atoms, one nitrogen atom, and one chlorine atom. Follow-up studies illuminated its likely formation process: chloronitramide arises as an intermediate when dichloramine undergoes hydrolysis to become nitroxyl, which subsequently reacts with dissolved oxygen to yield peroxynitrite. Peroxynitrite then breaks down to release nitronium cations, highly reactive intermediates that nitrate either monochloramine or dichloramine to create chloronitramide.
#### Health Risk Concerns and the Need for Immediate Research
Although the exact health impacts of chloronitramide remain unclear, its structural likeness to hazardous compounds necessitates urgent investigation. Utilizing the US Environmental Protection Agency’s (EPA) Generalized Read Across (GenRA) algorithm, researchers established connections between chloronitramide and other substances recognized for their adverse effects. This finding is particularly distressing as the levels of chloronitramide in certain U.S. tap water samples—especially in regions like California and Texas—are higher than those of regulated harmful substances like trihalomethanes (THMs) and haloacetic acids (HAAs).
Numerous experts regard this discovery as representative of broader safety concerns surrounding chloraminated drinking water. Nitrosamines, a category of compounds generated under comparable chemical conditions that the World Health Organization classifies as probable human carcinogens, share structural similarities with chloronitramide. Kristopher McNeill from ETH Zurich states, “If you removed one of the oxygen atoms from the nitro group, you’d have a nitrosamine.”
#### Reassessing the Chloramine Controversy
For decades, chlorine-based disinfectants have been the gold standard in water treatment, praised for their low cost and effectiveness against microbial contaminants. However, starting in the 1970s, fears about chlorine’s reactivity with organic matter led the EPA to enforce strict limits on harmful by-products like THMs and HAAs, which are associated with cancer and other health problems. Consequently, numerous water utilities in the U.S. and globally have shifted to using chloramines, a blend of chlorine and ammonia, to minimize these disinfection by-products (DBPs).
While chloramines create lower amounts of THMs and HAAs, they bring their own challenges. Beyond the newly identified chloronitramide, chloraminated water has been associated with other detrimental by-products, such as nitrosamines. Additionally, chloramines can exacerbate the corrosion of lead pipes, with serious public health ramifications, as evidenced by the Flint water crisis. Chloraminated water is also notorious for its “pool smell,” resulting from the release of ammonia and various nitrogenous by-products.
Daniel McCurry, an environmental engineer at the University of Southern California, describes the discovery of chloronitramide as a “highly significant” finding that should trigger prompt reassessments of chloramine’s function in water treatment. He emphasizes that effective treatment