A mystery byproduct of a disinfectant used in the drinking water of more than 113 million people in the US has finally been identified in a finding that has scientists concerned.
Though just one of a number of known break-down products resulting from the germ-killing inorganic chloramines, the compound recently uncovered by a team of researchers in the US and Switzerland is yet to be declared risk-free to the public, requiring further testing to ensure safety.
The use of inorganic chloramines has saved countless lives from biological contaminants in water supplies around the world, chosen as a low-risk alternative to chlorine. Adding low levels of chlorine to drinking water also improves public health enormously by killing pathogens. But chlorine is notorious for reacting with other things in the water, forming a range of chemicals that can have harmful effects at certain concentrations over a lifetime.
Since the 1970s, scientists have found chlorinated water can contain chemical byproducts that at high enough doses have been linked to bladder and colon cancer, as well as low birth weight and miscarriage. These byproducts are therefore regulated by the US Environmental Protection Agency.
To minimize the concentration of these chlorine byproducts, utilities today often switch between chlorine and related chemicals, called chloramines, which make fewer of the byproducts known to be harmful.
But new research, led by University of Arkansas environmental engineer Julian Fairey, highlights the fact that other, so-called 'unidentified', byproducts can emerge in water disinfected with chloramines too, and these may also potentially be toxic in concentrations that are yet to be determined.
But we can't test the toxicity of a chemical without actually tracking it down first.
Scientists noticed one of these chloramine byproducts more than 40 years ago, though its identity wasn't immediately obvious. Extensive studies in the '80s and '90s found the unknown byproduct contained chlorine and nitrogen, and was an anion (a negatively charged ion). But they struggled to determine its molecular composition and chemical structure.
Fairey has been on its heels for ten years, and finally, he and his team have it pinned down.
"Prior characterization efforts [were] stymied by analytical limitations and an incomplete understanding of chloramine decomposition chemistry, which my lab group has worked to address, in collaboration with Dave Wahman at US EPA," Fairey explained at a recent press briefing.
Known as a chloronitramide anion, it's a remarkably stable chemical with a low molecular weight, which made it difficult to find in water samples or synthesize in the lab.
Many of the usual routes for characterizing environmental samples were unsuccessful, so they turned to ion chromatography coupled with mass spectrometry.
"With this technique, we were able to partially separate the compound from sulfate and determine its accurate mass. So then, we could determine the chemical formula, which was found to be chlorine with two nitrogens and two oxygens… as an anion," Juliana Rose Laszakovits explained.
And while no toxicity studies have yet been conducted, let alone anything linking it to cancers or other health risks, it does have some features similar to other toxic molecules.
"Its presence is expected, quite honestly, in all chlorinated drinking waters to some extent, because of the chemistry, and it has similarity to other toxic molecules," US EPA environmental engineer David Wahman stated in the press briefing.
"Therefore, future research on chloronitramide, and occurrence and toxicity, is needed to understand potential implications of it in drinking water."
Wahman also pointed out that other systems using chlorine-based disinfectants – swimming pools, ponds and cleaning products, for instance – may warrant scientific investigation, particularly if there's nitrogen involved.
The real question, perhaps, is how newfound contaminants like this compare with not just other measures, but the deadly organisms its parent molecule protects us from.
"Regardless of whether chloronitramide anion is found to be toxic or not, its discovery warrants a moment of reflection for water researchers and engineers," writes environmental engineer Daniel McCurry from the University of California Los Angeles in an accompanying perspective.
As McCurry goes on to note, there is more to the chemistry of chloramination than its potential toxicity, with concerning reactions in the lead pipes to consider.
Safety is rarely an all-or-nothing decision for authorities. In an effort to make drinking water as safe as possible, weighing up the costs and benefits as we continue to make new discoveries is vital for public health.
The paper was published in Science.