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For more than four decades, scientists have noticed a mysterious chemical in the treated drinking water of millions of people in the United States, but no one has been able to pinpoint exactly what it is — until now.
The authors of the study, published Thursday in the journal Science, believe the chemical — which they called chloronitramide anion — is a decomposition product of chloramine, a chemical many treatment plants use to make water safe to drink. About 113 million people drink tap water that exposes them to chloronitramide anions, the study found.
While it's unclear whether the byproduct could cause harm to human health, the study's authors say its properties are similar to other molecules that the government could control.
And the researchers say there are some precedents for creating byproducts of chemicals used to purify drinking water. The US Environmental Protection Agency should regulate. Because they are probably carcinogens.
in the First 20Th CenturyMany public water systems have begun using low levels of chlorine to make drinking water safe.
He solved a major public health problem that had plagued leaders for centuries by purifying water of the deadly germs cholera and typhoid transmitted by drinking water. But it caused its own health problems.
Epidemiological studies It has shown that some people who drink chlorinated water for long periods of time are at increased risk. Colon And Bladder cancers. There may also be a connection for pregnant women who drink chlorinated water. Miscarriage And those who have given birth to children Low birth weight.
Although chlorine itself is safe to use at low levels, studies have shown that toxic byproducts are formed when it interacts with other substances in water.
Water systems Still use chlorine To purify, but the EPA controls and limits The amount of residues in drinking water to ensure that it is safe for human consumption.
In some systems, when chlorine and ammonia are combined, it is converted to chloramine. Chloramine did not appear to have potentially dangerous byproducts like chlorine, and tended to be more stable and last longer.
More recently, scientists began to notice that chloramine created byproducts. Some were familiar, but one remained a mystery, according to dog study co-authors Dr. Julian Fairey and Dr. David Wahman for years.
“There's this wonderful secret premise that's always there in the writing,” Fairey said Tuesday.
After graduating from the University of Texas, Ferrey and Wahman went on to study chloramine chemistry — Wahman at the EPA and Ferrey at the University of Arkansas — and decided to associate this unnamed and unknown compound appearing in 40 years of research.
It seemed simple at first, but it took them 15 years to solve the mystery.
One of the first people to ask for help was Dr. Juliana Lazakovits, an analytical instrument that measures the mass-to-charge ratio and determines the exact molecular weight of a substance.
“My first thought was, 'Let's put this on a mass spectrometer and try to figure out the exact mass, then determine the chemical formula,'” said study co-author Lazakovit. Environmental Chemistry at the Institute for Biogeochemistry and Pollutant Dynamics, ETH Zurich.
But she quickly realized there was a reason this substance had remained a mystery for so long. Water samples containing the substance had a much higher salinity than salt water. It was difficult to separate the compound from all the salts by mass measurement.
Laszakowitz had to innovate and use a technique called ion chromatography that separates and analyzes ions and polar molecules combined with mass spectrometry.
“This combination of techniques is not commonly used in environmental studies,” Lazakovits said. But it did the trick: she was able to help him identify the compound and then figure out its chemical formula.
Dr. Christopher McNeil, co-author of the study and professor of environmental chemistry at ETH Zurich, confirmed the structure, and Ferrey then created a similar compound using a different method to show the similarity.
Wanting to confirm that the substance was the result of chloramines breaking down, Wahmann searched drinking water systems across the US using the chemical and compared it to systems in Switzerland.
The chloronitramide anion was found in chlorinated water but not in Swiss water systems.
Although the team knew a lot about chloronitramide anions, they couldn't tell if it harmed human health.
“The toxicity is currently unknown,” Ferrey said. Its presence in all chlorinated drinking waters is actually expected due to its chemistry and its similarity to other toxic molecules. Therefore, future research on chloronitramide anion is needed to understand its effects on drinking water.
Dr. David Sedlak, a water expert, called the study “an interesting story and an excellent piece of science.”
“Chloramines have their own family of disinfectants, and probably over the last 30 years we've seen a little bit of buyer's remorse in switching from free chlorine to chloramine because we're getting these chloramine disinfectants,” he said. Sedlak, vice chair for graduate research and the Plato Malozemoff Professor of Environmental Engineering at UC Berkeley, was not involved in the new study.
“The challenge is that we don't really know about the health effects, because unlike free chlorine preservatives, not much toxicity has been done on these compounds.
Local water systems don't have the funding to investigate the health effects of these products, Sedlak said, but the federal government does.
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“It's very expensive to look at these things, and when you think about how much money we spend trying to find out whether new drugs are toxic to patients, we should be willing to spend that kind of money to make sure our water is safe for people to drink or not,” he said.
“It's the kind of thing that when the government works well, it does a good job of looking at these things and protecting us.” But I don't think the EPA or the CDC or the NIH have the funding to answer these questions.
Oliver Jones, professor of chemistry at RMIT University in Melbourne, said the study was doing some fancy chemistry and that the unknown compound was the chloronitramide ion. Although he agrees that toxicological testing of the anion would be beneficial now that it is identified, “I'm not overly concerned about my tap water,” Jones said.
Jones told the Australian Science Media Centre: “The compound in question is not newly discovered but newly described.” “We must remember that the presence of a compound does not mean that it will immediately cause harm.”
Everything can be poison in the right amount, even water. The question is, is it toxic at the level people are exposed to? “I think the answer is probably not,” Jones said.
In the meantime, the study authors say, if people are concerned about their drinking water, a simple filter could help, even if they're not sure it will work.
“I think a Brita filter or something like that is probably reasonable, any kind of carbon-based filter you have in your fridge would probably remove it if someone was concerned,” Wahman said.