A water treatment method may cause a new potential contaminant while taking care of an old one, researchers say.
The scientists examined what can result when treatment plants use peroxide radicals to remove phenols from water.
“We’re very good at developing methods to remove chemicals,” says lead author Carsten Prasse of Johns Hopkins University. “Once the chemical is gone, the job–it would seem–is done, but in fact we don’t always know what removal of the chemical means: Does it turn into something else? Is that transformation product harmful?”
Public water quality has received recent attention because of disturbing discoveries about lead levels in cities like Flint, Michigan. The new study suggests that there are other chemicals in water worth paying attention to, some of which may be created, ironically, during water treatment.
To rid water of toxic compounds, treatment plants now often use methods to oxidize them, turning them into other, presumably less harmful chemicals called “transformation products.” Though earlier studies have looked at the byproducts of water treatment processes like chlorination, not so much is known about the products formed during some of the newer processes, like oxidation with hydrogen peroxide and UV light, which are especially relevant in water reuse.
“Typically, we consider these transformation products to be less toxic, but our study shows that this might not always be the case,” says Prasse, assistant professor of environmental health and engineering at Johns Hopkins’ Whiting School of Engineering and Bloomberg School of Public Health. “Our results highlight that this is only half of the story and that transformation products might play a very important part when we think about the quality of the treated water.”
Prasse, along with colleagues from the University of California, Berkeley, chose to look at phenols, a class of organic chemicals that are among the most common in the water supply. They are present in everything from dyes and personal care products to pharmaceuticals and pesticides, and in chemicals that occur naturally in water.
The team, whose results appear in Proceedings of the National Academy of Sciences, first oxidized phenols using peroxide radicals, a process often used by water treatment plants. Next, they borrowed a method from biomedicine: They added amino acids and proteins to the mix. Depending on what chemical reactions took place, Prasse and his team could determine what compounds the phenols must have become in the earlier step.
They discovered that the phenols converted into products including 2-butene-1,4-dial, a compound that is known to have negative effects, including DNA damage, on human cells.
To test the specific effects of 2-butene-1,4-dial on biological processes more fully, the team exposed the compound to mouse liver proteins. They found that it affected 37 different protein targets, which are involved in a range of biological processes, from energy metabolism to protein and steroid synthesis.
One enzyme that 2-butene-1,4-dial affected is critical in apoptosis, or “cell suicide.” Inhibiting the enzyme in a living organism might lead to unchecked cell proliferation, or cancerous growth. Other compounds that 2-butene-1,4-dial interfered with play key roles in metabolism.
“There are a lot of potential health outcomes, like obesity and diabetes,” Prasse says.
Water purification is extraordinarily challenging, since contaminants come from so many different sources—bacteria, plants, agriculture, wastewater—and it’s not always clear what’s being generated in the process.
Prasse and his team point out that by the year 2050, it’s been estimated two-thirds of the global population will live in areas that rely on drinking water that contains the runoff from farms and wastewater from cities and factories. This means safe and effective purification methods will be even more critical.
“The next steps are to investigate how this [research] method can be applied to more complex samples and [to] study other contaminants that are likely to result in the formation of similar reactive transformation products,” Prasse says.
“Here we looked at phenols,” he says. “But we use household products that contain some 80,000 different chemicals, and many of these end up in wastewater. We need to be able to screen for multiple chemicals at once. That’s the larger goal.”
The National Institute for Environmental Health Sciences paid for the research.
Source: Johns Hopkins University
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