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Current Water Treatment Methods May Pose a Health Risk

The quality of drinking water in public distribution networks across the country has recently fallen under the spotlight following the Flint water crisis where an entire community was exposed to dangerously high levels of lead. There are concerns that Flint is not the only city with alarmingly high lead levels in its drinking water, spurring the initiation of an ongoing research project to assess the scope of the problem.

Harmful Chemicals May be Generated in the Water Treatment Process

Now, another study, which was recently published in the scientific journal, Proceedings of the National Academy of Sciences, identifies other harmful chemical contaminants that are of concern, including some that are actually created during the treatment process that is supposed to render water safe to drink.

During filtration, water passes through filters, some made of layers of sand, gravel, and charcoal that help remove even smaller particles. Filtration and later chemical treatment (e.g., chlorine) played a role in reducing the number of waterborne disease outbreaks in the early 1900s. During filtration, water passes through filters, some made of layers of sand, gravel, and charcoal that help remove even smaller particles. Filtration and later chemical treatment (e.g., chlorine) played a role in reducing the number of waterborne disease outbreaks in the early 1900s.

During the water treatment process, water treatment plants commonly use oxidization methods to remove toxic compounds from the water during the water treatment process. This oxidizes these compounds, transforming them into chemicals that are supposedly less harmful, known as 'transformation products'. While previous studies have focused on byproducts formed during conventional water treatment processes such as chlorination, we still have very little understanding of products that form when newer treatment processes, such as oxidation using hydrogen peroxide and ultraviolet light, are implemented. This is particularly relevant for the treatment of recycled wastewater.

"Typically, we consider these transformation products to be less toxic, but our study shows that this might not always be the case," says lead author Carsten Prasse, assistant professor in the Department of Environmental Health and Engineering at the Johns Hopkins Whiting School of Engineering and the university's 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, together with his research team, examined phenols — some of the most commonly occurring organic chemicals in drinking water due to the fact that they are found in a wide range of products, including pesticides, dyes, pharmaceuticals, personal care and hygiene products, and also in chemicals that naturally occur in water.


The team then conducted some chemical sleuth work, replicating the water treatment process typically used by treatment plants and borrowing a method used by biochemists, to determine what compounds the phenols transformed into.

They found that after treatment, phenols formed 2-butene-1,4-dial — a harmful compound that can damage DNA in human cells. Prasse points out that furan, a toxin found in car exhaust fumes and cigarette smoke, also converts to 2-butene-1,4-dial when absorbed by the human body, which may explain why it is so harmful to our health.

After testing the effects of 2-butene-1,4-dial on proteins found in mouse livers, the researchers discovered that it had an effect on 37 proteins, which are responsible for a variety of biological processes, including energy metabolism, and the synthesis of proteins and steroids in the body.

They also found that 2-butene-1,4-dial bonded with an enzyme that played a critical role in 'cell suicide', which if inhibited could result in cells proliferating unchecked, fueling cancer growth. It also interfered with compounds responsible for controlling metabolism, which could result in health issues such as diabetes and obesity. According to Prasse, the link between pesticide exposure and obesity has already been established, and studies such as this may help explain this connection.

Prasse hopes that these methods may be expanded to assess the prevalence of other compounds besides phenols in drinking water in the future.

Treating water to make it safe to drink is extremely challenging as contaminants originate from a wide range of sources, including agriculture, wastewater, bacteria and plants, and while its relatively easy to remove chemical contaminants, it's not always clear what compounds are being formed in the treatment process, and whether these are harmful or not.

It is estimated that by 2050 two-thirds of the world's human population will depend on drinking water that contains agricultural runoff and/or wastewater from factories and urban areas. So effective water purification methods that are safe will become even more essential in the future.

"The next steps are to investigate how this method can be applied to more complex samples and study other contaminants that are likely to result in the formation of similar reactive transformation products," says Prasse. "Here we looked at phenols. 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."

Journal Reference

Carsten Prasse, Breanna Ford, Daniel K. Nomura, David L. Sedlak. Unexpected transformation of dissolved phenols to toxic dicarbonyls by hydroxyl radicals and UV light. Proceedings of the National Academy of Sciences, 2018; 115 (10): 2311 DOI: 10.1073/pnas.1715821115

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