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To Catch a Carcinogen

Researchers identify a problematic molecule found in recycled wastewater

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As populations around the world face water scarcity, water reuse has gained recognition as a valuable resource. While today’s advanced filtration methods and water recycling technologies are highly sophisticated and continue to make tremendous progress, there remain a number of challenges to address with direct potable reuse.

One such challenge is the elimination of disinfection byproducts that are harmful to humans such as N-Nitrosodimethylamine, also known as NDMA. NDMA is a potent carcinogen that forms as an unintended product of the chlorination process. And it’s a substance that is not only detrimental to humans, it’s difficult to eliminate through traditional water treatment processes.

Indirect potable reuse systems process wastewater and pump it into the ground, where the soil can help remove chemicals and harmful compounds before it goes on to the drinking water plant. However this process is more expensive than direct potable reuse in which water is purified and made immediately available for human consumption.

Costs are rising, supplies are dwindling and the clock is ticking. Explore solutions and new ways to collaborate by joining your colleagues in San Diego January 22-23, 2019 at the Western Water Summit. Click here for details

In the 1990s, when high concentrations of NDMA were found in clean recycled wastewater, researchers identified monochloramine, a component of the chlorine mixture, as the molecular culprit since it is known to react with dichloramine and cause the formation of NDMA. Plant operators began changing chlorine chemistries in order to lower dichloramine concentrations and effectively reduce NDMA formation.

But subsequent studies found that other chemicals such as pharmaceutical antacids form NDMA when chlorinated, leaving researchers wondering if monochloramine was really to blame.

Through extensive research, USC Viterbi Assistant Professor Daniel McCurry, assisted by Meredith Huang and Shiyang Huang, determined recently that the chemical responsible for the formation of NDMA, in recycled wastewater is actually dichloramine. Their study, which demonstrated significantly higher NDMA yields from dichloramination than from monochloramination, is published in Environmental Science and Technology Letters.

“Our paper showed that dichloramine is responsible for the formation of NDMA from these pharmaceutical-derived precursors. And we were able to see that you get more and more NDMA as you increase monochloramine, but that’s just because of monochloramine going to dichloramine,” McCurry told Ashleen Knutson, reporting for USC’s Viterbi School of Engineering. “So, our results from fundamental chemistry work support the practical observation that minimizing dichloramine minimizes NDMA formation.”

The team hopes that their results serve as a resource to support further research and NDMA control strategies at wastewater reuse facilities. What experiences with chlorination byproducts can you share? How will this discovery affect your plant’s operations? WE_bug_web

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  1. A great question. It’s quite possible that aeration followed by UV exposure will prove to be more effective with fewer side effects. Since most wastewater treatment plants are invested in the chlorination process, it will be an uphill battle to convince the public to spend the $$$ to further reduce the cancer risk. In the decision process going forward, when faced with major upgrades that are needed for antiquated plants, the cost of switching to UV might be more palatable to the public that picks up the tab. So far, as a society, we have been willing to accept a fairly high risk of cancer to save $ in our food supply, transportation, energy, construction materials, and mainstream lifestyle(s). Whether or not that trade-off of safety for economy will change dramatically remains to be seen.

  2. We have found that airation by spraying the water into sunlit outside fresh air and then filtration through crushed limestone followed by further filtration would eliminate 99% of the undesirable byproducts of recycled waste water. In addition we also use this water to recharge a aquifer where it settles down for a long period before being used as wholesome safe drinking water.

  3. As a grad student in toxicology half a century ago, we were shooting water samples into our GLCs and noted that the curves coming out mimicked DDT. The answer turned out to be disinfection byproducts. Over the interim, what we, as intelligent beings in a substantially more complex society, are now able to do is look at the gut microbiome on long-term effects of diminishingly small amounts of xenobiotics. Shifts in the gut microbiota driven by chronic exposure can shift that critical biota and thus, set up the system for development of chronic disease, early aging, neurodegeneration and its associated disease. This is a direct result of shifts in the microbiota caused by intake of xenobiotics. See for example, the work of Rob Knight at UC San Diego.
    It is not just the use of recycled water going into the drinking water systems, but its usage for irrigating crops where those crops can up-take and then biomagnify these xenobiotics. Currently, our sewer plants are simply being asked to do things that they were never designed to do. This is well understood, and has been for some time, but the politics involved have retarded transparency, hence the full societal costs of externalities.
    This flow-through of ingested xenobiotics results in a shift within the microbiota thus impacting the ability of the body to utilize nutrients and thus leading to chronic disease. Again, looking back to grad student days, we could see the accumulation within carrots of dieldrin from contaminated soils. Many crops can bioaccumulate xenobiotics, thus impacting the various critical biological processes needed for health. Got organochlorine contaminated soils, simply plant carrots. This is the science of phytoremediation. Chad Kinney and the USGS studied the complex nature of various xenobiotic material accumulations in soils irrigated with recycled water.
    As we know more now, the question is why the State of California and the industry has been so slow in recognizing these potential adverse impacts on the public health?

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