Unmasking the Chemical Forming Carcinogens in Recycled Water

USC researchers identify the molecule responsible for a potent carcinogen found in recycled wastewater.

COVER ART FOR THE MARCH ISSUE OF ENVIRONMENTAL SCIENCE AND TECHNOLOGY LETTERS. ILLUSTRATION/ENVIRONMENTAL SCIENCE AND TECHNOLOGY LETTERS, Source: USC Viterbi

Engineers at wastewater recycling plants can rest easy knowing that their methods for minimizing the formation of a potent carcinogen are targeting the right chemical compound.

USC Viterbi Assistant Professor Daniel McCurry, undergraduate student Meredith Huang and master’s student Shiyang Huang have confirmed the chemical responsible for the formation of the carcinogen N-nitrosodimethyalmine, or NDMA, in recycled wastewater. They began their study after contradictory findings surfaced in the environmental research community, causing hesitation in the adoption of NDMA intervention methods at treatment facilities. Their work was published in Environmental Science and Technology Letters as the March cover study.

“The recent drought in California and subsequent water vulnerability has increased interest in water recycling,” said Meredith Huang, the study’s first author. “However, disinfection byproducts like NDMA, formed in the process of treating wastewater, are harmful to humans and introduce some issues when the goal is re-consumption.”

The origin story

In the late 90s, high concentrations of NDMA were found in what was otherwise extremely clean recycled wastewater, which in most states is discharged into rivers that are used as sources for drinking water. This discovery set off a years-long research effort by several labs to figure out how the harmful chemical compound was forming.

“The concentration of NDMA that we’re worried about is very, very low,” said McCurry, who works in the Sonny Astani Department of Civil and Environmental Engineering. “Unlike a lot of organic pollutants in drinking water where the regulatory limit may be in the microgram per liter range, for NDMA, the regulatory guideline in many places ranges from 10 nanograms per liter to 100 nanograms per liter. So, three to four orders of magnitude lower in concentration because it’s just a super potent carcinogen.”

Most recycled wastewater that will be used as drinking water through a process known as potable reuse, first enters the ground before it goes to a drinking water plant. The soil acts as a filter, removing chemicals and degrading harmful compounds like NDMA. But the high cost of pumping water into and out of the ground has led to an increased interest in direct potable reuse, where recycled wastewater goes directly to a drinking water plant.

“NDMA is one of the major obstacles to direct potable reuse because it is really difficult to get rid of thorough traditional treatment processes,” McCurry said. It is instead easier and more affordable to lower NDMA concentrations by eliminating the molecules responsible for its formation.

The villain

Originally, researchers found that NDMA is the result of the chlorination step of the recycled wastewater treatment process. Specifically, dichloramine, a minor component of the chlorine mixture, causes the formation of NDMA. These findings led treatment plants to begin manipulating chlorine chemistry in order to lower dichloramine concentrations and, ultimately, reduce NDMA formation.

However, researchers were still uncertain of what dichloramine was reacting with to form NDMA until five years ago when researchers in Toronto found that certain pharmaceuticals, like the antacid Zantac, can form NDMA when chlorinated in wastewater-like conditions. Subsequently, other researchers began looking into the formation mechanism from Zantac-like chemicals.

“They decided that it was monochloramine that was responsible in contrast to several practical studies showing that minimizing dichloramine in real recycled wastewater minimizes NDMA formation,” McCurry said. “They came to the wrong conclusion because monochloramine and dichloramine are interconvertible. So, experimentally, it’s pretty hard to separate them.”

With this in mind, McCurry and his team carefully designed their experiment to avoid conversions between the two molecules by using much lower doses. Then, by systematically applying a range of monochloramine and dichloramine doses to pharmaceutical precursors, they were able to determine which molecule was the root cause of NDMA formation.

Read full article: USC Viterbi

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Taxonomy

• Treatment
• Reclaimed Wastewater
• Treatment Methods
• Decontamination
• Wastewater Phycoremediation
• Industrial Wastewater Treatment
• Wastewater Treatment
• Contaminant Removal
• Filtration
• water treatment

5 Comments

1. Recycled water is safe, desalination isn't useless, but it does cost more than recycling. They each have a place. UV will knock out nitrosamines if that is deemed to be necessary for consumers' comfort.

   1 Comment reply

   1. Yes I did say recycled water is safe when properly done. Desalination is useful to those not wanting to use natures rain. Rain water collection, use, and long term storage will easily supply you all you need.  There is not one desert or arid country I can not change into a water wonderland. farming, forest, cities. Nature provides all.

2. Bioremediation technology has been around for at least 50 years. It is used to clean waste water compounds into their elemental state becoming nutrients. The water remaining is potable. Forty years of monthly health dept. testing has shown Zero pathogens, Oxygen content increased drastically, and water declared potable by the independent labs.  This makes desalination technology useless.  

3. It is still good to see researches sorting out knowledge gaps... BUT common sense must prevail...carcinogens are everywhere, Mountain stream may be "clean" but are still full of animal "by-products" (crypto, giardia etc,), we are all downstream of an upstream user and all water has been recycled many times. We should  be thank full for our access to abundant clean water sources ( "fresh" or recycled).

   The "fashionable pseudo-intellectuals" who argue against potable recycling need to think beyond their "anal" concern over NDMA,  endocrine disrupters  etc and focus on the broader issues of water availability and improved wastewater recycling. Urban dwellers are very lucky while rural and agricultural communities across first, second and third world communities are left dealing with whatever levels of water/wastewater treatment they can afford.

   As I used to tell my former students and staff... "If recycled water is good enough for astronauts to drink, its good enough for anyone!".

   Drink water, beer, wine, fruit juice, milk or whatever your "poison of choice". Don't drink and your will surely die with days... long before the nasties we fear  kill us!

   The water industry may be dominated by  a few professional, political and personal self-interested spokes people, but the vast silent majority of us provide invaluable services to our communities. Lets not let them down by allowing "over-anal" obsession with the minutia to dominate the future.

    

4. Don't get carried away, Guy. Read: Drinking Water as a Proportion of Total Human Exposure to Volatile N‐Nitrosamines” by Steve E. Hrudey, Richard J. Bull, Joseph A. Cotruvo, Greg Paoli, and Margaret Wilson, in Risk Analysis, 33(12):2179–2208. DW contributes less than 0.02% of daily small nitrosamine exposures. More than 99.9% of daily exposure is endogenous metabolic production from NO chemistry.

   1 Comment reply

   1. Thanks Joseph for the stats.  I do take any new or exaggerated threat with a lick of salt.  I only work with cutting edge technology. The elimination of all waste and toxins by microbes in nature has been common knowledge for about 40 years.  I share the facts to those not in the scientific community or scientists getting paid to ignore pure science.

5. Moving forward with the practical applications of waste water being the primary source of water is on everyone's mind.  The current use of chlorine as a disinfectant is finally winding down. Most scientist and nutritionists always knew there are no safe levels of chlorine in drinking water. Nature has always had her own method. It eliminates all organic waste and all toxic substances. 100%.  It appears one huge mistake in 1920 still has unknown deadly side effects.  In case you were wondering. There are no chlorine dosing stations on mountain rivers.