Carcinogens on tap

Far away from Flint, cancer-causing agents also taint drinking water, elevating lifetime risk

drinking water gif
Robert Hood / Fred Hutch News Service

Lead-laced water has endangered Flint residents and saturated presidential politics, but another frightening family of toxins continues fouling American drinking water: carcinogens.

This year alone, routine tests and new analyses showed elevated amounts of cancer-causing agents in municipal water supplies serving millions of people in at least three states.

The pollutants include an old-fashioned poison, an industrial solvent used in paint thinners and an emerging group of substances called “disinfection byproducts” – unintended residue of the chemicals, mainly chlorine, added to kill waterborne diseases.

All three types of carcinogens flowed recently from many U.S. faucets:

  • Levels of arsenic, a naturally occurring element linked to cancer of the bladder, kidneys and lungs, exceeded federal safety standards for a decade in water systems supplying 51,000 Texas consumers, according to a March report.
  • Dioxane, a manufacturing chemical listed as a “likely human carcinogen” by the U.S. Environmental Protection Agency, has been detected in water supplies feeding more than a dozen New Jersey towns and near the Wanaque Reservoir, a water source for 3 million people. Industrial waste is blamed.
  • Haloacetic acids, a chlorination byproduct tracked by the EPA as a potential cancer causer, spiked in a North Carolina water system used by more than 35,000 customers.

Local officials in North Carolina suggested pregnant women, people with babies and older people with immune issues talk with their doctors before imbibing. 

But other health experts – including the professor who alerted the public about Flint’s crisis – have advised more drastic measures when water becomes tainted.

If tap water is found to contain a known or suspected carcinogen, consumers should consider temporarily switching to bottled water – or drinking from another source, said Dr. Beti Thompson, a member of the Public Health Sciences Division at Fred Hutchinson Cancer Research Center.

“Yes, better not to drink any contaminated water,” Thompson said.

“Cancer usually takes a lengthy time to develop and may also require sustained exposure. People should check with their local water safety group to determine what to do. Immediate cancer is unlikely but prolonged exposure is inadvisable,” Thompson said. “It depends on the contaminant [found, but] brushing teeth and washing hands is a definite stop – bathing, maybe.”

How risky is tainted water?

One fundamental question surfaces when tap water harbors a cancer-causing substance: Just how real is the risk? Unlike the fluids gushing into our sinks, the answers aren’t always clear.

“A hard question,” said Craig Mains, an engineering scientist with the National Environmental Services Center at West Virginia University. “ … We are talking about an individual’s risk of cancer [being] increased a small amount over their lifetime.

“We also have to keep in mind that ingestion of carcinogens through drinking water is only one route. People are also exposed to carcinogens in food and by inhalation [during showers],” Mains said.

The EPA sets limits on more than 90 contaminants in public water, including 31 pollutants it lists as potentially increasing cancer risk. Through scheduled water testing, each state is responsible for ensuring federal water standards are met. If any tested levels outstrip the federal maximums, water suppliers are required to notify the public.

But the number of suspected carcinogens on tap has grown, in part, due to the very process cities and towns have long used to cleanse pathogens from public supplies.

Is disinfection helping or hurting?

Treating water with chlorine creates two byproducts regulated by the EPA as possible cancer-causing agents – haloacetic acids, like those just detected in North Carolina, and a group of chemicals called trihalomethanes, or THMs.

Scientists suspect THMs in water “may cause thousands of cases of bladder cancer every year,” according to a 2013 report by the Environmental Working Group, a non-partisan outfit that researches chemicals in products.

Under federal regulations, the peak level of THMs allowed in drinking water is 80 parts per billion. That ceiling has recently been exceeded by several cities.

In Seattle, one test of public water in August 2015 found THMs at 90.7 parts per billion, according to Washington State Department of Health records. In Temple, Texas, the city notified its 66,000 residents in late March that local drinking water had topped the EPA’s limit on THMs for six months with readings as high as 105 parts per billion.

Yet THMs also offer a helpful case study of the moving targets that can exist within water-safety rules – eliciting the question: Do we really know how much is safe?

Several international studies found that people unwittingly boost their bladder cancer odds by drinking THM-contaminated water at levels far below what the EPA allows – as low as 21 parts per billion, according to an Environmental Working Group analysis.

The EPA considered lowering the legal limit for THMs from 80 to 40 parts per billion a decade ago, calculating the move "would prevent nearly 1,300 bladder cancer cases each year,” the Environmental Working Group also has reported. Instead of tightening that cap, the EPA opted to improve how government officials measure THMs for compliance with the existing standard. 

But beyond the legal limits of known pollutants, a different health mystery lurks in the water. 

Some disinfection byproducts (DPBs) are not monitored or measured by federal or local governments – and yet are thought to be even more harmful to health than EPA-regulated byproducts like THMs or haloacetic acids, water experts say.

This new crop of DBPs is rising as many water utilities drop chlorine disinfection for cheaper techniques, including the use of chloramine, a derivative of ammonia.

“Many emerging, unregulated DBPs are much more toxic,” said Dr. Marc Edwards, the Virginia Tech water engineering professor credited with blowing the whistle on the crisis in Flint, Michigan.

About 25 percent of U.S. water utilities have now switched from chlorine to chloramine, Edwards said.

Water filters may be a workaround

One irony in that shift: utilities also chose chloramine because it generates fewer THMs, Edwards said.

But alternative disinfectants like chloramine are known to produce other troubling chemical compounds, including some called nitrosamines, says the Water Research Foundation, a water-science nonprofit.

Nitrosamines are the compounds “people warned you about when they told you you shouldn’t be eating those nitrite-cured hot dogs,” Dr. David Sedlak, a University of California environmental engineering professor, told National Public Radio. “They’re about a thousand times more carcinogenic than the disinfection byproducts that we’d been worried about with regular old chlorine.”

The growing list of regulated and unregulated carcinogens in public pipelines may cause some consumers to consider buying handheld water filters or even whole-house filtration systems.

Before large purchases are made, however, water experts suggest first reading water quality reports published annually by utilities. Here’s an example posted by officials in New York City.

If contaminants are still suspected, consumers can buy a personalized water test – the EPA’s Safe Drinking Water Hotline at 800-426-4791 helps link people to certified labs.

Filters run the gamut – from $20 pitchers kept in the refrigerator to faucet-attached devices to large systems that treat all water entering a home.

Most pitcher-type filters use granular-activated carbon and resins to bond with and trap contaminants, and many will lower the amount of lead and other contaminants in water, according to the EPA.

“An activated carbon filter will remove THMs and haloacetic acids,” said Mains, of the National Environmental Services Center.

For those willing to spend several hundred dollars, reverse osmosis units – which attach beneath sinks – are effective in eliminating all disease-causing organisms and most chemicals, the EPA says.

When it comes to blocking carcinogens, that pricey filter type may be a safe bet, said Edwards, the Flint whistleblower.

“Reverse osmosis,” he said, “will remove almost everything from water.”

Water worries? Join the conversation on Facebook.

Bill Briggs is a former Fred Hutch News Service staff writer. Follow him at @writerdude. Previously, he was a contributing writer for and, covering breaking news, health and the military. Prior, he was a staff writer for The Denver Post, part of the newspaper's team that earned the Pulitzer Prize for coverage of the Columbine High School massacre. He has authored two books, including "The Third Miracle: an Ordinary Man, a medical Mystery, and a Trial of Faith." 

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