Disinfectants Turn Swimming Pools Into Toxic Brews

The process of disinfecting water with chlorine and chloramines and other types of disinfectants generates a class of compounds in the water called disinfection by-products.

"The disinfectant reacts with the organic material in the water and generates hundreds of different compounds," said University of Illinois geneticist Michael Plewa, who led the team conducting the study. "Some of these are toxic, some can cause birth defects, some are genotoxic, which damage DNA, and some we know are also carcinogenic."

Plewa says that disinfection by-products, DBPs, in water are the unintended consequence of water purification. Over 270 million Americans - more than 90 percent of the U.S. population - consume disinfected tap water, he says.

"Our lab has assembled the largest toxicological data base on these emerging new DBPs," Plewa said. "And from them we've made two fundamental discoveries that hopefully will aid the U.S. EPA in their regulatory decisions."

A swimming pool (Photo by John Watson)

First, the scientists learned that DBPs containing iodine are much more toxic and genotoxic than the regulated DBPs that currently EPA uses," Plewa said.

Second, he said, "Disinfectant by-products that have a nitrogen atom incorporated into the structure are far more toxic and genotoxic, and some even carcinogenic, than those DBPs that don't have nitrogen. And there are no nitrogen-containing DBPs that are currently regulated."

Plewa says that swimming pools and hot tubs are DBP reactors. "You've got all of this organic material called people - and people sweat and use sunscreen and wear cosmetics that come off in the water. People may urinate in a public pool. Hair falls into the water and then this water is chlorinated. But the water is recycled again and again so the levels of DBPs can be ten-fold higher than what you have in drinking water," Plewa warned.

He pointed to studies showing higher levels of bladder cancer and asthma in people who do a lot of swimming - professional swimmers as well as athletic swimmers. These individuals have greater and longer exposure to toxic chemicals which are absorbed through the skin and inhaled.

"The big concern that we have is babies in public pools because young children and especially babies are much more susceptible to DNA damage in agents because their bodies are growing and they're replicating DNA like crazy," he said.

Public pools are highly chlorinated to keep bacteria and pathogens down but very little research has evaluated levels of disinfection by-products generated.

Michael Plewa (Photo courtesy UI)

"The idea is to keep the pools disinfected, keep them in compliance, just as with drinking water but then use engineering techniques that reduce the levels of these toxic by-products," advises Plewa.

This is why people are asked to bathe or shower before entering a public pool. "It's the organic material that gets in the pool that is disinfected and then recirculated over and over again. That's why we call swimming pools disinfectant by-product reactors," said Plewa. "But by public education, by personal behavior, there should be ways that we can reduce the levels of the dissolved organic material that should reduce the level of DBPs."

The University of Illinois scientist is working with engineers and chemists to develop new technologies that will disinfect water, desalinate water, or remove pharmaceuticals from water but in so doing, does not generate toxic by-products.

Plewa and his team of scientists received a Science and Technology award from the U.S. Environmental Protection Agency for their paper, "Occurrence, genotoxicity and carcinogenicity of regulated and emerging disinfection by-products in drinking water: A review and roadmap for research." It was published in the scientific journal "Mutation Research."

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