Time to Get Out of the Pool? Contaminants May Lead to Bladder Cancer, Study Says

Swimming -- an exercise that improves your health -- may also have a downside. A new study suggests that swimming in indoor chlorinated pools may lead to bladder cancer.

The study, just published online in Environmental Health Perspectives, a highly-regarded, peer-reviewed government journal, found that people who swam just 40 minutes a day were exposed to sufficient levels of disinfection by-products (DBPs) to cause damage to the DNA that may develop into cancer. People with a type of gene found in one quarter of the population were most vulnerable.

"Nobody should stop swimming because of our study," said Dr. Manolis Kogevinas, the lead researcher on the report, which was done in collaboration with the U.S. Environmental Protection Agency. "Physical activity is so important for health."

But, he added, "We seem to have a problem here. There are some contaminants in swimming pools that need to be better regulated."

DBPs are formed in swimming pools from the reaction between disinfectants such as chlorine, or bromine, and organic material that naturally occurs in the water or is brought in by swimmers, via sunscreens, makeup, sweat, skin cells and urine. This study found more than 100 kinds of DBPs in swimming pools, some never previously reported. DBPs also occur in drinking water. Earlier studies have shown that exposure to DBPs may increase the risk of bladder cancer, but this is the first study that assessed the different types of DBPs found in indoor swimming pools and examined their effects on swimmers.

The new study is being published as a set of three papers, authored by a group of researchers, including Kogevinas and his colleagues at the Centre for Research in Environmental Epidemiology in Spain. They collaborated with the EPA and researchers elsewhere in the U.S., as well as with scientists from Germany, the Netherlands, and Canada. EPA staffers Susan Richardson and David DeMarini wrote two of the three papers.

Researchers collected samples of urine, blood, and exhaled breathe from 49 healthy adults, before and after their workouts. They reported increases in two genotoxicity biomarkers which have been associated with cancer risk in healthy subjects.

"We were not looking at disease, but at changes in the blood or urine that could indicate that in the future we could have some clinical disease," Kogevinas said.

In an internal "Qs and As" document regarding the studies, obtained by Politics Daily, the EPA wrote: "We have increasing evidence that disinfection byproducts are associated with cancer." The agency also said "Given the potential importance of these findings for the population and the high frequency of swimming in pools, public health authorities should first take measures to ensure that all existing guidelines for reducing DBPs in pool water are rigorously enforced and they should develop a research agenda that can quickly give a definitive answer."

Previous studies found associations between exposure to DBPs in drinking water and bladder cancer. Other studies have shown that exposure to DBPs can cause asthma. Swimming pools tend to use chlorine for disinfectant, while hot tubs and spas more often use bromine, which has been considered to be less of an irritant.

Based on the results, Kogevinas says researchers now need to study swimmers and non-swimmers. He expects swimmers will be in better overall shape, but that "they may have a higher incidence of bladder cancer."

An EPA scientist who worked on the study said it's expected that there would be even more potent DBPs in hot tubs because of the bromine used to keep them clean. "I would say limit your exposure," the scientist said.

Kirstin Pires, a spokeswoman for Association of Pool & Spa Professionals, which represents much of the industry, said that most swimming pools have less DBPs than found in drinking water. "We're not in a position to challenge EPA on what levels they think are safe," she said.

But Kogevinas said that DBPs in drinking water differ substantially from those in pools, due to less contamination from people.

Jennifer Sass, a senior scientist with the Natural Resources Defense Council, said she understands the fine line that EPA is trying to walk between protecting the public from toxic chemicals in pools, and discouraging them from a healthy activity.

"For some people, swimming is the only option for exercising," Sass said. "For the swimming pools, the part that is really bad is right at the surface of the water, where the chlorinated gases are. So, if kids are playing in the water, near the surface, they might not want to spend so much time." Sass added, "we suggest people use filters on their tap water, to screen out the DBPs."

In its internal report, EPA said that it would like to see this pool study replicated with a larger sample of swimmers and led by a different research team, as is typical when trying to duplicate results. The agency also called for long-term investigations, including evaluations of different types of swimming pools, under a variety of conditions.