Chlorine is added to swimming pools to kill bacteria, but Spanish researchers say the chemical in large quantities can cause DNA damage that could increase the risk of cancer.

Their study is published in Environmental Health Perspectives (EHP) journal, coordinated by researchers from the Centre for Research in Environmental Epidemiology (CREAL) and the Research Institute Hospital del Mar.

The evidence of DNA damage, known as genotoxic effects, was observed in 49 healthy adults after they spent 40 minutes in a chlorinated indoor pool. Specifically, researchers found increased levels of two biomarkers of genotoxicity in relation to the concentration of the most common types of DBPs in exhaled breath after swimming.

The observed biomarkers include micronuclei, a biomarker that indicates the type of DNA damage levels, a biomarker of cancer risk predictor in healthy subjects, and a biomarker of exposure to genotoxic agents.

Despite these results, the co-director of CREAL, Manolis Kogevinas, says swimming in chlorinated water is still safer than swimming in water without it. He says pools should just have less of it.

Just cut back on the chlorine

"The positive health impacts of swimming can be increased by reducing the levels of these chemicals," Kogevinas said. "In no case we want to stop swimming but to encourage the reduction of chemicals in swimming pools to ensure disinfection of the same."

In fact, he says reducing the levels of disinfection by-products (DBPs) can be achieved rigorously applying measures such as showering before swimming, bathing cap, avoid urinating in the pool and perform proper maintenance.

The DBPs formed in the pools are the result of the reactions appeared between the water disinfectants such as chlorine pools and organic matter, which occurs naturally or is introduced by swimmers through sweat, skin cells and urine.

Previous studies found an association between exposure to DBPs of drinking water and bladder cancer risk. Specifically, one such report, coordinated by the CREAL, concluded that this association was given by skin and inhalation exposure as occurs during showering, bathing or swimming.