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.

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.