Chemicals in Indoor Swimming Pools May Increase Cancer Risk

Swimming in indoor chlorinated pools may induce genotoxicity (DNA damage that may lead to cancer) as well as respiratory effects, but the positive health effects of swimming can be maintained by reducing pool levels of the chemicals behind these potential health risks, according to a new study published in a set of three articles online September 12 ahead of print in the peer-reviewed journal Environmental Health Perspectives (EHP). This study is the first to provide a comprehensive characterization of disinfection by-products (DBPs) in an indoor pool environment and the first to study the genotoxicity of exposure to these chemicals among swimmers in an indoor chlorinated pool.

DBPs form in pool water from reactions between disinfectants such as chlorine and organic matter that is either present naturally or is introduced by swimmers, such as sweat, skin cells, and urine. Previous epidemiologic studies have found an association between exposure to DBPs in drinking water and risk of bladder cancer, and one such study has found this association for dermal/inhalational exposure such as occurs during showering, bathing, or swimming.

The new study details a comprehensive investigation of DBPs and mutagenicity of water samples collected from two indoor pools, one disinfected with chlorine, the other with bromine. In addition, short-term changes in biomarkers of genotoxicity and respiratory effects were studied in swimmers who swam in the chlorinated pool.

No previous studies have combined investigations of the mutagenicity (ability to cause permanent DNA mutations) of pool water with a comprehensive chemical characterization of the water and studies of human exposures, the authors stated.

Evidence of genotoxic effects were seen in 49 healthy adults after they swam for 40 minutes in the chlorinated pool. Specifically, researchers found increases in two genotoxicity biomarkers relative to the concentration of the most common types of DBPs in exhaled breath, which were used as a measure of the swimmers' exposures. The biomarkers that increased were micronuclei in blood lymphocytes, which have been associated with cancer risk in healthy subjects, and urine mutagenicity, which is a biomarker of exposure to genotoxic agents.

Detailed measurements were also made of the most common exhaled DBPs (trihalomethanes) in air around the pool and in exhaled breath of the swimmers before and after swimming. Researchers measured several biomarkers of respiratory effects after swimming and found changes in only one—a slight increase in serum CC16, which suggests an increase in lung epithelium permeability. This result was explained by the effects of exercise itself as well as exposure to DBPs. Further research is needed to sort out the clinical relevance of this acute change, the researchers stated.

In addition, the authors identified more than 100 DBPs in the pool waters, some never reported previously in swimming pool water and/or chlorinated drinking water. In vitro assays showed that the swimming pool water was mutagenic at levels similar to that of drinking water but was more cytotoxic (can kill cells at a lower concentration) than drinking water.