Chemicals in indoor swimming pools may increase cancer risk

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.

The human exposures studied were short-term, and further investigations of genotoxic and respiratory effects of longer-term exposures are needed, the authors stated. Also noted was a need for further research on an array of swimming pools under various conditions of maintenance and use, as well as more complete evaluations of the uptake and potential effects of the wide range of compounds present in pool water. These are preliminary results that should be confirmed in studies with larger sample sizes.

This work was supported by the Spanish organizations Plan Nacional and Fondo de Investigación Sanitaria, Instituto de Salud Carlos III; and also by the U.S. Environmental Protection Agency.