Three new “ahead of print” articles in Environmental Health Perspectives look at potential health effects from swimming in pools with chlorinated water. One study (by Richardson et al.) identified the disinfection by-products present in chlorinated and brominated swimming pool water, and related them to mutagenicity. A pair of related studies looked at biomarkers of genotoxicity/carcinogenicity (Kogevinas et al.) and respiratory effects (Font-Ribera et al.). Among other conclusions, the authors of the studies stated that swimming pool water is mutagenic and genotoxic. So, what do these studies tell us, and do they mean we should be worried about swimming in chlorinated water?
I’ll start with the Richardson et al. study looking at the by-products present in swimming pools. They collected water samples from two public swimming pools in Barcelona, Spain; one of the pools used chlorine (sodium hypochlorite) and the other used bromine (1-bromo-3-chloro-5,5-dimethyl-2,4-imidazolidinedione) for disinfection. They identified more than 100 by-products, including haloacids, halomethanes, haloacetonitriles, haloaldehydes, haloketones, halonitromethanes, haloamides, haloalcohols, and halophenols – essentially a variety of different organic molecules with chlorine or bromine attached. They also collected some indoor air samples, and found a respiratory toxin called trichloramine in air, with (as would be expected) a much higher concentration at the chlorine-using pool. Finally, they did some mutagenicity tests, which basically involve exposing bacteria to the water and seeing if it causes genetic mutations; they found that the swimming pool water was mutagenic, which indicates it has the potential to cause cancer.
Of course, the presence of a long list of chemicals does not mean that these chemicals are causing significant harm to people in the pools. Even the mutagenicity does not necessarily mean there is a health risk; the authors note that the level of mutagenicity was actually similar to drinking water. That’s where the other studies come in.
The Kogevinas et al. study involved collecting blood, urine and exhaled air samples from 49 non-smoking adults before and after a 40-minute swim in an indoor chlorinated pool. They measured concentrations of trihalomethanes (molecules with a carbon atom, a hydrogen atom, and 3 chlorine or bromine atoms) in exhaled air and used this to represent exposure to these chemicals. They ran several tests looking for damage to DNA on the blood samples. They also looked for DNA damage in urothelial cells (cells that line the urinary tract) in urine samples collected 2 weeks after swimming, and conducted mutagenicity tests on urine samples collected just before and 90 to 120 minutes after swimming. They found that several markers of DNA damage were increased in blood and urine, but that the increases were not statistically significant; there was a statistically significant decrease in DNA damage in blood lymphocytes after swimming. The mutagenicity of urine was also increased, but again this was not statistically significant. Further analysis related the effects primarily to brominated trihalomethanes. The authors concluded that swimming in chlorinated water could have genotoxic effects.
The Font-Ribera et al study involved 50 adults, with several markers of respiratory effects measured before and after a 40-minutes swim. They found a small but statistically significant increase in the permeability of the lung epithelium; no other significant changes in lung function were observed. They concluded that the epithelial permeability change was related to both exercise and disinfectant by-products, and that further research was needed to determine if there was any clinical relevance to this result or any potential for long-term impacts.
Personally I don’t find the results of these studies to be very convincing, though there’s maybe enough there to warrant further study. The increase in DNA damage measured in blood and urine samples was marginal and non-significant. The increase in mutagenicity of urine was larger (though still non-significant), but that may represent chemicals being excreted in urine rather than absorbed by the body, and does not mean that there would be any potential for health effects.
However, these results were based on a single swimming event. Given that several mutagenic chemicals have been measured in pool water, and that the pool water itself has been shown to have at least some mutagenicity, the potential for long-term effects after repeated exposures can’t be excluded. These effects would be very difficult to measure; using this same experimental design for repeated exposures over a long period of time would be very costly and time-consuming. It would also be fairly onerous for the subjects, making it very difficult to get volunteers. An alternative approach would be to evaluate people who swim frequently in chlorinated pools against those that don’t, and see if there are increases in any cancers associated with trihalomethanes or other disinfection by-products. Another approach might be to look for DNA damage in people who swim a lot versus those who don’t. Either of these approaches requires accounting for other factors that could cause cancer or DNA damage.
Regardless of whether the pool water shows any mutagenicity, it’s also important to consider the effects of microbial organisms that would be present in the absence of disinfectants; whatever slight potential there would be for health effects from the disinfectants would be more than offset by the potential for diseases and other effects from these organisms. Furthermore, there are significant health benefits to swimming, which the authors acknowledge.
Overall, these results do not support avoiding swimming in chlorinated pools. While further studies are needed, and continually working to develop “safer” disinfectants is worthwhile, any health effects from occasional swimming in chlorinated pools appear to be minimal and likely offset by the benefits. Health effects from extensive exposure to pool disinfectants (e.g. competitive swimmers or lifeguards) might be worth some follow-up though.
Kogevinas, M., Villanueva, C., Font-Ribera, L., Liviac, D., Bustamante, M., Espinoza, F., Nieuwenhuijsen, M., Espinosa, A., Fernandez, P., DeMarini, D., Grimalt, J., Grummt, T., & Marcos, R. (2010). Genotoxic Effects in Swimmers Exposed to Disinfection By-products in Indoor Swimming Pools Environmental Health Perspectives DOI: 10.1289/ehp.1001959
Font-Ribera, L., Kogevinas, M., Zock, J., Gómez, F., Barreiro, E., Nieuwenhuijsen, M., Fernandez, P., Lourencetti, C., Pérez-Olabarría, M., Bustamante, M., Marcos, R., Grimalt, J., & Villanueva, C. (2010). Short-Term Changes in Respiratory Biomarkers after Swimming in a Chlorinated Pool Environmental Health Perspectives DOI: 10.1289/ehp.1001961
Richardson, S., DeMarini, D., Kogevinas, M., Fernandez, P., Marco, E., Lourencetti, C., Ballesté, C., Heederik, D., Meliefste, K., McKague, A., Marcos, R., Font-Ribera, L., Grimalt, J., & Villanueva, C. (2010). What’s in the Pool? A Comprehensive Identification of Disinfection By-Products and Assessment of Mutagenicity of Chlorinated and Brominated Swimming Pool Water Environmental Health Perspectives DOI: 10.1289/ehp.1001965