Risk of pool water 'unclear'

Behind the Headlines

Friday July 23 2010

It is difficult to judge whether pool water poses a health risk

A study suggests that “swimming pools can give you cancer, because disinfectants in the water react with sunscreen, sweat, and skin to form a toxic cocktail of chemicals”, said The Daily Telegraph.

This study examined the effects of water from seven different swimming pools on the DNA of cells from hamsters. It found that pool water had more DNA-damaging potential than tap water and that the effects differed according to the chemicals in the water and whether the pool was indoor or outdoor. The researchers say the results suggest that brominating agents may be the most toxic, and that combining chlorine with ultraviolet treatment may be beneficial.

Using this study alone, it is difficult to judge whether pool water poses a health risk. This research was in animal cells and it is uncertain how this applies to humans. Other studies have looked at associations between pool water and bladder cancer, but these are not covered here. In addition, relatively few pools were sampled, and others may have different results. It is also unclear how commonly the most genotoxic of the disinfectants (BCDMH) is used in either the UK or Spain.

 

Where did the story come from?

The study was carried out by researchers from Universitat Autonoma de Barcelona in Spain, and the University of Illinois at Urbana-Champaign in the US. The work was funded by the National Science Foundation. The study was published in the peer-reviewed journal Environmental Science and Technology.

What kind of research was this?

This laboratory research investigated whether swimming pool water can damage mammal DNA. The study follows recent research that has reportedly demonstrated an association between the disinfectants used in recreational pools and adverse health outcomes, principally respiratory problems such as asthma. Other studies have also noted a link between chlorinated water and the risk of bladder cancer. The problems are believed to be a result of disinfection by-products (DBPs) reacting with iodide and bromide in the water, and other organic matter, such as sweat, hair and skin.

The researchers aimed to compare the genotoxicity (ability to cause DNA damage) of recreational swimming pool water and pure tap water derived from the same water source. The swimming pool water had been treated with different disinfectants under different conditions, for example, different temperature and level of exposure.

 

What did the research involve?

The research involved samples taken from seven public swimming pools, and a sample of pure tap water, which came from the same water source supplying each of the pools. The pools featured in the study included indoor and outdoor, and warm- and cold-water pools. The pools used different chemical mixtures for disinfection. The researchers collected 8-10L samples of water from each and recorded their temperatures. In the laboratory special analysers were used to measure total residual chlorine and total organic carbon (for example, traces of skin).

A chemical reagent (MtBE) was used to extract the DBPs to assess the genotoxicity of each water sample. Nine, five microlitre samples were extracted from each pool sample, each with a different concentration of DBPs. To examine the effect of the DBPs on mammal DNA, the researchers mixed the samples with ovarian cells from a hamster.

The damage caused to the cells by the DBPs was measured using a genetic assay called single cell gel electrophoresis (SCGE). This technique measures the level of DNA damage induced in the cell nucleus, and is reported to be a good measure of carcinogenic potential. In addition to the nine concentrations of each of the seven swimming pool waters, control water samples and the source tap water were also tested.

 

What were the basic results?

Analysis showed the different chemical samples had varied effects on genotoxicity. In general, all of the swimming pool water samples were more genotoxic than the source tap water. The most toxic sample was from an indoor pool that used bromochlorodimethylhydantoin (BCDMH) as a disinfectant, which has chloride and bromide by-products. Chlorine was also more toxic than chlorine in combination with UV treatment.

A particular pool that was covered by a retractable roof in cold weather and open to the air in hot weather was found to have reduced genotoxicity when open to the sun.

The total chlorine residue in tap water was comparable to three of the pool samples. However, the researchers say that the duration for which the disinfectant and water were in contact would be much less than the several months’ duration that could be expected in swimming pools.

 

How did the researchers interpret the results?

The researchers conclude that all the included disinfected recreational pool water samples were more genotoxic than the source tap water.

 

Conclusion

The researchers say that this is one of the first studies that has directly examined the effects of different recreational swimming pool waters on mammalian cells and compared this with the source tap water supplying each of the pools.

The pool waters were found to have more potential to damage DNA than tap water. The chemicals in the pool water and the type of pool, for example indoor or outdoor, also had different effects. The researchers say the results suggest that brominating agents may be the most toxic, and combining chorine with ultraviolet treatment may be beneficial. However, it is not clear how common the use of brominating agents is, and only one out of the eight pools tested here used the brominating disinfectant that was associated with the highest levels of genotoxicity.

Although The Daily Telegraph reports a link between chlorinated swimming pool water and a greater risk of cancer (notably bladder cancer), this particular study did not directly examine this or look at any other particular health outcomes in people. As such, it is difficult to gauge from this study the actual effects on human health. Other research, not examined here, may be able to shed further light on this.

Only a small extraction from each of the water samples was tested on the mammalian cells. To increase the chances that the samples were representative of the range of chemicals that a bather would typically be exposed to in the pool, the researchers concocted different concentrations of DBP-containing water. However, it is uncertain whether the concentrated DBPs contained within these small samples would be directly comparable to the more dilute exposure that may be expected in the swimming pool.

As the researchers say, future research is needed to examine the genotoxicity of swimming pool water and its relationship with pool disinfectants, the environment and other particulates that are thrown into the mix, such as sun lotions and urine.

Using this study alone, it is difficult to judge whether pool water poses a health risk. This research was in animal cells and it is uncertain how this applies to humans. Other studies have looked at associations between pool water and bladder cancer, but these are not covered here. In addition, relatively few pools were sampled, and others may have different results. It is also unclear how commonly the most genotoxic of the disinfectants (BCDMH) is used in either the UK or Spain.

The researchers advise that a combination of chlorination and UV treatment to clean pools may be the most beneficial. They also suggest that the effects of human behaviour, such as showering before and after entering the pool, be examined further.

Links to the headlines

Swimming pool disinfectants linked to cancer. The Daily Telegraph, July 23 2010

Links to the science

Liviac D, Wagner ED, Mitch WA, et al. Genotoxicity of Water Concentrates from Recreational Pools after Various Disinfection Methods. Environmental Science and Technology 2010; Environ. Sci. Technol, 2010, 44l: 3527–3532

 

Ratings

How helpful is this page?

Average rating

Based on 2 ratings

All ratings

Add your rating

Comments

Analysis by Bazian

Edited by NHS Choices