Pool Water Genotoxicity Study in Perspective

A new pool water study is being misrepresented in some media reports as linking swimming in treated pools to a potential cancer risk.  This suggested link is not backed by the research, according to an evaluation by the U.K. National Health Service (NHS).

To understand the issue, we must separate facts (those items accepted by scientists as proven to be true) and hypotheses (those items suggested as possibly being true but which remain unproven by scientific investigations).

1.      FACT: In properly managed pools, chlorinated swimming pool disinfectants help destroy waterborne germs that can cause diarrhea, swimmers’ ear and skin infections.

2   HYPOTHESIS: Chemical byproducts of disinfection may affect human health.

3.      FACT: Chemical byproducts of disinfection are formed when disinfectants react with organic compounds (e.g., urine, perspiration, perfumes, cosmetics, etc.) in swimming pools. The amount of disinfection byproducts formed is directly related to the quality of pool management. For example, chloramines, which can cause eye and skin irritation, are formed when nitrogen-containing compounds in urine and perspiration, etc. combine with chlorine.

In the new study, researchers concentrated disinfection byproducts from swimming pools, exposed mammalian (hamster ovary) cells to these concentrated disinfection byproducts and measured the resultant genotoxicity (i.e. damage or mutation to DNA). The authors examined pool and spa waters derived from a common tap water source, but treated using different water disinfectants and under different chemical conditions.

The study data reported by the authors demonstrate that every variable tested (i.e. type of disinfectant, amount of light, water temperature) produced more DNA damage to hamster ovary cells than tap water (which was the source water use for the pools and spas). The authors:

  • STATE that “…disinfection of recreational pools is essential to prevent outbreaks of infectious disease.”
  • SUGGEST that “…brominating agents should be avoided…in recreational pools…” and “…combining UV treatment with chlorine may be beneficial compared to chlorine alone.”
  • The difference between what is STATED and what is SUGGESTED is the strength of the supporting scientific data.


In spite of cautions by the NHS and the study authors themselves regarding the limited meaning of these study results, some media reports have ignored these cautions and have ‘cherry-picked’ the information until all that is left is fear-mongering, a saleable commodity. These study related cautions, ignored by the media, put the results into the correct perspective and include:

1. The test (of genotoxicity) is one employed as an ‘early screen or prescreen’ because it is easy and inexpensive to perform (its advantages).  Its disadvantages are a) that its predictive validity to man (i.e. whether the results of the test have any meaning to predicting what might happen in man) is relatively unknown (this test is NOT accepted as definitive by either the FDA or EPA) and b) the test produces highly variable results in laboratories that do not routinely perform the assay (in other words, those labs that don’t normally do the test are expected to produce variable results)

2.      The materials tested (disinfection by products) were highly concentrated prior to testing. Whether the results obtained from tests using these enormous and non-natural levels of disinfection byproducts have any relationship to what might happen in a pool situation is outside the realm of current scientific knowledge.

3. The number of pools/spas evaluated in the study was very small making the data generated in this study inadequate for use in definitive human risk evaluation

4.      The NHS states: “This particular study did not directly examine [a link between chlorinated swimming pool water and a greater risk of cancer] or look at any other particular health outcomes in people…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.”

The scientific ‘bottom-line’ at this point in time is:

Medical experts agree that swimming is an excellent form of exercise for people of all ages and the World Health Organization stated that it is important to consider the benefits of aerobic exercise and the proven significantly decreased health risks for infectious disease in a properly chlorinated pool versus the hypothesized and small potential risks from chlorinated byproducts.

For more information on Healthy Pools, please see www.healthypools.org.


(Bruce Bernard, Ph., is the Associate Editor of the Journal of Toxicology and a member of the Water Quality and Health Council)