When people bathe in swimming pools and hot tubs, interactions between the chemicals in the water and their body can lead to potential damage to their DNA, scientists have said. The disinfectants used to clean the water react with sweat and urine, releasing by-products that may be harmful to humans.

Though these chemical reactions have been well studied in the past, little research had been dedicated to the mutagenic effects of these products – that is to their capacity of altering the DNA of people and increasing the risk of genetic mutations.

This latest study, published in the American Chemical Society's journal Environmental Science & Technology investigates the mutagenicity of disinfection by-products released in swimming pools and hot tubs treated with chlorine, bromine, ozone, or ozone-chlorine.

Water samples

The scientists collected 28 water samples from public and private swimming pools and hot tubs in the US, before and after use by humans. They also checked the composition of the tap water used to fill them.

More than 100 disinfectant by-products were found in the samples and all were tested for their mutagenicity. Compared with tap water samples, pool water was on average 2.4 times more mutagenic and hot tub water 4.1 times more. Mutagenicity increased with swimming pool or hot tub use.

Why is this a problem?

The European Commission defines mutagenicity as the induction of permanent transmissible changes in the structure of the genetic material of cells or organisms. These changes do not necessarily have a negative impact but they can in some cases cause irreparable damage to the DNA and lead to cancer.

More research is needed to understand how and to what extent the disinfectant by-products in swimming pools can impact the health of people.

However, the study already emphasizes that the potential risks can already be reduced by cleaning facilities and changing water more frequently. Additionally, swimmers should be encouraged to shower before entering the pool and to refrain from urinating in it.