Swimming in Chlorine Threat
New study shows important pool chemical added to the 'can potentially kill you' list
Drinking, bathing or swimming in chlorinated water may increase the risk of bladder cancer, a new study shows. The findings are the first to suggest that the chemicals can be harmful when they are inhaled or absorbed through the skin, as well as when they are ingested, Dr Cristina Villanueva of the Municipal Institute of Medical Research in Barcelona, and colleagues have reported.
The most prevalent chlorination byproducts, chemicals called trihalomethanes (THM), could be absorbed into the body through the skin or by inhalation, the researchers said.
To investigate lifetime THM exposure and bladder cancer risk, they matched 1,219 men and women with bladder cancer to 1,271 control individuals who did not have the disease, questioning them about their exposure to chlorinated water via drinking water, swimming pools, showering and bathing.
Study participants who drank chlorinated water were at 35% greater risk of bladder cancer than those who did not, while use of swimming pools boosted bladder cancer risk by 57%.
When THM was absorbed through the skin or lungs, it may have a more powerful carcinogenic effect because it did not undergo detoxification via the liver.
"If confirmed elsewhere, this observation has significant public health implications in relation to preventing exposure to these water contaminants," the researchers concluded.
People living in households with an average household water THM level of more than 49mg a litre had double the bladder cancer risk of those living in households where water THM concentration was below 8 mg a litre, the researchers found. THM levels of about 50mg a litre are common in industrialised societies, they note.
And those who took longer showers or baths and lived in municipalities with higher THM levels were also at increased cancer risk.
A spokesman for the National Pure Water Association said: "There is now a lot of research on chlorine in drinking water that shows we should be concerned.
"Water firms use the cheapest products possible to disinfect water, such as chlorine. Yet there are safer methods used by other countries, such as ozone gas or ultraviolet light."
In 1999, a government committee decided against removing chlorine from water, despite evidence of a slight increase in the risk of bladder cancer.
"This report hasn't changed the World Health Organisation's view that the evidence is not sufficient to support chlorine being the cause of bladder cancer," she added.
Ed Yong, Campaigns Officer at Cancer Research UK, said: "This is one of a number of studies suggesting this link, but larger studies are needed before we can say for sure if high exposure to chlorinated water can cause bladder cancer.
"In the meantime, people shouldn't be worried every time they step into the bath, shower or swimming pool. Any potential cancer risks must be weighed against the risk of the many infectious diseases caused by improperly disinfected water."
Three years ago chlorine in water was linked to a risk of birth defects or miscarriages.
The Pool Water Treatment Advisory Group, PWTAG, maintains the view that control is important but chlorine is still an important tool in swimming pool hygiene.
PWTAG says that disinfection and dosing are best controlled continuously by automatic monitors. Strict control of bathing load and regular monitoring (every 2 hours in most pools) should ensure that combined chlorine levels are minimised ideally zero, usually under 1mg/I and certainly less than half the free chlorine figure.
Free chlorine itself should be maintained as low as is compatible with good results from microbiological testing (monthly tests for all pools). Figures as low as ft51 mg/1 (for chlorine gas and hypochlorites) should be sufficient in a well designed and well run pool. This may mean keeping pH values down to about 7.2 to make the chlorine really effective and using ozone or ultraviolet as extra plantroom treatment (to enhance the water quality).