Chlorinated Water in Ottawa May Raise Bladder Cancer Risk

Drinking, bathing or swimming in chlorinated water in Ottawa may increase the risk of bladder cancer.

The findings are the first to suggest that these chemicals can be harmful when they are inhaled or absorbed through the skin, as well as when they are ingested.

Chemicals, most commonly chlorine, used to disinfect water in your house or pool can produce by-products that have been tied to increased cancer risk. The most prevalent chlorination by-products, chemicals called trihalomethanes (THM), can be absorbed into the body through the skin or by inhalation.

To investigate lifetime THM exposure and bladder cancer risk, the researchers matched 1,219 men and women with bladder cancer to 1,271 control individuals who did not have the disease, surveying them about their exposure to chlorinated water via drinking water, swimming pools, showering and bathing. The researchers also analyzed the average water THM levels.

People living in Ottawa households with an average household water THM level of more than 49 micrograms per liter had double the bladder cancer risk of those living in households where water THM concentration was below 8 micrograms per liter. THM levels of about 50 micrograms per liter are common in industrialized societies.

Study participants who drank chlorinated water were at 35% greater risk of bladder cancer than those who didn't, while use of swimming pools boosted bladder cancer risk by 57%. And those who took longer showers or baths and lived in municipalities with higher THM levels were also at increased cancer risk.

When THM is absorbed through the skin or lungs, it may have a more powerful carcinogenic effect because it does not undergo detoxification via the liver.

If confirmed elsewhere, this observation has significant public health in Canada implications in relation to preventing exposure to these water contaminants.