Jan 22, 2007

Chlorinated Water May Increase Cancer Risk

A new study shows that drinking, bathing or swimming in chlorinated water may increase the risk of bladder cancer.

According to the American Journal of Epidemiology, these are the first findings that suggest chlorine can be harmful when inhaled, absorbed through the skin, or ingested. Dr. Christina M. Villanueva of the Municipal Institute of Medical Research in Barcelona led the study with colleagues.

Villanueva and her team discovered that chemicals used to disinfect water, mainly chlorine, produce by-products that increase the risk of cancer. The most prevalent by-product is known as trihalomethanes (THM).

To investigate lifetime THM exposure and its relation to bladder cancer, 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 through drinking water, swimming pools, bathing and showering. The researchers also analyzed the average water THM levels in the 123 municipalities included in the study.

The study found that people living in a household with an average water THM level of more than 49 micrograms per liter had double the bladder cancer risk of those living in households where the THM concentration in water was below 8 micrograms per liter. Researchers also noted that THM levels of about 50 micrograms per liter are common in industrialized societies.

According to the American Journal of Epidemiology, 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%. People who took longer showers or baths and lived in municipalities with higher THM levels also increased their risk of developing cancer.

Villanueva and her team noted that when THM is absorbed through the skin or lungs, it could have a more powerful carcinogenic effect since it does not undergo detoxification via the liver.