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 these chemicals
can be harmful when they are inhaled or absorbed through the
skin, as well as when they are ingested, Dr. Cristina M. Villanueva
of the Municipal Institute of Medical Research in Barcelona,
and colleagues note.
Chemicals, most commonly chlorine, used to disinfect water
can produce by-products that have been tied to increased cancer
risk, Villanueva and her team point out. The most prevalent
chlorination by-products, chemicals called trihalomethanes
(THM), can be absorbed into the body through the skin or by
inhalation, they add.
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 in
the 123 municipalities included in the study.
People living in 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,
the researchers found. THM levels of about 50 micrograms per
liter are common in industrialized societies, they note.
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, Villanueva
and her team note, it may have a more powerful carcinogenic
effect because it does not undergo detoxification via the
"If confirmed elsewhere, this observation has significant
public health implications in relation to preventing exposure
to these water contaminants," the researchers conclude.
SOURCE: American Journal of Epidemiology, January 2007.