Drinking, bathing or swimming in chlorinated water may all increase
the risk of bladder cancer, according to a study reported in the January issue of
American Journal of Epidemiology.
Chlorination is a process in which toxic chlorine is used to
Both chlorine and
certain by-products of the process are toxic.
Trihalomethanes, a major by-product, has already known to raise cancer
The study led by Dr. Cristina M. Villanueva of the Municipal
Institute of Medical Research in
and colleagues was meant to investigate a possible association between bladder
cancer and exposure to THM in chlorinated water.
For the study, researchers enrolled 1,219 men and women with
bladder cancer and 1,271 control individuals who did not have the disease.
They surveyed the participants for their
exposure to chlorinated water through drinking, swimming, showering and
bathing. They also tested THM in 123 communities involved in the study.
People exposed to household water with more than 49
micrograms per liter of THM, which is common in industrialized countries, were
at 200 percent higher risk of bladder cancer compared to those who exposed to
household water with less than 8 mcg per liter, according to the study.
Those who drank chlorinated water were 35 percent more
likely to develop bladder cancer than those who did not. Swimming in
chlorinated water was linked to a 57 percent increased risk of the
In addition, taking longer
showers or baths and living in municipalities with higher THM levels were also
at increased risk of cancer.
THM, which can be absorbed through the skin or by
inhalation, may have a powerful carcinogenic effect than others as unlike
others it does not go to the normal detoxification process in the liver,
according to the researchers.
The findings suggest for the first time that by-products induced
by chlorination can be harmful when they are ingested, inhaled or absorbed
through the skin, said Dr. Villanueva.
"If confirmed elsewhere, this observation has
significant public health implications in relation to preventing exposure to
these water contaminants," the researchers write.