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Canadian
Water Quality Association E- Bulletin
Date: 19th January
2007
Bulletin #: 07011901
To: All Members/Prospects
Subject: Chlorinated
water exposure may boost cancer risk
SOURCE: American
Journal of Epidemiology, January 2007.
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 and its subspecies, used to disinfect water can produce by-products
that have been tied to increased cancer risk, Villanueva and her team
point out. In the past the ingestion pathway has been proven, but this
study shows that the transdermal pathway for chlorine by-products is just
as important on the topic. The most prevalent chlorination by-products,
chemicals called trihalomethanes (THM), can be absorbed into the body
through the skin (transdermal absorption) 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 greater than 49 micrograms
per litre had double the bladder cancer risk of those living in households
where water THM concentration was below 8 micrograms per litre, the researchers
found. Researchers noted from review of THM concentrations in municipal
water that 50 micrograms per litre is 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, the researchers noted, 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 implications in relation
to preventing exposure to these water contaminants," the researchers conclude.
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