Chlorine in the water supply could be a cause of colon cancer, researchers have discovered.
The risk increases as the chlorine content rises; at the highest levels the chance of developing colon cancer goes up by over a half.
Researchers were alerted to the possible dangers of chlorine when experiments on animals discovered that chloroform, a by product of chlorine, is carcinogenic.
A team from the University of Minnesota questioned 28,237 postmenopausal women in Iowa about their drinking water source, and evaluated chloroform exposure from water surveys.
They found that women living in areas which were supplied with water containing higher concentrations of chlorine were at "significantly increased risk for colon cancer and total combined cancer" (Am J Public Health, 1997; 87: 1168-76).