EarthTalk: Does chlorine cause cancer?

Thousands of American municipalities add chlorine to their drinking water to get rid of contaminants like nitrates, arsenic and pesticides. But this inexpensive and highly effective disinfectant has a dark side. "Chlorine, added as an inexpensive and effective drinking water disinfectant, is also a known poison to the body," says Vanessa Lausch of filter manufacturer Aquasana. "It is certainly no coincidence that chlorine gas was used with deadly effectiveness as a weapon in the First World War." The gas would severely burn the lungs and other body tissues when inhaled, and is no less powerful when ingested by mouth.

Lausch adds that researchers have now linked chlorine in drinking water to higher incidences of bladder, rectal and breast cancers. Reportedly chlorine, once in water, interacts with organic compounds to create trihalomethanes - which when ingested encourage the growth of free radicals that can destroy or damage vital cells in the body. "Because so much of the water we drink ends up in the bladder and/or rectum, ingestions of THMs in drinking water are particularly damaging to these organs," says Lausch.

The link between chlorine and bladder and rectal cancers has long been known, but only recently have researchers found a link between common chlorine disinfectant and breast cancer, which affects one out of every eight American women. A recent study conducted in Hartford, Conn., found that women with breast cancer have 50 percent to 60 percent higher levels of organochlorines (chlorine by-products) in their breast tissue than cancer-free women.

But don't think that buying bottled water is any solution. Much of the bottled water for sale in the U.S. comes from public municipal water sources that are often treated with, you guessed it, chlorine. A few cities have switched over to other means of disinfecting their water supplies. Las Vegas, for example, has followed the lead of many European and Canadian cities in switching over to harmless ozone instead of chlorine to disinfect its municipal water supply.