Chlorination raises cancer risk.

Adding chlorine to drinking and bathing water reduces the risk of pathogen-caused diseases, like typhoid fever, dysentery, and cholera; but it also produces disinfection byproducts, some of which are carcinogenic. Chlorine reacts with organic and inorganic matter in waterways to produce trihalomethanes (THMs) and haloacetic acids (HAA5). THMs include chloroform, bromodichloromethane, dibro-mochloromethane, and bromoform. HAA5 include monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. The Environmental Protection Agency (EPA) regulates the amount of four disinfection byproducts--THMs, HAA5, bromate, and chlorite--found in drinking water.

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In epidemiologic research, chlorinated water has been associated with a "higher total risk of combined cancers" and specifically with an increased risk of gastrointestinal cancer, rectal cancer, bladder cancer, and melanoma in humans. "Long-term risks of consuming chlorinated water include excessive free radical formation, which accelerates aging, increases vulnerability to genetic mutation and cancer development, hinders cholesterol metabolism, and promotes hardening of arteries," writes Joseph G. Hattersley in a 2000 article for the Journal of Orthomolecular Medicine 

Bathing or swimming in water disinfected with sodium hypochlorite can be even more damaging than drinking it. During warm showers or baths, the skin absorbs THMs "like a sponge," says Hattersley. In addition, chlorinated water releases chloroform into the air. Hattersley suggests opening an outdoor window in the shower room to release the vapors and installing a water filter on the shower head to remove chlorine from bathing water. Swimming pools are more problematic, since sodium hypochlorite or calcium hypochlorite is often added to the already chlorinated public water supply. The chlorine reacts with organic matter--skin cells, sweat, mucus, urine, blood, and feces--from swimmers to produce more THMs.

"Canadian researchers found that after an hour of swimming in a chlorinated pool, chloroform concentrations in the swimmers' blood ranged from 100 to 1,093 ppb," says Hattersley. "Chloroform risk can be 70 to 240 times higher in the air over indoor pools than over outdoor pools. If the pool smells very much of chlorine, don't go near it."

Since the discovery of disinfection byproducts in 1974, scientists have sought ways to lessen the cancer risks. One way is to use something other than free chlorine, the most common disinfectant used by US water-treatment plants. A second tactic is to filter out as much organic matter as possible before adding the disinfectant. Some US cities and many European cities use granulated activated carbon (GAC) filtering systems to remove organic matter. In Europe, ozonation is a popular alternative to chlorination. Ozonation (passing ozone through water) kills pathogens in the water supply without producing a measurable amount of disinfection byproducts, but this treatment does not have a residual effect. Since ozonated water can become recontaminated in the delivery system to homes, a small amount of chlorine, usually chlorine dioxide, is added. Chlorine dioxide produces fewer THMs than free chlorine, but it also produces chlorite, one of the EPA's regulated byproducts.

Chloramines, a chlorine-based disinfectant made from chlorine and ammonia, does not product THMs or HAA5; but it is not as effective as chlorine. Chloramines have also been associated with red blood cell damage. No known disinfection system is risk free, but in this case the benefits outweigh the risks.

Environmental Protection Agency. Disinfection byproducts: a reference resource. www.epa.gov/enviro/html/icr/gloss_dbp.html. Accessed June 7, 2009.

Environmental Protection Agency. The effectiveness of disinfectant residuals in the distribution system. www.epa.gov/ogwdw/disinfection/tcr/pdfs/issuepaper_effectiveness.pdf. Accessed June 7, 2009.

Hattersley JG. The negative health effects of chlorine. J Orthomol Med. 2000; 15(2). Available at: www.orthomolecular.org/librarY/jom/2000/articles/2000-v15n02-p089.shtml. Accessed January 28, 2009.

Tibbetts J. What's in the water: the disinfectant dilemma. Environl Health Perspect. January 1995;103(1). Available at; www.ehponline.org/docs/1995/103-1/focus1.html. Accessed May 27, 2009.

Wikipedia [Internet]. Water purification. http://en.wikipedia.org/wiki/Water_purification. Accessed June 1, 2009.

briefed by Jule Klotter [e-mail]