Cancer Risk From Chlorinated Water

June 18, 1997

NEW YORK (Reuters) - A substance created by a chemical reaction in chlorinated drinking water caused several types of tumors in rats, a new study shows.

The rats were given the substance, known as MX (officially called 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone), in their drinking water for up to 104 weeks. The researchers from the National Public Health Institute in Finland then killed the animals to study their bodies. They found large amounts of lesions on the rats' livers, thyroid glands and adrenal glands, as well as high levels of lymphomas, leukemias, and mammary gland tumors.

Dr. Hannu Komulainen and colleagues, who reported their findings in the June 18 issue of the Journal of the National Cancer Institute, caution that the reaction of the rats to MX is not necessarily how humans react to the substance. But they say "MX should be studied as a candidate risk factor in the possible association between consumption of chlorinated drinking water and cancer in humans."

Chlorine has been added to drinking water since the turn of the century in the U.S., as a way of preventing water-borne diseases. Chlorine prevents bacterial growth in water and helps prevent transmission of diseases such as typhoid fever, cholera, and dysentery.

In a related editorial in the same journal, Ronald L. Melnick of the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, and colleagues there and at the U.S. Environmental Protection Agency in Washington, D.C., say the study raises important concerns, but they caution against making rash decisions.

"Stopping water chlorination in the absence of an equally effective disinfection program is not a sensible choice," they write. "The potential risk from MX in drinking water... must be weighed against the benefits of chlorination as a proven disease prevention strategy."

Melnick and colleagues note that other substances added to drinking water for disease prevention have also been shown to cause cancer, but that the Environmental Protection Agency regulates the allowable levels of those substances. They say further studies about the effects of MX are needed.

SOURCE: Journal of the National Cancer Institute (1997;89:832-833, 848-856)

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