Chlorinated Water Focus of Cancer Probe

WASHINGTON — A byproduct of chlorination in drinking water has been linked to cancer in rats, prompting the government to begin an immediate study of adverse effects from water disinfectants.

A chemical byproduct called MX develops from organic compounds in chlorinated drinking water. Researchers in Finland say rats exposed to high levels of MX get a number of cancers.

“Although these findings cannot be extrapolated to humans, MX should be studied as a candidate risk factor” in the consumption of chlorinated drinking water, the researchers say in today’s Journal of the National Cancer Institute.

The National Toxicology Program, a part of the National Institutes of Health, announced that its scientists were immediately starting a two-year study on the effects of chlorination byproducts on rodents.

Among rats receiving the highest doses of MX for two years in the Finnish study, more than half developed cancer or tumors of the thyroid, compared to about 22% in a control group. The MX rats also developed cancers of the lungs, skin, breast, liver and pancreas.

The Finnish researchers used a dosage of MX that is thousands of times higher than what is in the typical U.S. water system treated with chlorine, researchers said.

Chlorination controls many waterborne diseases, including typhoid fever, cholera and dysentery.