CHAPEL HILL, NC — Trihalomethanes (THMs), byproducts from chlorination, appear to increase significantly in the bloodstream after showering, says a study by researchers at the University of North Carolina (UNC) at Chapel Hill School of Public Health.

Public health experts suspect the chemicals might boost the risk of cancer and contribute to reproductive problems such as miscarriages, a release by UNC said. The study involved 50 women living in Cobb County, GA, and Corpus Christi, TX, and indicated that showering shifted the distribution of THMs in blood toward that found in the tap water. Researchers picked those cities because water supplies in the former showed "moderately high" levels of chloroform, the most highly chlorinated THM, and, in the latter, lower total THM concentrations but a higher proportion of brominated species, which UNC said are believed to be potentially more hazardous.

The study aimed to evaluate whether health workers could use THM concentrations in drinking water to predict concentrations in people's blood.

Another finding was that the distribution of the four types of chlorinated and brominated THM species detected in the women's blood reflected the differences of type and concentration in their tap water.

Through blood sample analysis, researchers measured THMs in the blood of 25 women at each site before and soon after they showered, and compared those levels to concentrations found in tap water in their houses, the study said.

THM concentrations were around 1,000 times lower in blood than in tap water, but after the showers, median levels in blood increased by a factor of four, said Miles.

"This showed THMs were getting into blood as a result of water use. It could not address, however, whether the concentrations were harmful or were linked to any particular health problem," Miles added.

Chlorination of tap water should be studied further to prevent THMs, suggested Amy M. Miles, one of the authors of the report about the study that was published in the journal Environmental Science & Technology.

Support for the research came from the American Water Works Research Foundation, Denver; the Centers for Diseases Control and Prevention, Atlanta; and the EPA.

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