Shower filters may be critical THM defense Study says chlorination byproducts are absorbed at high rates in shower From the July 2002 edition of Water Technology magazine. Some consumers who are worried about trihalomethanes (THMs), byproducts of chlorination that have been associated with health risks, have typically felt that tap-water treatment alone was a full defense. However, a new study shows that consumers may be more exposed to THMs when they take showers, as opposed to when they drink water. Researchers at the University of North Carolina (UNC) at Chapel Hill's School of Public Health say THMs can sometimes get into the bloodstream via a shower at levels four times greater than THM levels in tap water. High THM concentrations have been linked to cancer, miscarriages and other reproductive problems after long-term exposure. The study The study — conducted over four weeks in 1999 on 50 women in Cobb County, GA, and Corpus Christi, TX — was done to evaluate whether health workers could use THM levels in drinking water to predict concentrations in people's blood. THM concentrations in blood were measured before and after showers. Researchers found that after subjects took showers, the THM levels in their bloodstreams were actually four times higher than the THM levels of the water coming out of their taps. The research showed that THMs were getting into blood as a result of water use, but it could not address whether concentrations were harmful or if they were linked to any health problem, according to Amy M. Miles, a co-author of the report about the study. Research support came from the American Water Works Research Foundation, Denver; the Centers for Diseases Control and Prevention, Atlanta; and the US Environmental Protection Agency (EPA). The groups will perform a follow-up study that will include additional variables, such as having each subject shower for a specified amount of time, and showering with the bathroom door closed so no THMs can escape the area, according to Miles.