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PUBLIC HEALTH Powerful Mutagen Found in Mass. Water Researchers have discovered small amounts of a powerful genetic mutation-causing agent in 36 Massachusetts towns served by 23 different public water systems. Known as mutagen X (MX), the compound is one of the most potent known mutagens in a toxic soup of disinfection by-products. Senior author Douglas Dockery (right) and co-author Larisa Altshul helped document the presence of a potent chlorine by-product in samples from three dozen towns in Massachusetts and evaluated the role of water treatment on mutagenic activity and disinfection by-products. Photo by Jeff Cleary The new report provides the first broad evidence that mutagen X, first discovered in Finland's drinking water more than ten years ago, also lurks in chlorinated U.S. drinking water. The findings may increase support for pending national regulations to tighten drinking water standards and refuel local efforts to identify safer ways to disinfect tap water. "We found a tremendous range of mutagenicity in the drinking water samples," said Joel Schwartz, HSPH associate professor of environmental epidemiology and a co-author of the study. "Numbers in some towns are higher than numbers in other towns, which suggests big differences among communities in how much risk they're seeing. The wide differences suggest there's something we can do about it." Low-profile Poison Mutagen X [also known as 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone] is not monitored or regulated in the U.S. water supply. Nine years ago, the World Health Organization recommended that it be limited in drinking water. The U.S. Environmental Protection Agency did lower the maximum contaminant level for two other more common and less mutagenic types of disinfection by-products for large public water systems, effective December 2002--and those that serve fewer than 10,000 people have another year to comply. But even the tighter standards may not lower the mutagenicity of the water, the paper suggests. "This study tells me, one, that there are higher levels of mutagen X in the water than previous estimates I've seen, and, two, that there are ways to reduce the level of mutagen X in the water through simple treatment options," said Erik Olson, senior attorney for the Natural Resources Defense Council. In Massachusetts, the lowest levels of mutagen X and overall mutagenicity were found in systems that used filtration to remove organic matter or systems treated primarily by chloramination (adding ammonia to freshly chlorinated water to shut down the chemical reactions that create disinfection by-products). In other results, the less acidic the water, the higher the levels of mutagen X. That is consistent with other studies correlating typical drinking water pH levels to other types of harmful by-products. Also, the mutagenicity levels were higher in the spring compared to the fall. The findings are published in the February 2002 issue of the journal Environmental Health Perspectives. The study is part of the doctoral thesis of Michael Wright, the first author and now an Oak Ridge Institute for Science and Education postdoctoral fellow at the EPA in Cincinnati. The Chlorine Downside In the last 25 years, studies have identified several kinds of disinfection by-products of chlorine. The most common are trihalomethanes (THM), which include chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Another family is the haloacetic acids, which include mono-, di-, and trichloroacetic acids and mono- and dibromoacetic acids. Both families have been linked to cancer, miscarriages, stillbirths, and birth defects. Mutagen X is found at much lower levels, but its cancer potency is estimated to be 170 times greater than chloroform and 17 times greater than bromodichloromethane. Scientists suspect there are many more harmful by-products. In this study, researchers also tested the general mutagenicity of the water. Mutagen X levels accounted for about one half of the mutagenicity, evaluated via the Ames test using salmonella bacteria with a single mutation that prevents them from dividing unless a mutation occurs. Imperfect public water systems are not news. In population and toxicological studies, disinfection by-products have been correlated with cancer as well as liver and kidney disease. More recent studies suggest by-products and other impurities also may cause some miscarriages and birth defects. Chlorine seems to work most of its mutagenic mischief at the treatment plant when it bumps into organic compounds dissolved in the water from leaves floating on the surface and dirt washing into a reservoir from the rain. Surface water systems, the kind most likely to have more organic matter, serve about 61 percent of the U.S. population and about 74 percent of the state's water drinkers. Most groundwater systems and private wells are less likely to have organic matter. One for the Road No matter what kind of disinfection is used at the treatment plant, water needs a little chlorine for its journey down miles of pipe to inhibit bacteria and parasites. Along the way, some by-products accumulate as the chlorine continues to react with organic matter, and others may degrade. Five years ago, Ronald Melnick, a staff scientist at the National Institute of Environmental Health Sciences, figured that the extra risk of cancer to people drinking water with mutagen X was about two extra cases per million. He reported the back-of-the-envelope calculation in an editorial accompanying findings of increased thyroid gland, liver, and other tumors in rats who had been fed mutagen X in their drinking water for two years. Epidemiological studies suggest that may be an underestimate, says Robert Morris, an environmental epidemiologist at Tufts University who has published a meta-analysis of cancer risk from disinfection by-products. "The most remarkable thing about MX is that a chemical that's present in much lower quantities can account for such a large portion of mutagenicity," Morris said. "People take comfort in the fact that some chlorination by-products found in higher concentrations appear to be weak carcinogens in animal studies, but if other chemicals that are present in lower concentrations can be so potent, that's a cause for concern." It is clear that chlorine can take a lot of credit for improving public health. Typhoid fever and cholera were nearly eliminated in this country when chlorination was introduced more than 100 years ago. Public health experts agree: chlorinated water is one of the most important public health accomplishments of the 20th century. "Safe drinking water is not a trade-off between producing dangerous chemicals or allowing infectious organisms," said Schwartz. "There are things we can do to help with both problems. But one of the questions we had to answer first was, how much stuff is out there? This study suggests we need to think about setting a standard for mutagen X." --Carol Cruzan Morton