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Unanswered Questions

July 19, 2007

Chlorine Pollutants High in DC Tap Water: Unanswered Questions

This study highlights many of the unanswered questions surrounding tap water disinfection in the DC area. Ultimately, the most important questions involve the decision to alter disinfection practices at the Washington Aqueduct, switching from chlorine to chloramines. This is of primary importance due to the exposure of 1.1 million people to a number of compounds that have not been fully assessed for long-term health effects in humans. In a recent nationwide DBP study conducted by the EPA (2002) it was reported that chloraminated drinking water had the highest levels of iodinated DBPs and studies have found that iodoacetic acid, one of these iodinated DBPs, is a potent toxin to cells and cellular DNA in mammalian cells (Plewa 2004). Although switching to chloramination achieved the desired effect of reducing THM levels, the decision may have inadvertently exposed the population to additional unregulated byproducts that are more harmful in the long run.

The second issue that needs to be addressed is the necessity of the annual “chlorine burn” and the potential health effects of this continual cycling of disinfectants and the resulting mix of disinfection byproducts to which people are exposed. Since chlorination of tap water is known to produce DBPs associated with adverse health effects, the fact that this annual procedure has to be performed poses questions about the efficacy of chloramines for water disinfection and, more importantly, raises concerns about whether enough amount of research was conducted before this decision was imposed upon the public.

Third, evidence presented in several studies strongly suggests that the current EPA MCLs are not adequate to protect public health. These studies show occurrences of adverse health effects below the MCLs, especially in the case of THMs, where reproductive and developmental effects have been observed as a result of exposures as low as 40 ppb. The EPA must, therefore, revise their standards, using data based on current studies, so that their "safe dose" is in fact safe for all populations.

Finally, since the formation of DBPs result from a reaction between chlorine, whether from chlorination or chloramination, and organic matter in surface waters, cleaner source water is the critical step to reliably reduce these byproducts while at the same time guaranteeing water as free of pathogens as possible. By failing to clean up source water, the Congress, EPA, and polluters are leaving Americans with no choice but to consume high levels of DBPs.

For the majority of the water systems with elevated DBP levels, cleaner source water will require aggressive action to reduce agricultural pollution, runoff from suburban sprawl and upstream sewage discharges. The public and policy makers have been led to believe that they must accept either water polluted with pathogens or water contaminated with high levels of chlorination and chloramination byproducts. This is simply not true. Tap water in DC and, in fact, the entire United States, can meet pathogen standards and be low in DBPs as well.