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Chlorine Pollutants High in DC Tap Water

Chlorine Pollutants High in DC Tap Water

Tests Find Hazardous Chlorination Byproducts
Thursday, July 19, 2007

In spite of the best efforts of the Washington Aqueduct to provide quality drinking water to the District of Columbia, tap water tests from May, 2007 revealed toxic by-products of the chemicals used to purify Potomac River water, at levels above annual federal health limits. These results illustrate the tremendous difficulties that water utilities face when trying to provide tap water that is free of potentially deadly bacteria and pathogens, yet not contaminated with toxic by-products of the chemicals used to kill these same microbes. This problem is particularly acute when utilities draw water from poorly protected water sources like the Potomac River. As recently reported in the Washington Post, the Potomac may not even be suitable for swimming; turning this water into safe drinking water is a serious public health challenge.

Based on these test results the Environmental Working Group (EWG) is recommending carbon filtration for all 1.1 million consumers of tap water from the Washington Aqueduct in Washington DC and northern Virginia. Carbon filtration of tap water will dramatically lower levels of toxic disinfection byproducts; it is also 10 to 20 times less expensive than bottled water, and does not produce the waste and pollution associated with the packaging and transport of bottled water.

Source: EPA. 2004. Estimated Per Capita Water Ingestion and Body Weight in the United States–An Update. October, 2004. EPA-822-R-00-001
American Water Works Association. 2007. Questions and answers about your water. http://www.drinktap.org


EWG collected tap water samples in May, 2007, from 18 locations across Washington D.C., including the U.S. Capitol, EPA headquarters, parks, schools, and residences of pregnant women and other groups susceptible to health harms from exposures to disinfection byproducts. We commissioned tests from an accredited lab for two classes of disinfection byproducts — trihalomethanes, or THMs, and haloacetic acids, or HAAs. The laboratory analyses found:

  • More than 40 percent of the tap water samples contained chemical byproducts of water treatment above annual federal health limits. The group of contaminants known as haloacetic acids (HAAs) were found at their highest levels since 2001, the last year before the Washington Aqueduct modified its treatment techniques in an attempt to reduce levels of trihalomethanes, related byproducts of tap water chlorination.

  • HAAs were highest at the Martin Luther King Jr. Memorial Library, an elementary school in the district's Northwest quadrant, and the home of a woman who was 9 months pregnant.

  • Almost 90 percent of the samples had THMs at levels associated in epidemiological studies with low birth weight and serious birth defects in infants. TTHM levels were highest at the National Mall, the same elementary school, and the home of a 2-year-old infant.

Benefits of water disinfection come at a price. Chlorination of tap water is one of the greatest public health improvements of the last 100 years, vastly reducing deaths from water-borne diseases. But chlorination produces disinfection byproducts (DBPs) like THMs and HAAs that are themselves potentially harmful.

Because of the recognized health risks of the byproducts, in particular THMs, many utilities, including the Washington Aqueduct, have switched from treatment using so-called free chlorine to compounds called chloramines, which tend to produce lower levels of the handful of disinfection byproducts for which EPA has set legal limits, including THMs and HAAs. But because chloramines are not as effective at disinfection as free chlorine, the Aqueduct, like other utilities that use chloramine, periodically switches back to chlorine. This so-called "chlorine burn" removes sludge and sediment from the pipes, but also temporarily raises the level of disinfection byproducts. This year the utility's chlorine burn was conducted between April 7 and May 7.

While chloramines appear to help lower THM levels, they also produce an entirely different set of byproducts, including the HAAs and other byproducts, for which we have less information about long-term human health effects. A recent EPA study found that water treated with chloramines had the highest levels of iodacetic acid, a byproduct that in animal studies has been found toxic to cells and DNA. In general, however, the long term public health consequences of exposure to chloramines and chloramine byproducts is poorly understood.

What is known about HAAs, however, raises concerns. EPA classifies HAAs as possible human carcinogens, and peer-reviewed studies have identified adverse reproductive and developmental effects, and the ability to damage DNA. The state of Oregon has warned that long term exposure to HAAs at levels equal to those found in DC tap water could cause injury to the brain, nervous system, the eyes, and the reproductive system.

Disinfection byproducts are a bigger problem than these tests show. EPA scientists have identified a total of 600 disinfection byproducts in tap water but EPA has set legal limits in tap water for only 11. And these legal limits, such as those for HAAs and THMs, are established as a balance between health, treatment cost and feasibility.

This is a critical point for most consumers: The legal limit, or MCL, is not intended to be a true safe exposure level. For almost all contaminants in tap water, including those identified in this analysis, the MCL allows far more contamination than the truly safe level, or what EPA refers to as the public health goal.

In 1999, EPA strengthened the legal limit for THMs in tap water and set a first-time standard for HAAs due to these chemicals' potential links to cancer, birth defects, and other adverse health outcomes. To comply with these tighter standards, DC Water and Sewer Authority began using chloramine as a disinfectant because of its known capacity to lower levels of the regulated byproducts. This switch, which the utilities' water quality test reports show did indeed lower THM and HAA levels, also spurred some significant negative consequences: it likely created a complex, new suite of disinfection byproducts that are neither defined nor studied; and it contributed to elevated lead levels in tap water across the District, a problem that prompted additional manipulations in water chemistry by the utility that are still under study.

Protecting tap water at the source. If the Potomac River were less polluted as it flowed into the utility's intake pipe, less chlorine and chloramines would be needed, and levels of disinfection byproducts would be lower as a result. But government policies, in general, do little to advance this goal. Instead, taxpayers pour billions of dollars into federal programs like farm subsidy payments that actually exacerbate pollution problems, and then pile on additional billions for water treatment facilities that try to clean it up. Very little is spent on more effective and efficient measures to protect rivers and streams from pollution in the first place.

Agriculture is the top source of pollution in the Potomac River watershed, but efforts to control agricultural pollution remain largely unfunded. From 1999 through 2005, taxpayers spent five times more money subsidizing farmers in the Potomac River basin as they did on programs to control agricultural pollution - $287 million on subsidies compared to $57 million on conservation and pollution control. Many farmers received no money at all. In an era of tight federal budgets, political pressure to fully fund farmer subsidies almost always trumps whatever concerns might exist about controlling agricultural pollution. In 2004 and 2005, 4,155 farmers in the Potomac watershed were denied funding for conservation and water quality projects due to lack of available funds.

Recommendations. The findings presented here make a strong case for keeping sources of tap water clean before they require expensive and potentially harmful treatment with chlorine or chloramines. But until such measures are in place and contaminant levels are dramatically reduced from current levels, EWG recommends that anyone drinking DC tap water use some form of carbon filtration designed to reduce levels of THM and HAAs. In addition:

  • Farm polices must be reformed to fully fund programs specifically designed to keep agricultural pollutants of all kinds – manure, fertilizer, pesticides and soil – out of tap water supplies.
  • Safety standards for chlorination and chloramine byproducts must be reevaluated in light of research indicating that current regulations are not stringent enough.

  • Greater efforts are put in place to educate the public about the health risks of chlorine and chloramine byproducts and to warn all Aqueduct water consumers of the annual chlorine burn.
Key Issues, Toxics, Health Concerns: