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Pollution + Disinfectants = Problems

Chlorine Pollutants High in DC Tap Water: Pollution + Disinfectants = Problems

July 19, 2007

There is no question that the wide scale use of chemical disinfectants in public drinking water supplies has been one of the greatest public health advances in the twentieth century. Over time, however, we have become overly reliant on chemical treament of tap water as we have simultaneously failed to protect and clean up the sources of this water. This has placed water purveyors like the Washington Aqueduct in an intractable bind where the process of purification of polluted source water exposes consumers to unnecessarily high and potentially unsafe levels of toxic chemicals formed during the treatment process.

Chlorine is very effective at killing and inactivating disease-causing microganisms in tap water. The problem is that if the water also contains "natural organic matter" the chlorine will react with the humic and fulvic acids that form as the organic matter breaks down. These reactions, in turn, produce numerous other chemical compounds that are collectively called disinfection byproducts (DBPs).

Although scientists have identified 600 different kinds of DBPs, the Environmental Protection Agency (EPA) currently only regulates just eleven (Richardson 1998, 1999a, 1999b, 2003). These regulated compounds include four trihalomethanes (chloroform, bromodichloromethane, bromoform, and dibromochloromethane), and five haloacetic acids (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid), which together are linked to a variety of adverse health effects such as cancer (DeAngelo 1997; Villanueva 2007), birth defects (Klotz, 1999; Porter 2005), and an increased incidence of miscarriage (Waller 1998).

After the EPA tightened its health standards for the trihalomethanes (THMs) and implemented health standards for the haloacetic acids (HAAs) in 1999, several utilities decided to alter their disinfection practices by switching to a new disinfectant called chloramine, which is made from chlorine and ammonia gases. Washington Aqueduct, the utility responsible for the treatment of drinking water in the District of Columbia, and Arlington County and Falls Church in Northern Virginia, made the switch to chloramines in November of 2000 (EPA 2006).

There are several reasons why utilities find chloramines appealing: they are more stable than chlorine and reduce the peak levels of at least some toxic chlorination byproducts – particularly THMs. The EPA has reported, for example, that the Washington Aqueduct's switch to chloramines resulted in an estimated average reduction in monitored DBPs of 47% (EPA 2006).

But chloramines also have significant drawbacks. They are not only toxic to kidney dialysis patients, who cannot drink chloraminated water, they are also extremely toxic to fish, which die if chloraminated water is used in their tanks. And chloramines also produce a whole new complex of contaminants that are very poorly studied.

To make matters even more complicated, many utilities that use chloramines decide to temporarily switch back to free chlorine in order to "dislodge biofilms and sediment in water mains" (EPA 2007). Since spring 2002, the Washington Aqueduct has used this practice on a more or less annual basis, implementing a month-long "chlorine flush" of its system roughly every year. This means that customers of chloramines-using utilities often end up being exposed to multiple different sets of DBPs over time, at varying levels.

It is tempting to chalk up all of the problems with DBPs to an unwanted but unavoidable consequence of the organic matter naturally found in the rivers, lakes, and reservoirs. But the underlying sources of this "natural organic matter" are not actually natural at all. In much of the country, the bulk of organics in drinking water supplies stems from agriculture in the form of uncontrolled soil erosion, manure and fertilizer runoff, and from municipal sewage treatment plant discharges:

  • About one billion tons of topsoil erode from U.S. cropland each year (USDA 2001), much of it deposited in streams and rivers. Soil contains organics that combine with chlorine to form disinfection byproducts. Soil in combination with manure eroding from pasture and range lands contains even higher amounts of DBP-forming organics.

  • Studies released by the US Geological Survey (USGS) found that fertilizer used in agriculture accounted for 17% of total phosphorus that entered major river basins in the U.S. (CSP, 2007). Excess phosphorus causes uncontrolled algae blooms that create massive slugs of organic matter, which then combine with chlorine to form chlorination byproducts. Most phosphorus is absorbed to soil particles in the field and is carried to streams and rivers through soil erosion. USGS studies show that three-quarters of all streams and rivers in the U.S. are polluted with phosphorus at levels that can support uncontrolled algae growth (USGS 1999, Cooke 1989).

  • In urban areas, sewage treatment plants flush large quantities of organics and phosphate into rivers that serve as drinking water supplies. Some of these organics can combine with chlorine to form chlorination byproducts. The phosphate stimulates algae growth that ultimately leads to chlorination byproducts. In national water quality surveys, USGS finds the highest phosphate levels in the country in urban areas impacted by sewage discharges (USGS 1999).

For the Potomac River watershed, agriculture is the top pollution source. Efforts to control farm runoff of soil, fertilizer and manure, however, 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. In an era of tight federal budgets, political pressure to fully fund farmer subsidies almost always trumps whatever concerns there might be about controlling agricultural pollution. As a result, 4,155 farmers in the Potomac watershed were denied funding for conservation programs in 2004 and 2005 due to lack of available funds.

This has real-world consequences for DC residents. If the Potomac River were less polluted as it flowed into the utility's intake pipe, disinfectant loads could be reduced, and levels of disinfection byproducts would be lower as a result.