Chlorine Pollutants High in DC Tap Water

Tests Find Hazardous Chlorination Byproducts

July 19, 2007

Chlorine Pollutants High in DC Tap Water: THM levels often higher than what studies show are safe

Although the THM concentrations in the samples were all below the EPA’s MCL, 89% were above the level (40 parts per billion) that epidemiological studies have associated with adverse health effects in infants, ranging from low birth weight to neurological abnormalities. The locations with the highest THM concentrations were the National Mall, the home of a 2-year-old infant and the elementary school. The Capitol and the headquarters of the EPA had the lowest concentrations of both HAAs and THMs.

Epidemiological studies have found increased incidences of neural tube defects, small body length, and small head size in women drinking water containing only 40 ppb THMs (Kanitz 1996; Klotz 1999), and a recent study finds an increased risk of bladder cancer associated with exposures as low as 50 ppb (Villanueva 2007). Researchers have also found links to low birth weight and first trimester miscarriage in pregnant women drinking water with just 60 ppb and 75 ppb, respectively (Bove 2002). These levels are all below the EPA’s current MCL of 80 ppb, suggesting that the federal limit is not low enough to be health protective.

Chart showing health effects at various THM concentrations


Source: D.C. tap water samples collected by EWG from May 1 to May 4 2007. Samples analyzed by Environmental Engineering and Technology, Inc. laboratories in Newport News, VA. Potential health risks noted on graph are from peer-reviewed scientific literature, with full references listed in graph footnotes.

Notes: 1. Bove FJ, Fulcomer MC, Klotz JB, Esmart J, Dufficy EM, Savrin JE. 1995. Public drinking water contamination and birth outcomes. Am J Epidemiol 141: 850-62.
2. Waller K, Swan SH, DeLorenze G, Hopkins B. 1998. Trihalomethanes in drinking water and spontaneous abortion. Epidemiology 9: 134-40.
3. Gallagher MD, Nuckols JR, Stallones L, Savitz DA. 1998. Exposure to trihalomethanes and adverse pregnancy outcomes. Epidemiology 9: 484-489.
4. Klotz JB, Pyrch LA. 1999 Neural tube defects and drinking water disinfection by-products. Epidemiology 10: 383-90.
5. Kanitz S, Franco Y, Patrone V, Caltabellotta M, Raffo E, Riggi C, et al. 1996. Association between drinking water disinfection and somatic parameters at birth. Environmental health perspectives 104: 516-20.
6. Villanueva C, Cantor K, Grimalt J, Malats N, Silverman D, Tardon A, et al. 2007. Bladder cancer and exposure to water disinfection by-products through ingestion, bathing, showering, and swimming in pools. American journal of epidemiology 165(2): 148-56.

In addition, while its findings remain controversial, one 1996 study found a relationship between women exposed to just 10 ppb of one particular THM (chloroform) and an increased risk of intrauterine growth retardation and babies born small for their gestational age (Reif 1996). This finding is notable because all of the samples in our study had chloroform levels exceeding this value, by as much as six times in some cases.

Other epidemiological studies have found that levels of THMs between 80 and 100 ppb and above are associated with increased incidences of neural tube, central nervous system, and major cardiac birth defects (Bove 1995; Klotz 1999), providing more evidence that the EPA’s MCL may only be marginally health protective. Researchers have also found associations with oral cleft defects (Bove 1995) and stillbirth (Dodds 1999) in women who were exposed to more than 100 ppb of THMs during pregnancy. And animal studies have found that at high doses individual THMs can cause decreased body weight, decreased heart, livers and kidney weights, and renal tube degeneration, among other effects (NTP 2007).