Chloramines again linked to lead in drinking water
High blood lead levels discovered in two boys this spring are being linked to drinking water in Greenville, N.C. Local public health authorities are advising pregnant women, infants, and young children to avoid tap water, and state officials are evaluating drinking water throughout the state.
The episode is being compared to Washington, D.C.’s recent problems with lead in drinking water (Environ. Sci. Technol. 2004, 38, 224A–227A). Utilities in both cities had switched from free chlorine disinfectant to chloramines in the past few years to comply with the U.S. EPA’s 1998 disinfectants and disinfection byproducts rule. However, unlike Washington, Greenville lacks lead pipes, and the utility has used a polyphosphate corrosion inhibitor for years. The inhibitor should have created a protective film on plumbing.
Lead solder in the home is being blamed for the boy with the highest blood lead levels of 20 milligrams per decaliter (mg/dL). His home’s tap water contained 400 parts per billion (ppb) total lead, according to Ed Norman, an epidemiologist with the North Carolina Department of Environment and Natural Resources. The Centers for Disease Control and Prevention lists 10 mg/dL as the minimum blood lead level of concern; 20 mg/dL is considered lead poisoning.
Corrosion expert Marc Edwards at Virginia Polytechnic Institute and State University says that the release of lead due to corrosion of solder and brass is consistent with his experimental results involving chloramines. “For certain brasses and solders, the corrosion can be extensive, although it is difficult to predict,” he says. Edwards’s results were recently published (J. Am. Water Works Assoc. 2004, 96, 69–81). The effectiveness of different corrosion inhibitors in the face of changing disinfection practices is still not resolved, he says.
But Richard Maas of the Environmental Quality Institute at the University of North Carolina, Asheville, says that the corrosion is due to a combination of chloramines, excess ammonia, and fluorosilicic acid, which is commonly used to fluoridate water supplies. His findings, yet to be peer-reviewed, are described in a technical report released June 13 by his institute.
The Greenville treatment plant began adding chloramines into its distribution pipes in December 2002 and switched from free chlorine to ozone as its primary disinfectant in August 2003. Under the reduced sampling requirements of EPA’s 1991 lead and copper rule, utilities must test household drinking water for lead in some of the homes they serve every three years, says Greenville water treatment plant manager Barrett Lasater. A problem emerged during the scheduled tap-water sampling in the summer of 2004, when about 25% of the samples exceeded EPA’s 15 ppb total lead action level. As a result, the district switched to orthophosphate inhibitor in August 2004, anticipating that the additive would quickly reduce lead levels. Thus, the increased lead levels puzzle Lasater, who says that several bench-scale pilot studies did not find that chloramines increased lead corrosion.
The confusion may be frustrating, but it’s understandable, says Edwards. “We barely understand the effects of chloramines on plumbing.”
