Lead in the water: mapping gets a handle on disinfectant's danger.

In 1854, Dr. John Snow stopped a cholera outbreak in London by mapping the sick residents' homes and the locations of the city water pumps. Most people who had fallen ill, it turned out, lived near the Broad Street pump, which Snow would later discover delivered pathogen-tainted water. Snow removed the pump's handle, and the outbreak abated.

Health researchers are now using geographic data to understand a different waterborne threat: lead poisoning. Researchers in North Carolina have used a mapping program called a geographic information system (GIS) to investigate the link between lead-contaminated water and an increasingly common water disinfectant.

Municipal water systems add disinfectant chemicals such as chlorine to the water. However, byproducts of chlorine disinfection can be carcinogenic, so nearly a third of the nation's waterworks have switched to a disinfectant called chloramine.

In the past few years, officials in several U.S. cities--including Washington, D.C., and Durham and Greenville, N.C.--have discovered lead contamination in drinking water after they switched to chloramine. Many researchers have assumed that those incidents were exceptions.

But some studies have suggested that chloramines in combination with other drinking-water additives may chemically release lead particles from the interior surfaces of plumbing.

To investigate, Marie Lynn Miranda and her colleagues at Duke University in Durham, analyzed data from Wayne County. In that county, the city of Goldsboro switched its water system from chlorine to chloramine in 2000.

The researchers used GIS software to link data on children's blood-lead concentrations, the age of each residential building, and areas where chloramine disinfection went into use. The age of a home could affect the lead content in tap water because older homes are more likely to have lead pipes or lead solder in the plumbing.

The scientists compared data from before and after Goldsboro switched from chlorine to chloramine disinfection.

"There was an increase in blood-lead levels in the period after chloramines were introduced," Miranda says. The magnitude of the increase depended on the age of the housing. Children living in homes built before 1965 experienced a greater increase in blood lead than children living in newer housing did, Miranda's team reports in an upcoming issue of Environmental Health Perspectives.

Miranda and others are cautious about extrapolating the finding to other cities and water-treatment systems, although they say that Wayne Count, s system is unexceptional.

Goldsboro has a relatively new water system, with few lead pipes but some lead-soldered joints. "This would be one of the last places where you'd expect to see any significant impact on blood lead from a switch [in disinfectants]," says Marc A. Edwards, an engineer at Virginia Polytechnic Institute in Blacksburg.

"The good news [is that the] increase in blood lead was of short duration and of relatively limited magnitude," says Edwards.

GIS studies of lead exposure are already under way in other cities, including Washington, D.C., Edwards says.