Children whose blood was tested showed increased levels of lead after an Eastern North Carolina city switched its water purification chemicals, Duke University researchers have found.

The findings add to a growing mystery about whether lead is creeping undetected into drinking water, even though federal rules require water systems to routinely test for it.

The study doesn't prove cause and effect between the higher lead levels and the purification chemicals. But it adds more heft to warnings that families with children in older homes should not presume their drinking water is safe and should take measures against lead exposure.

Marie Lynn Miranda, director of the Children's Environmental Health Initiative at Duke University, analyzed lead tests performed on hundreds of Wayne County children from 1999 to 2003. After the Goldsboro water system switched disinfecting chemicals, blood lead levels of tested children served by the system -- on average -- ticked up.

Few Goldsboro children absorbed enough lead to require medical intervention, and over time, the average lead levels detected by tests fell. No one can prove that the water was a primary source of contamination.

But lead averages peaked after March 2000, when Goldsboro started using chloramines, a mix of chlorine and ammonia used to destroy bacteria in water supplies. Chlorine alone can produce carcinogens that the federal Environmental Protection Agency is working to cut in water supplies. The biggest change detected in Goldsboro was among children living in homes built before 1950.

Goldsboro's drinking water complies with EPA rules limiting lead levels, city utility director Karen Brashear noted. The utility tested household taps in the city in 2003 and August of this year. State public health officials tested for lead in Goldsboro in late 2005 and found no trouble.

"We have always been in compliance," Brashear said.

But Miranda says science can't yet adequately guide water utilities -- or even the EPA -- on when and where to be on the lookout for lead.

"We need to invest more in the environmental chemistry," she said. "Once we figure that out, more communities can carefully monitor blood lead levels at the right times."

Miranda's research team is compiling information from Durham and Wake counties to see whether detected blood lead levels in children changed after local utilities started using chloramines.

EPA cracking down

The EPA is in the process of toughening regulation of lead screening in public water supplies. It wants municipal water systems to get approval from state regulators before switching water treatments. And the EPA wants to improve its own education on the potential of some chemicals to make water more prone to leach lead.

Lead contamination in North Carolina drinking water has moved from a non-issue to a public health concern only recently. Two children, one in Greenville in 2004 and one in Durham this year, were the first in the state's history suspected of getting lead poisoning solely from drinking water.

Lead can cause developmental difficulties and brain damage if consumed by children or pregnant women.

Water utilities don't release lead-contaminated water from their treatment plants. But changes in the corrosive quality of water can allow lead to leach from home plumbing systems, including plumbing fixtures containing the lead and lead solder, which North Carolina allowed in home plumbing systems until 1985.

In Greenville and Durham, a change in the ratio of two chemicals may have made water more corrosive. In Goldsboro, Miranda is suspicious about a switch from free chlorine to chloramines. Such a switch in Washington, D.C., has been identified as causing high lead levels at household taps in 2003.

Marc Edwards, a scientist at Virginia Polytechnic Institute and State University, identified the chemical ratio that may have elevated lead in multiple Greenville and Durham homes. He said Miranda's study reinforces his sense that even when utilities are doing their best to screen for lead, they may miss it.

"The water industry is doing everything it can to make sure water is less corrosive," Edwards said. "At the same time, there is no guarantee that an individual's water will be safe."

Given the uncertainties, it's more important than ever that people living in homes built before 1985, when lead solder was banned, take pains to reduce the risk of lead in their drinking water by flushing lines before using water at home and taking other easy steps, said Marc Meyer, Durham County Health Department's lead program specialist.

"We wash our hands before we eat. Why not let the water flush," Meyer said. "It's better to be cautious than to be foolish."