Fingerprinting Test Helps Pinpoint The Sources Of Lead Poisoning

SANTA CRUZ, CA–A technique that detects the "fingerprints" of various lead sources may help target the causes of childhood lead poisoning, according to scientists at the University of California, Santa Cruz. In a new study, researchers used the method to identify the environmental sources that caused lead poisoning in three Santa Cruz County children.

"It is typically very hard to identify the source of lead poisoning in children," said Donald Smith, an associate professor of environmental toxicology at UCSC.

Smith performed the study with lead author Roberto Gwiazda, an assistant researcher in environmental toxicology. Their research was reported in the November 2000 issue of Environmental Health Perspectives.

"This test is not always successful at identifying sources of lead exposure, but it provides a lot of information that should allow public health officials to reduce household lead contamination more effectively," Smith said.

Almost one in every 20 children in the United States under age six suffers from lead poisoning, according to the Centers for Disease Control and Prevention. Exposure to even low levels of lead can cause aggressiveness, hyperactivity, impaired growth, a drop in IQ, learning disabilities, and other behavioral problems. Children are most vulnerable, because their bodies absorb lead more readily than adult bodies do, and their nervous systems are still developing.

The main sources of lead exposure in children are lead-based paint and lead-contaminated dust and soils. Although lead-based paint was banned in 1978 and leaded gasoline was phased out in the 1970s, about 38 million homes in the United States still contain leaded paint, and urban soils contain residual lead from deteriorated paint, leaded gasoline, and other sources. But few children are screened for lead poisoning.

"People think the problem is solved because we’ve eliminated lead in gas and paint," Gwiazda said. "But the number of children being exposed, mostly in old, deteriorated housing, is staggering."

If a blood test shows that a child has an abnormally high lead level, public health officials are dispatched to the child’s house to try to identify the source. "If they find several potential lead sources in the house, they don’t know which is actually affecting the child," Gwiazda said. "It’s a guessing game."

The new technique exploits the fact that lead comes in several different varieties, called isotopes. Each of the paints in a house and the soil surrounding it may contain a different blend of these isotopes, enabling researchers to try to match the blend found in the child’s bloodstream to the specific lead source poisoning the child.

A single match cannot always be found. If the lead in a child’s bloodstream comes from several different sources, it can be virtually impossible to figure out what combination of sources produced that mix of isotopes. And if the child was exposed to lead in a previous home, lead stored in the bones from the earlier exposure can leach into the bloodstream, adding factors to the mix.

But even when isotope measurements do not point to a single culprit, they can help researchers discard lead sources whose isotope mix is widely different from that in the child’s blood. In two of the three cases studied, researchers found that the lead poisoning came from earlier exposure, not from contamination in the child’s house.

Ridding a house of lead can be labor-intensive and can cost as much as $15,000, Smith said. Using the test could save a great deal of effort and allow public health agencies to use their resources more effectively.

Lead isotope tests have been around for awhile, but they are only now growing affordable enough to be used to test for potential sources of lead contamination, thanks to technological advances, Gwiazda said. To evaluate whether this approach could be viable in public health applications, the researchers limited their analysis to the paint and soil samples collected by public health officials in the normal course of their activities.

"The point was to see whether it will work as a routine tool in household risk assessments as they are done today," Gwiazda said. "The study certainly shows that the technique is cost-effective and provides valuable information to the public health official."

Gwiazda and Smith have begun a collaboration with pediatricians in Philadelphia to study the isotope method further, in research funded by the U.S. Department of Housing and Urban Development.