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February 22, 1999

New study targets household sources of lead poisoning in children

By Tim Stephens

UCSC researchers have received a $138,000 grant from the U.S. Housing and Urban Development Agency (HUD) to conduct an innovative study of lead poisoning in children. The researchers will collaborate with public health officials in Santa Cruz, Monterey, and Santa Clara Counties to evaluate the use of a powerful analytical tool for identifying sources of contamination in the homes of children with dangerous amounts of lead in their blood. The researchers will also examine how lead moves from bones into the bloodstreams of affected children.

The new study may help public health agencies improve the effectiveness of their strategies for controlling household lead hazards to children, said Donald Smith, assistant professor of biology and environmental toxicology, who will lead the investigation. Roberto Gwiazda, a postdoctoral researcher in environmental toxicology, is also involved in the study.

Exposure to lead can cause permanent damage to the nervous system and widespread health problems. Lead-based paint, which was banned from use in homes in 1978, is a major source of lead exposure. Education and hazard-reduction efforts by HUD and other agencies aim to prevent lead exposure, especially in children, who are most vulnerable to its effects. Unfortunately, lead hazards are often not recognized until a screening test reveals an unhealthy amount of lead in a child's blood.

Even then, it can be difficult to identify the source of the lead, Smith said. "It has been very difficult to assess sources of lead in the environment and determine exactly where the child's elevated exposure came from," he said.

In recent years, however, Smith and his colleagues have perfected a tracing method that allows them to match the lead from a blood sample with the lead in samples taken from potential environmental sources. The technique relies on precise measurements of the different forms, or isotopes, of lead in a sample.

Four stable isotopes of lead occur naturally and their relative abundances vary among different sources of lead ore. These differences persist when the lead is mined and incorporated into paint and other products. As a result, there tend to be measurable differences in lead isotope abundances between different sources of lead exposure, such as paint, soil, dust, or food.

"The relative abundances of these isotopes in any given lead source can provide a fingerprint of the lead from that source," Smith explained.

Until recently, expensive and time-consuming analytical procedures limited the usefulness of this technique, Smith noted. But new instrumentation at UCSC now allows rapid and precise measurements of lead isotopes, and Smith hopes the technique can be routinely used for the evaluation of lead hazards.

Public health nurse Carol Sparks, who coordinates Santa Cruz County's Childhood Lead Poisoning Prevention Program, said the UCSC researchers have been able to provide her with valuable information in several cases.

"It helps us get a more complete picture of where the lead is coming from, so we can give more specific advice to parents and landlords about how to protect children from further exposure," Sparks said.

The lead isotope technique may also save money by directing control efforts toward specific sources of lead exposure.

"In our pilot studies, one of the most powerful benefits of this approach has been to show that in some cases none of the household sources matched the blood sample, meaning that the child was exposed from some other source outside the house," Smith said.

The HUD grant will enable Smith to evaluate carefully the usefulness of the lead isotope technique as a tool for those involved in the assessment of lead hazards to children. A second part of the study will look at what happens to children's blood lead levels after the source of their exposure has been removed.

One of the troubling findings of past studies is that the changes in children's blood lead levels are often relatively small even after extensive interventions to remove sources of lead exposure. According to Smith, this may be because lead continues to leach out of a child's bones into the bloodstream.

"Lead behaves somewhat like calcium in the body, so it tends to accumulate in bones," Smith explained. "In a child, about 75 percent of the lead in the body is in bone."

Smith plans to use the lead isotope technique to determine how much and how quickly lead moves from bones into the bloodstream.

"We may find that it takes a year or two to leach the lead out of the bones before you can see a benefit from the intervention," he said.

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