July 5, 1995

NCSU nuclear engineer to improve test for bone lead in humans

It may seem a long time ago that you had the choice of leaded gasoline for your car. But if you pumped leaded gas, you probably inhaled the fumes--and still carry the lead in your body.

Although blood lead levels have gone down in recent years because consumers no longer pump leaded gas, lead poisoning from other sources is still a problem and, unfortunately, so is determining low levels of lead stored in our bodies.

Dr. Robin Gardner, professor of nuclear and chemical engineering at North Carolina State University and an expert in radioisotope measurement applications, hopes to help solve the second problem. With a $432,000 National Institute of Environmental Health Services (NIEHS) grant, Gardner has begun a three-year project to render current bone lead testing more sensitive.

Because most of the lead entering our bodies concentrates in the skeleton, testing involves screening bones in the legs and fingers by X-ray fluorescence analysis (XRF). (Health officials use two types of X-ray analysis, one of which was developed by a former graduate student of Gardner's.)

The procedure is quick and painless, but the minimum concentration it detects is at the level of mild chronic poisoning. Therefore, health officials cannot intervene in the early stages to prevent a serious condition. Gardner's aim is to detect lower levels of contamination.

"What Dr. Gardner is doing is helping refine the sensitivity of the measurement, which hopefully will lead to making the instrument more helpful on a diagnostic level," said Dr. Annette Kirshner, a health science administrator at NIEHS and contract monitor for Gardner's research. "This certainly would help in the intervention and treatment of lead poisoning."

According to Kirshner, the average blood lead content in adults is 4 micrograms per deciliter. The action level set by the national Centers for Disease Control and Prevention is 10 micrograms per deciliter, and anyone with a blood level over that amount needs treatment for lead poisoning. Kirshner estimates that four million children in the U.S. are over this limit.

Children suffer an array of ill effects from lead poisoning; learning, attention, memory, hearing, and postural balance are most affected. Kirshner cited a researcher in child development at the National Institute for Health who has found that for every 10 micrograms per deciliter of lead in the blood, a person loses three to four IQ points.

Kirshner said that health officials use X-ray fluorescence successfully in school-aged children. Parents shouldn't be concerned about radiation exposure; according to Kirshner, the amount of exposure is less than that from a dental X-ray.

Adults can take in lead any number of ways. For example, people who make stained glass use lead for joining the pieces of glass together, and workers who remove leaded paint from structures also are exposed. Smelter workers are particularly vulnerable because they breathe vaporized lead, which gets into the blood very quickly. Such repeated occupational and hobby exposure can damage the kidneys and lead to high blood pressure.

Lead gets into the blood by two means: inhaling and ingesting. Inhaled lead enters the blood more rapidly than ingested lead. Because a blood test measures only recent exposures to lead, Gardner's work to improve bone lead testing is critical.

As Kirshner explained, "One exposure within weeks would move in rapid order out of the bloodstream. It then goes to the soft tissues--brain, kidney, etc. Eventually the reservoir for lead in the body becomes the skeletal system.

"The bone," she added, "is the reservoir for your cumulative lead exposure over your lifetime."

According to Gardner, there is a procedure to eliminate lead from the system, but it is expensive and very uncomfortable for the patient. Finding lead at smaller concentrations can prevent this measure.

Gardner will use his Monte Carlo computer model to lower the minimum detectable concentration while maintaining a radiation dose as low as possible. He described Monte Carlo as "a method of simulating the actual path of an individual particle (or radiation) by choosing from appropriate random distributions in the computer. Many such paths are followed, and the average result of all paths is the desired answer.

"Random number distributions for this purpose are generated by special mathematical techniques within the computer," he said, "but they could be obtained in principle by tossing coins or dice or by selecting numbers out of phone books."

He added, "These latter techniques are valid but not as handy as the computer method."

The Monte Carlo code was developed by Gardner and seven of his graduate students over the past twenty years. He believes that "the Monte Carlo code will help do the work efficiently and without lots of experimentation."

The work will take place in the center Gardner directs, the Center for Engineering Applications of Radioisotopes (CEAR), at N. C. State University. Assisting Gardner are Dr. Qi Ao, a research associate who has worked on X-ray fluorescence in China, and Sang Hoon Lee, a doctoral student.

Gardner's investigation of radioisotopes in lead measurement is just one example of new applications of nuclear energy. PHOTOS AVAILABLE

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