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Dangers of Lead Still Linger

by Dixie Farley

Lead Absorption

While adults absorb about 11 percent of lead reaching the digestive tract, children may absorb 30 to 75 percent. When lead is inhaled, up to 50 percent is absorbed, but less than 1 percent of lead is absorbed when it comes in contact with the skin. The body stores lead mainly in bone, where it can accumulate for decades. "Anyone in poor nutritional status absorbs lead more easily," adds Cecilia Davoli, M.D., a pediatrician with Kennedy Krieger Institute's Lead Poisoning Prevention Program, in Baltimore. Calcium deficiency especially increases lead absorption, as does iron deficiency, which can also increase lead damage to blood cells. A high-fat diet increases lead absorption, and so does an empty stomach.

The Risks of Lead

Lead disrupts the functioning of almost every brain neurotransmitter, says David Bellinger, Ph.D., a psychologist and epidemiologist at Children's Hospital in Boston. Neurotransmitters are chemical messengers between the body's nerve cells. The messenger calcium, for example, is essential to nerve impulse transmission, heart activity, and blood clotting, but if it doesn't work right, affected systems may also be askew.

"Lead fits into binding sites that calcium should," Bellinger says, "so it can disturb cellular processes that depend on calcium. But there's no unifying theory that explains in detail what lead does to the central nervous system, which is where lead typically affects children." Bellinger estimates that each 10 mcg/dL increase in blood lead lowers a child's IQ about 1 to 3 points. "Evidence is less clear," he says, "on whether mild blood lead elevations in pregnancy cause permanent effects on the fetus. Studies have tended not to find that early developmental delays related to minor fetal exposure carry through to school age, when IQ is measured." Studying middle- and upper-middle-class children exposed before birth to mild lead levels, Bellinger and colleagues found delays in early sensory-motor development, such as grasping objects, but did not find such effects by school age. However, he adds, "When lead exposure in the uterus is quite high, the impact can be devastating on the fetus, causing serious neurological problems." High lead exposures can cause a baby to have low birth weight or be born prematurely, or can result in miscarriage or stillbirth.

"Symptoms of lead poisoning can be highly variable depending, in part, on the age of the child, the amount of lead to which the child is exposed, and how long the exposure goes on," says pediatrician Randolph Wykoff, M.D., FDA associate commissioner for operations. Children exposed to lead may have no symptoms, he says, or may report sometimes vague symptoms, including headache, irritability or abdominal pain.

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