Dangers of Lead

by Food and Drug Administration (FDA)

The hazardous substance lead was banned from house paint in 1978. U.S. food canners quit using lead solder in 1991. And a 25-year phaseout of lead in gasoline reached its goal in 1995.

As a result of such efforts, the number of young children with potentially harmful blood lead levels has dropped 85 percent in the last 20 years, as shown in National Health and Nutrition Examination Surveys conducted by the National Center for Health Statistics. Interested in measuring the impact of lead solder's removal from food cans, the Food and Drug Administration funded collection of the data during the 1976-1980 period and has continued to support the survey efforts.

Similarly, FDA's 1994-1996 Total Diet Studies showed that, since 1982-1984, daily intakes of lead from food dropped 96 percent in 2- to 5-year-olds (from 30 micrograms a day to 1.3) and nearly 93 percent in adults (from 38 micrograms a day to 2.5).

Yet in 1997, FDA approved a new, portable blood lead screening test kit for health professionals to use. In the face of so much success, why is another screening tool even necessary?

The answer: Lead is still around.

Lead paint abounds in older housing. The deteriorating paint exposes youngsters indoors to lead-laden dust and paint chips and outdoors to exterior paint lead residues in nearby soil — residues that remain unless removed. Lead particles emitted by the past use of leaded gasoline are also in the soil, especially near major highways. Lead persists at some work sites and, occasionally, in drinking water, ceramicware, and a number of other products.

"The risk of lead exposure remains disproportionately high for some groups, including children who are poor, non-Hispanic black, Mexican American, living in large metropolitan areas, or living in older housing," the national Centers for Disease Control and Prevention noted in its Feb. 21, 1997, Morbidity and Mortality Weekly Report. Indeed, CDC reports that nearly a million children under 6 still have blood lead levels high enough to damage their health. While CDC considers the blood lead level of concern in adults to be 25 micrograms per deciliter (mcg/dL) of blood, this level in young children is only 10 mcg/dL.

Based on CDC's levels, FDA's "tolerable" daily diet lead intakes are 6 mcg for children under age 6, 25 mcg for pregnant women, and 75 mcg for other adults. However, some risk exists with any level of lead exposure, says toxicologist Michael Bolger, Ph.D., chief of FDA's contaminants branch in the Office of Plant and Dairy Foods and Beverages.

And harmful levels need never occur, according to Sheryl Rosenthal, M.S.P.H., R.D., a lead educator at FDA's Center for Food Safety and Applied Nutrition. "Lead poisoning is preventable and just should not happen today," she says.

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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