Low lead levels can harm kids' hearing.

Low lead levels can harm kids' hearing

Children whose blood-lead levels fallwell within the generally accepted "safe" range may have incurred subtle but significant hearing loss, according to a new study by Environmental Protection Agency (EPA) scientists. "This may be a possible explanation for at least some of the learning disabilities that have been observed previously" in lead-exposed children, says David A. Otto, one of the study's authors and a physiological psychologist at EPA's Health Effects Laboratory in Research Triangle Park, N.C.

Otto says these results, when taken togetherwith other new data on childhood effects of low-level lead (SN: 11/22/86, p.333), suggest there is now justification for reducing the current federal guideline on what constitutes an excessive body burden of lead in children -- 25 micro-grams per deciliter ([mu]g/dl) of blood.

Using data on 3,000 youths between theages of 4 and 19 from the most recent National Health and Nutrition Examination Survey (NHANES), the EPA scientists correlated blood-lead levels with hearing at pitches between 500 and 4,000 hertz, a range that Otto says covers most speech.

"We found that as blood-lead levels increasedfrom approximately 10 [mu]g/dl to approximately 30 or 35 [mu]g/dl, there was a hearing loss in the range of about 10 decibels," he says. Though adult lead workers have experienced hearing losses at blood-lead levels of about 50 [mu]g/dl, deficits in Otto's study could be linked with lead levels as low as 12 [mu]g/dl. He notes that most audiologists would not consider the 5- to 10-decibel losses detected in the children to be "clinically significant." However, he says the EPA researchers believe that this slight impairment in hearing might contribute to learning disabilities, even speech impairments, that could go unnoticed in pre-school children.

Otto says he is not sure of the exactmechanisms that might trigger the hearing impairment. But his earlier studies have linked potentially serious adverse hearing changes, such as significant delays in conduction velocity within the auditory nerve, to high lead exposures in children. Because symptoms persisted five years after blood levels dropped to normal U.S. levels -- between 10 and 15 [mu]g/dl -- Otto worries that "these may be long-term effects that do not go away."

"It's not surprising that an agent [lead]that impedes cell-to-cell communication would in fact affect auditory processing," says Ellen Silbergeld, a lead toxicologist with the Environmental Defense Fund in

Washington, D.C. But she believes the major importance of Otto's new study may be the clue it offers to how lead affects learning and IQ. Silbergeld says she is particularly troubled by how low the lead levels were that affected hearing; NHANES data suggest, she says, that 80 percent of U.S. children have blood-lead levels above 10 [mu]g/dl. However, Otto notes, a near phaseout in U.S. use of leaded gasoline--believed to be the leading source of lead in children -- means average childhood lead levels should be declining.