No threshold to lead's learning effect.

No threshold to lead's learning effect

For years studies have been linkingchildhood learning problems with body levels of lead in the range of 20 to 35 micrograms per deciliter of blood. When two new studies over the past year reported related effects in developing infants and toddlers at even lower levels--8 to 10 g/dl--scientists began to wonder whether infants might be more vulnerable to lead's neurotoxic effects than previously believed (SN: 5/2/87, p.277). Now a Scottish study suggests that any body burden of the metal risks diminishing the cognitive ability and learning skills of children.

The new study, reported in the May 30LANCET, involved 501 Edinburgh schoolchildren aged 6 to 9 years. Their mean blood-lead level was 10.4 g/dl--roughly half what the Atlanta-based Centers for Disease Control now deems "excessive.' After accounting for 33 possible confounding variables, the study found a 5.8-point differential in score results between the least and most lead-exposed children on the British Ability Scales, a test measuring cognitive ability and educational attainment.

Against a mean score of 100 for childrenin general, this differential is "a small effect,' according to University of Edinburgh epidemiologist Mary Fulton, one of the study's authors. However, she notes, a lead effect "is definitely there, is statistically significant' and extends down into the lowest-exposure group. Moreover, she told SCIENCE NEWS, compared with previous reports of neurological deficits linked to lead, "it's a larger effect than other studies have found.'

Three factors her study identified asmore influential than lead were a parent's verbal ability, a parent's nonverbal mental ability and the child's interests, such as playing with others and reading. Together, the effect these three could have on the score--23.5 points--is considerably greater than any contribution attributable just to lead.

Nevertheless, Scotland is already activelyworking to reduce exposures to environmental lead, Fulton notes. "Our study indicates that this should be continued and perhaps even be stepped up,' she says.

The Edinburgh study "is an importantconfirmation' that asymptomatic levels of lead can be neurotoxic, says lead researcher Herbert Needleman of Children's Hospital in Pittsburgh. And, points out Ellen Silbergeld, a lead toxicologist with the Environmental Defense Fund in Washington, D.C., the finding that these effects occur at blood-lead concentrations well below 10 g/dl suggests that at least 88 percent of all U.S. children-- who also fall into this range--may be suffering similar effects.