Children apparently suffer impaired mental development early in their lives if exposed to low levels of lead, possibly even doses below those deemed safe under some government standards, Australian researchers reported this week.

The findings add to a growing body of data indicating lead exposure, in addition to being toxic at high levels, can cause brain damage to children even at relatively low levels."We think the evidence is increasing (that low lead levels can impair mental development), and this (study) may contribute to it," said Dr. Alan Leviton, an associate professor of neurology at Harvard Medical School.

The University of Adelaide researchers studied 537 children born from 1979 to 1982 to women living in the town of Port Pirie, a southern Australian community located downwind from a large lead-smelting factory.

The researchers took blood samples from the children when they were born and again periodically until they were 4 years old, when they were given a standard test to gauge their cognitive development.

Children who had an average of about 30 micrograms of lead per deciliter of blood scored an average of 7.2 points lower on a test that measure general cognitive ability than those who had blood lead levels of about 10 micrograms per deciliter, which is considered about normal, the researchers reported.

"We conclude that postnatal blood lead concentration is inversely related to cognitive development in children," the Australian researchers wrote in reporting their findings in The New England Journal of Medicine.