A study of 116 Boston children found that children with "slightly elevated" levels of lead in their bodies scored significantly lower on intelligence tests than children with lower lead levels.
According to the recently completed study by Harvard psychiatrist Herbert Needleman, children with blood-lead levels well below the range of classic lead poisoning had an average IQ of 102.3 while a carefully matched group of children with even lower lead levels had an average IQ of 108.8.
The release of Needleman's study comes at a time when concern is high about levels in Washington children.
A study last year by Bailus Walker Jr., director of the District's Department of Environmental Services, found that over 40 percent of the children surveyed in far Northwest Washington had elevated lead levels in their blood.
A follow-up study by the Department of Human Resources, which has responsibility for eliminating lead-based paint from housing in Washington and was caught by surprise by the Walker study, found only about 30 of 700 children in the same, affluent, area with elevated lead levels.
That study, however, was conducted in November, when lead levels are usually low. Ron Thomas, director of DHR's lead elimination project, said the same children will be retested in July and August of this year to see what their summer blood-lead levels are.
The significance of the Needleman study is that it determines, apparently for the first time that there is a definite correlation between low levels of lead previously considered safe and poor performance on intelligence tests.
"There have been seven or eight studies" of the same question, said Needleman, "most of which were flawed. I and my colleagues attempted to address what were those basic design problems and we've demonstrated neurological differences in children with higher levels of lead in the bodies. The results may be important in terms of school function."
A 1943 study of 20 children who had been lead poisoned and were thought to have recovered found that 19 of the 20 were failing in school. But that study did not account for the variable conditions that may have caused the failure, and was focused on children with much higher levels of lead than those in the Needleman study.
Needleman and his associates at the Harvard Medical School and Children's Hospital Medical Center in Boston studied the lead level in the interior of the baby teeth of the children involved in the study.
Because lead, which can find its way into the body in the form of paint chips, air pollution or lead-laden dust, eventually is deposited in the bones, collecting baby teeth when they come out naturally is the simplest way of studying the long-term buildup of lead in children.
The children in the study's two groups were carefully matched: They were of similar birthweight, almost all whites, evenly divided between males and females, of the same birth order, had the same number of childhood immunizations and hospitalizations, were the same age - 7 years and 2 months - and almost 80 percent came from two-parent families.
In addition, the mothers of the children in the two groups and similar IQs, gave birth to their children at the same age, had the same number of pregnancies and were rated equal on a widely used scale to determine socio-economic status. The only thing that differed was the amount of lead in the children's teeth and blood.
On the verbal IQ test with low amounts of lead in their bodies scored 106.9 compared to the average score of 99.2 recorded by the "high" lead group. The children with more lead in their teeth scored lower on every one of the individual tests that makes up the over-all IQ score.
Neddleman said that, using a statistical method called multiple regression analysis, the researchers were able to determine that "the second most important contributing factor to the child's IQ was the lead level." The mother's IQ was the most important factor, he said.
"This group truely represents low level lead exposure," said Needleman, who added that any child whose "mother said another doctor suspected lead poisoning was" eliminated from the test.
Dr. Felix Delacruz, of the Mental Retardation and Disabilities Branch of the National Institute of Child Health and Development, called the test "the scientific attempt to determine subclinical effects of lead."
Delacruz, whose agency provided the $650,000 funding for the three-year study, said Needleman has shown "there is some deleterious effect of what is today considered a safe level" of lead in the body. "We are really excited about his work. It is really startling, amazing . . ."
One of the more startling aspects of the study is that only 12 percent of the "high lead" group had a history of putting foreign objects, other than toys, in their mouths.
While Needleman was quick to point out that statistic was derived from mothers' answers on a questionnaire and may not be totally accurate, it is still significant because of the widely held belief that children pick up lead by placing objects they find on the floor or on the ground in their mouths.
There have been studies, including Ballus Walker's, that show a direct correlation between the distance of a home from the roadway - and presumably therefore from pollution caused by cars using leaded gasoline - and the lead levels of the children living in the house.
Needleman has now received funding for a study of the lead levels of blood in the umbilcal cords of newborn infants, giving him a chance to study the relationship between lead in the blood of the mother and in the fetus.
That study is expected to take place in the coming year.