Study Says Lead Exposure May Contribute to Crime
Exposure to lead in the environment may contribute significantly to criminal behavior, a possibility that might help explain the high rates of crime in America’s inner cities, researchers said Tuesday.
A study released today suggests that even nominal doses of lead, well below those associated with poisoning, can lead to the antisocial behavior and delinquency in young boys that is routinely considered a foreshadowing of violent adult criminality.
The new research extends a landmark 1990 study that demonstrated that lead poisoning in childhood is the single most important predictor of criminality among adults. It far outweighed poverty, the absence of a father in the household and other major social factors commonly cited by criminologists.
Using a new technique that is more accurate than blood levels in reflecting lifetime exposure to lead, Dr. Herbert L. Needleman and his colleagues at the University of Pittsburgh School of Medicine studied 301 boys from Pittsburgh’s inner city.
They found that boys with above-normal lead values were more aggressive and had higher delinquency scores when evaluated by teachers, parents and, most important, themselves.
These delinquent behaviors, which include bullying, vandalism, setting fires, theft and fighting, are highly predictive of adult criminality, alcoholism and domestic abuse, said psychologist Terrie E. Moffitt of the University of Wisconsin.
The findings, published in the Journal of the American Medical Assn., should add a new component to the already controversial arguments about the causes of the ever-increasing violence in America’s urban areas. In particular, they could help remove the element of racism from the argument because the new results apply equally to whites and African Americans.
“We’re not saying that lead is the cause of all the . . . decay in our cities, but it is not unreasonable that it is a part of the picture, perhaps a measurable part,” Needleman said.
“This is extremely important for crime and violence research,” added criminologist Deborah W. Denno of Fordham University. “Lead is a factor that we should start seriously looking at among criminals and adults” charged with crimes.
But Dr. David Bellinger of Children’s Hospital in Boston cautioned that the case against lead is far from proven. “This study is very compelling, but one epidemiological study still doesn’t answer all the questions,” he said. “Lead is a factor that ought to be considered . . . but criminality and violence is a final pathway for many different [social] processes. We need to have more evidence.”
The importance of these other factors is demonstrated by the fact that violent crime has been increasing even as lead exposure has declined.
Society has made remarkable progress in protecting children from lead by banning its use in gasoline, paint and food cans. As recently as 1969, about 88% of young children had blood levels above the recommended maximum of 10 micrograms per deciliter. Today, that figure is about 9%--but that still represents about 3 million preschool-age children.
The most important sources of lead are in soil--deposited over decades by automobiles burning gasoline containing tetraethyllead as an octane enhancer--and in houses built before 1978. Paint in such houses often contains as much as 50% lead and, even though it has been covered by newer, lead-free paints, it still flakes or rubs off. Studies have found that the old houses and contaminated soils of inner cities are by far the highest sources of lead.
Researchers have long known that lead exposure reduces IQ by damaging brain cells in children during their early years, when neural pathways are still being formed.
Some studies have shown as much as a 5.8-point decline in IQ--on a scale where 100 is average--for every 10-microgram increase in blood lead levels.
Lead researchers have suspected a link to behavior as well. Studies have shown that lead increases children’s distractibility, impulsiveness and restlessness, and leaves them with a shortened attention span--all factors that are considered precursors of aggressive or violent behavior.
Anecdotal reports suggest that children with lead poisoning become more violent, Needleman said. Prison doctors often find that violent inmates have high lead levels, Denno added.
But Needleman’s new report “is the first rigorous study to demonstrate a significant association between lead and antisocial behavior,” said lead expert Kim N. Dietrich of the University of Cincinnati.
Needleman’s group used a technique called X-ray fluorescence to measure the total amount of lead in the boys’ shinbones, a technique that is increasingly being used to monitor industrial exposure to the element. The boys were all part of an ongoing study of delinquency in Pittsburgh, and none had lead poisoning.
Parents and teachers completed a standard behavioral analysis of the boys when they were, on average, ages 7 and 11. The boys also participated in periodic confidential interviews about their behavior. Sociologists have previously shown that such analyses and interviews can be highly accurate if carefully conducted.
Although the team could not directly associate bone lead levels with blood levels, they found that boys with the highest bone lead levels were the most aggressive and delinquent, regardless of any other social or economic factor.
The effects of lead also were independent of race, Needleman found. The results suggest that the relatively high incidence of crime in some black communities does not result from a racial predisposition toward crime, as some have suggested, but from a phenomenon increasingly known as “environmental racism,” Denno said. Environmental racism, she said, reflects the fact that pollutants, such as lead, tend to be dumped or to accumulate in areas where blacks and other minorities reside.
And the effect emerged in all three evaluations--by parents, teachers and the boys themselves. “If [the effect appeared] only in the teachers’ assessments, or in the parents’, it would be much less compelling,” Bellinger said.
The boys in the study are now 16, and Needleman plans to look at them again next year. None of them had been arrested for criminal activity during his study, but that, he predicted, is likely to change by the time they are 17.
Then, he hopes, the link between lead and criminal behavior will be demonstrated more firmly, and the research effort can shift toward new ways of preventing exposure.
