By JOAN LOWY
June 30, 2004
Lead exposure in early childhood may have played an important role in the national epidemic of violent crime in the late 20th century and the equally spectacular decline in crime rates of the past decade, some researchers contend.
Economic consultant Rick Nevin, hired by the Department of Housing and Urban Development to do a cost benefit analysis of removing lead paint from public housing, said he was stunned to discover a strong relationship between the use of leaded gasoline and violent crime.
The post World War II use of leaded gasoline, which peaked in the 1970s, made lead poisoning virtually ubiquitous. Nearly 80 percent of children had lead levels in their blood that would exceed today's safety threshold of 10 micrograms per deciliter.
The problem was especially severe for inner city children who were not only breathing lead laced auto exhaust, but also living in older housing contaminated with lead paint. Studies at the time showed that black 2-year-olds in New York City and Chicago had average lead levels over 30 micrograms.
Nevin, senior vice president of ICF Consulting in Fairfax, Va., found that juvenile crime began to rise in the 1950s about the time the first generation of children to suffer significant exposure to leaded gasoline reached their teens.
As lead pollution increased, so did violent crime of all kinds, including murder, rape and aggravated assault, Nevin found. Violent crime unexpectedly began to decline in the early- to mid-1990s, the same time that children who benefited from decreasing use of leaded gasoline were reaching their teens, he said.
Similar trends can be seen in Great Britain, Australia, France, New Zealand and other countries, Nevin said.
"My intuitive reaction was lead couldn't possibly still be a big problem because (contamination) was so much worse in the 1950s and the 1960s and it seemed to me that we all turned out just fine," Nevin said. "But when you see how profoundly lead affected crime trends, you realize that we didn't all just turn out fine - not by a long shot."
Nevin's research, part of which was published in the journal Environmental Research in 2000, has drawn the attention of scientists and public health advocates.
"It is something you look at and it just blows your socks off," said Ruth Ann Norton, executive director of the Coalition to End Childhood Lead Poisoning, an advocacy group in Baltimore.
Nevin's results are so startling, Norton said, that she might be tempted to dismiss them, except that "when you look at the rest of the research it all points in the same direction," that there is a strong connection between childhood lead exposure and criminal behavior later in life.
"You are not seeing studies coming out saying there is no connection. We're not hearing dissent," Norton said.
Dr. Herbert Needleman, the nation's most prominent lead researcher, said lead exposure was probably a "substantial" factor in the rise and fall of crime rates, but he is skeptical that it was the driving force behind those trends, as Nevin's research implies.
"I think the fact that it is worldwide, or at least Western worldwide, is very intriguing and worth examination," Needleman said.
Criminologists do not know why violent crime rose steadily for decades and then began an abrupt decline in the 1990s. Theories related to economic prosperity, greater incarceration, changing demographics and the crack cocaine epidemic have all been advanced, but none fully explain the trends.
"I think that it's fairly clear now that some of the differences in delinquency in individuals are associated with lead levels, but I'm highly skeptical that environmental declines in lead can explain the crime decline of the 1990s," said Richard Rosenfeld, professor of criminology at the University of Missouri.
"Any theory that is going to explain the decline has to include multiple factors," Rosenfeld said. "I'm not saying that lead couldn't be one of those factors, but it seems clear to me that it's not the most important."
Needleman estimates that 11 percent to 38 percent of the juvenile delinquency in Allegheny County, Pa., where he has been researching the relationship between lead and crime, can be attributed to lead exposure.
"Mothers of children who have been lead poisoned will frequently report to you that their children are violent," Needleman said.
Researchers at the Children's Environmental Health Center in Cincinnati, who have been following 195 children born between 1979 and 1985, found that the children who had higher blood lead levels at a young age, or whose mothers had higher blood lead levels when they were pregnant, were more likely to engage in aggressive behavior, commit delinquent acts or be incarcerated.
Higher lead exposure was still associated with increased antisocial behavior after adjusting for other factors - home environment, low birth weight, parental intelligence and social class - that could lead to similar behavior, the study found. Girls were just as likely as boys to be violent and institutionalized for their behavior, the study said.
The most frequent complaint today from study participants, who are now in their early 20s, is that they have trouble holding down a job because they find it so difficult to concentrate at work, said researcher Kim Dietrich, a professor of environmental health and pediatrics at the University of Cincinnati.
Deborah Denno, a law professor at Fordham University in New York who examined 3,000 factors for links to criminal behavior in 1,000 children, found that lead poisoning was the best predictor of delinquent and violent behavior. She concluded that most criminal behavior has environmental origins and therefore can be eliminated.
Other studies have found a link between industrial lead emissions and local crime rates.