The theory offered by the economist, Rick Nevin, is that lead poisoning accounts for much of the variation in violent crime in the United States. It offers a unifying new neurochemical explanation for fluctuations in the crime rate and is based on studies linking exposure to lead in children with violent behavior later in their lives.
What makes Nevin's work persuasive is that he has shown an identical, decades-long association between lead poisoning and crime rates in nine countries.
"It is stunning how strong the association is," Nevin said. "Sixty-five to 90 percent or more of the substantial variation in violent crime in all these countries was explained by lead."
Through much of the 20th century, lead in U.S. paint and gasoline fumes poisoned toddlers as they put contaminated hands in their mouths. The consequences on crime, Nevin found, occurred when poisoning victims became adolescents. Nevin does not say lead is the only factor behind crime, but he says it is the biggest factor.
....The centerpiece of Nevin's research is a century-long analysis of crime rates and lead-poisoning levels: The United States has had two spikes of lead poisoning, one at the turn of the 20th century, linked to lead in household paint, and after World War II, when the use of leaded gasoline increased sharply. Both times, the violent-crime rate went up and down in concert — with the violent crime peaks coming two decades after the lead-poisoning peaks.
Other evidence has accumulated in recent years that lead is a neurotoxin that causes impulsivity and aggression, but these studies have also drawn little attention. In 2001, sociologist Paul Stretesky and criminologist Michael Lynch showed that U.S. counties with high lead levels had four times the murder rate of counties with low lead levels, after controlling for multiple environmental and socioeconomic factors.
In 2002, Herbert Needleman, a psychiatrist at the University of Pittsburgh, compared lead levels of 194 adolescents arrested in Pittsburgh with lead levels of 146 high-school adolescents: The arrested youths had lead levels that were four times higher.
"Impulsivity means you ignore the consequences of what you do," said Needleman, one of the country's foremost experts on lead poisoning, explaining why Nevin's theory is plausible. Lead decreases the ability to tell yourself, "If I do this, I will go to jail."