Removal of Lead from Gas and Paint Linked to Drop in Violent Crime

According to FBI records, violent crime has been in decline since the early 1990s. A new theory explaining the drop has been gaining traction, and its focus isn't on politicians or the criminal justice system. An article in Chemical & Engineering News details the mounting data that suggests taking lead out of gas and paint has played a critical role.

Lauren K. Wolf, associate editor at C&EN, explains that violent crime rates in America reached an all-time high in the early 90s. But by the end of the decade, homicide rates dropped by more than 40 percent. Economists and criminologists have proposed varying theories to explain the sudden drop.

"Some have pointed to an increase in police officers. Others have suggested a rise in the number of offenders put behind bars. Economist and 'Freakonomics' coauthor Steven D. Levitt famously hypothesized that the legalization of abortion in 1973 even played a role. Once the Supreme Court decided Roe v. Wade, he argued, fewer unwanted babies grew into disturbed, crime-prone adults two decades later," writes Wolf.

In her article, Wolf points out a recent theory that experts have been discussing: lead. Until 1973, when the Environmental Protection Agencies mandated its removal from gasoline, lead was spewed into the atmosphere from car exhaust. Then later, in 1978, lead-based paint was banned from being used in newly built homes.

"Because of these actions, children born in the mid- to late-1970s grew up with less lead in their bodies than children born earlier. As a result, economists argue, kids born in the '70s reached adulthood in the '90s with healthier brains and less of a penchant for violence," the article reads. "In 1976, the average US resident had a blood-lead level of 16 µg/dL [micrograms per deciliter], according to the National Health & Nutrition Examination Survey. By 1991, when there was less lead in the air and in housing, the average had dropped to 3 µg/dL."

In the 1960s, doctors would label a child as lead poisoned only if he or she had a blood-lead level of at least  60 µg/dL. Researchers of the University of Pittsburgh psychiatrist Herbert L. Needleman questioned the seemingly arbitrary cut off value.

"Needleman and others began observing 'silent lead poisoning' in children with blood-lead levels below the established limit. Rather than overt physical symptoms like hallucinations and kidney damage, these kids had low IQ scores, attention problems, and antisocial tendencies," writes Wolf. "The boys rated worst by their parents and teachers in terms of aggressive...behaviors had been exposed to the highest levels of lead," behaviors that could lead to a tendency toward crime, a press release announcing the article suggested.

Despite lowered levels of lead in the environment, many children from low-income families still experience higher than average blood-lead levels.

"There are nearly a half-million children between the ages of one and five with a blood-lead level above the 5-µg/dL threshold. These are mostly kids who are growing up in dilapidated inner-city houses with lead paint still on the walls or in neighborhoods with elevated levels of lead in the soil," the article reads.

Children in these circumstances would benefit from a "reevaluation of crime policies and a re-invigoration of cleanup efforts," said Paul B. Stretesky, a criminologist at the University of Colorado, Denver, as quoted in the article.