Could there be a link between crime and lead ingestion? Back in 1996 a study in Pittsburgh (“Bone Lead Levels & Delinquent Behavior”), suggested there’s a link between childhood lead exposure and juvenile delinquency later on, Even moderate levels of lead in the bloodstream of an infant or toddler significantly increase the odds that he will suffer behavioral disorders in childhood, and will engage in delinquency and criminal behavior later on.
Some wondered if reducing lead exposure had an effect on violent crime. Across America, in city after city, violent crime peaked in the early ’90s and then began a steady and spectacular decline. Rick Nevin, who was a consultant working for the US Department of Housing and Urban Development on removing lead paint from old houses, knew that the biggest source of lead in the postwar era, wasn’t paint. It was leaded gasoline. If you chart the rise and fall of atmospheric lead caused by the rise and fall of leaded gasoline consumption, you get a pretty simple upside-down U: Lead emissions from tailpipes rose steadily from the early ’40s through the early ’70s, nearly quadrupling over that period. Then, as unleaded gasoline began to replace leaded gasoline, emissions plummeted.
Intriguingly, violent crime rates followed the same upside-down U pattern. The only thing different was the time period: Crime rates rose dramatically in the ’60s through the ’80s, and then began dropping steadily starting in the early ’90s. The two curves looked eerily identical, but were offset by about 20 years.
In a 2000 paper, he concluded that if you add a lag time of 23 years, lead emissions from automobiles explain 90 percent of the variation in violent crime in America. Toddlers who ingested high levels of lead in the ’40s and ’50s really were more likely to become violent criminals in the ’60s, ’70s, and ’80s.
During the ’70s and ’80s, the introduction of the catalytic converter, combined with increasingly stringent Environmental Protection Agency rules, steadily reduced the amount of leaded gasoline used in America. Following on Nevin’s work, public health policy professor Jessica Wolpaw Reyes discovered that this reduction wasn’t uniform.
In fact, use of leaded gasoline varied widely among states. If childhood lead exposure really did produce criminal behavior in adults, you’d expect that in states where consumption of leaded gasoline declined slowly, crime would decline slowly too. Conversely, in states where it declined quickly, crime would decline quickly. And that’s what she found!
“Lead changes who we are,” she says. “If you wanted to say I don’t believe that story, then my answer is that you need to come up with another story that would explain why we have found this particular pattern to lead in the 1970s and 80s and then crime in the 1990s and 2000s.
Then Tulane University researcher Howard Mielke and demographer Sammy Zahran researched the correlation of lead and crime at the city level. They studied six US cities that had both good crime data and good lead data going back to the ’50s, and they found a good fit in every single one. In fact, Mielke has even studied lead concentrations at the neighborhood level in New Orleans and shared his maps with the local police. When they overlaid them with crime maps, they matched up.
In a 2014 BBC interview, Dr Bernard Gesch, a physiologist at Oxford University who has studied the effect of diet and other environmental factors on criminals, reported that data suggests lead could account for as much as 90 per cent of the changing crime rate during the 20th Century across all of the world.
“Lead is a very potent neurotoxin,” says Gesch. “It has a range of effects on the brain that have been demonstrated through hundreds of different biological studies. Lead alters the formation of the brain. It reduces the grey matter in areas responsible for things such as impulse control and executive functioning – meaning thinking and planning.”
“A lot of people would say that correlation isn’t cause,” he says. “But it seems that the more the exposure, the more extreme the behavior. I’m certainly not saying that lead is the only explanation why crime is falling – but it is certainly the most persuasive. Unless someone is telling us that the brain is not involved in decision-making then lead has to be relevant to crime.”