From 1960 to the early 1990s, the rate of violent crime in the U.S. rocketed from 150 to 750 per 100,000 people. Then it dropped just as precipitously, falling below 450 per 100,000 by 2009. A host of theories were been put forward to explain the turnaround: New crime fighting practices, economic booms and slumps, the crack epidemic, legalized abortion leading to fewer unwanted children, prison expansion, gun control, the list goes on. All of them have been knocked down by econometric and statistical analysis, or by the failure of follow-up studies to replicate results. But, as Kevin Drum lays out in a new piece for Mother Jones, the public health risks posed by lead emissions could be the missing link.
Lead emissions from cars increased by a factor of four between the late 1930s and the early 1970s, then plummeted back down with the introduction of unleaded gasoline, the catalytic converter, and stricter regulations. Allow a 23-year time lag to give the lead time to work its way into people’s bodies, and those changes in lead emissions explain 90 percent of the changes in violent crime, according to a 2000 paper by economist Rick Nevin:
Nevin also replicated his study at the international level and found that Canada, Australia, Britain, Finland, Italy, France, New Zealand and West Germany all fit the same pattern.
Since then, other researchers have also demonstrated the connection between crime and lead in six different U.S. cities. In New Orleans, connections emerged on the basis of individual neighborhoods. Lead emissions didn’t drop uniformly across the country — and in the states where lead reductions occurred slowly, there was a slower drop in crime than in the states where lead was reduced more quickly.