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.
Studies have also followed groups of individuals from before birth into their adult years, finding consistent connections between higher levels of lead in the blood at childhood and higher levels of arrest rates in adulthood. Science suggests that’s because lead exposure poses a huge health risk — even tiny concentrations can reduce IQ levels by several points — and can even permanently damage the grey matter in the brain that is responsible for regulating aggression, impulse control, attention, and mental flexibility. In short, lead exposure destroys the psychological capacities an individual needs to be productive, well-socialized, and to avoid falling into criminal behavior. The damage even turned out to be greater in boys than in girls.
Even though leaded gasoline was banned in 1996, the lead that was already emitted remains in our food, our homes, our soil, and the dust when the weather’s dry. Not surprisingly, the concentrations are worse in areas that are poor, minority, and inner-city. Studies in New Orleans found 10 different census tracts in the city where lead levels in the soil were dangerously high. As Drum sums up, “There were plenty of kids already on the margin, and millions of those kids were pushed over the edge from being merely slow or disruptive to becoming part of a nationwide epidemic of violent crime.” And with the rise of gentrification and old neighborhoods with high costs of living, lead exposure is becoming economically stratified.
Drum points out that if the United States were to spend $20 billion per year cleaning up lead in our environment — $10 billion to clean up older houses and $10 billion to clean up the soil — it could produce over $200 billion in benefits from both reduced crime and increased IQs that lead to higher incomes.