How Unleaded Gas Cut Crime And Made Us All Safer

January 7, 2013

If you keep up with the news, you know how often violent crime makes headlines. But despite some heart-wrenching stories that have played out on 24-hour news channels in recent months and years, violent crime is on the decline in the U.S. -- and according to some theoreticians, we may have unleaded gasoline to thank for that.

In the current issue of Mother Jones, Kevin Drum looks at an interesting series of facts. Among them:

  • Rates of rape, assault, robbery, murder, and other violent crime peaked in many U.S. cities in the early 1990s, then went into decline.
  • Those declines have largely continued despite (a) a growing population of young men and (b) economic troubles like the Great Recession, both of which should've theoretically caused a spike in violent crime rates.
  • While some credit the declines to legislation like the Federal Assault Weapons Ban, violent crime has continued to abate, even though that particular ban expired in 2004.

How is this possible? Some point to increased incarceration rates, others to larger police forces, and still others to various forms of birth control, which helped couples manage the size of their families and all the attendant expenses.

But Drum suggests that the decline in violent crime may be due to a molecule -- namely, that of lead.


We've long known that lead can cause serious health problems in humans, especially children and pets. Even low levels of exposure have been shown to affect IQ and behavior.

Most of that research has come from studies of lead paint, which was banned in the U.S. in 1978. However violent crime in the U.S. took off in the 1960s and didn't really start declining until the early 1990s. In other words, there's no neat overlap between lead paint and violent crime.

However, economist Rick Nevin discovered that there is, in fact, a very close correlation between tailpipe emissions from leaded gasoline and violent crime. Those emissions began climbing during the 1940s, and in the 1960s, as the children of the 1940s reached adolescence and young adulthood, crime began to spike.

Soon afterward, the detrimental effects of leaded gas on the environment became clear, and its gradual phase-out began in 1973. Roughly two decades years later -- as children of the early 70s reached their late teens and early adulthood in the 1990s, crime began its steep decline.

As of January 1, 1996, the Clean Air Act outlawed the use of leaded gasoline in on-road vehicles, so you'd think that by about 2016, lead would be a non-contributing factor to crime rates in the U.S. But as Drum points out, lead doesn't disappear so easily. It hangs out in the atmosphere, and even more importantly, it penetrates the ground, where it remains hazardous. (To back that up, Drum posts data from a detailed study of lead levels in the soil of New Orleans and its correlation to crime rates.) A nationwide cleanup and prevention effort would cost around $20 billion today, but Drum claims that such an investment would generate $210 billion in returns via reduced crime and higher IQs.


Drum is a journalist, not a scientist, so his arguments don't carry the same weight as trained researchers in the field. However, the dangers of lead are very, very well documented, and Drum connects some very intriguing dots. At the very least, he's done a great job of generating thoughtful debate.

If you have time this Monday, be sure to check out his entire article -- and for comparison/contrast, you might also watch Steven Pinker's TED talk on the relatively peaceful era in which we live. As always, feel free to leave your comments below.

[via John Voelcker]

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