Kevin Drum, a blogger for Mother Jones, has a provocative article out that sifts through mounds and mounds of research and finds a significant link between the phasing out of leaded gasoline and the overall decline in the rate of violent crime since the early 1990s. He begins with seminal research done by Rick Nevin, a consultant for the Department of Housing and Urban Development in the 1990s. To wit:

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.

Why offset by 20 years? Exposure to lead as children, he postulated, manifested itself as violent behavior in young adulthood. (Connections between lead exposure and a host of behavioral and cognitive problems has been long- and well-documented.) Now, as we all know, correlation is not causation. Nevin had the same concern:

maybe the real culprit in the United States was something else happening at the exact same time, but what are the odds of that same something happening at several different times in several different countries? Nevin collected lead data and crime data for Australia and found a close match. Ditto for Canada. And Great Britain and Finland and France and Italy and New Zealand and West Germany. Every time, the two curves fit each other astonishingly well. When I spoke to Nevin about this, I asked him if he had ever found a country that didn't fit the theory. "No," he replied. "Not one." Just this year, Tulane University researcher Howard Mielke published a paper with demographer Sammy Zahran on 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 overlay them with crime maps," he told me, "they realize they match up."

Furthermore:

Groups of children have been followed from the womb to adulthood, and higher childhood blood lead levels are consistently associated with higher adult arrest rates for violent crimes.

Now, obviously, violent crime is a complex phenomenon and Drum admits that lead isn’t the whole story. But it is a very large part of the overall story. Something we should be aware of when folks assume that environmental protection and cleanup is a major financial burden with no discernible benefit.