We Got The Lead Out, But Replaced It With . . . What?

I recently heard of a few data points I found interesting. The first, from Mother Jones Magazine, presents a strong case linking violent crime with earlier exposure to tetraethyl lead, "the gasoline additive invented by General Motors in the 1920s to prevent knocking and pinging in high-performance engines." As automotive use increased, so increased the lead flowing from the tailpipes; in cities, the concentration of cars increased each city dweller's exposure. As lead was phased out, the exposure likewise phased out. Researcher Rick Nevin made the first connection:

The biggest source of lead in the postwar era, it turns out, wasn't paint. It was leaded gasoline. And 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.

So Nevin dove in further, digging up detailed data on lead emissions and crime rates to see if the similarity of the curves was as good as it seemed. It turned out to be even better: In a 2000 paper (PDF) 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.

(I emboldened.)

( Ah, but that was only one data point, and I did promise two! )

X-Posted to talk_politics.