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I remember many, many years ago when my dad decided to buy an old house for the rental income. The house itself was built at the turn of the last century and had originally been the servants quarters for a much larger house down the street. It was a charming little cottage, but required a lot of renovation before my dad could lease it out. But the one thing that my dad didn't count on was his largest expense: lead paint removal. The entire house, inside and out, was painted using lead paint. The contractor warned my dad that this 50 year old paint job could be killing us as we stood there, with lead dust flaking off the walls and into our lungs. That was all it took for my dad to remove my brother and I from the site and to sigh that his investment didn't seem as smart as it did at first.

I was reminded of that event when I read Kevin Drum's article this week in Mother Jones' on the correlations of lead toxicity and violent crimes, lower IQs and even ADHD.

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.

And with that we have our molecule: tetraethyl lead, the gasoline additive invented by General Motors in the 1920s to prevent knocking and pinging in high-performance engines. As auto sales boomed after World War II, and drivers in powerful new cars increasingly asked service station attendants to "fill 'er up with ethyl," they were unwittingly creating a crime wave two decades

Amazingly simple and yet compelling evidence. Rick Nevin has written a similar piece showing the same correlations in other countries. Per Drum, Nevin forecasts:

• The USA violent crime rate is now down about 50% from its peak in 1991, and I expect that the violent crime rate in Western Europe will be down by about 50% from its peak over the next 20 years, with the largest part of that decline over the next ten years.
• Eastern Europe will follow the same trend, but will take a few years longer because they left gasoline lead levels quite high through the end of the Soviet era.
• Crime will also plummet over the next 10 to 20 years in Latin America, where leaded gasoline use and air lead levels fell sharply from around 1990 through the mid-1990s.

It would be interesting if we took a far more holistic approach to these issues, looking at environmental issues as much as punitive measures.