Comment: 90% of crime rate changes linked to lead exposure (Score 5, Informative) 424
Mother Jones recently published an article America's Real Criminal Element: Lead, detailing the correlation between decrease in environmental lead levels (mostly due to unleaded gasoline laws) and the decrease in crime rates (with a 20-year delay). The numbers are impressive, and they've correlated across areas of the country that enacted lead control laws at different times. The research is thorough and they make bold claims: "Gasoline lead may explain as much as 90 percent of the rise and fall of violent crime over the past half century." I highly recommend giving it a thorough read.