Leaded gas was banned in 1996, but exposure to the poison cost people born before then several IQ points on average, researchers estimated.
(On a historical note, it is theorized that the Romans also suffered from lead poisoning, as their aqueducts were lined with lead to seal them. It is theorized that the drop in intelligence was one of many factors that lead to the fall of the Roman Empire.)
I worked at a gas station back in the sixties, that explains a lot!
The correlation between adult criminal behavior and childhood exposure to lead is extremely robust more than poverty, income inequality or race. Mother Jones published some very enlightening studies a few years back.