To be clear, everyone alive today is still on average multiple iq points dumber than they would have been had we not burned tetraethyl lead 50 years ago, even though it has been banned for quite a while. Lead is THAT toxic.
Any source for this? Most of the research I've seen with regards to lead and IQ is correlational and could be confounded by intelligence being correlated with income which is associated with living in places with less lead exposure.
Basically the IQ gap between the lead exposed and non exposed has stayed the same even though the amount of lead in the bloodstream has dropped by orders of magnitude. So either the first part of lead exposure is 100x more damaging then the 100th part of lead exposure (which animal models do not bear out) or a lot of the lead exposure IQ research is confounded.
I believe when in life you are exposed makes a difference too. Children are at a higher risk for being harmed by lead for a number of reasons including having less blood than an adult, and being more likely to eat paint chips off the ground than (most) adults. I'd imagine that lead replacing calcium in the brain during critical developmental periods also matters a lot.
