IQ is a very poor measure of intelligence and mostly shows your aptitude for taking the type of test they give to measure IQ.
You could be an absolutely brilliant Amazonian hunter-gatherer and you would fail every IQ test.
Hell, I knew a guy- so illiterate that he could barely sign his own name- but he was one of the best fiddle players I ever saw. Was he smart or stupid?
This is not to downplay the effect of lead on intelligence, I’m not saying it’s not there, I’m just saying this is a bad metric.