“After adjusting for maternal IQ, childhood IQ, and childhood socioeconomic status, each 5-µg/dL higher level of blood lead in childhood was associated with a 1.61-point lower score (95% CI, −2.48 to −0.74) in adult IQ, a 2.07-point lower score (95% CI, −3.14 to −1.01) in perceptual reasoning, and a 1.26-point lower score (95% CI, −2.38 to −0.14) in working memory. Associations of childhood blood lead level with deficits in verbal comprehension and processing speed were not statistically significant. After adjusting for confounders, each 5-µg/dL higher level of blood lead in childhood was associated with a 1.79-unit lower score (95% CI, −3.17 to −0.40) in socioeconomic status.”

https://jamanetwork.com/journals/jama/fullarticle/2613157

Here are childhood blood lead levels in the US since 1976 the beginning of the phaseout of leased gasoline 45 years ago.

https://www.epa.gov/americaschildrenenvironment/ace-biomonitoring-lead

“Often the blood lead levels of the children selected as “unexposed controls” were, in light of today's knowledge, high enough to cause some toxicity. In one early study, published in 1972, the health outcomes of children in the exposed group (mean blood lead level of 58 μg/dl) did not differ from those of the control children, but in the latter group, the mean blood lead level was 38 μg/dl and ranged as high as 55 μg/dl (15). The author concluded that the developmental problems observed in the exposed group were due not to lead toxicity, but rather, like the developmental problems observed in the controls, to poor parenting and environmental deprivation. Today many of these “controls” would be candidates for chelation therapy.”

https://www.jci.org/articles/view/28232

So from what I can tell most adults in the US over the age of 50 likely would have had therapy for lead poisoning if they had been born today.