Trying to find it I stumbled upon this https://www.pnas.org/doi/10.1073/pnas.2118631119 -> "The average lead-linked loss in cognitive ability was 2.6 IQ points per person as of 2015." Quite insane to think about. Obviously that's more than merely leaded gasoline though.
Regarding the map, not what I was looking for, but https://media.springernature.com/full/springer-static/image/... from https://www.nature.com/articles/s43247-025-02735-x is interesting.
Still an ongoing issue, interesting article, some insane metrics in that image though. Lower image is showing `relative IQ cost` for children 0-9 years of age as of 2019,... as in `estimated loss of earning due to less IQ`, boy oh boy, let that sink in: Starting with incomplete exposure data, estimating the resulting IQ loss, then translating that into lifetime earnings (projected somehow into the future economy)...