It's been pretty well accepted for decades that this is the case:
>A highly significant association was found between lead exposure and children's IQ (P < 0.001)... There was no evidence that the effect was limited to disadvantaged children and there was a suggestion of the opposite.
>A highly significant association was found between lead exposure and children's IQ (P < 0.001)... There was no evidence that the effect was limited to disadvantaged children and there was a suggestion of the opposite.
https://pubmed.ncbi.nlm.nih.gov/8162884/
That's a 1994 meta-study that turned up in 30 seconds of googling, and I'm sure more recent evidence also exists.