“each increase of 10 µg per deciliter in the lifetime average blood lead concentration was associated with a 4.6-point decrease in IQ” https://pmc.ncbi.nlm.nih.gov/articles/PMC4046839/

“cities/towns with more firearms had higher pediatric blood lead levels (highest quartile fully adjusted prevalence ratio ((aPR) = 1.18; 95% CI, 1.09, 1.30) with a significant increase in pediatric blood lead per increase in firearms” https://www.sciencedirect.com/science/article/abs/pii/S001393512300511X