There is a study about different African countries that could be compared to the average IQ levels in these countries: > In total, 144 of the 593 paints analyzed (24 percent of paints) contained dangerously high lead concentrations above 10,000 ppm. However, the percentage of paints included in the study with a lead content above 10,000 varied substantially between countries from zero percent in Guinea to 54 percent in Nigeria. https://ipen.org/documents/africa-lead-paint A first random sample shows the opposite: Average IQ in Guinea: 67 Average IQ in Nigeria: 84 .. but maybe there is more: > Furthermore, 22 paints from nine countries contained extremely high lead levels of 100,000 ppm or more.