I am sure you are right, it was so widely used
Right, lead paint, the settled particulates from car exhaust from the days of leaded fuel, and even today brake linings and tires still have lead. Any lead in anything that moves will be shed into the surrounding landscape. There are other sources, but I asked myself if this should be hopeless, or if there might be a way to restore the soil and get rid of the lead. This is an extensive article about it, and it turns out there are certain plants, many of them actually, and tree species, that take up lead from the soil (phytoremediation):
(Image source: rawpixel.com) Lead is a toxic heavy metal that poses a significant risk to humans, wildlife and natural habitats, as heavy metals are not degraded in the environment and consequently…
deepgreenpermaculture.com
Again, it's a long article, but you may find it interesting. Would I eat a carrot that was grown to take the lead out of the soil? I think not, but an easily identifiable crop that you could move along to a different spot each year, such as the sunflower, would work and you would know not to eat the seeds.