Eh, I learned it primarily by word of mouth from gardening enthusiasts who are buying homes. But here’s one article about the phenomenon: https://www.hgtv.com/outdoors/gardens/planting-and-maintenance/when-to-test-garden-soil-for-lead-contamination-and-how-to-garde
I don’t have a lot of statistics to back it up except that it seems worse on the East Coast and Rust Belt
I2P is still around? I remember experimenting with it a decade ago. Sounds like it’s still a slow experience.