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
Yeah this is an example of “lying with graphs 101”.
The data probably didn’t fit the narrative when they separate “always” and “sometimes”