It's not so much from walls, but dust from joints around windows and doors.

But seriously: we vaporized 200,000 tons a year in gasoline. Where do you think it all went? Places with lots of cars: cities. Definitely do not eat food grown in a city garden- always use raised planters filled with country dirt.

https://archive.epa.gov/epa/aboutepa/epa-requires-phase-out-...

See figure 2 here:

https://www.edf.org/sites/default/files/the-hour-of-lead.pdf