I mean, the much more obvious sources of lead are paint and pipes, which are still present in many homes. The federal government estimates that about 30% of homes still have lead-based paint, and one nonprofit estimates that about 20% of utilities still have lead pipes somewhere in use. One depressing estimate is that roughly 70% of children in Chicago, the US's third largest city, are in households served by lead pipes.

Gun use may lead to lead exposure, sure, but lead itself was such a commonly used substance that guns aren't the only source of lead.