All the small airplanes spewing leaded gas fumes, and that’s spread all over this country. As I understand it, leaded fuel is still used in them because it’s more important to stay running and not fall out of the sky than to worry about a few emissions. And the reason we don’t have it on the street anymore is it poisons catalytic converters.
Years ago (maybe 47?) my parents gave me and my sister a fish tank. After about a month the fish started dying and we kept replacing them. We did many water changes but it kept happening. Turns out a gas station in the area had a leak and they didn’t say that lead was going to be the problem, it was MTBE. They had to put an aerator and filter on the aquifer