> almost definitely a small, negligible amount of lead in the solder in them

Emphasis on negligible. Assuming 0.07 to 0.28 ppm lead [1] in meteoroids, space is dosing us with half to 2 kg a year [2].

[1] https://www.sciencedirect.com/science/article/abs/pii/001670...

[2] https://earthsky.org/space/tons-of-extraterrestrial-dust-fal...