With pathogens, my standards go the other way: I prefer proof they're not spread before using them. It is very reasonable to assume that grating metals against

With pathogens, my standards go the other way: I prefer proof they're not spread before using them. It is very reasonable to assume that grating metals against each other will create dust. That's what happens in a tip cleaner. And as for the sponges, I can see very small balls of solder on them. And I would call balls smaller than I can see "dust". Should I just assume that there is a lower bound to their size? That they're not there because I can't see them?