As noted in another comment, I wouldn't consider Polonium to be "harmless."
But I grew up in an environment that would cause most parents, today, to defecate masonry. I grew up in Africa, and we had some really fun critters going through our backyard, like Black Mambas, Gaboon Vipers, and even the damn bugs were nasty. Bug bites could hurt for a month.
I somehow survived.
But it was just "minute traces."