They're breathing far more dead skin. So are you, though.
Yes, but that's organic and pretty normal. Aren't meteors and say moon dust dangerous because its very sharp and jagged?
Once it’s flashed to a plasma and turned into sub-micron dust? Probably not. The danger if there is any would be if the remaining particulates (assuming it wasn’t mostly reduced to heat, light and some basic elements) are friable.
I would expect much more stuff to be in the air under zero gravity. On earth dust will settle on the ground but I assume in the ISS it will keep floating around.