This is basically a follow-up to the post on Colloidal Silver, immediately below. Read it for the details, but the main thing you need to know is that if enough silver builds up inside the body, a condition called Argyria results. This is not life-threatening; it just causes skin, tissues, or organs to turn blue, grey, or black.
I put a link to that post on Facebook, and one of my friends remarked that if her husband manages to turn blue, "we all get to vote for Smurf names!"
Well, that reminded me of something I'd read years ago, which said that the Smurfs were probably taken from a bit of germanic folklore about creatures called Kobolds, who were frequently represented as small, blue-skinned, creatures who haunted mines. (Those of you who remember kobolds as weak but exceedingly annoying cannon fodder from D'n'D, be advised: Dungeons and Dragons is a great repository for misrepresentations of folklore from all over the world, as well as other data. Two-handed swords weighed fifteen pounds? Seriously?) The wikipedia article suggests that the name "Kobold" can actually be applied to a wide number of different kind of creatures, rather like the Celtic "Faerie". In fact, judging by the descriptions, "Kobold" and "Faerie" look like two different terms for the same kind of beings. (And, now that I think of it, Faeries are sometimes referred to as the Grey Folk.)
Staying with the idea of Kobolds as small, blue-skinned beings who hang out in mines, though... I can't help but wonder if the folklore grew out of early cases of argyria. There are cases of argyria among workers in the silver industry, presumably from breathing too much silver dust; and I can easily imagine the same thing happening to people carving ore out of mineshafts.
I don't know enough about early mining practices, or the types of ore found in that area of the world, to be sure; but it certainly seems possible.