Well, there are many preparations of solder, for different applications. Traditional solder is made of lead, sometimes with a rosin 'flux' added to it to help adhesion to the metal being soldered. Flux is often made of tree sap, and I imagine would be quite tarry and bod for you if there was any residue left, and lead- well, that one goes without saying! More modern solders can be purchased lead-free; these are much more expensive and made of tin.
The safest method would actually be BRAZING, which uses metal such as brass that requires a lot higher temperature to melt, or of course welding, where the metal itself is melted together without use of a second metal.

Personally, I'd avoid anything containing lead. The others probably won't give you issues at Bic temperature, lol.