What material is used in the common 5mm LED?
Generally the plastic part is epoxy and the leadframe is mild steel with tin plating. 

This is not a complete description- the exact composition of the resin will include additives, for example. The bonding wire might be gold or possibly some other metal. There's a small amount of adhesive to bond the die to the lead frame too. Maybe there is some mold release compound clinging to the outside of the plastic. 

A reputable manufacturer should be able to tell you the package composition with reasonable precision.