A method for inhibiting mercury from leaching from a land-filled arc discharge lamp containing a quantity of elemental mercury at least partially convertible to soluble mercury, provides for including within the lamp a quantity of a non-metallic copper-containing compound and an ingredient X, said ingredient X including a noble metal or a noble metal compound selected from the group consisting of silver and compounds of silver, gold and platinum, and a lamp containing same. The inhibiting compound is preferably included with the basing cement.