I've seem a number of bronze tubes that have been half-embedded in concrete for at least 50 years. The bronze that was next to the concrete doesn't seem any worse for wear, although this may depend on the type of concrete. Some which is fine and seals tightly against the bronze will not allow water in, and that's good.
The bronze that remains exposed to the elements is the part that is dissolved by the acid rain, as I think has already been mentioned. Almost any kind of paint (NOT epoxy) could be used to keep the elements off of the surface. If they want it to be the same color, gold paint could be used, or the patina color could be matched by a blended paint. Wax is OK but doesn't last long, and it will keep the paint from adhering when someone finally decides they want it painted. Any paint used must be of a type that isn't permanent, as being able to reverse the process (unpaint it) is one of the universal rules of conserving such objects.
