There is a city tree, an American Elm, that has a diameter of about
4'. It is a source of sewer backups, the roots get into the pipes.
This tree is on the tree belt and between two houses. I don't really
care for all the extra trouble because of the tree but don't want to
see it destroyed. Today a neighbor told me that he had poured copper
sulfate around the base of the tree. I understand that this is
poisonous to the tree roots.

Can this really kill a large tree?, it's about 80 ft tall with a
spread of at least 50'. Is there something I can do to neutralize the
copper sulfate? If the copper sulfate does harm the tree what should
I look for and what kind of timetable?

Is there something that I can put around the tree that will absorb the
copper sulfate if the neighbor adds more?

The tree is in MA and I think that this is not legal. Any ideas on
how to best proceed to first save the tree and second stop this nut?