I have some old pieces of Lava rock i got from a LFS awile back (The big red porus ones with a big hole in the center), they where in my old saltwater aquarium, but i heard they can contain toxic metals in them.
If they were in a previous tank without problem, they are likely safe. I've used lava rock without problems in my reef. I've heard people say it can cause problems, but have never talked to anyone who actually had a problem.