Just thinking, there's no guarantee that terracotta is safe either. You don't know where the clay came from, and even though it is baked (which would kill bacteria and other pathogens) soil-borne toxins could still leach out of the clay.
I got some terracotta pots from Lowe's a couple of years ago, and broke one before I was able to plant it. Discovered that there was a layer of the red clay on the outside surfaces of the pot, but inside that there was plain grey clay.