You should not use "potting soil" for sals. The dangers are from the added fertilizer and the bead-sized bits of perlite and/or styrofoam that are in it. If swallowed, these bits can lodge in the digestive tract. Vermiculite is just tiny bits of mica (a mineral), which is fairly harmless unless it is the right size for swallowing. Some amphibian products (Jungle Mix) contain finely crushed vermiculite, and it's probably not bad. It is also OK to use plain old "top soil" or even soil from outdoors.