Well, even if the plant isn't deadly, and your fertilizer isn't deadly,
you still don't know what the previous owner has done insofaras
spraying, etc., and what contaminants might be in the media or on the
leaves. In the past, I've been rather cavalier about toxic
substances--BUT since I've garnered cats (one of whom like to use
orchid leaves as floss), I'm more cautious. I repot plants when I get
them and don't use pesticides as a free-for-all spray. I'm not sure WHY
you want to know whether orchids are poisonous, but if you're having a
party and want to use orchid flowers as platter garnishes, you might
want to rethink.