That's very possible as I have never looked up the list for both. I do believe rock dusts contain a certain level of metals as well. Not sure if it's less or more than kelp if kelp does contain any. Again I've never looked but was just giving advice on alternatives. Someone with more knowledge will chime in to inform better options. I do know you should stay away from pacific kelp if at all possible as that's where a lot of nuclear waste is leaking yet.