Define "Hazardous". I've seen prints of all kinds toned in anything from coffee to Uranium. Uranium and Mercury being on one extreme end (definitely in the Hazardous range), coffee being the other. I've even heard of bodily fluids being used (don't ask). A lot of toners would fall in the middle between mercury and coffee. To me, most toners are perfectly safe so long as you use reasonable precautions - rubber gloves, don't drink it, don't put it up your nose. Even sepia toner is more stinky than harmful. Just use well-ventilated and you're fine.