A lot of the silk plants I see in the dollar or craft stores, have wires imbedded in the stems to allow them to be bent and hold position. That is the part I'd be worried about. I have found some good looking plasic ones with no wires and used them in the past. If it was just the dyes you are concered about you could soak them in very warm water for a few days, allowing most of the dyes to leach.