Jesus wept. Nobody is putting blackboard chalk and nicotine into flour mate. UK-milled white and brown flour has mandatory calcium, iron, thiamin and niacin added because that brings it back up to match the nutritional profile of wholemeal flour. Nothing there to worry about. Individual millers add other things, like additional enzymes (to bolster the exact same ones already naturally in the flour) to assist raising, and of course the usual additives to self-raising flour needed to make it rise without the need for separate bicarb.
Wikipedia is free to read, you know.