It is salt. That is all it is. 99% of the stuff at feed stores says not for human consumption or not for human use. Having spent years in feed mills, working at feed stores and on farms, working with veternarians, and so on, I will tell you there is not one medication there I would be afraid to use on myself if I had to, or one feed I would be afraid to eat under any circumstance. Just think farmers feed their animals this stuff. Their animals are their livelyhood, they usually treat thier animals better than themselvs.
We are talking about a bag of solar salt here, not an unknown chemical cocktail. Use the salt if you want, nothing in there that will harm you. I am 31 and have an engineering degree and just this morning I grabbed a handfull of wet cob from the bag and chewed on it on my way to work while drinking coffee. If the appocolypse comes tomorrow I will run to the nearest feed store as fast as I can and load up on salt, corn, wheat, rice bran, and antibiotics.