Anyone know of or can recommend a brand of "Food Grade" epsom salts?

I have read a number of places that it is ideal to get a "food grade" brand of epsom salts, otherwise the bath salts could have been processed with toxins.

Does anyone have any thoughts on this or a brand of magnesium salts they recommend?

I have searched through Neurotalk and generally online and haven't seen any recommendations along these lines.

Thanks for any thoughts,

Natalie