Marginal Revolution has a continuing series called "Markets in Everything" which highlights unusual markets. But for some reason they don't seem to have the opposite corollary, "Market Failures in Everything". I may not have their readership, but perhaps I can help anyhow.
MR pointed to an amazing NY Times article, In Raising the World’s I.Q., the Secret’s in the Salt.
The money quote is: "Worldwide, about two billion people — a third of the globe — get too little iodine, including hundreds of millions in India and China. Studies show that iodine deficiency is the leading preventable cause of mental retardation. Even moderate deficiency, especially in pregnant women and infants, lowers intelligence by 10 to 15 I.Q. points, shaving incalculable potential off a nation’s development."
And the solution is government regulation of private salt producers, forcing them to iodize the salt at a trivial cost, a little over a dollar a ton. The article details why this is necessary, but just on the surface it is obvious from the fact that universal iodization has never been market driven.