<P> After later studies were conducted with a larger number of birds, the advisories were revised and another was added for cinnamon teal . Seven other species of duck were studied and found to have levels of mercury below EPA guidelines, thus being determined safe to eat . </P> <P> A study in 2010 concluded that the main source of the mercury is likely worldwide industry, rather than local sources . As water levels rise and fall, mercury accumulation does as well . About 16 percent of the mercury comes in from rivers, and 84 percent comes from the atmosphere in a non-toxic, inorganic form . The non-toxic mercury is converted into toxic methyl mercury by bacteria which thrive in the more saline water of the North arm affected by the causeway . </P> <P> Great Salt Lake contributes an estimated $1.3 billion annually to Utah's economy, including $1.1 billion from industry (primarily mineral extraction), $136 million from recreation, and $57 million from the harvest of brine shrimp . </P> <P> Solar evaporation ponds at the edges of the lake produce salts and brine (water with high salt quantity). Minerals extracted from the lake include: sodium chloride (common salt), used in water softeners, salt lick blocks for livestock, and to melt ice on local roadways (food - grade salt is not produced from the lake, as it would require further costly processing to ensure its purity); potassium sulfate, used as a commercial fertilizer; and magnesium - chloride brine, used in the production of magnesium metal, chlorine gas, and as a dust suppressant . US Magnesium operates a plant on the southwest shore of the lake, which produces 14 percent of the worldwide supply of magnesium, more than any other North American magnesium operation . Mineral - extraction companies operating on the lake pay royalties on their products to the State of Utah, which owns the lake . </P>

Where does the salt come from in utah