In 2013 U.S. officials applied about 17 million tons of salt to roads. Salt lowers the freezing temperature of water and thus melts street-clogging snow and ice. But its public safety benefits do come with some ecological drawbacks.

Salt not only damages metal and concrete, it contaminates drinking water, kills vegetation, and accumulates in streams, lakes, reservoirs, and groundwater, harming aquatic plants and animals.  As much as 70% of salt spread on roadways stays within the watershed.

Now that we know where the salt goes, where does it come from?

The U.S. is the second-largest road salt producer worldwide after China, but we also import a good deal of the salt it uses to coat its streets. At 12 million tons per year, America is the biggest salt importer in the world. Most salt imports come from Canada and Chile.

Former Salt Mine in Remlingen, Germany

Rock salt is formed in the ocean.  The chlorine coming from the volcanoes at the bottom of the ocean mixes with the sodium washing off the continents with rainwater to create salt.  There is a lot of salt in the oceans, but it is only about 3½% of the worlds salt supply.   Areas with thick salt deposits was probably one where an ocean was, but has since evaporated.

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