As much of the country endures from the heavy snowfall and bitter cold that has marked the start of 2014, municipalities in 26 states will rely on a crucial tool in clearing their roads: salt. Because the freezing point of salty water is a lower temperature than pure water, scattering some salt atop ice or snow can help accelerate the melting process, opening up the roads to traffic that much sooner.
It’s estimated that more than 22 million tons of salt are scattered on the roads of the U.S. annually—about 137 pounds of salt for every American. But all that salt has to go somewhere. After it dissolves—and is split into sodium and chloride ions—it gets carried away via runoff and deposited into both surface water (streams, lakes and rivers) and the groundwater under our feet. Consider how easily salt can corrode your car.
Unsurprisingly, it’s also a problem for the surrounding environment—so much that in 2004, Canada categorized road salt as a toxin and placed new guidelines on its use. And as more and more of the U.S. becomes urbanized and suburbanized, and as a greater number of roads criss-cross the landscape, the mounting piles of salt we dump on them may be getting to be a bigger problem than ever. Data from long-term studies of watersheds bear this out.
A group of scientists that tracked salt levels from 1952 to 1998 in the Mohawk River in Upstate New York, for instance, found that concentrations of sodium and chloride increased by 130 and 243 percent, respectively, with road salting the primary reason as the surround area became more developed.
More recently, a study of a stream in southeastern New York State that was monitored from 1986 to 2005 found a similar pattern, with significant annual increases and road salting to blame for an estimated 91 percent of sodium chloride in the watershed.
What Happens to All the Salt We Dump On the Roads?