Anyone who lives in Minnesota appreciates the value of salt in its non-culinary form.
The massive plows that push the snow off of highways leave a layer of salt in their trail, and the crystals prevent dangerous layers of ice from forming. In Minnesota alone, more than 350,000 tons of salt is dumped on the winter roads each year, along with almost 200,000 gallons of salt brine.
While the salt creates clear roads for drivers, a new federal study shows that levels of chloride, a component of salt, are high enough in more than 40 percent of urban streams to threaten aquatic life. Urban streams carried an average of 88 tons of chloride per square mile of drainage area compared to 6 tons in streams in forests. In comparison to the 40 percent of urban streams that exceeded federal safety limits on chloride, only 4 percent of rural streams exceeded those limits.
The study from the U.S. Geological Survey also found that as the chloride levels in streams have increased as cities have turned more and more to salt to deice roads. The researchers noted that the expansion of roads and parking lots that require deicing is also contributing to the problem.
Jim Dawson reports for Inside Science News Service, which is supported by the American Institute of Physics, a not-for-profit publisher of scientific journals.