Look down at your pant hems. How about your shoes? Are they covered in a ghostly white film?

Recent snowstorms in the area dumped a ton of snow and ice. Then came the snowplows and then, the dreaded road salt.

That salt might get rid of the snow in no time flat but Chicagoans know all too well how it lingers on in other ways.

Environmentalists have long raised concerns about the effects of salt runoff and seepage on our groundwater—and the region’s plant and animal life.

It turns out that de-icers also have a big impact on our roads and bridges.

To find out more, we called David Schulz, director of the Infrastructure Technology Institute at Northwestern University.

He says road salt is a necessary evil in our car-dependent world.