Many people associate a fresh snowfall with pleasures such as hot chocolate and winter sports. But for city dwellers, it also can mean caked-on salt that sticks to shoes, clothing hems and cars. That’s because as soon as the mercury dips below freezing and precipitation is in the forecast, local governments start spreading de-icing salts to keep roads from freezing over.
These salts are typically a less-refined form of table salt, or sodium chloride, but also can include other compounds, such as magnesium chloride and potassium chloride. They work by lowering the freezing point of water.
De-icing salts also do extensive damage to autos, infrastructure and the environment. And cities use them in enormous quantities — nearly 20 million tons per year in the U.S. Snowbelt cities in Canada, Europe and Japan also heavily use de-icing salts.
But new options are in the works. I am a materials scientist seeking solutions for our overly salted sidewalks by analyzing ways in which the natural world deals with ice. Fish, insects and even some plants have learned to adapt to cold climates over hundreds of thousands of years by making their own antifreeze agents to survive subfreezing temperatures. By taking a page from nature, my colleagues and I hope to develop effective but more benign antifreeze compounds.
Harmful impacts of salt
As many drivers know too well, road salt reduces cars’ lives by speeding up the rusting process. A 2010 study estimated that the use of de-icing salts costs U.S. drivers $23.4 billion nationwide yearly in vehicle damage due to corrosion.
Road salts also damage the surfaces we drive on. They contain chlorine ions — atoms with a negative charge — that alter the chemistry of water and make it more corrosive when it comes in contact with materials such as concrete and steel.
Scientists have found insects and spiders in Alaska that create antifreeze proteins in their bodies that lower the freezing point of water by a few degrees.
De-icing salts have widespread effects in nature, too. If you drive along a forested road after a long snowy winter, you may notice that trees next to the road look a little more brown than the others. That’s because road salts displace minerals in soil and groundwater, creating a condition known as physiological drought.
This means that trees cannot take up water through their roots even if it is freely available in the soil. When natural drought conditions already exist, in such places as Colorado, physiological drought can increase the risk of wildfires by making plants more prone to ignition.
Streams, rivers and lakes are especially vulnerable to water runoff that contains de-icing salts. Chlorine from the salt can inhibit fish from spawning and reduce dissolved oxygen levels in the…