Since we are still under several feet of snow here at National Geographic headquarters in Washington, DC, with more snow on the way, now is as good a time as any to talk about the chemicals used to de-ice the roads.
The most commonly used, and least expensive, de-icing chemical is sodum chloride (or rock salt), which is the same salt you use on your food. Millions of tons of salt are poured on roadways around the country, but where all that salt goes after the snow has melted has garnered more attention recently.
Once the snow melts, the salt dissolves and the chloride ions end up in soil and water, affecting everything from the bacteria in the soil to trees, large mammals, birds, fish, and possibly humans.
Only a small increase in the chloride content of soil can kill off important bacteria that help break down plant matter, which can change soil fertility and erosion properties.
Pine trees are especially sensitive to increased chloride levels, and plants that can tolerate higher chloride levels, like cattails, can move in and choke out other native species.
Birds can’t distinguish between pebbles, which they require to digest their food, and salt grains, and some studies suggest that swallowing a few large road salt grains can be fatal. Larger animals, like deer, elk, and moose, like to lick the salt off the roads, which puts them at increased risk to be hit by traffic.
Once the salty runoff hits freshwater streams and lakes, it can disrupt oxygen absorption in the water, and stress fish and aquatic creatures that live on the bottom of streams and ponds. The melting caused by the salt can also lift toxic chemicals and sediment off roadways into the water system.
Road salt has little effect on human health, but it is sometimes possible to taste a little salt in your drinking water after a winter of heavy salting. Increased salt intake can cause hypertension (high blood pressure) or make it worse. Most human inconveniences come from corrosion the salt causes on vehicles, bridges, and structural steel.
Other, more environmentally safe options have popped up as alternatives to rock salt. Calcium Magnesium Acetate is less harmful to the environment and works at lower temperatures. Urea, a fertilizer, can also be used and it will actually help plants, as does potassium chloride to some extent (although chloride ions still end up in the environment). A product called SafePaw has been selected by the Vancouver Olympic Committee to be used as an environmentally-safe deicer in its sensitive mountain ecosystems. And, finally, Missouri is using a mixture of rock salt and beet juice to keep roads clear.