Does the salt on the roads affect the environment?
-Hera Y., Moriches, NY
Good question, given that this year's especially snowy weather has prompted cities to dump millions of tons of salt on the roads. That's a lot of salt being introduced to environments where high concentrations of sodium chloride (the chemical name for rock salt and table salt) aren't otherwise present.
Salt is a natural compound (NaCl) that is typically harvested by evaporating the water from salt water or mining underground deposits. But if you've ever heard of “salting the earth,” you know that salt doesn't play very nice with flora and fauna outside of the ocean. For example, the strip of your lawn adjacent to the road may wither after your city spreads salt during the winter. Dead grass is a relatively minor consequence compared to the larger ecological impact, though.
Any salt spread on the road doesn’t stay on the road. It enters water runoff and eventually makes its way into streams, lakes, and groundwater. This can wreak havoc on water quality, especially where water turnover is low. NaCl contamination can strangle aquatic life by preventing oxygen from reaching the bottom layer of a body of water. It can damage vegetation and degrade soil fertility. On top of the environmental impact, it damages cars and transportation infrastructure.
It is difficult to unseat salt as the de-icer of choice, since the infrastructure to spread it is already in place, and it's simply cheap and effective. But environmental concerns, as well as cost and supply concerns, have prompted some cities to seek alternatives that supplement salt and reduce the amount needed. Polk County in Wisconsin is mixing their salt with cheese brine, a waste byproduct that extends the county's salt supplies and is effective at temperatures lower than a salt-only spread. More than 100 municipalities are using a beet concoction with their salt. This mixture is also more effective at lower temperatures, and the stickiness helps keep it on the road. De-icing roads is crucial for human safety, but we hope cities will continue to look for ways to make it safer for the environment too.