Rock slat is widely used to melt ice and snow.
When considering substances that damage our environment, most people do not immediately think of rock salt. People hardly notice it when it is sprinkled on the ground after a snow or ice storm. But the silent harm that using rock salt does is affecting bodies of water and aquatic life.
“Salt is something of a ticking time bomb for freshwater,” explains Riverkeeper President and Earth Institute adjunct professor Paul Gallay. “Studies suggest that the increasing concentrations we see in many places may be the result of road salt spread decades ago, which reached groundwater, and is only now slowly reaching surface waters.”
We started using road salt in the 1940s to melt ice. Rock salt lowers the freezing point of water and is usually able to melt ice around temperatures of 15-20 degrees Fahrenheit. Its chemical formula is NaCl, and this makes it not the most effective substance for dissolving ions.
NaCl dissolves only into Na+ and Cl-. The higher number of ions that a compound dissociates into, the more effect it can have on lowering the freezing point.
Road salt can have negative effects on the environment. The salt eventually washes into soil, lakes, and streams. There has been an increase in salinity in 37% of the drainage area of the contiguous United States. This can contaminate drinking water reservoirs and wells as water from these areas exceed EPA-approved salt levels.
The chloride from the salt also affects aquatic life in freshwater ecosystems. The effects can be seen in aquatic species’ growth and reproduction, impacting food sources and osmoregulation, the maintenance of fluid pressure in an organism. Oxygen depletion in bodies of water is also caused by runoff containing road salt.
As 8-12 million tons of salt are dumped on roads each year, they have lasting impacts.
Aquatic ecologist Andrew Juhl explains that “Once salt gets into the soil, or into a waterway, there really are no biological processes that will remove it. Salt can leave the system through transport and it can be diluted by fresher water coming in so that the levels become less concerning. However, without transport out of the system, like in an isolated lake or aquifer, the salt will continue to persist over very long time scales.”
There are some alternatives to rock salt that we can consider. Stone grits, or sand, make it safer to walk and drive on icy surfaces but do not melt the ice and snow. This is mainly the only alternative that is viable as others are simply chemical alternatives or financially unfeasible. It is difficult to grapple with this problem because road salt is something that people usually put out of their minds.
Like many things that harm our environment, the general public does not notice the effects until it is too late. Humans have come to rely on it, and there has yet to be a viable alternative. We can keep the effects in mind, though, and actively observe our environment to better understand it.
