The Road to Water Contamination: Road Salts Environmental Impact
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As winter begins to come to an end, warming temperatures and sunny days melt the snow around us, bringing a taste of spring and promising good weather to come. But what happens to snow as it melts? Where does it end up? And what does it take with it? Our biggest hitchhiker when it comes to snow melt is the very thing we use to combat snow and ice: Road salt. Today, we’re going to take an in depth exploration into road salt, a variety of Sodium Chloride, to understand its origin, use, and impacts.
Sodium chloride is a naturally occurring molecule found in nature through the process of weathering, dissolving, and precipitation. Individual ions of both sodium and chloride are picked up by water as rocks are naturally weathered. These ions are then dissolved and suspended in water until high enough concentrations of each are reached, typically through water evaporation. When enough ions are present, they begin to interact, binding together and forming a solid white, crystalline structure. Its likely in your home right now— in the form of table salt used in cooking. Think of when you add said salt to a boiling pot of water. The salt dissolves and as the water heats and begins to evaporate, that salt becomes concentrated. Once the pot begins to cool, you may begin to see a white crust forming on the sides. That is how salt deposits form naturally in nature! These deposits– typically from ancient seas– are what we now mine today.
*Fun fact, the largest salt mine in the United States resides in Detroit, MI.
While salt has been mined for centuries, the history of road salt in the U.S. begins in New Hampshire, 1938. The state began to experiment with sodium chloride as a tool for deicing due to its ability to lower the freezing point of water. By the 1940’s sodium chloride was mined in excess to de-ice military equipment during WWII, and any overabundance was used to salt roads and paths. Noting its success, its use grew, until eventually salt was being used to treat roads nationwide! As the country continued to expand, so did its use of salt. In recent years, the United States averages 15 to 32 million metric tons of road salt used each year.
So what does this have to do with the environment? Road salt is a naturally occurring substance, imperative in making roadways and sidewalks safe for human travel. While it is the same as salt utilized by plants and animals for many biological functions- including water intake and our own blood pressure- issues begin to arise not because it is simply used, but because of its overuse. This article is not to dissuade readers from using salt to make roads and pathways safer, but rather to consider the amount being used after understanding its effects.
And what exactly are those effects?
Many of the impacts caused by road salt are not due to the compound as a whole, but rather its individual ions (sodium and chloride). Because road salt dissolves in water, these ions can easily be transported by runoff. Hitchhiking its way across the ground and through soil within water, these ions make their way into rivers, lakes, streams, and groundwater reserves.
When a lot of road salt is used, these ions end up highly concentrated in these waterways, each with their own individual effects.
While the effects of sodium are less prominent, in high concentrations, these ions can affect the natural level of nutrients found in soil and freshwater. This can impact vegetation by making it more difficult for plants to absorb the right nutrients needed to thrive. In addition, high levels of sodium affect the quality of drinking water, and can become a concern for those with restricted or low-sodium diets.
The bigger threat to aquatic environments is chloride. Chloride is highly soluble in water, meaning it can be transported easily, and for long distances. There is no fast process in which chloride is metabolized or taken up by vegetation. Where it lands is where it stays. While naturally found in freshwater, high concentrations of chloride can have a lasting impact on aquatic life at anything greater than 150 ppm (parts per million), or even become toxic to aquatic life ( ≥322 ppm) like our frogs, fish, turtles, and insects.
Let's get personal
To understand the impacts more clearly, we here at Woldumar ordered two chloride tests from Stroud Water Research Center in an attempt to gauge how road salt has affected the nature center. For the first sample, we tested the woodland pond, which experiences surface runoff, but no direct drainage from roadways. Our second test was conducted on the Hunter-Branches storm drain outlet, which directly drains from local roadways and empties into the Grand River.
Once a sample was collected from each site, chloride QuantTabs test strips were inserted into each sample. After a couple of minutes, the chloride concentrations were recorded as such:
Woodland Pond: ~ 29 PPM Hunter-Branches Storm Drain: ~354-381 PPM
From these results, we can directly see how elevated chloride concentrations are in waterways with road runoff. It should be noted that these samples were taken without the presence of inclement weather, where salt was not currently being added to roadways. If it had been, the concentrations would have likely increased.
While these tests were only conducted on-site at Woldumar, many other tests have been done around the state in recent years, and almost all show the same trend: Salt pollution is on the rise.
So what?
So what can we as a community do about it? Most road salt usage comes from cities, counties, and private plow companies. While there have been developments in the quest to replace sodium chloride with a more sustainable alternative (beet juice brines, calcium chloride, and magnesium chloride as examples), these alternatives can be unsustainable due to cost, availability, and even their own environmental drawbacks. Until further research is done, limiting the usage of sodium chloride even at an individual level can still help to lessen its impact.
Some tips include:
Shovel snow first: Shoveling snow before salting reduces the amount of salt needed to clear walkways and driveways of snow and ice.
Shovel early: when temperatures drop, snow can compact and become harder to remove. Shoveling snow before it has the chance to freeze to a surface prevents the buildup of ice.
Use deicers sparingly: Salt works more effectively as it melts, creating a saltwater solution known as a brine. Even a small amount of salt can cover larger surfaces as it mixes with water and spreads.
While the usage of salt has hit near record levels in recent years, there’s still time to limit its use and reverse its effects before our freshwater reserves are permanently impacted. For those that have taken the time to read this article, you’ve already taken the first step toward limiting your impact.
Stay Curious,
Ashley
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Sources:
https://www.des.nh.gov/sites/g/files/ehbemt341/files/documents/wmb-4.pdf
https://www.caryinstitute.org/sites/default/files/public/reprints/report_road_salt_2010.pdf https://www.draglamsalt.com/blogs/the-history-of-road-salt
https://www.caryinstitute.org/news-insights/feature/road-salt-tips-homeowners
