Q&A: What are the impacts of road salt on the environment, vehicles and more?

UNIVERSITY PARK, Pa. — It’s sprinkled on sidewalks and driveways, tracked into building entryways, and the Pennsylvania Department of Transportation uses almost 600,000 tons of it each winter — but what exactly is road salt, and what are its impacts?

For this Q&A, Bill Burgos, Penn State professor of environmental engineering in the College of Engineering, spoke about why road salt — one of the most common tools for de-icing roads and walkways in Pennsylvania — is used, what its impacts are, and what some alternatives might be.

Q: What is road salt? How and under what conditions does it work to de-ice roadways?

Burgos: From a mineralogical standpoint, road salt is halite, or sodium chloride. Road salt is different from table salt in that the halite is processed to remove impurities and ground to a uniform small particle size. Table salt is safe for human consumption while road salt is not.

Road salt is applied as both “anti-icing” and “de-icing” products. Anti-icing road salts are applied in liquid form before a snow or ice storm event. Sodium chloride on the road helps lower the freezing point of water — for example, salt water in the ocean freezes at a lower temperature compared to freshwater lakes — and prevents ice from forming or reforming. De-icing road salts are applied as solid coarse particles that will dissolve and help lower the melting point of water to prevent ice from forming — that is, they don’t “melt” the ice — and improve tire traction. In solid form, road salts might be blended with sand or cinders to further improve traction.

Additives in anti-icing liquids are used to create a more uniform application through the spreading bar on a truck — for example, creating the parallel lines on treated roads. Additives in de-icing solids are used to avoid clumping of the spread materials.

It’s important to note that sodium chloride can only lower the freezing point of water to 15 degrees Fahrenheit (F). Therefore, during particularly frigid times, sodium chloride is not effective to remove ice from road surfaces. Instead, gravel, sand and/or cinders would be used to improve traction. Alternatively, calcium chloride or magnesium chloride salts could be used because they can lower the freezing point of water to -20F and -13F, respectively.

Q: What are its advantages and disadvantages? Why do we use it in Pennsylvania, and is it what other states use as well?

Burgos: The great advantage of road salt is improved traffic safety. Disadvantages of road salt are the corrosion of the undersides of our vehicles and the salinization of runoff and our receiving streams. As water becomes more saline — that is, more salty — certain animals and plants become stressed and struggle to survive. As water becomes more saline, corrosion reactions that degrade our infrastructure — for example, leading to cracking concrete and asphalt, and corrosion of steel — occur more quickly.

Pennsylvania uses road salt, or sodium chloride, to keep our roads safe in the winter. Most other states also use sodium chloride. Most extremely cold regions focus on improved traction versus trying to melt ice. While calcium chloride or magnesium chloride could work, they are more expensive than materials used to improve traction.

Q: What are the environmental impacts of road salt?

Burgos: Salinization of adjacent freshwater is the primary impact of road salt.

But in Pennsylvania and several other states, produced waters from oil and gas wells have been approved for use as deicers and dust suppressants and are most likely in use in counties with conventional oil and gas wells, mainly in the northwest part of the state. Oil and gas-produced waters in Pennsylvania are hyper-saline — that is, five- to 10-times saltier than seawater — so they can lower the melting point of water on the road. However, oil and gas-produced waters also contain elevated concentrations of radioactive radium, other heavy metals and petroleum hydrocarbons. The use of oil and gas produced waters as deicers create several additional environmental impacts from the uncontrolled release of these contaminants, in addition to freshwater salinization.

Q: What are some alternatives to salt for making roads drivable and safe in the wintertime? What are the advantages and disadvantages to these alternatives?

Burgos: There are few alternatives to salt for improving winter traffic safety. A great new practice has been the use of applying anti-icing liquids before a storm. Studies have shown that pre-application of liquid sodium chloride requires less salt, which leads to less freshwater salinization, than solid road salt to achieve the same traffic safety.

Q: Based on your research, what options are a good solution to keeping winter roads safe when taking into account financial cost, environmental impact and effectiveness?

Burgos: The judicious application of road salt is the best solution. Apply the minimum amount of liquids needed before the storm to save money, because you're using less product, and limit environmental impacts since there is less salinization. Blend in more traction materials into the solids to lessen the amount of salt added to the environment.