Photos courtesy of the University of Minnesota Duluth
In Minnesota, salt is essential for keeping roads safe in the winter. But what if the salt we put on the roads and sidewalks doesn’t degrade? What happens when it only accumulates in the ecosystem?
“Some people think more salt will be safer, but that is not always true,” says Chan Lan Chun, PhD, a professor in the Department of Civil and Environmental Engineering at the University of Minnesota Duluth (UMD) and an environmental engineer at the University’s Natural Resources Research Institute (NRRI). Accumulating salt, she adds, can have a cascade effect on the nearby ecosystem.
So Chun and her team are working to identify road-safe, environmentally friendly alternatives to de-icing, as well as methods to prevent ice from forming in the first place — something Chun calls “anti-icing.”
Maxwell Brubaker and Chan Lan Chun, PhD, take water samples from Lake Superior.
Their dual-ended goal is to reduce road salt use and better understand its effect on the ecosystem.
De-icing decision-making
For years, experts have noticed that the salt concentration in Lake Superior and other freshwater systems is on the rise, often surging after winter.
“It is very important we apply the right amount [of salt],” says Chun. “At the same time, safety is first. So we cannot avoid salt altogether.”
While most individuals and municipalities use sodium chloride to salt roads and sidewalks, Chun says alternatives like calcium chloride and potassium acetate also work. While these alternatives are more expensive, Chun says they are also more effective. “That means you can use less.”
And Minnesotans can use less salt at home, too, if they clear snow at the right times. “If we can do the physical shovel when the sun is out there, we can reduce a lot of salt use,” she says.
Abrasive materials like sand and mulch can also work well on sidewalks and side streets. Plus, using these materials instead of salt also can lower the local carbon footprint, since they can be sourced locally rather than shipped in.
Experts at the Minnesota Department of Transportation (MnDOT) have been looking into potassium acetate as an alternative to road salt because of its biodegradable qualities. But it appears to be more effective as an anti-icer than a de-icer.
“High-traffic areas, like bridges or highways, might be the right place to use it as a pretreatment [before a storm],” Chun says.
Exploring hidden tradeoffs
When MnDOT wanted to better understand potassium acetate’s environmental impact, they reached out to Chun’s team at the NRRI and experts at the St. Anthony Falls Laboratory on the University of Minnesota’s Twin Cities campus. Combining field sampling, biodegradation tests and modeling, the intercampus team investigated how potassium acetate would affect nearby water bodies.
The researchers found that potassium acetate does biodegrade, but very slowly — especially in cold weather — so its effect on the oxygen level in water was minimal. Once potassium acetate enters water, it separates into potassium and acetate, and Chun was surprised to find that each has a different toxicological effect.
“Potassium was more toxic for aquatic organisms, but acetate was more toxic for roadside grass germination,” she says.
Still, it all depends on how much potassium acetate is used, Chun says. And larger bodies of water like Lake Superior might withstand potassium acetate better than smaller ones.
Katie Cassidy measures salt concentrations in the water sample. Cassidy received CFANS Graduate Fellowship funding during her time as a graduate student working in Chun's lab.
Collaboration toward a common goal
Pinpointing the right dosage, timing and means of distributing potassium acetate (and organic materials at a larger scale) are on Chun’s radar for future research directions. She’s also interested in discerning how a buffer system, such as strategically placed bioretention ponds, could intercept anti-icing and de-icing materials before they seep into Lake Superior and smaller water bodies.
Since Lake Superior is both the largest and the most pristine freshwater resource in the world, Chun says UMD is well-positioned to investigate how road salt affects freshwater systems today and into the future as our climate changes.
The NRRI has been a steadfast resource for Chun, with its established field-safe research tools and techniques for winter investigation. She says the Minnesota Department of Natural Resources, U.S. Environmental Protection Agency, and the City of Duluth also have been crucial partners.
“It is true collaboration, and that is very University of Minnesota,” she says. “I am glad to be a part of it.”
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