As massive snow piles melt across Ontario cities after a heavy winter, researchers say the road salt mixed into them could pose serious risks to waterways, ecosystems and even drinking water.
Cities commonly pile snow cleared from streets and parking lots into large mounds. But those piles often contain more than just snow.
“What we’re getting is a really concentrated salt solution that can be released from it,” said University of Toronto professor emeritus and ecology expert Don Jackson. “And that’s ultimately draining into our streams and rivers and then to Lake Ontario.”
Researchers say salt runoff can have significant environmental effects.
According to research from the University of Waterloo, road salt can accumulate in soils and water bodies after winter, altering their natural chemical composition and harming freshwater ecosystems.
Scientists say the primary ingredient in road salt, sodium chloride, can persist in the environment indefinitely once introduced through road runoff.
Jackson said salt contamination can damage nearby vegetation and eventually seep into groundwater.
“You can also have that salt sinking into the ground, eventually getting into the groundwater,” he said.
“We can end up with very elevated levels of salt in our groundwater, which have potential consequences both for the environment but also for humans.”
He added that salt contains both sodium and chloride, each with different impacts on the ecosystem.
“The chloride part is what is quite toxic to aquatic organisms,” Jackson said.
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“But the sodium part, if we get high levels of that in our water, that can affect our human health because that’s what contributes to hypertension, high blood pressure.”
The environmental impact also varies depending on the species affected.
Jackson said some aquatic organisms are highly sensitive to salt, particularly in early life stages.
“Some species can be really quite tolerant,” he said. “Some other species are really sensitive, so very low levels of salt can affect particularly some of the juvenile organisms.”
Salt pollution can also change how lakes behave.
University of Waterloo research suggests increased salinity can alter the density of water, reducing mixing in lakes and contributing to oxygen depletion in deeper water.
“Nutrient enrichment can trigger algal blooms that, in turn, lower the oxygen level in the lake’s deeper waters,” a research paper conducted by water institute members read.
Jackson added that this can create areas where oxygen becomes scarce for fish that depend on colder, oxygen-rich waters.
“What we can end up with, in deeper water, potentially we might have areas that lack oxygen,” he said. “And that’s going to impact fish that live in deeper water and require cold water … things like lake trout.”
Despite these risks, road salt remains widely used because it is inexpensive and effective at melting ice.
But Jackson says the broader economic cost may be far greater than many people realize.
“We use lots of salt because it’s cheap and we see it as being effective,” he said. “But we don’t recognize all the other costs associated with it.”
Damage to roads, bridges, vehicles and infrastructure has been estimated at hundreds to thousands of dollars per tonne of salt used, he added.
“If we’re in Canada using five million or more tonnes of salt each year … you’re talking about billions of dollars’ worth of damage a year,” Jackson said.
Jackson said removing salt from water after it enters the environment is possible but extremely costly.
“Many areas, like California or the Middle East, much of their drinking water is coming from marine origins,” he said. “They’re dealing with salt water where they’re trying to extract fresh water from it, and it becomes really expensive.”
He added that desalination processes also produce highly concentrated brine that must be disposed of, creating additional environmental challenges.
Some municipalities have begun acknowledging the environmental impacts of road salt and are introducing measures to reduce its use.
The City of Toronto says it manages salt through a Salt Management Plan aimed at balancing road safety with environmental protection, noting the city typically uses between 130,000 and 150,000 tonnes of salt each year.
Measures include monitoring pavement temperatures, calibrating salt spreaders and improving storage facilities.
In recent years, city officials in Toronto, Halton and Markham have also been reminding residents to limit salt use on private property, such as driveways and sidewalks.
In colder regions of Canada, some municipalities have opted to rely more on sand or sand-salt mixtures to improve traction and reduce the amount of salt entering the environment.
Jackson added that reducing salt use, rather than trying to remove it later, may be the most effective long-term solution.
“It’s not something that’s going to be a simple fix,” he said. “We’re adding millions of tonnes of salt annually.”
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