Ontario has a road salt addiction. And it’s turning our rivers and lakes into saltwater, experts say

Ontario dispenses nearly half of the 5 million tonnes of road salt spread across Canada each year and experts say it’s changing our environment.

Thestar.com
Nov. 29, 2023
Kevin Jiang

Winter is coming, and with Ontario’s first major snowfall of the season currently underway, trucks carrying millions of tonnes of road salt are preparing to season the province’s roads and infrastructure.

Ontario dispenses a colossal amount of salt each year, making up nearly half of all the road salt spread across Canada annually. Experts warn its overuse is turning Ontario’s vast stores of freshwater salty, threatening our ecosystem.

“Road salt has a long history of known environmental impacts,” said Donald Jackson, a professor of ecology and evolutionary biology at the University of Toronto. “We, over time, have been turning many of our streams, ponds, lakes into something more similar to oceans or saltwater.”

Meanwhile, some regions have partially replaced their salt use with other measures like beet juice, cheese brine or sand. But could they be trading one problem for another?

How much road salt is used in Ontario and Toronto?

In total, Ontario dispenses around 2.2 million tonnes of road salt each year, a spokesperson for the province’s Ministry of the Environment, Conservation and Parks told the Star. That’s enough to fill 687 Olympic swimming pools -- and nearly half of the roughly five million tonnes of road salt spread in the country each year, according to Environment Canada.

Virtually all of this will eventually enter into our waterways, Environment Canada continued.

According to a spokesperson for Toronto, the city dispenses around 130,000 to 150,000 tonnes of road salt annually on its roughly 5,100 kilometres of roads -- roughly the combined weight of more than 1,000 blue whales. That’s not counting private businesses and individuals, which often salt more than they need, Jackson added.

Most of this is dispersed when temperatures are still mild, as road salt works by lowering the melting point of ice -- and as such, is only effective when temperatures are above around -7 C.

“The City is aware of the risks of road salt to the environment and although there is ongoing research into the use of alternatives, road salt continues to be the most cost-effective de-icer across Canada,” Toronto’s spokesperson said over email. “Toronto’s reduction in salt use is balanced with the need to keep roads and sidewalks safe for users at a reasonable cost.”

A report from the World Wildlife Fund Canada suggests some waterways in southern Ontario can become as salty as the ocean during the spring and winter. Meanwhile, Jackson’s lab’s research implies salts can persist in high concentrations year-round -- even during the height of summer, months after it was dispersed.

“We have summertime concentrations that could be well above what the Ministry of the Environment views as critical thresholds for acute toxicity in some of our streams and rivers around the Toronto area,” he said, citing his 2021 study on the topic.

Out of 214 surveyed sites near Toronto, Jackson’s research found 89 per cent exceeded the federal long-term exposure guidelines to chloride, and 13 per cent surpassed acute toxicity guidelines.

“(Those levels) could kill off many species within 48 hours,” Jackson said.

Why does road salt harm the environment?

We’ve known of salt’s environmental impact for centuries, dating back to when ancient armies would salt the farms of their conquered enemies so no crops can grow. We can see this same phenomenon to a lesser degree on Ontario’s highways, Jackson said.

“If you’re driving along the downwind side of a highway, you might see vegetation like conifers that are brown rather than being green,” he continued.

“That’s just because of road salt spray that’s coming off roadways.”

Road salts are mostly composed of sodium chloride, or table salt, but can also include calcium chloride, magnesium chloride or potassium chloride. These are mostly interchangeable when it comes to their environmental impact, said Gail Krantzberg, an aquatic scientist, professor and program lead for McMaster University’s Masters of Engineering and Public Policy Program.

“It’s really the chloride ion that is doing the work,” she said.

This ion can be “extremely corrosive,” eating through steel on snowplows and buildings, and harming living organisms in a number of ways, Krantzberg continued. For example, chloride ions can rust rebar and mobilize metals locked into soil, releasing toxic metals into our waters.

“It will kill eggs, it’ll kill larvae. It will, at high enough concentrations, kill things like salamanders and frogs and turtles, aquatic plants,” she explained.

Other research shows that water fleas are dying from chloride levels far below Environment Canada’s limits, Jackson added. This is particularly concerning, as water fleas help make up the base of the food chain; their disappearance can upset the entire system.

At the same time, as our rivers and lakes grow increasingly salty, it opens the door to invasive species tolerant of saltwater, which may out-compete Ontario’s native species, he said.

What are other places using instead of road salt?

The salt-ernatives to road salt being tested in cities across Canada may read like a bizarre shopping list, from beet juice and cheese brine to kitty litter. And yet, even these substitutes have their flaws, experts say.

For example, abrasives like sand and even cat litter are often used when the weather gets too cold; Calgary still uses salt in the fall and spring, for example, but will apply a mix of mostly gravel with a sprinkling of salt when in colder temperatures. This means they won’t have as much salt runoff, said Krantzberg, but the tradeoff is it’s unable to melt the ice.

Other jurisdictions like Halifax mulled using beet juice, cheese brine and molasses to supplement their salt use over winter, but these are far from perfect as well, Jackson explained. The organic liquids can harbour bacterial growth, which when introduced to water systems, could starve them of oxygen, he said.

“It might be trading off one problem for another.”

Chemical alternatives to salt, like calcium magnesium acetate de-icer, has also been contemplated. But, according to the spokesperson for Ontario’s Environment Ministry, “some studies have found that these alternatives are more toxic. More research is needed to ensure we do not replace one harmful substance with another.”

The best way to limit road salt’s impact isn’t by replacing it with another, potentially more harmful substance, but to limit our own use, Jackson said. The province -- and especially individuals and businesses -- are likely using far more salt than they need, he continued.

More salt is needed to melt ice the colder it gets. At 0 Celsius, a pound of salt can melt around 46 pounds of ice, according to Cargill. Nearing -7 Celsius, that same pound of salt can only melt around nine pounds.

“In cities, on people’s properties, the only way of putting (road salt) down safely is not to put it down,” Krantzberg added. “Just get snow tires!”