Snow covered road and bicycle

Get Salty About this Ongoing Threat to Aquatic Life

That winter road salt keeps wreaking havoc all year round, especially in dense urban centres. We all have a role to play to reduce the impact.


With spring in the air, it’s time to put away your road salt – but the environmental impacts will linger on.

Every year residents and municipalities spread millions of tonnes of salt on roads and walkways. In Canada, we use roughly seven million tonnes of road salt annually for commercial and industrial functions, as well as to de-ice sidewalks.

Keeping roads and walkways ice-free helps keep Canadians on the move. But salt inflicts significant damage on road surfaces, road users (including the paws of four-legged friends) and the environment. Chloride, the main component of road salt, is not filtered by soil, plants or water treatment processes. As a result, it accumulates in waterways. In cities, where road density is highest, salt runoff poses a year-round threat to aquatic life.

To understand more about the impact of winter salt use on urban waterways, researchers from the University of Toronto Faculty of Arts & Science measured chloride levels at 214 sites along four GTA waterways: the Humber and Don rivers, as well as Mimico and Etobicoke creeks.

Samples were collected in July and August, with winter months a distant memory and chloride concentrations typically at their lowest.

The researchers, PhD student Lauren Lawson and Donald Jackson, a professor of aquatic ecology in the department of ecology and evolutionary biology, found that 89% of samples exceeded federal guidelines for long-term exposure of aquatic life to chloride.

“Increased chloride concentrations in freshwater can be toxic and lead to changes in an organism’s behaviour and ability to withstand other stressors,” says Lawson. “It can increase lethality, alter food webs and lead to biotic homogenization where only hardier species survive.”

The levels were so high that the team estimates more than 30% of sites had concentrations lethal to two-thirds or more of aquatic species. These levels are particularly concerning during the summer months when species are reproducing. In light of these findings, the authors call for increased attention to the year-round impact of road-salting.

Many cities, including Toronto, are trying to reduce winter salt use. In future, we could rely on de-icing alternatives and solutions that aid traction such as sand or biodegradable wood chips. Some regions are even using a mixture of salt and beet juice to reduce salt levels.

However, these alternatives can be costly and come with their own environmental impacts. For now, salt is the go-to winter solution so efficient application is key for more sustainable winter management.

Shovelling snow early and often, clearing ice and removing slush as temperatures rise can help limit the amount of salt needed. In fact, a handful should be plenty for 2.5 square meters of well managed sidewalk.

“We need private citizen education – including for businesses – on the proper amount and application of road salt,” says Jackson. “A little salt goes a long way when applied correctly.”

‹ Previous post
Next post ›

Amy Noise is a science communicator who is fascinated by how and why the world works. Always learning, she is passionate about science and sharing it with the world to improve and protect our health, society and environment. Amy earned her BSc (biology and science communication) at the University of Manchester, and MSc (nutrition science and policy) at King’s College London, UK. She tweets sporadically @any_noise