Study finds Toronto rivers and watershed contaminated with road salt -- even in summer

Thestar.com
March 11, 2021

Road salt applied in wintertime is threatening at least two-thirds of the aquatic life found in the four rivers within the Greater Toronto Area.

A new University of Toronto study, published Thursday, shows that even during the summer, almost 90 per cent of the 214 sampled sites exceeded the federal chronic exposure guidelines for chloride.

The United States and Canada, respectively, apply roughly 24.5 million and seven million tonnes of road salt annually. In Ontario, chloride enters water systems primarily through the annual application of three to five million tonnes of road salt, used as an anti-icing method for winter road maintenance, according to the city of Toronto.

“Our results suggest that even presumed low seasons for chloride show concentrations sufficient to cause significant negative impacts to aquatic communities,” the study concludes.

Canadian Lauren Lawson, a graduate student at the University of Toronto, and Donald A. Jackson, an ecology and evolutionary biology professor at University of Toronto, were lead authors of the study.

The study was funded by the NSERC Discovery Grant and funding from Fisheries and Oceans Canada and published in FACETS, Canada’s first and only multidisciplinary open access science journal.

The study looked at Humber River, Don River, Etobicoke Creek, Mimico Creek and their associated tributaries from headwater locations north and northwest of Toronto.

Almost all sites in Toronto surpassed the chronic threshold for chloride of 120 mg/L during summertime. For the most part, only upstream sites away from the urban areas, such as largely forested regions sampled in the less urbanized upper Humber River, show concentrations below the chronic threshold.

As many species reproduce in the spring and summer, often moving to locations different from where they may have been during wintertime, they are more at risk to higher chloride concentrations in groundwater.

Egg or juveniles stages of species may show greater sensitivity to chloride concentrations than adults and are likely most impacted by increased levels of road salt.