Tuesday November 11, 2025
Times Colonist —
Excessive use of road salt in winter is most toxic to salmon during the 24 hours after egg fertilization, according to an updated study by a group of B.C. researchers.
The research follows the preliminary results of a five-year study, released in January, that found that high levels of salt are killing trout and coho.
The study — a collaboration of UBC, SFU, the B.C. Institute of Technology, the federal government, community scientists and volunteer stream keepers — involved monitoring salt pulses in more than 30 streams in Metro Vancouver.
In the latest update, the researchers revealed road salt’s adverse effect on chum eggs, adding to data that show how salt pulses harm coho and rainbow trout eggs.
“Canada reportedly uses five million tonnes of road salt annually, and that is clearly an underestimate, because that only captures what’s spread on roads, not what private contractors do, not what businesses do, not what homes do. And it’s been increasing over time,” said Chris Wood, adjunct professor of zoology at UBC, during a presentation of the results.
Road salt is made up of sodium and chloride. When it dissolves on the road, it seeps into groundwater and streams.
High concentrations of sodium chloride were found in streams during the winter. Some were notably bad, such as Serpentine Creek in Surrey and Stoney Creek in Burnaby.
Under the guidelines, a safe limit is 600 milligrams a litre, but in some cases, researchers found up to 6,600 milligrams a litre — 11 times more than what is considered safe.
“Road salt is used in fall, winter, early spring sometimes, and it’s really overlapping with the period when salmon are spawning in the stream and the young salmon are trying to develop,” said Wood.
Researchers found that fertilization can still take place during these high pulses of road salt, but something happens in the following 24 hours when delayed mortality begins.
They also noted that the amount of salt entering the streams was not higher during harsher winters. For example, the largest amounts recorded were in the winter of 2024, when there was not very much snow.
“So what we conclude is that salt distribution is very poorly managed, that salt is distributed whether or not it’s actually really needed,” said Wood.
Researchers studied chum eggs 24 hours after fertilization and found high levels of sodium but not chloride. Then they followed the fish for two months and found a spike in calcium. After another two months, they found many deformities and mortality.
“So if they’re exposed for 24 hours, most of them are going to die,” said Wood.
By following these fish for a long period of time as they developed in fresh water after that first 24-hour salt pulse, researchers could see the mortality gradually developing.
New data show that chum eggs that have been exposed to high levels of salt in the first 24 hours do not harden as well as those that are not exposed to salt in that time frame.
“This is data hot off the press,” said Wood, noting there is still work to be done to analyze the findings.
Research from SFU also found that road salt is toxic to damselfly larvae, which causes a reduction in food for juvenile salmon, and that it’s more toxic at low temperatures in the winter.
“The whole point of this project is to find out the nature of the problem, document it and then convince individuals, businesses, government to do better on road salting. It’s a tough, uphill climb,” said Wood, pointing to photos showing a thick layer of road salt used at UBC last winter.
“They’re completely resistant to changing their salting. So this is the problem we have to really face.”