Don River sends 500 billion microplastics into Lake Ontario each year

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A new study of one of Canada's most urban rivers suggests it dumps the equivalent of about 18 cars' worth of microplastics into Lake Ontario each year. The discovery shocked the lead author and highlighted efforts to reduce pollution.

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A peer-reviewed study published Thursday estimates that the Don River basin dumps about 500 billion microplastic particles weighing about 36,000 kilograms into the lake each year. This is much more than the estimated 160 kilograms of larger plastic items.

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“I was very shocked to see that the levels we see here are more consistent with places where waste management is not as good,” said co-author Chelsea Rochman, a plastic pollution expert and assistant professor at the University of Toronto.

Microplastics, no larger than a pencil eraser and down to particles smaller than what is visible to the human eye, have become ubiquitous, found in everything from human blood to Arctic sea ice. Broken pieces of larger plastic have been linked to a number of problems in the wild, including lower levels of fish growth and reproduction, and have also raised concerns about possible impacts on human health.

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Some common sources of microplastics in the Don River include construction foam, car tires, plastic pellets and tiny pieces of larger single-use plastics, Rochman said.

The study found that the most common large plastic waste found in the river were bags and wet wipes, each accounting for about 20 percent. Rochman estimates there are tens of thousands of these wipes in the river system, especially Taylor-Massie Creek, at any given time.

By comparison, another study co-authored by Rochman and published in June found that the Don River dumps far more large plastic waste than the river that runs through Chicago.

“By understanding these sources, we can work with the appropriate stakeholders to shut down access to each of these sources,” Rochman said.

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That includes working with companies to prevent foam from blowing off construction sites, continuing to support sewer infrastructure upgrades and banning some single-use plastics, Rochman said.

“We can do a lot, but it is very important that we control the situation.”

Part of the problem, she said, is Toronto's outdated combined sewer system.

When heavy rains stretch the system, untreated sewage is discharged into the river and Lake Ontario. When people flush plastic wet wipes down the toilet—“which we should never do,” Rochman says—they can end up in the river during a storm.

The city is undertaking a $3 billion program to modernize the system and remove sewage from the river.

Researchers who conducted the study measured the amount of plastic before, during and after the storm at four locations along the river basin. The study suggests the amount of plastic in the river was about the same before and after the storm.

According to Rochman, this discovery suggests that if all plastic pollution were stopped, the river could naturally “clean up” over time.

“We could truly protect this watershed that many of us here in Toronto know and love,” she said.

The research was published in the Royal Society's academic journal Philosophical Transactions A.

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