River Study Finds Our Biggest Plastic Problem Is Very Small

A jarring amount of waste flows from a Toronto river into one of the Great Lakes—one very, very, very tiny piece at a time, a new study from the University of Toronto suggests. "Urban rivers are hypothesized to be major transporters of plastic pollution into lakes and oceans, with storm events playing a pivotal role," though few studies have delved into that, the researchers write in Philosophical Transactions of the Royal Society A. And so they measured plastic concentrations before, during, and after storms in four places: in two streams that feed into Toronto's Don River, in the river itself, and then closer to the point where the river meets Lake Ontario.

They calculated that the Don—"Canada's most urbanized watershed," per Phys.org—dumps roughly 80,000 pounds of microplastics into Lake Ontario each year. That's about the weight of 18 cars, per Phys.org, but it's made up of something much smaller—roughly 500 billion plastic fragments measuring 1/5" or less. It's also vastly more than the roughly 350 pounds of macroplastics (meaning bigger than 1/5") they estimate run through the river each year.

"There were way more microplastics being exported than macroplastics," lead author Jacob Haney tells the Toronto Star. "The bigger pieces, they tended to get caught in the river and not make it to Lake Ontario versus the microplastics, which were getting flushed through." As for where the microplastics come from, the researchers say the sources are wide-ranging and include "construction foam, car tires, plastic pellets, and tiny pieces shed from larger single-use plastics," per the CBC.

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The findings came as a shock to senior author Chelsea Rochman, who tells the Star "the amount we found in the Don was actually higher than the Chicago River—an equally large city with a huge urban area." She continues: "By understanding these sources, we can work with the relevant stakeholders to turn off the tap on each of those sources," suggesting moves like coordinating with construction companies to prevent foam from blowing off construction sites.