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Researchers at the University of Toronto Scarborough helped discover a chemical by-product in tires that may be responsible for killing wild salmon.

The chemical by-product, , was first identified in Professor Andre Simpson’s lab at ����TV Scarborough.

Simpson and his team were able to map out the structure of the chemical based on two tiny, 10-microgram samples sent to them by the study’s lead investigator Ed Kolodziej, an associate professor at the University of Washington. 

“The U.S. team had isolated and broken the chemical soup from tires down to the sub-component causing the toxicity, but they didn’t know what the individual chemical was,” says Simpson, an environmental chemist and director of the Environmental NMR Centre at ����TV Scarborough.

Over the course of six weeks, Simpson and his team were able to map out the chemical’s structure using nuclear magnetic resonance (NMR) technology. The Simpson lab is renowned for this work, and one of the few in North America doing environmental NMR research.

Simpson’s team was able to map out every single bond in the molecule and worked out how they linked together. Then, the team ran it through a database and realized it was a new chemical structure.

“It was kind of like a puzzle without a picture,” Simpson says. “We were given the pieces – we just had to figure out how they fit together.”

The chemical 6PPD is commonly used in automobile tires to make them last longer, but as the tire tread breaks down it leaves behind small microplastics on the road. As 6PPD reacts with ozone it becomes a different chemical by-product, known as 6PPD-quinone, that dissolves easily in water and shows greater stability, meaning it can easily enter aquatic environments and stay there for an extended period.      

Researchers found the chemical, which is highly toxic to coho salmon, in roadway runoff at sites across the west coast of the U.S. In recent years, scientists have been trying to figure out why the fish have been turning up dead in large numbers after heavy rain during the fall when the salmon swim inland to spawn.  

"We started with a mix of 2,000 chemicals and were able to get all the way down to this one highly toxic chemical – something that kills large fish quickly and we think is probably found on every single busy road in the world," says Kolodziej.

The researchers say more work needs to be done to see if this chemical is toxic to other fish and aquatic wildlife in general.