Study seeks to discover extent of coho-killing chemical’s effect

Jen McIntyre wearing waders as she stands in Longfellow Creek.
Jen McIntyre at Longfellow Creek. Credit: Bob Hubner/ WSU

After helping identify a tire chemical that is deadly to coho salmon, Washington State University researcher Jen McIntyre is now working to find out more about how widespread the problem is. Working with colleagues from the University of Washington and the U.S. Geological Survey, McIntyre, an associate professor at WSU’s Puyallup Research and Extension Center, is investigating whether the chemical 6PPD-quinone affects young coho in the field as it has been found to affect adults.

In a hatchery next to a creek near Seattle, McIntyre’s team set up two raceways. One had creek water flowing through it, and the other had well water. Just before a storm began, the team added young coho to tanks in each raceway. Soon after the coho were exposed to stormwater, many of them rose to the surface, swam in circles, wobbled, and died. In the first of what will be three trials, 80% of the coho that were exposed to stormwater died.

The problem is even more widespread than McIntyre’s team imagined.

McIntyre’s team is also taking tissue samples to study what changes to their genes could be behind the fatal effects. It’s a two-year project, and the data collection will conclude after the third trial. 

Coho in streams near Seattle have been dying mysteriously for years before researchers figured out why. First, they identified that it was something in stormwater, which typically runs off surfaces into streams without being treated. Then in 2020, McIntyre and her colleagues found it was the previously undiscovered chemical, 6PPD-quinone, a product of 6PPD in tires reacting with ozone in the atmosphere.

“We were able to identify this chemical that nobody had heard of before. It’s highly toxic and yet we didn’t know that it existed,” said McIntyre.

In the Pacific Northwest, salmon are essential to ecosystems and communities, particularly Indigenous communities. 6PPD-quinone’s deadly effects on salmon, and its cascading effects on ecosystems and communities, are just part of the problem. It also affects other species, from rainbow trout to brook trout, in areas around the world.

But there are solutions.

“If we want to have healthy runs of salmon in our more developed watersheds, we have to make a lot of changes,” said McIntyre.

She has been working with tire manufacturers and environmental regulators to replace 6PPD in tires. Meanwhile, green infrastructure such as rain gardens and green roofs can filter out 6PPD-quinone before it enters streams. She has found that coho exposed to stormwater filtered through rain gardens survived whereas coho exposed to unfiltered stormwater died.

Ani Jayakaran, a professor and green stormwater infrastructure specialist at WSU’s Puyallup Research and Extension Center, recently demonstrated that permeable pavements, which, unlike regular pavements, water can infiltrate, can filter out some 6PPD-quinone. That could help coho survive. Adding green infrastructure to urban areas is especially impactful because it filters many toxic chemicals in addition to 6PPD-quinone. McIntyre said there needs to be political will to implement solutions. And before that researchers need to spread awareness of the problems. Her work is doing just that.

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