By: Zoe Dearing, GEHS 2025
Salmon have been struggling for a long time, but not always for the same reasons. Recently, the most lethal killer has been confirmed: toxic tire dust. It destroys adult salmon’s brains, before they can even have a chance to spawn.
In the previous decades, researchers and scientists alike have noticed a sharp decline in successful coho salmon spawning runs. In the Pacific Northwest, adult coho salmon are dying in freshwater at an alarming rate before they’re able to reproduce. Research conducted in 2018 established the connection between salmon pre-spawning deaths and “urban stormwater mortality syndrome.” A research report was published to the journal of Environmental Science & Technology to publicize the new observations. Yet, it still took another two years for scientists to pin-point the specific coho killing chemical.
In 2020, an article published in Science revealed the discoveries to the public. A chemical compound byproduct in tires was found to be the reason for the coho salmon's sudden and devastating deaths in urbanized creeks. It’s called N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylene-diamine, or more commonly known as 6PPD. Although, it’s not 6PPD alone that is toxic to the coho, rather the oxidized transformation product called 6PPD-quinone.
So, how does this mystery chemical get into a salmon’s ecosystem to begin with? It’s all because of stormwater. When it rains, pollutants on roads and other impervious surfaces find their way to the nearest body of water. Whether it’s a babbling brook or a raging river, these chemicals use stormwater as a form of transportation.
Typically, in a healthy forest landscape, stormwater has a natural direction to flow, so issues such as natural overfertilization and flooding are dealt with through groundwater filtration. This is because the soil creates a pervious surface for stormwater to soak into, unlike the solid concrete we see everywhere else. Impervious surfaces force stormwater to find a downward slope, and majority of the time, at the bottom of the hill is a body of water.
We now know that the primary chemical that is killing coho salmon before they’re able to spawn comes directly from us. Every single day, someone will drive a car and release 6PPD onto roadways. As of right now, there is no safe replacement for these tire preservatives, as we all need our tires to be durable and functional. And since the killing transformation product 6PPD-quinone is the reaction of 6PPD being exposed to oxygen, there’s not much everyday citizens can do.
However, despite the bad news, there’s good news too! Researchers are actively working with tire companies to find a replacement chemical that will still ensure safety on the roads. While they may not have answers yet, there’s other things you can do to help keep this deadly chemical out of salmon-spawning waters.
For starters, you can encourage your local government to install more green stormwater infrastructure along major roadways. Green stormwater infrastructure offers a natural way to filter out many different pollutants before they can reach a body of water. They can also create a gateway to groundwater systems to reduce flooding, plus so much more! You can even create your own green stormwater infrastructures on your own property. Every little action will help!
To learn more about what you can do to help the salmon, check out Sustainability Ambassador’s Impact Project page and sign up with the Eastside Climate Challenge for more easy and actionable projects to do at home! Also, take a look at some of Sustainability Ambassador’s other green stormwater infrastructure resources linked below!
Check out our events page to learn more about Salmon and the Green-Duwamish Watershed from our PBL series: https://www.sustainabilityambassadors.org/events
View our Living Textbook for more resources and information on Salmon, Stormwater, and the Watershed: https://www.sustainabilityambassadors.org/local-living-textbook-stormwater
Take a look at our student Stormwater Managements Project Ideas to create an impact in your Community: https://www.sustainabilityambassadors.org/_files/ugd/d1f035_9dc73d1cb2f146b593910863174a59e5.pdf
Watch these Student Voiced videos to learn more about 6PPD effects on salmon and see the accompanying questions to stretch your thinking: https://docs.google.com/document/d/1EK_RSXIWgjC3SrJyEMsLht1b1To2zUyAi4qfwPpN91E/edit
Zhenyu Tian et al. A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon. Science 371,185-189(2021). DOI: 10.1126/science.abd6951
Kyoshiro Hiki, Kenta Asahina, Kota Kato, Takahiro Yamagishi, Ryo Omagari, Yuichi Iwasaki, Haruna Watanabe, and Hiroshi Yamamoto. Acute Toxicity of a Tire Rubber-Derived Chemical, 6PPD Quinone, to Freshwater Fish and Crustacean Species. Environmental Science & Technology Letters, 2021 8 (9), 779-784 DOI: 10.1021/acs.estlett.1c00453
Katherine T. Peter, Zhenyu Tian, Christopher Wu, Peter Lin, Sarah White, Bowen Du, Jenifer K. McIntyre, Nathaniel L. Scholz, and Edward P. Kolodziej. Using High-Resolution Mass Spectrometry to Identify Organic Contaminants Linked to Urban Stormwater Mortality Syndrome in Coho Salmon. Environmental Science & Technology, 2018 52 (18), 10317-10327. DOI: 10.1021/acs.est.8b03287