Specific, common chemical linked to death of coho salmon in Puget Sound creeks

Coho salmon continue to die in Puget Sound creeks after rainstorms. The deaths were linked to bits of car tires shed from road friction into stormwater runoff in 2018.

Washington State University’s (WSU) Puyallup Research and Extension Center identified a tire preservative, known as 6PPD, as the main culprit in 2020. Now, after years of digging, WSU Ph.D. student Stephanie Blair figured out how that chemical kills fish.

6PPD becomes a toxic chemical when it interacts with ozone, according to Blair. That chemical, called 6PPD-quinone, breaks through the cellular walls that protect the brain and vascular system, leading to oxygen deprivation.

“Prior to publication of this study, nobody really knew what the event was that drove what they call ‘coho urban runoff mortality syndrome,'” Blair stated in a news release from WSU.

Now, researchers are seeking alternatives to 6PPD, which can be found in nearly every car tire. Studies show 6PPD is toxic for other fish and mammals, and could even be harmful for humans.

“We need those tools to be available so we can start screening for alternatives to 6PPD,” Blair stated in the release. “This tells us how to evaluate a potential substitute.”

Multiple coho salmon populations listed as endangered

WSU noted that several coho salmon populations are listed as threatened or endangered, which has significant implications for both the environment and the economy.

Co-founder and board president of the Orca Network, Howard Garrett, told KIRO Newsradio that the decline of the Southern Resident orcas is most likely due to a lack of nutrients. While coho isn’t the animals’ main dish, orcas are running out of options.

“Basically, Chinook salmon, which have been their primary diet for eons, are now very scarce out there,” he explained. “So they’re relying on other fish, coho, chum salmon, sometimes sablefish, other fish, steelhead when they can find them, but those don’t have the caloric value that a nursing mother, a lactating mother, needs to have in order to feed the baby and maintain her own body health.”

The SeaDoc Society’s website offers recommendations that people can implement in their everyday lives to help protect salmon, such as washing cars at a car wash instead of driveways and using public transportation.

Now that researchers have a better understanding of 6PPD, creating an alternative might be on the horizon.

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