For decades, toxic tire dust has suffocated coho salmon before it lays it in streams of Natal. Now, King County scientists say they have made “potential breakthroughs” on how they save them.
Preliminary results from recently completed studies show that certain soil mixtures can effectively filter toxic chemicals from rainwater and significantly increase the survival rate of Coho salmon. According to King County scientists, the key could be a special soil mixture containing organic fertilizers like sand, coconut fiber and charcoal.
The results suggest that there is a potential solution to the difficult-to-looking question of how Coho salmon can survive in urban streams where pollution from traffic is ubiquitous.
Scientists first identified toxic tire dust, or more specifically, chemical 6PPD quinone, in 2020, as a salmon killer.
A 2020 study found that scientists, including Tacoma’s urban waters, Washington University and parts of Washington State University, were able to separate 6PPD quinone as a fault chemical out of about 2,000 chemicals in road spills.
Researchers have discovered that the chemical is very deadly and kills 40% to 90% of cohoes that return cohoes to streams in several cities before they can spawn. The chemical was the perpetrator behind the deaths of about 40% of the coho in the Puget Sound area.
“We’re talking about the concentration of a few drops in an Olympic-sized swimming pool. It could kill half of the cohos that could be put in that pool.”
The 6ppd-quinone is a by-product of tire preservatives that are created when tires come into contact with ozone from the atmosphere or from the vehicle exhaust, Mitchell said.
Research is growing on how toxic tire dust affects other fish. Chemicals also kill other species, such as rainbow trout and whites’ char, she said.
In a recent King County study, researchers, including Mitchell and county science manager Josh Lattel, tried to assess how effective certain soil mixtures approved for stormwater treatment are in removing toxic tire dust.
In this study, researchers filtered untreated water through four different soil mixes at a lab at Western Washington University, including a mix of compost and sand, coconut fiber, and three “high-performance” mixes consisting of sand and biochar.
All four soil mixes exclude 6ppd-quinone and the high-performance mix delivers the best performance. In a King County lab, researchers then exposed 20 boys Coho Salmon to untreated, treated water. What they found dropped their jaws, Lutterell said.
Of the baby cohoes exposed to untreated stormwater runoff, only one or two survived. However, of the cohoes exposed to treated water, all 20 survived.
“For me, this is like a microphone drop moment,” he said. “You have a time machine and you go back to 25 years and when people first start to look at plant mortality rates, they’ll dance on the streets to see this.”
King County researchers continue to finalise their results reports and intend to share them with the state’s Department of Ecology, which provides guidelines for stormwater treatment for the state.
Compost and sand soil mixtures widely used around the state tend to release nutrients and minerals into the waterways, Mitchell said. Since 2013, the ecology department has recommended use close to sensitive waters. The department has permitted the use of “high performance” soil mixes since 2021, including those tested by King County.
Researchers are currently testing high-performance soil mixes outside the lab at a site near Bellingham. There’s more work to make sure the mix is ​​safe, but Lutterell said he hopes to use it by 2027 or 2028 to see more stormwater treatment projects.
Lutterell said he remembers in 1999 that his colleagues were just beginning to realize that Coho appears mysteriously dead in a stream.
“I was really pleased to see that a determined, systematic scientific investigation led to me… realizing what was going on here,” he said.
King County is working to identify roads with high concentrations of toxic tire dust and create a list of areas that require stormwater treatment.
This report uses information from the Seattle Times Archives.
