Breakthrough Discovery: Scientists Find Solution to Protect Salmon from Toxic Tire Dust
For decades, toxic tire dust has threatened coho salmon populations, preventing them from reaching their spawning grounds. Now, scientists in King County have made a groundbreaking discovery that could help save these fish from a deadly urban pollutant.
Innovative Soil Mixes Could Protect Salmon from Pollution
Recent research reveals that specialized soil blends can effectively filter out a lethal chemical—6PPD-quinone—from stormwater, significantly increasing the survival rates of coho salmon. These soil mixtures, which contain sand, coconut fiber, and biochar, show promise in mitigating pollution from roadway runoff, according to King County scientists.
This breakthrough offers a potential solution to the long-standing issue of urban stream pollution, which has been devastating coho salmon populations. The chemical 6PPD-quinone, a byproduct of tire preservatives, was identified in 2020 as the primary culprit behind coho salmon deaths. Scientists discovered that even trace amounts of this toxic compound could wipe out entire populations of returning salmon before they could spawn.
The Deadly Impact of 6PPD-Quinone
Researchers from the University of Washington, Washington State University, and the Center for Urban Waters in Tacoma confirmed that 6PPD-quinone is responsible for killing 40% to 90% of returning coho in some urban waterways. The toxin, present in tire dust, is so potent that just a few drops in an Olympic-sized swimming pool could kill half of the coho salmon exposed to it, according to Chelsea Mitchell, a senior ecotoxicologist with King County.
Beyond coho salmon, 6PPD-quinone has also been found to be fatal to other fish species, including rainbow trout and whitespotted char. As urban runoff continues to flow into streams, finding an effective filtration method is critical for aquatic ecosystems.
Groundbreaking Study Demonstrates Soil-Based Filtration Success
In a recent King County study, researchers tested various soil blends to determine their ability to remove 6PPD-quinone from stormwater. The team collected contaminated runoff from the Ship Canal Bridge on Interstate 5 and filtered it through four different soil mixtures, including a traditional compost and sand mix, as well as three “high-performance” blends containing coconut fiber, sand, and biochar.
Results showed that all four soil mixes successfully filtered out the toxin, with the high-performance blends performing the best. In a controlled experiment, juvenile coho salmon were exposed to both treated and untreated stormwater. The results were staggering—while nearly all salmon exposed to untreated water perished, every single fish exposed to filtered water survived.
Josh Latterell, King County’s science section manager, described the findings as a “mic-drop moment,” emphasizing the immense impact this discovery could have on salmon conservation.
Next Steps: Implementing Solutions for Cleaner Waterways
King County researchers are finalizing their study and plan to share their findings with the Washington Department of Ecology, which regulates stormwater treatment in the state. Although widely used, traditional compost and sand mixes can release nutrients and minerals into waterways, making them unsuitable for sensitive aquatic environments.
To address this, scientists are currently testing high-performance soil mixes outside of lab conditions near Bellingham. If these trials confirm the effectiveness of the filtration method, the hope is to implement more stormwater treatment projects utilizing these specialized soil blends by 2027 or 2028.
Latterell, who has been studying coho salmon deaths since 1999, expressed optimism about the future. “It’s been incredibly rewarding to see how persistent scientific research has led to meaningful solutions,” he said.
As part of a broader effort, King County is also working to identify high-risk roadways and prioritize areas in need of stormwater treatment. With continued research and strategic implementation, this innovative filtration method could play a crucial role in protecting salmon populations and restoring urban waterways.