Every fall more than half of the coho salmon that return to Puget Sound’s urban streams die before they can spawn. In some streams, all of them die. Scientists investigating the phenomenon have discovered that a vast chemical soup is threatening aquatic life, and one toxic chemical in particular is responsible for wiping out the creatures. The killer resides in the mix of chemicals that leach from tire wear particles: a molecule related to a preservative that keeps tires from breaking down too quickly: 6PPD-quinone.
Overview of findings
Ozone, a gas created when pollutants emitted by cars and other chemical sources react in the sunlight, breaks the bonds holding the tire together. 6PPD helps by reacting with ozone before it can react with the tire rubber, sparing the tires. But when 6PPD reacts with ozone, the researchers found that it was transformed into multiple chemicals, including 6PPD-quinone, the toxic chemical that is responsible for killing the salmon. (This chemical is not limited to the Puget Sound region. The team also tested roadway runoff from Los Angeles and urban creeks near San Francisco, and 6PPD-quinone was present there as well.)
Now that 6PPD-quinone has been identified as the “smoking gun” behind coho death in freshwater streams, the team can start to investigate why this chemical is so toxic.
One way to protect salmon and other creatures living in the creeks is to treat storm-water before it hits the creeks. But, while tests have shown that there are effective environmentally friendly storm-water technologies for removing 6PPD-quinone, it would be almost impossible to build a treatment system for every road, the team added.
Another option is to change the composition of the tires themselves to make them “salmon-safe.”
“Tires need these preservative chemicals to make them last. It’s just a question of which chemicals are a good fit for that and then carefully evaluating their safety for humans, aquatic organisms, etc.”
-Dr. Edward Kolodziej, researcher and associate professor, University of Washington Tacoma Division of Sciences & Mathematics and Department of Civil & Environmental Engineering
Journal Reference: Zhenyu Tian, Haoqi Zhao, Katherine T. Peter, Melissa Gonzalez, Jill Wetzel, Christopher Wu, Ximin Hu, Jasmine Prat, Emma Mudrock, Rachel Hettinger, Allan E. Cortina, Rajshree Ghosh Biswas, Flávio Vinicius Crizóstomo Kock, Ronald Soong, Amy Jenne, Bowen Du, Fan Hou, Huan He, Rachel Lundeen, Alicia Gilbreath, Rebecca Sutton, Nathaniel L. Scholz, Jay W. Davis, Michael C. Dodd, Andre Simpson, Jenifer K. Mcintyre, Edward P. Kolodziej. A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon. Science, 2020 DOI: 10.1126/science.abd6951