Understanding why salmon, particularly coho, are dying in urban streams before spawning has challenged scientists for over a decade. Researchers from the University of Washington recently released the jaw-dropping news that they had found the chemical causing the premature death (Science, Seattle Times, New York Times). The toxic chemical, 6PPD-quinone, is a previously unstudied transformation product of 6PPD, a chemical intentionally added to rubber to prevent breakdown from oxidation. Most notably, the chemical is used in tire rubber. As cars drive over the road and the tire rubber wears off it can then find its way—by way of rain and storm runoff -- into urban streams where salmon live.
Salmon in an urban Seattle stream.
Dr. Zenhyu Tian, of UW Tacoma, has been presenting a summary of the research findings for Puget Sound stormwater professionals, including Aspect stormwater staff. Below we discuss the implications for the community and municipalities looking for guidance on how to grapple with this new threat to water quality and stormwater runoff challenges.
Learn More about New Tire Dust Research
Feb 19, 2021 seminar hosted by Stewardship Partners
Dr. Tian’s presentation to the Puget Sound Partnership is available here.
The new research is raising a lot of good questions
How do you pronounce 6PPD-quinone?
Dr. Tian pronounces it “6 P P D kwi-nohn”
What products contain it?
According to a representative from the U.S. Tire Manufacturer’s Association, 6PPD is used in most forms of rubber including passenger vehicle and truck tires, hoses, belts, etc.
Coho appear to be uniquely sensitive to 6PPD-quinone. Why?
This is a key research question being addressed by Dr. Jennifer McIntyre’s research at Washington State University.
What treatments work for removing 6PPD quinone from stormwater?
Although 6PPD-quinone wasn’t studied directly as it hadn’t been identified yet, a 2016 study found that bioretention was effective at reducing the toxic effects of urban runoff on coho.
Aspect staff checking the health of developing trout embryos during in-situ toxicity monitoring
Is there a better alternative for tire manufacturers?
Currently, tire manufacturers promoting green tire advancements are focused on sourcing renewable raw materials, increased fuel-economy and durability, and reusable (i.e., retread) ready tires. Reducing 6PPD in tires is a newly emerged issue and warrants further investigation into alternative compounds meeting performance standards. The U.S. Tire Manufacturers Association (USTMA) issued a promising statement in January expressing willingness to work with scientists to explore alternatives to 6PPD.
Voluntary exclusion of 6PPD by tire manufacturers or regulatory restrictions limiting use of the compound will take time, and neither outcome is guaranteed. In the interim, engineers and scientists will continue researching treatment options and technologies to help prevent tire wear particles and 6PPD-quinone from reaching critical salmon habitat. As noted above, early research indicates bioretention (e.g., bioswales and rain gardens) offers promising treatment option. Gaining a better understanding of removal efficacy from various bioretention facility types and treatment media requires further testing.
Developing Water Quality and Toxicity Monitoring Methods
6PPD-quinone isn’t currently a EPA Priority Pollutant, which is a group of regulated toxins with developed testing procedures and discharge limits. Because of this, analytical labs aren’t testing for 6PPD-quinone, leaving water quality experts without options to readily collect and analyze stormwater samples. Aspect is coordinating with partner labs regarding stormwater testing methods for 6PPD-quinone. The next steps include developing defensible testing procedures pairing analytical chemistry and bioassay toxicity (I.e., whole effluent toxicity) metrics. Continuing this type of research will expand our understanding of additional species that are impacted by 6PPD-quinone (such as rainbow trout), effective treatment options, and water quality conditions posing the greatest risk.
Stay Tuned for More on This Emerging Stormwater Management Issue
The University of Washington’s research is likely to lead to expanded monitoring programs targeting 6PPD-quinone, involving municipalities, ports, and transportation departments throughout Washington State and beyond. As a touchstone Pacific Northwest icon, salmon are a focus for stormwater runoff management and treatment throughout the region. Aspect’s stormwater team is dedicated to supporting the latest science and engineering strategies showing the greatest promise with this emerging issue.
Contact Us to Learn More
If questions, please contact Owen Reese, PE, Senior Associate Engineer and Brad Kwasnowski, Senior Environmental Scientist