Researchers in Vancouver have found a promising natural solution to one of the most persistent threats facing Pacific Northwest waterways: a toxic chemical generated by tire wear that has been linked to mass salmon deaths. In a study published recently, scientists tested a bioretention cell — commonly known as a rain garden — and found it removed more than 90 percent of 6PPD-quinone from stormwater runoff before the water could flow into nearby drainage systems.
6PPD-quinone is formed when an additive called 6PPD, which is mixed into tires to prevent cracking and degradation, reacts with ozone in the atmosphere. Once produced, the compound washes off road surfaces during rain and enters storm drains, ultimately reaching rivers and streams. In salmon populations, particularly the endangered Puget Sound steelhead and Chinook, exposure to 6PPD-quinone at concentrations as low as parts per billion has been shown to cause rapid mortality. The discovery of this chemical as the likely culprit behind sudden, unexplained fish kills made headlines across the region and raised alarms among environmental agencies.
The Vancouver study measured the performance of a bioretention cell installed in an urban watershed. These green infrastructure features are designed to capture and filter stormwater through layers of soil, gravel, and vegetation. The research team collected samples of stormwater entering and exiting the cell during rainfall events and analyzed the concentration of 6PPD-quinone in each. The results were striking: the rain garden acted as an effective barrier, retaining the vast majority of the toxin within its filtration media rather than allowing it to pass through into the drainage network.
Experts say the findings carry significant implications for city planners and environmental managers across the Pacific Northwest and beyond. As municipalities increasingly adopt green infrastructure to manage stormwater and reduce flooding, this research provides evidence that such systems can also serve as a frontline defense against tire-related pollution. Scientists note that while rain gardens alone cannot fully eliminate the problem — tire wear remains a pervasive source of the chemical on roadways — they represent a practical, scalable intervention that can be integrated into urban design.
The study adds to a growing body of research exploring how engineered natural systems can address emerging contaminants. Researchers emphasize that further testing across different climates and soil compositions is needed to confirm whether similar results can be replicated elsewhere. Still, the Vancouver findings offer a tangible example of how cities might begin to tackle a contaminant that traditional treatment methods have struggled to address.
