91´óÉñapp

Since the 1960s, a chemical called 6PPD has been added to tires to prevent cracking and extend performance. But when 6PPD is exposed to ozone, it transforms into 6PPD-Quinone (6PPD-Q)—a compound recently discovered to be acutely toxic to several fish species. 

The breakthrough came in 2020, when researchers identified 6PPD-Q as the cause of decades-long coho salmon die-offs in Pacific Northwest streams. Fish were exhibiting erratic behavior and dying before spawning, a phenomenon that puzzled scientists for more than three decades before this groundbreaking discovery. As stormwater washes tire particles from roads into waterways, it carries 6PPD-Q directly into fish habitats—often with fatal consequences. 

While the initial discovery was made in Washington state, 6PPD-Q is a national issue. The chemical is formed anywhere tires meet ozone, making every road a potential source. Studies now suggest that multiple fish species—including brook trout, steelhead and lake trout—are also vulnerable. The full scope of ecological harm remains unknown, but ongoing research suggests the impacts could be far-reaching. 

Regulatory drivers and project challenges 

As evidence mounts, regulatory agencies are responding. Washington State’s Department of Ecology has already adopted an Aquatic Life Toxics Criteria for 6PPD-Q, and the U.S. Environmental Protection Agency is developing national screening levels. But the compound’s connection to fish mortality adds a new layer of complexity under the Endangered Species Act (ESA). 

In the Pacific Northwest, stormwater that isn’t fully infiltrated is now considered a potential threat to endangered species. Projects with a federal nexus—such as those receiving federal funding, requiring a federal permit or approval, or located on federal lands—that discharge stormwater from impervious surfaces, are increasingly required to undergo formal ESA consultation with the National Marine Fisheries Service (NMFS). These consultations can take two to four years, delaying both National Environmental Policy Act (NEPA) reviews and project delivery. 

Compounding the issue is the sheer ubiquity of the source. Every roadway and parking lot is a potential contributor. Treating stormwater at every outfall isn’t feasible—especially in dense urban environments where space is limited and suitable soils for stormwater treatment are scarce. 

What can be done 

A new Programmatic Biological Opinion is currently being negotiated between the Federal Highway Administration (FHWA) and NMFS for use in Washington state. Another Programmatic Biological Opinion is under development by the Federal Aviation Administration (FAA), FHWA and NMFS for aviation facilities in the Pacific Northwest. Once finalized, these programmatic agreements could streamline reviews and avoid lengthy delays for many projects—a major step forward for local governments, airport managers and developers in the region. 

In the meantime, 91´óÉñapp is helping clients navigate ESA and stormwater permitting complexities associated with 6PPD-Q and evaluate and select stormwater best management practices (BMPs) to mitigate 6PPD-Q. Research indicates that bioretention soil mixes, media filters, sorbent media and infiltration-based BMPs are effective at reducing the contaminant. We’re working closely with clients to identify the right tools based on site conditions, regulatory requirements and evolving science. 

Why broader awareness matters 

6PPD-Q may not be a household name yet, but the public should care. Salmon are a keystone species in the Pacific Northwest with immense cultural, ecological and economic importance. The degradation of one species affects the broader food web—and we don’t yet know the full implications for other wildlife or even human health. 

Like PFAS, 6PPD-Q is a chemical that’s been widely used for decades without a full understanding of its environmental impact. What we do know, however, is that there are practical, proven methods to reduce it from stormwater—if there is sufficient funding, awareness and policy alignment to deploy them at scale. 

91´óÉñapp is committed to staying at the forefront of this issue. We’re presenting at upcoming conferences, including the American Public Works Association Spring Conference, the International Conference on Ecology and Transportation and the Washington Airport Management Association conference, to share insights and solutions with peers and clients alike. As more jurisdictions recognize the risks of 6PPD-Q, early planning and expert guidance will be critical.