Scientists at forum say 6PPD quinone from tire wear is widespread in urban runoff and lethal to salmon

Researchers, agency staff and community scientists attending Day 1 of the 6PPD State of the Science Forum described growing evidence that 6PPD quinone — a transformation product of the tire additive 6PPD — forms in road runoff and can produce acute kills in salmon at extremely low concentrations.

The forum opened with a brief history: "In 2020, researchers in the Pacific Northwest identified 6PPD quinone as the long‑sought cause of coho salmon deaths during spawning runs," host Tanya Williams said. Presenters then summarized laboratory dose‑response work and field monitoring showing short, high‑magnitude pulses of 6PPD quinone during storms.

Nathan Ivy, a doctoral student at Washington State University, described field experiments in Miller Creek that tracked real storm pulses and compared survival of coho exposed to creek water versus clean controls. "The reaction creates 6PPD quinone, the brownish tire bloom that washes off and kills salmon at parts per trillion levels," Ivy said, and reported juvenile exposures during storms produced approximately 80 percent mortality in the study's storm events. Ivy and others emphasized that these submerged mortality events are often unseen and therefore undercounted.

Speakers from multiple groups reinforced the pattern: time‑series monitoring in urban streams typically shows a dominant first‑24‑hour spike in concentrations after the start of sustained rainfall, with later pulses possible if additional rain mobilizes more material. Mason King (Simon Fraser University) summarized multi‑event monitoring noting time‑averaged first‑24‑hour concentrations that can approach published LC50 values for sensitive life stages.

Why it matters: coho and other salmonids are culturally and ecologically central in the Pacific Northwest and are often highly sensitive to short, acute toxic pulses in small urban streams. Tribal governments and others have raised regulatory concerns: forum organizers noted that tribal nations petitioned the U.S. Environmental Protection Agency under the Toxic Substances Control Act to address 6PPD use and risks.

Next steps identified at the forum include prioritizing hotspot monitoring with passive samplers and autosamplers, expanding lab capacity for 6PPD quinone analysis, and evaluating targeted green infrastructure to capture or degrade the compound before it reaches receiving waters. Multiple presenters urged managers to focus scarce retrofit dollars on estuarine mouths and other locations where untreated runoff concentrates.

The forum will continue on Day 2 with breakout sessions on monitoring protocols, human‑health implications and mitigation pathways.