6PPD-quinone, a chemical from tire wear particles, kills 40-100% of adult coho salmon returning to spawn in urban Pacific Northwest streams after every rainstorm

Every time it rains in the urbanized Pacific Northwest, stormwater washes tire wear particles off roads and into streams. These particles contain 6PPD, a rubber preservative used in virtually all car and truck tires worldwide. When 6PPD reacts with ground-level ozone, it forms 6PPD-quinone (6PPD-Q), a transformation product that is acutely lethal to coho salmon at environmentally relevant concentrations. In urban stream networks across Washington State, 40-100% of adult coho salmon die before they can spawn, a phenomenon researchers called 'urban runoff mortality syndrome' for decades before identifying 6PPD-Q as the culprit in 2020. This is not an abstract ecological concern. Coho salmon are a keystone species in Pacific Northwest ecosystems, and their commercial and tribal fisheries are worth hundreds of millions of dollars annually. The salmon runs that sustain Indigenous treaty rights are being decimated by a chemical that was never tested for aquatic toxicity before being added to every tire on the road. Each spawning adult that dies before reproducing represents a permanent loss to the population — coho are semelparous, meaning they spawn once and die, so every pre-spawn mortality is a 100% reproductive failure for that individual. Populations in urbanized watersheds are collapsing. The problem persists because 6PPD is in essentially every tire manufactured globally — it prevents tires from cracking due to ozone exposure, which is a safety-critical function. California's DTSC became the first regulator in the world to require tire manufacturers to find alternatives (effective October 2023), but the tire industry has stated that finding a substitute that preserves tire safety while eliminating aquatic toxicity could take years. Meanwhile, billions of tires continue shedding 6PPD onto roads worldwide. Stormwater treatment infrastructure in most cities was designed to handle sediment and basic pollutants, not to filter out nanoscale chemical transformation products from tire rubber. Retrofitting stormwater systems with bioretention or activated carbon filters is estimated to cost billions across the Pacific Northwest alone.