When large numbers of coho salmon heading upstream to spawn started becoming disoriented, swimming on their sides, gasping, and dying in urban waterways before they could lay their eggs, no one knew why. Stormwater runoff was eventually linked to the die-offs, and in 2020 researchers at the University of Washington and Washington State University identified 6PPD-quinone (6PPD-q), a highly toxic aquatic contaminant, as the cause.
6PPD-q is a toxic chemical that can contaminate waterways. It is lethal to coho salmon in low concentrations, can cause harm to other fish and wildlife, and may have human health impacts. 6PPD-quinone, pronounced “kwi-KNOWN”, results when vehicle tires wear down and are exposed to ozone, a form of oxygen. All vehicle tires manufactured since 1960 contain 6PPD, the precursor to 6PPD-q. 6PPD is an additive designed to extend product life by preventing synthetic rubber products from cracking. Other products that contain 6PPD include footwear, artificial turf, and synthetic playground surfaces. While manufacturers are investigating other options, there is currently no known alternative to 6PPD.
As vehicle tires wear down through normal use, dust particles thinner than a human hair are deposited on roadways. These tiny particles can become airborne through wind or traffic movement and then land on surfaces, soils, and plants. When it rains, tire-wear particles can wash into waterways in runoff or through storm drains. These particles can leach 6PPD, 6PPD-q, and other toxic chemicals into the environment. The particles can also be ingested and absorbed by invertebrates and fish, including migrating salmon.
In the fall, rainstorms that raise river levels for coho and other salmon species to swim upstream to spawn also wash accumulated roadway pollutants into urban waterways. Concentrations of 6PPD-q found in stormwater after heavy rains can exceed toxicity levels for coho, and may reach toxic levels for significant numbers of steelhead and Chinook. Clean waterways are crucial for salmon and steelhead survival. Together with the Department of Ecology, other state agencies, and federal, local, and tribal governments, the Washington Department of Fish and Wildlife (WDFW) is studying the effects of 6PPD-q on the ecosystem while working to help reduce 6PPD-q pollution. WDFW’s Toxics Biological Observation System (TBiOS) team is partnering with the National Oceanic and Atmospheric Administration (NOAA) Northwest Fisheries Science Center to develop analytical methods that will allow the team to monitor for 6PPD-q in indicator species. Detectable levels of 6PPD-q have been found in aquatic species such as mussels, juvenile Chinook salmon, and English sole; however, the potential health impact for humans and wildlife who consume fish and shellfish contaminated with 6PPD-q at the observed concentrations are currently unknown.
Visit the Department of Ecology website for up-to-date information on 6PPD-q and more details on reduction of priority toxic chemicals.