"Potentially Lethal Concentrations of 6PPD-Quinone Occur in Endangered Species Act Listed Aquatic Habitats of Central California" Environmental Science & Technology Letters
Endangered coho salmon and steelhead trout live and spawn in habitats surrounded by human activity, such as the San Francisco Bay area. During a recent storm, researchers found high levels of the tire-derived pollutant 6PPD-quinone in roadway outflows, creeks, and rivers. They report in ACS' Environmental Science & Technology Letters that many samples exceeded levels considered fatal to juvenile salmon. Treating stormwater runoff and creating less toxic or non-toxic tire materials could make healthier environments.
6PPD-quinone is not the only harmful component of roadway runoff, so finding scalable and cost-effective solutions is important." - Ed Kolodziej
Adapted from Environmental Science & Technology Letters 2026, DOI: 10.1021/acs.estlett.6c00745
Rubber tires contain a protectant chemical, called 6PPD, that reacts with ozone in the air and forms 6PPD-quinone. Wind and rain transport tire debris and 6PPD-quinone into waterways, where it's highly toxic to several fish species, including brook and rainbow trout . Coho salmon and steelhead trout are also highly susceptible to 6PPD-quinone, but not much is known about their exposure to the pollutant at the southern end of where the fish live along the U.S. West Coast. So, Ed Kolodziej and colleagues wanted to measure its concentration in critical watersheds where the fishes live and spawn along the Central California coast.
"These species are protected under the Endangered Species Act, and these are their most vulnerable and high-risk habitats," says Kolodziej, the corresponding author of this study.
The researchers collected water samples from six road outfalls, 14 creeks and rivers, and two estuaries around the San Francisco Bay and the nearby coast in the peak of a rainstorm to provide a snapshot of potential exposure. Several sampling sites are designated as Endangered Species Act critical habitats for coho salmon and steelhead trout, and habitat protections are mandated. The team found that:
- 6PPD-quinone levels in 78% of the samples exceeded the U.S. Environmental Protection Agency's value for the potential to cause acute harm to aquatic organisms.
- In 69% of samples, the pollutant exceeded the concentration that's considered lethal to half of juvenile coho salmon exposed within 24 hours.
- Concentrations of 6PPD-quinone tended to be higher in creeks near heavy traffic and substantially lower at estuary locations, indicating that proximity to busy roadways will have the biggest impact on the pollutant's accumulation in bodies of water.
One of the creeks had extensive habitat restoration efforts, but it also had some of the highest 6PPD-quinone levels measured in the study. "A great habitat with toxic water quality makes the problem worse. You are creating an ecological trap for the fish," says Kolodziej. The authors suggest that physical habitat restoration and water quality improvement be addressed together, especially in watersheds that support endangered and threatened species.
"6PPD-quinone is not the only harmful component of roadway runoff, so finding scalable and cost-effective solutions is important," says Kolodziej. He shares that potential strategies include treating stormwater in heavily traveled areas and developing tires with materials that are less toxic or non-toxic in the environment.
The authors acknowledge funding from Earthjustice and the Allan and Inger Osberg Endowed Professorship. A National Oceanic and Atmospheric Administration grant also supported the purchase of analytical instruments.
