Dec 4, 2020

Scientists at the San Francisco Estuary Institute (SFEI) have found a highly toxic tire-related contaminant at levels lethal to coho salmon in stormwater flowing through four sites in the Bay Area. The contaminant, derived from a tire preservative, has been discovered by Washington state researchers to be responsible for high levels of coho salmon deaths in Puget Sound streams. These findings will  inform a petition by state stormwater leaders to the Department of Toxic Substances Control to address pollution of California streams caused by tires.

The research team, led by scientists at the University of Washington and Washington State University, published the results of their investigation yesterday in the journal Science. The chemical, 6PPD-quinone (pronounced "kwih-known"), can wash into streams along with tire wear particles when it rains. Scientists at San Francisco Estuary Institute collected samples from nine Bay Area streams and storm drains during storm events; four contained levels of this contaminant above the concentration at which half the coho salmon die after a few hours of exposure in laboratory experiments. SFEI’s Alicia Gilbreath and Rebecca Sutton are co-authors on the study.

A previous study by SFEI found that nearly half of the estimated seven trillion microplastic particles in urban stormwater flowing through local streams into S.F. Bay could potentially be linked to tire wear. These new findings indicate such particles can be toxicologically relevant. 

Coho salmon no longer reside in San Francisco Bay and its streams, but they are being restored to coastal streams from Santa Cruz to Sonoma County. They currently populate the Klamath, Smith and Eel Rivers further north. Researchers are also concerned that steelhead trout and Chinook salmon exhibit some sensitivity to tire rubber chemicals, and studies are ongoing on those species.

California’s stormwater leaders have petitioned the state Department of Toxic Substances Control for over two years to act on the issue of water pollution caused by another harmful chemical in tires, zinc.  These new findings will be presented to DTSC as they determine whether to investigate this issue.  

Key news stories about these important findings:

Programs and Focus Areas: 
Clean Water Program
Contaminants of Emerging Concern