Oct 15, 2023

Update: On October 1, 2023: California Department of Toxic Substance Control (DTSC) 6PPD regulations became effective, making it the first government in the world to regulate the chemical content of vehicle tires to protect salmon. DTSC is requiring tire manufacturers to identify alternatives to the tire preservative that is the source of the chemical toxic to coho salmon.

More information on DTSC’s website.







As we drive our cars, the tires wear down and release tiny tire particles into the environment.  Due to our car culture, scientists estimate that the US has the highest tire particle emissions in the world—7 to 12 pounds per person every year! Most of this tire wear material lands on the ground close to roads, while some of it flies up into the air and contributes to local and global air pollution. Tire particles may be the biggest global source of microplastic (plastic particles smaller than 5 mm) pollution.

When it rains, stormwater runoff carries tire particles—and the toxic chemicals they contain—from city streets and highways to storm drains. In California, stormwater is usually not treated alongside wastewater, meaning urban stormwater runoff carries tire particles directly to surface waters through separate storm drain systems designed to prevent flooding and avoid sanitary sewer overflows. This means vehicle tire particles and associated chemicals are carried into fish habitat in creeks and estuaries like San Francisco Bay where they threaten water quality. 

SFEI completed a major field study of microplastics in San Francisco Bay in 2019 (report here; journal paper here), funded by the Gordon and Betty Moore Foundation, with support from the San Francisco Bay Regional Monitoring Program (RMP) and others. This work showed stormwater washes trillions of tire particles into the Bay each year. Furthermore, other recent work co-authored by SFEI has shown Bay Area stormwater contains a highly toxic chemical (“6PPD-quinone”) derived from vehicle tires at levels that are lethal to coho salmon and may pose risks to local steelhead.

In 2021, SFEI published a report funded by the California Ocean Protection Council and the RMP to identify the sources of microplastics in urban runoff and potential solutions. In this report, we identified a broad spectrum of prevention and treatment options to address tire pollution. The report is here.

Partially in response to SFEI’s recent findings and growing concern about the potential for adverse impacts to aquatic organisms from exposure to chemicals in tires, the California Department of Toxic Substances Control (DTSC) added motor vehicle tires to their 2021-2023 Priority Product Work Plan as a new product category.

A summary fact sheet on tires, related materials, and past microplastics work can be found on the SFEI microplastics page.


Related stories in the news:

West Coast Salmonids All Tired Out? 

Urban Stormwater presents pollution challenge 

Recent storms washed microplastics into San Francisco Bay, studies show

California moves to curb harmful tire pollutant collecting in Bay, threatening wildlife

DTSC news release


Ezra Miller and Kelly Moran
Associated Staff: 
Programs and Focus Areas: 
Clean Water Program
Bay Regional Monitoring Program
Contaminants of Emerging Concern