Chemical in Tires Killing Coho Salmon in California

The state Department of Toxic Substances Control (DTSC) has adopted a rule that requires manufacturers of motor vehicle tires for sale in California to evaluate safer alternatives to 6PPD, a chemical that helps reduce tire cracking and extends the useful life of tires. 

The Department said this is to protect California’s environment and public health.

6PPD reacts with ozone in the air to form another chemical, 6PPD-quinone, that was found to kill coho salmon as they migrate upstream to spawn. This toxic chemical has been detected in California streams at concentrations shown to kill at least half of coho in laboratory studies.

DTSC’s regulation to add motor vehicle tires containing 6PPD to the state’s list of Priority Products, which was proposed in 2022, will take effect on October 1, 2023. Domestic and foreign manufacturers will have until November 30, 2023 to notify DTSC if they manufacture 6PPD-containing tires that are placed into the stream of commerce in California. DTSC is working with the US Tire Manufacturers Association (USTMA) to help tiremakers navigate the process.

“We are working with the EPA, other states, researchers, and the Tire Manufacturers Association to find a path to make tires safer for our environment without compromising on-road safety,” said DTSC Director Dr. Meredith Williams.

The new regulation is the culmination of work that started after scientists in the Pacific Northwest found a startling link between coho salmon deaths and 6PPD used in motor vehicle tires. In California, the loss of coho salmon has significantly affected Native American tribes, whose lifeways rely on the fish. The confirmed presence of 6PPD-quinone in California’s waterways threatens the state’s remaining coho salmon populations, which have been classified as endangered or threatened by the state. Mounting evidence indicates that 6PPD and 6PPD-quinone also pose threats to other aquatic organisms.

“DTSC’s Alternatives Analysis process requires manufacturers to identify and compare the impacts of potential alternatives with those of the Chemical of Concern across a product’s life cycle,” said DTSC Deputy Director Karl Palmer. “6PPD plays a crucial role in the safety of tires on California’s roads and, currently, there are no widely available safer alternatives. For this reason, our framework is ideally suited for identifying alternatives to 6PPD that ensure the continued safety of the tires on California’s roads while protecting California’s fish populations and the communities that rely on them.”