USTMA backs California's plan to study 6ppd, coho salmon

WASHINGTON—The tire manufacturing additive 6ppd, an antioxidant and antiozonant essential to passenger safety and harmful to coho salmon when transformed into 6pp-quinone, has been elevated in priority as a substance to be studied.

This was due, in part, to the efforts of the U.S. Tire Manufacturers Association, which on May 23 endorsed a same-day decision by the California Department of Toxic Substances Control to list 6ppd as a "priority product" under the Safer Consumer Products Regulations.

"USTMA supports the decision by the California DTSC to list 6ppd as a priority product under the state's green chemistry program," said USTMA President and CEO Anne Forristall Luke. "We are fully committed to continuing to work with the DTSC team to find a viable alternative."

The USTMA has been partnering with the University of Washington since 2019 on the study of urban runoff mortality syndrome, the technical name for what is affecting the coho salmon, according to a report from Nov. 17, 2021.

Ultimately, a study by Tian et. al known as "A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon" was published in December 2020, drawing a scientific link between 6ppd-quinone and coho salmon (and possibly other aquatic species') mortality rates.

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"We are pleased that there have been many advancements in the body of research on 6ppd-quinone," said Sarah Amick, vice president of Environmental Health Safety and Sustainability and senior counsel for USTMA. "However, many data gaps still remain, so we remain committed to collaborating with researchers, regulators and stakeholders to fill these knowledge gaps and help find a viable alternative to 6ppd that does not compromise tire performance or driver safety and also ensures environmental safety."

The additive 6ppd is an organic chemical used to prevent cracking and heat buildup in tires, physical performance characteristics that are crucial to passenger safety.

But at some point, when 6ppd has ozone (O3) introduced to it during tire wear, the chemical can become what the University of Washington identified 18 months ago as 6ppd-quinone. And 6ppd-quinone, the study pinpointed, is responsible, through stormwater runoff, for killing the coho salmon.

"Any viable alternative to 6ppd in tires must provide the same critical protection as 6ppd to ensure driver and passenger safety," the USTMA said May 23. "Importantly, any potential substitute must also avoid any regrettable environmental impacts of its own."

Also known as silver salmon, coho are prized among fishermen and an important indicator species for environmental health. Their range stretches from creeks nestled in the redwood forests near Santa Cruz north to the waters of Alaska.

The few coho populations that still exist in California are either endangered or threatened, according to the California Natural Resources Agency.

The USTMA notes that it recommended adding 6ppd to the California regulatory list immediately following the December 2020 Tian et al. study.

The USTMA said Nov. 15, 2021, at the 42nd Society for Environmental Toxicology and Chemistry Conference that it will provide cryogenically milled tire tread (CMTT), a difficult-to-produce research material not currently available on the market.

The USTMA told Rubber News May 23 that the material is likely to be available for shipment by mid-third quarter of this year, though an exact date was not yet known.

Producing CMTT helps to circumvent problems that can occur with the study of tire and road wear particles (TRWP), a known source of 6ppd-quinone in the environment.

The main problem, Amick told sister publication Rubber News late last year, is that researchers do not know if 6ppd-quinone is formed from the wear of the tire tread itself, or from within the chemical soup that is urban stormwater runoff.

Even identifying 6ppd-quinone—a causal agent but perhaps not the only causal agent that is inimical to coho salmon—took the experts at the University of Washington "quite a long time," another study collaborator told Rubber News last year.

The USTMA will contract with an outside laboratory to create CMTT, essentially a laboratory version of TRWP but without any of the chemicals or minerals associated with pavement interaction (eliminating the infinite variables introduced by the natural environment) and mass-producing the material for anyone wishing to study TRWP and its effects.

The CMTT to be manufactured and distributed by the USTMA will use tread particles from passenger, light truck and bus tires, all from North American manufacturers.

This selection was decided between the USTMA and the University of Washington as the best possible representation of TRWP.

USTMA members will fund production of the material, Amick said.

"As global leaders in manufacturing, USTMA member companies embrace a shared responsibility of helping to achieve a more sustainable society," the USTMA said May 23. "Tire manufacturers are dedicated to understanding and reducing the environmental impact of their products."

While continued research is underway, USTMA said it supports bio-retention technologies such as rain gardens and bioswales, which have shown to reduce the impact of 6ppd-quinone on coho salmon.

The USTMA comprises 12 member companies that operate 57 tire-related manufacturing facilities in 17 states and generate more than $27 billion in annual sales.