USTMA tackling tire additive issue harming coho salmon

WASHINGTON — It is somewhat ironic that a chemical additive in tire manufacturing meant to protect against degradation caused by the environment can morph into a previously unknown substance that is inimical to the environment.

Specifically, a chemical known as 6ppd-quinone is killing coho salmon in the Pacific Northwest before the fish can spawn in freshwater streams.

As such, research on this toxic substance (a previously unknown transformation product that may form when the additive 6ppd interacts with ozone)—and other chemicals that can be found in tire road wear particles—has taken on an immediacy like few other sustainability issues, one that has gotten the attention of the U.S. Tire Manufacturers Association and the CEOs leading the Tire Industry Project.

"We know that researchers face limitations in trying to cost-effectively create tire wear particles for accurate scientific study," said Sarah Amick, vice president of environmental health and safety and sustainability and senior counsel for the USTMA. "To support these researchers and help advance their work, USTMA is using a standardized methodology to produce cryogenically milled tire tread (CMTT), samples of which we will provide to researchers who study the potential human health and environmental impacts associated with tire wear particles."

The USTMA announced Nov. 15 at the 42nd Society for Environmental Toxicology and Chemistry Conference that it will provide this difficult-to-produce research material, not currently available on the market, by the second quarter of 2022.

The USTMA will contract with an outside laboratory to create CMTT, essentially a laboratory version of tire road wear particles (TRWP) but without any of the chemicals or minerals associated with pavement interaction, mass-producing the material for anyone wishing to study TRWP and its effects.

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

"This underscores the tire industry's commitment to sustainability," Amick said in an interview with Rubber News. "All of our member companies embrace achieving a more sustainable society—and one of the ways we can do that is by engaging with the research community."

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.

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 fish are born in freshwater streams, where they stay for about a year before making the long journey through rivers and estuaries and into the ocean. They return more than a year later to lay and fertilize eggs before dying.

Many obstacles have made this journey across different environments more difficult, according to CNRA, including shrinking estuaries, blocked passages from dams and culverts, drought and a changing climate.

And now 6ppd-quinone.

The additive 6ppd is an organic antioxidant and antiozonant 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 a year ago (in the study "A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon") as 6ppd-quinone.

And 6ppd-quinone, the study pinpointed, is responsible, through stormwater runoff, for killing the coho salmon.

The main problem, Amick said, 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 (which contains TRWP).

"How do you create something that is representative of what is in the environment?" Amick said. "And I think we are having some challenges with that.

"How much comes from the tire itself? How much is coming from TRWP? Our industry takes this study very seriously."

Even identifying 6ppd-quinone—a causal agent but perhaps not the only causal agent—took the experts at the University of Washington "quite a long time," said Julie Panko, principal scientist at Tox Strategies, a scientific consulting firm and close partner with the USTMA in the study.

"I think nearly all the researchers who have been studying tire wear and particles in the environment have acknowledged the challenges, the wide variety of tires on the road with so many different tire manufacturers," Panko said. "And there are pavement types as well that are incorporated into the tread.

"There are concerns over whether this is a newly generated particle as opposed to those that might come from used tires. There are just a whole lot of different challenges."

The CMTT methodology developed by the Tire Industry Project addresses many of those challenges—and eliminates the infinite variables presented by the natural environment.

"This will give everybody an opportunity to be researching the same thing so there is less variability in the test designs," Panko said."They have identified a causal material ... but we are still not sure how 6ppd-quinone causes the toxicity (in coho salmon). There are still many data gaps to be found."

Manufacturing CMTT

CMTT is the product of a standardized and reproducible laboratory process that grinds (or mills) tire tread to simulate the tire particles that are normally generated by the friction between tires and road surfaces. It is a mix of tiny rubber pieces that are representative of tire tread but do not contain chemicals or elements arising from pavement or any interactions with pavement.

"It involves removing the tread, which can be a very difficult thing to do in making sure we not capturing other compounds underneath the tread," Amick said.

The CMTT to be manufactured and distributed by the USTMA will use treads from passenger, light truck and bus tires, Panko said, all from North American manufacturers. This selection was decided between the USTMA and the University of Washington as the best possible representation of TRWP.

For researchers who study TRWP, CMTT offers a surrogate material that eliminates external contamination sources that make contact with tires during normal operational use, according to the USTMA.

CMTT is not a direct replacement for the study of TRWP, but allows researchers to isolate and focus studies on the tire tread component.

At this point it does not appear that any other fish or animal species are affected by the chemical 6ppd-quinone, but the University of Washington study cautioned that the possibility should be considered.

"A couple of researchers have looked at other aquatic species ... and there is no acute toxicity to those species," Amick said.

While tire manufacturing is a complex process, ensuring passenger safety takes top priority.

Finding an alternative to the performance additive 6ppd may be the ultimate goal (an alternative that currently does not exist), however mitigating the effects of 6ppd-quinone might be the only short-term option.

Whether that comes through biotechnologies like rain gardens and bioswells to dilute urban runoff; through infrastructure changes like specific roadway gutters or vacuums; or through automotive advancements like wheel wells that can catch the tire road wear particles, remains to be seen.

"We need to mitigate the impacts while we work on an alternative," Amick said.

USTMA, Tire Industry Project lead the way

The Tire Industry Project is a scientific research organization that began in 2005, dedicated to research on sustainable topics in the tire industry, especially as they relate to end-of-life tire issues.

Led by global CEOs—all TIP members are USTMA members—the project is guided by a scientific review board that analyzes how tire wear exists in the environment, and how the minerals in the roadway and the tread material itself interact.

TIP is the pioneer of the cryogenically milled tire tread process that will be followed by the USTMA in production of CMTT. TIP is under the auspices of the World Business Council for Sustainable Development and is co-led by Bridgestone, Goodyear and Michelin.

The group meets once every two years and brings in oversight from independent scientists who review the research.

"The Tire Industry Project created this methodology to support research on tire wear by providing a reliable and affordable material for lab experiments," said TIP Director Anne Cecile Remont. "With more than a decade of experience researching TRWP and producing tire test materials, we understand the scientific importance of representative test materials. CMTT is complicated and costly to produce, and we support efforts to remove barriers to the use of appropriate materials for TRWP research."

Researchers will be able to request CMTT samples via the USTMA website at ustires.org/CMTT beginning in November, with samples available by 2022 to ship to researchers.

"We wanted to make it easy as possible for researchers. Whether (environmental impacts) are happening in the U.S. or abroad, this is for anyone to conduct their research," Amick said.

Members of the Tire Industry Project include Bridgestone, Continental, Goodyear, Hankook, Kumho Tire, Michelin, Pirelli, Sumitomo Rubber, Toyo Tire and Yokohama Rubber.

The USTMA is the national trade association for tire manufacturers that produce tires in the U.S. The association's 12 member-companies operate 57 tire-related manufacturing facilities in 17 states and generate more than $27 billion in sales annually.