"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."
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.