USTMA, USGS collaborate on research into 6ppd alternative

WASHINGTON D.C.—The push to find an alternative to the tire antidegradant 6ppd—an additive that is critical to consumer safety but can transform into an offshoot chemical that is fatal to some fish species—continues for the U.S. Tire Manufacturers Association.

The group said Nov. 15 it will partner with the U.S. Geological Survey in a 10-month joint research project intended to "assess and refine methods of evaluating potential alternatives to 6ppd for use in tires."

"Every day, with every partner we can, USTMA is pushing forward in the industry's effort to identify potential alternatives to 6ppd, and we recognize that additional research is necessary," Anne Forristall Luke, USTMA president and CEO, said in a statement. "As USTMA continues its mission of advancing sustainability in the tire industry, our work with USGS will break new scientific ground, benefiting the environment, communities, researchers and manufacturers alike."

According to academic studies that took place in 2020 at the University of Washington, the antiozonant and antioxidant 6ppd at some point becomes 6ppd-quinone during tire abrasion when it interacts with ozone.

Stormwater runoff, which contains both tire wear particles (and therefore 6ppd-q) as well as road-related particles, ultimately finds its way into the streams and waterways of the region, killing coho salmon and "other salmonids."

Announcement of the USTMA-USGS partnership comes eight days after two Pacific Northwest fishing groups, under the counsel of the Seattle-based non-profit Earthjustice, sued the 13 North American USTMA member companies for immediate injunctive relief from any further commercial use of tires containing 6ppd.

The Nov. 8 lawsuit was filed under the auspices of the Endangered Species Act.

In addition, the U.S. EPA on Nov. 2 granted a petition submitted in August by three Pacific Northwest Indian tribes affected by the waning numbers of coho salmon—and other fish species—caused by 6ppd-quinone.

The EPA's approval of the petition essentially means the organization will engage in a science-based rulemaking process in regards to 6ppd, using the Toxic Substances Control Act as guidance.

6ppd has been used to increase tire endurance and decrease the likelihood of cracking in motor vehicle tires since the 1970s.

In this study, USTMA and the USGS' Western Fisheries Research Center will work to establish a new method for the testing of 6ppd alternatives.

Toxicological data, gleaned through in vitro toxicity testing of fish cell linings, will be available by March 2024—the same month by which the USTMA must submit a report to meet requirements for the 6ppd Alternatives Analysis under the California Safer Consumer Products regulation.

The goal of the recently announced partnership, according to the USTMA, is not necessarily to find an alternative to 6ppd, but rather to help narrow the parameters for tire manufacturers in the search for one.

"An attractive component of this methodology is that it does not require testing on a live fish," the USTMA said.

According to the USGS, fish cell lines will be exposed to rubber containing three 6ppd alternatives and their respective "transformation products."

The toxicity levels of each fish cell line then will be compared to the toxicity levels of those exposed to 6ppd-quinone.

"While this initial research is not expected to immediately identify a 6ppd alternative, each of the three alternatives represent a different class of chemical compounds and will inform future research," according to the USTMA.

A USGS spokesperson said he hopes the results will assist as the search for an alternative continues.

"The USGS is committed to working with federal, state, tribal, industry and other partners who share our scientific rigor to address this complex challenge," said Michael Schmidt, director at the USGS Western Fisheries Research Center. "This joint research with USTMA is one important piece of our work aimed at filling top-priority knowledge gaps, not only on potential 6ppd alternatives, but also in how to evaluate them with brand new investigative methods."

The effort to find an alternative to 6ppd already is underway, with the USTMA compiling a consortium of 16 of the world's largest tire manufacturers to tackle the aforementioned Alternatives Analysis research.

"As a science-driven industry, committed to safety and environmental stewardship, U.S. tire manufacturers take the environmental impact of 6ppd-quinone seriously," the USTMA said in a Nov. 2 statement.

In December 2020, USTMA requested that the California Department of Toxic Substances Control include 6ppd in tires on the 2021‐23 "Priority Products Work Plan."

DTSC listed motor vehicle tires containing 6ppd as a priority product in California, effective Oct. 1 of this year.

"Well before this date, USTMA members began a comprehensive Alternatives Analysis to seek an effective alternative," the organization stated. "Any premature prohibition on the use of 6ppd in tires would be detrimental to public safety and the national economy."

In the Alternatives Analysis, USTMA-affiliated companies are guided in their research by California's Safer Consumer Product Regulations, and the listing of 6ppd as a "priority product" within the program.

The SCPR framework helps products and chemicals comply with Federal Motor Vehicle Safety Standards and other consumer, vehicle and tire manufacturer requirements.

Domestic and foreign tire manufacturers have until Nov. 30 to notify DTSC if they manufacture 6ppd-containing tires that are used in California, a DTSC spokesman recently confirmed to Rubber News.

The USTMA believes a full mitigation strategy also must be undertaken, one that includes infrastructure efforts to filter or eliminate tire road wear particles, which contain roughly 50 percent tire abrasion particles and 50 percent road-related particles.