6ppd research intensifies entering 2024

The last year saw the tire additive 6ppd and its transformational offshoot 6ppd-quinone take center stage for tire manufacturers, Pacific Northwest fisheries and Native American tribes—as well as the U.S. EPA and California Department of Toxic Substances Control.

The additive is critical to consumer safety in preventing tire cracking and wear, but a 2020 University of Washington study found that at some point during tire abrasion, the chemical transforms into 6ppd-quinone, which is killing some salmon species via tire and road wear runoff.

Two major fisheries—the Institute for Fisheries Resources and the Pacific Coast Federation of Fisherman's Associations—filed a lawsuit Nov. 8 against 13 of the world's largest tire manufacturers, demanding an immediate end to the use of 6ppd in tire manufacturing.

In August, on behalf of a coalition of three American Indian tribes in the Pacific Northwest, the non-profit Earthjustice filed a petition with the U.S. EPA demanding an immediate ban on the manufacture and sale of tires containing 6ppd.

And it has been all hands on deck to find an alternative to 6ppd since the 2020 discovery of 6ppd-q.

Tire manufacturers are pursuing a small-molecule, drop-in alternative, while other, private firms—like Flexsys America L.P. and Austin, Texas-based Molecular Rebar Design L.L.C.—have received federal grants to pursue other avenues to replace or reduce the use of 6ppd in tire manufacturing.

In the public realm, the state of California has taken the lead in its own alternative analysis, working with the U.S. Tire Manufacturers Association in researching 6ppd as a "priority product."

The agency had set a Nov. 30 deadline for tire makers—both domestic and international—to notify it if they produced tires containing 6ppd "in the stream of commerce" in California.

The Institute for Fisheries Resources and the Pacific Coast Federation of Fisherman's Associations filed a lawsuit Nov. 8 against 13 of the world's largest tire manufacturers, seeking "immediate injunctive relief" against the use of 6ppd in tire production.

The complaint was filed by the non-profit Earthjustice under Section 9 of the Endangered Species Act, in the U.S. District Court for Northern District of California in San Francisco.

"Defendants' inclusion of 6ppd in their tires directly harms plaintiffs, because the proliferation of 6ppd-quinone—and resulting die-offs of coho salmon, Chinook salmon and other salmonids—has decimated the commercial salmon fishing industry in which many of their fishing family members make their livelihoods," the lawsuit states.

The tire makers named in the suit are: Bridgestone Americas Inc.; Continental Tire the Americas L.L.C.; Giti Tire U.S.A. Ltd.; Goodyear; Cooper Tire and Rubber Co.; Hankook Tire America Corp.; Kumho Tire U.S.A. Inc.; Michelin North America Inc.; Nokian Tyres; Pirelli Tire North America; Sumitomo Rubber North America; Toyo Tire Holdings of Americas Inc.; and Yokohama Tire Corp.

All of the manufacturers named produce tires containing 6ppd, according to the complaint.

The two fishing industry groups cite nine Chinook salmon, four coho salmon and 11 steelhead trout fisheries that have been affected by 6ppd (and are protected under the ESA) in the 65-page complaint.

The fisheries—which account for an estimated 16,000 jobs in the region—extend from Alaska to Southern California.

The Nov. 8 lawsuit filed by Earthjustice on behalf of the fisheries came on the heels of an August petition filed by three Native American tribes in the Pacific Northwest—comprising nearly 10,000 people—who also are demanding an immediate ban on the manufacture and sale of tires containing 6ppd.

That petition was granted by the EPA Nov. 2, meaning the EPA will analyze the use and toxicity of 6ppd under the lens of the Toxic Substances Control Act.

Earthjustice filed this petition on behalf of the Port Gamble S'Klallam, Puyallup and Yurok tribes.

"This is a victory for salmon and all species and people," the Puyallup Tribal Council said in a statement to Rubber News. "6ppd is a major and uniquely lethal threat to the health of salmon in urban streams on our reservation. Banning this chemical from tires will be hugely important in protecting fish. We thank the EPA for taking our concerns seriously."

Under the TSCA, the EPA "in the coming months" will begin the rulemaking process.

However, while the agency added it will "promptly commence" an "appropriate proceeding" under TSCA, the agency said in its 6-page approval of the petition that it "cannot commit to a specific rulemaking timeframe or outcome."

Still, the petition's approval by the EPA is being hailed as a win by the tribes.

The U.S. Tire Manufacturers Association said in a Nov. 3 statement that it will work with the EPA on the TSCA risk management approach.

The 6ppd and 6ppd-quinone conundrum has not changed: How does the tire industry come up with a way to replace the essential chemical 6ppd with an environmentally friendly filler that continues to provide tire safety for consumers?

To research this, Akron-based Flexsys America L.P. in July said it will partner with the U.S. Department of Agriculture, as the Northeast Ohio chemical supplier explores potential bio-based alternatives for 6-para-phenylene-diamine.

The issue has become especially pressing as the California Department of Toxic Substances, under the auspices of the California EPA, approved tires containing 6ppd as "priority products" earlier this year.

And on Oct. 1, the rulemaking documents concerning 6ppd alternatives took effect with the California Office of Administrative Law.

"We are maximizing our efforts to bring the right scientists and researchers together to explore possible molecular structures to protect tires, people and the environment," Neil Smith, Flexsys chief technology and sustainability officer, told Rubber News.

Flexsys' collaboration and exploration of a bio-based 6ppd replacement is a critical undertaking.

Flexsys will work with the Agricultural Research Service on fundamental chemistry, bio-based materials and applications testing, the chemical supplier said.

Some basic research has been performed in the past 50 years on 6ppd alternatives, as the troublesome and transformational chemical 6ppd-quinone had not been identified until three years ago.

Therefore, there are no known, commercially viable replacements "that exhibit equivalent or better passenger safety, tire performance and anti-degradation properties," according to Flexsys.

The U.S. EPA has awarded Molecular Rebar Design L.L.C. a grant of just less than $100,000 to study the "reduction or replacement of 6ppd" in commercial tires, through improved tire cracking resistance.

The $99,989 grant, awarded Nov. 28 to the 14-year-old company that works in carbon nanotube technology, will allow MRD to study whether CNTs can be a drop-in replacement for 6ppd; complement the chemical additive to allow lesser loadings of 6ppd per tire; or be used in conjunction with another, less effective but perhaps more environmentally friendly chemical additive, like 77PD.

"We are looking at whether you can take a combination of technologies and get something commercial in a couple years," August Krupp, director of rubber development for MRD, told Rubber News. "Improvements for treadwear, within the rubber itself, is our focus."

By design, 6ppd migrates to the tire surface during use to create a protective film against degradation.

But herein lies the conundrum.

6ppd exists everywhere within a tire—in the tread, carcass and sidewall—because it is a small-molecule chemical intended to be mobile.

And this mobility also allows the chemical to get into tire roadway runoff very easily.

CNTs may provide a replacement for the embattled 6ppd—but not as a small-molecule chemical drop-in replacement, as other tire manufacturers and some private companies are analyzing.

Essentially, MRD is looking at preventing or minimizing the microcracking that can lead to larger crack growth—"treating the cold itself, rather than the symptoms of a cold."

Thus far, the public has heard from the U.S. EPA, the USTMA, the California DTSC and from companies involved in the search for an alternative for 6ppd.

With the petition granted Nov. 2 by the EPA for the three tribes and the lawsuit filed Nov. 8 by the two fishing industry groups, five more groups have joined the conversation under the counsel of Earthjustice.

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 research, and the California DTSC outlining the process for the USTMA.

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

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.

In addition, the USTMA announced 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."