California approves first stage of USTMA's 6ppd analysis

WASHINGTON—The wheels are turning at both the federal and state levels in the search for an alternative to 6ppd.

The California Department of Toxic Substances Control on Aug. 26 issued a notice of compliance to the U.S. Tire Manufacturers Association for the group's Stage 1 alternatives analysis report, clearing the way for a second, final stage to begin.

Simultaneously, the tire antidegradant that has been linked to salmon deaths in the Pacific Northwest is under consideration for rulemaking by the U.S. EPA, as petitioned by several Native American tribes in 2023.

"USTMA and the (tire manufacturing) consortium deeply appreciate the collaboration with California DTSC to produce the most thorough possible Stage 1 report on potential 6ppd alternatives," said USTMA President and CEO Anne Forristall Luke. "We remain committed to our industry being a leading force in the search for solutions. We look forward to producing a similarly rigorous Stage 2 report and continuing additional work on identifying viable 6ppd alternatives."

The California DTSC did not immediately return requests for comment from Rubber News.

According to the USTMA, the DTSC commended the group for "its continued efforts to seek safer alternatives to 6ppd" and "open communication about research updates and results."

The USTMA requested that 6ppd be added to the agency's priority product consideration in 2020. The California DTSC listed tires containing 6ppd as a priority product to be studied under its Safer Consumer Product Regulations Oct. 1, 2023.

At the heart of the study is the additive 6ppd, a small-molecule ozone and oxygen scavenger that "blooms" to the surface of a tire to protect the tire from cracking and splitting as it wears.

However, as 6ppd is shed, its molecular structure can morph into the salmon-killing 6ppd-quinone, which ultimately finds its way into the streams and waterways of the Pacific Northwest via tire road wear particles.

While 6ppd-q was identified in December 2020 (Tian et al., 2021), 6ppd has been used since the late 1960s in tire compounding.

"Elimination of 6ppd without a replacement is not an option," the Stage 1 report, released March 25, states.

A total of 60 initial chemical candidates were considered during the Stage 1 alternatives analysis for 6ppd, with 21 non-ppd-derived chemicals and 19 ppd-derived chemicals making an initial cut to 40.

Of those, seven made the Stage 2 cut as "potential possibilities" to replace 6ppd, including 7ppd, Ippd, 77pd, CCpd and a specialized graphene, known as Prophene.

While non-ppds "pose greater challenges in terms of incorporation into tire chemistry," alternative ppds represent "the most logical and possibly easiest to implement" options, the Stage 1 report states.

With about 36.5 million tires shipped into California last year alone, there are no tires, according to the report, that are absent of 6ppd. 6ppd also can be found in non-tire rubber products.

The Stage 1 report cautions that there are major information gaps as well, including the biochemical mechanisms by which salmonids are affected by 6ppd-q; the environmental effects of the alternatives that "made the cut" for further study; and the transformational products (like 6ppd exhibits with 6ppd-q) of the identified alternatives.

But the mission is clear, according to the report: "Do potentially safer, functionally acceptable and technically feasible alternatives to the priority product exist that should be given more in-depth consideration to determine if they qualify as acceptable alternatives?"

USTMA officials say they are optimistic that, by the end of the alternatives analysis process, "one or more possible 6ppd alternatives with potential to replace or materially reduce the level of 6ppd in motor vehicle tires" will be identified, subject to performance testing and comparable safety performance.

"The rigor, collaboration and transparency involved in this preliminary evaluation demonstrates our industry's commitment to this alternatives analysis process," Tracey Norberg, USTMA executive vice president and general counsel and project lead on the report, told Rubber News earlier this year. "Investigation of possible alternatives to 6ppd is a dynamic area of research."

During Stage 2, USTMA and the consortium will confirm an even shorter list of possible alternatives (in light of any new data that emerges), assess the potential impacts of these options and initiate a more detailed review of the chemicals' potential hazards and exposure-related chemical properties.

The consortium's Stage 2 report is due to DTSC Aug. 19, 2026, with an annual progress report due Aug. 19, 2025.

The consortium conducting the alternatives analysis comprises 32 global tire manufacturers, including all 16 of USTMA's member companies.

Other options (outside of an alternative to 6ppd), such as the non-pneumatic tire, infrastructure tire road wear particle collection options and tire-particle catchers on vehicles themselves were mentioned, but purposefully not considered as options as part of the alternatives analysis.

Non-pneumatic tires still will require an antidegradant, and tire manufacturers cannot dictate policy for something like a tire particle catcher, according to the report.

6ppd is the subject of at least one major lawsuit, the request for an immediate ban on 6ppd brought in October 2023 under the Endangered Species Act by two Pacific Northwest fisheries against the tire manufacturers.

And the chemical is under consideration for rulemaking by the EPA prohibiting the manufacturing, processing, use and distribution of 6ppd in tires under the Toxic Substances Control Act, as petitioned in August 2023 by several Pacific Northwest Native American tribes.

EPA granted the tribes' petition in November 2023, effectively entering 6ppd in "consideration of" the rulemaking process.

However, EPA also stated in granting the petition that the agency "cannot commit to a specific rulemaking timeframe or outcome," aiming to publish a notice of proposed rulemaking by fall 2024 and to finalize a rule before 2025.

In addition, EPA has finalized water quality screening guidance for determining 6ppd and acute 6ppd-quinone levels in freshwater ecosystems, including stormwater runoff.

The threshold values and methodology, known as EPA Method 1634 and published in the Federal Register under the Clean Water Act June 10, is intended for measurement of short-term concentrations of 6ppd and 6ppd-q.

The guidance was fast-tracked for use by tribes, states and local governments, EPA said.

"Achieving clean water that protects aquatic life and supports commercial, recreational and cultural fishing practices takes partnership at all levels of government," said Bruno Pigott, acting EPA assistant administrator for water. "6ppd and 6ppd-q can be lethal to fish, so it's important we know where it's polluting waterways. The EPA's screening values provide important information that our partners can use to protect fish populations—especially coho salmon on the Pacific coast."