SACRAMENTO, Calif.—The California Department of Toxic Substances Control is set to finalize its listing of "motor vehicle tires that contain 6ppd" as "priority products" by the end of the first quarter of this year.
If the listing goes into effect, "anyone who manufactures motor vehicle tires containing 6ppd for sale in California" has to submit a priority product notification and comply with the alternatives listed in the Safer Consumer Product Regulations.
"The way the California law works, the manufacturers of the products—tire manufacturers—are primarily responsible for completing the alternative analysis," Sarah Amick, USTMA senior vice president of environmental, health, safety and sustainability, and senior counsel, told Rubber News. "Once we complete the alternative analysis, we provide (it) to DTSC for review.
"Their process is one of the most stringent (alternative analysis) processes in the world, (and) it requires our members to assess over 100 environmental factors in evaluating potential alternatives."
The antioxidant and antiozonant 6ppd, essential for tire performance and consumer safety, can transform into 6ppd-quinone at some point during tire wear, a chemical offshoot that is fatal in minute toxicity levels to coho salmon in the Pacific Northwest.
As such, 6ppd remains the focus of alternative analysis studies by the U.S. Tire Manufacturers Association, considered the stakeholder in the priority product listing. The USTMA represents tire firms that produce tires in the U.S.
Here are four key points to keep in mind as the DTSC and USTMA work toward a viable solution for the environment and consumer safety.
The public comment period for the proposed rule adding tires containing 6ppd to the Safer Consumer Product Regulations in California closed on July 20, 2022, according to Karl Palmer, deputy director for the Safer Consumer Products Program at DTSC.
"DTSC reviewed all the public comments we received and determined that no modifications to the proposed rule were needed," Russ Edmondson, media information officer with the DTSC, told Rubber News recently. "We are finalizing the rulemaking documents now and expect to submit them to the Office of Administrative Law this quarter."
If the regulation is approved by OAL, the effective date would be July 1, 2023, Edmondson said.
And two months after that, the implications for the tire manufacturing community, certainly in California and likely outside of the state as well, become very real.
"Within 60 days of this date of the regulation, anyone who manufactures motor vehicle tires containing 6ppd for sale in California must submit a 'Priority Product Notification' and determine how they will choose to comply with the Safer Consumer Products requirements," Edmondson said.
For the USTMA, the scope of possible alternatives for 6ppd include a "drop-in replacement;" a redesign of the product to reduce exposure; a reduction in the use of the chemical; or infrastructure mitigation measures.
By design, 6ppd migrates to the tire surface during use to create a protective film against degradation.
Somewhere between tire abrasion and the streams and waterways of the Pacific Northwest, 6ppd morphs into the previously undiscovered chemical 6ppd-quinone when it comes into contact with ozone.
In turn, 6ppd-quinone then finds its way into urban runoff via tire road wear particles.
Amick said it is important to note that tire road wear particles are "roughly 50 percent tire tread and 50 percent road surface."
And tire road wear particles can be affected by tire type, size and design; vehicle characteristics such as weight and engine torque; weather; driving behavior; and road characteristics.
For this reason, infrastructure mitigation (including permeable pavements) should be given its due diligence as a possible alternative, Amick said.
"On mitigation, we know while we are working toward evaluating existing alternatives that there are things that can be done to mitigate 6ppd-quinone in the environment today," Amick said. "So while we are supporting the chemical manufacturers in the possible development of a new molecule ... we think that 360-approach is important."
Cryo-milled tire tread (CMTT), developed jointly by the USTMA and the World Business Council for Sustainable Development's Tire Industry Project, now is available free of charge for researchers, governments and academic institutions to study the 6ppd/6ppd-quinone conundrum.
CMTT is not a direct replacement for the study of TRWP, rather it allows researchers to isolate and focus on the tire tread component. The CMTT methodology developed by the Tire Industry Project essentially eliminates the infinite variables presented by the natural environment.
The CMTT uses treads from passenger, light truck and bus tires, all from North American manufacturers.
USTMA members are funding production of the material, Amick said.
"So far, we have received and fulfilled roughly 40 requests," Amick said.
More information is available at ustires.org/cmtt.
"As we have shared," Amick said, "6ppd serves a critical purpose in a tire—to help tires resist degradation and cracking—which is vital for driver and passenger safety.
"One thing that is often overlooked but important to understand is the amount of engineering and chemistry that goes into manufacturing tires. It is not an easy task to change a material in a tire because all the materials in a tire must function together in order to meet critical performance and safety requirements."
The two-year-old Tian et al. study is the root motivation for the process today that has 6ppd in the crosshairs of the California Environmental Protection Agency, which oversees the DTCS.
"While heavy metals and polycyclic aromatic hydrocarbons have long been regulated pollutants in stormwater, recent studies have reported numerous emerging organic contaminants such as various pesticides, pharmaceuticals, plasticizers, and vehicle and tire rubber-related contaminants," the Tian study states.
Calling it "stormwater-linked urban runoff mortality syndrome," death rates for coho salmon across Pacific Northwest sub-basins correlated with road density and traffic intensity, according to the study.
The academic researchers ultimately used juvenile coho salmon provided by the Puyallup Tribe of Indians to conduct the "in-house" studies.
Five outdoor sites were used, with two roadway runoff sites measured in Seattle and one in Los Angeles; and one site "receiving water" in Seattle (Puget Sound) and another in San Francisco.
In specific northern California areas, coho salmon, which are integral to Native American diets and cultures, are declining to a fraction of what they were at their peak in the 1960s, at around 55,000 "new individuals" per year counted through fish ladders in the Pacific Northwest.
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