6PPD and Tire Manufacturing

The tire industry uses 6PPD to help tires resist degradation and cracking, which is vital for passenger safety. 6PPD has been studied, but not enough is known about the newly discovered transformation product, 6PPD-quinone. USTMA and its members are committed to collaborating with researchers and regulators to better understand this material, fill knowledge gaps and determine next steps.

USTMA Positions on 6PPD and 6PPD-Quinone

6PPD and 6PPD-quinone are two distinct materials.

  • 6PPD is used in all USTMA member-company tires to resist degradation and cracking, which is vital for passenger safety.
  • 6PPD-quinone is not used in tire manufacturing. 6PPD-quinone is a newly discovered transformation product of 6PPD and likely forms when 6PPD in tires reacts with oxygen and/or ozone.

  • 6PPD in tire manufacturing has been studied, but not enough is yet known about 6PPD-quinone, including how 6PPD-quinone forms and how long it lasts in the environment.

Additional research is needed to understand 6PPD-quinone.

  • Recent research published by Washington State researchers, suggests a connection between exposure to 6PPD-quinone and coho salmon mortality.

  • USTMA supports additional research on 6PPD-quinone to understand the mechanism of toxicity in coho salmon, and whether 6PPD-quinone has similar impacts on other salmon and fish species.

  • USTMA recently requested the California Department of Toxic Substance Control (DTSC) add 6PPD in tires to the 2021-2023 Priority Products Work Plan for the Safer Consumer Products Regulations.  USTMA was pleased to see that DTSC included 6PPD in tires on the draft Work Plan, which will provide a rigorous and transparent scientific, regulatory framework to analyze whether alternatives exist that will enable tire manufacturers to meet vehicle safety and consumer product safety requirements.

  • To address knowledge gaps raised by the recent research, the global tire industry has formed a joint task force representing USTMA, the European Tyre and Rubber Manufacturers’ Association (ETRMA) and the World Business Council for Sustainable Development’s Tire Industry Project (TIP) to identify gaps in existing science and develop a plan to fill those gaps.

  • USTMA is committed to collaborating with researchers at the University of Washington and other scientists to better understand this transformation product, fill knowledge gaps and determine next steps.


USTMA Position on Tire and Road Wear Particles (TRWP)

USTMA members continually look for new ways to improve both their products and operations and their understanding of the impact of tires on the environment. The World Business Council for Sustainable Development’s Tire Industry Project (TIP) and the European Tyre & Rubber Manufacturers’ Association (ETRMA) have performed studies to assess the fate and transport of tire and road wear particles (TRWP). While the research conducted to date demonstrates TRWP do not present a significant risk to humans and the environment, USTMA supports additional and ongoing research that considers the latest science and most comprehensive methodologies.


FAQs on 6PPD and 6PPD-Quinone

Can USTMA provide a list of chemicals used to manufacture tires?

The exact formulation of the materials in an individual tire company’s rubber compounds are proprietary, but quite a bit of public information is available about common materials used in tire manufacturing. The innovation section of USTMA’s website identifies broad categories of materials being used. Also, several publications contain additional information about the various chemistries used in tire manufacturing. The Vanderbilt Rubber Handbook has a helpful overview of common rubber compound formulations and materials used to manufacture tires.

Why is 6PPD used in tire manufacturing?

6PPD is an antioxidant and antiozonant used industry-wide in tires to resist degradation and cracking, which is critical to tire safety. Antioxidants support increased tire endurance.

How long has the tire industry been using 6PPD?

6PPD has been used by some tire manufacturers since the 1970s and adopted by others in the early 2000s because it effectively resists degradation and cracking and is critical to tire safety.

Is 6PPD used in all tires?

6PPD is used by all USTMA members in manufacturing tires.

Are there alternatives to 6PPD?

6PPD is used as an antioxidant and an antiozonant in tires to prevent degradation and cracking, which is critical for tire safety. There are no known alternatives to 6PPD available that provide the same safety and performance characteristics in a tire.

What is the tire industry’s reaction to the recent Tian et al. paper?

We are a science-driven industry committed to safety and sustainability, as evidenced by the tens of millions of dollars invested in peer-reviewed research with the World Business Council for Sustainable Development’s Tire Industry Project. The focus of our research is to assess the impact of tire materials on the environment, wildlife, and human health, including tire and road wear particles (TRWP). 6PPD is used in tires to resist degradation and cracking, which is vital for passenger safety. It has been studied, but not enough is yet known about the newly discovered transformation product 6PPD-quinone (for example, 6PPD degrades quickly, but it may form 6PPD-quinone under certain conditions).



Does 6PPD in tires contribute to Coho Salmon mortality?

The tire industry is reviewing recent research and preliminary findings related to 6PPD-quinone and we are in contact with researchers at the University of Washington. We will continue to collaborate with researchers to advance understanding of these initial findings. The tire industry is committed to safety and sustainability and understanding the impact of tire materials on the environment.

Why do tires produce particles?

Tires are one of the most important safety components of a car. They support the vehicle’s weight, absorb impact, withstand multiple weather conditions and are a car’s only connection to the road. The grip between a tire and the road surface is essential to tire safety and performance. This critical grip leads to abrasion of both tire and road surfaces, producing TRWP, a mixture of tire tread and road pavement material. Since 2005, our members have supported peer-reviewed scientific studies related to TRWP conducted by the Tire Industry Project (TIP). To date, these studies have found that TRWP do not present a significant impact to human health and the environment; however, TIP continues its research to improve scientific understanding of potential impacts. 

What factors impact the production of TRWP?

Many factors impact tire wear including tire design; vehicle characteristics (weight, distribution of load, location of driving wheels and suspension types); road surface (material, runoff design, roughness); weather (humid or dry, hot or cold); road topology (hilly or flat, winding or straight); and driving behavior (aggressive or smooth driving, high or moderate speed, respecting the correct inflation pressure, braking). As a result, there is no one-size-fits-all solution to reduce tire wear and the generation of TRWP. Rather, effective reduction of TRWP will require a multi-faceted approach, and effective strategies could include reducing the generation of particles from tires through automotive and infrastructure innovations and ensuring proper tire inflation.

What can be done to reduce TRWP in the environment?

Incorporating sustainable infrastructure in roadway development can provide long-term solutions. Rebuilding America’s roads should be done with investments in technologies that increase driver safety and reduce environmental impacts, including roadway runoff. USTMA is encouraged by the documented benefits of rubber-modified asphalt and bioretention technologies, such as stormwater infiltration galleries and bioswales. A 2006 study, conducted by the Arizona Department of Transportation, found that rubber-modified asphalt can reduce tire wear by up to 50%. CalRecycle research found that stormwater infiltration galleries made with tire-derived aggregate reduce stormwater pollutants such as zinc and iron by over 80% and research by the University of Minnesota found stormwater galleries with tire chips reduce pollutants in stormwater runoff by over 60%. To learn more about mitigation options for TRWP please see the summary note from the OECD Workshop on Microplastics from Tyre Wear: Knowledge, Mitigation Measures, and Policy Options. Motorists can also help reduce the amount of TRWP produced by maintaining proper tire pressure. Under-inflated tires can impact tire safety, performance, and tread life. USTMA recommends that consumers check their tire pressure at least monthly to maximize the performance and life of the tire.


6PPD & TRWP Resources


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