USTMA Maintains Support for California Department of Toxic Substances Control (DTSC) Proposed Rulemaking for Alternatives Analysis for Critical Tire Safety Additive 6PPD

On behalf of its 12 member companies, the U.S. Tire Manufacturers Association (USTMA) submitted formal comments in support of the proposed rulemaking by California’s Department of Toxic Substances Control (DTSC) to list 6PPD in tires as a Priority Product in the state’s Safer Consumer Products (SCP) program.

“USTMA thanks DTSC for adding 6PPD in tires to the 2021‐2023 work plan and for advancing the listing of 6PPD in tires as a Priority Product,” said Sarah Amick, Vice President Environment Health Safety and Sustainability and Senior Counsel. “Our members have pushed to fill existing data gaps related to 6PPD since learning of the newly discovered transformation product, 6PPD-Quinone, in late 2020. We look forward to working with DTSC to complete an Alternatives Analysis of 6PPD in tires and coordinating with other stakeholders, including Washington State’s Department of Ecology, to advance this process transparently,” said Amick.

The SCPR provides a rigorous, transparent, scientific, regulatory framework to analyze whether potential alternatives exist that ensure tire safety and environmental protection. The SCPR recognizes the need for products to continue to comply with other state and federal laws, which includes the ability of tires to continue to comply with Federal Motor Vehicle Safety Standards (FMVSS). The use of protection materials, including 6PPD, are essential to ensure tire safety. Any potential alternative to 6PPD identified through the SCPR process must provide the same performance requirements as 6PPD to ensure tire safety and performance.

USTMA highlighted four primary points in its formal comments to DTSC. The following are partial excerpts from USTMA’s formal comments for each of these four points:

1. USTMA supports a review of 6PPD in tires under the SCPR. In December 2020, a research paper by Tian et al. 2020 was published that suggests a link between 6PPD‐Quinone and coho salmon mortality. 6PPD‐Quinone is not used in tire manufacturing. It is a transformation product of 6PPD that may form when 6PPD reacts with oxygen and/or ozone. 6PPD is an antioxidant and antiozonant that helps prevent the degradation and cracking of rubber compounds caused by exposure to oxygen, ozone, temperature fluctuation, and flexing induced fatigue. These benefits of 6PPD are critical to effective tire endurance and thus ultimately to motor vehicle safety.

As a science‐driven industry, committed to safety and environmental stewardship, U.S. tire manufacturers take the findings of this study seriously. In December 2020, USTMA requested that DTSC include 6PPD in tires on the 2021‐2023 Priority Products Work Plan for the SCPR. A review of 6PPD in tires under the SCPR provides a scientific, regulatory framework to analyze whether alternatives exist that will enable tire manufacturers to ensure both tire and environmental safety. DTSC added 6PPD in tires to the Priority Products Workplan in early 2021 and since that time, USTMA has worked to support a review of 6PPD in tires under the SCPR.

2. Protection materials, such as 6PPD, are essential for tire performance and safety and any potential alternative must continue to ensure compliance with Federal Motor Vehicle Safety Standards (FMVSS). 6PPD provides critical functions in manufacturing safe and durable tires. Alternatives to 6PPD must also meet these critical functions and have the following qualities:

• Continuously present at the surface of the tire to ensure protection of the rubber compound from degradation due to oxygen and ozone;
• Adequate solubility and diffusivity in rubber compounds;
• Reactive with ozone but not too reactive in order to prevent premature depletion;
• No adverse effects on the rubber processing;
• Available in rubber compound over a tire’s entire life cycle to ensure protection of the rubber;
• Low toxicity of the material and any transformation products; and
• No adverse effects on tire safety and performance  

Any potential alternative to 6PPD, identified through the SCPR process, must provide the same critical functions as 6PPD to ensure tire safety and performance. The composition and nature of the chemicals present in tires impart a function and the exact composition of tires cannot be modified without great care. It is not a simple process to change the composition of tires; any change could affect the stopping distance of tires, durability, vehicle fuel economy, tire wear and other safety‐related components. DTSC’s ability to impart a material change required under the SCPR would be significantly limited by the FMVSS that tire manufacturers must meet.

3. As a newly discovered transformation material, the science on 6PPD‐Quinone is still emerging. The Tian et al. 2020 paper identified a new transformation product of 6PPD, 6PPD‐Quinone. As a previously unknown transformation product, very little is understood about 6PPD‐Quinone in the environment and the potential impact to human health and the environment. Additionally, in order to assure that any potential alternative to 6PPD in tires is also safe for the environment, it is critical to fill the knowledge gaps regarding the formation of 6PPD‐Quinone, its environmental fate, its mode of action in coho salmon and its potential impact on other aquatic species. USTMA continues to engage with stakeholders and the research community to fill relevant data gaps related to 6PPD‐Quinone.

4. USTMA recommends that the product category “tires” be focused to provide a workable Priority Product to perform an alternatives analysis. USTMA recommends that DTSC focus the definition of Priority Product to replacement, all‐ season, passenger tire tread and sidewall compounds. A more focused definition of “tire” will enable tire manufacturers to complete one Alternatives Analysis that will likely be applicable to other tire types. Moreover, focusing the regulatory definition of “tire” to those areas of a tire that are exposed to oxygen and ozone would provide much more focus to this rulemaking.

For more information, visit 6PPD and Tire Manufacturing.