SAN FRANCISCO — A tire chemical already flagged by the Environmental Protection Agency for killing salmon may now be linked to Alzheimer’s disease in humans. Researchers at the University of California, San Francisco have published preliminary findings connecting 6PPD-quinone, or 6PPD-Q, to the neurodegenerative condition. The study appeared in Environmental Health Perspectives in 2024.
The chemical 6PPD-Q is a transformation product of 6PPD, a compound widely used in tires to prevent cracking and degradation. When tires wear down on roads, 6PPD reacts with ozone to form 6PPD-Q, which then washes into waterways or becomes airborne as particulate matter.
The EPA has already listed 6PPD as a chemical of concern due to its documented toxicity to aquatic life. In 2023, the agency announced plans to evaluate 6PPD under the Toxic Substances Control Act risk evaluation process. The updated 2016 TSCA gives the EPA authority to require testing and impose restrictions on chemicals that pose unreasonable risks.
The UCSF researchers called for epidemiological studies to assess human exposure levels and health outcomes. They emphasized the need for more data on how people encounter 6PPD-Q, including through inhalation of tire particles and ingestion of contaminated water.
The findings are preliminary, the scientists stressed, and require further research to confirm the connection in humans. The tire industry is watching closely. The U.S. Tire Manufacturers Association, which represents major tire producers, has funded studies on alternatives to 6PPD.
In 2020, the USTMA announced a goal to find a safer alternative by 2025. Washington state has considered its own regulations on 6PPD in tires, with a bill introduced in 2023. The new UCSF study may accelerate those efforts, as state regulators look for federal guidance that has yet to fully materialize.
The EPA’s potential action on 6PPD under TSCA could have significant implications for tire manufacturers and the broader automotive supply chain. The agency already has the chemical on its radar for environmental harm; a human health link would substantially broaden the regulatory stakes.
The researchers at UCSF were careful to note the preliminary nature of their work. Alzheimer’s disease is complex, with multiple genetic and environmental factors believed to contribute. Establishing a causal role for 6PPD-Q will require years of additional study, including large-scale human exposure monitoring and long-term health tracking.
What to watch next: whether the EPA moves to formally evaluate 6PPD-Q under the TSCA risk evaluation process, and whether the USTMA can deliver on its 2020 promise of a safer alternative. The state of Washington’s legislative efforts may also provide an early signal of regulatory momentum.
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