6PPD-Quinone

6PPD [N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine] is a chemical currently used in tire production to protect tire rubber from degrading due to reactions with ozone and other reactive oxygen species in the air. This antioxidant helps prevent tires from forming cracks and deteriorating when exposed to sunlight and other environmental factors. When 6PPD reacts with ozone, it forms the transformation product 6PPD-Q.

As vehicles travel, their tires undergo constant wear and tear resulting in the release of tiny tire-wear particles, and when it rains, stormwaters can wash these particles into streams and other water bodies. As a result, aquatic species can be exposed to 6PPD and 6PPD-Q. Concerns have been raised specifically about contamination from 6PPD-Q and its potential environmental impact. Coho salmon seem to be exceptionally sensitive to the toxic effects of 6PPD-Q. Tian et al. (2021) showed that 6PPD-Q was present in runoff at levels high enough to cause death among juvenile coho salmon and explain acute mortality events in the Pacific Northwest.

While additional research is needed to address 6PPD-Q in the environment, a key area is whether 6PPD-Q exposure has adverse effects on human health.

In early 2023, the White House Office of Science and Technology Policy’s NSTC JEEP identified 6PPD-Q as an emerging contaminant that would benefit from coordination across federal agencies. In response to this outreach, the NTP formed a working group as a focal point for federal efforts related to 6PPD-Q. While the working group has a focus on understanding the effects on human health, the coordination effort is broad reflecting the diversity of activities and interests of the participating agencies with broader expertise including ecotoxicological and environmental exposure science.