States target toxic tire compound

Two West Coast states, Washington and California, are making efforts to limit the amount of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, known as 6PPD, that gets into the environment.

Tire makers add 6PPD to rubber to protect it from damage caused by reacting with ozone and other oxygen compounds. However, when 6PPD reacts, it forms another chemical called 6PPD-quinone. This byproduct can kill coho salmon within hours of entering streams near roads, and it can be deadly to other fish within days.

In mid-August, Washington became the first US state to limit the amount of 6PPD-quinone that can be present in water. Washington updated its water quality rules based on the latest scientific research, new testing methods, and guidance from the US Environmental Protection Agency and tribal governments. The new rules, which also set limits for other chemicals including perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and aluminum, will start on Sept. 14 and apply to all surface waters in the state.

“The new limits are customized to Washington’s unique environment and the species we need to protect,” Vince McGowan, water quality program manager for Washington’s Department of Ecology, says in a statement.

In California, a consortium of tire manufacturers is trying to find an alternative to 6PPD that doesn’t have the same effects. The California Department of Toxic Substances Control has given the US Tire Manufacturer Association’s 6PPD Alternatives Analysis Consortium the green light to go ahead with research into seven possible alternatives to 6PPD.

This list includes four compounds that are similar to 6PPD, plus octyl gallate, specialized graphene, and a compound known as Irganox 1520. Octyl gallate is a synthetic antioxidant used as a food additive. The consortium says that while it can’t find ozone performance tests of the compound on tires, a similar chemical is a known biological antiozone compound. Irganox 1520 is a phenolic antioxidant that has undergone some tire ozone performance tests, although not many.

The consortium has until August 2026 to submit a detailed report, which will include a closer look at the potential risks and properties of the seven chemicals.