What do nail polish, children's foam-padded sleeping mats and tires have in common? Not much at first glance, but all have been identified as "priority products" under California's Safer Consumer Products regulations administered by the California Department of Toxic Substances Control (DTSC) under the state's Green Chemistry law.

The Regulation and Its Requirements

The regulation designating motor vehicle tires containing the chemical N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) as a priority product became final on July 3, 2023, making tires containing 6PPD the seventh priority product identified under the law. DTSC's priority product designation for tires containing 6PPD will become effective on Oct. 1, 2023. As a result of the priority product designation, foreign and domestic manufacturers of motor vehicle tires whose products enter the stream of commerce in California will have until Nov. 30, 2023, to submit Priority Product Notifications to DTSC identifying those products. The notifications must be submitted through DTSC's online Safer Consumer Products Information Management System (CalSAFER).

Tires containing 6PPD subject to the regulation include those intended for use on light-duty vehicles (passenger cars, light trucks, vans and sport utility vehicles), motorcycles, motor homes, medium- and heavy-duty trucks, buses and trailers (including trailer coaches, park trailers and semitrailers). Significantly, tires containing 6PPD imported or sold into California as a component of a motor vehicle are excluded from the regulation, as are tires intended for use exclusively on off-road equipment, such as aircraft, construction, agricultural and industrial equipment, airport support equipment, ice grooming machines and military equipment. In addition, retread materials containing 6PPD are not covered.

Under the Safer Consumer Products regulations, in addition to timely submitting Priority Product Notifications, manufacturers of tires containing 6PPD will have until March 30, 2024, to take one of four additional actions with respect to their products: 1) submit a notification of intent to remove the chemical from their products, 2) submit a notification of intent to remove their products from the California market, 3) submit a notification of intent to replace 6PPD with a different chemical in their products or 4) submit a preliminary alternatives analysis examining possible replacements for 6PPD in their products.

6PPD Background and Impact

6PPD is a chemical that prevents the rubber in car tires from degrading or breaking down (cracking) prematurely due to exposure to ozone in the atmosphere. It has been in nearly ubiquitous use in that application since the 1960s and makes up about 2 percent of the material in most commercially available tires.

However, it was not until 2020 that researchers seeking to understand the cause of annual migratory coho salmon die-offs in the Pacific Northwest discovered that a transformation product of 6PPD when exposed to ozone at the tire's surface – 6 PPD-quinone (sometimes abbreviated as 6PPD-q) – could induce acute toxicity to coho salmon at concentrations around 1 microgram per liter (a level often measured in waters receiving storm runoff from roadways). Other salmonids – Chinook salmon, steelhead, char and several trout species – are likely to be similarly impacted.

Related Regulatory Efforts

Because of the effects on coho salmon and related fish species, the Washington Department of Ecology is in the process of addressing 6PPD and 6PPD-q. In addition, earlier this month, the Yurok, Port Gamble S'Klallam and Puyallup tribes petitioned the U.S. Environmental Protection Agency (EPA) to ban the use of 6PPD under the Toxic Substances Control Act (TSCA). Under the TSCA, EPA has the authority to regulate, including phasing out the use of, chemicals in commerce that pose an unreasonable risk to human health or the environment. EPA has not yet responded to the petition.

6PPD and its transformation product 6PPD-q are among the emerging contaminants garnering significant attention from regulators and activists alike. As reflected in the state of Washington's actions and the recent petition to EPA, California's efforts are certainly only the beginning of attempts to phase out use of these chemicals in tires.