6PPD Testing for Products – FAQ

6PPD-quinone (6PPD-q, CAS 2754428-18-5) is a transformation product formed when 6PPD reacts with ozone and oxygen at the tire surface. As tires wear against the road, the particles they shed carry 6PPD and 6PPD-q; rain then washes these particles from roads into streams and other water bodies. A 2021 publication in Science (Tian et al.) identified 6PPD-q as the cause of “urban runoff mortality syndrome” – the death of adult coho salmon returning to spawn in urban streams of the US Pacific Northwest after storm events. Its acute toxicity to sensitive species is extraordinary: the reported 24-hour LC50 for juvenile coho salmon is about 95 ng/L, and a later study found early-life-stage coho even more sensitive (24-h LC50 of 41 ng/L), roughly three orders of magnitude more sensitive than juvenile Chinook in the same study. Coastal cutthroat trout have since been identified as the second most sensitive species tested. In June 2024, US EPA issued a final (non-regulatory) acute aquatic-life screening value of 11 ng/L for 6PPD-q in freshwater. Research has also detected 6PPD-q in human urine and cerebrospinal fluid, prompting expanding toxicological study, though the aquatic effects remain the established regulatory driver.

Because concentrations of 6PPD-q measured in salmon-bearing urban waterways after storms can reach or exceed the levels shown to kill coho salmon in the laboratory, and affected populations include species listed as endangered or threatened. In California, DTSC documented 6PPD-q in state waterways at levels above laboratory-lethal concentrations for coho and noted the significant impact of coho losses on Native American tribes; the loss of salmon also affects treaty-reserved tribal fishing rights in the Pacific Northwest, which is why the Yurok, Port Gamble S’Klallam and Puyallup Tribes petitioned US EPA under the Toxic Substances Control Act (TSCA) to address 6PPD in tires – a petition EPA granted. Importantly, no jurisdiction has yet enacted an outright ban (see Regulatory Trend below); the current instruments are alternatives-analysis mandates, priority-chemical designations, water-quality values and rulemaking processes designed to drive the industry toward a safer, performance-equivalent substitute.

The tire industry is the direct target: California’s Priority Product regulation and Washington’s priority-product designation both apply to motor vehicle tires containing 6PPD, and compliance duties fall first on tire manufacturers (domestic and foreign) whose products enter those markets. Adjacent sectors affected in practice include: the broader rubber goods industry (6PPD is used as an antiozonant/antioxidant in rubber products generally); recycled-tire product sectors – Washington’s Safer Products Cycle 2 draft report (November 2024) highlighted artificial turf (which commonly uses recycled tire crumb) alongside tires as priority products; chemical suppliers of antidegradants, who are developing alternatives (e.g., Flexsys’ replacement program, reported by Rubber News to have narrowed to two candidate molecules); stormwater utilities and transportation agencies, which face monitoring and mitigation expectations; and testing laboratories supporting all of the above.

Not yet a proven, widely available one – DTSC itself stated when the California regulation took effect that 6PPD plays a crucial role in tire safety and that no widely available safer alternatives currently exist. The search is well underway, though: through California’s Preliminary Alternatives Analysis process, tire manufacturers collectively selected 21 candidate antidegradants for detailed evaluation in the Final Alternatives Analysis; a USTMA-coordinated consortium of more than 30 tire manufacturers screened some 60 candidates down to 7 warranting further investigation, with a final report expected in August 2026. A key complication is the risk of “regrettable substitution”: several candidates are structurally related para-phenylenediamine (PPD) derivatives that can also form quinones on reaction with ozone and may pose similar concerns (although evidence suggests some alternative PPDs and their quinones may be less hazardous to coho than 6PPD-q). Regulators are responding – DTSC proposed adding PPD derivatives to its Candidate Chemicals list (July 2025), and Washington’s 2026 phase-out bills expressly targeted “regrettable 6PPD substitutes” as well. Non-chemical mitigation avenues discussed by regulators and researchers include stormwater treatment (e.g., biofiltration/green infrastructure), tire coatings, and slowing the rate at which 6PPD leaches from wear particles – the approach Ace Laboratories’ leachability research is designed to support.

Ace Laboratories developed a proprietary method for analyzing 6PPD and 6PPDq migration into water. The workflow has three stages.

1. Generate representative wear particles: a tread compound is mixed and molded, then synthetic TRWP are produced. Methods used across the industry include DIN abrasion testing (ISO 4649/ASTM D5963), an RTM friction tester running a wheel over an asphalt-surfaced track with a rain-flush and runoff collection basin, USTMA-recommended cryo-grinding to produce CMTT, and a Lambourn abrasion tester used as a field performance simulator, which varies load and slip ratios and has a built-in particle collection system, giving a particle-morphology spread closer to normal driving.
2. Weather and leach: when the target analytes are 6PPD/6PPD-q, the ground particles are first exposed to ozone for a period to form the transformation products, then soaked in water and agitated; when transformation products are not the target, samples go directly to the water soak and agitation. Particles are then filtered out and the water is analyzed.
3. Analyze the leachate: Ace analyzes the filtered water by GC-MS using solid-phase micro-extraction (SPME), and separately runs elemental analysis by ICP after EPA digestion methods. Timing is critical, every sample must reach the instrument at the same interval after agitation because the concentration curve is highly time-sensitive, especially for 6PPD, whose half-life is at roughly 75 days in soil but only about three hours in water.