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This page is run by the Washington State Department of Ecology and provides information about identifying a safer alternative to 6PPD. For more general information about 6PPD, please visit our website.

Urban Runoff Mortality Syndrome and 6PPD

Urban runoff mortality syndrome (URMS), also known as Coho pre-spawn mortality, is a condition where Coho salmon die prior to spawning. It's directly related to urbanization density, specifically proximity to roadways—roadway runoff contains a mixture of chemicals that pollutes streams during rain events and is shown to cause URMS. 

While the source was narrowed to roadway runoff, UW and WSU scientists only recently identified the specific chemical responsible for URMS: 6PPD-quinone, a transformation product of 6PPD, which is used as an anti-degradant in almost every automobile tire on the road. 6PPD-quinone is toxic to Coho salmon at very low concentrations (less than 1 part per billion). Concentrations of 6PPD-quinone in urban streams in cities such as Seattle, San Francisco, and Los Angeles frequently exceed this level, particularly during storm events.

Hazard Assessment and Alternatives Assessment

In 2021, the Washington State Legislature passed an operating budget proviso allocating $195,000 to Ecology to assess “potential hazards of 6PPD and other chemical classes and breakdown products used as antioxidants and/or antiozonants in tires. A technical memo outlining the results of this study is included in the "documents" section below.

Following the hazard assessment, the Washington State Legislature tasked the Department of Ecology with performing an Alternatives Assessment on 6PPD in motor vehicle tires to identify compounds with the potential to replace 6PPD in these products. We have published 6PPD Alternatives Assessment Hazard Criteria, which we will use to conduct an alternatives assessment around 6PPD. 

These hazard criteria are similar to the Safer Products for Washington criteria for safer, with three additions: 1) Alternatives must have data on acute aquatic toxicity to coho salmon and rainbow trout, as well as data on two other trophic levels; 2) alternatives must have data on the toxicity of transformation products after exposure to ozone; and 3) we will place a limit on the acute toxicity LC50 values allowed in the minimum criteria (>0.1 mg/L). We originally published the 6PPD Hazard Criteria in June 2023. The 6PPD Hazard Criteria linked above was revised in response to public input received from June 14, 2023, to July 14, 2023. You can view our responsiveness summary here.

Funding Research

We are currently funding studies to make progress on the alternatives assessment and evaluate the toxicity of 6PPD, 6PPD-q, and potential alterantives on several aquatic species. Below are several reports and updates detailing these research efforts.

• Bioavailability of 6PPD-quinone and testing alternative antiozonants - Washington State University, Washington Stormwater Center
• Solvent extraction and aqueous leaching of tire tread particles - University of Washington - Tacoma
• OECD toxicty testing of 6PPD-quinone using rainbow trout - Enthalpy Analytical
• Tire chemicals OECD toxicity testing of ozonated 6PPD and related alternatives (7PPD and 77PD) - Enthalpy Analytical
• Tire chemicals OECD toxicity testing of 6PPD and related alternatives - Enthalpy Analytical
• Antioxidant/Antiozonant Sidewall Study - ACE Laboratories
• Toxicity Testing Results: 6PPD Alternative Testing - EcoAnalysts, Inc.

Contact information

6PPD team
Department of Ecology | Hazardous Waste & Toxics Reduction Program
6PPD@ecy.wa.gov

ADA Accessibility

The Department of Ecology is committed to providing people with disabilities access to information and services by meeting or exceeding the requirements of the Americans with Disabilities Act (ADA), Section 504 and 508 of the Rehabilitation Act, and Washington State Policy #188.

To request an ADA accommodation, contact Ecology by phone at 360-407-6700 or hwtrpubs@ecy.wa.gov. For Washington Relay Service or TTY call 711 or 877-833-6341. Visit Ecology’s website for more information.