6PPD, a chemical widely used in tires to prevent rubber degradation and extend tire lifespan, has raised environmental concerns due to its breakdown product, 6PPD-quinone. When 6PPD reacts with ozone, it forms 6PPD-quinone, a compound that can enter waterways through stormwater runoff, posing significant risks to aquatic ecosystems. Research has identified 6PPD-quinone as acutely toxic to coho salmon and other sensitive fish species, with potential implications for human health as well.
In December 2025, the EPA, in collaboration with the Interstate Technology and Regulatory Council (ITRC), hosted a webinar to share updates on 6PPD-quinone research, explore mitigation strategies, and discuss resources aimed at addressing the environmental and health challenges posed by this chemical.
EPA research on 6PPD and 6PPD-quinone
Kate Saili, a toxicologist in EPA’s Office of Research and Development (ORD), began the presentations with an update on 6PPD-quinone research completed at EPA over the last couple of years.
In 2021, Tian et al. published the paper, “A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon,” identifying 6PPD-quinone as the cause of coho salmon mortality in streams of the Pacific Northwest. 6PPD-quinone is a transformation product of the tire rubber antiozonant, which is added to tires to extend tire life. However, tire wear inevitably results in the release of tire wear particles, which are washed into streams through roadway runoff following rain events. These particles can carry 6PPD-quinone and other chemicals into the streams where fish and other aquatic species are exposed.
6PPD-quinone is highly toxic to coho salmon and coastal cutthroat trout. It is also toxic to brook trout, rainbow trout, and lake trout, but notably non-toxic to several other species.
The known toxicity of 6PPD-quinone to coho salmon and its potential impact on their populations are key issues. These fish have cultural, commercial and ecological importance. Some populations are threatened and endangered. Many tribal nations rely heavily on salmon and other aquatic resources for food and cultural practices, yet limited information is available on releases to the environment, fate and transport, and potential human health effects. Therefore, there is a need for data to inform decision-making to protect sensitive species.
Since the Tian et al. paper was published, EPA has collaborated with partners and stakeholders to address research needs, explore mitigation strategies, and begin identifying potential alternatives to 6PPD for use in tire manufacturing. EPA has supported the development of 6PPD alternatives through the Small Business Innovation Research program.
Although research has been conducted in other EPA regions, this webinar focused on the work in Region 10, the Pacific Northwest.
Study: Watershed analysis of urban stormwater contaminant 6PPD-Quinone hotspots and stream concentrations using a process-based ecohydrological model
In the paper, Watershed analysis of urban stormwater contaminant 6PPD-Quinone hotspots and stream concentrations using a process-based ecohydrological model, Researcher Jonathan Halama and the team based in Corvallis, Oregon, used Visualizing Ecosystem Land Management Assessments (VELMA) to model 6PPD-quinone deposition in a watershed in Seattle, Washington that drains into the Puget Sound estuary.
This study shows that the VELMA model is a good tool for prioritizing locations for green infrastructure placement to reduce 6PPD-quinone concentrations entering streams and thereby protect sensitive species. An example of that green infrastructure is shown in the image at the bottom.
Study: Bioactivity of the ubiquitous tire preservative 6PPD and degradant, 6PPD-quinone in fish- and mammalian-based assays
The study, Bioactivity of the ubiquitous tire preservative and degradant, 6PPD-quinone in fish- and mammalian-based assays, by Mark Jenkowski et al, looked at a range of high-throughput assays available at EPA to see if any of them could be used to detect the toxicity of quinone.
The figure from the paper, shown on the slide, shows the assays tested on the y-axis and the effect concentrations on the x-axis. Red symbols are 6PPD-quinone; blue symbols are 6PPD. These assays ranged in complexity from cell-free to cell-based, and included in vivo larval fish assays across both fish and mammalian systems.
The study determined that 6PPD was bioactive in a broader set of assays than 6PPD-quinone. They also found that 6PPD may be a developmental neurotoxicant, based on cell-based assays in rats that reflect what is present in the developing brain. The study also found that 6PPD-quinone was much more potent than in altering the intracellular phenotype of rainbow trout gill cells. Rainbow trout are a sensitive species, so this assay could be useful for other applications.
The impact of this paper was that high-throughput screening assays can inform health assessments.
Study: Phenotypic Profiling of 6PPD-quinone and Structurally Diverse Antiozonants in RTgill-W1 Cells Using the Cell Painting Assay
The paper, Phenotypic Profiling of 6PPD-quinone and Structurally Diverse Antiozonants in RTgill-W1 Cells Using the Cell Painting Assay, by Harris et al, which built on the rainbow trout gill cell phenotype assay to look at not just 6PPD and 6PPD-quinone, but other structurally related compounds.
They found that, based on the bioactivity profile, these chemicals can be grouped by similar bioactivity. Quinones of 7PPD and 77PD exhibited bioactivity similar to that of 6PPD-quinone, suggesting they may not be suitable replacements for 6PPD in tires. However, other tested chemicals showed less toxic effects; thus, one outcome of this study was that the model can be used to inform testing and identify potential alternatives to 6PPD that are less toxic for tire manufacturing.
Other EPA activities
These research projects, along with other projects completed at EPA, have all informed other activities in the agency, including:
- A cross-Agency technical review of 6PPD-quinone and the development of the 6PPD-quinone Action Plan
- Publication of a draft laboratory testing method (EPA Method 1634) that will enable government agencies, Tribal Nations, and other groups to determine where and when 6PPD-quinone is present in local stormwater and surface waters
- Finalization of a rule under Section 8(d) of TSCA that requires manufacturers (including importers) to report lists and copies of unpublished health and safety studies on 6PPD and 6PPD-quinone to the EPA
- Development of acute screening values for 6PPD and 6PPD-quinone and to protect sensitive salmon and other aquatic life (Jarvis et al., 2025)
- For more information, see EPA’s 6PPD-quinone website.
Tools and resources available at EPA
- CompTox Chemicals Dashboard has chemical property information on more than a million chemicals, including 6PPD-quinone and 6PPD.
- ECOTOX Knowledgebase has ecotoxicity information on ecologically relevant species, and was recently updated with records from publications and research completed in 2025 on 6PPD-quinone and related compounds.
- ChemExpo Knowledgebase has human health exposure information.
- Science Inventory lists publications with EPA co-authors.
ITRC Overview of the tire-derived chemicals & 6PPD-quinone
Tanya Williams, Washington State Department of Ecology, is a team lead for the Interstate Technology and Regulatory Council (ITRC). The ITRC is a state-led coalition working to reduce barriers to the use of innovative environmental technologies and approaches so that compliance costs are reduced and clean-up efficacy is maximized. ITRC produces documents and training that broaden and deepen technical knowledge and expedite high-quality regulatory decision-making while protecting human health and the environment, with participation from private and public sector members from all 50 states and the District of Columbia. ITRC truly provides a national perspective.
In mid-2024, the ITRC published its first guidance on 6PPD and 6PPD-quinone, which provided an important early synthesis of what was known about these chemicals. The ITRC team of experts compiled the state of the science to provide an in-depth background and scientific findings to date, and to identify data gaps and additional research needs.
The discovery of 6PPD-quinone was driven by the need to identify the cause of coho salmon mortality in the Pacific Northwest. Since its discovery, 6PPD-quinone has been found to be acutely toxic to brook trout, rainbow trout, steelhead, lake trout, and coastal cutthroat trout, which are important ecological and recreational species throughout the United States. The blue color represents native distribution, and the tan color represents non-native distributions of these five species.
The graphic from the guidance document, shown below, illustrates the conceptual exposure model for tire wear particles containing 6PPD and 6PPD-quinone and their potential transport pathways through the environment. The particles can be inhaled by people and deposited on surfaces, soil, and plants. 6PPD and 6PPD-quinone in surface waters can be ingested and absorbed by fish. Humans and other species can then consume exposed organisms. Research is ongoing to further define the environmental behaviors and potential exposures of 6PPD and 6PPD-quinone.
Effects characterization and toxicology
The species most sensitive to 6PPD-quinone are salmonids, which include salmon, trout, and char. Among those, coho salmon are the most sensitive, with a median LC50 of 0.08 micrograms per liter. The LC50 is the exposure concentration that’s lethal to half the study population.
“This represents one of the lowest LC50s ever identified in aquatic organisms,” said Dr. Kelly Grant, California Department of Toxic Substances Control. “To put this into perspective, this concentration is the equivalent of about four drops in an Olympic-sized swimming pool. New data also shows that coastal cutthroat trout have a similar range of sensitivity.”
These LC50s are below concentrations commonly measured in traffic-impacted stormwater. 6PPD-quinone has been measured as high as 2.85 micrograms per liter in surface water, and the onset of symptoms occurs within just 90 minutes of exposure. Several salmonid species have been shown to be very sensitive as well, although not to the same extent as coho. These LC 50s are still considered to be highly toxic.
“The table is cropped from our guidance document, and for the whole table, please visit the guidance document, but I want to emphasize that numerous salmon and trout species are not sensitive to 6 PPD quinone at its limit of solubility,” she said. “In addition, most of the tested invertebrates are not sensitive to 6PPD-quinone. This toxicant is extremely species specific.”
The exact mechanism by which 6PPD-quinone causes rapid mortality in salmonids remains unclear, but hypotheses include blood vessel leakage, failure of the blood-brain barrier, mitochondrial dysfunction, or chemical metabolism. Research suggests these factors may act individually or in combination, but further study is needed to identify the molecular cause. Beyond acute mortality, sub-lethal effects such as developmental toxicity, delayed mortality, and gill remodeling—reducing oxygen exchange during critical energy demands—have also been observed in salmonids, potentially impacting populations.
6PPD-quinone also impairs swimming behavior in coastal cutthroat trout and zebrafish. The zebrafish data are really important because the behavior changed at environmentally relevant concentrations, indicating that even tolerant species may experience adverse effects.
Humans are exposed to 6PPD and its breakdown product, 6PPD-quinone, with both chemicals detected in various bodily fluids and tissues. While studies in mice show these compounds can accumulate in multiple organs, including during pregnancy and lactation, the implications for human health remain unclear. Research suggests 6PPD may cause hepatotoxicity, skin allergies, anemia, and neurotoxic effects, while 6PPD-quinone has shown neurobehavioral and organ toxicity in mice. Oxidative stress is believed to play a role in their toxic effects, but further research is needed to understand human health risks.
Occurrence of 6PPD and 6PPD-quinone
Since the discovery of 6PPD and 6PPD-quinone in 2020, the number of peer-reviewed studies on their occurrence has increased. Additional information can be found in the guidance document tables 4-1 through 4-10, where each media type has its own table and study summary. These studies are from peer-reviewed literature, and it is important to note that they do not capture all the monitoring effects by state, tribal, and local agencies. There has been a significant increase in the number of studies since March 2024.
There are currently limited studies on groundwater, drinking water, and roadside soil, but stormwater, surface waters, and dust have many publications. Dr. Rachel Lane, USGS, highlighted key areas of occurrence data, focusing on the transport and exposure pathways.
Surface water and stormwater are primary mechanisms for transporting tire and road wear particles into receiving surface waters, where concentrations of 6PPD-quinone have been observed above the lethal levels for coho salmon. Dr. Lane notes that the highest level of 6PPD-quinone in surface water, the 2.85 micrograms per liter, was published before there was a standardized method and could be an overestimation of the concentration. More studies are needed to understand how environmental conditions, such as landscape, watershed, and storm characteristics, affect the fate and transport of contaminants.
There is limited data about which stormwater and water treatment technologies are most effective at preventing the transport of these particles and their chemicals. In many places in the US, the stormwater is not treated before it’s discharged to surface waters. So stormwater and surface water transport tire and road wear particles and related chemicals, and the models and measurements we have for 6PPD and 6PPD-quinone suggest it readily binds to soil and organic matter. There have been detections in river, estuary, coastal, and deep-sea sediments. Detections have also been reported in roadside soil, and biodegradation has been observed. Additional studies are needed to understand the relationship between suspended concentrations and the amounts deposited onto soil and sediment. Research is ongoing to fill data gaps for the deposition, composition, biodegradation, and transformation processes.
6PPD and 6PPD-quinone have been found in a variety of foods. European studies found that one or both chemicals were present in leafy greens, cabbage, carrots, onions, bell peppers, potatoes, pumpkins, zucchini, and tomatoes. More studies are needed to determine whether the levels of these chemicals in produce and other foods pose a concern for human health.
A substantial knowledge gap exists regarding the presence of 6PPD and 6PPD-quinone in edible fish tissue and other aquatic biota consumed by humans, as well as whether these levels are sufficiently elevated to pose a risk to human health. Preliminary data from the Washington Department of Fish and Wildlife show 6PPD-quinone in adult Chinook salmon filets, but it is not known if these levels are cause for concern. Preliminary studies in China have also shown that these chemicals in edible aquatic species such as shrimp.
Determining concentrations in other aquatic food sources and assessing the impact of various cooking techniques are important for evaluating potential human exposure and establishing informed consumption guidelines. It is also not yet known whether 6PPD or the 6PPD-quinone poses a bioaccumulation risk, but early indications are that the bioaccumulation potential is low to moderate. Direct toxicity probably poses the greatest ecological risk. More research is needed to confirm the bioavailability and bioaccumulation of both compounds across different species.
Tools for measuring, mapping, and modeling
Mapping tools can help focus sampling and mitigation efforts by locating 6PPD and 6PPD-quinone hot spots and potentially vulnerable ecological populations. Key mapping layers that can inform sampling locations include urban areas with high traffic, watershed characteristics with precipitation data, and the habitat range for these sensitive species. Additional information on mapping tools and data layers is available in Section Five of the guidance document.
Some examples of state and federal mapping tools that can be used to inform sampling:
The Washington Department of Ecology story map is a state-level mapping tool to identify potential hot spots of 6PPD-quinone near salmon-bearing waterbodies. Areas of interest for 6PPD-quinone sampling are shown in dark blue. You can zoom to specific streams of interest to see additional information.
The USEPA Freshwater Explorer is a federal-level tool highlighting streams that are in close proximity to impervious surfaces. When zooming in on a specific location, this mapping tool highlights streams near roadways in red and yellow. These locations could have high concentrations of 6PPD or 6PPD-quinone during runoff events.
The US Geological Survey has released a tool for exploring sources of 6PPD-quinone during storm events. Known and suspected sources of 6PPD-quinone and relevant landscape characteristics are incorporated into heat index values at a small watershed scale. When zooming in on a specific stream or watershed, this mapping tool will highlight the heat score and provide additional information about the location. Additionally, modeled fish presence for several potentially vulnerable species can be overlaid on the heat layer, informing sampling efforts for both scientists and land managers.
Considerations for watershed and stormwater sampling
Once the locations of interest have been identified, sampling and streams during urban runoff provide information about the environmentally relevant concentration. Tire-derived contaminants are washed into water bodies during these storm events, which may lead to a temporary peak in 6PPD-quinone concentrations. The storm hydrograph shows the rise and fall in the concentration of 6PPD-quinone in gray versus the storm water discharge, shown in blue.
One potent dose in a single storm is enough to cause acute effects in sensitive fish species, even if the average concentrations are very low. “This is a key difference of 6PPD-quinone relative to many other stormwater contaminants,” said Dr. Lane. “A current study should take this into account, as a single time point grab sample may not represent an ecologically relevant concentration, if you miss the peak. Sampling should be timed with rainfall to capture the rise in 6PPD-quinone. This means that during dry weather, on those really nice days, is not when you’ll be in the fields, sampling for 6PPD-quinone.”
Dr. Lane noted that the peak concentration can vary by river, stream, and watershed. In larger rivers and watersheds, peak concentration of 6PPD-quinone may not be observed for many hours after peak discharge; in smaller tributaries with high amounts of impervious surfaces, peak concentrations may occur in that first hour and are easy to miss. General guidance for field sampling is available in chapter five of the guidance document and in a standard operating procedure from the Washington State Department of Ecology.
6PPD-quinone is water-repellent and sticks to plastic, so it’s important to minimize its contact with plastic during sampling and analysis. Sampling can be done using grab, automated, or passive sampling methods. Selection of the sampling type will depend on the project’s goals and the ability to time sampling with the storm or runoff event. After samples are collected, commercial, public, and research laboratories are available for the analysis of 6PPD and 6PPD-quinone in a range of environmental matrices. EPA draft method 1634 is available for the determination of 6PPD-quinone and aqueous matrices. When selecting a laboratory, be sure it provides the analytical rigor required for the project or program goals, realizing that analytical method accreditation requirements will vary by state, organization, and agency.
The data generated from mapping, sampling, and measuring can be used with established modeling tools to predict the occurrence of 6PPD or 6PPD-quinone, helping to inform and focus sampling on hot spots near potentially vulnerable ecosystems and temporal locations for mitigation.
EPA tools for atmospheric fate and transport modeling have been applied to understand tire and road wear particle emissions and transport, and the VELMA modeling tool has been applied with 6PPD-quinone to predict hot spots and types of green infrastructure to reduce 6PPD-quinone. Recently, other models have also been investigated, such as the USGS Stochastic Empirical Loading and Dilution Model (SELDM), which is being used to model stormwater mitigation effectiveness.
Storm Control Measures
There are several types of storm water control measures, or SCMs, that are projected to have a high probability of mitigating 6PPD-quinone by inhibiting their ability to enter storm water and reach the receiving waters. They might include street sweeping and the cleaning of roadside ditches, catch basins, and storm pipes.
Preliminary studies have intuitively demonstrated that increased frequency of street sweeping reduces tire wear particles, and thus 6PPD and 6PPD-quinone are assumed to be present in storm water.
Flow controls slow runoff and reduce its volume through on-site water stormwater management. This method of management contradicts the design of many of the older roadways in our cities, where stormwater is flushed off the road and directly into waterways very quickly. Examples of flow controls include bio retention, swales, infiltration basins, detention ponds, and permeable pavement.
Runoff treatments reduce concentrations of targeted pollutants through means of physical infiltration and chemical sorption. To date, bioretention soil mixes with a 60% sand and 40% compost mix are among the most effective methods for reducing 6PPD-quinone exposure and mortality in fish. High-performance bioretention mixes, optimal for nutrient-sensitive water bodies, are also removing 6PPD quinone. The picture shows a compost sock in a detention pond that treats stormwater before it enters waterways. Runoff treatments are most effective when designed together with flow controls.
Currently, researchers are working to optimize technologies for the most efficient and long-lasting stormwater control measures and to maximize 6PPD-quinone and tire wear particle removal. In 2022, the best management practices effectiveness report published by the Washington State Department of Ecology examined existing stormwater control measures to assess each for its potential to mitigate 6PPD-quinone. The primary takeaway was that mitigation measures should leverage the 6PPD and 6PPD-quinone chemical properties, which have a high affinity for partitioning out of water and onto organic matter.
Policy-related actions
In 2023, the Yurok Tribe, the Port Gamble S’Klallam Tribe, and the Puyallup Tribe petitioned the EPA to regulate 6PPD under the Toxic Substances Control Act; the Affiliated Tribes of Northwest Indians later supported this petition. EPA granted the petition and issued an advanced notice of proposed rulemaking, or ANPRM, in the fall of 2024. In June of 2025, the EPA extended the deadline for collecting health and safety data to the middle of 2026.
A second regulatory governance is the Clean Water Act. Washington State submitted an aquatic life toxics criteria rule package to the EPA for review and approval in 2024. The package includes an acute aquatic life criteria for 6PPD-quinone of .012, micrograms per liter. The rule package also requires consultation under the Endangered Species Act.
The EPA has published water quality thresholds under the Clean Water Act. They issued fresh water acute screening values to provide a threshold for consideration when assessing solutions to these chemicals. These values are non-regulatory. There is a slight difference between the two values for 6-PPD-quinone due to differences in calculation methodology between Washington Ecology and the EPA.
Washington and California both have ongoing regulatory processes to identify a replacement for 6PPD. Both programs are working alongside industry to identify possible alternatives to 6PPD through alternative assessment processes. Alternative assessments are tools to compare the performance and the toxicity of 6PPD and its alternatives. The evaluation of toxicity includes human and aquatic hazards and, in some cases, other adverse health and environmental impacts across a tire’s life cycle.
California, through its Safer Consumer Products regulation, requires tire manufacturers to investigate alternatives to 6PPD in tires. Seventy-five tire manufacturers have completed preliminary analyses of 20 possible alternatives to 6PPD. Washington is assessing 6PPD in tires through the Safer Products for Washington Program to review hazards and identify alternatives. Washington’s alternatives assessment uses hazard criteria developed specifically for 6PPD and includes data requirements for sensitive species and other trophic levels, as well as requirements to test the toxicity of ozonated chemicals.
In summary …
It’s important to keep up with the new research. Emerging contaminants are the subject of rapidly evolving research, and it’s important to stay up to date when making decisions on mitigation and policy.- 6PPD is used in tires worldwide, and therefore, these chemicals are being found throughout the environment. More information is needed on the fate and transport of these across different media and within trophic levels.
- So far, the acute toxicity of 6PPD-quinone seems limited to salmonid species, but research is emerging daily, and some researchers are still looking at other species.
- Studies have detected 6PPD-quinone in humans, but research to better understand the risks posed by these chemicals is still evolving.
- Many tools have been developed to help identify where to start looking for 6PPD-quinone in your watersheds. Mapping tools and tools on how to sample, monitor, measure, and begin addressing 6PPD-quinone.
- Although California and Washington are currently assessing alternatives, more research is still needed to understand the toxicity of these potential alternatives and also whether they meet tire performance and safety requirements.
