To: Senior Management

From: Dr. Lauren E. Barth, LEB Aquatic

Subject: Briefing for the Director General: Additional funding to assess and mitigate 6PPD-Q risks in Canadian freshwater ecosystems

 

Purpose

This memo provides a briefing on 6PPD-quinone as an emerging threat to freshwater quality and aquatic ecosystem health in Canada and recommends how additional funding could be used to identify high-risk watersheds, assess ecological exposure, and support mitigation planning.

 

Issue

6PPD-quinone, or 6PPD-Q, is an emerging contaminant associated with tire wear particles transported from roads into stormwater systems, tributaries, and receiving waters. Tire wear particles are a significant source of microplastics and associated chemical contaminants in aquatic environments (4, 5). 6PPD is an antioxidant and antiozonant commonly added to vehicle tires to prevent oxidative breakdown and extend tire life (2). When 6PPD reacts with ozone, it forms several transformation products, including 6PPD-Q, which has been linked to mortality of coho salmon exposed to contaminated urban stormwater, known as urban runoff mortality syndrome (6).

 

The issue is most relevant in highly urbanized watersheds with dense road networks and in watersheds that support sensitive salmonid species, including coho salmon, rainbow trout, and brook trout. Recent research indicates that 6PPD-Q toxicity is species-specific, with several commercially, ecologically, and culturally important salmonids showing sensitivity to environmentally relevant concentrations (7–9).

 

Regional Relevance

The highest-risk areas are urban watersheds where road runoff enters streams, rivers, stormwater infrastructure, and nearshore receiving waters. 6PPD-Q has been found across environmental media, including water, air particles, dust, sediments, and soil, with the highest concentrations generally associated with stormwater draining urban areas and areas with high road density (2, 11).

 

In Canada, priority regions include highly urbanized watersheds in southern Ontario draining to Lakes Erie, Lake Ontario, and the St. Lawrence River. These watersheds combine dense road networks, rapid urban growth, stormwater inputs, and the presence of salmonid species that spend part of their life cycle in rivers and nearshore waters (15–17). Coastal streams in British Columbia, including the Fraser River watershed, are also a priority because they support natural populations of coho salmon that may be vulnerable to urban runoff mortality syndrome (17, 18).

 

Risks to Aquatic Ecosystems

6PPD-Q poses several risks to freshwater ecosystems. First, it is acutely toxic to some salmonids at environmentally relevant concentrations, with sensitivity varying by species and life stage (7–9). Coho salmon, rainbow trout, and brook trout are of particular concern because they are ecologically, culturally, and economically important and may be exposed during vulnerable life stages in rivers and urban streams.

 

Second, exposure is likely episodic and event-driven. Rainfall and snowmelt can mobilize tire wear particles and associated chemicals from roads into stormwater systems and receiving waters (4). This creates a risk of short-duration but high-concentration exposure during periods when aquatic organisms may already be responding to hydrological or seasonal stressors.

 

Third, 6PPD-Q does not occur in isolation. Tire wear particles can enter aquatic environments as a chemical mixture that may include other transformation products, heavy metals, polycyclic aromatic hydrocarbons, formaldehyde, and other additives (24). This creates uncertainty about cumulative or mixture effects on aquatic organisms and food webs.

 

Finally, 6PPD-Q is bioaccumulative and has been detected in humans through multiple exposure routes, including inhalation, ingestion, and dermal contact (10, 11). Although long-term human health risks remain uncertain, recent evidence suggests potential adverse effects in mammalian and human cell systems (12–14). While the primary concern for this funding proposal is aquatic ecosystem health, these findings reinforce the need to better understand environmental exposure pathways.

 

Current Actions

Several actions are underway, but they remain limited relative to the scope of the risk. In 2018, 6PPD was assessed under the Canadian Environmental Protection Act and identified as being of low ecological concern and not a risk to the environment or human health (19). However, that assessment did not address 6PPD-Q, the transformation product now associated with salmonid mortality.

 

A public request was made in 2024 under section 76 of CEPA to add 6PPD and its transformation products to the proposed Plan of Priorities (17, 19). Federal funding has also supported research in the Great Lakes region, including work investigating 6PPD-Q contamination from recycled rubber products (20).

 

These actions indicate increasing federal attention, but key gaps remain. Canada still lacks a coordinated freshwater monitoring approach to identify 6PPD-Q hotspots, quantify exposure in priority watersheds, assess risk to sensitive salmonid habitats, and evaluate whether stormwater management practices effectively reduce tire wear particle and 6PPD-Q loading.

 

Risks if No Additional Action is Taken

If no additional action is taken, Canada will remain unable to identify where 6PPD-Q poses the greatest risk to freshwater ecosystems. This would limit the ability to prioritize watersheds, stormwater outfalls, transportation corridors, and salmonid habitats for mitigation.

 

The risk is expected to increase with ongoing urbanization, road densification, and continued reliance on private automobiles. Pollution from tire wear particles is increasing with growing global automobile use (7), while urban expansion and road densification are increasing the likelihood that contaminants from roads will be transported into aquatic environments (15, 21, 22). Widespread adoption of electric vehicles may also increase tire wear particle release because electric vehicles are generally heavier and produce greater torque than internal combustion vehicles (23).

 

Without additional monitoring, mitigation research, or source-control planning, Canada could see increased incidence of urban runoff mortality syndrome in sensitive species, with cascading effects through aquatic food webs and associated losses to cultural, ecological, and economic ecosystem services. Delayed action would also weaken Canada’s ability to respond with evidence-based regulation or guidance. Without Canadian monitoring data, decision-makers may need to rely heavily on studies from other jurisdictions, even though risk depends on local road density, stormwater infrastructure, hydrology, land use, and species distributions.

 

Recommended Use of Additional Funding

Additional funding should be directed toward a targeted Canadian 6PPD-Q freshwater assessment and mitigation program. The program should focus on high-risk urban watersheds and salmonid habitats and should produce evidence that can support federal assessment, stormwater guidance, and future source-control options.

 

Funding should support four linked activities:

 

  1. Targeted monitoring of priority watersheds. Measure 6PPD-Q in stormwater, tributaries, sediments, and receiving waters across selected high-risk watersheds, including southern Ontario Great Lakes–St. Lawrence tributaries and salmon-bearing coastal watersheds in British Columbia.
  2. Identification of exposure pathways and hotspots. Identify road runoff pathways, stormwater outfalls, combined sewer overflow locations, and urban tributaries most likely to deliver tire wear particles and 6PPD-Q to aquatic habitats.
  3. Assessment of risk to sensitive salmonid habitats. Overlay monitoring results with salmonid distribution, spawning areas, migration pathways, and urban land-use gradients to identify locations where ecological risk is highest.
  4. Evaluation of mitigation options. Assess the effectiveness of green and grey stormwater infrastructure, including stormwater ponds, wetlands, filtration systems, and other best management practices, for reducing tire wear particle and 6PPD-Q loading. Because prevention at the manufacturing stage is likely the most effective long-term solution, this work should also support broader source-control discussions, including safer tire additives and reduced release of tire wear particles at the source (24, 25).

 

Expected Results

Additional funding would achieve the following results:

 

·       a prioritized list of Canadian freshwater watersheds and stormwater systems at greatest risk from 6PPD-Q;

·       baseline Canadian monitoring data for 6PPD-Q in stormwater-impacted freshwater ecosystems;

·       improved understanding of exposure risk to sensitive salmonid species and habitats;

·       evidence on whether existing stormwater management practices reduce 6PPD-Q and tire wear particle loading;

·       recommendations for targeted mitigation in high-risk urban watersheds;

·       stronger scientific support for CEPA assessment, interjurisdictional water quality planning, and future source-control or stormwater guidance.

 

Recommendation

It is recommended that additional funding be allocated to a targeted monitoring and mitigation assessment program for 6PPD-Q in high-risk Canadian freshwater ecosystems. This investment would allow Canada to address an emerging contaminant before impacts become more widespread, protect sensitive salmonid species, and provide senior management with the evidence needed to support future regulatory, monitoring, and watershed-management decisions.

 

References

  1. E. S. Bernhardt, E. J. Rosi, M. O. Gessner, Frontiers in Ecology and the Environment 15, 84–90 (2017).
  2. K. Zoroufchi Benis et al., Environmental Science & Technology Letters 10, 815–823 (2023).
  3. G. Cao et al., Environmental Science & Technology 56, 4142–4150 (2022).
  4. P. A. Helm et al., ACS EST Water 4, 1422–1432 (2024).
  5. Q. T. Birch, P. M. Potter, P. X. Pinto, D. D. Dionysiou, S. R. Al-Abed, Reviews in Environmental Science and Biotechnology 19, 275–336 (2020).
  6. Z. Tian et al., Science 371, 185–189 (2021).
  7. L. Calle et al., Journal of Hazardous Materials 484, 136694 (2025).
  8. R. S. Prosser, J. Salole, S. Hang, Environmental Pollution 337, 122512 (2023).
  9. M. Brinkmann et al., Environmental Science & Technology Letters 9, 333–338 (2022).
  10. S. C. Ihenetu et al., Environmental Research 258, 119492 (2024).
  11. X. Hua, D. Wang, Journal of Hazardous Materials 459, 132265 (2023).
  12. X. Wan, G. Liang, D. Wang, Science of the Total Environment 949, 175057 (2024).
  13. B. Du et al., Environmental Science & Technology Letters 9, 1056–1062 (2022).
  14. X. Chen et al., Journal of Hazardous Materials 452, 131245 (2023).
  15. Ontario, “A Place to Grow: Growth Plan for the Greater Golden Horseshoe” (2020).
  16. Statistics Canada, “Annual Demographic Estimates: Subprovincial Areas, July 1, 2022” (2023).
  17. C. Beck, L. Daniel, “Request to assess 6PPD under s. 76 of the Canadian Environmental Protection Act, 1999” (Ecojustice, 2024).
  18. J. R. Irvine, “COSEWIC Assessment and Status Report on the Coho Salmon Oncorhynchus kisutch Interior Fraser Population in Canada” (Committee on the Status of Endangered Wildlife in Canada, Ottawa, 2002).
  19. ECCC, “Proposed Plan of Priorities: substances prioritized for assessment under CEPA” (2024).
  20. ES&E, “Four Ontario universities funded to research impacts of PFAS, 6PPD in Great Lakes” (2024).
  21. Statistics Canada, “Canada’s large urban centres continue to grow and spread” (2022).
  22. J. R. Meijer, M. A. J. Huijbregts, K. C. G. J. Schotten, A. M. Schipper, Environmental Research Letters 13, 064006 (2018).
  23. J. Carey, Proceedings of the National Academy of Sciences of the United States of America 120, e2220923120 (2023).
  24. P. M. Mayer et al., Science of the Total Environment 927, 171153 (2024).
  25. B. Baensch-Baltruschat, B. Kocher, F. Stock, G. Reifferscheid, Science of the Total Environment 733, 137823 (2020).

 

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