Frequently asked questions

In this section, we’ve assembled a collection of frequently asked questions on tire and road wear particles (TRWP) and our work. If you can’t find what you’re looking for here, please contact us.

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We are science-driven.

For more than a decade we have supported – and continue to support – research into TRWP; we commission independent research with the aim of publishing studies in peer-reviewed scientific journals.  

TRWP is a relatively new field of research. 

Initial research has contributed to help answer questions about the physical and chemical characteristics of TRWP, their behavior in the environment, and their potential risk to human health and the environment. 

FAQ

  1. What are Tire and Road Wear Particles (TRWP)?
  2. TRWP are tiny debris produced by necessary friction between tires and road surface; they are an approximately half-and-half mixture of tire tread and road pavement material. With a density of ~1.8g/cm3, TRWP are expected to sink in water.

    Since 2005 the Tire Industry Project (TIP) has supported research into the potential human health and environmental impacts of tires throughout their lifecycle.

    The studies we have sponsored have found TRWP are unlikely to negatively impact human health and the environment; however, we’re engaged in continued research to improve the scientific understanding of the potential risks associated with TRWP.

  3. What do TRWP look like, how big are they, can I see them with the naked eye?
  4. TRWP are tiny, elongated particles of tire tread and road pavement material.

    TRWP are tiny – measured in the scale of micrometers (μm). 1μm = 0.001mm.

    TIP sponsored studies have placed the size of most TRWP in the range of 100μm. This is very small, but large enough for the human eye to see. A human hair is approximately 100μm (0.1mm) thick.

    Importantly, these studies have demonstrated that the shape, size and composition of TRWP is the specific result of the wear mechanism created at the tire pavement interface. Particles generated through lab-based mechanical abrasion / grinding of tire tread have different physical and chemical characteristics than those of TRWP.

  5. Are TRWP a form of microplastic?
  6. There is no globally accepted definition of microplastics. However, our focus is not on how TRWP may or may not be categorized, but to study them to learn more about any potential impacts they may have on human health and the environment.

    TRWP exist regardless of how we choose to categorize them. Our mission is to better understand the distribution of these particles in the environment and their potential impact on human health and the environment.

    TRWP are tiny – less than 5 mm – and contain some polymeric material. According to some definitions, this would qualify TRWP as a form of microplastic.

    The “microplastic” label is important because it helps draw broad attention to a complex multi-faceted societal challenge. A challenge that requires an evidence-based response and the engagement of a multitude of stakeholders.

  7. What can tire consumers and drivers do to help limit the generation of TRWP?
  8. Methods for more efficient fuel consumption when driving that achieve direct positive impact on reduction of TRWP generation (Adapted from the European Tyre and Rubber Manufacturers’ Association (ETRMA)):

    - Accelerate gently

    - Maintain a steady speed

    - Anticipate traffic

    - Avoid high speeds

    - Coast to decelerate

    - Maintain appropriate tire pressure

    - Avoid carrying unnecessary weight

    Regional tire trade associations are working with stakeholders to address the collective question "how can we reduce tire and road wear particles without impacting the important role tires play in road safety and mobility?" - you can discover the ETRMA initiative on this topic, here: https://www.tyreandroadwear.com/

  9. How much TRWP is generated?
  10. According to Unice et al., (2019), "Tire tread particles are distributed into the environment as tire and road wear particles (TRWP) formed at the frictional interface of the tire and road surface consisting of polymer-containing tread with pavement mineral and binder encrustations (Kreider et al., 2010). TRWP has been estimated to be approximately 50% tread, of which approximately half consists of a polymeric fraction (Kreider et al., 2010; Panko et al., 2013; Unice et al., 2013). Recent emission inventories conducted in seven continental European countries (DE, DK, IT, NL, NO, SE and UK) found a tread mass generation rate (excluding road mineral encrustations) of approximately 1 kg tread per capita per year (range: 0.52 to 1.5) (Kole et al., 2017)."

  11. What is 6PPD-quinone?
  12. TIP welcomes efforts to improve scientific understanding of the potential impacts of TRWP. We are aware of the recent identification of 6PPD-quinone and of the preliminary studies that have investigated potential environmental impacts of this chemical. 6PPD-quinone – also known as 6PPD-q – is a transformation product of the important tire ingredient 6PPD. 6PPD is an antioxidant and antiozonant that helps stop rubber from breaking down, which is critical for tire safety.

    Following the identification of 6PPD-quinone, building on more than a decade of TIP-sponsored research into TRWP, TIP’s research plan now includes efforts to contribute to the body of scientific knowledge on this chemical.

  13. Do you provide materials to support TRWP research?
  14. Using a Tire Industry Project (TIP) methodology, the U.S. Tire Manufacturers Association (USTMA) will produce cryogenically milled tire tread (CMTT) and provide samples to researchers to advance scientific study on tire and road wear particles (TRWP).

    CMTT is the product of a standardized and reproduceable laboratory process developed by TIP, that grinds (or mills) tire tread to simulate the tire particles that are generated by the friction between tires and road surfaces. CMTT is comprised of tiny pieces of the vulcanized rubber compound found in tire tread, but does not contain elements arising from pavement or any interactions with pavement.

    Researchers can request samples via the USTMA website. Complementing the USTMA initiative, TIP has committed to make representative CMTT available for other regions by the end of 2022.

  1. Are TRWP a threat to my health?
  2. Our sponsored studies have indicated that TRWP do not pose risk to human health, and we’re engaged in continued research to improve this knowledge.

    Specifically, studies into airborne TRWP have concluded that TRWP make a relatively low contribution to particulate matter of the size fractions of most concern to human health. Additionally, inhalation studies suggest that TRWP is unlikely to pose risk to humans through airborne exposure.

    With relevance to improving scientific understanding of potential human exposure to TRWP, our ongoing and planned research includes sampling of TRWP in the environment, studying the degradation of TRWP, modelling the fate and transport of TRWP in air, rivers, soil, and oceans, and investigating the potential impacts on organisms of long-term exposure to TRWP. Discover more about TRWP human health risk assessment:

    http://dev.bitsia.com/wbcsd/wbcsd-wp/our-research/human-health-risk-assessment/

  3. When and why did TIP begin supporting research into TRWP and their potential health and environmental impact?
  4. We began working on tire particles in 2005 – the same year that TIP was founded – to help answer questions that TIP members were asking about the fate and potential human health and environmental impacts of the particles generated as tires move over road surfaces.

    There were no existing data to help answer these questions, so we established a TRWP working group to study the potential human health and environmental impacts of tire particles.

    We soon realized that a significant and coordinated investment of resources (expertise and financial capital) would be required to help answer these questions. WBCSD tire manufacturing members’ CEOs agreed that as a non-competitive topic, TIP should lead industry efforts to fill knowledge gaps on tire particles.

    Toward an improved understanding of the potential hazards and exposure scenarios relevant to TRWP, initial studies focused on identifying and quantifying TRWP in the environment and delivering human health and environmental risk assessments. These first studies examined toxicity and exposure relevant to the airborne environment, and soils and freshwater sediments.

  1. Where can TRWP be found? 
  2. Studies have suggested that most TRWP finds its way to roadside soils or is removed from the road surface as runoff; a small fraction of TRWP are released to the air.

    A study that considered the Seine watershed, France, concluded that more than 60% of TRWP released to freshwater are transported to wastewater treatment. The research indicated that most TRWP finds its way to roadside soils or is removed from the road surface as runoff. A small fraction is released to the air. The same research estimated that 18% of TRWP is transported to freshwater, with 2%-5% of total TRWP transported to the estuary.

    TIP is supporting ongoing studies into TRWP pathways to better understand where TRWP can be found.

  3. What has TIP-sponsored research revealed about any potential environmental impacts of TRWP?
  4. TIP-sponsored risk assessments have to-date found that tire and road wear particles (TRWP) are unlikely to have adverse effects on the environment. However, TIP recognizes the importance of continued research into the potential impacts of TRWP.

    Early TIP-sponsored studies have shown some potential for toxicity for TRWP, but few studies have evaluated the toxicity of TRWP using freshwater sediment – such as that found in rivers and lakes – which is likely an important sink of tire wear particles in the environment. Accordingly, TIP sponsored research into the toxicity of TRWP to freshwater – and freshwater-sediment-dwelling organisms.

    In these studies, limited toxicity was observed on test species, indicating that under typical exposure conditions TRWP in sediments pose a low risk of toxicity to aquatic organisms.

  5. Are TRWP a source of marine (microplastic) pollution?
  6. The presence of TRWP in oceans has not been demonstrated, but peer-reviewed studies have suggested that around 2-5% of generated TRWP is transported to estuaries.

    Some modelling exercises have suggested that TRWP are transported by natural processes to the marine environment; however, the presence of TRWP in the marine environment has not been demonstrated through field studies.

    TIP is supporting ongoing studies into TRWP pathways – focusing on air, soil, sediment and estuaries.

    A 2018 two-part, peer-reviewed study estimated that as little as 2-5% of TRWP is transported to estuaries. The study suggests that most TRWP finds its way to roadside soils or is removed from the road surface as runoff. A small fraction is released to the air.

    A 2018 peer-reviewed and journal-published study into micro(plastic) fluxes in Lake Geneva basin concluded that most of the plastic input is likely to be accumulated in lake sediments – not reaching the marine environment.

  1. When and why did TIP begin supporting research into TRWP and their potential health and environmental impact?
  2. We began working on tire particles in 2005 – the same year that TIP was founded – to help answer questions that TIP members were asking about the fate and potential human health and environmental impacts of the particles generated as tires move over road surfaces.

    There were no existing data to help answer these questions, so we established a TRWP working group to study the potential human health and environmental impacts of tire particles.

    We soon realized that a significant and coordinated investment of resources (expertise and financial capital) would be required to help answer these questions. WBCSD tire manufacturing members’ CEOs agreed that as a non-competitive topic, TIP should lead industry efforts to fill knowledge gaps on tire particles.

    Toward an improved understanding of the potential hazards and exposure scenarios relevant to TRWP, initial studies focused on identifying and quantifying TRWP in the environment and delivering human health and environmental risk assessments. These first studies examined toxicity and exposure relevant to the airborne environment, and soils and freshwater sediments.

  3. How does TIP ensure the validity of the research that it sponsors?
  4. TIP research benefits from contributions from tire industry experts, independent scientists and institutions, and the robustness of the academic peer review process.

    We have established an Assurance Group of academics who provide additional independent review of completed studies and make recommendations on future studies based on an understanding of new research opportunities. We have also put in place an Advisory Panel of academic experts in the field of hydrology, marine biology, and ecotoxicity. They bring valuable big-picture thinking to the study-plan design phase.

    TIP-sponsored research is conducted by different academic institutions and scientific consultancies who are selected based on their expertise in the various subjects of relevance to improving the scientific understanding of TRWP. Thereafter, TIP-sponsored research is subject to the academic peer review process and published in academic journals.

    The peer-review process is the system used to assess the quality of a scientific manuscript before it is published. Independent researchers in the relevant research area review manuscripts for originality, validity, and significance to help the editors of scientific journals determine whether a manuscript should be published in their journal.

  5. What is the final goal of TIP’s TRWP Working Group?
  6. Our focus is on the journey, not the destination. Our aim is to support research into the most relevant aspects of TRWP for human health and environment.

    TIP does not have a single final goal for its work on TRWP; instead, our aim is to continue to grow the evidence base important for an effective understanding of the potential impacts on human health and the environment.

    Specifically, this implies continued research to better understand the characteristics of TRWP, where TRWP can be found in the environment, and the potential risks that this TRWP poses to human health and the environment.

    There is much still to be understood about the movement of TRWP through the environment and its potential impacts. Mindful of this, TIP is committed to continued research toward closing knowledge gaps.

  7. What is the mandate of the TIP TRWP Working Group, and does the mandate evolve?
  8. We sponsor research where findings can contribute toward understanding the potential impacts of TRWP on human health and the environment. The focus of our work is on filling knowledge gaps about TRWP.

    Our TRWP Working Group is mandated to ensure a scientific approach to the study of TRWP pathways.

    We consider our work on TRWP a journey. We began our journey by developing a first understanding of the fundamentals of TRWP (a scientifically valid description of the particles, and hazard and exposure studies for first risk assessments) and follow a multi-year plan that is updated to ensure the prioritization of research to fill the most significant knowledge gaps.

    Initial studies focused on identifying and quantifying TRWP in the environment and delivering human health and environmental risk assessments. These first studies examined toxicity and exposure relevant to the airborne environment, and soils and freshwater sediments. Our ongoing and planned research includes sampling of TRWP in the environment, studying the degradation of TRWP, modelling the fate and transport of TRWP in air, rivers, soil, and oceans, and investigating the potential impacts on organisms of long-term exposure to TRWP.

    The TIP TRWP Working Group is comprised of technical experts from TIP member companies, and we have established an Assurance Group of academics who provide additional independent review (all published TIP-sponsored studies undergo academic peer review) of completed studies and make recommendations on future studies based on an understanding of new research opportunities.

    We have also put in place an Advisory Panel of academic experts in the field of hydrology, marine biology, and ecotoxicity. They bring valuable big-picture thinking to the study-plan design phase.

    TIP-sponsored research is conducted by different academic institutions and scientific consultancies who are selected based on their expertise in the various subjects of relevance to improving the scientific understanding of TRWP.

  9. Does TIP work on topics other than TRWP?
  10. TRWP is a priority research topic for us, but we’re engaged in a variety of important projects that research the potential human and environmental impacts of tires at different stages of their lifecycle.

    TIP works on a range of topics relevant to the key-stages of the lifecycle of tires; from raw-material sourcing – through manufacturing and use phases – to the management of end-of-life tires. TIP working groups contribute to fill knowledge gaps on the potential human and environmental impacts of tires throughout their lifecycle. Discover more at www.wbcsd.org/tip