The discussion of potential adverse effects of particulate tire wear emissions on ecosystems and human health highlights the need for systematic evaluation of their sources, exposure pathways, and health impacts. Global urbanization may increase exposure to tire and road wear particles (TRWP) and tire-related chemicals, especially in high-traffic areas. This literature review examines current knowledge on human exposure to TRWPs and tire-related chemicals and explores whether TRWP pose a distinctive risk compared with airborne particulate matter (PM). Analytical challenges persist in identifying airborne TRWP, as most research focuses on tire wear particles (TWP) alone, due to difficulties in defining mass ratios within the TRWP aggregate. TWP constitute <5 wt % of ambient PM2.5 and PM10; however, inconsistent analytical methodologies hinder a conclusive exposure assessment. Actual data on human exposure to TWP or TRWP are scarce. Tire-related chemicals have been found in human body fluids, but their exposure pathways are unclear. Toxicological data mainly derive from in vitro studies with few harmonized designs. Comparative research suggests that TRWP are not more toxic than other PM fractions. This review emphasizes the need for harmonized methods, global and regional exposure characterization, and identification of TRWP exposure pathways for humans to address potential health implications more accurately.

© 2026 by the authors. Published by American Chemical Society. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY 4.0) license.

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Tire and road wear particles (TRWPs) are formed at the frictional interface of the tire and road surface and consist of polymer-containing tread with pavement mineral and binder encrustations. Their detection in various environmental compartments globally sparks increasing societal and regulatory interest. Solid quantitative information as a basis for managing and mitigating TRWPs in the environment is lacking, however. This paper presents and demonstrates a model approach that produces catchment-scale terrestrial and aquatic TRWP mass balances anywhere in the world. A spatially and temporally explicit modeling method was used that builds on publicly available global datasets and process-based open-source modeling frameworks to describe hydrological processes, TRWP releases, fate and transport under a wide range of climatic conditions. High-resolution (<1 km) models were implemented and evaluated by demonstrating consistency with available field data for three watersheds on different continents. The approach provides comprehensive mass balances to underpin management of TRWPs that account for socio-economic, climate, geography and stormwater management gradients. Case study results revealed strong climate-induced differences: the fraction of vehicle-generated TRWPs exported to the estuarine environment varied between 2% (Seine watershed, France) to 18% (Yodo River watershed, Japan), corresponding to an increase in the fraction released to freshwater ecosystems from 20% to 36%, respectively. The modeling framework provides a consistent comparison between watersheds across the world. Limitations of the approach are its lack of local details and the uncertainties stemming from the still-developing scientific knowledge base.

© 2026 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.

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Para-phenylenediamines (PPDs) are antioxidants added to tires to protect the rubber. They are released from tire and road wear particles (TRWP) but the extent of their aerobic microbial degradation and the transformation products (TPs) formed are not known. Therefore, aerobic microbial degradation of seven tire-related PPDs, parent compounds as well as known transformation products, was studied for up to 28 days. Half-lives ranged from 0.2 ± 0.1 days (N-(1,3-dimethylbutyl)-N'-phenyl-1,4-benzenediamine, 6-PPD) and 0.6 ± 0.1 days (N-isopropyl-N’-phenyl-1,4-phenylenediamine, IPPD) to 3 ± 0.1 days (N-(1,3-dimethylbutyl)-N'-phenyl-1,4-benzenediamine quinone, 6-PPDQ). A total number of 48 TPs was tentatively identified by liquid chromatography-high resolution-mass spectrometry for the seven study compounds. Of these TPs, only four did not decrease in concentration when the parent compounds were degraded completely. Biotransformation in aqueous solution forms several TPs not known for abiotic, photolytic or oxidative transformation. For the PPDs with aliphatic substituents (6-PPD, IPPD) hydrolysis to 4-HDPA was the major initial transformation. Formation of 6-PPDQ from 6-PPD was not detectable. For the fully aromatic DPPD aerobic microbial transformation, likely, proceeded via a quinone diimine intermediate, leading to products different to those of the aliphatic PPDs. From 6-PPDQ, 26 TPs were detected. A suspect screening for the TPs detected from the biodegradation experiments was performed in data of a soil degradation study over 23 months with TRWP and cryo-milled tire tread (CMTT) and in data from the influent and effluent of a municipal wastewater treatment plant during a rain event. In total, 10 TPs were found in those data with variable intensities, most of which originated from 6-PPDQ. While all seven test compounds were (primary) degraded under aerobic conditions, mineralization was not studied. A number of TPs remain as suspects to search for in the environment.

This work, “Biodegradation pathways and products of tire-related phenylenediamines and phenylenediamine quinones in solution – a laboratory study” by "Han et al." was originally published in Water Research, and is licensed under the Creative Commons Attribution 4.0 International License. You may view the original publication here.

Tire and road wear particles (TRWP) are continuously formed by automotive traffic on roads. This study reports effects of long-term degradation over 2 years in water and in soil in the presence of microbes on TRWP and on cryo-milled tire tread (CMTT). Degradation in water had little measurable effect on physical properties of TRWP; a shift towards larger particle sizes was mainly due to the mechanical stress from stirring. The total quantified extractables (TQE) of 27 chemicals and transformation products determined from tire particles were reduced by 90 % from TRWP and CMTT in water and by 85 % in soil. Most of this decrease occurs within the first months. For both materials, however, the speed of loss of TQE in water and in soil decreased drastically over time. Its kinetics was approximated by two phases of 1st order kinetics, resulting in half-lives from 17 days for diphenylguanidine (DPG) in phase 1 to 520 days for 6-PPD-quinone (6-PPDQ) in phase 2 of TRWP biodegradation in water. For soil, half-lives tend to be clearly longer in phase 2 compared to water but remained <1000 days for chemicals such as benzothiazole sulfonic acid (BTSA), N,N′-diphenyl-p-phenylendiamine (DPPD) and hydroxybenzothiazole (OH-BT). For N-(1,3-dimethylbutyl)-N′-phenyl-1,4-phenylenediamine (6-PPD) and 6-PPDQ they exceeded 2000 days from TRWP. Only 1–15 % of TQE lost from the tire materials remained detectable at the end of the experimental period in the supernatant of the suspension or in leachates of the soil. Mostly benzothiazoles were determined from solution. The biodegradation experiments show an effective reduction of a large part of the chemical burden of TRWP of polar and moderately polar compounds. Despite that, TRWP may serve as a long-term reservoir for some of the tire related chemicals or their transformation products in the environment.

This work, “Long term biodegradation study on tire and road wear particles and chemicals thereof” by "Weyrauch et al." was originally published in Science of the Total Environment, and is licensed under the Creative Commons Attribution 4.0 International License. You may view the original publication here.

There is a growing interest in the development of reliable analytical methods for characterizing tire and road wear particles (TRWP). The current research extends the use of single particle analysis techniques to various experimental biota samples. TRWP and cryogenically milled tire tread (CMTT) were identified using a weight of evidence framework including density separation, optical microscopy, and chemical mapping (scanning electron microscopy coupled with energy dispersive X-ray spectroscopy). Our techniques successfully identified CMTT particles in laboratory earthworms exposed to soil spiked with CMTT. A river biota sample (bivalves) collected from the Seine with no detectable TRWP was spiked with road dust containing TRWP. Particle identification was performed after a biota digestion protocol and density separation of particles > 1.5 g/cm³ and < 2.2 g/cm³ which resulted in sufficient TRWP for identification and characterization. The average TRWP particle size from the road dust spiked biota sample was 126 μm by number and 220 μm by volume (range: 9 –572 μm). The size distribution overlay of TRWP identified from spiked biota were consistent with TRWP identified from the original road dust sample suggesting that the current method for biota digestion, dual density separation, and TRWP characterization is feasible for similar samples.

This work, “Characterization of tire and road wear particles in experimental biota samples” by "Kovochich et al." was originally published in Nature, and is licensed under the Creative Commons Attribution 4.0 International License. You may view the original publication here

The ongoing energy transition, marked by notable advancements in electric vehicles, presents new challenges related to tire emissions. In addition, these emissions and their distribution may be affected by other future trends like prolonged heat periods and an increase in stormwater events, which are both related to the ongoing climate change. An understanding of future trends and robust data on tire emissions during the use phase that inform these trends is essential for evaluating the potential environmental impact and implementing effective mitigation strategies even today. In this structured literature review current and future environmental exposure pathways of tire emissions during vehicle use including particulate tire wear, leachables and volatiles are discussed. A total of 502 publications between 1985 and 2024 were reviewed, resulting in a conceptual exposure model (CEM) for tire emissions during the use phase. Analytical tools are discussed and a proposal for a fit-for-purpose analytical methodology is adapted from microplastic research to inform the CEM of tire emissions. This concept follows a tiered approach covering exploratory, screening, mass, single particle, and chemical analysis of environmental samples with dedicated analytical methods and quality assessment criteria for each tier. Further, the current state of knowledge on factors controlling tire emissions is assessed to determine whether sufficient information is currently available to predict future emissions from tires during use. In conclusion, knowledge needs that need to be solved for a predictive environmental assessment of tire emissions during the use phase are identified.

Tread wear emission inventories, uncertainty about the future development of the emissions and observed adverse effects of tire constituents in the environment have raised the need for an environmental risk assessment of tire wear emissions. While progress has been made in exposure and hazard assessment of tire wear emissions in the environment, the complexity of tire wear emissions creates some challenges which are not yet overcome. For instance, there is no universal agreed risk assessment framework for tire wear emissions. It was proposed that existing frameworks, for example for microplastics, be adapted to tire wear emissions because there are similarities between particulate tire wear emissions and microplastics, e.g. particulate material with a polymer backbone. The review discusses whether these are applicable for tire wear emissions and proposes adaptations. It provides a comprehensive assessment of exposure and hazard data for tire wear emission and reveals needs and data gaps for environmental risk assessment of tire wear. Based on the available exposure and hazard data sets a low risk prioritization of particulate tire wear emissions in aquatic and terrestrial environments was estimated. Risk prioritization of leachables from tire emissions is not yet possible due to inconsistent hazard data sets. It was found that for environmental risk assessment, insufficient consistent exposure and hazard data is available. It is suggested to develop clear harmonization guidelines how exposure and hazard studies should be designed. Such guidelines should be developed between all relevant stakeholders covering the entire product life cycle.

Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) enables quantification of tire and road wear particles (TRWP) in environmental matrices, but method refinements are needed to account for elastomer subunit variations. Environmentally distributed elastomers are a composite of formulations from many tire manufacturers, which can be represented by specially prepared reference materials. Thus, this study analyzed cryogenically milled tire tread (CMTT) composite materials blended from United States and European Union market-representative tire mixtures to determine operationally defined styrene (S_t) and 1,4-butadiene (B_t) monomer subunit content fractions in synthetic rubber (SR) fractions. Bootstrap resampling with least squares optimization revealed similar B_t (0.64–0.73) and S_t (0.06–0.09) contents across market composites, though precision decreased with larger particle sizes. Calibration polymer solutions stored at 4 °C maintained stability for three months, with response ratio changes below 15 %. Although alternative internal standards were evaluated, structural similarity between target and calibration polymers proved essential for complex environmental matrices, with up to 20 % quantitation differences observed when using dissimilar standards. This study demonstrates that market-representative composite CMTT materials provide operationally-defined elastomer subunit profiles that account for commercial variability in tire formulations. This approach enables accurate environmental TRWP quantification without requiring individual elastomer characterization.

This work, “Pyrolysis-GC/MS calibration for environmental quantification of tire tread: Standards and marketplace averaged elastomer subunit profiles” by "Thornton et al." was originally published in Chemosphere, and is licensed under the Creative Commons Attribution 4.0 International License. You may view the original publication here.

• Uptake kinetics in earthworms are chemicals dependant.
• No significant effects of tire particles on reproduction were observed.
• Avoidance tests showed positive results for highly contaminated soils.

Tire and Road Wear Particles (TRWP) are produced during the wear of tire rubber on the road pavement and contain various chemicals originating from the road environment and from the rubber. Toxic effects of TRWP and their associated chemicals on soil organisms remain poorly characterized. In a series of laboratory experiments, this study investigated the bioaccumulation kinetics of several common tire-related chemicals in the earthworm species Eisenia andrei using Cryogenically Milled Tire Tread (CMTT), as a surrogate for environmental TRWP. Effects on survival, growth, reproductive output and behaviour were determined. Average biota-soil accumulation factors ranged from 0.8 to 4.7 indicating low to moderate bioaccumulation of the tire-related chemicals. Toxicokinetics showed both high uptake (0.0–13.2 days⁻¹) and elimination rates (0.0–6.3 days⁻¹) in E.andrei. Still, the uptake of tire-related chemicals in earthworms' tissues and ingestion of tire particles could lead to trophic transfer to preys feeding on earthworms and requires further investigated. No significant effects on survival and growth were recorded after exposure to 0.05 and 5% CMTT. In the reproduction test, a slight increase of the reproductive output with increasing CMTT concentration and a slight decrease of the weight of the juveniles were observed. Moreover, a strong and significant avoidance behaviour was observed for worms exposed to 5% CMTT. This work highlights that soil highly contaminated with tire particles can negatively impact habitat function due to changes in texture and/or chemical stressors, lead to uptake of tire-related additives by earthworms and that high concentrations can impact organism's fitness.

• First mass-based TRWP concentrations reported in marine samples.
• Improved Py-GC/MS method enhanced TRWP measurement accuracy.
• Second density separation improved particulate Zn method comparability.
• Organic-rich matrices challenged TRWP quantification via Py-GC/MS, particulate Zn.
• Sediment traps showed highest TRWP deposition near input from urban areas.

Tire and road wear particles (TRWP) are generated at the frictional interface between tires and the road surface. This mixture of tire tread and road pavement materials can migrate from roads into nearby water bodies during precipitation events. The absence of mass-based measurements in marine environments introduces uncertainty in environmental risk assessments and fate and transport models. Surface water and sediment samples were collected from nine Osaka Bay (Japan) locations for TRWP mass determination in June 2023. Additionally, sediment traps were deployed for approximately nine weeks at three locations near the mouth of the Yodo River. Large volumes of surface water (approximately 10,000 L/sample) were sequentially filtered (100, 10, 0.5 μm) to capture retained solids between 0.5 μm and 5 mm. Sediment and retained solids were analyzed for TRWP using Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) and the particulate zinc (Zn) method. TRWP concentrations in surface water retained solids and sediment showed spatial variation, with median concentrations of 231 μg/g dw and 312 μg/g (grab samples) and 460 μg/g (trap samples), respectively, with higher concentrations near the mouth of the Yodo River, indicating greater influence from urban areas. The study's findings improve understanding of the Py-GC/MS method, highlighting the necessary adjustments to reduce biases and enhance accuracy, as well as the relationship between Py-GC/MS and the particulate Zn method. These results can inform future environmental risk assessments, fate and transport models, and strategies for mitigating TRWP in marine environments.

Emissions due to tires retread/repair and incineration are a cause of concern owing to the presence of nanoparticles in the products. The assessment exposure to humans hereto related is a challenge in an environmental context. The first object of this work is to develop a method to characterize the emission sources using online (counting and sizing) and offline measurements. The second objective of this work is to apply this new metrological strategy to two tire samples. One of these samples contains nanoparticles made of silver to trace the nanoparticle emissions and assess the performance of the characterization method presented here.

Retread/repair testing involves different tasks i.e., drilling, grinding, cutting and regrooving. Testing evidence that emissions adding dried droplets or carbon films and irregular-shaped particles are discernible in microscopy. Carbon and oxygen, and to a lesser extent silicon and sulfur are the most common chemical elements. The compound containing nano-Ag emitted the same amount or sometimes less nanoparticles (i.e., drilling, cutting and regrooving) than the compound having no nano-Ag. Silver embedded in the rubber matrix was found at low concentration in irregular-shaped particles originating from one of these two samples and highlights the approach interest.

Incineration testing were carried out in a laboratory scale tubular furnace. The generated aerosol is dominated by soot whatever the sample. Few particles containing ZnO or silver are identified in residue samples. A STEM/EDX mapping analysis exhibits few nanoscale objects from incineration residue containing free nanosized silver particles and separated from the large silver object.

This work was originally published in Science of The Total Environment, and is licensed under the Creative Commons Attribution 4.0 International License. You may view the original publication here.

Tire and road wear particles (TRWP) contain complex mixtures of chemicals and release them to the environment, and potential toxic effects of these chemicals still need to be characterized. We used a standardized surrogate for TRWP, cryogenically milled tire tread (CMTT), to isolate and evaluate effects of tire‐associated chemicals. We examined organic chemical mixtures extracted and leached from CMTT for the toxicity endpoints genotoxicity, estrogenicity, and inhibition of bacterial luminescence. The bioassays were performed after chromatographic separation on high‐performance thin‐layer chromatography (HPTLC) plates. Extracts of CMTT were active in all three HPTLC bioassays with two estrogenic zones, two genotoxic zones, and two zones inhibiting bacterial luminescence. Extracts of CMTT artificially aged with thermooxidation were equally bioactive in each HPTLC bioassay. Two types of aqueous leachates of unaged CMTT, simulating either digestion by fish or contact with sediment and water, contained estrogenic chemicals and inhibitors of bacterial luminescence with similar profiles to those of CMTT extracts. Of 11 tested tire‐associated chemicals, two were estrogenic, three were genotoxic, and several inhibited bacterial luminescence. 1,3‐Diphenylguanidine, transformation products of N‐(1,3‐dimethylbutyl)‐N′‐phenyl‐p‐phenylenediamine, and benzothiazoles were especially implicated through comparison to HPTLC retention factors in the CMTT samples. Other bioactive bands in CMTT samples did not correspond to any target chemicals. Tire particles clearly contain and can leach complex mixtures of toxic chemicals to the environment. Although some known chemicals contribute to estrogenic, genotoxic, and antibacterial hazards, unidentified toxic chemicals are still present and deserve further investigation. Overall, our study expands the understanding of potential adverse effects from tire particles and helps improve the link between those effects and the responsible chemicals. Environ Toxicol Chem 2024;43:1962–1972. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Chemicals leaching from cryogenically milled tire tread detected by high‐performance thin‐layer chromatography bioassays. 6PPD = N‐(1,3‐dimethylbutyl)‐N′‐phenyl‐p‐phenylenediamine; DPG = diphenylguanidine.

Herein, we examine the generation of nanoparticles from tire and road interactions, with a focus on two key aspects: replicating real-world conditions in a controlled environment for particle generation and analysing the collected particles through both online and offline techniques. In order to generate realistic wear patterns, third body particles were used in a standardized laboratory tire testing facility across dynamic and static speeds and load profiles. The findings indicated that milled stone dust as a third body particle significantly disrupted the nanoparticle size range, complicating the differentiation between tire-based and third-body-based nanoparticles. However, using sand as a third body particle, the interference showed comparatively lower background noise within the nanoparticle region. Here, steady-state cycles were employed to discern the relationships between force events and nanoparticle generation, which were compared to analyses conducted over an entire dynamic drive cycle. The steady-state cycles revealed that high lateral forces (>2 kN) yielded the highest nanoparticle concentrations, surpassing background levels by over two orders of magnitude. Meanwhile, the drive cycle trials indicated that approximately 70% of the emitted nanoparticles throughout the entire drive cycle were semi-volatile emissions, likely originating from vaporization events. ICP-MS results confirmed the presence of tire-related elements in the nanoparticle region, but definitive attribution to the tire or road surface remains a challenge for the field. This study underscores the complexities inherent in generating, collecting, and assessing submicron tire wear particles, laying the groundwork for addressing uncertainties and refining non-exhaust tire emission methodologies.

• On average, tire wear and brake wear account for 3% and 1% of road dust, respectively, when using elemental markers.
• Tire wear is most prominent in the particle size fractions below 10 μm, at <10%, compared to the larger size fractions.
• Tire and road wear particles from test stands may not reflect elemental composition of those from the environment.

To gain better understanding of how the transition to electric vehicles affects road dust (RD) composition, and potential health and environmental risks, it is crucial to analyze the chemical composition of RD and identify its sources. Sources of RD include wear of tire tread (TT), brake wear (BW) and road wear (RW). A relevant component of RD are tire and road wear particles (TRWPs). This literature review compiles data on the chemical bulk composition of RD sources, RD in Asia, Europe and North America and TRWP as a RD component. The focus is on elements such as Cd, Co, Cr, Cu, Ni, Pb, V, and Zn. Although the comparability of global RD data is limited due to differences in sampling and analytical methods, no significant differences in the composition from Asia, Europe, and North America were found for most of the investigated elements studied, except for Cd, Co, and V. Sources of RD were analyzed using elemental markers. On average TT, BW, and RW contributed 3 %, 1 %, and 96 %, respectively. The highest concentrations of TT (9 %) and BW (2 %) were observed in the particle size fraction of RD ≤ 10 μm. It is recommended that these results be verified using additional marker compounds. The chemical composition of TRWPs from different sources revealed that (i) TRWPs isolated from a tunnel dust sample are composed of 31 % TT, 6 % BW, and 62 % RW, and (ii) test material from tire test stands show a similar TT content but different chemical bulk composition likely because e.g., of missing BW. Therefore, TRWPs from test stands need to be chemically characterized prior to their use in hazard testing to validate their representativeness.

• Assessment of tire and road wear particles' toxicity to fish using fish cell lines
• Specific toxicity of tire particles, leachates and in vitro digestate investigated
• Acutely toxic concentration of tire particles exceeds environmental concentrations
• Tire particles continuously leach chemicals, Zn and 6PPD main drivers of toxicity
• 6PPD-quinone (6PPD-Q) detected but not toxic to RTgill-W1 and RTgutGC cell lines

Tire and road wear particles (TRWP) resulting from tire abrasion while driving raise concerns due to their potential contribution to aquatic toxicity. This study aimed to assess cryogenically milled tire tread (CMTT) particle toxicity, used as a proxy for TRWP, and associated chemicals to fish using two Rainbow Trout (Oncorhynchus mykiss) cell lines representing the gill (RTgill-W1) and the intestinal (RTgutGC) epithelium. CMTT toxicity was evaluated through several exposure pathways, including direct contact, leaching, and digestion, while also assessing the impact of particle aging. Following OECD TG249, cell viability was assessed after 24 h acute exposure using a multiple-endpoint assay indicative of cell metabolic activity, membrane integrity and lysosome integrity. In vitro EC50 values for the fish cell lines exceeded river TRWP concentrations (2.02 g/L and 4.65 g/L for RTgill-W1 and RTgutGC cell lines, respectively), and were similar to in vivo LC50 values estimated at 6 g/L. Although toxicity was mainly driven by the leaching of tire-associated chemicals, the presence of the particles contributed to the overall toxicity by inducing a continuous leaching, highlighting the importance of considering combined exposure scenarios. Aging and digestion conditions were also found to mediate CMTT toxicity. Thermooxidation resulted in a decreased chemical leaching and toxicity, while in vitro digestion under mimicked gastrointestinal conditions increased leaching and toxicity. Specific chemicals, especially Zn, 2-mercaptobenzothiazole, 1,3-diphenylguanidine, and N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) were identified as contributors to the overall toxicity. Although 6PPD-quinone was detected in CMTT digestate, cytotoxicity assays with RTgill-W1 and RTgutGC cell lines showed no toxicity up to 6 mg/L, supporting the notion of a specific mode of action of this chemical. This study provides insights into the toxicological mechanisms induced by tire particles and their associated chemicals and can help in the evaluation of potential risks to aquatic life associated with TRWP.

• The first reported results of TRWP in retained solid samples collected from a river
• TRWP concentrations in retained solids were significantly higher than in sediment
• (SBR/BR)/NR ratio was lower than expected based on passenger/truck tires literature
• First study to evaluate the temporal trend of TRWP in river sediment
• Lower TRWP concentrations over time could indicate improvements in water quality

Tire and road wear particles (TRWP) are formed at the frictional interface between tires and the road surface. Tire tread and road pavement materials are denser than water but can be washed from the road surface into receiving water bodies, ultimately depositing into sediment, soil, or other media depending on the receiving environment. However, the paucity of mass-based measurements has limited the knowledge on the nature and extent of environmental concentrations necessary for environmental risk assessment of TRWP. Surface water and sediment samples were collected from the Seine River, France to characterize TRWP concentration. Sample locations were established upstream, within, and downstream of a major metropolitan area (Paris); downstream of smaller urban areas; adjacent to undeveloped land; and near the confluence of the estuary. Surface water and sediment were collected from the left and right banks at each of the eight locations, including two duplicates, for a total of 18 samples. Additionally, three sediment traps were deployed near the mouth of the river to quantify the flux of TRWP to sediment. Retained solids and sediment samples were analyzed using a modified pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) method that minimized the matrix interferences in the samples thus improving the current ISO Technical Specification ISO/TS 21396 : 2017 for TRWP mass concentration by Py-GC/MS. TRWP concentration was alternatively estimated by separating the sediment into the <1.9 g cm−3 fraction and analyzing for tread-derived zinc content. TRWP concentrations estimated by zinc method were significantly higher than results from the modified Py-GC/MS method. TRWP and total zinc concentrations show a decreasing trend from available historical data.

• Aging of tire and road wear particles changes their properties in an unknown manneer
• A lab study simulates temperature (3 a), sunlight (0.5 a) and mechanical stress
• Aging effects on particle size distribution and density of TRWP were not significant
• Chemical composition shifted from parent compounds to transformation products
• TRWP aging significantly alters environmental exposure to tire-related chemicals.

Tire and road wear particles (TRWP) are generated in large quantity by automobile traffic on roads but their way of degradation in the environment is largely unclear. Laboratory experiments were performed on the effect of elevated temperature (simulating 2–3 years), sunlight exposure (simulating 0.5 years) and mechanical stress on the physical properties and chemical composition of TRWP and of cryo-milled tire tread (CMTT). No significant effects were observed of the applied mechanical stress on mean properties of pristine particles. After sunlight exposure up to 40 % in mass were lost from the TRWPs, likely due to the loss of mineral incrustations from their surface. The chemical composition of TRWP and CMTT was characterized by determining 27 compounds, antioxidants (phenylene diamines), vulcanization agents (benzothiazoles and guanidines) and their transformation products (TPs). Extractables of TRWP (580–850 μg/g) were dominated by TPs, namely benzothiazolesulfonic acid (BTSA). CMTT showed much higher amounts of extractables (4600 μg/g) which were dominated by parent chemicals such as N-(1,3-dimethylbutyl)-N′-phenyl-1,4-phenylenediamine (6-PPD), diphenylguanidine (DPG) and mercaptobenzothiazole (MBT). Sunlight exposure affected the amount of extractables more strongly than elevated temperature, for TRWP (−45 % vs −20 %) and CMTT (−80 % vs −25 %) and provoked a clear shift from parent compounds to their TPs. After sunlight exposure extractables of TRWP were dominated by BTSA and DPG. Sunlight exposure drastically reduced the 6-PPD amount extracted from both, TRWP and CMTT (−93 %, −98 %), while its quinone (6-PPDQ) increased by around 1 % of the 6-PPD decrease, only. For many TPs, concentration in leachates were higher than in extracts, indicating ongoing transformation of their parent compounds during leaching. These results highlight that abiotic aging of TRWPs leads to strong changes in their chemical composition which affect their particle properties and are of relevance for the environmental exposure to tire-related chemicals.

This study by Kovochich et al. extends recently developed single particle analysis methods to various urban river samples which belong to more complex media types. The study presents one of the first published particle size distributions of TRWP including single particle elemental chemical mapping of river sediment. These data may help increase specificity of TRWP identification and provide information on TRWP size distribution for fate and transport models. The results help advance the methods for TRWP identification and characterization of TRWP in various environmental matrices.

Tire and road wear particles (TRWP) consist of tread rubber elastomers with pavement encrustations generated from tire-road friction. Our previous work utilized density separation and chemical mapping to characterize chemical and physical properties of individual TRWP. The current research extends the use of chemical mapping methods to urban river samples including sediment from the Seine River (France). TRWP were identified using a weight of evidence framework including density separation, optical imaging, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) mapping, and Fourier-transform infrared (FTIR) spectroscopy. River sediment collected immediately downstream of the Rouen urban area (with an average TRWP concentration of 930 mg TRWP/kg sediment; n = 3) subsequently density separated demonstrated an average TRWP size of 133 µm by number and 171 µm by volume. Sediment from a second location (190 mg TRWP/kg sediment; n = 1) was density separated and showed an overlap in features of tire tread and bitumen/asphalt in the FTIR signatures (operationally defined as weathered bitumen/TRWP). Average particle size for weathered bitumen/TRWP were 250 µm and 981 µm by number and volume, respectively. Pulverization pre-treatment of the second location sediment sample reduced larger particle agglomerates to an average weathered bitumen/TRWP particle size of 97 µm and 116 µm by number and volume, respectively. A quantitative TRWP or bitumen/TRWP size distribution in filtered suspended river solids (3300 mg TRWP/kg suspended solid) could not be determined due to lack of TRWP enrichment in pre- or post-density separation steps; however, average particle size for all collected river particles were 27 µm and 160 µm by number and volume, respectively. Additionally, TRWP were not identified in a river biota sample (bivalves) with or without chemical digestion and future research was discussed. Taken together, our single particle analysis methodologies were useful for the determination of particle size distribution (including bitumen and TRWP) in urban river sediment samples. These results are expected to help advance the methods for identification and characterization of TRWP and potentially other microplastics in various environmental matrices.

• Improved method for tire and road wear particle mass concentration measurement
• Microfurnace pyrolysis evaluation included artificial and environmental sediment
• Enhancements included thermal desorption and chemical pretreatment
• Matrix effects successfully mitigated observed in complex environmental matrices

Tire and road wear particles (TRWP) are produced by abrasion at the interface of the pavement and tread surface and contain tread rubber with road mineral encrustations. Quantitative thermoanalytical methods capable of estimating TRWP concentrations are needed to assess the prevalence and environmental fate of these particles. However, the presence of complex organic constituents in sediment and other environmental samples presents a challenge to the reliable determination of TRWP concentrations using current pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) methodologies. We are unaware of a published study evaluating pretreatment and other method refinements for microfurnace Py-GC–MS analysis of the elastomeric polymers in TRWP including polymer-specific deuterated internal standards as specified in ISO Technical Specification (ISO/TS) 20593:2017 and ISO/TS 21396:2017. Thus, potential method refinements were evaluated for microfurnace Py-GC–MS, including chromatography parameter modification, chemical pretreatment, and thermal desorption for cryogenically-milled tire tread (CMTT) samples in an artificial sediment matrix and a sediment field sample. The tire tread dimer markers used for quantification were 4-vinylcyclohexene (4-VCH), a marker for styrene-butadiene rubber (SBR) and butadiene rubber (BR), 4-phenylcyclohexene (4-PCH), a marker for SBR, and dipentene (DP), a marker for natural rubber (NR) or isoprene. The resultant modifications included optimization of GC temperature and mass analyzer settings, along with sample pretreatment with potassium hydroxide (KOH) and thermal desorption. Peak resolution was improved while minimizing matrix interferences with overall accuracy and precision consistent with those typically observed in environmental sample analysis. The initial method detection limit for an artificial sediment matrix was approximately 180 mg/kg for a 10 mg sediment sample. A sediment and a retained suspended solids sample were also analyzed to illustrate the applicability of microfurnace Py-GC–MS towards complex environmental sample analysis. These refinements should help encourage the adoption of pyrolysis techniques for mass-based measurements of TRWP in environmental samples both near and distant from roadways.

Tire and road wear particles (TRWP) account for an important part of the polymer particles released into the environment. There are scientific knowledge gaps as to the potential bioaccessibility of chemicals associated with TRWP to aquatic organisms. This study investigated the solubilization and bioaccessibility of seven of the most widely used tire-associated organic chemicals and four of their degradation products from cryogenically milled tire tread (CMTT) into fish digestive fluids using an in vitro digestion model based on Oncorhynchus mykiss. Our results showed that 0.06–44.1% of the selected compounds were rapidly solubilized into simulated gastric and intestinal fluids within a typical gut transit time for fish (3 h in gastric and 24 h in intestinal fluids). The environmentally realistic scenario of coingestion of CMTT and fish prey was explored using ground Gammarus pulex. Coingestion caused compound-specific changes in solubilization, either increasing or decreasing the compounds’ bioaccessibility in simulated gut fluids compared to CMTT alone. Our results emphasize that tire-associated compounds become accessible in a digestive milieu and should be studied further with respect to their bioaccumulation and toxicological effects upon passage of intestinal epithelial cells.

• Tire tread and TRWP quantification in the environment is challenging
• Reliable quantitative methods are critical for environmental risk assessment
• Utility and transferability of an established Py-GC-MS method is evaluated
• Three pyrolysis technologies: Curie point, microfurnace and resistive were compared
• Curie point and microfurnace are suitable for quantitative Py-GC-MS of tire tread

Transferable and reliable methods for tire and road wear particles (TRWP) environmental mass quantification are needed for environmental risk assessment. The comparative performance of three pyrolysis-gas chromatography-mass spectroscopy (Py-GC-MS) technologies with internal standard was assessed for pure polymers and three cryomilled tire tread (CMTT) samples with or without a standard artificial sediment matrix following ISO Technical Specification (TS) 21396:2017. The pyrolyzer technologies included Curie Point (CP; ferromagnetic induction), microfurnace (MF; ceramic heater), and resistive (R; platinum filament). The dimeric pyrolysis markers for tire tread polymer included: 4-vinylcyclohexene (4-VCH), a marker for styrene-butadiene rubber (SBR) and butadiene rubber (BR); dipentene (DP), a marker for natural rubber (NR) or isoprene; and 4-phenylcyclohexene (4-PCH), a marker specific to SBR not considered in the ISO TS. Comparing the performance of three pyrolysis technologies for quantifying six samples (two tread amount levels for three formulations), the average relative standard deviation in pure-CMTT measured in triplicate using 4-VCH and DP was 6.8% (MF), 26% (CP), and 60% (R) without matrix (100 or 1000 ug CMTT), and 19% (MF), 26% (CP) and 105% (R) with matrix (0.5% or 5% CMTT). The recovery of CMTT was greater than 50% for all MF and CP samples with good separation at the two amount levels. An increased frequency of CMTT recoveries >150% for MF and CP artificial sediment analysis suggests future consideration of pre-treatment (e.g., thermal desorption or labile organic digestion) in addition to the previously identified importance of polymer microstructure. The magnitude of variability observed with the resistive instrument indicates that further method development may be necessary to optimize thermal transfer. Overall, Curie point and microfurnace were found to be excellent candidate pyrolysis technologies for ongoing quantitative Py-GC-MS of TRWP in environmental method development, capable of a low likelihood of underestimating polymer mass with reasonable replicate precision.

• Knowledge on tire aging is partially applicable to tire and road wear particles (TRWPs)
• Suitability of various TRWP test materials for aging studies is evaluated
• Aging processes have a joint impact on TRWP properties and composition
• Quantitative understanding of TRWP aging is lacking
• Future research needs on TRWP aging are identified

The environmental fate of tire and road wear particles (TRWPs) receives increasing attention due to the per capita emission volumes of 0.2–5.5 kg/(cap year) and recent reports on the environmental hazard of TRWP constituents. It is expected that aging impacts TRWPs fate in the environment but detailed knowledge is quite limited, yet. Making use of information on tire aging, the available knowledge on environmental aging processes such as thermooxidation, photooxidation, ozonolysis, shear stress, biodegradation and leaching is reviewed here. Experimental techniques to simulate aging are addressed as are analytical techniques to determine aging induced changes of TRWPs, covering physical and chemical properties. The suitability of various tire wear test materials is discussed. Findings and methods from tire aging can be partially applied to study aging of TRWPs in the environment. There is a complex interplay between aging processes in the environment that needs to be considered in future aging studies. In addition to existing basic qualitative understanding of the aging processes, quantitative understanding of TRWP aging is largely lacking. Aging in the environment needs to consider the TRWPs as well as chemicals released. Next steps for filling the gaps in knowledge on aging of TRWPs in the environment are elaborated.

Tire and road wear particles (TRWP) have been shown to represent a large part of anthropogenic particles released into the environment. Nevertheless, the potential ecological risk of TRWP in the different environmental compartments and their potential toxic impacts on terrestrial and aquatic organisms remain largely under investigated. Several heavy metals compose TRWP, including Zn, which is used as a catalyst during the vulcanization process of rubber. This study investigated the solubilization potential of metals from cryogenically milled tire tread (CMTT) and TRWP in simulated gastric fluids (SFGASTRIC) and simulated intestinal fluids (SFINTESTINAL) designed to mimic rainbow trout (Oncorhynchus mykiss) gastrointestinal conditions. Our results indicate that the solubilization of heavy metals was greatly enhanced by gastrointestinal fluids compared to that by mineral water. After a 26 h in vitro digestion, 9.6 and 23.0% of total Zn content of CMTT and TRWP, respectively, were solubilized into the simulated gastrointestinal fluids. Coingestion of tire particles (performed with CMTT only) and surrogate prey items (Gammarus pulex) demonstrated that the animal organic matter reduced the amount of bioavailable Zn solubilized from CMTT. Contrastingly, in the coingestion scenario with vegetal organic matter (Lemna minor), high quantities of Zn were solubilized from L. minor and cumulated with Zn solubilized from CMTT.

Tire and road wear particles (TRWPs) are generated from friction between tires and the road and contain polymer tread with pavement encrustations. Single particle analysis (SPA) of tire source contribution in environmental samples has been limited by interferences in common spectroscopic polymer techniques. This study extends a density separation and chemical mapping protocol for road simulator generated TRWPs toward the identification and characterization of individual TRWPs in more complex road dust, road-dust-spiked artificial sediment, tunnel dust, and environmental settling pond sediment samples. TRWPs were identified by a combination of physical (elongated/round shape with variable amounts of mineral encrustation) and elemental surface characteristics [co-localization of (S + Zn/Na) ± (Si, K, Mg, Ca, and Al)]. Organic surface markers (C7H7+), overlapping FTIR spectra with tread reference material, and resistance to heat-induced deformation were selectively used to confirm particle identification. The TRWP size displayed an increasing average trend of 54, 158, and 267 μm by number (94, 224, and 506 μm by volume) in tunnel dust, road dust, and environmental sediment, respectively. TRWP size distributions within road dust 10× diluted with artificial sediment agreed with those of pure road dust. Our SPA methodologies determined the size distribution of TRWPs in environmental sample types with increasing sample complexity.

Thermogravimetric methods with internal polymer standards have successfully quantified environmental tire and road wear particle (TRWP) concentrations. However, TRWP quantification in environmental matrices via pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) using butadiene rubber (BR) and styrene-butadiene rubber (SBR) marker 4-vinylcyclohexene (4-VCH; 1,4-butadiene-1,4-butadiene dimer) may be uncertain because of variable polymer compositions and BR and SBR microstructures. To determine if tire polymer microstructure is contributing to potentially over- or underestimating TRWP in the environment in py-GC-MS analyses, SBR materials (n = 8) commonly found in tire tread with varying microstructure were quantified via py-GC-MS, using 4-VCH and the deuterated internal standard d-4-VCH to provide a response ratio for each polymer. The response ratios of the dimer response to the total polymer quantity (instrument response slope) varied up to 6.8-fold for SBR, with a reduction to a 3.6-fold range when the polymer quantity was expressed as 1,4-butadiene mass rather than total polymer mass. Variability was reduced further when considering the polymerization method for emulsion-SBRs (n = 3; 1.4-fold range), but not solution-SBRs (n = 5; 2.7-fold range), which reflects the random versus structured heterosequencing of the two rubber types, respectively. Our findings suggest that py-GC-MS response should be interpreted based on empirical analysis of an appropriate number of regionally representative tire tread materials, rather than individual rubbers, because of the lack of methods available for determining unknown average microstructure in environmental samples.

• Reliable analytical methods to characterize microplastic particles are needed.
• Chemical mapping data to characterize tire and road wear particles are presented.
• Size distribution of single particles after density separation was also determined.
• The single particle analysis methods can be applied to future microplastic research.

Tire and road wear particles (TRWP), which are comprised of polymer-containing tread with pavement encrustations, are generated from friction between the tire and the road. Similar to environmentally dispersed microplastic particles (MP), the fate of TRWP depends on both the mass concentration as well as individual particle characteristics, such as particle diameter and density. The identification of an individual TRWP in environmental samples has been limited by inherent characteristics of black particles, which interfere with the spectroscopic techniques most often used in MP research. The purpose of this research was to apply suitable analytical techniques, including scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) mapping and time-of-flight secondary ion mass spectrometry (ToF-SIMS) mapping, to characterize the specific physical and chemical properties of individual TRWP. Comparisons of TRWP with other polymeric (polystyrene) and non-polymeric (carbon black) particle types demonstrated that a combination of physical and chemical markers is necessary to identify TRWP. Addition of a density separation step to the single particle analysis techniques allowed for the determination of average primary TRWP particle size (34 μm by number distribution and 49 μm by volume distribution) and aspect ratio (65% of TRWP with an aspect ratio > 1.5). The use of chemical mapping techniques, such as SEM/EDX and/or ToF-SIMS mapping as demonstrated herein, can support future research efforts that aim to identify complex MP.

This risk assessment addresses potential human health impact of exposure to tire and road wear particles (TRWP), which are formed at the interface of the pavement and road comprising rubber with embedded mineral from the pavement. To conduct the risk assessment, the authors reviewed literature on hazards associated with and exposures to TRWP and developed a screening value for TRWP reliant on the available hazard data and appropriate dosimetric adjustments. The species- and time- adjusted no-observed-adverse-effect-concentration (NOAEC) for respirable TRWP was 55 µg/m3. This NOAEC was compared to exposure estimates for respirable TRWP for both typical and worst case exposure scenarios based on age-specific activity patterns to determine the margin of exposure for TRWP. The estimated daily exposure to TRWP ranged from 0.079 to 0.147 µg/m3, resulting in a margin of exposure for TRWP ranging from approximately 400 to 700. Though there remain uncertainties in the risk assessment stemming from both the hazard and exposure assessments, the current weight of evidence suggests that TRWP presents a low risk to human health.

Vehicle-related particulate matter (PM) emissions may arise from both exhaust and non-exhaust mechanisms, such as brake wear, tire wear, and road pavement abrasion. This study was undertaken to quantify TRWP in PM2.5 at roadside locations in urban centers including London, Tokyo and Los Angeles. TRWP levels in PM2.5 were significantly different between the three cities, with no significant correlation between TRWP in PM2.5 and traffic count. This study provides an initial dataset to understand potential human exposure to airborne TRWP and the potential contribution of this non-exhaust emission source to total PM2.5.

• Tire and road wear particles (TRWP) are a recognized microplastic (MP) material.
• TRWP fate was assessed using integrated MP model described in Part I.
• Local and global (probabilistic) sensitivity and uncertainty analyses were performed.
• TRWP diameter and density are important determinants of estuarial export.
• Central tendency of fraction of TRWP exported to estuary was between 1.4 and 4.9%.

Integrated models addressing microplastic (MP) generation, terrestrial distribution, and freshwater transport are useful tools characterizing the export of MP to marine waters. In Part I of this study, a baseline watershed-scale MP mass balance model was developed for tire and road wear particles (TRWP) in the Seine watershed. In Part II, uncertainty and sensitivity analysis (SA) methods were used to identify the parameters that determine the transport of these particles to the estuary. Local differential, local range and global first-order variance-based SA identified similar key parameters. The global SA (1000 Monte Carlo simulations) indicated that most of the variance in TRWP exported to the estuary can be apportioned to TRWP diameter (76%), TRWP density (5.6%), the fraction of TRWP directed to combined sewers with treatment (3.9%), and the fraction of TRWP distributed to runoff (versus roadside soil; 2.2%). The export fraction was relatively insensitive to heteroaggregation processes and the rainfall intensity threshold for road surface washoff. The fraction of TRWP exported to estuary in the probabilistic assessment was centered on the baseline estimate of 2%. This fraction ranged from 1.4 to 4.9% (central tendency defined as 25th to 75th percentile) and 0.97% to 13% (plausible upper bound defined as 10th to 90th percentiles). This study emphasizes the importance of in situ characterization of TRWP diameter and density, and confirms the baseline mass balance presented in Part I, which indicated an appreciable potential for capture of TRWP in freshwater sediment.

This study was sponsored by the European Tyre and Rubber Manufacturers Association (ETRMA).

• Tire and road wear particles (TRWP) are a recognized microplastic (MP) material.
• TRWP fate in two European watersheds was assessed using an integrated MP model.
• The model integrated terrestrial and freshwater transport processes.
• Mass balance estimate indicated 2% of generated TRWP is exported to the estuary.
• Model uncertainty and parameter sensitivity were assessed in Part II.

Human and ecological exposure to micro- and nanoplastic materials (abbreviated as MP, < 5 mm) occurs in both aquatic and terrestrial environments. Recent reviews prioritize the need for assessments linking spatially distributed MP releases with terrestrial and freshwater transport processes, thereby providing a better understanding of the factors affecting MP distribution to the sea. Tire and road wear particles (TRWP) have an estimated generation rate of 1 kg tread inhabitant−1 year−1 in Europe, but the fate of this MP source in watersheds has not been systematically assessed. An integrated temporally and geospatially resolved watershed-scale MP modeling methodology was applied to TRWP fate and transport in the Seine (France) watershed. The mass balance considers TRWP generation and terrestrial transport to soil, air, and roadways, as well as freshwater transport processes including particle heteroaggregation, degradation and sedimentation within subcatchments. The per capita TRWP mass release estimate in the Seine watershed was 1.8 kg inhabitant−1 yr−1. The model estimates indicated that 18% of this release was transported to freshwater and 2% was exported to the estuary, which demonstrated the potential for appreciable capture, degradation, and retention of TRWP prior to export. The modeled pseudo-steady state sediment concentrations were consistent with measurements from the Seine watershed supporting the plausibility of the predicted trapping efficiency of approximately 90%. The approach supported the efficient completion of local and global sensitivity analyses presented in Part II of this study, and can be adapted to the assessment of other MPs.

This study was sponsored by the European Tyre and Rubber Manufactures Association (ETRMA).

ISO/TS 20593:2017 specifies a method for the determination of the airborne concentration (μg/m3), mass concentration (μg/g) and mass fraction (%) of tyre and road wear particles (TRWP) in ambient particulate matter (PM) samples.

ISO/TS 20593:2017 establishes principles for air sample collection, the generation of pyrolysis fragments from the sample, and the quantification of the generated polymer fragments. The quantified polymer mass is used to calculate the fraction of tyre tread in PM and concentration of tyre tread in air. These quantities are expressed on a TRWP basis, which includes the mass of tyre tread and mass of road wear encrustations, and can also be expressed on a tyre rubber polymer or tyre tread basis.

Air sample collection is on quartz fibre filters with size-selective input in a range of PM2,5 or PM10. The method is suitable for the determination of TRWP in indoor or outdoor atmospheres.

Determining accurate TRWP concentrations in sediment is necessary in order to evaluate the likelihood that these particles present a risk to the aquatic environment. Sampling was completed in the Seine (France), Chesapeake (U.S.), and Yodo-Lake Biwa (Japan) watersheds to quantify TRWP in the surficial sediment of watersheds characterized by a wide diversity of population densities and land uses. The study used a novel quantitative pyrolysis-GC/MS analysis for rubber polymer, and should provide useful information for assessing potential aquatic effects related to tire service life.

In addition to industrial facilities, fuel combustion, forest fires and dust erosion, exhaust and non-exhaust vehicle emissions are an important source of ambient air respirable particulate matter (PM10). Non-exhaust vehicle emissions are formed from wear particles of vehicle components such as brakes, clutches, chassis and tires. Although the non-exhaust particles are relatively minor contributors to the overall ambient air particulate load, reliable exposure estimates are few. In this study, a global sampling program was conducted to quantify tire and road wear particles (TRWP) in the ambient air in order to understand potential human exposures and the overall contribution of these particles to the PM10. The sampling was conducted in Europe, the United States and Japan and the sampling locations were selected to represent a variety of settings including both rural and urban core; and within each residential, commercial and recreational receptors. The air samples were analyzed using validated chemical markers for rubber polymer based on a pyrolysis technique. Results indicated that TRWP concentrations in the PM10 fraction were low, representing an average PM10 contribution of 0.84%. The TRWP concentration in air was associated with traffic load and population density, but the trend was not statistically significant. Further, significant differences across days were not observed. This study provides a robust dataset to understand potential human exposures to airborne TRWP.

Tire and road wear particles (TRWP) are a component of ambient particulate matter (PM) produced from the interaction of tires with the roadway. Inhalation of PM has been associated with cardiopulmonary morbidities and mortalities thought to stem from pulmonary inflammation. To determine whether TRWP may contribute to these events, the effects of subacute inhalation of TRWP were evaluated in rats. Particle size distribution of the aerosolized TRWP was found to be within the respirable range for rats. Toxicity was assessed following OECD guidelines (TG 412). No TRWP-related effects were observed on survival, clinical observations, body or organ weights, gross pathology, food consumption, immune system endpoints, serum chemistry, or biochemical markers of inflammation or cytotoxicity. Rare to few focal areas of subacute inflammatory cell infiltration associated with TWRP exposure were observed in the lungs of one mid and four high exposure animals, but not the low-exposure animals. These alterations were minimal, widely scattered and considered insufficient in extent or severity to have an impact on pulmonary function. Furthermore, it is expected that these focal lesions would remain limited and may undergo resolution without long-term or progressive pulmonary alterations. Therefore, from this study the authors identified a no-observable-adverse-effect-level (NOAEL) of 112 μg/m3 of TRWP in rats for future use in risk assessment of TRWP.

Pyrolysis(pyr)-GC/MS analysis of characteristic thermal decomposition fragments has been previously used for qualitative fingerprinting of organic sources in environmental samples. A quantitative pyr-GC/MS method based on characteristic tire polymer pyrolysis products was developed for tread particle quantification in environmental matrices including soil, sediment, and air. The feasibility of quantitative pyr-GC/MS analysis of tread was confirmed in a method evaluation study using artificial soil spiked with known amounts of cryogenically generated tread. Tread concentration determined by blinded analyses was highly correlated (r2 ≥ 0.88) with the known tread spike concentration. Two critical refinements to the initial pyrolysis protocol were identified including use of an internal standard and quantification by the dimeric markers vinylcyclohexene and dipentene, which have good specificity for rubber polymer with no other appreciable environmental sources. A novel use of deuterated internal standards of similar polymeric structure was developed to correct the variable analyte recovery caused by sample size, matrix effects, and ion source variability. The resultant quantitative pyr-GC/MS protocol is reliable and transferable between laboratories.

Tire and road wear particles (TRWP) consist of a complex mixture of rubber, and pavement released from tires during use on road surfaces. Subsequent transport of the TRWP into freshwater sediments has raised some concern about the potential adverse effects on aquatic organisms. Previous studies have shown some potential for toxicity for tread particles, however, toxicity studies of TRWP collected from a road simulator system revealed no acute toxicity to green algae, daphnids, or fathead minnows at concentrations up to 10,000 mg/kg under conditions representative of receiving water bodies. In this study, the chronic toxicity of TRWP was evaluated in four aquatic species. The results of this study, together with previous studies demonstrating no acute toxicity of TRWP, indicate that under typical exposure conditions TRWP in sediments pose a low risk of toxicity to aquatic organisms.

Previous studies have indicated that tire tread particles are toxic to aquatic species, but few studies have evaluated the toxicity of such particles using sediment, the likely reservoir of tire wear particles in the environment. In this study, the acute toxicity of tire and road wear particles (TRWP) was assessed in Pseudokirchneriella subcapita, Daphnia magna, and Pimephales promelas using a sediment elutriate (100, 500, 1000 or 10000 mg/l TRWP). Under standard test temperature conditions, no concentration response was observed and EC/LC50 values were greater than 10,000 mg/l. Additional tests using D. magna were performed both with and without sediment in elutriates collected under heated conditions designed to promote the release of chemicals from the rubber matrix to understand what environmental factors may influence the toxicity of TRWP. Toxicity was only observed for elutriates generated from TRWP leached under high-temperature conditions and the lowest EC/LC50 value was 5,000 mg/l. In an effort to identify potential toxic chemical constituent(s) in the heated leachates, toxicity identification evaluation (TIE) studies and chemical analysis of the leachate were conducted. The TIE coupled with chemical analysis (liquid chromatography/mass spectrometry/mass spectrometry [LC/MS/MS] and inductively coupled plasma/mass spectrometry [ICP/MS]) of the leachate identified zinc and aniline as candidate toxicants. However, based on the high EC/LC50 values and the limited conditions under which toxicity was observed, TRWP should be considered a low risk to aquatic ecosystems under acute exposure scenarios.

The purpose of this study was to characterize the physical and chemical properties of particles generated from the interaction of tires and road surfaces. Morphology, size distribution, and chemical composition were compared between particles generated using different methods, including on-road collection, laboratory generation under simulated driving conditions, and cryogenic breaking of tread rubber. Both on-road collected and laboratory generated particles exhibited the elongated shape typical of tire wear particles, whereas tread particles were more angular. Despite similar morphology for the on-road collected and the laboratory generated particles, the former were smaller on average. It is not clear at this stage if the difference is significant to the physical and chemical behavior of the particles. The chemical composition of the particles differed, with on-road generated particles containing chemical contributions from sources other than tires, such as pavement or particulates generated from other traffic-related sources. Understanding the differences between these particles is essential in apportioning contaminant contributions to the environment between tires, roadways, and other sources, and evaluating the representativeness of toxicity studies using different types of particulate generated.