Published research

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.