Published research

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.