Accelerated aging of tire and road wear particles by elevated temperature, artificial sunlight and mechanical stress - A laboratory study on particle properties, extractables and leachables

Contamination by benzothiazoles in the Arctic: First evidence in the seawater of the Greenland Sea

Benzothiazoles (BTHs), used in industrial chemistry, consumer products, and pharmaceuticals, are emerging contaminants due to their environmental presence and toxicological risks to aquatic life and human health. However, their environmental fate in seawater remains poorly investigated. This study reports for the first time the occurrence and distribution of six BTHs in the sub-Arctic seawater of the Greenland Sea. Using solid-phase extraction combined with ultrahigh performance liquid chromatography tandem mass spectrometry, total BTHs were detected at concentrations ranging from 0.2 to 1043 ng L-1. Benzothiazole, 2-hydroxy-benzothiazole, 2-methylthio-benzothiazole, and 2-methyl-benzothiazole exhibited higher mean concentrations (355 ± 335, 114 ± 80, 34 ± 7, 15 ± 8 ng L-1, respectively) compared to 2-thiocyanomethylthio-benzothiazole (0.5 ± 0.9 ng L-1) and 2-amino-benzothiazole (0.3 ± 0.2 ng L-1). Local emissions and both short- and long-range transport may account for BTHs presence in the Greenland Sea. The spatial distribution of BTHs along the 75° N transect and in the water column appears influenced by the Greenland Sea Gyre circulation and deep convection processes. Total BTHs distribution showed no significant differences between superficial and water column concentrations or between the outermost and innermost transect zones, as determined by the Mann-Whitney test, although concentrations were generally higher in the zone influenced by the Norwegian Atlantic Current. The ecological risks of BTHs, assessed using the risk quotient methodology, indicate a low threat to aquatic life. This research underscores the need for monitoring BTHs in the Arctic to understand their sources, transport, and environmental fate, providing a foundation for future studies.

Elucidating the size distribution of p‑Phenylenediamine-Derived quinones in atmospheric particles

Transformed from p-phenylenediamines (PPDs) antioxidant, PPD-derived quinones (PPD-Qs) have recently been recognized as emerging contaminants due to their potential negative impacts on the environment and human health. While there have been measurements of airborne PPD-Qs, the size distribution of PPD-Qs and the impact of particle size on PPD transformation chemistry remain largely unknown. Here, through the measurements of atmospheric particles in three megacities in China (Beijing, Xi'an, and Hefei), we find that PPD-Qs are widely distributed in these cities. Further analysis of the size-fractioned particles in Hefei indicates that 48 % of PPD-Qs reside in coarse particles. Given that previous studies mainly focus on the measurement of PPD-Qs in fine particles, the previously reported PPD-Q concentrations and the corresponding human exposure dosages are likely to be significantly underestimated. Furthermore, the ratio of PPD-Q to PPD concentration (PPD-Q/PPD) for particles with size range of 0.056 - 0.1 μm is up to 3 times higher than that with size range of 10 - 18 μm, highlighting the key role of particle size in determining the atmospheric oxidation reactivity of PPDs. Model simulations reveal a size-dependent pattern for the estimated concentration of particulate PPD-Qs in human body. In addition, we also demonstrate that PPD-Qs can induce the formation of cellular reactive oxygen species, suggesting that they may pose risks to human health. Overall, our results emphasize the importance of considering the particle size effect when evaluating the reaction potential and exposure risk of airborne PPD-Qs.

Measurement of tyre-based microplastics using traditional and quantum cascade laser-based infrared spectrometry

BACKGROUND

Despite the potential environmental impact of TWPs (tyre wear particles), there is a lack of reliable analytical methodologies suitable for their routine identification and characterization. The number of papers dealing with this topic is, so far, very reduced and, therefore, there is a need for addressing it, mostly because traditional transmittance-based IR techniques are suboptimal due to scattering caused by black carbon in tyres.

RESULTS

This study aims to evaluate the most appropriate infrared (IR) spectrometric technique for monitoring TWPs. Macro attenuated total reflectance (ATR), reflectance microscopy, and quantum cascade laser-based micro transflectance (QCL-LDIR) were employed to analyse samples from used car and truck tyres in two sample configurations: small tyre fragments (∼1 cm2) and TWPs (< 1 mm). ATR yielded well-defined spectra with good signal-to-noise ratios, allowing for a straightforward interpretation of the major functional moieties. Despite reflectance measurements on tyre fragments provided good results, those on TWPs offered limited information due to noise and scattering. Transflectance offered clear peaks and enhanced resolution in the fingerprint region -compared to the other techniques-, much faster analysis times and the ability to effectively measure particles down to 20-10 µm, thus, emerging as the most effective technique for TWPs analysis. However, spectral interpretation is not immediate. Further, a proof-of-concept chemometric study was done to evaluate whether the analytical techniques contain information to differentiate types of tyres. An unsupervised pattern recognition and a supervised classification technique (principal components analysis and classification trees, respectively) were used, which were able to differentiate among the tyres, notably the truck tyre from the cars tyres.

SIGNIFICANCE

The study presents first time the use of micro transflectance IR to study tyre particles down to 20 µm. Traditional total attenuated reflectance is demonstrated as a suitable way to analyse bigger microplastics. These two options open pathways to monitor this important emerging contaminant in environmental matrices.

Long-Term Exposure to Tire-Derived 6-PPD Quinone Causes Neurotoxicity and Neuroinflammation via Inhibition of HTR2A in C57BL/6 Mice

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6-PPDQ), a novel contaminant derived from tire wear, has raised concerns due to its potential neurotoxicity, yet its long-term effects on mammalian neurological health remain poorly understood. This study investigates the neurotoxic and neuroinflammatory impacts of prolonged 6-PPDQ exposure using male C57BL/6 mice. Behavioral assessments revealed significant cognitive deficits, while biochemical analyses demonstrated increased levels of reactive oxygen species, apoptosis, and blood-brain barrier (BBB) disruption. Elevated pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) and activation of microglial cells were observed, indicating a robust neuroinflammatory response. Network pharmacology and molecular docking identified serotonin receptor HTR2A as a key target through which 6-PPDQ mediates its toxic effects. Activation of HTR2A by the agonist DOI (2,5-dimethoxy-4-iodoamphetamine) mitigated these effects, suggesting a potential therapeutic strategy. These findings provide the first evidence of 6-PPDQ-induced neurotoxicity in mammals, underscoring the need for preventive measures to protect neurological health.

Pavement wear generates microplastics in stormwater runoff

Tire and road wear particles are a major source of microplastics to urban stormwater. They are composed of hetero-aggregates of abraded tire and pavement particles that are difficult to distinguish. While tire wear is a known source of microplastics, little is known on the contribution of pavement wear. This two-year field study with complementary lab testing evaluates the effects of pavement degradation on microplastic generation in stormwater from different pavement types: asphalt, concrete, and recycled rubber pavers. Pavement specimens from each site were collected and underwent degradation testing. We directly demonstrated that pavement wear is a source of microplastics in stormwater separate from tire wear. We showed that the rubber pavement released the most microplastics in lab testing, suggesting that the formulation of such novel recycled-tire pavers must undergo thorough testing before wide application. The asphalt pavement was the most susceptible to rutting and released the most microplastics in the field, including a large proportion of tire wear particles. Both land-use and pavement surface characteristics influenced microplastic generation. These results demonstrate the need to consider microplastic generation during pavement material selection and mitigate the spread of microplastics from pavement wear to nearby environments.

Stress of soil moisture and temperature exacerbates the toxicity of tire wear particles to soil fauna: Tracking the role of additives through host microbiota

Tire wear particles (TWPs) are considered as an emerging threat to soil fauna. However, how TWP toxicity to soil fauna responds to the stress of soil moisture and temperature remains unclear. We assessed the toxicity of environmentally relevant TWPs to the soil model species Enchytraeus crypticus under three soil moisture and two temperature gradients. Typical thermoplastic polypropylene (PP) was selected for comparison. Results showed that compared with PP, TWPs exerted stronger toxicity, including decreasing the worm growth, survival and reproduction rates, disturbing the soil and worm gut microbiota, and leaching more diverse and higher contents of additives. Stress of soil moisture and temperature exacerbated TWP toxicity mainly through affecting the leaching and transformation of additives. Fourteen mediated additives significantly contributed to the shift of the gut microbiota under soil moisture and temperature stress, among which 1,3-diphenylguanidine, N,N'-bis(methylphenyl)-1,4-benzenediamine quinone, N-tert-butyl-2-benzothiazolesulfenamide, and 2-aminobenzothiazole were identified as the main drivers. In addition, this study provided the first clear evidence that increased soil moisture and temperature promoted the transformation of additives in the soil. Our study revealed the non-negligible aggravated toxicity of TWPs to soil fauna under stress of soil moisture and temperature, providing novel insights into the environmental behavior of additives.

Unveiling spatiotemporal distribution, partitioning, and transport mechanisms of tire additives and their transformation products in a highly urbanized estuarine region

Numerous tire additives are high-production volume chemicals that are used extensively worldwide. However, their presence and partitioning behavior remain largely unknown, particularly in marine environments. This study is the first to reveal the spatiotemporal distribution, multimedia partitioning, and transport processing of 22 tire additives and their transformation products (TATPs) in a highly urbanized estuary (n = 166). Nineteen, 18, and 20 TATPs were detectable in water, suspended particulate matter (SPM), and sediments, respectively, with total levels of 59.7-2021 ng/L, 164-6935 ng/g, and 4.66-58.4 ng/g, respectively. The multimedia partitioning mechanisms of TATPs are governed by their molecular weight, hydrophobicity, and biodegradation rate. Mass inventories coupled with model simulations have revealed that substantial quantities of TATPs accumulate within estuarine environments, and these compounds can be continuously transported into the ocean, particularly during the wet season. According to the multi-criteria evaluation approach, four and three TATPs were identified as high-priority pollutants during the dry and wet seasons, respectively. Unexpectedly, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone was only listed as a medium-priority pollutant. This study underscores the importance of marine surveillance and advocates for particular attention to these ubiquitous but underexplored TATPs in future studies.

Quantification and occurrence of 39 tire-related chemicals in urban and rural aerosol from Saxony, Germany

Tire and road wear particles (TRWP) are a major contributor to non-exhaust traffic emissions, but their contribution to and dynamics in urban aerosol is not well known. Urban particulate matter (PM) in the size fraction below 10 µm (PM10) from two German cities was collected over 2 weeks and analysed for 39 tire-related chemicals, including amines, guanidines, ureas, benzothiazoles, p-phenylenediamines, quinolines and several transformation products (TPs). Of these, 37 compounds were determined in PM10 at median concentrations of 212 pg/m3 for 1,3-diphenylguanidine (DPG) and 132 pg/m3 for benzothiazole-2-sulfonic acid (BTSA); 10 of the compounds have not been reported in urban aerosol before. Median concentrations of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6-PPD), 6-PPD quinone (6-PPDQ), and 1,2-dihydro-2,2,4-trimethylquinoline (TMQ) were 1.0, 4.1, and 8.1 pg/m3, respectively. Some parent compounds showed positive correlation with their TPs, e.g. 6-PPD with 4-aminodiphenylamine (4-ADPA), N,N'-diphenyl-p-phenylenediamine (DPPD) with DPPD quinone (DPPDQ), and DPG with phenylguanidine (PG). The concentration pattern of the compounds in PM10 did not agree to the pattern found for cryo-milled tire tread (CMTTmix), likely reflecting transformation processes in tires or the aerosol and the influence from other sources than TRWP. Concentrations in PM2.5 were determined from one of the sites and were by a factor of 4 - 10 lower than in PM10-2.5 for 9 compounds, but a few others, mostly benzothiazoles showed similar or higher concentrations. Many of the tire-related chemicals were also determined in PM10 of one rural site, although at median concentrations up to two orders of magnitude lower. A large number of tire chemicals with a wide concentration range is present in urban PM10 and PM2.5 aerosol and requires scrutiny with respect to its relevance for human exposure.

Emerging investigator series: in-depth chemical profiling of tire and artificial turf crumb rubber: aging, transformation products, and transport pathways

Crumb rubber generated from end-of-life tires (ELTs) poses a threat to environmental and human health based on its widespread use. Of particular concern is the use of ELT crumb rubber as infill for artificial turf fields, as people are unknowingly exposed to complex mixtures of chemicals when playing on these fields. Additionally, there is concern regarding transport of rubber-related chemicals from artificial turf into the environment. However, existing knowledge does not fully elucidate the chemical profile, transformation products, and transport pathways of artificial turf crumb rubber across different ages. To address these knowledge gaps, we utilized a multi-faceted approach that consisted of targeted quantitation, chemical profiling, and suspect screening via ultra-high performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS). We collected and processed 3 tire and 11 artificial turf crumb rubber samples via solvent extraction, leaching, and a bioaccessibility-based extraction. Nineteen rubber-derived chemicals were quantified using parallel reaction monitoring and isotope dilution techniques. In solvent extracts, the most abundant analytes were 1,3-diphenylguanidine (0.18-1200 μg g-1), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD, 0.16-720 μg g-1), 2-mercaptobenzothiazole (0.47-140 μg g-1), and benzothiazole (0.84-150 μg g-1). Chemical profiling assessed changes in sample diversity, abundance, polarity, and molecular mass. Suspect screening identified 81 compounds with different confidence levels (16 at level 1, 53 with level 2, 7 at level 3, and 5 at level 4). The formation rate of transformation products and clustering analysis results identified time-based trends in artificial turf field samples. We found that the first two years of aging may be critical for the potential environmental impact of artificial turf fields. Our analysis provides insight into the chemical complexity of artificial turf crumb rubber samples ranging from 0-14 years in age.

Tire Wear Chemicals in the Urban Atmosphere: Significant Contributions of Tire Wear Particles to PM2.5

Tire wear particles (TWPs) containing tire wear chemicals (TWCs) are of global concern due to their large emissions and potential toxicity. However, TWP contributions to urban fine particles are poorly understood. Here, 72 paired gas-phase and PM2.5 samples were collected in the urban air of the Pearl River Delta, China. The concentrations of 54 compounds were determined, and 28 TWCs were detected with total concentrations of 3130-317,000 pg/m3. Most p-phenylenediamines (PPDs) were unstable in solvent, likely leading to their low detection rates. The TWCs were mainly (73 ± 26%) in the gas phase. 2-OH-benzothiazole contributed 82 ± 21% of the gas-phase TWCs and benzothiazole-2-sulfonic acid contributed 74 ± 18% of the TWCs in PM2.5. Guangzhou and Foshan were "hotspots" for atmospheric TWCs. Most TWC concentrations significantly correlated with the road length nearby. More particulate TWCs were observed than model predictions, probably due to the impacts of nonexchangeable portion and sampling artifacts. Source apportionment combined with characteristic molecular markers indicated that TWPs contributed 13 ± 7% of urban PM2.5. Our study demonstrates that TWPs are important contributors to urban air pollution that could pose risks to humans. There is an urgent need to develop strategies to decrease TWP emissions, along with broader urban air quality improvement strategies.

Combined toxicity of pristine or artificially aged tire wear particles and bisphenols to Tigriopus japonicus

Tire wear particles (TWPs) are considered an important component of microplastic pollution in the marine environment and occur together with a variety of aquatic pollutants, including frequently detected bisphenols. The adverse effects of TWPs or bisphenols on aquatic organisms have been widely reported. However, the combined toxicity of TWPs and bisphenols is still unknown. In this study, the combined toxicity of both pristine (p-) and aged TWPs (a-TWPs) and four bisphenols ((bisphenol A (BPA), bisphenol F (BPF), bisphenol S (BPS), and bisphenol AF (BPAF)) to Tigriopus japonicus was evaluated. TWPs increased the toxicity of BPA and BPF but decreased the toxicity of BPAF. For BPS, there was synergistic toxic effect in the presence of p-TWPs, but slightly antagonistic effect was observed in the presence of a-TWPs. This adsorption of BPAF by TWPs resulted in a reduction of its toxicity to the copepod. A-TWPs could release more Zn than p-TWPs, and the released Zn contributed to the synergistic effect of TWPs and BPA or BPF. The aggregation formed by TWPs in certain sizes (e.g., 90-110 μm) could cause intestinal damage and lipid peroxidation in T. japonicus. The synergistic effect of p-TWPs and BPS might be due to the aggregation size of the binary mixture. The results of the current study will be important to understand the combined toxic effect of TWPs and bisphenols and the potential toxic mechanisms of the binary mixture.

Neurotoxicity from long-term exposure to 6-PPDQ: Recent advances

The recent acceleration of industrialization and urbanization has brought significant attention to N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6-PPDQ), an emerging environmental pollutant from tire wear, due to its long-term effects on the environment and organisms. Recent studies suggest that 6-PPDQ can disrupt neurotransmitter synthesis and release, impact receptor function, and alter signaling pathways, potentially causing oxidative stress, inflammation, and apoptosis. This review investigates the potential neurotoxic effects of prolonged 6-PPDQ exposure, the mechanisms underlying its cytotoxicity, and the associated health risks. We emphasize the need for future research, including precise exposure assessments, identification of individual differences, and development of risk assessments and intervention strategies. This article provides a comprehensive overview of 6-PPDQ's behavior, impact, and neurotoxicity in the environment, highlighting key areas and challenges for future research.

Estrogenic, Genotoxic, and Antibacterial Effects of Chemicals from Cryogenically Milled Tire Tread

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.

Behind conventional (micro)plastics: An ecotoxicological characterization of aqueous suspensions from End-of-Life Tire particles

Million tons of tires become waste every year, and the so-called End-of-Life Tires (ELTs) are ground into powder (ELT-dp; size < 0.8 mm) and granules (ELT-dg; 0.8 < size < 2.5 mm) for recycling. The aim of this study was to evaluate the sub-lethal effects of three different concentrations (0.1, 1, and 10 mg/L) of aqueous suspensions from ELT-dp and ELT-dg on Danio rerio (zebrafish) larvae exposed from 0 to 120 h post-fertilization (hpf). Chronic effects were assessed through biomarkers, real-time PCR, and proteomics. We observed a significant increase in swimming behavior and heart rate only in specimens exposed to ELT-dp suspensions at 1 and 10 mg/L, respectively. Conversely, the activities of detoxifying enzymes ethoxyresorufin-O-deethylase (EROD) and glutathione-S-transferase (GST) showed significant modulation only in specimens exposed to ELT-dg groups. Although no effects were observed through real-time PCR, proteomics highlighted alterations induced by the three ELT-dp concentrations in over 100 proteins involved in metabolic pathways of aromatic and nitrogen compounds. The results obtained suggest that the toxic mechanism of action (MoA) of ELT suspensions is mainly associated with the induction of effects by released chemicals in water, with a higher toxicity of ELT-dp compared to ELT-dg.

Aging increases the particulate- and leachate-induced toxicity of tire wear particles to microalgae

The toxic effects of tire wear particles (TWPs) on organisms have attracted widespread concerns over the past decade. However, the underlying toxicity mechanism of TWPs, especially aged TWPs to marine microalgae remains poorly understood. This study investigated the physiological and metabolic responses of Phaeodactylum tricornutum to different concentrations of TWPs (Experiment 1), virgin and differently aged TWPs (Experiment 2) as well as their leachates and leached particles (Experiment 3). Results demonstrated that TWPs promoted the growth of microalgae at low concentrations (0.6 and 3 mg L-1) and inhibited their growth at high concentrations (15 and 75 mg L-1). Moreover, aged TWPs induced more profound physiological effects on microalgae than virgin TWPs, including inhibiting microalgae growth, decreasing the content of Chla, promoting photosynthetic efficiency, and causing oxidative damage to algal cells. Untargeted metabolomics analysis confirmed that aged TWPs induced more pronounced metabolic changes than virgin TWPs. This study represented the first to demonstrate that both particulate- and leachate-induced toxicity of TWPs was increased after aging processes, which was confirmed by the changes in the surface morphology of TWPs and enhanced release of additives. Through the significant correlations between the additives and the microalgal metabolites, key additives responsible for the shift of microalgal metabolites were identified. These results broaden the understanding of the toxicity mechanism of aged TWPs to microalgae at the physiological and metabolic levels and appeal for considering the effects of long-term aging on TWP toxicity in risk assessment of TWPs.

Leaching of tire particles and simultaneous biodegradation of leachables

The fate of organic compounds released from tire wear particle (TWP) in the aquatic environment is still poorly understood. This is especially true near sources where biotic and abiotic transformation and leaching from TWP are simultaneous and competing processes. To address this knowledge-gap an experiment was performed, allowing for biodegradation (a) during the leaching from a suspension of cryo-milled tire tread (CMTT) and (b) subsequent to leaching. Besides measuring the Dissolved Organic Carbon (DOC) content, 19 tire-related chemicals were quantified, and non-target screening was performed by LC-HRMS. The non-inoculated control experiment exhibited a DOC of up to 4 mg g-1, with up to 700 µg g-1 of 1,3-diphenylguanidine (DPG) as the most prominent compound, followed by three benzothiazoles (2-mercaptobenzothiazole (2-MBT), 2-hydroxybenzothiazole (2-OHBT) and benzothiazole-2-sulfonic acid (BTSA); 50 µg g-1 each) and 4-hydroxydiphenylamine (4-HDPA) (50 µg g-1). Biodegradation reduced the DOC by 88 % and the concentration of most organic compounds by more than 85 %. At the end of the experiment hexamethoxymethylmelamine (HMMM) was the most prominent single compounds (18 µg g-1). Non-target screening showed a more complex picture. Another 25 transformation products (TPs) of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6-PPD) and 44 TPs and derivatives related to DPG were detected in solution, of which 11 and 28 were still present after or formed by biodegradation, respectively. Of these 39 TPs and derivatives, 31 could be detected in road runoff samples. This study provides a more comprehensive picture of the leachables of tire particles that are of environmental relevance. It also outlines that derivatives of tire additives formed during tire production and use may deserve more attention as leachables. The large extent of biodegradation of tire leachables suggests that settling ponds may be a useful treatment option for road runoff.