Environmental occurrence, fate, impact, and potential solution of tire microplastics: Similarities and differences with tire wear particles

Critical evaluation of hyperspectral imaging technology for detection and quantification of microplastics in soil

In this study, we critically evaluated the performance of an emerging technology, hyperspectral imaging (HSI), for detecting microplastics (MPs) in soil. We examined the technology's robustness against varying environmental conditions in five groups of experiments. Our findings show that near-infrared (NIR) hyperspectral imaging (HSI) effectively detects microplastics (MPs) in soil, though detection efficacy is influenced by factors such as MP concentration, color, and soil moisture. We found a generally linear relationship between the levels of MPs in various soils and their spectral responses in the NIR HSI imaging spectrum. However, effectiveness is reduced for certain MPs, like polyethylene, in kaolinite clay. Furthermore, we showed that soil moisture considerably influenced the detection of MPs, leading to nonlinearities in quantification and adding complexities to spectral analysis. The varied responses of MPs of different sizes and colors to NIR HSI present further challenges in detection and quantification. The research suggests pre-grouping of MPs based on size before analysis and proposes further investigation into the interaction between soil moisture and MP detectability to enhance HSI's application in MP monitoring and quantification. To our knowledge, this study is the first to comprehensively evaluate this technology for detecting and quantifying microplastics.

Tire and road wear particles in the aquatic organisms - A review of source, properties, exposure routes, and biological effects

With the continuous development of the modern social economy, rubber has been widely used in our daily life. Tire and road wear particles (TRWPs) are generated by friction between tires and the road surface during the processes of driving, acceleration, and braking. TRWPs can be divided into three main components according to their source: tire tread, brake wear, and road wear. Due to urban runoff, TRWPs flow with rainwater into the aquatic environment and influence the surrounding aquatic organisms. As an emerging contaminant, TRWPs with the characteristics of small particles and strong toxicity have been given more attention recently. Here, we summarized the existing knowledge of the physical and chemical properties of TRWPs, the pathways of TRWPs into the water body, and the exposure routes of TRWPs. Furthermore, we introduced the biological effects of TRWPs involved in size, concentration, and shape, as well as key toxic compounds involved in heavy metals, polycyclic aromatic hydrocarbons (PAHs), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), and benzothiazole on aquatic organisms, and attempted to find the relevant factors influencing the toxic effects of TRWPs. In the context of existing policies that ignore pollution from TRWPs emissions in the aquatic environment, we also proposed measures to mitigate the impact of TRWPs in the future, as well as an outlook for TRWPs research.

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.

A review of tire wear particles: Occurrence, adverse effects, and control strategies

Tire wear particles (TWPs), common mixed particulate emerging contaminants in the environment, have global per capita emissions accounting for 0.23-1.9 kg/year, attracting global attention recently due to their wide detection, small size, mobility, and high toxicity. This review focuses on the occurrence characteristics of TWPs in multiple environmental media, adverse effects on organisms, potential toxicity mechanisms, and environmental risk prevention and control strategies of TWPs. The environmental fate of TWPs throughout the entire process is systematically investigated by the bibliometric analysis function of CiteSpace. This review supplements the gap in the joint toxicity and related toxicity mechanisms of TWPs with other environmental pollutants. Based on the risks review of TWPs and their additives, adverse impacts have been found in organisms from aquatic environments, soil, and humans, such as the growth inhibition effect on Chironomus dilutes. A multi-faceted and rationalized prevention and control treatment of "source-process-end" for the whole process can be achieved by regulating the use of studded tires, improving the tire additive formula, growing plants roadside, encouraging micro-degradation, and other methods, which are first reviewed. By addressing the current knowledge gaps and exploring prospects, this study contributes to developing strategies for reducing risks and assessing the fate of TWPs in multiple environmental media.

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.

Tapping into fungal potential: Biodegradation of plastic and rubber by potent Fungi

Plastic polymers are present in most aspects of routine daily life. Their increasing leakage into the environment poses a threat to environmental, animal, and human health. These polymers are often resistant to microbial degradation and are predicted to remain in the environment for tens to hundreds of years. Fungi have been shown to degrade complex polymers and are considered good candidates for bioremediation (biological pollutant reduction) of plastics. Therefore, we screened 18 selected fungal strains for their ability to degrade polyurethane (PU), polyethylene (PE), and tire rubber. As a proxy for plastic polymer mineralization, we quantified O2 consumption and CO2 production in an enclosed biodegradation system providing plastic as the sole carbon source. In contrast to most studies we demonstrated that the tested fungi attach to, and colonize the different plastic polymers without any pretreatment of the plastics and in the absence of sugars, which were suggested essential for priming the degradation process. Functional polymer groups identified by Fourier-transform infrared spectroscopy (FTIR), and changes in fungal morphology as seen in light and scanning electron microscopy (SEM) were used as indicators of fungal adaptation to growth on PU as a substrate. Thereby, SEM analysis revealed new morphological structures and deformation of the cell wall of several fungal strains when colonizing PU and utilizing this plastic polymer for cell growth. Strains of Fusarium, Penicillium, Botryotinia cinerea EN41, and Trichoderma demonstrated a high potential to degrade PU, rubber, and PE. Growing on PU, over 90 % of the O2 was consumed in <14 days with 300-500 ppm of CO2 generated in parallel. Our study highlights a high bioremediation potential of some fungal strains to efficiently degrade plastic polymers, largely dependent on plastic type.

A ubiquitous tire rubber additive induced serious eye injury in zebrafish (Danio rerio)

Previous studies have indicated that tire wear particles (TWPs) leachate exposure induced serious eye injury in fish through inhibiting the thyroid peroxidase (TPO) enzyme activity. However, the main TPO inhibitors in the leachate were still unknown. In this study, we identified 2-Mercaptobenzothiazole (MBT) as the potential TPO inhibitor in the TWPs leachate through references search, model prediction based on Danish QSAR and ToxCast database, molecular docking, and in vivo assay. We further explored the toxic mechanism of MBT under environmentally relevant concentrations. The decreased eye size of zebrafish larvae was mainly caused by the decreased lens diameter and cell density in the inner nuclear layer (INL) and outer nuclear layer (ONL) of the retina. Transcriptomics analysis demonstrated that the eye phototransduction function was significantly suppressed by inhibiting the photoreceptor cell proliferation process after MBT exposure. The altered opsin gene expression and decreased opsin protein levels were induced by weakening thyroid hormone signaling after MBT treatment. These results were comparable to those obtained from a known TPO inhibitor, methimazole. This study has identified MBT as the primary TPO inhibitor responsible for inducing eye impairment in zebrafish larvae exposed to TWPs leachate. It is crucial for reducing the toxicity of TWPs leachate in fish.

Environmental fate of tire-rubber related pollutants 6PPD and 6PPD-Q: A Review

To enhance tire durability, the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is used in rubber, but it converts into the toxic 6PPD quinone (6PPD-Q) when exposed to oxidants like ozone (O3), causing ecological concerns. This review synthesizes the existing data to assess the transformation, bioavailability, and potential hazards of two tire-derived pollutants 6PPD and 6PPD-Q. The comparative analysis of different thermal methods utilized in repurposing waste materials like tires and plastics into valuable products are analyzed. These methods shed light on the aspects of pyrolysis and catalytic conversion processes, providing valuable perspectives into optimizing the waste valorization and mitigating environmental impacts. Furthermore, we have examined the bioavailability and potential hazards of chemicals used in tire manufacturing, based on the literature included in this review. The bioavailability of these chemicals, particularly the transformation of 6PPD to 6PPD-Q, poses significant ecological risks. 6PPD-Q is highly bioavailable in aquatic environments, indicating its potential for widespread ecological harm. The persistence and mobility of 6PPD-Q in the environment, along with its toxicological effects, highlight the critical need for ongoing monitoring and the development of effective mitigation strategies to reduce its impact on both human health and ecosystem. Future research should focus on understanding the chronic effects of low-level exposure to these compounds on both terrestrial and aquatic ecosystems, as well as the potential for bioaccumulation in the food chain. Additionally, this review outlines the knowledge gaps, recommending further research into the toxicity of tire-derived pollutants in organisms and the health implications for humans and ecosystems.

Recycled tire rubber materials in the spotlight. Determination of hazardous and lethal substances

One way of recycling end-of-life tires is by shredding them to obtain crumb rubber, a microplastic material (<0.5 mm), used as infill in artificial turf sports fields or as playground flooring. There is emerging concern about the health and environmental consequences that this type of surfaces can cause. This research aims to develop an analytical methodology able to determine 11 compounds of environmental and health concern, including antiozonants such as N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD) or N, N´-diphenyl-1,4-phenylenediamine (DPPD), and vulcanization and crosslinking agents, such as N-cyclohexylbenzothiazole-2-sulfenamide (CBS), 1,3-di-o-tolylguanidine (DTG) or hexamethoxymethylmelamine (HMMM) from tire rubber. Ultrasound assisted extraction followed by liquid chromatography coupled to tandem mass spectrometry (UAE-LC-MS/MS) is validated demonstrating suitability. The methodology is applied to monitor the target compounds in forty real crumb rubber samples of different origin including, football pitches, outdoor and indoor playgrounds, urban pavements, commercial samples, and tires. Several alternative infill materials, such as sand, cork granulates, thermoplastic elastomers and coconut fibres, are also collected and analysed. All the target analytes are identified and quantified in the crumb rubber samples. The antiozonant 6PPD is present at the highest concentrations up to 0.2 % in new synthetic fields. The tire rubber-derived chemical 6PPD-quinone (2-((4-methylpentan-2-yl)amino)-5-(phenylamino)cyclohexa-2,5-diene-1,4-dione), recently linked to acute mortality in salmons, is found in all types of crumb rubber samples attaining concentrations up to 40 μg g-1 in football pitches. The crosslinking agent HMMM is detected in most of the playing surfaces, at concentrations up to 36 μg g-1. The tested infill alternatives are free of most of the target compounds. To the best of our knowledge, this study is the largest study considering the target compounds in tire rubber particles and the first to focus on these compounds in playgrounds including the analysis of HMMM, 6PPD-quinone and DTG in crumb rubber used as an infill material.

Effect of tire wear particle accumulation on nitrogen removal and greenhouse gases abatement in bioretention systems: Soil characteristics, microbial community, and functional genes

Tire wear particles (TWPs), as predominant microplastics (MPs) in road runoff, can be captured and retained by bioretention systems (BRS). This study aimed to investigate the effect of TWPs accumulation on nitrogen processes, focusing on soil characteristics, microbial community, and functional genes. Two groups of lab-scale bioretention columns containing TWPs (0 and 100 mg g-1) were established. The removal efficiencies of NH4+-N and TN in BRS significantly decreased by 7.60%-24.79% and 1.98%-11.09%, respectively, during the 101 days of TWPs exposure. Interestingly, the emission fluxes of N2O and CO2 were significantly decreased, while the emission flux of CH4 was substantially increased. Furthermore, prolonged TWPs exposure significantly influenced the contents of soil organic matter (increased by 27.07%) and NH4+-N (decreased by 42.15%) in the planting layer. TWPs exposure also significantly increased dehydrogenase activity and substrate-induced respiration rate, thereby promoting microbial metabolism. Microbial sequencing results revealed that TWPs decreased the relative abundance of nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Dechloromonas and Thauera), reducing the nitrification rate by 42.24%. PICRUSt2 analysis further indicated that TWPs changed the relative abundance of functional genes related to nitrogen and enzyme-coding genes.

Understanding microplastic pollution of marine ecosystem: a review

Microplastics are emerging as prominent pollutants across the globe. Oceans are becoming major sinks for these pollutants, and their presence is widespread in coastal regions, oceanic surface waters, water column, and sediments. Studies have revealed that microplastics cause serious threats to the marine ecosystem as well as human beings. In the past few years, many research efforts have focused on studying different aspects relating to microplastic pollution of the oceans. This review summarizes sources, migration routes, and ill effects of marine microplastic pollution along with various conventional as well as advanced methods for microplastics analysis and control. However, various knowledge gaps in detection and analysis require attention in order to understand the sources and transport of microplastics, which is critical to deploying mitigation strategies at appropriate locations. Advanced removal methods and an integrated approach are necessary, including government policies and stringent regulations to control the release of plastics.

Influencing factors of microplastic generation and microplastic contamination in urban freshwater

This research analyzes data on the microplastic (MP) contamination in the environmental systems (atmosphere, lithosphere, hydrosphere) and the levels of MPs in freshwater of cities with different levels of national income. This study investigates the influencing factors of MP generation, i.e., mismanaged plastic waste, untreated wastewater, number of registered motor vehicles, and stormwater runoff. The statistical correlations between the MP contamination in urban freshwater and the four influencing factors of MP generation are determined by linear regression. The results indicate that MPs are most abundant in aquatic systems (i.e., hydrosphere) and pose a serious threat to the human food chain. The regression analysis shows a strong correlation between mismanaged plastic waste and microfragment smaller than 300 μm in particle size in urban freshwater with high goodness-of-fit (R2 = 0.8091). A strong relationship with high goodness-of-fit also exists between untreated wastewater and microfragment of 1000-5000 μm in particle size (R2 = 0.9522). The key to mitigate the MP contamination in urban freshwater is to replace improper plastic waste management and wastewater treatment with proper management practices.

Application of organoid technology in the human health risk assessment of microplastics: A review of progresses and challenges

Microplastic (MP) pollution has become a global environmental issue, and increasing concern has been raised about its impact on human health. Current studies on the toxic effects and mechanisms of MPs have mostly been conducted in animal models or in vitro cell cultures, which have limitations regarding inter-species differences or stimulation of cellular functions. Organoid technology derived from human pluripotent or adult stem cells has broader prospects for predicting the potential health risks of MPs to humans. Herein, we reviewed the current application advancements and opportunities for different organoids, including brain, retinal, intestinal, liver, and lung organoids, to assess the human health risks of MPs. Organoid techniques accurately simulate the complex processes of MPs and reflect phenotypes related to diseases caused by MPs such as liver fibrosis, neurodegeneration, impaired intestinal barrier and cardiac hypertrophy. Future perspectives were also proposed for technological innovation in human risk assessment of MPs using organoids, including extending the lifespan of organoids to assess the chronic toxicity of MPs, and reconstructing multi-organ interactions to explore their potential in studying the microbiome-gut-brainaxis effect of MPs.

Distribution patterns and environmental risk assessments of microplastics in the lake waters and sediments from eight typical wetland parks in Changsha city, China

The quality of water in urban parks is closely related to people's daily lives, but the pollution caused by microplastics in park water and sediments has not been comprehensively studied. Therefore, eight typical parks in the urban area of Changsha, China, were selected, and Raman spectroscopy was used to explore the spatial distributions and compositions of the microplastics in the water and sediments, analyze their influencing factors, and evaluate their environmental risks. The results showed that the abundances of surface water microplastics in all parks ranged from 150 to 525 n L-1, and the abundances of sediment microplastics ranged from 120 to 585 n kg-1. The microplastics in the surface water included polyethylene terephthalate (PET), chlorinated polyethylene (CPE), and fluororubber (FLU), while those in the sediments included polyvinyl chloride (PVC), wp-acrylate copolymer (ACR), and CPE. Regression analyses revealed significant positive correlations between human activities and the abundances of microplastics in the parks. Among them, the correlations of population, industrial discharge and domestic wastewater discharge with the abundance of microplastics in park water were the strongest. However, the correlations of car flow and tourists with the abundance of microplastics in park water were the weakest. Based on the potential ecological risk indices (PERI) classification assessment method, the levels of microplastics in the waters and sediments of the eight parks were all within the II-level risk zone (53-8,549), among which the risk indices for Meixi Lake and Yudai Lake were within the IV risk zone (1,365-8,549), which may have been caused by the high population density near the park. This study provides new insights into the characteristics of microplastics in urban park water and sediment.

Effects of tire wear particles on the water retention of soils with different textures in the full moisture range

Tire wear particles (TWPs) are significant contributors to microplastic pollution in the environment, yet there is limited scientific information concerning their impact on soil hydraulic properties. This study aimed to investigate the impact of TWPs at different concentrations (1, 4, 8, and 16% of the air-dried mass of packed soil samples, w/w) on the water retention curves (WRC) of southern California soils with five different textures (clay, clay loam, silt loam, sandy loam, and loamy sand). The concentrations of 8% and 16% were selected to represent extreme pollution scenarios that might occur near highway corridors. High-resolution water retention data, spanning from saturation to oven dryness, were generated using HYPROP™ and WP4C dew point meter instruments. We also developed WRC scaling equations based on the quantity of TWPs. The bulk density of the samples decreased as the TWP concentration in soils increased. The inclusion of very high concentrations of TWPs (8% and 16% w/w) led to a significant reduction in soil moisture content in the intermediate and dry ranges across various soil textures. However, at the same moisture range, adding 1% TWPs had a minimal impact on soil moisture reduction, while the influence of the 4% TWPs concentration treatment was noticeable only in loamy sand and partially in clay loam soils. Additionally, the overall plant available water decreased with increasing TWP concentrations, except for the clay soil. The texture-specific scaling models exhibited promising performance, with RMSE values ranging from 0.0061 to 0.0120 cm3 cm-3. When bulk density was included as an additional input predictor to construct a single scaling model for all textures, the RMSE increased. Nevertheless, it still indicated a good fit ranging from 0.007 to 0.024 cm3 cm-3, highlighting the suitability of simple scaling for identifying WRC in TWPs-polluted soils, particularly for practical purposes. The findings of this study can contribute to a better understanding and quantification of the impact of TWPs on soil hydrology.

Microfluidic Detection and Analysis of Microplastics Using Surface Nanodroplets

Detection of microplastics from water is crucial for various reasons, such as food safety monitoring, monitoring of the fate and transport of microplastics, and development of preventive measures for their occurrence. Currently, microplastics are detected by isolating them using filtration, separation by centrifugation, or membrane filtration, subsequently followed by analysis using well-established analytical methods, such as Raman spectroscopy. However, due to their variability in shape, color, size, and density, isolation using the conventional methods mentioned above is cumbersome and time-consuming. In this work, we show a surface-nanodroplet-decorated microfluidic device for isolation and analysis of small microplastics (diameter of 10 μm) from water. Surface nanodroplets are able to capture nearby microplastics as water flows through the microfluidic device. Using a model microplastic solution, we show that microplastics of various sizes and types can be captured and visualized by using optical and fluorescence microscopy. More importantly, as the surface nanodroplets are pinned on the microfluidic channel, the captured microplastics can also be analyzed using a Raman spectroscope, which enables both physical (i.e., size and shape) and chemical (i.e., type) characterization of microplastics at a single-particle level. The technique shown here can be used as a simple, fast, and economical detection method for small microplastics.

Eco-Transformation of construction: Harnessing machine learning and SHAP for crumb rubber concrete sustainability

Researchers have focused their efforts on investigating the integration of crumb rubber as a substitute for conventional aggregates and cement in concrete. Nevertheless, the manufacture of crumb rubber concrete (CRC) has been linked to the release of noxious pollutants, hence presenting potential environmental hazards. Rather than developing novel CRC formulations, the primary objective of this work is to construct an extensive database by leveraging prior research efforts. The study places particular emphasis on two crucial concrete properties: compressive strength (fc') and tensile strength (fts). The database includes a total of 456 data points for fc' and 358 data points for fts, focusing on nine essential characteristics that have a substantial impact on both attributes. The research employs several machine learning algorithms, including both individual and ensemble methods, to undertake a comprehensive analysis of the created databases for fc' and fts. In order to ascertain the correctness of the models, a comparative analysis of machine learning techniques, namely decision tree (DT) and random forest (RF), is conducted using statistical evaluation. Cross-validation approaches are used in order to address the possible issues of overfitting. Furthermore, the Shapley additive explanations (SHAP) approach is used to investigate the influence of input parameters and their interrelationships. The findings demonstrate that the RF methodology has superior performance compared to other ensemble techniques, as shown by its lower error rates and higher coefficient of determination (R2) of 0.87 and 0.85 for fc' and fts respectively. When comparing ensemble approaches, it can be seen that AdaBoost outperforms bagging by 6 % for both outcome models and individual decision tree learners by 17% and 21% for fc' and fts respectively in terms of performance. The average accuracy of AdaBoost algorithm for both the models is 84%. Significantly, the age and the inclusion of crumb rubber in CRC are identified as the primary criteria that have a substantial influence on the mechanical properties of this particular kind of concrete.

Hazardous elements in plastic and rubber granules as infill material from sports facilities? Field Portable-XRF spectroscopy as 'white analytical technique' reveals hazardous elements in fall sports facilities in Rzeszów (Podkarpackie, Poland)

Plastic and rubber granules are commonly used as infill material in all-weather sports facilities, providing an ideal activity surface for millions of Europeans on a daily basis. However, concerns have been raised about the presence of hazardous elements in these granules, which can pose risks both to the environment and human health. Our study focusses on the elemental composition of rubber granules used in fall sports facilities in Rzeszów, (Podkarpackie, Poland) using field portable X-ray fluorescence (FP-XRF) as a non-destructive and 'white analytical technique'. The results show the content of Zn, Fe, Cr, Ba, Br, Ti, Cu, Cd, As, Au, Bi, Pb, Ni, Sb, and Sn in the rubber granule samples. This study highlights the need for stringent quality control measures and regulations to ensure the safety of all-weather sports facilities and protect the well-being of sportsman. When modern FP-XRF spectrometry is employed as a "white analytical technique," for the first time it becomes possible to identify the presence of hazardous elements, addressing the pressing concerns highlighted by the ECHA and enabling proactive measures to mitigate potential risks. This approach ensures the protection of the health and sustainability of sports facilities, contributing to the ongoing hot topics in the field.

Photoaged Tire Wear Particles Leading to the Oxidative Damage on Earthworms (Eisenia fetida) by Disrupting the Antioxidant Defense System: The Definitive Role of Environmental Free Radicals

Tire wear particles (TWPs) have caused increasing concerns due to their detrimental effects on the soil ecosystem. However, the role of weathering in altering the toxicity of TWP to soil organisms is poorly understood. In this study, the toxicity of original and photoaged TWP was compared using earthworms (Eisenia fetida) as soil model organisms. The obtained results indicated that photoaging of TWP resulted in an increase of environmentally persistent free radicals (EPFRs) from 3.69 × 1017 to 5.20 × 1017 spin/g. Meanwhile, photoaged TWP induced the changes of toxic endpoint in E. fetide, i.e., the increase of the weight loss and death ratio from 0.0425 to 0.0756 g/worm and 23.3 to 50% compared to original TWP under a 10% concentration, respectively. Analyses of transcriptomics, antioxidant enzyme activity, and histopathology demonstrated that the enhanced toxicity was mainly due to oxidative damage, which was induced by disruption in the antioxidant defense system. Free-radical quenching and correlation analysis further suggested that the excessive production of ex vivo reactive oxygen species, induced by EPFRs, led to the exhaustion of the antioxidant defense system. Overall, this work provides new insights into the potential hazard of the weathered TWP in a soil environment and has significant implications for the recycling and proper disposal of spent tire particles.

Tire particles and its leachates: Impact on antibiotic resistance genes in coastal sediments

Tire particles (TPs), a significant group of microplastics, can be discharged into the coastal environments in various ways. However, our understanding of how TPs impact the antibiotic resistance and pathogenic risks of microorganisms in coastal sediments remains limited. In this study, we used metagenomics to investigate how TPs and their leachates could affect the prevalence of antibiotic resistance genes (ARGs), virulence factor genes (VFGs), and their potential risks to the living creatures such as soil invertebrates and microorganisms in the coastal sediments. We discovered that TP addition significantly increased the abundance and diversity of ARGs and VFGs in coastal sediments, with raw TPs displayed higher impacts than TP leachates and TPs after leaching on ARGs and VFGs. With increasing TP exposure concentrations, the co-occurrence frequency of ARGs and mobile genetic elements (MGEs) in the same contig also increased, suggesting that TPs could enhance the dispersal risk of ARGs. Our metagenome-based binning analysis further revealed that exposure to TPs increased the abundance of potentially pathogenic antibiotic-resistant bacteria (PARB). In addition, chemical additives of TP leachates (e.g., Zn and N-cyclohexylformamide) significantly affected the changes of ARGs in the pore water. In summary, our study provides novel insights into the adverse effects of TP pollutions on aggravating the dissemination and pathogenic risks of ARGs and PARB in the coastal environment.

Revealing the long-term impact of photodegradation and fragmentation on HDPE in the marine environment: Origins of microplastics and dissolved organics

The extensive usage of high-density polyethylene (HDPE) materials in marine environments raises concerns about their potential contribution to plastic pollution. Various factors contribute to the degradation of HDPE in marine environments, including UV radiation, seawater hydrolysis, biodegradation, and mechanical stress. Despite their supposed long lifespans, there is still a lack of understanding about the long-term degradation mechanisms that cause weathering of seawater-exposed HDPE products. In this research, the impact of UV radiation on the degradation of HDPE pile sleeves was studied in natural as well as laboratory settings to isolate the UV effect. After nine years of exposure to the marine environment in natural settings, the HDPE pile sleeves exhibited an increase in oxygen-containing surface functional groups and more morphological changes compared to accelerated UVB irradiation in the laboratory. This indicated that combined non-UV mechanisms may play a major role in HDPE degradation than UV irradiation alone. However, UVB irradiation was found to release dissolved organic carbon and total dissolved nitrogen from HDPE pile sleeves, reaching levels of up to 15 mg/L and 2 mg/L, respectively. Our findings underscore the significance of taking into account both UV and non-UV degradation mechanisms when evaluating the role of HDPE in contributing to marine plastic pollution.

The characteristics and influencing factors of farmland soil microplastic in Hetao Irrigation District, China

Microplastic pollution, a major global concern, has garnered increasing attention in agricultural ecosystem research. China's Hetao Irrigation District, vital for grain production in the Yellow River Basin, lacks sufficient research on microplastic pollution of agricultural soils. This study, based on a detailed background investigation and testing of 47 samples, is the first to elucidate the characteristics and potential influencing factors of microplastics in the Hetao Irrigation District. The abundance of microplastics in the farmland soil ranged from 1810 to 86331 items/kg, with 90% measuring below 180 µm and mainly in film and fragment forms. Predominant polymers were polyethylene (PE, 43.0%) and polyamide (PA, 27.8%). Key pollution influencers were identified as agricultural inputs, with low-density polyethylene (LDPE) being the most extensively used plastic type. The carbonyl index and hydroxyl indices of the detected LDPE microplastics ranged from 0.041 to 0.96 and 0.092 to 1.20, respectively. The study highlights the significance of mulching management and agronomic practices in shaping microplastic characteristics. Potential pollution sources include agricultural inputs, irrigation equipment, domestic waste, and tire wear. Proposed effective strategies include responsible plastic use, robust waste management, and irrigation system upgrades, establishing a foundation for future ecological risk assessments and effective management approaches in the Hetao Irrigation District. ENVIRONMENTAL IMPLICATION: The harmful substances studied in this paper are microplastics, which are widely distributed in the environment and have potential ecological risks. This study is the first to investigate the characteristics of microplastics in farmland soil within the Hetao Irrigation Area, a region that is of critical importance to agricultural production in the Yellow River Basin of China. The study provides comprehensive insights into the factors influencing the characteristics of microplastics and speculates on their sources. These findings offer a novel perspective on the assessment of microplastic contamination in the area and provide valuable recommendations for prevention and control measures.

Tire additives: Evaluation of joint toxicity, design of new derivatives and mechanism analysis of free radical oxidation

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is one of the most widely used antioxidant agents in tire additives. Its ozonation by-product 6PPD-quinone has recently been recognized as inducing acute mortality in aquatic organisms such as coho salmon. In this study, we aimed to develop an in-silico method to design environmentally friendly 6PPD derivatives and evaluate the joint toxicity of 6PPD with other commonly used tire additives on coho salmon through full factorial design-molecular docking and molecular dynamic simulation. The toxicity mentioned in this study is represented by the binding energy of chemical(s) binding to the coho salmon growth hormone. The recommended formula for tire additives with relatively low toxicity was then proposed. To further reduce the toxicity of 6PPD, 129 6PPD derivatives were designed based on the N-H bond dissociation reaction, and three of these derivatives showed improved antioxidant activity and 6PPD-106 was finally screened as the optimum alternative with lower toxicity to coho salmon. Besides, the mechanism of free radical oxidation (i.e., antioxidation and ozonation metabolic pathway) for 6PPD-106 was also analyzed and found that after ozonation, the toxicity of 6PPD-106's by-products is much lower than that of 6PPD's by-products. This study provided a molecular modelling-based examination of 6PPD, which comprehensively advanced the understanding of 6PPD's environmental behaviors and provided more environmentally friendly 6PPD alternatives with desired functional property and lower ecological risks.

Adsorption of Pb(II) by UV-aged microplastics and cotransport in homogeneous and heterogeneous porous media

To investigate the adsorption effects of aged microplastics (MPs) on Pb(II) and their co-transport properties in homogeneous (quartz sand) and heterogeneous (quartz sand with apple branches biochar) porous media, we explored the co-transport of UV-irradiated aged MPs and coexisting Pb(II) along with their interaction mechanisms. The UV aging process increased the binding sites and electronegativity of the aged MPs' surface, enhancing its adsorption capacity for Pb(II). Aged MPs significantly improved Pb(II) transport through homogeneous media, while Pb(II) hindered the transport of aged MPs by reducing electrostatic repulsion between these particles and the quartz sand. When biochar, with its loose and porous structure, was used as a porous medium, it effectively inhibited the transport capacity of both contaminants. In addition, since the aged MPs cannot penetrate the column, a portion of Pb(II) adsorbed by the aged MPs will be co-deposited with the aged MPs, hindering Pb(II) transport to a greater extent. The transport experiments were simulated and interpreted using two-point kinetic modeling and the DLVO theory. The study results elucidate disparities in the capacity of MPs and aged MPs to transport Pb(II), underscoring the potential of biochar application as an effective strategy to impede the dispersion of composite environmental pollutants.

Tire particles and their leachates reduce the filtration rate of the mussel Mytilus edulis

Microplastics (MPs) are found in aquatic environments all over the world. Among MPs, tire wear particles (TWPs) are a major contributor to microplastic pollution, and their effects on marine ecosystems are of emerging concern. The blue mussel (Mytilus edulis) is a keystone species in coastal ecosystems with a high risk of exposure to microplastic pollution as the microplastics often overlap in size with the plankton consumed by mussels. In the present study, we investigated the effect of tire particles and their leachates on the filtration rates of M. edulis after short (72 h) and long-term (3 weeks) exposure. Acute exposure to leachates alone causes a significant decrease in the filtration rates of M. edulis with a low observed effect concentration (LOEC) of 1.25 g L-1 and a median effect concentration (EC50) = 3 g L-1. At a concentration of 1.25 g L-1, the filtration rate was reduced compared to the control on average by 38% when mussels were exposed to either TWP or leachates for 72 h. Similarly, mussels exposed to tire particles or their leachates for 3 weeks showed a 46% reduction in filtration rates, compared to the control group. A non-significant difference in filtration rate decrease was found between leachates alone or TWP, which indicates that leachates are the main responsible for the observed toxicity. Our findings indicate that elevated levels of TWP pollution can cause an adverse impact on M. edulis. This could disrupt the natural grazing pressure exerted by M. edulis on phytoplankton, potentially leading to an increased likelihood of algal blooms and hypoxia occurrence in coastal ecosystems.

Contamination of Thames Estuary sediments by retroreflective glass microbeads, road marking paint fragments and anthropogenic microfibres

Surface and subsurface sediment samples (n = 16) from the highly urbanised inner Thames Estuary (UK) have been physically and chemically characterised and analysed for anthropogenic microdebris. Sediments were gravelly sands throughout and were heavily contaminated by lead (Pb, up to 12,500 mg kg-1) and zinc (Zn, up to 9500 mg kg-1). Microfibres of mm-dimensions and retroreflective glass microbeads (median diameter = 188 μm) used in road markings were the most abundant types of microdebris present, and concentrations (as numbers, N) on a dry weight basis were spatially heterogeneous (ranging from about 4000 to 60,000 N kg-1 and 100 to 28,000 N kg-1, respectively). Nevertheless, concentrations of the two types of particle were significantly correlated and both displayed an inverse, non-linear relationship with sediment grain size. Road marking paint fragments of different colours were detected in most cases (n = 13) but quantification was difficult because of analytical constraints related to size, shape, colour, fragmentation and encrustation. Concentrations of up to about 500 mg kg-1 Pb were determined in isolated paint fragments but road paint particles are unlikely to make a significant contribution to Pb pollution in Thames Estuary sediments. Overall, our observations suggest that stormwater runoff is a significant source of multiple types of anthropogenic microdebris in urban estuaries, with additional, direct atmospheric deposition contributing to microfibre accumulation. More generally, it is recommended that studies of microplastics consider additional debris and sediment characteristics for a better understanding of their sources and transport.

Are volatile methylsiloxanes in downcycled tire microplastics? Levels and human exposure estimation in synthetic turf football fields

Downcycled rubber, derived from end-of-life tires (ELTs), is frequently applied as crumb rubber (CR) as infill of synthetic turf in sports facilities. This practice has been questioned in recent years as numerous studies have reported the presence of potentially hazardous chemicals in this material. CR particles fall into the category of microplastics (MPs), making them possible vectors for emerging micropollutants. A preliminary study where volatile methylsiloxanes (VMSs) were found in CR originated the hypothesis that VMSs are present in this material worldwide. Consequently, the present work evaluates for the first time the levels and trends of seven VMSs in CR from synthetic turf football fields, while attempting to identify the main sources and impacts of these chemicals. A total of 135 CR samples and 12 other of alternative materials were analyzed, employing an ultrasound-assisted dispersive solid-phase extraction followed by gas chromatography-mass spectrometry (GC-MS), and the presence of VMSs was confirmed in all samples, in total concentrations ranging from 1.60 to 5089 ng.g-1. The levels were higher in commercial CR (before field application), a reflection of the use of VMS-containing additives in tire production and/or the degradation of silicone polymers employed in vehicles. The VMSs generally decreased over time on the turf, as expected given their volatile nature and the wearing of the material. Finally, the human exposure doses to VMSs in CR (by dermal absorption and ingestion) for people in contact with synthetic turf in football fields were negligible (maximum total exposure of 20.5 ng.kgBW-1.year-1) in comparison with the European Chemicals Agency (ECHA) reference doses: 1.35 × 109 ng.kgBW-1.year-1 for D4 and 1.83 × 109 ng.kgBW-1.year-1 for D5. Nevertheless, more knowledge on exposure through inhalation and the combined effects of all substances is necessary to provide further corroboration. This work proved the presence of VMSs in CR from ELTs, another family of chemical of concern to take into account when studying MPs as vectors of other contaminants.

Gene expression analysis of Chironomus riparius in response to acute exposure to tire rubber microparticles and leachates

Tire rubber microparticles (TRPs) entering aquatic ecosystems through stormwater runoffs is a significant challenge. TRPs are formed by the abrasion of tires with the road surface and include chemical additives that are an additional cause for concern. Currently, information on the molecular effects of TRPs, or especially its additives, in freshwater organisms is scarce. To address this problem, an array covering different cellular processes has been designed for the freshwater midge Chironomus riparius. Fourth-instar larvae were exposed to two concentrations of TRPs (1 mg L-1, 10 mg L-1) and tire rubber leachates (TRLs) (0,0125 %, 5 %) to evaluate the transcriptional activity by Real-Time PCR. To assess acute toxicity, larvae were exposed for 24 h and genes related to the endocrine system, stress response, DNA repair mechanisms, immune system, oxidative stress, and detoxification mechanisms were evaluated. The activity of the enzymes: glutathione S-transferase (GST) and catalase was also examined. The main pathway affected was the stress response showing overexpression of HSPs (HSC70.3, HSC70.4, HSC70.5, HSP60). Moreover, there was a reduction of the GSTd3 and catalase disrupting the antioxidant system. The upregulation of InR indicates a potential disturbance in the insulin pathway and ABCB6 activation only in TRPs exposure suggests its potential implication in their transport. However, most of these alterations are caused by TRLs, showing higher toxicity than TRPs. The results obtained in this work provide the first approach at the molecular and cellular levels to elucidate the impact of TRLs in freshwater organisms. To perform a realistic evaluation of the TR effects, additional research is required to assess the TR's long-term effects at the molecular level.

Mechanistic understanding on the uptake of micro-nano plastics by plants and its phytoremediation

Contaminated soil is one of today's most difficult environmental issues, posing serious hazards to human health and the environment. Contaminants, particularly micro-nano plastics, have become more prevalent around the world, eventually ending up in the soil. Numerous studies have been conducted to investigate the interactions of micro-nano plastics in plants and agroecosystems. However, viable remediation of micro-nano plastics in soil remains limited. In this review, a powerful in situ soil remediation technology known as phytoremediation is emphasized for addressing micro-nano-plastic contamination in soil and plants. It is based on the synergistic effects of plants and the microorganisms that live in their rhizosphere. As a result, the purpose of this review is to investigate the mechanism of micro-nano plastic (MNP) uptake by plants as well as the limitations of existing MNP removal methods. Different phytoremediation options for removing micro-nano plastics from soil are also described. Phytoremediation improvements (endophytic-bacteria, hyperaccumulator species, omics investigations, and CRISPR-Cas9) have been proposed to enhance MNP degradation in agroecosystems. Finally, the limitations and future prospects of phytoremediation strategies have been highlighted in order to provide a better understanding for effective MNP decontamination from soil.

Ascertaining appropriate measuring methods to determine tire wear particle pollution on driving school grounds in China

Tire wear particles (TWPs) are garnering increasing attention due to their potential adverse environmental impacts. However, precisely ascertaining TWPs content is challenging due to the complexity and variability of the tire components used in the environment, indicating that more reliable methods to accurately determine TWPs are necessary. In this study, driving school grounds were used as a case study to ascertain an appropriate and reliable method to determine TWPs levels based on a comprehensive comparison between different analytical results using styrene butadiene rubber (SBR), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), and zinc (Zn) as analytical markers. Thermogravimetric analysis-Gas chromatography mass spectrometry (TGA-GC-MS) method reliability using SBR was verified and applied to measure TWPs levels on driving school grounds. By reliably converting SBR content to TWPs content, the average TWPs content on driving school grounds was measured at 190.13 ± 101.89 mg/g. The highest TWPs content was 281.83 ± 171.44 mg/g under the reverse stall parking driving programs, while the slope start and stop driving programs was lower at 208.36 ± 124.11 mg/g. Our findings highlight the importance of accurately determining TWPs content within specific environments while comprehensively exploring associated patterns of change to better understand the environmental risks of TWPs.

Atmospheric deposition is an important pathway for inputting microplastics: Insight into the spatiotemporal distribution and deposition flux in a mega city

Microplastics (MPs) refer to plastic particles with a size less than 5 mm, which attracted widespread attention as an emerging pollutant. The monitoring of atmospheric microplastics (AMPs) in a megacity was carried out to study the characteristics and spatiotemporal distribution of AMPs, explore the sources and estimate the deposition flux. The results showed that the annual average abundance of AMPs in Wuhan was 82.85 ± 57.66 n·m-2·day-1. The spatiotemporal distribution characteristics of AMPs show that spring was the highest season, followed by autumn, winter, and summer; the city center was higher than the suburbs. Fiber was the main type of AMPs in Wuhan, followed by fragment, film and pellet. The proportion of AMPs were mainly small (<0.5 mm) and medium (0.5-1.0 mm). Transparent and white were the main colors of AMPs, followed by red, brown. A total of 10 types polymers were detected, polyethylene terephthalate (PET) was dominant. There are positive correlations between AMPs and SO2, NO2 in the atmosphere, indicating that they might be influenced by intense human activity. The polycyclic aromatic hydrocarbons (PAHs) and AMPs in spring showed an extremely significant positive correlation (p < 0.05). AMPs might mainly originate from the wear and tear shedding of textiles, the aging of agricultural films and plastic waste based on their polymer types and main uses. The potential geographical sources of AMPs were mainly the surrounding cities. The annual deposition flux of AMPs was about 308 tons if there were no remove processes, which highlighted the importance of atmospheric transport and deposition of MPs. The analysis of the abundance, morphological characteristics and sources of AMPs can provide data support and reference for mega-cities with high global population activities, or cities in global mid-latitude regions.

Sulfate radical-based advanced oxidation process effects on tire wear particles aging and ecotoxicity

Tire wear particles (TWPs) are widely distributed in natural water and pose as major pollutants in aquatic environments. In this study, heat-activated persulfate (HPT) and ultraviolet-activated persulfate treatments (UPT) were employed to investigate the influence of sulfate radical (SO4-•)-based advanced oxidation process (SAOPs) on TWP physicochemical properties and to clarify their ecotoxic effects in laboratory-level studies. Results showed that the specific surface areas of TWPs increased after UPT but decreased after HPT. In terms of chemical properties, the increase of oxygen-containing functional groups on the surfaces of TWPs was more evident in UPT than that in HPT. The atrazine (ATZ) adsorption capacity of TWPs after HPT and UPT was increased compared with the untreated TWPs. Atrazine adsorbed by TWPs was easily resolved and released in artificial intestinal fluid (1.89-2.08 mg/g) and artificial gastric fluid (1.60-2.04 mg/g) conditions. Acute toxicity experiments of Photobacterium phosphoreum and SEM-EDS detection results suggested that various heavy metals (e.g., Zn2+, Cu2+) in the TWPs would be released into the water system in SAOPs. ATZ released from TWPs that adsorbed ATZ herbicide, rather than TWPs themselves, had a negative effect on aquatic plant growth (e.g., C. vulgaris). The leaching solution of oxidized TWPs (after HPT and UPT) showed a more significant inhibition effect on the zebrafish survival compared with that of untreated TWPs, which was possibly caused by the generation of oxidation byproducts such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone.

Effect of bioturbation of the mitten crab on distribution of tire wear particles and their combined effect on sediment ecosystem

Tire wear particles (TWPs) are a major source of environmental microplastic pollution which gradually settle and accumulate in sediments after entering the aquatic environment, which can affect the behaviors of benthic organisms. Bioturbation of benthic species could affect the fate, impacts and potential risks of TWPs by altering the properties and structure of sediments. Therefore, in this study, the effect of TWPs on the burrowing activity of Chinese mitten crab (Eriocheir sinensis) was investigated. In addition, the effects of crab bioturbation on the distribution of TWPs and their additives were studied. The combined effects of TWPs and crab bioturbation on the microbial communities in the sediments were also explored. The results of this study showed that both TWPs and the leachate significantly inhibited the burrowing activity of crabs. TWPs in the surface layer of sediments were re-distributed by crab bioturbation and enriched mainly in the sediments near the burrow walls. Meanwhile, the heavy metals (i.e., Zn, Ca, Mg, Ba and Al) used as additives during the tire production in the burrow walls significantly increased as the accumulation of TWPs near burrow walls. In this study, TWP exposure decreased the bacterial diversity and abundance, as well as the functional genes related to carbon and nitrogen cycling process, but crab bioturbation increased them in the sediments of burrow walls by constructing a unique habitat. However, after TWPs entering into burrows, they were significantly decreased in the sediments near the burrow walls like the effects of TWPs, suggesting the negative effects of TWPs could play a dominant role in this combined system. Overall, this study is important for evaluating the distribution and effects of TWP pollution in the sediment ecosystem under biological factors such as bioturbation.

Review of emerging contaminants in green stormwater infrastructure: Antibiotic resistance genes, microplastics, tire wear particles, PFAS, and temperature

Green stormwater infrastructure is a growing management approach to capturing, infiltrating, and treating runoff at the source. However, there are several emerging contaminants for which green stormwater infrastructure has not been explicitly designed to mitigate and for which removal mechanisms are not yet well defined. This is an issue, as there is a growing understanding of the impact of emerging contaminants on human and environmental health. This paper presents a review of five emerging contaminants - antibiotic resistance genes, microplastics, tire wear particles, PFAS, and temperature - and seeks to improve our understanding of how green stormwater infrastructure is impacted by and can be designed to mitigate these emerging contaminants. To do so, we present a review of the source and transport of these contaminants to green stormwater infrastructure, specific treatment mechanisms within green infrastructure, and design considerations of green stormwater infrastructure that could lead to their removal. In addition, common removal mechanisms across these contaminants and limitations of green infrastructure for contaminant mitigation are discussed. Finally, we present future research directions that can help to advance the use of green infrastructure as a first line of defense for downstream water bodies against emerging contaminants of concern.

Integrating metabolomics and high-throughput sequencing to investigate the effects of tire wear particles on mung bean plants and soil microbial communities

Tire wear particles (TWPs) generated by vehicle tires are ubiquitous in soil ecosystems, while their impact on soil biota remains poorly understood. In this study, we investigated the effects of TWPs (0.1%, 0.7%, and 1.5% of dry soil weight) on the growth and metabolism of mung bean (Vigna radiata) plants over 32 days in soil pots. We found that TWPs-treated soils had high levels of heavy metals and polycyclic aromatic hydrocarbons (PAHs). However, there was no significant impact of TWPs exposure on plant growth, suggesting that mung bean plants have a degree of tolerance to TWPs. Despite the lack of impact on plant growth, exposure to TWPs had significant effects on soil enzyme activities, with a decrease of over 50% in urease and dehydrogenase activity. Furthermore, TWPs exposure resulted in marked changes in the plant metabolite profile, including altered levels of sugars, carboxylic acids, and amino acids, indicating altered nitrogen and amino acid-related metabolic pathways. TWPs exposure also disrupted the rhizospheric and bulk soil microbiota, with a decrease in the abundance of bacterial (Blastococcus) and fungal (Chaetomium) genera involved in nitrogen cycles and suppressing plant diseases. In summary, our study provides new insights into the effects of TWPs on plants and soil, highlighting the potential ecological consequences of TWPs pollution in terrestrial ecosystems and underscoring the need for further research in this area.

Rapid estimation of tire-wear particle concentration in road dust using PM10 and traffic data in a ternary plot

Air pollution, a pressing global issue, is significantly exacerbated by airborne particulate matter (PM), affecting air quality and human health. Urban vehicular activities majorly contribute to PM rise through both exhaust and non-exhaust emissions. Despite strides in managing exhaust emissions, non-exhaust particles, such as tire wear particles (TWP) remain under-addressed. This research proposes a method for estimating TWP concentrations using PM10 data and traffic activity, which could offer a valuable tool for controlling roadside fine particles and TWP. This paper introduces a ternary plotting technique and step-by-step procedure to estimate TWP levels in road dust using only PM10 and traffic data. Traditional analysis of TWP via pyrolysis-gas chromatography-mass spectrometry is complex and time-consuming. Hence, our proposed approach presents an alternate method that leverages readily accessible PM and traffic data, providing critical information for road management interpretation. The triangular plot analysis demonstrated a linear correlation: [log(Traffic) + 2]-[250,000/TWP-13]-0.18PM10. While the resulting correlation may vary based on specific road conditions, the method can be tailored to different regions, offering insights into efficient estimation of TWP concentrations and promoting improved roadside pollution management.

High salinity promotes the photoaging of polystyrene microplastics with humic acid in seawater

The photoaging of microplastics (MPs) accumulated in the sea can be influenced by humic acid (HA). However, the role of salinity cannot be ignored, as it may potentially disrupt the interaction between MPs and HA, thereby altering the photoaging of MPs. Herein, this study investigated how salinity influences the effect of humic acid (HA, derived from lignite) on the photoaging of polystyrene microplastics (PS MPs) in artificial and natural seawater. The results revealed that HA promoted the photoaging of PS MPs under both low (5 PSU) and high salinity (35 PSU) in light conditions (L), reflected in the formation of fragments, the production of oxygen-containing functional groups (OH, CO, and OCO), and the increase in hydrophilicity of PS MPs. Furthermore, high salinity promoted the photoaging of PS MPs with HA more significantly, as evidenced by the similar indicators and the order of oxygen/carbon atom ratio (O/C): L-HA-High (0.15) > L-HA-Low (0.10) > Unaged (0.02). Interestingly, due to the reduction of electrostatic repulsion, the adsorption of HA on photoaged PS MPs in natural and artificial high salinity seawater was 1.77 mg/g and 0.39 mg/g, respectively, which was significantly higher than those PS MPs photoaged in the low salinity seawater. Furthermore, the electron spin resonance (ESR) results confirmed that more hydroxyl radicals (OH) were generated after adsorbing HA under high salinity conditions, thus promoting the fragmentation and oxidation of PS MPs. Overall, our findings highlight the crucial role of salinity in influencing the photoaging of MPs with HA and help to assess the marine risk of MPs accurately.

Toxicity of 6PPD-quinone to four freshwater invertebrate species

The antioxidant N-(1,3-Dimethylbutyl)-N'-phenyl-p- phenylenediamine (6PPD) is used to protect the rubber in tires from oxidation, which extends the life of the tire. When oxidized, 6PPD is transformed into 6PPD-quinone (6PPDQ). 6PPDQ, along with other tire ingredients, can enter aquatic ecosystems through the transport of tire wear particles in runoff during a precipitation event. The mass mortality of coho salmon following precipitation events in urban areas lead to the discovery that 6PPDQ is the likely cause due to coho salmon's relatively high sensitivity to 6PPDQ. The assessment of 6PPDQ toxicity to other aquatic species has expanded, but it has focused on fish. This study investigated the toxicity of 6PPDQ to four freshwater invertebrate species, larval burrowing mayfly (Hexagenia spp.), juvenile cladoceran (Daphnia magna), file ramshorn snail embryo (Planorbella pilsbryi), and adult washboard mussel (Megalonaias nervosa). For all four species, the highest concentration of 6PPDQ tested did not result in significant mortality. This translated into the determination of the highest concentration that did not cause significant mortality (NOEC) for Hexagenia spp., D. magna, P. pilsbryi, and M. nervosa of 232.0, 42.0, 11.7, and 17.9 μg/L, respectively. The data from this study indicate that freshwater invertebrates are not as sensitive to 6PPDQ as some salmonid species (e.g., coho salmon Oncorhynchus kisutch). This study also analyzed 6PPDQ in road runoff from around the city of Guelph in Ontario, Canada. 6PPQ was detected in all samples but the concentration was two orders of magnitude lower than the NOECs for the four tested species of freshwater invertebrate.

Toxic effects of tire wear particles and the leachate on the Chinese mitten crab (Eriocheir sinensis)

Tire wear particles (TWPs) were considered as an important component of microplastic pollution in the aquatic environment. To understand the ecotoxicity of TWPs to crustacean, this study investigated toxic effects of TWPs and the leachate on the mitten crab Eriocheir sinensis and the accumulation of TWPs in the crabs. Although TWPs could be accumulated in various tissues (i.e., liver, gills and gut) of the crabs, exposure to TWPs or the leachate had no lethal effect on the crabs in this study. Lower concentrations of TWPs and the leachate exposure could stimulate the antioxidant defense system of the crabs, while higher concentrations could disrupt the stress defense system. In addition, the energy supply and metabolism of the crabs could also be affected by TWPs or the leachate. The transcriptomic profiles showed that the toxic mechanisms of TWPs and the leachate were not exactly the same. Similar to the results of biochemical analysis, several Gene Ontology (GO) terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to oxidative stress and energy metabolism were significantly regulated by both TWPs and the leachate. However, TWPs could affect the expression of genes enriched in immune-related pathways, while the leachate regulated the enrichment of some other signaling pathways including FoxO signaling pathway, insulin signaling pathway, RIG-I-like receptor signaling pathway, NOD-like receptor signaling pathway, PPAR signaling pathway and neuroactive ligand-receptor interaction. Overall, our study could provide basic biological information for assessing the ecological risk of the TWP pollution in the aquatic environment and was useful to understand the potential toxic mechanisms of the TWPs and the leachate to crustaceans.

Acute toxicity of tire wear particles and leachate to Daphnia magna

Tire wear particles (TWP) are a new pollutant widely present in the environment, and have been identified as microplastics (MPs), which are receiving increasing attention due to their toxic effects on aquatic organisms. In this study, D. magna was used as test organism, and the leachate from TWP was prepared by hot water extraction for 30 (30-E) and 120 min (120-E). The acute toxic effects of particles and leachate on D. magna were studied under different exposure concentrations. The results showed that zinc and pyrene were the highest detected contaminants in the leachate. The 48 h-LC50 values for particles and leachate were determined to be 56.99, 461.30 (30-E), and 153.00 mg/L (120-E), respectively. Following a 48 h exposure period, the immobilization of D. magna exposed to the particles and their leachate were increased with the concentration increase. The physical damage of the gut was found to be a possible mechanism for particle-induced biotoxicity. The compounds leached from TWP were responsible for the acute toxicity of leachate. Particles usually demonstrated a greater degree of toxicity in comparison to their leachate, especially at environmentally relevant concentrations. Exposure to particles and leachate resulted in the inhibition of swimming speed, swimming acceleration, filtration rate, and ingestion rate in D. magna. Furthermore, thoracic limb activity was observed to be inhibited. The heart rate of D. magna was significantly increased by the presence of particles at a concentration of 200 mg/L and leachate at concentrations of 400 and 800 mg/L (120-E). The observed alterations in behavior and physiological endpoints may be related to oxidative stress and neurotoxicity in the organism. Reduced superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) activities indicated that D. magna may suffer from excessive oxidative stress, whereas the increase of acetylcholinesterase (AChE) activity may serve as a biomarker of susceptibility to evaluate the environmental risks of TWP and corresponding leachates as potential aquatic pollutants.. Therefore, a more comprehensive risk assessment of TWP in the environment is necessary.

River export of macro- and microplastics to seas by sources worldwide

Seas are polluted with macro- (>5 mm) and microplastics (<5 mm). However, few studies account for both types when modeling water quality, thus limiting our understanding of the origin (e.g., basins) and sources of plastics. In this work, we model riverine macro- and microplastic exports to seas to identify their main sources in over ten thousand basins. We estimate that rivers export approximately 0.5 million tons of plastics per year worldwide. Microplastics are dominant in almost 40% of the basins in Europe, North America and Oceania, because of sewage effluents. Approximately 80% of the global population live in river basins where macroplastics are dominant because of mismanaged solid waste. These basins include many African and Asian rivers. In 10% of the basins, macro- and microplastics in seas (as mass) are equally important because of high sewage effluents and mismanaged solid waste production. Our results could be useful to prioritize reduction policies for plastics.

Mechanistic insight into the adverse outcome of tire wear and road particle leachate exposure in zebrafish (Danio rerio) larvae

Tire wear particles (TWP) have become the major microplastic pollution in China. Road runoff containing TWP leachate can decrease the eye size and even induced mortality in the aquatic organisms. However, the toxic mechanism of TWP and road particles (RP) leachate on aquatic organisms is still unclear. In this study, the zebrafish embryos were exposed to TWP or RP leachate for 5 days at both environmental relevant and high concentrations. The adverse outcome pathways (AOPs) were screened from individual to molecular levels. The morphological and behavioral analysis demonstrated that the leachate exposure mainly impaired the eye development of zebrafish larvae and inhibited the larval swim behavior and phototactic response, which are the adverse outcomes. The phototransduction modulated by zebrafish retina was significantly down-regulated through transcriptomics and metabolomics analysis. The eye histopathological analysis showed that the decreased thickness of the retinal outer nuclear layer (ONL) and retinal pigmented epithelium (RPE) after leachate exposure were caused by the decreased photoreceptor cells. Moreover, the expression of NR2E3 and TPO genes showed concentration-dependent down-regulation after leachate exposure. The inhibition of photoreceptor cell proliferation was identified as the main reason for photoreceptor cell decrease in zebrafish larval eye. This study, for the first time, uncovered the underlying toxic mechanism of TWP and RP on zebrafish larval eyes.

Statistical analysis, machine learning modeling, and text analytics of aggregation attachment efficiency: Mono and binary particle systems

The aggregation attachment efficiency (α) is the fraction of particle-particle collisions resulting in aggregation. Despite significant research, α predictions have not accounted for the full complexity of systems due to constraints imposed by particle types, dispersed matter, water chemistry, quantification methods, and modeling. Experimental α values are often case-specific, and simplified systems are used to rule out complexity. To address these challenges, statistical analysis was performed on α databases to identify gaps in current knowledge, and machine learning (ML) was used to predict α under various particle types and conditions. Moreover, text analytics was employed to support knowledge from statistics and ML, as well as gain insight into the ideas communicated by current literature. Most studies investigated α in mono-particle systems, but binary or higher systems require more investigation. Furthermore, our work highlights that numerous variables, interactions, and mechanisms influence α behavior, making its investigation complex and difficult for both experiments and modeling. Consequently, future research should incorporate more particle types, shapes, coatings, and surface heterogeneities, and aim to address overlooked variables and conditions. Therefore, building a comprehensive α database can enable the development of more accurate empirical models for prediction.

Identifying potential toxic organic substances in leachates from tire wear particles and their mechanisms of toxicity to Scenedesmus obliquus

Tire wear particles (TWPs) are increasingly being found in the aquatic environment. However, there is limited information available on the environmental consequences of TWP constituents that may be release into water. In this study, TWP leachate samples were obtained by immersing TWPs in ultrapure water. Using high-resolution mass spectrometry and toxicity identification, we identified potentially toxic organic substances in the TWP leachates. Additionally, we investigated their toxicity and underlying mechanisms. Through our established workflow, we structurally identified 13 substances using reference standards. The median effective concentration (EC₅₀) of TWP leachates on Scenedesmus obliquus growth was comparable to that of simulated TWP leachates prepared with consistent concentrations of the 13 identified substances, indicating their dominance in the toxicity of TWP leachates. Among these substances, cyclic amines (EC₅₀: 1.04-3.65 mg/L) were found to be toxic to S. obliquus. We observed significant differential metabolites in TWP leachate-exposed S. obliquus, primarily associated with linoleic acid metabolism and purine metabolism. Oxidative stress was identified as a crucial factor in algal growth inhibition. Our findings shed light on the risk posed by TWP leachable substances to aquatic organisms.

From prey to predators: Evidence of microplastic trophic transfer in tuna and large pelagic species in the southwestern Tropical Atlantic

Plastic pollution is present in most marine environments; however, contamination in pelagic predators, including species of economic interest, is still poorly understood. This study aims to access the macro- and microplastic contamination in tuna and large pelagic species and verify whether a trophic transfer occurs from prey to tunas captured by two fleets in the Southwestern Tropical Atlantic (SWTA). We combined different methodological approaches to analyse the intake of macro- and microplastics. In addition to examining the plastics in the fish' stomachs, we investigated the contamination in the prey retrieved from the guts of predators. A low frequency of occurrence (3%) of macroplastic was detected in the tuna and large pelagic species; conversely, we observed a high frequency of microplastic in the tuna's stomachs (100%) and prey analysed (70%). We evinced the trophic transfer of microplastics by analysing the ingestion rate of particles in prey retrieved from the tuna stomachs. In the 34 analysed prey, we detected 355 microplastic particles. The most contaminated prey were cephalopods and fishes of the Bramidae family. The most frequent microplastic shapes in both prey and tuna stomachs were foams, pellets and fibres (<1 mm). A variety of polymers were identified; the most frequent were styrene-butadiene rubber (SBR), polyamide (PA), polyethylene terephthalate (PET) and polyethylene (PE). Our findings enhance scientific knowledge of how the ecological behaviour of marine species can affect microplastic intake.

Identification and quantification of tire wear particles by employing different cross-validation techniques: FTIR-ATR Micro-FTIR, Pyr-GC/MS, and SEM

Tire wear particles (TWPs) are one of the environment's most important emission sources of microplastics. In this work, chemical identification of these particles was carried out in highway stormwater runoff through cross-validation techniques for the first time. Optimization of a pre-treatment method (i.e., extraction and purification) was provided to extract TWPs, avoiding their degradation and denaturation, to prevent getting low recognizable identification and consequently underestimates in the quantification. Specific markers were used for TWPs identification comparing real stormwater samples and reference materials via FTIR-ATR, Micro-FTIR, and Pyrolysis-gas-chromatography-mass spectrometry (Pyr-GC/MS). Quantification of TWPs was carried out via Micro-FTIR (microscopic counting); the abundance ranged from 220,371 ± 651 TWPs/L to 358,915 ± 831 TWPs/L, while the higher mass was 39,6 ± 9 mg TWPs/L and the lowest 31,0 ± 8 mg TWPs/L. Most of the TWPs analyzed were less than 100 μm in size. The sizes were also confirmed using a scanning electron microscope (SEM), including the presence of potential nano TWPs in the samples. Elemental analysis via SEM supported that a complex mixture of heterogeneous composition characterizes these particles by agglomerating organic and inorganic particles that could derive from brake and road wear, road pavement, road dust, asphalts, and construction road work. Due to the analytical lack of knowledge about TWPs chemical identification and quantification in scientific literature, this study significantly contributes to providing a novel pre-treatment and analytical methodology for these emerging contaminants in highway stormwater runoff. The results of this study highlight the uttermost necessity to employ cross-validation techniques, i.e., FTIR-ATR, Micro-FTIR, Pyr-GC/MS, and SEM for the TWPs identification and quantification in the real environmental samples.

Refinement of a microfurnace pyrolysis-GC-MS method for quantification of tire and road wear particles (TRWP) in sediment and solid 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.

Chemical toxicity screening of tire particle leachates from vehicles and their effects on organisms across three trophic levels

Tire particles (TPs) generated on roads are a main contributor to microplastic environmental pollution. In this study, TP leachates from three vehicle types (bicycle, car, and electric scooter) were prepared. TP leachate toxicity impacts on three organisms (Vigna radiata, Daphnia magna, and Danio rerio) were analyzed, in addition to their chemical compositions. Zinc and benzothiazole were the most commonly detected compounds in all three leachate types. Growth inhibition of V. radiata, mortality of D. magna, and abnormality in D. rerio were observed as toxicological impacts. Overall, the lethal effects of TP leachates showed a significant, positive relationship with zinc and benzothiazole concentration. The results confirmed that TPs are complex contaminants, which release chemicals into the environment that affect both soil and aquatic organisms. These findings highlight the need for stricter control measures and environmental regulations to mitigate the ecotoxic effects of TPs and related contaminants across ecosystems and trophic levels.

Silent Contamination: The State of the Art, Knowledge Gaps, and a Preliminary Risk Assessment of Tire Particles in Urban Parks

Tire particles (TPs) are one of the main emission sources of micro- and nano-plastics into the environment. Although most TPs are deposited in the soil or in the sediments of freshwater and although they have been demonstrated to accumulate in organisms, most research has focused on the toxicity of leachate, neglecting the potential effects of particles and their ecotoxicological impact on the environment. In addition, studies have focused on the impact on aquatic systems and there are many gaps in the biological and ecotoxicological information on the possible harmful effects of the particles on edaphic fauna, despite the soil ecosystem becoming a large plastic sink. The aim of the present study is to review the environmental contamination of TPs, paying particular attention to the composition and degradation of tires (I), transport and deposition in different environments, especially in soil (II), the toxicological effects on edaphic fauna (III), potential markers and detection in environmental samples for monitoring (IV), preliminary risk characterization, using Forlanini Urban Park, Milan (Italy), as an example of an urban park (V), and risk mitigation measures as possible future proposals for sustainability (VI).

Overall distribution of tire-wear particles, nano‑carbon black, and heavy metals in size-fractionated road dust collected from steel industrial complexes

Tire-wear particles (TWP) from vehicles serves as a non-exhaust emission source. The mass content of metallic species in road dust may increase owing to the traffic of heavy vehicles and industrial activity; consequently, metallic particles are also present in road dust. Herein, road dust collected from steel industrial complexes with high traffic of high-weight vehicles and the composition distribution of five size-fractioned particle sizes were analyzed. Road dust samples were collected from three areas near steelmaking complexes. The mass distribution of TWP, carbon black (CB), bituminous coal, and heavy metals (Fe, Zn, Mn, Pb, Ni, As, Cu, Cd, and Hg) in different size fractions of road dust was quantified by combining four different analytical techniques. In the magnetic separation for <45 μm fraction, 34.4 wt% and 50.9 wt% was removed for steelmaking and steel-related industrial complexes, respectively. As the particle size decreased, the mass content of Fe, Mn, and TWP increased. The enrichment factors of Mn, Zn, and Ni were higher than two, indicating that they were related to industrial activities in steel complexes. The maximum concentrations of TWP and CB originating from the vehicle varied depending on the region and particle size range: TWP 2.066 wt% at 45-75 μm (industrial complex) and CB 5.559 wt% at 75-160 μm (steel complex). Coal was only found in the steel complex. Finally, to reduce the exposure of the finest particles to road dust, three methods were suggested. Magnetic fraction must be removed from road dust using magnetic separation; the fly dust of coal during transportation must be suppressed, and covers must be used in coal yards; the mass contents of TWP and CB in road dust should be removed by vacuum cleaning instead of water flushing.