Tire wear particle emissions: Measurement data where are you?

Co-exposure of TMPs and antibiotics in zebrafish: The influence of additives on the risk of hepatotoxicity

Co-exposure of tire microplastics (TMPs) and antibiotics has been confirmed to pose toxic risks to aquatic organisms. However, the contributions of TMP additives to these risks and the underlying mechanisms remain underreported. In this study, factor analysis and molecular docking and molecular dynamics simulations were employed to investigate the differential additive-related hepatotoxicity risks associated with TMP-antibiotic exposure in zebrafish. The differential hepatotoxicity risks of five types of TMPs and six antibiotics were simulated in the presence of additives. Zebrafish exposed to different TMPs showed significant differences in hepatotoxicity risks, with styrene-butadiene rubber (SBR) exhibiting the most pronounced toxic effects. The additive contribution analysis revealed that in the presence of SBR additives, TMPs-antibiotics posed higher toxicity risks to the cytochrome P 17A2 (CYP17A2) isoenzymes CYP2K19, CYP1A, CYP3A65, and CYP2K22 in zebrafish, showing synergistic effects primarily driven by plasticizers. Furthermore, the hepatotoxicity risks of TMPs-antibiotics in zebrafish in the presence of additives were significantly mitigated by the selection of alternative plasticizers. The micromechanisms by which additives affected the TMP-antibiotic hepatotoxicity risks in zebrafish were elucidated through mechanistic analysis. This study aimed to characterize the additive-influenced hepatotoxicity risks of TMPs-antibiotics, providing micro-level insights and theoretical support for ecological risk assessments in aquatic environments.

Soil properties explain the variability in tire wear particle effects in soil based on a laboratory test with 59 soils

Tire wear particles (TWPs) are among the most prevalent microplastics in the environment, with potential detrimental effects on ecosystem health and functionality. While little is known how the effects of TWPs on soil physicochemical and microbial properties vary across different soil types, and if so, which factors contribute to this variability. To address this knowledge gap, we conducted a laboratory experiment involving soils from 59 grassland plots across two sampling regions in Germany, each experienced varying land-use intensities. These soils were treated with (at a concentration of 10 mg g-1) and without TWPs. At harvest, we measured soil water-stable aggregates (WSA), pH, respiration, and decomposition rate. Our results revealed that TWPs negatively, neutrally, or positively impacted these parameters depending on soil types. Random forest analysis indicated that the variability in TWP effects was significantly explained by grazing frequency for WSA (14.5 %), by clay content for pH (9 %), by bulk density for respiration (7.9 %), and by silt content for decomposition rate (12 %). Partial dependence analysis and piecewise regression further suggested that low-intensity grazing (∼0.7-1.2) reduced TWP effects on WSA; clay content (420-550 g kg-1) increased TWP effects on pH; bulk density (0.75-0.88) decreased TWP effects, and silt content (460-620 g kg-1) enhanced TWP effects on decomposition rate, with the identified thresholds of 1.45, 353 g kg-1, 0.84, and 327 353 g kg-1, respectively. These results highlighted the context-dependent nature of TWP pollution, with significant variability observed across different sampling points. Additionally, our findings suggest that TWP pollution is particularly of concern in soils with high clay, silt, high bulk density, and areas with intensive land-use intensity. Our study contributes to a better understanding of the mechanisms by which TWPs impact soil, and how these effects are regulated by environmental factors.

A Tiered Quantification and Source Mapping Framework for Tire Wear Particle Analysis in Environmental Matrices

Tire wear particles (TWPs) are a major source of microplastic emissions, accurate quantification of TWPs remains challenging due to tread composition heterogeneity and inconsistent methods. To improve the quantification accuracy under scarce tire composition data, a novel method was established based on real treads to establish more accurate quantitative curves using pyrolysis gas chromatography-mass spectrometry. For the first time, the rubber content of three types of treads was quantified using a comprehensive group of pyrolysis monomers and derivatives. The approach was validated by tread cryogrinds, which showed the accuracy was improved to 94-113% compared with previous methods. A tiered approach was established to calculate worn tread mass while distinguishing and eliminating interfering signals in matrices. Further, an analytical framework for TWPs in various environmental samples to identify their sources and quantify fluxes was proposed with the availability of auxiliary data. This framework can serve as basis for more efficient management of TWPs contamination.

Effects of tire particles on earthworm (Eisenia andrei) fitness and bioaccumulation of tire-related chemicals

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

Impact of tire particle leachates on microplankton communities in the Canary Islands

Tire wear particles (TWP) are a major source of microplastics in the environment. Despite their prevalence, the effects of tire particle leachates on marine microplankton communities remains poorly understood. In this study, we assessed the acute impacts of tire particle leachates on the structure of coastal microplankton assemblages from the Canary Islands. Five laboratory experiments were conducted, exposing microplankton to a range of leachate dilutions over 72 h, with TWP leachates prepared from an initial concentration of 1 g L⁻¹ .Our results revealed that the abundances of diatoms, most dinoflagellates, and ciliates were significantly reduced following exposure to leachates, with median effective concentrations (EC50) ranging from 30 to 660 mg L-1 depending on the plankton community. Interestingly, Ostreopsis cf. ovata, a harmful algal bloom (HAB)-forming species, exhibited relatively high tolerance to tire particle leachates compared to other microplankton. Compared to other marine biota, ciliates appear to be most vulnerable plankton group to tire particle leachates (EC50 = 30 and 146 mg L-1). The higher tolerance of O. cf. ovata to pollution compared to other phytoplankton species (resource competitors), in combination with other factors, may contribute to the rise of HABs in polluted coastal areas. Although field data on TWP are limited, the observed negative effects on microplankton occurred at environmentally relevant concentrations. Our results indicate that TWP pollution can significantly impact marine planktonic communities, highlighting the urgent need to reduce TWP emissions and develop less toxic tire rubber additives.

Carryover effects of tire wear particle leachate threaten the reproduction of a model zooplankton across multiple generations

The toxic additives that leach from tire wear particles (TWPs) cause mass die-offs in fish and impact zooplankton as secondary consumers in the aquatic food web. In addition to the direct impacts of TWP leachate on a single generation, there may be potential delayed carryover effects across multiple generations from parental exposure, which may amplify the adverse effects of the leachate on individual reproduction and, consequently, on the entire population. In this study, the single, multiple, and transgenerational effects of TWP leachate at various concentrations on the reproduction and lifespan of the rotifer Brachionus calyciflorus were investigated. The results indicated that the lifespan and reproductive output of rotifers exposed to TWP leachate (0-1500 mg/L) decreased as the concentration increased above 250 mg/L. There was a clear multigenerational effect of TWP leachate on rotifer reproduction. The inhibition rates were consistently greater at 500 mg/L than at 250 mg/L leachate. Although the reproduction of rotifers exposed to 250 mg/L TWP leachate increased in the first two generations (P and F1), it was inhibited in subsequent generations. The inhibitory effect of 500 mg/L TWP leachate persisted across all generations, leading to population extinction by the F4 generation. A significant transgenerational effect of TWP leachate was found on reproduction. The adverse impact of exposure to 250 mg/L leachate for fewer than three generations could be reversed when offspring were transferred to clean media. However, this recovery was not observed after continuous exposure for more than four generations. Exposure to high-dose TWP leachate also caused irreversible damage to reproduction. Therefore, TWP leachate can result in cascading toxicity on zooplankton populations through carryover and cumulative effects on reproduction.

Determination of Tire Wear Particle-Type Polymers by Combination of Quantitative Nuclear Magnetic Resonance Spectroscopy and Soxhlet Extraction

Tire wear particles (TWPs) are among the most relevant sources of microplastic pollution of the environment. Nevertheless, common analytical methods like IR and Raman spectroscopy are highly impaired by additives and filler materials, leaving only thermogravimetric methods for chemical analysis of TWPs in most cases. We herein present quantitative NMR spectroscopy (qNMR) as an alternative tool for the quantification of the polymeric material used for the production of tires, including natural rubber (NR), styrene-butadiene-copolymer (SBR), polyethylene-co-propylene (EPR) and polybutadiene (BR). Limits of quantification (LOQ) between 3 µg and 43 µg per sample and recovery rates of 72-92% were achieved for all tested polymer types. The first results of combining these measurements with Soxhlet extraction as a sample preparation tool are presented alongside the qNMR experiments.

Airborne Tire Wear Particles: A Critical Reanalysis of the Literature Reveals Emission Factors Lower than Expected

Tires are a ubiquitous part of on-road transport systems serving as the critical connecting component at the interface of the motive power and road surface. While tires are essential to automobile function, the wear of tires as a source of particulate air pollution is still poorly understood. The variety of reported emissions found in the secondary literature motivated us to summarize all known mass-based tire wear emission factors for light-duty vehicles in primary research. When excluding road wear and resuspension, mean emissions of 1.1 mg/km/vehicle (median 0.2 mg/km/vehicle) were found for tire wear PM10 and mean emissions of 2.7 mg/km/vehicle (median 1.1 mg/km/vehicle) when including studies with resuspended tire wear. Notably, these factors are substantially lower than broadly cited and accepted factors in the secondary literature with mean emissions of 6.5 mg/km/vehicle (median 6.1 mg/km/vehicle). As revealed by our analysis, secondary literature reports emission factors systematically higher than those of the primary sources on which they are based. This divergence is due to misunderstandings and misquotations that have been prevalent since the year 1995. Currently accepted mass-based emission factors for directly emitted airborne tire wear particles need revision, including those from the United States Environmental Protection Agency and the European Environment Agency.

Tire wear particle leachate exhibits trophic and multi-generational amplification: Potential threat to population viability

The toxic additives leached from tire wear particles (TWPs) in road runoff can directly poison aquatic organism through high-dose exposure in sporadic hotspots. Given the ubiquity of road runoff carrying TWPs, it is necessary to assess whether there are lagging effects from low-dose exposure, as the toxicity of TWPs leachate can be transferred and amplified across multi-generations and different trophic levels: microalgae, zooplankton and larval fish. In this study, Chlorella pyrenoidesa exposed to different concentrations of TWPs leachate were fed to rotifer Brachionus calyciflorus, which were subsequently used as the initial feeding for fry of Cyprinus carpio. Below 1000 mg/L, the growth of microalgae was not influenced by TWPs leachate. Rotifer fed with contaminated microalgae for a single generation exhibited hormesis in their reproduction. After multigenerational feeding, the microalgae from 500 mg/L treatment were sufficient to suppress reproduction of rotifer since the third generation. For the secondary consumer carp fry, survival, growth, and feeding rate were significantly inhibited at first generation when consuming the rotifers fed with microalgae exposed to 250 mg/L TWPs leachate. So, evidence was presented for the generational and trophic amplification of toxicity in TWPs leachate within the food chain. A seemingly innocuous low dose can exhibit evident ecotoxicity after trophic and generational transfer, which could decline population viability of the aquatic organisms in the future.

Tracking the biogeochemical behavior of tire wear particles in the environment - A review

The environmental fate and risks associated with tire wear particles (TWPs) are closely linked to their biogeochemical behaviors. However, reviews that focus on TWPs from this perspective remain scarce, hindering our understanding of their environmental fate and cascading effects on ecosystems. In this review, we summarize the existing knowledge on TWPs by addressing five key areas: (i) the generation and size-dependent distribution of TWPs; (ii) the release and transformation of TWP-leachates; (iii) methodologies for the quantification of TWPs; (iv) the toxicity of TWPs; and (v) interactions of TWPs with other environmental processes. It has been established that the size distribution of TWPs significantly influences their transport and occurrence in different matrices, leading to the release and transformation of specific TWP-chemicals that can be toxic to organisms. By highlighting the challenges and knowledge gaps in this field, we propose critical issues that need to be addressed to enhance the risk assessment of TWPs. This review aims to provide a comprehensive framework for evaluating the environmental behavior of TWPs.

All black: a microplastic extraction combined with colour-based analysis allows identification and characterisation of tire wear particles (TWP) in soils

While tire wear particles (TWP) have been estimated to represent more than 90% of the total microplastic (MP) emitted in European countries and may have environmental health effects, only few data about TWP concentrations and characteristics are available today. The lack of data stems from the fact that no standardized, cost efficient or accessible extraction and identification method is available yet. We present a method allowing the extraction of TWP from soil, performing analysis with a conventional optical microscope and a machine learning approach to identify TWP in soil based on their colour. The lowest size of TWP which could be measured reliably with an acceptable recovery using our experimental set-up was 35 µm. Further improvements would be possible given more advanced technical infrastructure (higher optical magnification and image quality). Our method showed a mean recovery of 85% in the 35-2000 µm particle size range and no blank contamination. We tested for possible interference from charcoal (as another black soil component with similar properties) in the soils and found a reduction of the interference from charcoal by 92% during extraction. We applied our method to a highway adjacent soil at 1 m, 2 m, 5 m, and 10 m and detected TWP in all samples with a tendency to higher concentrations at 1 m and 2 m from the road compared to 10 m from the road. The observed TWP concentrations were in the same order of magnitude as what was previously reported in literature in highway adjacent soils. These results demonstrate the potential of the method to provide quantitative data on the occurrence and characteristics of TWP in the environment. The method can be easily implemented in many labs, and help to address our knowledge gap regarding TWP concentrations in soils.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43591-024-00102-9.

Quantification of tire wear particles in road dust based on synthetic/natural rubber ratio using pyrolysis-gas chromatography-mass spectrometry across diverse tire types

Increase in road traffic leads to increased concentrations of tire-wear particles (TWPs), a prominent source of microplastics from vehicles, in road dust. These particles can re-enter the atmosphere or move into aquatic ecosystems via runoff, impacting the environment. Consequently, accurately assessing and managing TWP levels in road dust is crucial. However, the ISO method (ISO/TS 20593 and 21396) uses a constant ratio of styrene-butadiene rubber (SBR) to natural rubber (NR) for all tires, disregarding the variability in tire composition across different types and brands. Our study found substantial SBR content (15.7 %) in heavyweight truck tires, traditionally believed to be predominantly NR. We evaluated the SBR/NR content in 15 tire types and proposed a method to more accurately evaluate TWP concentrations in road dust from five different locations. Our findings suggest that the conventional ISO method may underestimate the concentrations of TWP due to its reliance on a static ratio of SBR/NR. This study underscores the necessity for a more flexible approach that can adapt to the variability in SBR and NR content across different tire types. By delineating the limitations inherent in current assessment methods, our research contributes to a more adaptable understanding of TWP concentrations in road dust. This advancement prompts the development of a revised methodology that more accurately reflects the diverse compositions of tire rubber in environmental samples.

Investigations of airborne tire and brake wear particles using a novel vehicle design

Non-exhaust emissions have become an increasingly important issue as their levels continue to rise and the health effects of particulate matter (PM) are more widely discussed. To address this issue, a vehicle demonstrator with integrated emission reduction of tires and brakes was developed as part of the Zero Emission Drive Unit Generation-1 (ZEDU-1) project. This novel concept includes the removal of tire road wear particles (TRWP) with a strong ventilation/filtering system and an enclosed multi-disk brake, making it a suitable tool for the investigation of non-exhaust emissions. Particle number (PN) and particle size distribution (PSD) measurements down to 2.5 nm were performed on a chassis dynamometer and on a test track. Due to the low background concentrations on the chassis dynamometer, it is possible to distinguish between tire and brake wear and to characterize even a small number of particle emissions. It could be shown that about 30 % less particles are emitted by the vehicle, when using the novel multi-disk brake instead of the conventional brake. The highest TRWP emissions were collected during acceleration and harsh braking. Characterization of the collected particles using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed diverse particle shapes and differences between particles generated on the dynamometer and on a test track.

Pilot analysis of tire tread characteristics and associated tire-wear particles in vehicles produced across distinct time periods

Owing to stringent vehicle emission regulations and the shifting automotive landscape towards clean-energy vehicles, the emission of non-exhaust tire-wear particles and its implications for microplastic contamination have garnered substantial attention, emerging as a focal point of research interest. Unlike traditional source apportionment methods involving direct environmental sampling, this study focuses on the physical and chemical attributes of tire treads, the tread temperature changes, and the tire-wear particle emissions of three light-duty vehicles manufactured between 2011 and 2021. This study advances the understanding of the effects of tire properties on particle emissions, which provides preliminary information on low-wear tires. The results show that tire-wear particle emissions, mainly composed of ultrafine particles in terms of number, heavily depend on the elevated tread temperatures. The change in tread temperature is influenced not only by the initial tread temperature but also by tread pyrolysis characteristics. Ca, Mg, and Zn are abundantly contained in the tire tread and tire-wear particles.

Where the rubber meets the road: Emerging environmental impacts of tire wear particles and their chemical cocktails

About 3 billion new tires are produced each year and about 800 million tires become waste annually. Global dependence upon tires produced from natural rubber and petroleum-based compounds represents a persistent and complex environmental problem with only partial and often-times, ineffective solutions. Tire emissions may be in the form of whole tires, tire particles, and chemical compounds, each of which is transported through various atmospheric, terrestrial, and aquatic routes in the natural and built environments. Production and use of tires generates multiple heavy metals, plastics, PAH's, and other compounds that can be toxic alone or as chemical cocktails. Used tires require storage space, are energy intensive to recycle, and generally have few post-wear uses that are not also potential sources of pollutants (e.g., crumb rubber, pavements, burning). Tire particles emitted during use are a major component of microplastics in urban runoff and a source of unique and highly potent toxic substances. Thus, tires represent a ubiquitous and complex pollutant that requires a comprehensive examination to develop effective management and remediation. We approach the issue of tire pollution holistically by examining the life cycle of tires across production, emissions, recycling, and disposal. In this paper, we synthesize recent research and data about the environmental and human health risks associated with the production, use, and disposal of tires and discuss gaps in our knowledge about fate and transport, as well as the toxicology of tire particles and chemical leachates. We examine potential management and remediation approaches for addressing exposure risks across the life cycle of tires. We consider tires as pollutants across three levels: tires in their whole state, as particulates, and as a mixture of chemical cocktails. Finally, we discuss information gaps in our understanding of tires as a pollutant and outline key questions to improve our knowledge and ability to manage and remediate tire pollution.

Current Concerns about Microplastics and Nanoplastics: A Brief Overview

The widespread and increasing use of plastic-based goods in the present-day world has been raising many concerns about the formation of microplastics, their release, their impacts on the environment and, ultimately, on living organisms. These concerns are even greater regarding nanoplastics, i.e., nanosized microplastics, which may have even greater impacts. In this brief review, although without any claim or intention to exhaustively cover all the aspects of such a complex and many-sided issue, the very topical problem of the formation of microplastics, and the even more worrisome nanoplastics, from polymer-based products was considered. The approach is focused on a terse, straightforward, and easily accessible analysis oriented to the main technological engineering aspects regarding the sources of microplastics and nanoplastics released into the environment, their nature, some of the consequences arising from the release, the different polymers involved, their technological form (i.e., products or processes, with particular attention towards unintentional release), the formation mechanisms, and some possible mitigation pathways.

The chemical composition and sources of road dust, and of tire and road wear particles-A review

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

Everything falls apart: How solids degrade and release nanomaterials, composite fragments, and microplastics

To ensure the safe use of materials, one must assess the identity and quantity of exposure. Solid materials, such as plastics, metals, coatings and cements, degrade to some extent during their life cycle, and releases can occur during manufacturing, use and end-of-life. Releases (e.g., what is released, how does release happen, and how much material is released) depend on the composition and internal (nano)structures of the material as well as the applied stresses during the lifecycle. We consider, in some depth, releases from mechanical, weathering and thermal stresses and specifically address the use cases of fused-filament 3D printing, dermal contact, food contact and textile washing. Solid materials can release embedded nanomaterials, composite fragments, or micro- and nanoplastics, as well as volatile organics, ions and dissolved organics. The identity of the release is often a heterogenous mixture and requires adapted strategies for sampling and analysis, with suitable quality control measures. Control materials enhance robustness by enabling comparative testing, but reference materials are not always available as yet. The quantity of releases is typically described by time-dependent rates that are modulated by the nature and intensity of the applied stress, the chemical identity of the polymer or other solid matrix, and the chemical identity and compatibility of embedded engineered nanomaterials (ENMs) or other additives. Standardization of methods and the documentation of metadata, including all the above descriptors of the tested material, applied stresses, sampling and analytics, are identified as important needs to advance the field and to generate robust, comparable assessments. In this regard, there are strong methodological synergies between the study of all solid materials, including the study of micro- and nanoplastics. From an outlook perspective, we review the hazard of the released entities, and show how this informs risk assessment. We also address the transfer of methods to related issues such as tyre wear, advanced materials and advanced manufacturing, biodegradable polymers, and non-solid matrices. As the consideration of released entities will become more routine in industry via lifecycle assessment in Safe-and-Sustainable-by-Design practices, release assessments will require careful design of the study with quality controls, the use of agreed-on test materials and standardized methods where these exist and the adoption of clearly defined data reporting practices that enable data reuse, meta-analyses, and comparative studies.

Characteristics of particulate matter from asphalt pavement and tire of a moving bus through driving tests in city road and proving ground

Non-exhaust PM emissions from vehicles in real road have been conducted, but heavy vehicles have rarely been tested. In this study, PM2.5 and PM10 samples were directly collected from a tire of a moving bus and the composition was analyzed to investigate the sources of PM emissions. Driving tests were conducted at a proving ground (PG) and a city road (CR). PM2.5 emissions considerably increased when the lateral force of the tire increased and the vehicle accelerated. The PM emission rate was higher in the PG test than in the CR test because of the harsher driving conditions at PG. The emission rates of PM10 in the PG and CR tests were higher than those of PM2.5 by approximately 6 and 11 times, respectively. In the PG and CR tests, the proportions of tire wear particles (TWPs) were 4.9% and 2.1% in the PM2.5 samples, and 6.8% and 8.2% in the PM10 samples, respectively. Furthermore, TWPs with PM (TWPPM) were generated by other sources: secondary production of TWPPM by fragmentation of TWPs and resuspension of TWPPM on the road. The contributions of other sources to TWP2.5 generation were at least 6% and 57% in the PG and CR tests, respectively, whereas that to TWP10 generation was at least 3.5% in the CR test. Iron derived from brake abrasion and mineral particles was observed in the PM samples, and the Fe concentrations were higher in the PM10 samples than in the PM2.5 samples by over 9 and 18 times for the PG and CR tests, respectively. Sulfur sources, such as TWPs, exhaust gas, and bitumen, were observed in the PM samples. Based on our findings, we recommend that road wear particles should be removed from roads to reduce PM emissions upon driving.

Causes of coastal waters pollution with nutrients, chemicals and plastics worldwide

Worldwide, coastal waters contain pollutants such as nutrients, plastics, and chemicals. Rivers export those pollutants, but their sources are not well studied. Our study aims to quantify river exports of nutrients, chemicals, and plastics to coastal waters by source and sub-basin worldwide. We developed a new MARINA-Multi model for 10,226 sub-basins. The global modelled river export to seas is approximately 40,000 kton of nitrogen, 1,800 kton of phosphorous, 45 kton of microplastics, 490 kton of macroplastics, 400 ton of triclosan and 220 ton of diclofenac. Around three-quarters of these pollutants are transported to the Atlantic and Pacific oceans. Diffuse sources contribute by 95-100 % to nitrogen (agriculture) and macroplastics (mismanaged waste) in seas. Point sources (sewage) contribute by 40-95 % to phosphorus and microplastics in seas. Almost 45 % of global sub-basin areas are multi-pollutant hotspots hosting 89 % of the global population. Our findings could support strategies for reducing multiple pollutants in seas.

Assessing biodegradation of roadway particles via complementary mass spectrometry and NMR analyses

Roadway particles (RP) that can be collected with on-vehicle system, consist of a mixture of Tire and road wear particles (TRWP) with other traffic-derived particles (exhaust or non-exhaust) and/or biogenic compounds and represent a significant source of xenobiotics, susceptible to reach the different environmental compartments. The study of the RP fate is thus a major challenge to tackle in order to understand their degradation and impact. They offer a variety of carbon sources potentially usable by microorganisms, ranging from the tire-derived plasticizers, vulcanizing agents, protective agents and their transformation products, to other traffic, road and environmental-derived contaminants. A multi-analytical approach was implemented to characterize RP and study their biodegradation. Kinetics of RP extractions were monitored during 21 days in water, methanol, acetone and chloroform to identify leaching and extractable compounds and monitor the particle composition. The results confirmed that hundreds of readily leachable chemicals can be extracted from RP directly into water according to a dynamic process with time while additional poorly soluble compounds remain in the particles. Mass spectrometry (LC-HRMS and GC-MS) allowed us to propose 296 putative compounds using an extensive rubber database. The capacity of 6 bacterial strains, belonging to Rhodococcus, Pseudomonas and Streptomyces genera, to biodegrade RP was then evaluated over 14 days of incubation. The selected strains were able to grow on RP using various substrates. Elastomer monitoring by 1H NMR revealed a significant 12 % decrease of the extractable SBR fraction when the particles were incubated with Rhodococcus ruber. After incubation, the biodegradation of 171 compounds among leachable and extractable compounds was evaluated. Fatty acids and alkanes from rubber plasticizers and paraffin waxes were the most degraded putative compounds by the six strains tested, reaching 75 % of biodegradation for some of them.

Assessment of road run-off and domestic wastewater contribution to microplastic pollution in a densely populated area (Flanders, Belgium)

Plastics are omnipresent in our daily life. Unfortunately, the produced plastics will partly end up in the environment including aquatic ecosystems. People often refer to littering or illegal waste dumping as sources of plastic emission to the environment. However, daily-life sources could also, unknowingly, contribute considerably to the total microplastic pollution in the ecosystem. Hence, there is an urgent need to study these potential sources. In this research, two common sources, i.e. domestic wastewater and road run-off from tire and road wear particles, were studied in detail to quantify the relative contribution of both domestic sources towards microplastic pollution in freshwater ecosystems in Flanders, Belgium. This assessment shows that every person (in studied area) emits on average 1145 microplastics (25-1000 μm) daily through domestic wastewater, resulting in a yearly discharge of 418,000 microplastic particles per person. The road run-off samples contained between 0.02 and 9.2 mg tire wear particles per litre per day, which corresponds to an emission of 10.8 mg tire wear particles per driven vehicle km. The gross and net emissions of both above mentioned microplastic sources were extrapolated to the whole Flanders region using an emission model. From the yearly gross microplastic pollution in the domestic wastewater, 623 kg (20%) will be discharged in the freshwater. The highest losses originated from the households that have a private drain or are not (yet) connected to an active wastewater treatment plant. In Flanders, the yearly net microplastic emission into the aquatic environment of tire wear particles is estimated to be 246 tonnes (38%), mainly from the direct run-off from the road surface. Based on the results, specific mitigation measures can be installed to reduce the emission of microplastics towards the freshwater ecosystem. Other sources should be quantified in a similar way for a more holistic strategy to counteract plastic pollution.

Microplastics and Tire Wear Particles in Urban Stormwater: Abundance, Characteristics, and Potential Mitigation Strategies

Stormwater has been identified as a pathway for microplastics (MPs), including tire wear particles (TWPs), into aquatic habitats. Our knowledge of the abundance of MPs in urban stormwater and potential strategies to control MPs in stormwater is still limited. In this study, stormwater samples were collected from microlitter capture devices (inlet and outlet) during rain events. Sediment samples were collected from the material captured in the device and from the inlet and outlet of a constructed stormwater wetland. MP (>25 μm) concentration in stormwater varied across different locations ranging from 3.8 to 59 MPs/L in raw and 1.8 to 32 MPs/L in treated stormwater, demonstrating a decrease after passage through the device (35-88% removal). TWPs comprised ∼95% of all particles, followed by polypropylene (PP) and poly(ethylene terephthalate) (PET). The concentration of TWPs ranged from 2.5 to 58 TWPs/L and 1450 to 4740 TWPs/kg in stormwater and sediment, respectively. A higher abundance of MPs was found in the sediment at the inlet of the constructed wetland compared to the outlet, indicating a potential role of wetlands in removing MPs from stormwater. These findings suggest that both constructed wetlands and microlitter capture devices can mitigate the transport of MPs from stormwater to the receiving waterways.

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.

Permeable pavements: A possible sink for tyre wear particles and other microplastics?

In this study, seven roads and parking lots were sampled by a road surface cleaning truck and approximately 100 kg of particulate material was collected per site. Thereafter, the samples were analysed for microplastics, including tyre wear particles. The analyses revealed that tyre wear constituted 0.09 % of the dry mass of the samples on average. Other plastic types were also identified in the samples, but at on average 49 times lower concentrations compared to tyre wear particles. Although the roads and parking lots were used for residential, industrial, and commercial purposes, no correlation between land use and the total concentrations of microplastics was identified. Of microplastics other than tyre wear particles, polypropylene constituted an important fraction in all samples, whereas other polymers were present at various degrees. The contents of heavy metals, sulphur, and total organic carbon were also measured in the samples, but no correlation between them and microplastics was determined. A back-of-the-envelope estimation indicated that the tyre wear material retained by permeable pavements constituted a non-negligible fraction of the total mass of microplastics released on roads and parking lots. Therefore, permeable pavements can serve as a tool for the management of this pollutant.

Uptake, Metabolism and Accumulation of Tire Wear Particle-Derived Compounds in Lettuce

Tire wear particle (TWP)-derived compounds may be of high concern to consumers when released in the root zone of edible plants. We exposed lettuce plants to the TWP-derived compounds diphenylguanidine (DPG), hexamethoxymethylmelamine (HMMM), benzothiazole (BTZ), N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), and its quinone transformation product (6PPD-q) at concentrations of 1 mg L-1 in hydroponic solutions over 14 days to analyze if they are taken up and metabolized by the plants. Assuming that TWP may be a long-term source of TWP-derived compounds to plants, we further investigated the effect of leaching from TWP on the concentration of leachate compounds in lettuce leaves by adding constantly leaching TWP to the hydroponic solutions. Concentrations in leaves, roots, and nutrient solution were quantified by triple quadrupole mass spectrometry, and metabolites in the leaves were identified by Orbitrap high resolution mass spectrometry. This study demonstrates that TWP-derived compounds are readily taken up by lettuce with measured maximum leaf concentrations between ∼0.75 (6PPD) and 20 μg g-1 (HMMM). Although these compounds were metabolized in the plant, we identified several transformation products, most of which proved to be more stable in the lettuce leaves than the parent compounds. Furthermore, continuous leaching from TWP led to a resupply and replenishment of the metabolized compounds in the lettuce leaves. The stability of metabolized TWP-derived compounds with largely unknown toxicities is particularly concerning and is an important new aspect for the impact assessment of TWP in the environment.

Concentrations of tire wear microplastics and other traffic-derived non-exhaust particles in the road environment

Tire wear particles (TWP) are assumed to be one of the major sources of microplastic pollution to the environment. However, many of the previously published studies are based on theoretical estimations rather than field measurements. To increase the knowledge regarding actual environmental concentrations, samples were collected and analyzed from different matrices in a rural highway environment to characterize and quantify TWP and other traffic-derived non-exhaust particles. The sampled matrices included road dust (from kerb and in-between wheeltracks), runoff (water and sediment), and air. In addition, airborne deposition was determined in a transect with increasing distance from the road. Two sieved size fractions (2-20 µm and 20-125 µm) were analyzed by automated Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX) single particle analysis and classified with a machine learning algorithm into the following subclasses: TWP, bitumen wear particles (BiWP), road markings, reflecting glass beads, metals, minerals, and biogenic/organic particles. The relative particle number concentrations (%) showed that the runoff contained the highest proportion of TWP (up to 38 %). The share of TWP in kerb samples tended to be higher than BiWP. However, a seasonal increase of BiWP was observed in coarse (20-125 µm) kerb samples during winter, most likely reflecting studded tire use. The concentration of the particle subclasses within airborne PM_80-1 decreases with increasing distance from the road, evidencing road traffic as the main emission source. The results confirm that road dust and the surrounding environment contain traffic-derived microplastics in both size fractions. The finer fraction (2-20 µm) dominated (by mass, volume, and number) in all sample matrices. These particles have a high potential to be transported in water and air far away from the source and can contribute to the inhalable particle fraction (PM₁₀) in air. This highlights the importance of including also finer particle fractions in future investigations.

Toxicity of tyre wear particle leachates to marine phytoplankton

Tyre wear particles (TWP) are some of the dominant sources of microplastics in the aquatic environment. Once TWP enter aquatic systems, they can leach certain plastic additives that can be potentially toxic to biota. However, little is known about the impact of TWP lixiviates on marine phytoplankton, the base of marine food webs. This study aims to determine the acute toxic effect of leachates derived from TWP on three phytoplankton species: the cryptophyte Rhodomonas salina, the diatom Thalassiosira weissflogii and the dinoflagellate Heterocapsa steinii, using the median effect concentration (EC₅₀) for specific growth rate as endpoint. Leachates were obtained by incubating 1 g L^-1 of < 250 µm TWP in artificial seawater for 3 days. Each phytoplankton species was exposed to leachates at five different concentrations, and cell concentrations were measured every 24 h over 3 days. Leachates from TWP were toxic to marine phytoplankton. The dinoflagellate H. steinii was the most sensitive species, with 72-h EC₅₀ of 23% leachate concentration, whereas R. salina and T. weissflogii exhibited EC₅₀ values of 64% and 73%, respectively. Our results suggest that TWP leachates have a negative effect on phytoplankton growth, although more field data on the concentration of TWPs and their leachates is needed to fully evaluate the environmental impact of TWP.