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Physical and chemical characterization of tire-related particles: Comparison of particles generated using different methodologies
Abstract
The purpose of this study was to characterize the physical and chemical properties of particles generated from the interaction of tires and road surfaces. Morphology, size distribution, and chemical composition were compared between particles generated using different methods, including on-road collection, laboratory generation under simulated driving conditions, and cryogenic breaking of tread rubber. Both on-road collected and laboratory generated particles exhibited the elongated shape typical of tire wear particles, whereas tread particles were more angular. Despite similar morphology for the on-road collected and the laboratory generated particles, the former were smaller on average. It is not clear at this stage if the difference is significant to the physical and chemical behavior of the particles. The chemical composition of the particles differed, with on-road generated particles containing chemical contributions from sources other than tires, such as pavement or particulates generated from other traffic-related sources. Understanding the differences between these particles is essential in apportioning contaminant contributions to the environment between tires, roadways, and other sources, and evaluating the representativeness of toxicity studies using different types of particulate generated.
... TRWPs are generated when the outermost layer of the tire (i.e., the tread) is worn away by the friction between the tire and the road surface, especially during acceleration, braking and turning of vehicles, as well as due to the permanent side slip of the tire against the road surface during continuous driving [1,2,28]. These small tire particles mix with other NEE particles as well as RD, which includes road-surface fragments and natural materials (e.g., plant fragments, minerals derived from rocks and soils), resulting in an encrustation of the tire rubber particles [2,22,29]. TRWPs display widely varying densities, reported to range from 1.2 g/cm 3 to potentially 2.5 g/cm 3 [4,30]. Furthermore, tire treads contain proprietary blends of synthetic and natural rubbers as well as fillers (e.g., silica, carbon black) and various chemical additives (e.g., zinc oxide, benzothiazoles, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD)), some of which are toxic [2,15,23,29,[31][32][33][34]. ...
... TRWPs display widely varying densities, reported to range from 1.2 g/cm 3 to potentially 2.5 g/cm 3 [4,30]. Furthermore, tire treads contain proprietary blends of synthetic and natural rubbers as well as fillers (e.g., silica, carbon black) and various chemical additives (e.g., zinc oxide, benzothiazoles, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD)), some of which are toxic [2,15,23,29,[31][32][33][34]. ...
... The current analysis methods for microplastic characterization utilize instruments like Raman or Fourier transform infrared (FTIR) spectroscopy, which are not appropriate for TRWPs, because the various fillers (e.g., carbon black) exhibit strong fluorescence and absorb nearly all infrared light [7,9,[35][36][37]. Therefore, since the TRWPs can be identified by their elongated cylindrical shape, rough surface features, rubbery texture and black color, methods like scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy are utilized to characterize TRWPs [2,6,29,38]. In addition, TRWPs are opaque in transmitted light, and therefore, they can be easily identified by optical microscopy [2,6,33]. ...
Tire- and road-wear particles (TRWPs) are one of the main types of primary microplastics in the environment. Generated through driving a vehicle, they accumulate on roads, where they are often found encrusted with varying amounts of road dust. Here, we report physical and chemical data for individual TRWPs (> 150 µm across), which were collected in Charleston, South Carolina, and separated via density fractionation. For this study, image and elemental analysis of individual TRWPs was conducted on only the lowest (≤ 1.179 g/cm³) and highest (≥ 1.43 g/cm³) density categories. Images of TRWPs, captured through scanning electron microscopy, were processed to determine axial ratios, volumes, and degree of encrustations. The high-density TRWPs were overall more elongated than their low-density counterparts but the TRWP volumes were similar in both density categories. The particles were mapped using energy-dispersive X-ray spectroscopy to visualize the distribution of Na, Mg, Al, Si, K, Ca, Ti, and Fe on the surface of the TRWPs. Subsequently, these element distribution maps were used to identify the mineral phases present in the TRWP encrustations. The obtained data revealed the main types of minerals occurring in the encrustations were quartz, feldspar, and Fe-oxide/hydroxides. The high-density TRWPs exhibited a greater extent of mineral encrustation than their lower-density counterparts. Iron and Ti were more prominent in the encrustations of high-density particles than in those of low-density TRWPs. These results demonstrate that the density of TRWPs, and consequently their transport and fate, are influenced by the extent and mineralogical composition of their mineral encrustations.
... Tire wear particles (TWP) are heterogeneous aggregates generated by tire-road interactions [1], containing elements like S, Zn, Na, Si, and Al [2]. Their generation and transport pathways depend on local factors such as the type of road [3,4] and drainage systems [1,5,6], varying greatly between cities. Road runoff is its main transportation path up to 2 m from the road's edge [7][8][9][10][11], with most of the TWP ending up in the top layer (0-30 cm) of roadside soils [6,12]. Roadsides can, therefore, be considered a significant sink for TWP [6,[13][14][15][16], where they act as carriers for hazardous organic compounds like N-(1,3-dimethyl butyl)-N′-phenyl-p-phenylenediamine (6PPD), N,N′-diphenylguanidine (DPG), and 2-hydroxybenzothiazole (2-OHBT)) [9,17]. ...
... The road had been closed for two days for scheduled maintenance prior to sample collection. Sampling was conducted in July (1,2) and deceleration (3,4) lane. (f) Western roadside at sampling location 1 with a shovel at the 1 m point. ...
... The roadside soil samples were air-dried for 24 h, then sieved to eliminate all material >315 μm, using a woven stainless-steel sieve with 20 cm diameter (Retsch®, Haan, Germany) on a shaking plate (Retsch® AS200, Haan, Germany) for 2 h. The size was chosen as the soil content had fine fractions, and the size distribution of TWP in the soil is 4-280 μm, as Kreider et al. [3] discerned. The road dust particles <1000 μm and soil fraction <315 μm were weighed (Table S1) and stored in a dry, dark cupboard. ...
... Consequently, the establishment of a reference database for tyres has been suggested [43]. Where tyre particles are produced in a laboratory, the method used can have an effect [45]. For example, different methods produce different-sized particles, with fine particles produced by thermal wearing and coarser particles produced by mechanical wearing [46]. ...
... Tyres are also rarely found in their pure form in the environment [23]. Instead, the age of the tyre [47], the wearing process the tyre undergoes [36], the mixture it forms with other road particles [45], as well as the ageing of the particles in the environment [48], cause a change in the tyre particles' physical and chemical properties. Therefore, further analysis of commercial tyres is required to increase our poor understanding of their overall properties. ...
... Firstly, and most importantly, laser diffraction particle size analysis bases its calculations on the Mie theory, which assumes that the particles in the sample are spherical [96]. Tyre particles are inherently not spherical but elongated [45], and the SEM analysis conducted found this to be true for the tyre particles used here (see section 3.2). Therefore, from the offset, it is likely that these results are inaccurate. ...
... These results may suggest the presence of other factors that contribute to their measured fluorescence, such as the unintended presence of impurities or additives (i.e., unintentionally added substances; Bridson et al., 2023). Additionally, while polyolefins like PE and PP do not contain fluorophores in their chemical structure, photooxidation or thermal oxidation (Allen et al., 1977;Zhao et al., 2022), impurities (Bridson et al., 2023;Laatsch et al., 2023), fiber structural defects (Poszwa et al., 2016), or formation of high-molecular-weight clusters (Laatsch et al., 2023) can cause PE and PP to become fluorescent. For example, during the photooxidation process, enones and dienones can be formed (Allen et al., 1977), which makes those polymers gain fluorescent properties. ...
... These results may suggest the presence of other factors that contribute to their measured fluorescence, such as the unintended presence of impurities or additives (i.e., unintentionally added substances; Bridson et al., 2023). Additionally, while polyolefins like PE and PP do not contain fluorophores in their chemical structure, photooxidation or thermal oxidation (Allen et al., 1977;Zhao et al., 2022), impurities (Bridson et al., 2023;Laatsch et al., 2023), fiber structural defects (Poszwa et al., 2016), or formation of high-molecular-weight clusters (Laatsch et al., 2023) can cause PE and PP to become fluorescent. For example, during the photooxidation process, enones and dienones can be formed (Allen et al., 1977), which makes those polymers gain fluorescent properties. ...
... Thus, it can be assumed that many of the MPs in the environment also contain additives, which could alter their measured fluorescence in the SwisensPoleno. Additionally, further investigation is required to understand how components of airborne microplastics found in the environment -such as particles comprised of multiple components (i.e., tire and road wear particles; Kreider et al., 2010), those containing pollutants adsorbed onto the surface (e.g., Fu et al., 2021;Gao et al., 2021), or those that have undergone environmental weathering processes such as photooxidation (Sun et al., 2020) -contribute to changes in measured fluorescence and how this may impact their measurement in the SwisensPoleno. ...
The continued increase in global plastic production and poor waste management ensures that plastic pollution will be a serious environmental concern for years to come. Because of their size, shape, and relatively low density, plastic particles between 1 and 1000 µm in size (known as microplastics or MPs) emitted directly into the environment (“primary”) or created due to degradation (“secondary”) may be transported through the atmosphere, similarly to other coarse-mode particles such as mineral dust. MPs can thus be advected over great distances, reaching even the most pristine and remote areas of Earth, and may have significant negative consequences for humans and the environment. The detection and analysis of MPs once airborne, however, remains a challenge because most observational methods are offline and resource-intensive and, therefore, not capable of providing continuous quantitative information.
In this study, we present results using an online in situ airflow cytometer (SwisensPoleno Jupiter; Swisens AG; Emmen, Switzerland) – coupled with machine learning – to detect, analyze, and classify airborne single-particle MPs in near real time. The performance of the instrument in differentiating between single-particle MPs of five common polymer types (including polypropylene, polyethylene, polyamide, poly(methyl methacrylate), and polyethylene terephthalate) was investigated under laboratory conditions using combined information about their size and shape (determined using holographic imaging) and fluorescence measured using three excitation wavelengths and five emission detection windows. The classification capability using these methods was determined alongside other coarse-mode aerosol particles with similar morphology or fluorescence characteristics, such as a mineral dust and several pollen taxa.
The tested MPs exhibit a measurable fluorescence signal that not only allows them to be distinguished from other fluorescent particles, such as pollen, but also differentiated from each other, with high (> 90 %) classification accuracy based on their multispectral fluorescence signatures. The classification accuracies of machine learning models using only holographic images of particles, only the fluorescence response, and combined information from holography and fluorescence to predict particle types are presented and compared. The last model, using both the holographic images and fluorescence information for each particle, was the most optimal model used, providing the highest classification accuracy compared to employing models using only the holography or fluorescence response separately. The results provide a foundation for significantly improving the understanding of the properties and types of MPs present in the atmosphere.
... a) b) Fig. 11. Test results: microscopic images of collected tire particles, b) comparison of TRWP particle size distribution during cornering (left or right) for different lateral accelerations of the car [40] The factors affecting the size distribution characteristics of vehicle tires and road wear particles have been studied in laboratory tests [9,27,38,53,58,69,76,83,85,94,104,106]. Figure 12 shows the physical characteristics of tire and road wear particles. According to the research presented in [27], the tire and road wear particle diameter (TRWP) is mainly distributed in the range of 4-350 μm with an average diameter of 100 μm, which is larger than the volume of PM 2.5 (≤ 2.5 μm) and PM 10 (≤ 10 μm). ...
... The density of particulate matter is about 1800 kg/m 3 , which is higher than the density of water. [27] Figure 13 shows photos of road and tire wear particles [53]. Road wear particles ( Fig. 13a and 13b) are elongated and contain mineral inclusions from the road surface. ...
... Photos of particles: a, b) from road wear, c, d) from tire wear (b, d appropriate magnification of photos a and c, where mineral inclusions are visible)[53] ...
Gaseous and solid pollutants (dusts) of atmospheric air have been defined. Dusts have been divided according to various criteria and their properties have been given. The sources and characteristics of anthropogenic and natural pollutants of atmospheric air have been presented. It has been shown that the main sources of anthropogenic pollutants, apart from industry, are motorization, and internal combustion engines of cars are a source of gaseous pollutants and solid particles, the emission of which has been significantly reduced. The originality of the article consists in conducting an extensive literature analysis and proving that the emission of "non-engine" pollutants in the form of dust from the wear of friction linings of brakes, clutches and from the wear of tires and roads, as well as mineral dust raised from the ground, is currently a greater threat to human health and the environment than engine emissions. The impact of particulate matter emissions from road transport and mineral dust, which is the basic component of road dust, on human health, vegetation and on the operation of engine and vehicle systems is presented.
... pads, and body rust), leakage of lubricating and brake oils, road surface abrasion, catalytic converter wear, and road paint degradation [12][13][14][15][16] . ...
... Each of the 149 samples was classified into one of 19 land use categories, which include six primary types (1-6) and 13 mixed categories (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), as shown in Fig. S4 and detailed in Table S6. The classification identifies these 19 categories, with the first six representing the core land use types, while categories 7 to 19 are combinations of two or three of the primary categories. ...
Street dust was collected from 149 locations (“all”) and fractionated into five size-dependent categories: (1–0.8 mm) “0.8,” (0.8–0.6 mm) “0.6,” (0.6–0.4 mm) “0.4,” (0.4–0.2 mm) “0.2,” and (< 0.2 mm) “ < 0.2.” The main aims were to investigate the role of grain size in differentiating magnetic properties and identify land use factors affecting the magnetic and grain size distribution of street dust. The mass-specific magnetic susceptibility (χ) for “all” exhibited spatial variability, ranging from 30 to 545 × 10⁸ m³/kg. The average χ for “ < 0.2” was 68% higher in Area 1 and 195% higher in Areas 2&3 compared to the “all” samples. The 0.4–0.2 mm grain fraction was the most abundant and comprising 40% ± 7% of the samples in Area 1, 38% ± 9% in Area 2, and 39% ± 12% in Area 3. Area 1 “all” samples predominantly consisted of particles around 1 μm, while samples from Areas 2&3 featured grains ranging between 1 and 5 μm. This study is important as it provides new insights into how grain size and land use factors interact to affect the magnetic properties of street dust, which can be used as an effective indicator for monitoring urban pollution.
... Specifically focusing on tire abrasion, gravimetric analyses have been employed to measure weight loss in motorized vehicle tires over time, correlating this data with the distance travelled to estimate microplastic emissions (Kole et al., 2017). Laboratory simulations using road simulators and field studies tracking real-world tires use via air samplers have both been utilized to understand the rate of tire wear (Kreider et al., 2010;Panko et al., 2013). Results revealed that tire wear particles (TWPs), a mix of synthetic rubber and road debris, are a significant source of microplastics in urban runoff and atmospheric deposition (Kreider et al., 2010). ...
... Laboratory simulations using road simulators and field studies tracking real-world tires use via air samplers have both been utilized to understand the rate of tire wear (Kreider et al., 2010;Panko et al., 2013). Results revealed that tire wear particles (TWPs), a mix of synthetic rubber and road debris, are a significant source of microplastics in urban runoff and atmospheric deposition (Kreider et al., 2010). ...
... Athletic fields employ a significant amount of rubber particles during installation to satisfy the roughness and strength requirements for movement. In order to reduce the manufacturing cost of athletic fields, grinding waste tires into smaller particles for filling athletic fields has become a mainstream practice (Kreider et al., 2010;Perkins et al., 2019;Pronk et al., 2020). European Chemicals Agency research revealed that 43% of recycled rubber shavings are used for artificial turf (including fillers), and 45% are used for sports fields such as plastic runway, tennis court and basketball court. ...
... As the number of athletic fields increase, these rubber particles could enter the human body through skin contact or ingestion, causing ecological and health problems (Canepari et al., 2018). Typically, rubber polymers used in tires encompass ethylene propylene diene monomer (EPDM), thermoplastic elastomers, and styrene-butadiene rubber (SBR), or their recycled counterparts (ECHA, 2017;Kreider et al., 2010). When these synthetic polymers are present in the environment, they can be categorized as microplastics (Hartmann et al., 2019). ...
The occurrence of microplastics in athletic fields and their risk of ecological pollution have attracted widespread attention. The abundance, particle size, morphology, color and type of microplastics as well as their ecological risk are conducted in five types of athletic fields runoff on a campus in Beijing. The concentration of microplastics in the stormwater runoff of the five athletic fields ranges 2433 ± 493 to 5067 ± 839 particles/L, composed of fibers, granules and fragments. Fibers microplastics (41–64%) are the most abundant in stormwater runoff samples from most athletic fields, followed by granules (26–45%), and fragments (8–18%). ATR-FTIR and micro-FTIR identify the types of microplastics in runoff from athletic fields as EPDM, SBR, PE, PP, PO, rayon, and nylon. The degree of microplastic pollution is ranked level II–III pollution, which posing potential health and ecological risks. The adsorption behavior is tested for three types of microplastic particles including ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR) and aged-SBR particles derives from athletic fields surface materials towards runoff typical heavy metals Pb and Zn. The adsorption isotherms are more in line with the Langmuir model, indicating a chemical monolayer adsorption. The maximum adsorption capacity towards Pb and Zn follow the order of EPDM (2.67 mg/g) > aged-SBR (1.50 mg/g) > SBR (0.13 mg/g), and EPDM (2.61 mg/g) > aged-SBR (1.50 mg/g) > SBR (0.56 mg/g), respectively. Aged microplastics are subjected to processes such as UV aging and weathering, the surface layer is more likely to acquire charges and adsorb metals to maintain charge balance. EPDM, SBR and aged-SBR particles all contain Ca, Zn, and Mg, which can undergo displacement reactions with Pb and Zn. FTIR results indicate that the adsorption of heavy metals may alter the surface chemical properties of microplastics, rendering them more polar. XPS results reveal that the changes in surface functional groups of EPDM are more pronounced before and after adsorption compared to SBR and aged-SBR, indicating that chemical adsorption plays a dominant role in this process. Microplastics in runoff from athletic fields is an important source of microplastic release, and the occurrence of microplastics needs to attract further attention. The adsorption of microplastics and pollutants in athletic field runoff could exacerbate their combined pollution, thus their ecological risks cannot be ignored.
Graphical Abstract
... Finally, TRWP contain various amounts of heavy metals embedded in the rubber during abrasion on the road. Cu, Fe, Cr, Mn, Co, Ni, Ba and Pb originating from road debris, brake wear and unknown sources have been quantified in the μg/g range in TRWP (Hjortenkrans et al., 2007;Kreider et al., 2010;Masset et al., 2021;Thorpe and Harrison, 2008). ...
... A limitation of this study is the use of CMTT as a surrogate for environmental TRWP. It has been demonstrated that the chemical content of TRWP is not identical to that of pure tire tread due to encrustation of minerals and organic constituents originating from the road pavement (Kreider et al., 2010;Masset et al., 2021). The different density and surface areas of TRWP compared to CMTT could impact the diffusion and fate of the tire-related chemicals within the soil as well as their overall bioaccessibility. ...
... We use their lower and upper bounds for each size mode and emission type as our lower and upper case scenarios (Table 1). According to Kreider et al. (2010) and Broeke et al. (2008), PM10 emissions from RMPs account for 4% of the total emissions, whereas PM2.5 accounts for 1%. For PMBPs, the PM10 fraction is 35%, whereas PM2.5 is 10% (Snilsberg et al., 2008). ...
... As noted by Evangeliou et al. (2020), the size distribution within the PM10 and PM2.5 modes of road trafficrelated MPs are highly uncertain. We follow several studies that provide various scenarios for TWPs and BWPs (Evangeliou et al., 2020), road marking particles (Broeke et al., 2008;Kreider et al., 2010), and asphalt particles (Snilsberg et al., 2008). The scenarios are shown in Figures 1a-1d. ...
Microplastics (MPs) can be transported into clouds, where they may act as ice nucleating particles (INPs). However, MPs have not been considered as contributors to INP concentrations. Here, we quantify road traffic‐related MP number concentrations, and estimate their contribution to total INP concentrations using the atmospheric transport model FLEXPART. We find that under a high emission scenario ice‐active MPs can account from about 0.1% to more than 40% of the total INP number in immersion freezing conditions in the tropics, whereas for cirrus conditions, their contribution can be up to about 7% over the tropical Pacific and up to about 20% over East Antarctica. Thus, in regions where other effective INPs are rare, ice‐active MP concentrations may be sufficient to trigger heterogeneous nucleation of ice crystals in mixed‐phase clouds or cirrus. This suggests that MP may affect cloud formation and highlights the need to reduce uncertainty in MP emissions and their fate in the atmosphere as plastic use continues to grow.
... As a result of the friction process, tyre wear can also be emitted into the environment as an agglomerate, e.g., with wear from the road surface as so-called Tyre and Road Wear Particles (TRWP). The composition of the tread and the resulting wear particles contain mixtures of rubber (natural and synthetic) and have a particle size distribution of 4-350 µm [1]. Tyre wear is significant contributor to microplastics [2]. ...
... This result initially conflicts with the expected distribution from Kreider et al.'s work, where a normal distribution of the particle size with a peak at approx. 60 µm was found [1]. However, Kreider et al. sampled particles using on-board sampling and carried out no measurements in sediments. ...
Technical retrofit Sustainable Drainage Systems (SuDSs) are a suitable option in the numerous mitigation measures to reduce the amount of tyre wear entering the environment. In the study presented here, such a filter system was tested under extreme conditions at the ADAC Driving Safety Centre Berlin-Brandenburg. Despite a technical separation limit of 125 or 250 µm of the filter systems, particles > 6 µm were measured in the retained masses. In addition, the marker SBR was used to determine the residues of tyre wear in the filter system using the TED-GC-MS analysis method. The highest concentrations were found in the 20–63 µm fraction. The results indicate that tyre wear particles become smaller due to high forces generated by braking and cornering. Test stand investigations indicate a retention efficiency of the filter system of 2/3 of the tyre wear. Furthermore, the results show that the parameter ‘Total Suspended Solids < 63 µm’ (TSS63) is a relevant evaluation parameter for the road runoff.
... Tyres consist of 40-50% natural rubber (polyisoprene) and synthetic rubber [styrene-butadiene rubber (SBR) or butadiene rubber]; 20-30% fillers such as soot/carbon black (C) silicon dioxide (SiO 2 ), and chalk (CaCO 3 ); 15% oils and resins; and a small percentage of preservatives and vulcanising agents [3][4][5][6]. In addition, tyre wear particles found in the environment are generated by the abrasion of tyres on the road surface [7] and are therefore rich in road-related compounds such as metals or organic chemicals (e.g., polycyclic aromatic hydrocarbons) that are potentially harmful to living organisms [8][9][10][11]. The highest concentrations of tyre particles were measured along roads with a range of 0.7 to 210 g/kg −1 t.w. [12], while in soil a range of 0 to 117 g/kg −1 t.w. was found, depending on the distance of sampling from the road and the location [13][14][15]. ...
... Specifically, we analysed the duration of the animals' freezing (number of frames the animals remain motionless) in each trial. single-cell suspension cultures [10,11]. At the genomic level, MVA-CR19 is characterised by three-point mutations in structural proteins and an expanded inverted terminal repeat (ITR) of 27 kb compared to the 10 kb of wildtype (WT) MVA [10]. ...
(1) Car tyre microplastic particles (TMPs) significantly contribute to global microplastic pollution, with an estimated annual production of 6 million tonnes. However, the impact of TMPs, particularly tyre and road wear particles (TRWPs), resulting from tyre abrasion on the road on terrestrial organisms, is poorly understood. This study investigated the effects of TMPs and TRWPs on the growth, immune response, behaviour, and cognition of the woodlouse Armadillidium pallasii over 30 days; (2) TMPs and TRWPs were mixed together in the first experiment and provided at different concentrations of 1.25%, 2.5%, 5%, and 10% (w/w), and with soil at 5% and 10% (w/w) concentrations in the second experiment. (3) No differences in survival or immune responses were observed in both experiments. However, isopods exposed to TRWPs showed significant weight gain at lower concentrations but no gain at higher levels. Behavioural tests revealed increased vigilance in TRWP-exposed animals. Micro-FTIR analysis showed that the number of TMPs and TRWPs in the isopods correlated with soil concentrations, and particle size decreased during the experiment. (4) The study highlights the physiological and behavioural effects of TRWPs and the role of detritivorous species in the biofragmentation of TMPs and TRWPs, contributing to the biogeochemical plastic cycle.
... It is therefore assumed that: i) nearly all TWP D formed are intermingled at the tire-road interface with the abraded materials from the pavement and road surface contaminants to form a third body, and/ or ii) the TRWP embedment of TWP D occurs partially within the HVS unit or along its sampling lines. On the one hand, intermingling has already been probed using various techniques, and it has been found that tire fragments can both be incorporated into the hetero-aggregates formed at the tire-road interface and act as a "superglue" to which abraded materials and other debris adhere; resulting in a rubber tread core covered with a layer of incrustations, including additional tire fragments (Kreider et al., 2010;Sommer et al., 2018;Wagner et al., 2022). Our data further reveals that extensive and greater dust deposition on roads would exacerbate tire wear and thereby induce the formation of TWP D (Section 3.2) yet would also favor a mixing between road surface contaminants and worn materials at the tire-road interface, then ultimately the TRWP embedment of TWP D . ...
... Microphotographs show that coarse and oblong RoWP are comparable to TRWP reported in the literature or collected at roadside, on the road using alternative samplers (e.g. ELPI), or else generated by road simulators (Kreider et al., 2010;Kovochich et al., 2021;Gao et al., 2022;Rausch et al., 2022). ...
A method has been established to assess direct TWP emissions from vehicles. • Actual TWP D emission factors, size distributions , and determinants were specified. • Fine and ultrafine TWP D represent variable yet significant proportions of emissions. • The contribution of TWP D emissions to urban levels of (ultra)fine particles may be of concern. • Urban areas are conducive to higher and less TRWP-embedded TWP D emissions. In the range of 5-6 Mt/y tire wear particles (TWP) are emitted from vehicles in both developed and emerging countries. In an attempt to reduce these emissions, new regulations will come into force in the EU and USA, although currently no oversight methods are actually in place. This study proposes a method for assessing direct TWP emissions (TWP D) from vehicles. The method entails labeling the tire with mercury, then collecting and fractionating the particles emitted at the rear of the wheel (RoWP), and lastly analyzing their Hg content in the laboratory using atomic absorption spectroscopy. It provides access to the magnitude, size distribution and factors affecting TWP D emissions under actual driving conditions. Furthermore, the implementation of desorp-tion and dispersion models allows evaluation of the proportion of TWP D embedded in tire and road wear particles (TRWP) and estimating the TWP D contribution to the lower atmosphere PM 1 , PM 2.5 and PM 10 pollution within the EU-27. A key finding of this research is that ultrafine TWP D (accounting for 33-260 mg/g of abraded front tire material) account for 30-70 % of total TWP D emissions (with >93 % being in the form of inclusions), although they make up 0.5-5.7 % of RoWP mass emissions. Our data also draw attention to the magnitude and lower TRWP-embedment of TWP D emissions in urban areas.
... The amount and characteristics of TWP emitted depend on a variety of factors ranging from which initial material the tire and the road are made of, to the habits of the driver [1]. TWP produced in simulators were observed to have a minimum size of about 40 nm [19] and a maximum size of around 400 µm [20]. Once formed, TWP can be deposited on the road and be washed out with the road runoff or emitted to the air and transported to other environmental compartments [4]. ...
... For each sample, approximately 500 g of soil was sieved to < 2 mm (Retsch, stainless steel, 2 mm) and all visible organic structures (root fragments etc.) were removed with tweezers. As TWP are expected to be mainly in the size fraction < 40 nm to 400 µm (Gustafsson et al., 2008;Kreider et al., 2010), the < 2 mm fraction is expected to contain the majority of TWP. ...
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.
... Tire wear particles are generated while driving through frictional forces with the road surface (Rogge et al., 1993). These particles have a size distribution ranging from about 4 μm to 350 μm (Kreider et al., 2010) and also in the nanometer range (Dahl et al., 2006). TWP are emitted into all compartments: soil (near streets), air and water (rivers, lakes) (Baensch-Baltruschat et al., 2021). ...
Tire wear particles (TWP) are potential pollutants of emerging concern. Therefore, the EU is set to regulate the TWP emissions under the new Euro 7 emission standard. For Germany it is estimated that up to 20,000 t TWP reach the aquatic environment. Main transport pathways are via road runoff and separate sewage systems. Studies indicate that, apart from ecotoxicological concerns, the negatively charged surface of TWP can adsorb heavy metals like Cr, Ni, Zn, Cd and Pb, potentially deteriorating the chemical water quality of rivers. As rivers usually undergo a salt gradient from their source to the sea this may change the adsorption of heavy metals. We investigated the influence of salinity on the heavy metal adsorption on TWP using water samples from the Freiberger Mulde (Saxony, Germany), enriched with NaCl to simulate the salinity representative of different rivers in the Elbe catchment area, and additional water samples (Elbe, Saale, Bode, Schlenze). The adsorption of Cd and Zn appear to be highly salt-dependent. Above 12 mg L−1 Cl−, no significant adsorption was observed. It is assumed that both metals form [MCl4]2− complexes which are repelled from the negative surface of TWP. The potential in building these complexes is high enough to dissolve previously adsorbed Cd from TWP. These findings are important for assessing water quality of river systems as well as runoff filtration and water retention systems. In winter, for instance, when de-icing salt is applied, Cd and Zn bound on TWP may be mobilized entering water systems.
... However, they present clear differences with other microplastics. They are complex particles composed of elastomeric rubber polymers, namely Styrene-Butadiene and Butadiene rubbers (SBR + BR), fillers and other additives along with road mineral incrustation reaching between 6 % and up to 53 % of a tyre wear particle's volume (Eisentraut et al., 2018;Klöckner et al., 2021;Kreider et al., 2010;Sommer et al., 2018). Additionally, while microplastics are emitted from a diversity of sources, TRWP are specifically emitted from road traffic. ...
... The composition of tire rubber is characterized by complex proprietary formulations, differing across manufacturers and intended application [17,18]. Tire rubber formulations contain thousands of chemical constituents including polycyclic aromatic hydrocarbons (PAHs), heavy metals, antioxidants, antiozonants, plasticizers, vulcanizers, and other additives to create a functional and safe tire [19]. TPs can leach chemical additives from their surface into the aquatic environment, increasing organismal exposure and bioavailability of tire rubber contaminants [20,21]. ...
Rubber materials enter aquatic environments by stormwater runoff via sources such as playground mulch, athletic fields, and roadway surfaces. Tire rubbers are considered plastics as they comprise a substantial portion of synthetic polymers. Rubber particles are complex and variable depending on the type, source, and age of rubber. In this study, zebrafish embryos and daphnids were exposed to nano-scale or micro-scale particles, or leachate from recycled rubber (RR), crumb rubber (CR), and cryo-milled tire tread (CMTT). Zebrafish embryos were evaluated for lethal and sub-lethal effects over a 120 h exposure, while daphnids were tested over a 48 h period. Nano-scale RR, CR, and CMTT particles elicited a hatch delay in zebrafish embryos with similar EC50 values (1.3 × 109–1.4 × 109 particles/mL). Micro-scale particles did not elicit any significant effects in developing zebrafish. Nano-scale particles of all rubber materials significantly increased hatch delay compared to leachate, suggesting an adverse nanoparticle effect unexplained by chemical leaching alone, indicating tire particle-specific effects. Daphnia RR micro- and nanoparticle exposures resulted in mortality, with LC50 values of 9.8 × 105 microparticles/mL and 5.0 × 108 nanoparticles/mL, respectively. Leachate exposures did not elicit significant Daphnia mortality. Sublethal micro- and nano-TP exposures significantly decreased microalgae ingestion by Daphnia after 24 h. The effects of tire-derived exposures observed pose a risk to aquatic organism survival at environmentally relevant concentrations.
... Tire wear particles (TWP) consist of synthetic rubber (such as petroleum-based butadiene rubber and styrene-butadiene rubber), natural rubber (polyisoprene), and chemical additives. Due to their small size, ranging from 10 nm to 1000 μm, typically less than 250 μm (Baensch-Baltruschat et al., 2021;Kreider et al., 2010), TWPs are easily transported into aquatic environments through surface runoff, stormwater, drainage systems, wastewater effluent, and atmospheric deposition (Parker-Jurd et al., 2021). Once in these systems, TWPs release a complex mixture of chemicals, referred to as leachates. ...
... As such, these particles are ubiquitous in the terrestrial realm and are one of the largest sources of MPs (Wik andDave 2009, Luo et al. 2021). Tire particles contain chemical additives known to cause harm to the environment (Kreider et al. 2010). Still, such additives are used widely as granular artificial turf infills (e.g., rubber crumbs) in artificial turf fields (Zuccaro et al. 2024). ...
Microplastics (MPs) are a growing problem worldwide. Soils are long-term storage sinks of MPs because of the many pathways they enter the soil and their long degradation period. Knowing how MPs influence soil organisms, the effects of organisms on the fate of MPs, and what this means for soil additions, losses, transformations, and translocations is paramount. MPs in soil could impede the breakdown of organic matter by adult darkling beetles. We set up an experiment to test this hypothesis by adding finely ground scrap tire rubber to organic soil and a small population of adult darkling beetles (Zophobas morio, Fabricius 1776, Coleoptera: Tenebrionidae). The beetles are omnivores that accelerate the breakdown of soil organic matter when feeding on soil detritus. As a control, we released beetles into organic soil with no MPs. We also surveyed published manuscripts on the effects of MPs on insects, decomposers, and decomposition in soil, providing a reference frame for our findings. Darkling beetles ate, fragmented, and humidified the soil mixture, enhancing microbial decomposition. All treatments lost weight over the experiment period, with the control losing 10%, significantly more than the other treatments (an average loss of 5%). Higher concentrations of microplastics in soils led to lower reductions in soil mass through decomposition. These findings suggest that MPs impede detritivores from breaking down soil organic matter. Even so, only a handful of studies evaluated the effects of tire particles on soils and detritivores in the literature survey. Still, these particles are among the largest sources of MPs on land.
... Street dust is a heterogeneous composition of soils and particles originating from natural and anthropogenic sources occurring on road surfaces by dry or wet deposition (Cao et al., 2017;Gunawardana et al., 2012;Haynes et al., 2020). Anthropogenic sources of different types of pollutants (e.g., heavy metals, polycyclic aromatic hydrocarbons (PAH)) in street dust originate from industrial and exhaust and non-exhaust traffic-related processes and low-stack emission and including fuel combustion, wear of tires, brake pads, road surface, body rust, leakage of brake and lubricating oil, automotive three-way catalytic abrasion and wear, and road paint Khpalwak et al., 2018;Kosheleva et al., 2023;Kreider et al., 2010;Li et al., 2013;Logiewa et al., 2020;Pathak et al., 2013;Tanner et al., 2008;Yang et al., 2010;Yildirim & Tokalioğlu, 2016;Zhang et al., 2024). ...
Total concentrations, toxicity, and health risks of 16 polycyclic aromatic hydrocarbons (PAH) in street dust from Warsaw (Poland) in 6 granulometric fractions were investigated. Street dust was collected from 149 sampling points distributed among Area 1 (central districts, left bank of the Vistula River, mostly traffic-related pollution) and Area 2&3 (suburb area, mostly residential, right bank of the river). Street dust was investigated before (“all”) and after separating into 5 size-dependent samples: (1–0.8 mm) “0.8”, (0.8–0.6 mm) “0.6”, (0.6–0.4 mm) “0.4”, (0.4–0.2 mm) “0.2”, and (below 0.2 mm) “ < 0.2”. ΣPAH mean concentration was 3.21 mg/kg for Area 1 and 0.89 mg/kg for Area 2&3. ∑BaPTPE values calculated collectively for Area 1&2&3 were observed to be 318.3, 83.5, 131.1, 81.4, 164.3, and 339.7 ng/g for “all”, “0.6”, “0.4”, “0.2”, and “ < 0.2”, respectively. Significant differences in ∑BaPTPE values were observed between fractions and specific areas. The cancer risk levels for children and adults, for all particulate size fractions, were comparable for dermal contact and by ingestion and ranged from 10⁻⁵ to 10⁻⁴, whereas the cancer risk levels via inhalation always ranged from 10⁻¹⁰ to 10⁻⁸. Therefore, inhalation of resuspended street dust is almost negligible compared to other pathways. Environmental implication. Street dust pollution in cities is one of the most important issues in the world and it negatively affects the quality of the environment and people's health. This study contributed to filling the gap in knowledge about the characteristics of PAH contaminants in the subject of the grain size of street dust from Poland and assessing the potential health risks. Therefore, our work has provided new significant information on PAH pollution, methods of measuring PAHs content and assessing the risk to human health, which may be useful to the scientific community, policymakers, and the general public.
... However, the chemical composition of TWPs can change due to the heat generated during contact with the road surface or combine with existing road dust, RWPs, and minerals from the pavements and form a unique entity [52]. ...
... TRWP entering aquatic ecosystems via runoff can negatively affect these systems (Marwood et al., 2011;Panko et al., 2013). Despite an increasing number of studies focused on the environmental TRWP impacts, challenges in environmental monitoring persist (Rauert et al., 2021), and comprehensive data on TRWP concentrations-especially in marine environments-are still lacking (Barber et al., 2024;Kreider et al., 2010;Unice et al., 2019). ...
... Then the particles from a single point was filtered using a suction filtration device sequentially onto stainless filter membranes with three mesh sizes of 105, 40, 10 μm (DM-25-105, DM-25-040, DM-25-010, MOSSFIL CO, LTD, Japan) for observation. Kreider et al., 17) reported that MPs derived from tire dust are distributed within the 10 to 300 µm range, centered at 100 µm. Leads and Weinstein 18) also investigated the occurrence of MPs from tires; they reported that the highest number of particles was in the 150-499 µm size fraction. ...
Recently, microplastics originated from tire wear particle becomes a concern. This study surveyed occurrence of tire-derived mcroplastics (TMPs) on road by μATR-FTIR with a focus on road design. More specifically, samples were taken at different part of curvilinear section. The result shows the number of TMPs were higher at inner part of the curve, due to smaller rotating radius. In addition, the number of TMPs were found to be highest at the middle of the U-turn section, due to its smallest radius of curvature.
... About 5% of the total mass of tyre wear is estimated to be small enough to become airborne as PM. The mass size distribution shows bimodal maxima in the fine (< 2.5 μm) and very coarse range (> 10 μm) (Kreider et al., 2010). This produces only a small amount of tyre wear in the coarse mode (PM 2.5−10 ). ...
Air pollution is a risk to human health, especially in urban areas. While exhaust emissions from road traffic have decreased over the last decades, non-exhaust emissions remain and tend to increase. In this study, tyre and brake wear emissions are quantified applying a bottom-up model for the city of Hamburg in 2018. Their dispersion and contribution to total particulate matter (PM) concentrations are investigated with the urban scale chemistry transport model EPISODE-CityChem. For this purpose, EPISODE-CityChem has been extended to include six new particle components. These are tyre and brake wear in three size classes, PM 2.5 , PM 2.5−10 and PM 10+ , each. PM concentrations at traffic stations show a higher monthly mean contribution of tyre and brake wear to the total PM 2.5 and PM 10 than at urban background stations. The sum of airborne tyre and brake wear can locally exceed annual mean concentrations of 10 μg m −3 , with the highest concentrations in the inner city of Hamburg. The contribution of tyre and brake wear to the total particle concentrations varies locally and seasonally, which could be a difficulty in adhering to the recommended guideline values for particle concentrations. The results of this study can be transferred to other large European cities with high traffic volumes and can help to understand the problem's scope, as measurements rarely differentiate between particles caused by exhaust vs. non-exhaust emissions.
... 10−12 Our own work has sought to measure tire elemental tracers for source apportionment and quantification of tire particles, 13 which are reported to have sizes ranging from less than 10 nm to more than 100 μm. 14,15 The emission factors of airborne tire wear particles must be estimated such that meaningful health impacts can be studied based on representative exposures. Further, these factors play a critical role in the development of standards for industrial manufacturers and whether environmental policies should be developed targeting tire emissions, such as PM 10 . ...
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.
... The sample was sequentially filtered by a stainless steel mesh filter with a mesh size of 105, 40 or 10 μm (DM-25-105, DM-25-040 or DM-25-010, respectively, Mossfil Co., Ltd, Japan). These filter sizes were decided in reference to previous studies (Kreider et al. 2010;Leads & Weinstein 2019). The number of particles obtained for validation purposes was 370, 199, and 90 for the 10-40 μm, 40-105 μm, and 105 μm-4.75 mm ranges, respectively. ...
Introducing microplastics (MPs) into the marine environment is a global problem. Tire-derived microplastics (TMPs) are estimated to account for 60% of all secondary MPs dispersed in aquatic environments. To effectively detect TMPs in environmental samples using micro-Fourier transform infrared (μFTIR) spectroscopy, a high-quality reference library is essential. However, the use of conventional diamond crystals in FTIR presents challenges for the detection of materials containing carbon black, such as rubber and tires. In addition, there is a discrepancy between spectra from standard libraries and spectra from environmental samples, which makes detection difficult. In order to overcome these problems in the detection of TMPs by μFTIR, we developed four reference libraries to improve the detection, and ‘The 26 tire wear library’ was found to be the best among these four. Furthermore, a comparison of these new libraries revealed the following requirements to improve TMP detection: (i) the reference spectra must be acquired under the same setup used for material observation including prism material, (ii) tires, not rubber, must be used as reference materials, and (iii) tire wear samples must be prepared to replicate the actual generation conditions on roads.
... Due to the limitation on the number of element species from other available published data, only a part of the elements was listed in this section. In addition, the total concentrations of PAHs and their BaP eq values in industrial sectors (including power industry 22,72-74 , iron & steel industry 22,72 , and cement industry 72 ), residential sectors (including coal [75][76][77][78] , biomass burning 21,67,[78][79][80] , and cooking emission 81 ), and transportation sectors (including exhaust of vehicles and ships 68,[82][83][84] , and non-exhaust emission from vehicles 85,86 ) were selected to make comparison with other studies, which could comprehensively reflect the overall level of source-specific PAHs and their carcinogenic potency. ...
Particulate matter (PM) emissions from anthropogenic sources contribute substantially to air pollution. The unequal adverse health effects caused by source-emitted PM emphasize the need to consider the discrepancy of PM-bound chemicals rather than solely focusing on the mass concentration of PM when making air pollution control strategies. Here, we present a dataset about chemical compositions of real-world PM emissions from typical anthropogenic sources in China, including industrial (power, industrial boiler, iron & steel, cement, and other industrial process), residential (coal/biomass burning, and cooking), and transportation sectors (on-road vehicle, ship, and non-exhaust emission). The data was obtained under the same strict quality control condition on field measurements and chemical analysis, minimizing the uncertainty caused by different study approaches. The concentrations of PM-bound chemical components, including toxic elements and PAHs, exhibit substantial discrepancies among different emission sectors. This dataset provides experimental data with informative inputs to emission inventories, air quality simulation models, and health risk estimation. The obtained results can gain insight into understanding on source-specific PMs and tailoring effective control strategies.
Sewage treatment plants (STPs) act as either sinks or sources of microplastic (MP) contamination in the environment. This study examined and assessed the occurrence, removal efficiencies, abundance and characteristics of MPs in two STPs in Chennai, India. Large volumes of influent and effluent water were collected and filtered on site via a filter in a series system. The samples were later treated in the laboratory to isolate the MPs from other organic and inorganic particles. The MPs were analysed via Fourier Transform Infra-Red (FTIR) spectroscopy and Raman spectroscopy to analyse the chemical composition of the isolated microplastics. Pollution load index (PLI) and EU classification, labelling and packaging (CLP) standard was incorporated to assess the pollution risk of MPs in STP. According to the results obtained from this research work, the MP concentrations in the influent waters were high for both STPs (5443 MPs/L and 4800 MPs/L). Although the MP removal efficiency of the STPs were quite high (~96 % and ~93 %), the pollution load indices at Kodungaiyur and Koyambedu STPs were observed to be 0.272 and 0.208 respectively, which were moderately contaminated. PORI scores revealed that Kodungaiyur Plant is in danger level I with the hazard score of 9.25 and Koyambedu plant is in danger level II with the hazard score of 12.78. The estimated quantity of the MPs discharged from the monitored STPs was approximately 28.4 & 28.2 billion MPs/day.
Tire and brake-wear emissions, in particular nanoparticulate aerosols, can potentially impact human health and the environment adversely. While there is considerable phenomenological data on tire wear, the creation and environmental...
Tire wear particles (TWP) originating from tire abrasion on roads are a major source of microplastics to the environment. Together with associated pollutants like polycyclic aromatic hydrocarbons and trace metals, TWP are emitted to roadside soils in the immediate vicinity of road networks. Our study aimed at quantifying TWP number and mass concentrations and investigating particle features in low-traffic roadside soils using a novel particle-based analytical approach. On the example of fifteen Swiss cantonal roadside soils, with average daily traffic volumes of 2,290 vehicles per day− 1, we sampled composite samples from distances of 1, 2, 5 and 10 m to the roadside. TWP were extracted via density separation and wet-chemical sample purification. TWP analysis was performed using microscope images and trainable Weka segmentation image analysis. Furthermore, associated road pollutants like polycyclic aromatic hydrocarbons, benzop[a]pyrene and trace metals were analysed using TQ GC-MS/MS and ICP-MS. We found average concentrations of 111,000 TWP per kg soil dry weight (TWP kg− 1) highest values reaching 615,000 TWP kg− 1 and mean TWP masses of 52.7 ± 83.2 mg TWP kg− 1. TWP had a minimal Feret diameter of 62.8 ± 45.6 μm on average and showed mean circularity values of 0.7 ± 0.2, resulting in elliptic particle morphology. TWP concentrations and sizes decreased with increasing distance from the road. Positive relationships were found between TWP numbers and polycyclic aromatic hydrocarbons, benzop[a]pyrene and zinc concentrations in roadside soils. However, a moderate relationship to speed limits was identified. We were able to demonstrate that even in low-traffic areas, roadside soils act as an environmental sink for high concentrations of TWPs and associated pollutants and that spatial distribution and the spread of TWP to soils strongly dependent on the distance to the road.
Microplastics (MPs) have become pervasive pollutants in terrestrial ecosystems, raising significant ecological risks and human health concerns. Despite growing attention, a comprehensive understanding of their quantification, sources, emissions, transport, degradation, and accumulation in soils remains incomplete. This review synthesizes the current knowledge on the anthropogenic activities contributing to soil MP contamination, both intentional and unintentional behaviors, spanning sectors including agriculture, domestic activities, transportation, construction, and industry. Furthermore, it examines the spatial distribution, accumulation, and abundance of MPs across various land use types, alongside a critical assessment of existing quantification methodologies. While the predominant metric for MP quantification is particle number concentration, integrating mass and area concentration enhances the ability to compare pollution levels, assess fluxes, and conduct risk analyses. Additionally, the review explores the transport behavior of MPs in soil, distinguishing between external mechanisms (abiotic factors: wind, leaching, and runoff, biotic factors: soil bioturbation and food chain interactions), and internal mechanisms that are impacted by the characteristics of MPs themselves (e.g., shape, color, size, density, surface properties), soil properties (e.g., porosity, pH, ionic strength, organic matter and mineral content), coexisting substances, and soil structural dynamics. The study of MP transport in soil remains in its early stages, with substantial gaps in knowledge. Future research should focus on integrating number, mass concentration, and area concentration for the more holistic quantification of MP abundance, and prioritize the development of more accurate and efficient methodologies. In addition, the investigation of MP transport and degradation processes under varying environmental conditions and soil management practices is critical for addressing this emerging environmental challenge.
Plastic pollution poses a substantial environmental challenge on global scale. Recently, tyre and road wear particles (TRWPs) have been recognized as a source of microplastic pollution to the freshwater environment. Whilst there is a growing concern regarding the potential environmental effects of microplastics, TRWPs are especially concerning because of the additives they have. These additives are utilised in the manufacturing of tyres; persist in the final product; become environmentally available; and may pose significant threats to an ecosystem. A current issue is the identification of specific constituents of TRWPs responsible for these threats. A comprehensive review of the existing literature is presented focusing on the physical and chemical characteristics of TRWPs with the aim to identify suitable marker(s). Wear particles derived from tyre tread possess distinctive a sausage shape that is exclusive to TRWPs. A range of chemical additives linked to tyres have been employed to quantify TRWPs, overlooking other potential sources such as brake wear and exhaust emissions. We found that significant amounts of 6PPD is used for the formulation of tyres, which is why 6PPD, and a comparatively stable transformation product 6PPD-quinone, could be used for the identification of TRWPs. We recommend that sampling and analysis methods be thoroughly documented to enhance the reproducibility.
With the electrification of road vehicles leading to a reduction in tailpipe emissions, the relative contribution of non-exhaust emissions (NEEs) has become increasingly prominent. NEEs, particularly nanoparticles smaller than 100 nm in aerodynamic diameter (PM0.1), present significant health and environmental risks. A comprehensive understanding and strategic management of these emissions are urgently required to mitigate their impact. This article reviews existing studies and reveals that nanoparticles in NEEs are generated from brake and tyre wear under critical temperature conditions, while road wear and resuspension do not directly produce nanoparticles but contribute to larger particles. Common methodologies in studying these emissions include laboratory experiments (with brake dynamometers, tyre dynamometers, chassis dynamometers, and simulators), field tests (tunnel and real road emission tests), and source apportionments. The emission rate of PM0.1, calculated based on particle number concentration, ranges from 1.2% to 98.9%, depending on driving conditions. Extreme driving conditions result in high nanoparticle generation. Emission inventories reveal that PM0.1 emission levels have remained stable since 2020, without an observable reduction. Moreover, emissions attributable to brake wear are found to surpass those from tyre wear. Current mitigation strategies focus on material improvements for brake pads and tyres, better road maintenance, and regulatory measures. Mitigating the environmental and health impacts of nanoscale particulate matter requires additional research and regulations to control it at the source.
Pavement surface texture significantly contributes to tire wear and tire-pavement friction. Currently available relationships quantify tire wear and tire-pavement friction simply in terms of empirical pavement texture parameters. The objective of this paper is to present correlations with which the tire wear rate and tire-pavement friction on smooth concrete pavements can be predicted using actual texture properties. Using a laboratory tire wear simulator and an aircraft tread-rubber block, a number of wear and friction tests are performed on pavement samples having different fine aggregate sizes. Frequency characteristics of the texture of the pavements are achieved by decomposing the profilometer measurements using the fast Fourier transform technique and constructing power spectral density plots of texture over surface spatial frequency. Then the tire wear rates as well as dry friction and wet friction of the tire-pavement interface are correlated to microtexture and macrotexture components of the texture power spectral density. The developed correlations indicate that both tire wear and dry friction are significantly affected by pavement microtexture. The developed wear correlations can be also useful for predicting the wear index of a pavement based on conventional Mu-meter and grease patch test results. This is illustrated by an example in which the wear index for a concrete runway pavement at Luke Air Force Base, Ariz., is computed using the new relations.
Samples of creek bed sediment collected near seal-coated parking lots in Austin, Texas, by the City of Austin during 2001-02 had unusually elevated concentrations of polycyclic aromatic hydrocarbons (PAHs). To investigate the possibility that PAHs from seal-coated parking lots might be transported to urban creeks, the U.S. Geological Survey, in cooperation with the City of Austin, sampled runoff and scrapings from four test plots and 13 urban parking lots. The surfaces sampled comprise coal-tar-emulsion-sealed, asphalt-emulsion-sealed, unsealed asphalt, and unsealed concrete. Particulates and filtered water in runoff and surface scrapings were analyzed for PAHs. In addition, particulates in runoff were analyzed for major and trace elements. Samples of all three media from coal-tar-sealed parking lots had concentrations of PAHs higher than those from any other types of surface. The average total PAH concentrations in particulates in runoff from parking lots in use were 3,500,000, 620,000, and 54,000 micrograms per kilogram from coal-tar-sealed, asphalt-sealed, and unsealed (asphalt and concrete combined) lots, respectively.
In a road simulator study, a significant source of sub-micrometer fine particles produced by the road–tire interface was observed. Since the particle size distribution and source strength is dependent on the type of tire used, it is likely that these particles largely originate from the tires, and not the road pavement. The particles consisted most likely of mineral oils from the softening filler and fragments of the carbon-reinforcing filler material (soot agglomerates). This identification was based on transmission electron microscopy studies of collected ultrafine wear particles and on-line thermal treatment using a thermodesorber.The mean particle number diameters were between 15–50 nm, similar to those found in light duty vehicle (LDV) tail-pipe exhaust. A simple box model approach was used to estimate emission factors in the size interval 15–700 nm. The emission factors increased with increasing vehicle speed, and varied between 3.7×1011 and 3.2×1012 particles vehicle−1 km−1 at speeds of 50 and 70 km h−1. This corresponds to between 0.1–1% of tail-pipe emissions in real-world emission studies at similar speeds from a fleet of LDV with 95% gasoline and 5% diesel-fueled cars. The emission factors for particles originating from the road–tire interface were, however, similar in magnitude to particle number emission factors from liquefied petroleum gas-powered vehicles derived in test bench studies in Australia 2005. Thus the road–tire interface may be a significant contributor to particle emissions from ultraclean vehicles.
Pulmonary responses in rats were compared after short-term inhalation exposure to polymorphs of silica dust. Groups of CD rats were exposed 6 h a day for 3 d to crystalline silica or amorphous silica. Another group was exposed to Ludox colloidal silica for 6 h a day, 5 d a week for two or four weeks. Thereafter the groups were killed, and the lungs washed at several postexposure times. The crystalline silica produced persistent pulmonary inflammatory responses characterized by neutrophil recruitment and consistently elevated biomarkers of cytotoxicity in bronchoalveolar lavage fluids, and progressive histopathological lesions were observed within one month of the exposure. Amorphous silica produced a transient pulmonary inflammatory response, and Ludox elicited transient pulmonary inflammatory responses at 50 or 150 mg center dot m-3 but not at 10 mg center dot m-3. After three months most of the biochemical values of the Ludox-exposed animals had returned to the control level. These results demonstrate that crystalline silica dust is more potent in producing pulmonary toxicity when compared with amorphous or colloidal silica particles.
Tire dust is a significant pollutant, especially as a source of zinc in the urban environment. This study characterizes the morphology and chemical composition of heavy metal particles embedded in tire dust and traffic-related materials (brake dust, yellow paint, and tire tread) as measured by a field emission scanning electron microscope equipped with an energy dispersive X-ray spectrometer (FESEM/EDX). In 60 samples of tire dust, we detected 2288 heavy metal particles, which we classified into four groups using cluster analysis according to the following typical elements: cluster 1: Fe, cluster 2: Cr/Pb, cluster 3: multiple elements (Ti, Cr, Fe, Cu, Zn, Sr, Y, Zr, Sn, Sb, Ba, La, Ce, Pb), cluster 4: ZnO. According to their morphologies and chemical compositions, the possible sources of each cluster were as follows: (1) brake dust (particles rich in Fe and with trace Cu, Sb, and Ba), (2) yellow paint (CrPbO(4) particles), (3) brake dust (particulate Ti, Fe, Cu, Sb, Zr, and Ba) and heavy minerals (Y, Zr, La, and Ce), (4) tire tread (zinc oxide). When the chemical composition of tire dust was compared to that of tire tread, the tire dust was found to have greater concentrations of heavy metal elements as well as mineral or asphalt pavement material characterized by Al, Si, and Ca. We conclude that tire dust consists not only of the debris from tire wear but also of assimilated heavy metal particles emitted from road traffic materials such as brake lining and road paint.
Background
It is estimated that over 80% of respirable particulate matter (PM10) in cities comes from road transport and that tire and brake wear are responsible for the 3–7% emission of it. Data on the indicators of environmental impact of tire debris (TD), originated from the tire abrasion on roads, are extremely scarce, even though TD contains chemicals (zinc and organic compounds) which can be released in the environment.
Methods
TD particle morphology was analysed with SEM, TEM and FIB instruments. TD eluates and TD organic extracts were tested at dilution series on human cell lines and Xenopus laevis embryos. 50 and 100 g/L TD were used for the eluates obtained after 24 h at pH 3 and the quantity of zinc present was measured with a ICP-AES. Eluates diluted to 1%, 10%, 50% in culture media and undiluted were used on X. laevis embryos in the FETAX test. HepG2 cells were exposed for 24 h to 0.05 – 50 μg/ml of zinc salt while A549 cells were exposed for 24, 48 and 72 h to 10, 50, 60, or 75 μg/ml of TD extract. X. laevis embryos were exposed to 50, 80, 100, or 120 μg/ml TD extract.
Results
The solution of undiluted 50 g/L TD produced 80.2% mortality (p < 0.01) in X. laevis embryos and this toxic effect was three times greater than that produced by 100 g/L TD. Zn accumulation in HepG2 cells was evident after 4 h exposure. A549 cells exposed to TD organic extract for 72 h presented a modified morphology, a decrease in cell proliferation and an increase in DNA damage as shown by comet assay. The dose 80 μg/ml of TD extract produced 14.6% mortality in X. laevis embryos and 15.9% mortality at 120 μg/ml. Treatment with 80, 100, or 120 μg/ml TD organic extract increased from 14.8% to 37.8% malformed larvae percentages compared to 5.6% in the control.
Conclusion
Since the amount of Zn leached from TD is related to pH, aggregation of particles and elution process, the quantity of TD present in the environment has to be taken into account. Moreover the atmospheric conditions, which may deeply influence the particle properties, have to be considered. The TD organic fraction was toxic for cells and organisms. Thus, because of its chemical components, TD may have a potential environmental impact and has to be further investigated.
Road dust contributes a large percentage of the atmosphere's suspended particles in Taiwan. Three road dust samples were collected from downtown, electrical park, and freeway tunnel areas. A mechanical sieve separated the road dust in the initial stage. Particles > 100 microm were 75%, 70%, and 60% (wt/wt), respectively, of the samples. Those particles < 37 microm were resuspended in another mixing chamber and then collected by a Moudi particle sampler. The largest mass fraction of resuspended road dust was in the range of 1-10 microm. Ultrafine particles (< 1 microm) composed 33.7, 17, and 7.4% of the particle samples (downtown, electrical park, and freeway tunnel, respectively). The road dust compositions were analyzed by inductively coupled plasma (ICP)-atomic emissions spectroscopy and ICP-mass spectrometry. The highest concentration fraction contained more aluminum (Al), iron (Fe), calcium (Ca), and potassium than other elements in the road dust particle samples. Additionally, the sulfur (S) content in the road dust from the electrical park and freeway tunnel areas was 2.1 and 3.4 times the downtown area sample, respectively. The sulfur originated from the vehicle and boiler oil combustion and industrial manufacturing processes. Furthermore, zinc (Zn) concentration in the tunnel dust was 2.6 times that of the downtown and electrical park samples, which can be attributed to vehicle tire wear and tear. Resuspended road dusts (< 10 microm) from the downtown and freeway tunnel areas were principally 2.5-10 microm Al, barium (Ba), Ca, copper (Cu), Fe, magnesium (Mg), sodium (Na), antimony (Sb), and Zn, whereas arsenic (As), chromium (Cr), and nickel (Ni) were predominant in the ultrafine particle samples (< 1 microm). Al, Ba, and Ca are the typical soil elements in coarse particles; and As, and Cr and Ni are the typical fingerprint of oil combustion and vehicle engine abrasion in ultrafine particles. There was a special characteristic of resuspension road dust at electrical park, that is, many elements, including As, Ba, Ca, cadmium, Cr, Cu, Fe, manganese (Mn), Ni, lead (Pb), S, vanadium (V), and Zn, were major in ultrafine particles. These elements should be attributed to the special manufacturing processes of electric products.
In regions where studded tyres and traction material are used during winter, e.g. the Nordic countries, northern part of USA, Canada, and Japan, mechanically generated particles from traffic are the main reason for high particle mass concentrations in busy street and road environments. In many Nordic municipalities the European environmental quality standard for inhalable particles (PM(10)) is exceeded due to these particles. In this study, particles from the wear of studded and studless friction tyres on two pavements and traction sanding were generated using a road simulator. The particles were characterized using particle sizers, Particle Induced X-Ray Emission Analysis and electron microscopy. Cell studies were conducted on particles sampled from the tests with studded tyres and compared with street environment, diesel exhaust and subway PM(10), respectively. The results show that in the road simulator, where resuspension is minimized, studded tyres produce tens of times more particles than friction tyres. Chemical analysis of the sampled particles shows that the generated wear particles consist almost entirely of minerals from the pavement stone material, but also that Sulfur is enriched for the submicron particles and that Zink is enriched for friction tyres for all particles sizes. The chemical data can be used for source identification and apportionment in urban aerosol studies. A mode of ultra-fine particles was also present and is hypothesised to originate in the tyres. Further, traction material properties affect PM(10) emission. The inflammatory potential of the particles from wear of pavements seems to depend on type of pavement and can be at least as potent as diesel exhaust particles. The results imply that there is a need and a good potential to reduce particle emission from pavement wear and winter time road and street operation by adjusting both studded tyre use as well as pavement and traction material properties.
Each rubber formulation contains a carefully chosen mixture of chemicals which will react together during vulcanization to produce a new compound with properties suitable for its intended purpose. Many of the chemicals used in these formulations contain active groupings to enable them to effect these reactions, and perhaps because of this chemical activity many of them are likely to possess potential health hazards. The subject is discussed in three parts. Part I reviews the investigations which have been carried out on various aspects of health in the industry, with particular attention to the epidemiological studies. Part II contains details of health effects for the common rubber chemicals. The chemicals concerned have been grouped into nine classes according to their function in rubber processing, and are covered in Chapters 4-12. For simplicity of presentation, a standard format has been used wherever possible for each chemical with the structure of the materials shown and information given on proprietary names, physical form, acute toxic effects, skin and eye irritation and chronic toxic effects. Part III deals with physiological effects of chemicals, toxicological testing and atmospheric monitoring. Extensive bibliographic data are included.
The rubber mix for a tyre consists of several compounds. Depending on their different chemical and physical properties, some of the materials have to be regarded as a possible hazard to health, especially if they are not handled properly. In this paper a short overview is given about hazardous substances in a tyre factory, the situation concerning special hazardous substances in the German tyre industry, German legislation aspects and activities of the Ge/ man and European Rubber Manufacturers' Associations.
Proton induced X-ray emission (PIXE) is a spectroscopic analysis technique based on detecting the emitted radiation from an atom excited upon interaction with a high-energy proton. It has been used to quantitatively determine to ppm levels, the elements present in a variety of substrates including inorganic, organic and biological samples. The technique is particularly applicable to quantifying the inorganic materials present in rubber compounds: non-black fillers (clay, silica, talc), oxides (magnesium, titanium, zinc), cobalt adhesion promoters and total sulfur. The non-destructive nature of the experiment and facile sample preparation make PIXE measurements particularly useful when only small quantities of material are available. PIXE in conjunction with characterization techniques that afford structural information of specific compounding ingredients, can afford precise analytical characterizations of rubber compounds.
A study is reported which was undertaken to determine what happens to this tread material; whether or not the particulate matter remains airborne for long periods and hence constitutes an air pollutant in the usual sense. Extensive experimental data are presented and discussed. Airborne particulate matter worn from tires has been detected in the atmospheres of two vehicle tunnels and in the open air. The amount is about 20 per cent as great as that from vehicle exhausts, and represents a small fraction of the tread material that wears from tires. Tread rubber was found on tunnel walls and in roadside dust, dustfall, and topsoil. A material balance shows that most of the material lost by tires in service is particulate matter, of which only a small fraction is airborne.
In the reported experimental program, a tire emission facility has been built in which several tire-wear modes can be simulated while the gaseous, airborne particulate, and sedimentary particulate emissions are collected. The facility was shown to produce tire temperatures and wear rates typical of operating tires. Experimental data are tabulated, plotted, and evaluated. It was demonstrated that the emission rate of gases and airborne particulate matter was nearly independent of wear rate and accounted for only 1-20% of the total emissions. The balance of the emissions were large particles which would be expected to settle on or very close to roadways. Chemical analysis of these large particles showed that approximately 30% of the SBR is unvulcanized, compared to only 1-2% in the tread. The total organic content of the particles was unchanged. This degradation of the rubber leads to enhanced oxygen absorption rates. However, the full significance of the increased rate of oxidation is not known.
This paper describes the evolution of elastomer/rubber wear debris morphology from the in situ leading to trailing edges of sliding contacted wear surfaces. Special attention is given to establishing the role of grit size, slip rate, and contact length on the formation of wear particles, as well as the subsequent in situ aggregation of such product into a hierarchy of particulate material. Of specific interest is the determination of the in situ mass/number count partitioning between true wear particles and aggregates. This population balance is achieved by establishing and monitoring the morphological signature of the various particle types as one moves along various in situ positions to the wake location. The validity/reliability of the empirical trends obtained are verified through the use of the appropriate statistical measures.
Tires wear out in normal use. Tread rubber losses were investigated to find out if the rubber abrades to particles, degrades to an intermediate state, or oxidizes to volatile vapors and gases. Particulate erosion seems to be the dominant mechanism. Particles worn from tires were first collected on sticky panels mounted under the car. The particles are not spherical, but approach cylinders or sausage shapes as a limit. The particles range from about 0.1 mm, equivalent diameter, to a few microns minimum, in accord with the Schallamach description of tire abrasion. Later an isokinetic filter system was developed. The particles caught on filter plates were examined, transferred to microscope slides, photographed, then counted to obtain particle size distributions. Smooth distributions were obtained, linear on logarithm of volume, cumulative probability graphs. The geometric mean particle size is about 20 μ equivalent diameter. The curve is sharply peaked on its log scale. Special effort was devoted to a search for very small particles, from about 1/2 to 3 μ equivalent diameter. This is the diminishing tail on the distribution curve. Very few of these particles could be found. Attempts were made to identify volatile emissions from a running tire using chromatographic techniques and a flame ionization detector without success. Since hydrocarbon loss as a vapor from tires is nil, particulate erosion is the dominant loss mechanism. Tire dust particles have a high specific surface and are subject to oxidation. Simple chemical oxidation is slow, but biochemical oxidation at the soil surface under the combined influence of oxygen, photoexcitation, and enzyme catalysis can be rapid, returning the carbon content to the normal biological carbon cycle.
To measure traffic pollutants with high temporal and spatial resolution under real conditions a mobile laboratory was designed and built in Helsinki Polytechnic in close co-operation with the University of Helsinki. The equipment of the van provides gas phase measurements of CO and NOx, number size distribution measurements of fine and ultrafine particles by an electrical low pressure impactor, an ultrafine condensation particle counter and a scanning mobility particle sizer. Two inlet systems, one above the windshield and the other above the bumper, enable chasing of different type of vehicles. Also, meteorological and geographical parameters are recorded. This paper introduces the construction and technical details of the van, and presents data from the measurements performed during an LIPIKA campaign on the highway in Helsinki. Approximately 90% of the total particle number concentration was due to particles smaller than 50 nm on the highway in Helsinki. The peak concentrations exceeded often 200,000 particles cm−3 and reached sometimes a value of 106 cm−3. Typical size distribution of fine particles possessed bimodal structure with the modal mean diameters of 15–20 nm and ∼150 nm. Atmospheric dispersion of traffic pollutions were measured by moving away from the highway along the wind direction. At a distance of 120–140 m from the source the concentrations were diluted to one-tenth from the values at 9 m from the source.
The shift from explosive to effusive silicic volcanism seen in many historical eruptions reflects a change in the style of degassing of erupted magma. This paper focuses on such a transition during the largest eruption of the twentieth century, the 1912 eruption of Novarupta. The transition is recorded in a dacite block bed, which covers an elliptical area of 4 km2 around the vent. Approximately 700 studied blocks fall into four main lithologic categories: (1) pumiceous, (2) dense, (3) flow-banded dacites, and (4) welded breccias. Textural analyses of the blocks indicate portions of the melt underwent highly variable degrees of outgassing. Vesicle populations show features characteristic of bubble coalescence and collapse. A decrease in measured vesicularity and increased evidence for bubble collapse compared with pumice from earlier Plinian episodes mark the transition from closed- to open-system degassing. Block morphology and textures strongly suggest the magma was first erupted as a relatively gas-rich lava dome/plug, but incomplete out-gassing led to explosive disruption. Heterogeneous degassing of ascending magma began in Plinian Episode III and resulted in instability during Episode IV dome growth and a (series of) Vulcanian explosion(s). Modeling of the dynamics of explosion initiation and ejecta dispersal indicates that a significant concentration in gas is required to produce the explosions responsible for the observed block field dispersal. The amount of gas available in the hot pumiceous dome material appears to have been inadequate to drive the explosion(s); therefore, external water most likely contributed to the destruction.
Road dust samples were collected from central Shanghai in winter (January) and summer (August), respectively. Sixteen polycyclic aromatic hydrocarbons (PAHs) in the United States Environmental Protection Agency (USEPA) priority-controlled list were determined by GC/MS. Total PAH (t-PAH) concentrations in winter samples ranged from 9176 to 32,573ngg−1 with a mean value of 20,648ngg−1, while they varied from 6875 to 27,766ngg−1 in summer with an average of 14,098ngg−1. Spatial variation showed that city park (CP) samples had the lowest t-PAH concentration, while industrial area (ID) and traffic area (TR) and commercial area (CO) were the most polluted, in both seasons. PAH homologues concentrations were getting higher with the more rings and higher molecular weight (HMW) in all areas. The study of effective factors showed that grain size was only a minor factor influencing the accumulation of PAHs, whereas total organic carbon (TOC) was found to be closely correlated with t-PAH concentration. Prevailing winds could directly affect on the spatial distribution of PAHs. Chemical source apportionment studies took the form of principal component analysis (PCA), followed by compositional analysis. It was demonstrated that road dust PAHs in central Shanghai mainly came from the mixing of traffic and coal combustion. The contribution percentages of pyrogenic and petrogenic sources were respectively 71.0% and 11.4% in winter, while they were, 64.9% and 14.1% in summer, respectively. Road dust PAHs in Shanghai city mostly came from local sources.
We propose a new concept to understand the mechanism of rubber abrasion. Friction and fracture in abrasive wear of rubber are linked theoretically and experimentally through the formation of a periodic surface pattern, the abrasion pattern, generated by two kinds of periodic motion, stick-slip oscillation and microvibration.The direct driving force for fracture, i.e. the pattern formation, is the magnitude of the mean strain produced at the surface of the rubber by the two motions. The mean strain amplitude ε∗ is governed by the friction constant μ, Young's modulus E of the material and the normal load P, as ε∗ = μP/ES, where S is the cross-sectional area, which is correlated to the rate of abrasion loss V̇ with the relation, V̇ = dc(ε∗/dn. Thus, abrasive wear of rubber is strongly dependent on fracture resistant properties of the material under repeated deformation of the mean strain amplitude ε∗. Several questions in rubber abrasion remained unanswered are discussed according to the above concept.
The mechanism of rubber abrasion proposed in the previous paper was reconfirmed not only in unfilled and filled NR but in SBR and silicone rubber. It is an essential and general rule in rubber abrasion that the microvibration induced in the slip phase of stick-slip oscillation generates the initial abrasion patterns and the stick-slip motion propagates them to the final abrasion patterns. The initial pattern spacing agrees with the distance determined by the relation between the natural frequency of the material and the mean sliding velocity, meanwhile the final pattern spacing in the propagation reaches the distance given by the frequency of the stick-slip oscillation and the mean sliding velocity. Reinforcement by carbon blacks makes the frequencies of the both periodic motions in rubber larger, which of course gives the smaller initial and final pattern spacings in rubber abrasion. In addition, the microvibration attenuates more rapidly in more filled rubbers when it spreads over the rubber surface as a surface wave. Both phenomena have a great influence on the smaller abrasive wear of more filled rubbers.
This paper is directed to air pollution scientists interested in special mobile emission sources. The purpose was to determine the contribution which automobile tires make to air pollution. The gaseous hydrocarbon and sulfur compounds emitted in laboratory tests were identified. Although these hydrocarbons can participate in smog reactions, their mass emission rate is less than 0.1 % of the current exhaust hydrocarbon emission rate. Hydrocarbons from tires are not measurable near a freeway. The particulate emitted from tires ranges in size from 0.01 μm to more than 30 μm, with the larger particles dominating the total mass. Measurements along a California freeway showed that most of the tire debris had settled within 5 m of the pavement edge. Airborne rubber concentrations were less than 0.5 μg/m, or less than 5% of the total tire wear. These field measurements confirm the indoor emission pattern and verify that tire wear products are not a significant air pollution problem.
The driving force to generate the periodic surface patterns, and thus rubber abrasion consists of two kinds of periodic motions, stick-slip oscillation and the microvibration generated during frictional slidings of rubber. The stick-slip oscillation is the driving force to propagate cracks, then abrasion patterns and the microvibration with the natural frequency of the rubber induced in the slip phase of the stick-slip oscillation is another driving force for the initiation of the cracks. Although initial cracks originate in the slip region of the rubber surface, the propagation of the cracks is strongly excited in the stick region. Accordingly, the initial size of the abrasion pattern, pattern spacing, equals the distance determined by the natural period of the rubber and the mean sliding velocity while the constant pattern spacing after the critical number of frictional slidings agrees with the distance given by the period of the stick-slip oscillation and the mean sliding velocity. Consequently, during rubber abrasion, two driving forces produce bimodal size distribution of abraded particles, small particles of the order of ten micrometres by microvibrations and large ones of the order of a few hundred micrometres by the stick-slip motions.
Molecular distributions of polycyclic aromatic hydrocarbons (PAHs) in street dust samples collected from the Tokyo metropolitan area were determined by capillary gas chromatography following HPLC fractionation. Sixty-four compounds including three- to six-ring PAHs and sulfur heterocyclics were identified by capillary GC/MS. Total PAH concentrations were in the range of a few micrograms per gram of dust. The source materials (automobile exhaust, asphalt, fuel-oil combustion products) were also analyzed. The PAH profile, especially relative abundance of alkyl-PAHs and sulfur-containing heterocyclics, indicated that PAHs in the street dusts on the heavily trafficked streets are strongly affected by automobile exhaust and those in the residential area have a somewhat more significant contribution from combustion products in stationary sources. With both types of dusts, asphalt is through to contribute only a minor part of their PAHs.
More than 100 organic compounds are quantified in these samples, including n-alkanes, n-alkanoic acids, n-alkenoic acids, n-alkanals, n-alkanols, benozoic acids, benzaldehydes, polyalkylene glycol ethers, PAH, oxy-PAH, steranes, hopanes, natural resins and other compound classes. Paved road dust acts as a repository for vehicle-related particles, which can then be resuspended by the passing traffic. To evaluate the contributions from major urban sources to the road dust complex, source profiles representing different types of vehicle exhaust, brake dust, tire debris, and vegetative detritus are compared, and their fractional contributions are estimated using several groups of organic tracer compounds. -from Authors
In order to investigate the sources of roadside heavy metal pollution, auto tire, gasoline, gas oil, kerosene, paint for road markings (white, yellow and red), the soot from the discharge spout, auto tire rubber, asphalt pavement, gray paint and anticorrosive on the guardrail were gathered together and analyzed. As a consequence, Pb may be originally from yellow and red road markings, and gray paint or anticorrosive. Hg is mainly emitted from the combustion of premium gasoline and diesel soot is an important source of As, Ni and Zn. Cd and Zn are mainly emitted from the abrasion of tire rubber. The wear of asphalt pavement is considered to be a source of Ni and V.
Tire debris is produced by the normal wear of tires. Two problems are addressed herewith: characterization of debris particles and their identification in heterogeneous specimens, which come from laboratory wear tests and from the environment. Both problems are solved by analytical electron microscopy (EM). The scanning electron microscope (SEM) shows that tire debris has a typical, warped surface and pores, and that its characteristic elements, detected by energy dispersive X-ray spectroscopy (EDXS), are S and Zn. As a consequence, the identification of tire debris particles in heterogeneous laboratory specimens is straightforward. In those environmental specimens (road dust), where Zn cannot be detected, identification is possible in some cases, provided morphology, microanalysis, and X-ray mapping are combined. The analytical transmission electron microscope characterizes tire debris on the sub-micrometer scale by imaging, EDXS, and electron diffraction patterns. The microstructure exhibits typical elastomer–filler clusters. The representative elementary volume is found to be approximately 8×10−23 m3.
The concentrations of Cd, Cu, Pb and Zn in atmospheric particulates, roadside dust and soils have been determined along a major arterial highway in East London. Metal levels along the roadway were found to be elevated relative to those observed at a background site. Airborne Pb concentrations were within the E.C. Directive limit value of 2000 ng m−3. Soil metal levels were found to decline rapidly with distance from the road.
Twenty-six elements have been determined in street dust from London (U.K.), New York (U.S.A.), Halifax (Canada), Christchurch (N.Z.) and Kingston (Jamaica). The cities divide into two groups, London and New York (large urban) and Halifax, Christchurch and Kingston (small urban). The elements fall into two groups, those that originate mainly from soil (e.g. Al, K, Na, Th, Ce, La, Sm and Ti), and those (e.g. Ca, Cd, Pb, Cr, Zn, Cu and Au) that primarily originate from other sources, including cement, tyre wear, car emissions and salt. The first group of elements are in lower concentration in London and New York than in the other cities, while the reverse holds for the second group of elements. The concentrations of most elements increase with decrease in the size of the dust particles. The metals, Cd, Pb, Cu, Zn, Mn and Fe were sequentially extracted from the dust into five fractions, exchangeable metal, carbonate bound metal, MnFe oxide bound metal, organic bound metal and the residue.
A large fraction of urban PM10 concentrations is due to non-exhaust traffic emissions. In this paper, a mobile measurement system has been used to quantify the relative importance of road particle emission and suspension of accumulated dust versus direct pavement wear, tire type (studded, friction, and summer), pavement type, and vehicle speed. Measurements were performed during May–September on selected roads with different pavements and traffic conditions in the Stockholm region. The highest particle mass concentrations were always observed behind the studded tire and the lowest were behind the summer tire; studded-to-summer ratios were 4.4–17.3 and studded-to-friction ratios were 2.0–6.4. This indicates that studded tires lead to higher emissions than friction and summer tires regardless to the asphalt type. By comparing with measurements in a road simulator, it could be estimated that the pavement wear due to the friction tires was 0.018–0.068 of the suspension of accumulated road dust. Likewise for studded tires road-wear was estimated to be 1.2–4.8 the suspension of accumulated dust. This indicates that wear due to friction tires is very small compared to the suspension of accumulated dust and that suspension due to studded tires may sometimes be as large as the wear of the road. But this will vary depending on, e.g. the amount of dust accumulated on the roads. An important dependence on vehicle speed was also observed. During May, the particle mass concentrations behind the studded tire at vehicle speed 100 km h−1 were about 10 times higher than that at 20 km h−1. The speed dependence was not so pronounced in September, which could be due to less accumulated dust on the roads. The particle number size distribution of the emissions due to road wear by studded tire was characterized by a clear increase in number concentrations of the coarse fraction of aerosol particles, with a geometric mean diameter between 3 and 5 μm. The size distribution of the emissions due to the summer tire was very similar with smaller concentrations. An important limitation with the measurements presented is that they were made by using a van, which is bigger than regular cars and has bigger tires. Thus, road wear and dust suspension due to cars are expected to be different.
Tire particles (TP) represent a significant component of urban air pollution (PM), constituting more than 10% of PM10 mass at urban locations with heavy traffic. The purpose of this study was to evaluate the effects of size-fractionated TP in an animal exposure model frequently used to assess the health effects of air pollutants. Potential pro-inflammatory and toxic effects of TP2.5 (<2.5 microm) and TP10 (<10 microm) were investigated through instillation of suspensions of these materials in BALB/c mice. Bronchoalveolar lavage fluid (BALF) was screened for total protein, lactate dehydrogenase (LDH), alkaline phosphatase (AP), and beta-glucuronidase (B-Gluc) as markers of cytotoxicity; glutathione (GSH) and superoxide dismutase (SOD) as markers of oxidative potential; and tumor necrosis factor-alpha (TNF-alpha), macrophage inflammatory protein-2 (MIP-2), and inflammatory cells as markers of inflammation. Concomitantly, histological analysis of TP-exposed lungs was performed. A single intratracheal instillation of 10 microg/100 microl, 100 microg/100 microl or 200 microg/100 microl was performed, and after 24h mice were euthanized and BALF examined. Inflammatory cellular profiles showed dose-dependent responses after TP10 exposure, while strong cytotoxic effects, including increases in total protein, LDH and AP, were observed to be associated to TP2.5 exposure. Histologically, TP10-treated lungs mainly showed inflammatory tissue infiltration, in contrast to TP2.5-treated lungs, where lysis of the alveolar barrier appeared to be the most characteristic lesion. Our biochemical, cytological, and histological results indicated differential lung toxicity mechanisms elicited by size-fractionated TP, in agreement with other studies performed in in vivo systems that have shown that lung responses to inhaled or instilled particles are affected by particle size. We conclude that lung toxicity induced by TP10 was primarily due to macrophage-mediated inflammatory events, while toxicity induced by TP2.5 appeared to be related more closely to cytotoxicity.
Seventeen fibrous glasses of diverse type or dimensional distribution induced different incidences of malignant mesenchymal neoplasms when implanted in the pleurae of female Osborne-Mendel rats for periods of more than 1 year. Neoplastic response correlated well with the dimensional distribution of fibers. Fibers less than or equal to 1.5 mu in diameter and greater than 8 mu in length yielded the highest probability of pleural sarcomas, and probability trends suggested that pleural sarcoma incidence increased with increasing lengths of fibers with diameters of less than 1.5 mu, Morphologic observations indicated that fibers less than or equal to 8 mu in length were inactivated by phagocytosis. In fibers greater than 8 mu in length, the correlation of carcinogenicity witth increasing length was difficult to explain. Since neoplastic response to a variety of types of durable fibers, particularly asbestos fibers, was similar, our experiments reinforce the idea that the carcinogenicity of fibers depends on dimension and durability rather than physicochemical properties and emphasize that all respirable fibers be viewed with caution.
The sources and speciation of trace elements in street and house dusts are reviewed. Soil is a major component of both dusts, but a number of elements are enriched in both materials. These include Pb, Zn, Cu, Cd, As, Sb, Cr, Ca, Na, Au, Cl and Br. They arise from a number of contributing and polluting sources. In the case of house dust, some elements, such as Cu, Co, As, Sb, Zn, Cd, Au, Cl, C and Pb, are produced in the house. There are a number of problems associated with the determination of the speciation of trace elements in dusts. These include the low concentrations of many of the elements, and the interpretation of the results from selective sequential extractions. The mobility and potential availability of the trace elements from dust lies in the order Cd greater than Zn, Pb greater than Mn, Cu greater Fe.
The impact of traffic on environmental quality in urban areas has been widely investigated with major emphasis placed on air pollution and associated human health hazards from auto emissions. However, auto emissions are not the only source of metal pollution of the surrounding environments. Auto tires could be an important source of environmental pollution. As a result of wear, tire particles are scattered into the ambient environment and can contaminate it if these particles contain metals. Contributions to environmental pollution from auto tires will depend upon the rate of wear and the concentrations of potential pollutants in them. Information on metal concentrations in auto tires and tire wear coefficient under various road conditions are lacking in the literature. The objectives of this study are to determine metal concentrations in various auto tires and to evaluate metal pollution from auto tires.
In 72 experiments, durable minerals in the form of particles on respirable size and of wide chemical and structural varieties, were implanted in the pleurae of outbred female Osborne- Mendel rats for periods of more than 1 year. The incidence of induced malignant mesenchymal neoplasms correlated well with the dimensional distribution of the particles. The probability of pleural sarcoma correlated best with a number of fibers that measured 0.25 micro or less in diameter and more than 8 micrometer in length, but relatively high correlations were also noted with fibers in other size categories having diameters up to 1.5 micrometer and lengths greater than 4 micrometer. Morphologic observations indicated that short fibers and large-diameter fibers were inactivated by phagocytosis and that negligible phagocytosis of long, thin fibers occurred. The wide variety of compounds used in these experiments suggested that the carcinogenicity of fibers depended on dimension and durability rather than on physicochemical properties.
The quality of pavement runoff water from a 275-m motorway section has been studied for 1 year, during which approximately 50 rain events have been sampled. Two different types of pollution have been revealed. One type can be defined as chronic and includes suspended solids, chemical oxygen demand, total hydrocarbons, zinc and lead. The second type can be considered to be seasonal and incorporates chlorides, sulfates, suspended solids and heavy metals due to the use of deicing salt in winter. Pollutant loading as regards lead appears lower than in previous studies because of the increasing number of vehicles using unleaded gasoline. The study conducted on the sources of pollution and on heavy metal fluxes (Pb, Cu, CD, Zn) released by the traffic has been used to assess a mass balance with respect to pollutant loadings removed by runoff waters. It seems that a large proportion of the lead concentration may disperse in the atmosphere, whereas cadmium sources may be ill-identified or underestimated.
The concentrations of lead, copper, cadmium, zinc, nickel and chromium were measured in road dust and roadside soils from a French major highway. The profiles of total levels in the soil as a function of distance from the road edge and as a function of depth were investigated. Lead, zinc, copper and, to a lesser extent, cadmium contamination were found in samples taken on the surface and in the immediate vicinity of the road. The observed concentrations decreased rapidly with distance and depth. Soil samples appeared to exhibit little nickel and chromium pollution. The geochemical phases on which heavy metals (lead, copper, zinc, cadmium and chromium) were fixed preferentially, as well as the potential mobility of the different metals under certain physical and chemical conditions were evaluated. Sequential extractions and single extractions with different reagents were performed. Chromium, which was present mostly in residual form, was mainly of natural origin in the studied samples and was not highly mobilisable. Cadmium was the most easily exchangeable element in case of variations in the physical and chemical conditions but the quantities involved remained small. Lead and copper did not appear to be highly mobile. Only drastic conditions, such as those that may be produced by accidental spillage of a chemical product (acid or complexing agent), mobilised them quantitatively. A significant risk of mobilisation was to be feared only in the case of zinc, which is very sensitive to acid pH.
Urban stormwater runoff is being recognized as a substantial source of pollutants to receiving waters. A number of investigators have found significant levels of metals in runoff from urban areas, especially in highway runoff. As an initiatory study, this work estimates lead, copper, cadmium, and zinc loadings from various sources in a developed area utilizing information available in the literature, in conjunction with controlled experimental and sampling investigations. Specific sources examined include building siding and roofs; automobile brakes, tires, and oil leakage; and wet and dry atmospheric deposition. Important sources identified are building siding for all four metals, vehicle brake emissions for copper and tire wear for zinc. Atmospheric deposition is an important source for cadmium, copper, and lead. Loadings and source distributions depend on building and automobile density assumptions and the type of materials present in the area examined. Identified important sources are targeted for future comprehensive mechanistic studies. Improved information on the metal release and distributions from the specific sources, along with detailed characterization of watershed areas will allow refinements in the predictions.
The analysis of the 16 polyaromatic hydrocarbons (PAHs) listed as priority pollutants by EPA, was carried out on surface sediments at 32 stations at Todos Santos Bay, Baja California, Mexico. The purpose was to investigate concentration levels, distribution patterns and relate them to three suspected local sources. The PAHs composition of car exhaust, grass and shrubs combustion, and asphalt and tire dust, were all compared to the relative abundance of PAHs signature found on marine sediments of the bay. We used GC-MS analysis in selected ion monitoring (SIM) mode. The total concentration found was low (from 7.6 to 813 ng/g of dry sediment. The average concentration was 96 ng/g). PAHs concentration was somewhat correlated (r = 0.612; P < 0.05) with organic matter content. Surface distributions suggest depositional patterns conforming to the reported water circulation in the bay. The maximum concentration was found near Todos Santos Canyon. The largest concentrations found were those of fluoranthene (120.6 ng/g), Indene(1,2,3-c,d)pyrene (115.6 ng/g) and pyrene (109.9 ng/g). Percentagewise, the main components were PAHs with three and four rings. Several indexes were used to investigate origins including simple PAH ratios and ternary plots. These indexes and plots suggest the main origin as a combination of urban air and wood and brush fires with little influence of oil.
This is the first publication on the distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in riverine and coastal sediments in South East Asia where the rapid transfer of land-based pollutants into aquatic environments by heavy rainfall and runoff waters is of great concern. Twenty-nine Malaysian riverine and coastal sediments were analyzed for PAHs (3-7 rings) by gas chromatography mass spectrometry. Total PAHs concentrations in the sediment ranged from 4 to 924 ng/g. Alkylated homologues were abundant for all sediment samples. The ratio of the sum of methylphenanthrenes to phenanthrene (MP/P), an index of petrogenic PAHs contribution, was more than unity for 26 sediment samples and more than 3 for seven samples for urban rivers covering a broad range of locations. The MP/P ratio showed a strong correlation with the total PAHs concentrations, with an r2 value of 0.74. This ratio and all other compositional features indicated that Malaysian urban sediments are heavily impacted by petrogenic PAHs. This finding is in contrast to other studies reported in many industrialized countries where PAHs are mostly of pyrogenic origin. The MP/P ratio was also significantly correlated with higher molecular weight PAHs such as benzo[a]pyrene, suggesting unique PAHs source in Malaysia which contains both petrogenic PAHs and pyrogenic PAHs. PAHs and hopanes fingerprints indicated that used crankcase oil is one of the major contributors of the sedimentary PAHs. Two major routes of inputs to aquatic environments have been identified: (1) spillage and dumping of waste crankcase oil and (2) leakage of crankcase oils from vehicles onto road surfaces, with the subsequent washout by street runoff. N-Cyclohexyl-2-benzothiazolamine (NCBA), a molecular marker of street dust, was detected in the polluted sediments. NCBA and other biomarker profiles confirmed our hypothesis of the input from street dust contained the leaked crankcase oil. The fingerprints excluded crude oil, fresh lubricating oil, asphalt, and tire-particles as major contributors.
A chemical mass balance (CMB) receptor model using particle-phase organic compounds as tracers is applied to apportion the primary source contributions to fine particulate matter and fine particulate organic carbon concentrations in the southeastern United States to determine the seasonal variability of these concentrations. Source contributions to particles with aerodynamic diameter < or =2.5 microm (PM2.5) collected from four urban and four rural/suburban sites in AL, FL, GA, and MS during April, July, and October 1999 and January 2000 are calculated and presented. Organic compounds in monthly composite samples at each site are identified and quantified by gas chromatography/mass spectrometry and are used as molecular markers in the CMB model. The major contributors to identified PM2.5 organic carbon concentrations at these sites in the southeastern United States include wood combustion (25-66%), diesel exhaust (14-30%), meat cooking (5-12%), and gasoline-powered motor vehicle exhaust (0-10%), as well as smaller but statistically significant contributions from natural gas combustion, paved road dust, and vegetative detritus. The primary sources determined in the present study when added to secondary aerosol formation account for on average 89% of PM2.5 mass concentrations, with the major contributors to PM2.5 mass as secondary sulfate (30+/-6%), wood combustion (15+/-12%), diesel exhaust (16+/-7%), secondary ammonium (8+/-2%), secondary nitrate (4+/-3%), meat cooking (3+/-2%), gasoline-powered motor vehicle exhaust (2+/-2%), and road dust (2+/-2%). Distinct seasonality is observed in source contributions, including higher contributions from wood combustion during the colder months of October and January. In addition, higher percentages of unexplained fine organic carbon concentrations are observed in July, which are likely due to an increase in secondary organic aerosol formation during the summer season.
Tire debris contains significant quantities of zinc (Zn), and there is concern about the diffuse Zn contamination of soils from tire wear. An experiment was set up to quantify the fate and effect of Zn from tire debris in soil. Two different soils were mixed with the <100-microm fraction of car and truck tire debris (25 g kg(-1) soil) or zinc sulfate (ZnSO4) as a reference. Soils were transferred to soil columns with free drainage and placed outdoors for 11 months. Leachates of the tire debris amended soils did not contain significantly (P>0.05) more Zn than control soils except for a 3-fold increase in one soil amended with cartire debris. The increase in Zn leaching due to tire debris was only 3% of the corresponding increase in the ZnSO4 treatment at the same total Zn in soil. Tire debris application increased the soil nitrification potential, whereas ZnSO4 application, at corresponding or smaller total Zn concentration, decreased nitrification potential. An increase in soil pH was observed in all soils treated with tire debris and explains the increased nitrification potential. About 10-40% of the Zn from tire debris was isotopically exchangeable in soil sampled after 1 year weathering. It is concluded that a significant fraction of Zn is released from the rubber matrix within 1 year, but the parallel increase in soil pH limits the mobilization of Zn in soil.
Car tires contain several water-soluble compounds that can leach into water and have toxic effects on aquatic organisms. Due to tire wear, 10,000 tonnes of rubber particles end up along the Swedish roads every year. This leads to a diffuse input of emissions of several compounds. Emissions of polyaromatic hydrocarbons (PAHs) are of particular concern. PAHs are ingredients of the high aromatic oil (HA oil) that is used in the rubber as a softener and as a filler. The exclusion of HA oils from car tires has started, and an environmental labeling of tires could make HA oils obsolete. The toxicity to Daphnia magna from 12 randomly selected car tires was tested in this study. Rubber from the tread of the tires was grated into small pieces, to simulate material from tire wear, and the rubber was equilibrated with dilution water for 72 h before addition of test organisms. The 24-h EC50s of the rubber pieces ranged from 0.29 to 32 gl-1, and the 48-h EC50s ranged from 0.0625 to 2.41 gl-1. Summer tires were more toxic than winter tires. After the 48-h exposure, the daphnids were exposed to UV-light for 2 h, to determine if the tires contained compounds that were phototoxic. After UV-activation the EC50s ranged from 0.0625 to 0.38 gl-1. Four of the 12 tires had a very distinct photoactivation, with a toxicity increase of >10 times. This study has shown that the used method for toxicity testing with Daphnia magna according to ISO 6341 could be used as a basis for environmental labeling of car tires.
The work presented herein displays the results of a study addressing environmental concerns related to the possible leaching of pollutants from reclaimed asphalt pavement. Samples from an experimental site were tested in both static batch tests and column leaching tests. Selected heavy metals and polycyclic aromatic hydrocarbons (PAHs) were analysed in leachates. The results have allowed us to consider the leaching of pollutants to be rather weak for most of the parameters studied. Concentrations in solutions from batch leaching tests were generally below the EC limit values for drinking water. Pollutant concentrations from column experiments were higher in solutions as of the initial leaching stages, but then decreased rapidly and wound up at values below the detection limits. The factors influencing results proved to be the material grain size and the percolation water flow rate. Results from leaching experiments performed on core samples taken on two rebuilt road section pavements, containing 10% and 20% of reclaimed asphalt pavement, respectively, confirmed the results obtained from the batch and column experiments.
TD, produced by tire wear, is a significant constituent of PM(10) in urban areas where traffic related emissions are predominant. TD contains a lot of chemicals which can affect human respiratory system and it has received little attention until now, even the toxicity of PM has been extensively documented. A549 cells, a human alveolar lung cells, were exposed for 24, 48, 72 h to 10, 50, 60, 75 microg/ml of TD organic extract. MTT and Trypan Blue assays were used to evaluate cytotoxicity and Comet Assay to evidence DNA damage. TD extracts induced a dose-dependent increase in cell mortality and DNA damage. A significant toxicity was observed when cells were exposed to 60 microg/ml for 72 h. Moreover cell morphology observed at ultra structural level, was severely affected at the highest dose.
Large amounts of tire rubber are deposited along the roads due to tread wear. Several compounds may leach from the rubber and cause toxicity to aquatic organisms. To investigate the toxic effects of tire wear material from different tires, rubber was abraded from the treads of twenty-five tires. Leachates were prepared by allowing the rubber to equilibrate with dilution water at 44 degrees C for 72 h. Then the rubber was filtered from the leachates, and test organisms (Daphnia magna) were added. Forty-eight hour EC50s ranged from 0.5 to >10.0 g l(-1). The toxicity identification evaluation (TIE) indicated that non-polar organic compounds caused most of the toxicity. UV exposure of the filtered tire leachates caused no significant increase in toxicity. However, when tested as unfiltered leachates (the rubber was not filtered from the leachates before addition of D. magna) photo-enhanced toxicity was considerable for some tires, which means that test procedures are important when testing tire leachates for aquatic (photo) toxicity. The acute toxicity of tire wear for Daphnia magna was found to be <40 times a predicted environmental concentration based on reports on the concentration of a tire component found in environmental samples, which emphasizes the need for a more extensive risk assessment of tire wear for the environment.
Tire debris (TD) and its organic components were identified as a main source of PM10 atmospheric and water pollution. Because few data are available on the embryotoxic effects of TD organic components, the lethal and teratogenic potential of tire debris organic extract (TDOE) was evaluated using the frog embryo teratogenesis assay-Xenopus (FETAX), coupled with a histopathological screening of the survived larvae. From stage 8 to stage 47, Xenopus laevis embryos were exposed to TDOE at concentrations of 50, 80, 100, 120 and 140 mg/L. The results showed 50 mg/L TDOE to be the non-observable effect concentration (NOEC). TDOE mortality at 80 mg/L was significantly higher than the control, but did not increase further with higher concentrations. A good concentration-response was observed for percentages of malformed larva and from 80 mg/L on these percentages were significantly higher than the control. Therefore, probit analysis gave a 144.6 mg/L TC50. At 120 and 140 mg/L, many larvae were plurimalformed. The most frequent alterations observed were abnormal gut coiling, microphthalmia, monolateral anophthalmia, and narrowing eyes. The histological screening mainly revealed ocular malformations such as double retina, retina nervous cell layer coiling, and altered lens. Moreover severe vacuolisation and necrosis were scored in liver and axial musculature. These results strongly support the assumption that TDOE is a powerful teratogen for X. laevis.
Debris produced from the attrition of tires of motor vehicles constitutes 5-7% of the atmospheric particulate matter (PM10). Debris particles are indeed small enough to enter human lung and thus morphological and chemical characterization has been performed. We demonstrated that the organic fraction of tire debris induces a dose-dependent increase in cell mortality, DNA damage, as well as a significant modification of cell morphology at the dose of 60 microg/ml, which may correspond to the quantity present in the air humans inhale daily. The present research aims at investigating if reactive oxygen species (ROS) production and Hsp70 expression are involved in the cascade of toxic effects produced on the A549 cell line, as it has been suggested for the ultrafine atmospheric particles and diesel exhaust. To this end, cells were exposed at the doses of 10, 50, 60, 75 microg/ml of TD organic extract (TDOE) and analyzed at different exposure time. ROS were detected by the oxidation of 2'7'-dichlorodihydrofluorescein diacetate to dichlorofluorescein, and fluorescence was measured by flow cytometry. Hsp70 protein expression was determined by immunochemical analysis, and protein expression quantification performed by optical densitometry. ROS production was analysed after 2 h of treatment. A statistically significant increase in fluorescence was observed and the intensity of the stress response was parallel to the increasing concentrations used. An evident increase of Hsp70 expression at lower doses (10, 50 microg/ml) and at longer exposure times (72 h) was observed, during the time that our previous studies showed that cell viability, plasma membrane integrity, and DNA molecules were not affected. Thus it can be deduced that the increase in Hsp70 expression protected the cells from those damages, which became evident at the higher doses, and that this parameter might be used as a sensitive indicator of exposure. These data suggest that ROS production may be the first event caused by A549 exposure to TDOE and this result is in line with other evidences provided for the role of ROS generation in ultrafine PM toxicity. It can be suggested that this event induces an overexpression of Hsp70 only at the lower doses and longer exposure time, when cells still appear unaffected. Subsequently when ROS generation reaches high levels, a general inhibition of protein synthesis probably occurs, culminating in cell toxicity.
AP-42 section 4.12, manufacture of rubber products. United States Environmental Protection Agency
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