Tire Tread Particles Research Articles

Assessing the Biodegradability of Tire Tread Particles and Influencing Factors.

Abrasion of tire tread, caused by friction between vehicle tires and road surfaces, causes release of tire wear particles (TWPs) into various environmental compartments. These TWPs contribute to chemical, microplastic, and particulate matter pollution. Their fate remains largely unknown, especially regarding the extent and form in which they persist in the environment. The present study investigated (1) the biodegradability of tread particles (TPs) in the form of ground tire tread, (2) how accelerated ultraviolet (UV) weathering affects their biodegradability, and (3) which TP constituents are likely contributors to TP biodegradability based on their individual biodegradability. A series of closed-bottle tests, with aerobic aqueous medium inoculated with activated sludge, were carried out for pristine TPs, UV-weathered TPs, and selected TP constituents; natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and treated distillate aromatic extracts (TDAE). Biodegradation was monitored by manometric respirometry, quantifying biological oxygen consumption over 28 days. Pristine TP biodegradability was found to be 4.5%; UV-weathered TPs showed higher biodegradability of 6.7% and 8.0% with similar and increased inoculum concentrations, respectively. The observed TP biodegradation was mainly attributed to biodegradation of NR and TDAE, with individual biodegradability of 35.4% and 8.0%, respectively; IR and BR showed negligible biodegradability. These findings indicate that biodegradability of individual constituents is decreased by a factor of 2 to 5 when compounded into TPs. Through scanning electron microscopy analysis, biodegradation was found to cause surface erosion. Processes of TP biodegradation are expected to change throughout their lifetime as new constituents are incorporated from the road and others degrade and/or leach out. Tire emissions likely persist as particles with an increased fraction of synthetic rubbers and carbon black. Environ Toxicol Chem 2024;43:31-41. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Brand-Specific Toxicity of Tire Tread Particles Helps Identify the Determinants of Toxicity.

The widespread occurrence of tire tread particles (TPs) has aroused increasing concerns over their impacts. However, how they affect the soil fauna remains poorly understood. Here, based on systematically assessing the toxicity of TPs on soil model speciesEnchytraeus crypticusat environmentally relevant concentrations through both soil and food exposure routes, we reported that TPs affected gut microbiota, intestinal histopathology, and metabolites of the worms both through particulate- and leachate-induced effects, while TP leachates exerted stronger effects. The dominant role of TP leachates in TP toxicity was further explained by the findings that worms did not ingest TPs with a particle size of over 150 μm and actively avoided consuming TP particles. Moreover, by comparing the effects of different brands of TPs as well as new and aged TPs, we demonstrated that it was mainly TP leachates that resulted in the ubiquity of the disturbance in the worm's gut microbiota among different brands of TPs. Notably, the large variations in leachate compositions among different brands of TPs provided us a unique opportunity to identify the determinants of TP toxicity. These results provide novel insights into the toxicity of TPs to soil fauna and a reference for toxicity reduction of tires.

Micron-size tire tread particles leach organic compounds at higher rates than centimeter-size particles: Compound identification and profile comparison

Tire tread particles (TTP) are environmentally prevalent microplastics and generate toxic aqueous leachate. We determined the total carbon and nitrogen leachate concentrations and chemical profiles from micron (∼32 μm) and centimeter (∼1 cm) TTP leachate over 12 days. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were used to measure the concentration of leached compounds. Nontargeted chemical analysis by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC/TOF-MS) was used to compare the chemical profiles of leachates. After leaching for 12 days, DOC was 4.0 times higher in the micron TTP leachate than in the centimeter TTP leachate, and TDN was 2.6 times higher. The total GC×GC/TOF-MS chromatographic feature peak area was 2.9 times greater in the micron TTP leachate than the centimeter TTP leachate, and similarly, the total relative abundance of 54 tentatively identified compounds was 3.3 times greater. We identified frequently measured tire-related chemicals, such as 6PPD, N-cyclohexyl-N′-phenylurea (CPU), and hexa(methoxymethyl)melamine (HMMM), but nearly 50% of detected chemicals were not previously reported in tire literature or lacked toxicity information. Overall, the results demonstrate that smaller TTP have a greater potential to leach chemicals into aquatic systems, but a significant portion of these chemicals are not well-studied and require further risk assessment.

Evidence of non-tailpipe emission contributions to PM2.5 and PM10 near southern California highways

Particulate Matter (PM) concentrations near highways are influenced by vehicle tailpipe and non-tailpipe emissions, other emission sources, and urban background aerosols. This study collected PM2.5 and PM10 filter samples near two southern California highways (I-5 and I-710) over two weeks in winter 2020. Samples were analyzed for chemical source markers. Mean PM2.5 and PM10 concentrations were approximately 10–15 and 30 μg/m3, respectively. Organic matter, mineral dust, and elemental carbon (EC) were the most abundant PM components. EC and polycyclic aromatic hydrocarbons at I-710 were 19–26% and 47% higher than those at the I-5 sites, respectively, likely due to a larger proportion of diesel vehicles. High correlations were found for elements with common sources, such as markers for brake wear (e.g., Fe, Ba, Cu, and Zr) and road dust (e.g., Al, Si, Ca, and Mn). Based on rubber abundances, the contributions of tire tread particles to PM2.5 and PM10 mass were approximately 8.0% at I-5 and 5.5% at I-710. Two different tire brands showed significantly different Si, Zn, carbon, and natural rubber abundances.

Time-concentration profiles of tire particle additives and transformation products under natural and artificial aging

Tire and road wear particles (TRWP) are polymer-based microparticles that are emitted into the environment during tire usage. Growing efforts are currently being made to quantify these emissions, characterize the leachates and assess their environmental impact. This study aimed to investigate the effect of aging on TRWP composition. Cryomilled tire tread particles (CMTTP) and TRWP were exposed for different durations to three aging conditions: accelerated thermal and photochemical aging and natural outdoor aging. Particles were then extracted with cyclohexane/ethanol. The time-concentration profiles of 23 additives and transformation products present in these extracts were determined by UHPLC-HRMS. Several chemicals, such as N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6-PPD) or 1,3-diphenylguanidine (DPG), decayed exponentially under all aging conditions, with half-lives of a few days under artificial photoaging versus dozens of days under pure thermal aging at 60 °C. The natural aging profiles lie between those 2 laboratory aging conditions. Other chemicals, such as 6PPD-quinone, presented bell-shaped concentration profiles within CMTTP when particles were exposed to UV light. 6PPD-quinone reached a maximal concentration within a month under natural aging. For TRWP, the initial load of 6PPD-quinone had already reached a maximum prior to the aging experiments and decreased exponentially under natural aging with a half-life below one month. Pure thermal aging induced a significantly slower decay of 6PPD-quinone within TRWP (half-life of half a year), emphasizing a greater stability and persistence in environmental compartments without light. This study highlighted that the more readily accessible CMTTP could be considered a reasonable proxy of TRWP to investigate the fate of chemicals within rubber particles, at least from a qualitative standpoint. Overall, the concentrations of 20 of the evaluated chemicals decreased by >50 % within 50 days under natural aging.

Investigation of abiotic degradation of tire cryogrinds

The abundance of microplastics found in the environment is a major cause of concern. Tire tread particles containing additives such as curing accelerators and antioxidants, can be a major source of elastomer pollution in the environment. Such tire particles combined with road pavement particles are referred to as tire and road wear particles, TRWP. The environmental availability from parent elastomers and the release of additives in the process of abiotic degradation were evaluated using freeze-thaw, wet-dry and accelerated UV-weathering experiments. Acceleration factor determination tests were conducted to correlate UV-exposure to the natural aging in the environment. Freeze-thaw testing showed many additives such as diphenyl guanidine (DPG), benzothiazole sulfenamide (BTS) and para-phenylene diamine (6 PPD) as tetrahydrofuran leachates and BTS transformation products. Further, UV exposure equivalent to 1.5 yr., 3 yr. and 5 yr. aging resulted in the formation a combination of ketones and carboxylic acids for styrene butadiene rubber (SBR), natural rubber (NR), and butadiene rubber-based tire cryogrinds. Attenuated total reflectance- Fourier- transform infrared spectroscopy (ATR-FTIR) was used to detect the degradation of the elastomers on UV-exposure while gas chromatography-mass spectroscopy (GC-MS) was used as a nontargeted, suspect screening analysis technique. The degradation intermediates and leachates identified using GC-MS represents useful data for the life cycle analysis of the functional polymers and additives and their possibility of environmental release.

Tire tread particles turn streams toxic

Ecotoxicology For coho salmon in the U.S. Pacific Northwest, returning to spawn in urban and suburban streams can be deadly. Regular acute mortality events are tied, in particular, to stormwater runoff, but the identity of the causative toxicant(s) has not been known. Starting from leachate from new and aged tire tread wear particles, Tian et al. followed toxic fractions through chromatography steps, eventually isolating a single molecule that could induce acute toxicity at threshold concentrations of ∼1 microgram per liter. The compound, called 6PPD-quinone, is an oxidation product of an additive intended to prevent damage to tire rubber from ozone. Measurements from road runoff and immediate receiving waters show concentrations of 6PPD-quinone high enough to account for the acute toxicity events. Science , this issue p. [185][1] [1]: /lookup/doi/10.1126/science.abd6951

A ubiquitous tire rubber-derived chemical induces acute mortality in coho salmon.

In U.S. Pacific Northwest coho salmon (Oncorhynchus kisutch), stormwater exposure annually causes unexplained acute mortality when adult salmon migrate to urban creeks to reproduce. By investigating this phenomenon, we identified a highly toxic quinone transformation product of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), a globally ubiquitous tire rubber antioxidant. Retrospective analysis of representative roadway runoff and stormwater-affected creeks of the U.S. West Coast indicated widespread occurrence of 6PPD-quinone (<0.3 to 19 micrograms per liter) at toxic concentrations (median lethal concentration of 0.8 ± 0.16 micrograms per liter). These results reveal unanticipated risks of 6PPD antioxidants to an aquatic species and imply toxicological relevance for dissipated tire rubber residues.

Chemical mapping of tire and road wear particles for single particle analysis

Tire and road wear particles (TRWP), which are comprised of polymer-containing tread with pavement encrustations, are generated from friction between the tire and the road. Similar to environmentally dispersed microplastic particles (MP), the fate of TRWP depends on both the mass concentration as well as individual particle characteristics, such as particle diameter and density. The identification of an individual TRWP in environmental samples has been limited by inherent characteristics of black particles, which interfere with the spectroscopic techniques most often used in MP research. The purpose of this research was to apply suitable analytical techniques, including scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) mapping and time-of-flight secondary ion mass spectrometry (ToF-SIMS) mapping, to characterize the specific physical and chemical properties of individual TRWP. Detailed elemental and organic surface maps were generated for numerous samples including bulk tread material, cryogenically milled tire tread particles, and TRWP generated from two separate road simulator methods. Key physical and chemical characteristics of TRWP for single particle identification included (1) elongated/round shape with variable amounts of mineral encrustation, (2) elemental surface characteristics including co-localization of (S + Zn/Na) ± (Si, K, Mg, Ca, and Al), and (3) co-localization of organic surface markers, such as C6H5+ and C7H7+. Comparisons of TRWP with other polymeric (polystyrene) and non-polymeric (carbon black) particle types demonstrated that a combination of physical and chemical markers is necessary to identify TRWP. Addition of a density separation step to the single particle analysis techniques allowed for the determination of average primary TRWP particle size (34 μm by number distribution and 49 μm by volume distribution) and aspect ratio (65% of TRWP with an aspect ratio > 1.5). The use of chemical mapping techniques, such as SEM/EDX and/or ToF-SIMS mapping as demonstrated herein, can support future research efforts that aim to identify complex MP.

Ingestion and Chronic Effects of Car Tire Tread Particles on Freshwater Benthic Macroinvertebrates.

Micronized particles released from car tires have been found to contribute substantially to microplastic pollution, triggering the need to evaluate their effects on biota. In the present study, four freshwater benthic macroinvertebrates were exposed for 28 days to tread particles (TP; 10–586 μm) made from used car tires at concentrations of 0, 0.1, 0.3, 1, 3, and 10% sediment dry weight. No adverse effects were found on the survival, growth, and feeding rate of Gammarus pulex and Asellus aquaticus, the survival and growth of Tubifex spp., and the number of worms and growth of Lumbriculus variegatus. A method to quantify TP numbers inside biota was developed and here applied to G. pulex. In bodies and faces of G. pulex exposed to 10% car tire TP, averages of 2.5 and 4 tread particles per organism were found, respectively. Chemical analysis showed that, although car tire TP had a high intrinsic zinc content, only small fractions of the heavy metals present were bioavailable. PAHs in the TP-sediment mixtures also remained below existing toxicity thresholds. This combination of results suggests that real in situ effects of TP and TP-associated contaminants when dispersed in sediments are probably lower than those reported after forced leaching of contaminants from car tire particles.

Detection of tire tread particles using laser-induced breakdown spectroscopy

The objective of this paper is a study of the potential of laser induced breakdown spectroscopy (LIBS) for detection of tire tread particles. Tire tread particles may represent pollutants; simultaneously, it is potentially possible to exploit detection of tire tread particles for identification of optically imperceptible braking tracks at locations of road accidents. The paper describes the general composition of tire treads and selection of an element suitable for detection using the LIBS method. Subsequently, the applicable spectral line is selected considering interferences with lines of elements that might be present together with the detected particles, and optimization of measurement parameters such as incident laser energy, gate delay and gate width is performed. In order to eliminate the matrix effect, measurements were performed using 4 types of tires manufactured by 3 different producers. An adhesive tape was used as a sample carrier. The most suitable adhesive tape was selected from 5 commonly available tapes, on the basis of their respective LIBS spectra. Calibration standards, i.e. an adhesive tape with different area content of tire tread particles, were prepared for the selected tire. A calibration line was created on the basis of the aforementioned calibration standards. The linear section of this line was used for determination of the detection limit value applicable to the selected tire. Considering the insignificant influence of matrix of various types of tires, it is possible to make a simple recalculation of the detection limit value on the basis of zinc content in a specific tire.

Use of a Deuterated Internal Standard with Pyrolysis-GC/MS Dimeric Marker Analysis to Quantify Tire Tread Particles in the Environment

Pyrolysis(pyr)-GC/MS analysis of characteristic thermal decomposition fragments has been previously used for qualitative fingerprinting of organic sources in environmental samples. A quantitative pyr-GC/MS method based on characteristic tire polymer pyrolysis products was developed for tread particle quantification in environmental matrices including soil, sediment, and air. The feasibility of quantitative pyr-GC/MS analysis of tread was confirmed in a method evaluation study using artificial soil spiked with known amounts of cryogenically generated tread. Tread concentration determined by blinded analyses was highly correlated (r2 ≥ 0.88) with the known tread spike concentration. Two critical refinements to the initial pyrolysis protocol were identified including use of an internal standard and quantification by the dimeric markers vinylcyclohexene and dipentene, which have good specificity for rubber polymer with no other appreciable environmental sources. A novel use of deuterated internal standards of similar polymeric structure was developed to correct the variable analyte recovery caused by sample size, matrix effects, and ion source variability. The resultant quantitative pyr-GC/MS protocol is reliable and transferable between laboratories.

Acute aquatic toxicity of tire and road wear particles to alga, daphnid, and fish

Previous studies have indicated that tire tread particles are toxic to aquatic species, but few studies have evaluated the toxicity of such particles using sediment, the likely reservoir of tire wear particles in the environment. In this study, the acute toxicity of tire and road wear particles (TRWP) was assessed in Pseudokirchneriella subcapita, Daphnia magna, and Pimephales promelas using a sediment elutriate (100, 500, 1000 or 10000 mg/l TRWP). Under standard test temperature conditions, no concentration response was observed and EC/LC50 values were greater than 10,000 mg/l. Additional tests using D. magna were performed both with and without sediment in elutriates collected under heated conditions designed to promote the release of chemicals from the rubber matrix to understand what environmental factors may influence the toxicity of TRWP. Toxicity was only observed for elutriates generated from TRWP leached under high-temperature conditions and the lowest EC/LC50 value was 5,000 mg/l. In an effort to identify potential toxic chemical constituent(s) in the heated leachates, toxicity identification evaluation (TIE) studies and chemical analysis of the leachate were conducted. The TIE coupled with chemical analysis (liquid chromatography/mass spectrometry/mass spectrometry [LC/MS/MS] and inductively coupled plasma/mass spectrometry [ICP/MS]) of the leachate identified zinc and aniline as candidate toxicants. However, based on the high EC/LC50 values and the limited conditions under which toxicity was observed, TRWP should be considered a low risk to aquatic ecosystems under acute exposure scenarios.

Quantification of Tire-Tread Particles Using Extractable Organic Zinc as Tracer

Abstract A method for identifying and quantifying tire-tread particles in the environment has been developed. It is based on the measurement of extractable organic zinc. The high sensitivity of atomic absorption spectrometry (AAS) with a heated graphite atomizer (HGA) permits assessment of submilligram amounts of tire debris in environmental samples. The analysis is performed on aerosol and soil samples. This new method is more accurate and faster than the previously reported IR method.

Analysis of Tire Tread Rubber Particles and Rubber Additives in Airborne Particulates at a Roaddde.

Rubber particles emitted by abrasion of automobile tire tread have caused environmental pollution, and may be hazardous to our health. In this study, airborne particulate samples were collected on the glass fiber filter using high-volume air sampler at the roadside of the 2-nd Shinmei highway in Kobe. Rubber particles in the roadside atmosphere were analyzed by pyrolysis gas chromatography. The concentration of rubber particles was estimated from the total amount of styrene and isoprene, because these two compounds are pyrolysates of styrene butadiene rubber and natural rubber which are main materials for tires. These concentrations were 0.5-10.5 μg/m3, which corresponded to 0.4-6.3% of total airborne particulates. These concentrations were higher than those in other reports, because the sampling point was the roadside of the highway in this experiment. Furthermore quantitative and qualitative analyses of rubber additives (Zn-DMDTC and IPPD) in airborne particulates were carried out by HPLC, GC and MS. Zn-DMDTC, after converted into Co-DMDTC, in airborne particulates was analyzed by HPLC. The concentrations of Zn-DMDTC were 0-5.1 pg/m3. The detected amount of Zn-DMDTC did not show mutagenic activity. However, in the case of long term exposure to these tire tread particles, we must take a hazardous effect by Zn-DMDTC into consideration. On the other hand, IPPD was confirmed in none of samples by GC and MS.

Simultaneous determination of natural and styrene-butadiene rubber tire tread particles in atmospheric dusts by pyrolysis-gas chromatography

A method for simultaneous determination of natural rubber (NR) and styrene-butadiene rubber (SBR) tire tread particles in atmospheric dust is described. Particulate rubbers are pyrolyzed at 740°C for five seconds in a Curie-point pyrolyzer. The resulting pyrolyzates are separated and detected by a gas chromatograph equipped with dual flame ionization detectors. Among several pyrolysis products, isoprene and styrene are chosen as indicator compounds for NR and SBR, respectively. The method is applied to a suite of atmospheric dust samples collected in Seoul, Korea by an Andersen sampler and some analytical results are presented.