Chemical composition and potential health risks of tire and road wear microplastics from light-duty vehicles in an urban tunnel in China

A critical review of the ecotoxic effects of microplastics on aquatic, soil and atmospheric ecosystems and current research challenges

The extensive use of plastics has brought unparalleled convenience to human social development. However, this has also led to severe environmental and health challenges, with microplastic (MP) pollution emerging as one of the most pressing issues. As ubiquitous environmental pollutants, MPs persist in ecosystems and pose potential risks to both ecological and human health. Studies reveal that MPs impact aquatic, soil, and atmospheric ecosystems by altering their physicochemical properties and causing toxicological harm to resident organisms. Despite these findings, a comprehensive assessment and analysis of MP impacts, especially on atmospheric ecosystems, remains lacking. Similarly, the environmental biotoxicity mechanisms associated with MPs are yet to be systematically described. This review provides an in-depth discussion of the sources and characteristics of MPs, laying the background for elaborating their ecological effects. Current knowledge on MP ecotoxicity in aquatic, soil, and atmospheric ecosystems is then synthesized. Potential molecular mechanisms of biotoxicity are explored. Oxidative stress, inflammatory responses, and metabolic signaling pathway impairment are considered important pathways through which MPs induce toxic injury in environmental animals and have received widespread attention. Additionally, this review emphasizes the challenges faced in studying ecotoxic effects and mechanisms of MPs, such as the lack of reliable detection of environmental MPs and in-depth mining of relevant data, and suggests possible directions for future research. Although progress has been made, significant knowledge gaps remain. Addressing these gaps is critical if effective strategies are to be developed to reduce the environmental and health risks posed by MPs.

Dust Fall Microplastics from a Megacity of China Inhibit Autophagy via the PI3K/Akt/mTOR Pathway

The problem of microplastics (MPs) pollution has caused many health risks to residents of Chinese cities. In this study, nine kinds of MPs or microrubbers (MRs) from dust fall (DF) in Xi'an, a megacity in northwestern China, were measured by pyrolysis-gas chromatography-mass spectroscopy, namely, polyethylene, polypropylene, nylon 88, polybutylene, polytetrafluorethylene, polyisoprene, polyvinyl chloride, natural rubber, and synthesis rubber. Here, 51.20% of MPs were extracted from the original DF (samples denoted DF-O). After the subtracting procedure, MPs and their residual (DF-S samples) were divided into two parts. Our results indicated that the DF-O and MPs samples exhibited higher cytotoxicity, inflammatory, and oxidative stress levels than the DF-S samples did. The DF-O and MPs samples suppressed autophagy by decreasing expression levels of microtubule-associated protein light chain 3 (LC3B), p-phosphatidylinositol 3-kinase (p-PI3K), phosphorylated AKT protein (p-Akt), and p-mammalian target of rapamycin (p-mTOR) while increasing the level of p62. Meanwhile, DF-O and MPs samples induced apoptosis through increasing levels of Bax/Bcl-2 and Cleaved Caspase-3/Caspase-3 in Raw264.7 cells. These trends could be reversed through removing half of the MPs in DF-O. Therefore, dust fall microplastics inhibited autophagy and induced apoptosis via activating the PI3K/Akt/mTOR pathway, increasing the Bax/Bcl-2 and Cleaved Caspase-3/Caspase-3 ratios. Here we provide a comprehensive perspective into the studies of atmospheric MPs pollution status and mechanisms of inhalation toxicity for health risk assessment of MPs in DF.

Tire-based microplastics: Composition, detection, and impacts of advanced oxidation processes in drinking water treatment

Microplastic pollution, particularly that from tire, presents critical environmental and public health concerns. They contribute 60 % of the total microplastic pollution. Tire-based microplastics, which contain synthetic polymers and toxic chemical additives, are significant contributors to microplastic pollution in aquatic systems. They release various hazardous substances, including heavy metals, polycyclic aromatic hydrocarbons, and other persistent pollutants, which adversely affect ecosystems and pose risks to drinking water quality. Advanced oxidation processes (AOP) such as ultraviolet based treatment, ozonation and sulfate radical based processes show potential for mitigating these microplastics by fragmenting them and degrading the leached chemicals. Radicals generated during AOP (such as sulfate radicals (SO₄•-), peroxide radicals (HO₂•) and hydroxyl radicals (•OH), have also been successful in removing the transformation products associated with tire microplastics. This combined action of AOP has potential in mitigating the primary tire microplastics and the leached chemicals from it. AOP studies reported from the other microplastic researches (PP, PE, PVC etc.) shows promising results in mitigating them from drinking water sources. TMP appears to behave similarly to other microplastic polymers in terms of fragmentation. However, research is still lacking in quantifying this process due to the presence of complex chemicals additives in it. Additionally, studies focusing on their removal in DWTPs, particularly those that consider both TMP and their associated chemical leachates, remain limited. This review discusses the chemical composition, detection techniques, fragmentation of tire-related microplastics by AOP, and leaching of chemicals from them. This review also suggests modification of treatment techniques, challenges for implementing them to real world treatment and scopes in optimization of treatment conditions to mitigate tire wear particles and the associated chemicals.

Combined contamination of tire and road wear microplastics with heavy metals in expressway tunnels: occurrence characteristics and risk assessment

Tire and road wear microplastics (TRWMPs), as an important type of microplastics, have attracted increasing attention. However, current studies on their contamination within expressway tunnels remain limited. Therefore, we investigated the occurrence characteristics of TRWMPs in dusts from various tunnels, and combined contamination with heavy metals (HMs). The results showed that the abundance of TRWMPs in expressway tunnel dust (53,778 n/kg) was much higher than that sampled from other land use types (1360-4960 n/kg) in the same region. A large amount of polyamide was released into the environment along with wear particles from the vehicles. Also, the abundance of TRWMPs inside tunnels was greater than outside, and the proportion of large-size TRWMPs was higher inside tunnels. TRWMPs was symmetrically distributed with respect to the center of expressway tunnel. The pollution load index (PLI) and ecological risk index (H) indicated that study area was heavily contaminated with TRWMPs. There was a significant positive correlation between the abundance of TRWMPs and concentration of Cr (p < 0.01) in dust, and their risk assessment and health risk fluctuations were almost identical. Thus, the study is of great significance for elucidating the synergistic contamination and potential risk of TRWMPs and HMs in expressway tunnels.

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

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

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

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

A Review of N-(1,3-Dimethylbutyl)-N'-phenyl-p-Phenylenediamine (6PPD) and Its Derivative 6PPD-Quinone in the Environment

As an antioxidant and antiozonant, N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is predominantly used in the rubber industry to prevent degradation. However, 6PPD can be ozonated to generate a highly toxic transformation product called N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone), which is toxic to aquatic and terrestrial organisms. Thus, 6PPD and 6PPD-quinone, two emerging contaminants, have attracted extensive attention recently. This review discussed the levels and distribution of 6PPD and 6PPD-quinone in the environment and investigated their toxic effects on a series of organisms. 6PPD and 6PPD-quinone have been widely found in air, water, and dust, while data on soil, sediment, and biota are scarce. 6PPD-quinone can cause teratogenic, developmental, reproductive, neuronal, and genetic toxicity for organisms, at environmentally relevant concentrations. Future research should pay more attention to the bioaccumulation, biomagnification, transformation, and toxic mechanisms of 6PPD and 6PPD-quinone.

Atmospheric microplastic deposition associated with GDP and population growth: Insights from megacities in northern China

Microplastic (MP) pollution is evolving into one of the most pressing environmental concerns worldwide. This study assessed the impact of economic activities on atmospheric MP pollution across 17 megacities in northern China, analyzing the correlation between the deposition flux of atmospheric MPs and variables such as city population, gross domestic product (GDP), and industrial structure. The results have shown that the MP pollution is obviously impacted by human activities related to increased GDP, population, as well as tertiary service sector, in which the MP pollution shows most close relationship with the GDP growth. Polypropylene, polyamide, polyurethane, and polyethylene were identified as the primary components of atmospheric MPs. The average particle size of MPs in atmospheric dustfall is 78.3 µm, and the frequency of MP particles increases as the particle size decreases. The findings highlight the complex relationship between socio-economic development and atmospheric MP accumulation, providing essential insights for the formulation of targeted emission reduction strategies.

Tire plastic and road-wear particles on Yujing Expressway in the restoration area of Mu Us Sandy Land: Occurrence characteristics and ecological risk screening

Tire plastic and road-wear particles (TPR-WP) are a current research priority as one of the main environmental sources of microplastics. We selected a unique land use type - desert restoration area, collected soil and dust samples from the Yujing Expressway and its service areas, and analyzed TPR-WP abundance, type, size and morphology by laser direct infrared (LDIR). The abundance of TPR-WP in expressway dust (14,446.87 ± 10,234.24 n/kg) was higher than that in soil (7500 ± 3253.64 n/kg). Random forest model showed that the source of TPR-WP was highly correlated with economic factors and natural climate. Overall, the proportion of small and medium-sized TPR-WP in dust was higher than soil, more than half of the TPR-WP in dust were in 20 - 50 µm range. The proportion of small particle size TPR-WP increased with the rise of elevation. The pollution load index suggested that the survey region was generally at level I risk zone, while the ecological risk index indicated that the pollution level of expressway was III and IV, and the service area was IV. In general, the study was of great significance for clarifying the distribution and risk of TPR-WP in soil and dust of expressways and service areas.

Spatial distribution, source apportionment and potential ecological risk assessment of suspended atmosphere microplastics in different underlying surfaces in Harbin

Although suspended atmospheric microplastics (SAMPs) have been found to be ubiquitous and have potential impacts on human health, whereas studies related to source apportionment and potential ecological risk assessment in the atmospheric environment are still limited. This study investigated spatial distribution, source apportionment and potential ecological risk of SAMPs in six underlying surfaces of Harbin, China. The results show that all six underlying surfaces existed SAMPs, including polypropylene (PP), polyethylene terephthalate (PET) polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC), with approximate 26.13 %, 24.10 %, 23.87 %, 13.51 %, and 12.39 %, respectively. SAMPs abundances from filtered air were relatively high and averaged 1.76 n/m3. The SAMPs mainly contained fibrous (59.01 %), fragmented (30.18 %), and granular (10.81 %) with transparent (62.39 %), black 13.74 %), red (7.43 %), white (6.53 %), blue, and yellow (3.60 %), and particle size ranged from 1.3 to 518 μm. In addition, source apportionment of SAMPs shows that SAMPs were originated from five emission sources including living source (19.53 %), construction source (12.08 %), transportation source (47.25 %), industrial source (5.11 %), and agricultural source (16.13 %) in Harbin. A significant correction was observed between SAMPs abundances and human activity (R = 0.68, P = 0.66), atmospheric humidity (R = -0.40, P = 0.02), and wind direction (R = 0.22, P = 0.04) in different underlying surface. Furthermore, potential ecological hazardous single index (EI) of PVC and PS were higher than PP, PET, and PS in the construction land, cultivated land, forest land, grassland, water area, and unused land. An estimation of the potential ecological risk index (RI) from SAMPs using Positive Matrix Factorization (PMF) model indicated that Harbin presented a minor ecological risk with average 16.59 of RI index of microplastics in environments. In conclusion, data in this study indicate that SAMPs are existed in atmospheric environments, which have possible risks for human health via inhalation.