Concentrations of Tire Additive Chemicals and Tire Road Wear Particles in an Australian Urban Tributary

Unseen streams tracing emerging contaminants from stormwater to surface water: A brief review

Emerging contaminants (ECs) have raised global concern due to their adverse effect on ecosystems and human health. However, the occurrence and transport of ECs in stormwater remain unclear. The impact of ECs from stormwater on surface water quality and ecosystem health is also poorly documented. In this review, we examined the variations in EC concentrations in surface water resulting from stormwater. During the wet weather, the concentrations of most investigated ECs, e.g., microplastics, per- and polyfluoroalkyl substances, and vehicle-related compounds, significantly increase in surface water, indicating that stormwater may be a critical source of these contaminants. Furthermore, the potential pathways of ECs from stormwater enter surface water are outlined. Studies demonstrate that surface runoff and combined sewer overflows are important pathways for ECs, with discharges comparable to or exceeding those from wastewater treatment plants. Illicit connection also plays an important part in elevated EC concentrations in surface water. Overall, our findings underscore the importance of stormwater as a source for ECs in surface waters, and urge for increased emphasis on, and reinforcement of, stormwater monitoring and control measures to minimize the transport of ECs into receiving water bodies.

A critical review of sampling, extraction and analysis methods for tyre and road wear particles

Tyre and road wear particles (TRWPs) have become an increasing contamination concern because of their extensive distribution in the environment. A comprehensive overview of the methods for sampling, treatment and analysis of environmental samples for TRWPs (and their benefits and limitations) is lacking. We evaluate and critically assess the sampling, treatment and analysis methods previously reported for water, air, road dust and sediment/soil samples. We suggest research frameworks for studying TRWPs in these media. Microscopy and thermal analysis techniques such as scanning electron microscopy (with energy dispersive X-ray analysis), environmental scanning electron microscopy, 2-dimensional gas chromatography mass spectrometry and liquid chromatography with tandem mass spectrometry in the case of complex samples, are optimal methods for determination of the number and mass of TRWPs. Issues for further investigation and analysis recommendations are provided.

Source-specific dynamics of organic micropollutants in combined sewer overflows

Combined sewer overflows (CSOs) discharge organic micropollutants (MPs) into open water bodies, posing potential environmental threats. Knowledge of the numbers, sources, and dynamics of MPs during CSOs is scarce but crucial for assessing their impact and developing mitigation strategies. To shed light on the dynamics of dissolved organic MPs in CSOs, we conducted high-temporal-resolution sampling (10 min composite samples) followed by liquid chromatography high-resolution mass spectrometry analysis, both target (60 substances) and nontarget, at two CSO sites in a small [17 hectares reduced (hared)] and a large (368 hared) catchment for over 10 events each. We observe similar patterns among indoor substances in the large catchment and among tire-associated compounds in both catchments, indicating source-specific behavior. Due to high and diverse concentration variability, no temporal correlations were found among indoor substances in the small catchment or among pesticides in either catchment. A random forest classifier was applied to assign nontarget time series to indoor and road sources in the large catchment. The results indicate that CSOs discharge several thousand substances from indoor sources, followed by a few hundred from outdoor sources with continuous leaching. These high numbers substantially surpass the scope of traditional target lists and underscore the importance of broad-spectrum screening methods when assessing MP contamination.

Tire-additive chemicals and their derivatives in urban road dust: Spatial distributions, exposures, and associations with tire and road wear particles

Tires, as a globally utilized product, emit pollutants including various tire-additive chemicals (TACs), and tire and road wear particles (TRWPs) containing substantial microplastics. Several TACs have been proven to have aquatic toxicity, induce health risks including endocrine disruption, allergic effects, and cardiovascular problems, while TRWPs are also very strongly suspected. With the emergence of multiple novel TAC derivatives recently, yet knowledge of their occurrence, spatial distribution, and potential associations remains largely insufficient. In this work, we have systematically investigated 25 TACs, including para-phenylenediamine (PPDs), several newly identified quinones (PPD-Qs) first reported in urban dust, and TRWPs across road dust from Hong Kong and Berlin. By coupling UPLC-MS/MS and pyrolysis-GC/MS analyses, we achieved concurrent quantification of trace TAC derivatives and TRWPs. Distinct spatial patterns of these tire-derived contaminants were identified, in which Hong Kong exhibited higher TACs linked to dense traffic, while the TRWP levels reached 9420 μg/g near auto factory in Berlin. Highway dust contained maximum contaminant loads of both TACs (5.0-fold higher) and TRWPs (5.3-fold higher) compared to other road types. Significantly linear associations were found between emerging TAC derivatives and TRWPs, implying their potential as candidate markers. Exposure assessments revealed PPDs and PPD-Qs intake doses surpassed benzothiazole and its derivatives, highlighting non-negligible risks caused by emerging TAC derivatives. This work establishes a framework for evaluating region-specific emission drivers and provides critical baseline data of multiple tire-related contaminants across different compartments. Potential markers for TRWPs were identified, which may be further utilized for their identification and determination.

Comparative effects of 6PPD and 6PPD-Quinone at environmentally relevant concentrations on hepatotoxicity, glucolipid metabolism and ferroptotic response in adult zebrafish

The antioxidant 6PPD and its oxidized product 6PPD-Quinone (6PPDQ) have attracted considerable attention due to their various acute toxicities to aquatic organisms. However, the chronic toxicity of two compounds in aquatic animals is still unknown. Here, adult zebrafish were exposed to 6PPD and 6PPDQ at environmentally relevant concentrations (20 μg/L) for 28 days, and histological analysis showed that 6PPD caused more severe hepatic vacuolization than 6PPDQ. Meanwhile, 6PPD induced more serious lipid accumulation and a higher increase in triglyceride and total cholesterol levels than 6PPDQ, suggesting higher hepatotoxicity of 6PPD. Furthermore, transcriptomic analysis revealed that both compounds disturbed glucolipid metabolism to different degrees by altering the expression of different peroxisome proliferator-activated receptors (PPARs), in which 6PPD inhibited gene expressions in glucolipid metabolism possibly by PPARα, PPARβ and RXR, while 6PPDQ disrupted the expressions of partial genes in similar pathways probably via PPARγ. Additionally, 6PPD but not 6PPDQ increased Fe2+ content, decreased the protein levels of ferroportin 1, ferritin and glutathione peroxidase 4, accompanied with the increase of malondialdehyde level and the decrease of glutathione content, suggesting ferroptotic response by 6PPD. Overall, our data deepened the understanding of 6PPD- and 6PPDQ-induced hepatotoxicity association with glucolipid metabolism disorders and ferroptotic responses.

The effects of tread rubber and road dust particles on stress, immunity and digestive biomarkers in the larvae of the mealworm Tenebrio molitor

Airborne road and abrasive car parts particles penetrate into aquatic and soil environments, but also, settling on vegetation along highways, enter trophic chains as a result of consumption by herbivorous invertebrates. The effects of this exposure are poorly recognized. The study aimed to assess the toxicity of two traffic-connected materials: tread rubber (TR) particles and environmentally relevant field-collected road dust (RD), to the Tenebrio molitor larvae under laboratory conditions using a set of protective (heat shock protein - HSP70, metallothionein - Mts levels), immunity (lysozyme - Lys, defensin - Def levels) and digestive (protease, amylase, and celulase activities) biomarkers. ELISA assay was used for protein levels, while fluorimetric and spectrophotometric methods were used for enzymatic activity studies. RD and TR particles were characterized by SEM/EDS techniques. The representative TR particle sizes were within the range of 31 µm and 274 µm. For the RD, the size of the particles were 153-587 µm. Fat body HSP70 levels were, on average, twice lower in groups exposed to RD particles. For fat body Mts, RD and TR caused the decrease while in the gut, the effect depended on the particle type. Gut lysozyme levels increased for both particles while in fat body this effect was made by RD. Digestive enzyme activity did not reflect exposure to TR and RD particles. RD induced changes in more experimental groups than TR. This may be due to the greater complexity of their composition. Further studies focusing on material type, concentration, exposure duration, and particle size are necessary to understand the effects of traffic-connected material on terrestrial herbivores.

Environmental fate, toxicity, and mitigation of 6PPD and 6PPD-Quinone: Current understanding and future directions

N'-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), a widely used antioxidant in the rubber industry, has garnered global attention due to the high toxicity and ecological-health risks posed by its environmental oxidation product, 6PPD-quinone (6PPD-Q). With the continuous release of tire wear particles (TWPs), 6PPD-Q is ubiquitously distributed in atmospheric, aquatic, and terrestrial environments, as well as within organisms, where it bioaccumulates through food chains. Notably, 6PPD-Q has been detected in human urine, serum, and cerebrospinal fluid, and its association with abnormal α-synuclein aggregation in the brains of Parkinson's patients further underscores its neurotoxic risks. This review systematically examines the environmental occurrence and migration patterns of 6PPD and 6PPD-Q, their multisystem toxicity, highly sensitive detection technologies, and pollution control strategies, while highlighting critical gaps in current research, such as chronic exposure mechanisms, combined pollution effects, and environmental safety thresholds. By synthesizing existing knowledge, this review provides a scientific foundation for elucidating the ecological and health risks of 6PPD-Q, offering critical insights to advance environmental regulatory policies, promote green transformation in the rubber industry, and safeguard global ecological security. Future research should prioritize long-term toxicity studies, refined detection techniques, and sustainable regulatory frameworks to mitigate the ecological and health risks posed by these emerging contaminants.

Exploring the fate of 6PPD in zebrafish (Danio rerio): Understanding toxicokinetics, biotransformation mechanisms, and metabolomic profiling at environmentally relevant levels

In recent years, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) has attracted significant attention in environmental science, yet its behavior in biological systems remains poorly understood. This study involved a 28-day zebrafish exposure experiment at three concentrations (2, 20, and 200 μg/L), to investigate its physiologically based toxicokinetic (PBTK) properties, the formation of biotransformation products, and the metabolic characteristics of liver tissue. The results indicated that the liver and intestines are key organs for 6PPD accumulation, with tissue-specific distribution patterns. The biotransformation of 6PPD in the liver involves various phase I and phase II metabolic reactions, including hydroxylation, N-dealkylation, and sulfation processes. Furthermore, Metabolomics analysis revealed substantial changes in both the diversity and abundance of liver metabolites with increasing 6PPD concentrations, particularly in key biological processes such as lipid metabolism, amino acid metabolism, and redox balance. Notably, significant disruptions in sphingolipid and glycerophospholipid pathways suggest 6PPD may impair membrane fluidity and stability, potentially leading to membrane damage and dysfunction. Overall, this study provides crucial insights into the biological behavior of 6PPD in zebrafish, contributing essential knowledge for its ecotoxicological evaluation.

A comprehensive reconnaissance and risk assessment of rubber additives and their transformation products (RATPs) in groundwater: 1,3-Diphenylguanidine (DPG) as a pressing ecological concern

The widespread detection of rubber additives and their transformation products (RATPs) in surface water environments is well-documented, but their pollution characteristics in groundwater remain unclear. This study comprehensively revealed the occurrence and distribution of 27 RATPs in groundwater across southern China (n = 212). RATPs were detected in groundwater at total levels of 1.21-2,345 ng/L. The primary compounds detected were 1,3-Diphenylguanidine (DPG), 1,3-diphenylurea (DPU), and 2-hydroxybenzothiazole (2-OH-BTH), each with a detection frequency of 99.5 % and mean concentrations of 125, 58.4, and 51.2 ng/L, respectively. The spatial distribution of RATPs in groundwater shows significant lateral variations but lacks vertical differences. Correlation analysis indicates a strong relationship between the RATPs pollution levels and both the type of groundwater and the level of urban economic development, with karst water exhibiting particularly high pollution levels. Five RATPs exhibited medium to high ecological risks in groundwater. The daily intake of RATPs via groundwater in South China is 3.61 × 10-8-7.00 × 10-5 mg/(kg·d). According to the multicriteria evaluation approach and persistence, mobility, and toxicity (PMT) assessment, six RATPs, including DPG, have been identified as high-priority pollutants that require significant attention in groundwater management. This study highlights the contamination characteristics and ecological risks associated with RATPs in groundwater, emphasizing the need for increased focus on these widely used yet inadequately evaluated chemicals in future research.

6PPD and 6PPD Quinone Induce Endometrial Cell Dysfunction via Activating ERα and GPER at Human-Relevant Levels

The widespread environmental prevalence of tire-derived N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and 6PPD-quinone (6PPD-Q) has provoked public concern about their health risks. This study aimed to investigate the potential of 6PPD and 6PPD-Q to induce endometrial cell dysfunction through nuclear estrogen receptor (ER) and G-protein-coupled estrogen receptor (GPER) signaling pathways. Fluorescence competitive binding and reporter gene assays revealed that 6PPD and 6PPD-Q selectively bound to ERα (not ERβ) and activated ER transcriptional activity, with the lowest observed effective concentrations (LOECs) of 500 and 10 nM, respectively. Calcium mobilization assays further demonstrated that both 6PPD and 6PPD-Q activated the GPER nongenomic pathway in a concentration-dependent manner (LOEC = 1 nM). 6PPD-Q exhibited stronger ERα and GPER activation potency than 6PPD, which was explained well by molecular dynamics simulation. 6PPD and 6PPD-Q stimulated endometrial cell proliferation via ERα/GPER signaling pathways, mechanistically linked to Cyclin D1/Ki67 upregulation. Furthermore, 6PPD/6PPD-Q promoted endometrial cell migration through an ERα/GPER-regulated epithelial-mesenchymal transition and inflammatory responses. Notably, the LOECs for these functional disruptions reached nanomolar levels relevant to human exposure. Collectively, we elucidated the molecular initial events and downstream key events of 6PPD/6PPD-Q-induced endometrial cell dysfunction, which implied their threat to the reproductive system and provided novel perspectives for their health risk evaluation.

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

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

Enantioselectivity in human urinary excretion of N-(1,3-dimethylbutyl)-N'-phenyl-1,4-benzenediamine (6PPD) and 6PPD-quinone

Human exposure to of N-(1,3-dimethylbutyl)-N'-phenyl-1,4-benzenediamine (6PPD) has raised global concerns due to its documented toxic effects, including hepatotoxicity, metabolic disruption, and potential contributions to organ damage. 6PPD-quinone (6PPD-Q), a ubiquitous transformation product of 6PPD, has been identified as a major toxicant linked to acute mortality in aquatic species, underscoring its ecological and human health risks. While these compounds exist as enantiomers with demonstrated differences in environmental behavior and toxicity, their enantiomer-specific distribution and excretion patterns in humans remain unknown limiting accurate risk assessments. This study analyzed 6PPD and 6PPD-Q in 109 pairs of whole blood and urine from general Chinese adults at the enantiomer-specific level. Results showed that 6PPD (range < LOD-0.60 ng/mL) and 6PPD-Q ( Collapse

Key Words

• Enantioselectivity
• Human behavior
• Human exposure
• Renal clearance
• Rubber additives

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MESH Headings Collapse

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Affiliation(s)

Hanfeng Chen Department of Neurology, The First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, 324000, PR China
Hangbiao Jin Key Laboratory of Microbial Technology for Industrial Pollution Control of Zhejiang Province, College of Environment, Zhejiang University of Technology, Hangzhou, Zhejiang, 310014, PR China
Fangfang Ren Key Laboratory of Microbial Technology for Industrial Pollution Control of Zhejiang Province, College of Environment, Zhejiang University of Technology, Hangzhou, Zhejiang, 310014, PR China
Ruyue Guo Key Laboratory of Microbial Technology for Industrial Pollution Control of Zhejiang Province, College of Environment, Zhejiang University of Technology, Hangzhou, Zhejiang, 310014, PR China
Jianqiang Zhu Department of Environmental Engineering, Taizhou University, Taizhou, Zhejiang, 318000, PR China
Kaiyuan Huang Department of Neurosurgery, The First Affiliated Hospital, School of Medicine, Zhejiang University, Zhejiang, 310003, PR China.

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Associations of human exposure to 6PPD and 6PPDQ with colorectal cancer: A mixture analysis

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its oxidation product, 6PPD-quinone (6PPDQ), are widely present in the environment. Toxicological studies have demonstrated that they can induce adverse health effects on the intestinal system. However, epidemiological studies examining the association between human 6PPD and 6PPDQ exposure and colorectal cancer (CRC) risk remain scarce. In this study, human urinary 6PPD and 6PPDQ concentrations were analyzed in 329 controls and 367 CRC cases from Quzhou, China. A combination of analyses, including unconditional logistic regression, Bayesian kernel machine regression (BKMR), and restricted cubic spline analysis, was employed to evaluate associations between urinary 6PPD and 6PPDQ levels and CRC risk, adjusting for demographic and lifestyle variables. The median concentration of 6PPDQ in CRC cases (0.94 vs 0.14 μg/g creatinine) was significantly higher than that in controls (Mann-Whitney U test, p = 0.001), while the median concentration of 6PPD showed no significant (p = 0.061) difference between the two groups (0.31 vs 0.38 μg/g creatinine). Higher urinary 6PPDQ concentrations were significantly associated with increased CRC risk, especially among participants with third (adjusted OR = 2.79, 95 % CI: 1.76-4.47; p for trend <0.001) and fourth (adjusted OR = 7.13, 95 % CI: 4.31-12.0; p for trend <0.001) quartiles of exposure. Additionally, the joint effects of 6PPD and 6PPDQ exposure, assessed using the BKMR model, indicated a positive association with CRC risk, suggesting a cumulative risk from co-exposure. This study provides the first epidemiological evidence linking human 6PPDQ exposure to CRC risk, highlighting its potential role in colorectal carcinogenesis.

Tire-Derived Organic Chemicals in Urban Air at the Source-Sector Scale and Guidance on the Application of Polyurethane Foam Disk Passive Air Samplers

Tire-derived chemicals (TDCs) are shown to be elevated in urban environments. In this study, we analyzed 6PPD-quinone, 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), hexa(methoxy)methylmelamine (HMMM), as well as selected benzothiazoles and benzotriazoles, in different urban source-sectors. The chemical analyses were conducted on archived extracts of polyurethane foam (PUF) disk passive air samplers deployed across eight locations (including residential, industrial, semiurban, and traffic areas) over successive 2-month periods in the Greater Toronto Area, Canada. Principal component analysis showed distinct profiles in traffic-heavy locations, where benzothiazole and 6PPD-quinone had maximal concentrations of 2100 pg/m3 and 3.4 pg/m3, and where several TDCs including 6PPD-quinone, benzotriazoles, and some benzothiazoles were elevated during winter months. HMMM had elevated concentrations in nontraffic sectors, suggesting anthropogenic sources other than tires. This study recognizes the unique challenges to accurately quantifying TDCs in ambient air and that results presented here should be considered semiquantitative. To reduce uncertainty, temperature-dependent PUF disk-air partition coefficients (KPUF-AIR) and gas-particle partitioning fractions of TDCs in ambient air are presented. These are calculated from KOA values derived from quantum chemical methods using COSMOtherm and show that TDCs span a wide range of volatilities and gas-particle partitioning behavior, with implications for atmospheric fate and exposure. Lastly, guidance is provided on future measures to evaluate and minimize degradation losses of TDCs during sampling, extraction, and storage.

Development of a quantitative analytical method for 6PPD, a harmful tire antioxidant, in biological samples for toxicity assessment

This study developed and validated a high-sensitivity analytical method for the quantification of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), a hazardous antioxidant used in tires, to support the effective management of its environmental exposure. Using an HPLC-UV system with acetonitrile and deionized water as the mobile phase, the method did not require salts or acids. The calibration curve exhibited excellent linearity (R2 = 0.9999) with detection limits of 0.17 pg μL-1 (LOD) and 5.51 pg μL-1 (MDL), underscoring its ultra-trace detection capability. A pretreatment protocol was developed to quantify 6PPD in mouse liver samples. The protocol achieved a relative recovery rate of 71.89 % and high precision across all spiking concentrations (mean RSD = 2.20 ± 0.92 %). The validated methods were applied to analyze 6PPD residues in mouse liver following intratracheal instillation exposure. At 9 h post-exposure, residual 6PPD concentrations increased significantly in a dose-dependent manner (R2 = 0.9906), with a relative distribution of 0.06 ± 0.01 %. This cost-effective and reliable method provides a practical tool for quantifying 6PPD in environmental and biological matrices. The findings enhance the understanding 6PPD exposure dynamics and support the establishment of regulatory guidelines for managing its ecological and human health risks.

6PPD induces apoptosis and autophagy in SH-SY5Y cells via ROS-mediated PI3K/AKT/mTOR pathway: In vitro and in silico approaches

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), an extensively employed antioxidant in rubber materials, is considered as an emerging contaminant. 6PPD was proven to have potential neurotoxicity, which poses risks to human health. However, the research on its neurotoxicity is still limited. This work explored the neurotoxicity of 6PPD to SH-SY5Y cells and in-depth mechanisms with a combination of in vitro and in silico approaches. Our results indicated that 6PPD could reduce cell viability and cause oxidative damage by increasing reactive oxygen species (ROS) accumulation and altering the levels of glutathione (GSH), catalase (CAT), superoxide dismutase (SOD), and malondialdehyde (MDA). 6PPD induced neuronal apoptosis of mitochondrial pathway and autophagy dysfunction, as characterized by the increased expressions of Cleaved caspase-3, Bax/Bcl-2, Beclin-1, LC3-II/I, and P62. 6PPD downregulated the expression of PI3K, p-AKT, and p-mTOR, while the PI3K inhibitor suppressed PI3K/AKT/mTOR pathway and promoted both apoptosis and autophagy, indicating that PI3K/AKT/mTOR pathway was involved in 6PPD-induced apoptosis and autophagy. The inhibition of this pathway was attributed to ROS accumulation in SH-SY5Y cells. Molecular docking analysis further revealed that 6PPD exhibits strong binding affinity to PI3K, AKT, and mTOR protein molecules, which could effectively interfere with downstream signaling pathways. These findings enrich the understanding of 6PPD-induced neurotoxicity and contribute to the evaluation of ecological risks associated with 6PPD.

Assessment of tire-derived additives and their metabolites into fruit, root and leafy vegetables and evaluation of dietary intake in Swiss adults

Tire wear particles, released at an estimated 6 million tons annually worldwide, introduce various chemical substances into agricultural environments through atmospheric deposition, road runoff, and reclaimed wastewater. These tire-derived compounds are known to impact ecosystem health. This study investigates the transfer of such additives and their metabolites into vegetables, assessing human dietary intake. Using UPLC-MS/MS, eleven tire-related compounds were analyzed in 100 vegetable samples from nine Swiss retailers, including leafy (lettuce, cabbage, spinach), root (onion, potato, carrot), and fruit (tomato, bell pepper, zucchini, pumpkin) vegetables. Contamination was detected in all vegetable varieties. 31 % of the 100 samples contained benzothiazole (BTH), 1,3-diphenylguanidine (DPG), 6-PPD, or 1,3-dicyclohexylurea (DCU) at levels exceeding the limit of quantification (LOQ) whereas blank values remained below LOD. DPG was most frequently detected (18 %, n = 100), followed by 6-PPD (15 %, n = 100), DCU (10 %, n = 100), and BTH (3 %, n = 100). Spinach comprised 78 % of DPG-positive leafy samples. Daily intakes of 6-PPDQ, DCU, 6-PPD, and DPG from vegetables were estimated at 0-18.7, 0-57.7, 0-42.3, and 0-42.4 ng/person/day, respectively. While current toxicological data suggest no immediate health concerns, significant knowledge gaps remain regarding long-term toxicity. This study offers critical insights into the presence of tire-derived substances in agriculture and underscores the need for further research to better assess environmental and human health risks.

Distribution of synthetic antioxidants in outdoor and educational indoor dusts and assessment of human exposure

Antioxidants have been received recognized as contaminants in the environmental field due to the reports of adverse effects. In this study, a total of 35 outdoor dusts and 20 educational indoor dusts were sampled to investigated the occurrence and spatial distribution of antioxidants, and eight antioxidants were positively found in dusts. For the indoor dusts, the total antioxidant concentrations (Σ8Ant) were in the range of 15.7-5282 ng/g, 2,6-di-tert-butyl-4-methylphenol (BHT) was the dominate compound which constituted of 46.4% in the total concentrations of detected antioxidants. The composition profiles of antioxidants (67.9%) in outdoor dusts were different from that in indoor dusts, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) was the main component of all the identified antioxidants. Various microenvironments exhibited different contamination characteristics of antioxidants, the rank order of Σ8Ant was following as: campus roads (average concentration: 35.4 ng/g) < pedestrian streets (59.1 ng/g) < urban roads (92.9 ng/g) < teaching buildings (105 ng/g) < laboratory buildings (530 ng/g) < dormitories (1652 ng/g). Based on the measured Σ8Ant in dusts, we estimated daily intake via dust ingestion to be 3.90e-2 to 9.55e-2 ng/kg BW/day for adults under high exposure scenario. Overall, the occurrence and spatial distribution of antioxidants in outdoor and educational indoor spaces were investigated and the potential risks of detected antioxidants exposure in toddlers and adults were assessed in the present study.

Enhanced residual risk of abamectin induced by 6PPD: in water, soil, and vegetables

Abamectin, one of the most widely used pesticides globally, is known for its effectiveness in protecting crops and animal health. However, the residual risk of abamectin in agricultural products and the environment may be exacerbated by other pollutants, posing greater potential hazards. One such emerging environmental pollutant is N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), a common tire antioxidant found in various environments, including agricultural products and human urine. Our study is the first to reveal the co-existence of 6PPD and abamectin in water and soil, and it demonstrated that 6PPD significantly enhances the residual persistence of abamectin in environmental media and vegetables. Specifically, 6PPD extended the half-life of abamectin by 79% in pak choi and by 70% in cabbage. Additionally, 6PPD increased the photolysis half-life of abamectin by 191% in water and by 50% on soil surfaces. Furthermore, 6PPD also prolonged the photolysis half-life of four other macrolides in water. This study reveals the mechanism through which 6PPD extends the half-life of abamectin: by scavenging free radicals and inhibiting hydroxylation and oxidation, thus slowing its degradation. And this paper highlights that 6PPD significantly exacerbates the environmental risks and food safety issue associated with abamectin. Moreover, it provides valuable insights for studying the safe use of pesticides in complex environments with multiple contaminants.

Rubber-derived chemicals in urban sewer networks and receiving waters: Fingerprints, driving factors and ecological impacts

Rubber-derived chemicals (RDCs), which include rubber additives (RAs) and their transformation products (TPs), can be released into aquatic environments when rubber products, such as vehicle tires, are in use or discarded. However, RDCs and associated ecological risks have not been thoroughly investigated inside urban sewer networks and their receiving water bodies. To address these issues, we investigated the RDCs in Hong Kong's municipal sewer networks, including sewage and stormwater, as well as their receiving waters, such as rivers and coastal water. Among 45 target RDCs, the vulcanizing agents and corrosion inhibitors were found to be predominant in the water samples, accounting for 26-66 % and 29-72 % of total concentrations of 45 RDCs (∑45RDC), respectively, while antioxidants and their TPs presented in smaller quantities, accounting for 0.21-26 % and 0-15 % of ∑45RDC, respectively. Ten RAs from five classes were additionally identified by suspect screening. An estimated mass load of ∑45RDC amounting to 1690 kg/month is discharged into the coastal marine environment of Hong Kong, with sewage effluent being the primary source. Population density and vehicle-related factors (e.g., traffic load) were the major drivers shaping the spatial distribution of RDCs in surface water. Based on the ecological risk assessment outcomes, 16 out of 45 RDCs exhibited medium to high risks, and lists of candidate contaminants for various water bodies were proposed to support future risk management in water quality. These findings suggest that RDCs in stormwater and rivers should be carefully monitored, and management strategies should be developed to mitigate their risks.

Interaction between 6PPD/6PPD-Q and natural Fe-Mn nodules: Performance and mechanism of adsorption and oxidative transformation

The widely used rubber antioxidant N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its ozonated product, 6PPD-quinone (6PPD-Q), are highly toxic to aquatic life, yet understanding on their environmental behaviors is limited. This study comprehensively investigated their adsorption and transformation processes on natural Fe-Mn nodules (NFMN), which commonly exist in sediments and soils through a combination of diverse experimental and computational methods. The maximum adsorption capacity of 6PPD-Q (719.2 μg·g-1) is significantly higher than that of 6PPD (133.8 μg·g-1) at 293 K, and it is more difficult to desorb. They follow different kinetic and isothermal adsorption models, and environmental conditions (including temperature, pH, and anions) exert distinct influences on the adsorption of the two substances. Adsorption mechanisms involving electrostatic attraction, charge transfer, hydrogen bonding, and Lewis acid-base complexation were unveiled. For 6PPD, electrostatic adsorption and Lewis acid-base complexation contribute significantly to its adsorption. Conversely, for 6PPD-Q, the contribution of Lewis acid-base complexation outweighs that of hydrogen bonding, while the effect of electrostatic adsorption is relatively negligible. The stronger electrostatic attraction, more efficient charge transfer, and a greater number of binding sites for hydrogen bonding and Lewis acid-base complexation with NFMN results in more robust adsorption of 6PPD-Q. Furthermore, 6PPD can transform into 6PPD-Q on NFMN, facilitated by dissolved Mn(III). This study advances understanding of the adsorption behavior and mechanism of 6PPD and 6PPD-Q, and highlights a new pathway for 6PPD-Q formation, which provides valuable reference for assessing the water body exposure risks and formulating environmental remediation strategies for such pollutants. ENVIRONMENTAL IMPLICATION: This study offers the first comprehensive insight into the interactions between 6PPD/6PPD-Q and NFMN, illuminating their environmental behavior in water and soil systems. It reveals the adsorption discrepancy between 6PPD and 6PPD-Q, and elucidates the mechanisms underlying the difference in adsorption. Additionally, it uncovers a novel pathway for 6PPD-Q formation, offering valuable implications for risk assessment and environmental remediation strategies.

Molecule self-assembly of hydrangea-shaped hollow O, Cl -codoped graphite-phase carbon nitride microspheres for efficient N-(1,3-dimethyl butyl)-N'-phenyl-p-phenylenediamine quinone photodegradation and bacteria disinfection

6PPD-quinone (6PPD-Q) as a derivative of the rubber antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), is attracting intensive attention due to the significant hazard to ecosystems. However, the effective management of this type of contaminant has been scarcely reported. Hydrangea-like hollow O, Cl-codoped graphite-phase carbon nitride microspheres (HHCN), featuring open pores were readily prepared by molecular self-assembly and utilized to address 6PPD-Q in an aqueous system for the first time. More than 90 % of 6PPD-Q is efficiently photodegraded within 1 h on the as-prepared HHCN, which is 2.5 times more than that on bulk g-C3N4. Moreover, the as-synthesized HHCN demonstrates prominent photocatalytic activities for the degradation of doxycycline and tetracycline and the inactivation of Staphylococcus aureus (S. aureus) in an aqueous environment. The distinct hydrangea-like hollow structure imparts a large surface area and an abundance of active sites. In addition, the inclusion of Cl-3p orbitals also contributes to a reduction in the bandgap (2.01 eV) and facilitates carrier separation and transport. These combined characteristics synergistically enhance the remarkable photocatalytic performance of HHCN, which induces a more than 2 times higher degradation rate than bulk g-C3N4. This work offers a prospective route for template-free designing porous functional materials with improved properties and efficiently treating emerging pollutants such as 6PPD-Q, pathogenic bacteria, and antibiotic residues.

Adsorption of emerging micropollutants on tire wear particles

The aim of this study was to investigate the sorption behavior of tire wear particles (TWP), that represent a significant fraction of microplastics (MP) in aquatic environment. Two emerging micropollutants frequently detected in aquatic environment, bisphenol A and 1H-benzotriazole, were used as model compounds. Batch adsorption experiments were conducted to study kinetics and thermodynamic equilibrium as well as the effect of pH and ionic strength. Moreover, the impact of three aging processes, photoaging, chemical aging and biological aging on sorption behavior of TWPs was also studied. For comparison, similar experiments were conducted using polyethylene (PE), a microplastic consistently detected in aquatic environment. TWP exhibited higher adsorption tendency for BPA compared to BT. Photoaging of TWP enhanced the adsorption of target compounds. Bioaging and chemically aging significantly reduced the adsorption of BPA. Salinity affects negatively the adsorption of both compounds. TWP exhibited sorption behavior for BPA and BT comparable to polyethylene suggesting similar environmental risk as carriers of these micropollutants.

Role of Suspended Particulate Matter for the Transport and Risks of Organic Micropollutant Mixtures in Rivers: A Comparison between Baseflow and High Discharge Conditions

The partition dynamics of organic micropollutants between water and suspended particulate matter (SPM) in riverine ecosystems differs between dry and wet weather, as demonstrated at two sites at the Ammer River, Germany. One site was impacted by a wastewater treatment plant (WWTP) and the other by runoff of a mixed agricultural/urban area. Liquid and gas chromatography coupled to high-resolution mass spectrometry were used to quantify 415 organic chemicals, and their mixture effects were characterized with three in vitro bioassays indicative of the activation of the aryl hydrocarbon (AhR) and peroxisome proliferator-activated (PPARγ) receptors and the oxidative stress response. During wet weather, the total chemical concentrations and bioactivities in the water increased, but the concentrations in SPM did not change. As SPM levels increased, the SPM-bound chemicals contributed 6-16% to the overall concentrations in the water column during wet weather but only 0.1-0.9% during dry weather. The mixture effects were more strongly associated with SPM under wet conditions, particularly for AhR activity, where SPM accounted for over 90% of the observed effects. The AhR activity may therefore serve as an indicator for assessing the risks of SPM-related pollution in rivers. The high SPM-bound mixtures' activation of AhR and oxidative stress response during rain were primarily caused by polycyclic aromatic hydrocarbons, indicating a major contribution of road runoff.

Surveillance and environmental risk of very mobile pollutants in urban stormwater and rainwater in a water-stressed city

Urban stormwater and rainwater in water-stressed cities serve as critical vectors for the transport and dispersion of pollutants, including very mobile compounds These pollutants, which can be influenced by factors such as land use, rainfall intensity, and urban infrastructure, pose significant risks to both human and environmental health. Although several priority pollutants have traditionally been detected in urban stormwater, little is known about the presence of very mobile compounds that may threaten urban drinking water supplies and pose environmental risks to aquatic species. In this study, 131 urban rain and stormwater samples were collected from three districts of Barcelona (Spain) and analysed for 26 very mobile pollutants that are often overlooked in conventional monitoring efforts. The findings reveal that stormwater and rainwater are major contributors to the spread of pollutants in water-stressed cities, with particular emphasis on substances like lifestyle products, pharmaceuticals, and industrial chemicals. Among the 23 compounds detected, 12 were reported for the first time to occur in urban stormwater with concentrations as high as 271 µg L-1. Measurements of dissolved organic carbon, electrical conductivity, and the presence of wastewater-borne pollutants within the correlation analysis, suggested the contribution of sanitary sewer overflows (SSO) to urban stormwater. Finally, an environmental risk assessment (worst-case scenario) was performed, showing a moderate risk of target analytes such as acesulfame and 1-naphthalenesulfonic acid (ERQ > 0.1). The results highlight the need for improved surveillance systems, more sustainable stormwater management practices, and strategies for mitigating the environmental risk posed by very mobile pollutants in regions facing water scarcity.

Tire-derived compounds, phthalates, and trace metals in the Kiel Fjord (Germany)

Concerns about pollutants in the environment are increasing, with substances such as plastic additives drawing particular concern due to their potential harmful effects on organisms. This study investigates current levels of several contaminants in the Kiel Fjord. Some pose serious health risks to aquatic life. In September 2022, water and sediment samples were collected from fifteen stations across the inner and outer Kiel Fjord. The concentrations of selected phthalates, tire-derived compounds, and heavy metals were measured. Results indicate that the outer fjord has minimal contamination, while the inner fjord contains several hotspots with significant pollutant concentrations. For example, the highest levels of heavy metals were detected near Laboe and in deeper sediment layers (>6 cm) at Wik. The maximum concentrations of phthalates were observed near Laboe, with elevated levels also found near the city of Kiel and the Nord-Ostsee-Kanal. This study highlights the substantial anthropogenic impact on the region.

Targeted and untargeted discovery of UV filters and emerging contaminants with environmental risk assessment on the Northwestern Mediterranean coast

Marine ecosystems, particularly coastal areas, are becoming increasingly vulnerable to pollution from human activities. Persistent organic pollutants and contaminants of emerging concern (CECs) are recognized as significant threats to both human and environmental health. Our study aimed to identify the molecules present in the seawater of two bathing areas in the Western Mediterranean Sea. Polar Organic Chemical Integrative Samplers were employed for passive sampling of UV filters and other contaminants in the seawater. The concentrations of UV filters bemotrizinol (BEMT), benzophenone-3 (BP3), diethylamino hydroxybenzoyl hexyl benzoate (DHHB), octyl triazone (ET), and octocrylene (OC) were measured at these bathing sites during the summer of 2022. In addition, non-targeted chemical analysis was used to complement the list of pollutants in the sampling areas, leading to the identification of 53 contaminants and three natural products. Dodecyltrimethylammonium (DTA) and tetradecyltrimethylammonium (TTA) ions, 1,3-diphenylguanidine (DPG), N,N-diethyl-m-toluamide (DEET), and crystal violet (CV) were successfully quantified. Risk assessments showed that DEET, DPG, and BP3 present low environmental risks at the detected concentrations, while CV, DTA, and TTA pose medium to high risks, warranting further investigation. OC was found to pose a significant risk to marine biodiversity, as its environmental concentrations exceeded predicted no-effect concentration values. Overall, this study highlights the complexity of environmental pollution in coastal bathing areas and underscores the urgent need for comprehensive risk assessments to safeguard marine life and public health.

Impacts of climatic stressors on dissolved organic matter leaching from microplastics and their effects on biogeochemical processes: A review

This review explores the potential impact of microplastic-derived dissolved organic matter (MP-DOM) on biogeochemical processes associated with global carbon and nitrogen cycles, with consideration given to the possible influence of irregular climate changes. We synthesize literature on MP-DOM leaching behaviors during various natural aging processes, such as heavy rainfall, heat waves, and UV irradiation, which may be intensified by climate change. MP-DOM release varies with plastic type and conditions, with organic additives significantly influencing leaching under UV exposure. Increased turbulence from hydrological events and rising temperatures also enhances MP-DOM release. While most research has focused on specific additive releases, the broader effects of polymer degradation and subsequent impacts on microbial communities and biogeochemical cycles are only recently recognized. These disruptions may affect cellular processes in algae and plant roots, enhance microbial utilization of dissolved organic carbon, and potentially increase greenhouse gas production. Our review highlights overlooked roles of MP-DOM exacerbated by climatic stressors and calls for further research to understand its broader biogeochemical impacts. We also emphasize the importance of distinguishing between polymers and commercial plastics when assessing MP-DOM's effects on biogeochemical processes associated with carbon and nitrogen cycles and recommend investigating additional aging processes influencing MP-DOM release.

A Nationwide Investigation of Substituted p-Phenylenediamines (PPDs) and PPD-Quinones in the Riverine Waters of China

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) has been identified as the cause of the "urban runoff mortality syndrome." Thus, the ecological risks of substituted p-phenylenediamines (PPDs) and their quinone derivatives (PPD-Qs) in water have gained global attention. However, large-scale observation of their pollution characteristics in surface water is still lacking. Herein, a nationwide investigation revealed the pervasive occurrence of PPDs and PPD-Qs in riverine waters across China, with the mean concentration of ∑5PPD-Qs being 4.9 times higher than their parent ∑5PPDs. Notably, the 6PPD-Q concentrations at eight sampling sites exceeded the median lethal concentration for coho salmon. National annual riverine fluxes were estimated at 113.1 and 276.2 tonnes/year for PPDs and PPD-Qs, respectively, with the Yangtze River contributing more than one-third of the total fluxes. The transformation of PPDs to PPD-Qs was dependent on atmospheric hydroxylation rates and the half-lives of PPDs. A combined multimedia exposure assessment revealed that water exposure accounted for 82.5% of human exposure to PPDs and PPD-Qs, surpassing the contributions from dust and air exposure. This study provides a comprehensive spatial picture of PPDs and PPD-Qs in China. The national atlas highlights their potential ecological risks and implies that targeted actions should be taken to mitigate potential exposure to PPDs and PPD-Qs.

"Tire plastisphere" in aquatic ecosystems: Biofilms colonizing on tire particles exhibiting a distinct community structure and assembly compared to conventional plastisphere

Tire particles (TPs) significantly contribute to microplastics in aquatic ecosystems, which has recently attracted ecological concerns worldwide. Numerous studies have shown that biofilms on microplastics harbor unique species and harmful functions, but it remains unclear whether TPs could offer distinct niches for biofilms compared to conventional microplastics (CP). This study investigated the succession and assembly of biofilms on TPs compared with CP over 60 days. Our results showed the community structures of biofilms on TPs and CP were distinct. Intriguingly, a greater structural dissimilarity was observed between TPs-associated communities and natural biofilms compared to that between CP-associated communities and natural biofilms. This dissimilarity became more pronounced as biofilms progressed through succession. Furthermore, the bacterial community on the TPs exhibits a network of greater complexity, more stable structure, and higher activity than that on the CP, but the pattern was reversed in the eukaryotic community. Deterministic processes had a more critical impact on bacterial communities on TPs, whereas distinct stochastic processes controlled eukaryotic communities on TPs (dispersal limitation) and CP (undominated processes). Altogether, this study tentatively introduced the term "tire plastisphere" (i.e., TP-attached biofilms), emphasizing TPs could serve as more artificial microbial habitats and pose potential risks in disturbing aquatic ecology.

Lignocellulosic pruning waste adsorbents to remove emerging contaminants from tyre wear and pharmaceuticals present in wastewater in circular economy scenario

The following work explores a sustainable approach to repurpose organic waste from poplar pruning into lignocellulosic waste-based activated carbons (LPWACs) through environmentally friendly thermochemical processes and in line with circular economy principles. The developed LPWACs, activated by potassium hydroxide (KOH) at two different temperatures and weight ratios, exhibited promising textural properties with BET surface area (SBET) and total pore volume (VTOT) reaching up to 1336 m2·g-1 and 0.588 cm3·g-1, respectively. In addition, they displayed a developed microporous structure with a significant oxygen content (up to 11 %). These activated carbons were used to remove five emerging organic pollutants from the leaching of tyre wear particles (TWPs) and pharmaceuticals present in water. The increase in oxygen groups had a negative effect on the adsorption capacity of 1H-benzotriazole (BZTL), while electrostatic influences hindered diatrizoic acid (DZT) adsorption. LPWACs effectively remove pharmaceutical and tyre contaminants, supporting the circular economy in water treatment.

Effect of Plasma Treatment on Coating Adhesion and Tensile Strength in Uncoated and Coated Rubber Under Aging

The degradation of rubber materials under environmental and mechanical stress presents a significant challenge, particularly due to UV (ultraviolet light) exposure, which severely impacts the material's physical properties. This study aims to enhance the UV stability and longevity of rubber by evaluating the performance of modified polyurethane and silicone coatings as protective stabilizers. Natural rubber-styrene-butadiene rubber (NR-SBR), known for its exceptional mechanical properties, was selected as the base material. To ensure strong adhesion, cold atmospheric plasma treatment was applied, increasing the surface energy by 250%, primarily through an enhancement of the polar component. After treatment, supplier-recommended coatings were applied and tested for adhesion using the pull-out method. Aging tests under UV exposure, water immersion, and high temperatures were conducted to assess durability, with tensile tests used to monitor changes over time. Coatings exhibiting cracking after UV exposure were excluded from further analysis. A silicone coating demonstrating superior moisture resistance and durability under extreme conditions was identified as a promising candidate for future UV stabilization applications. These findings provide a foundation for developing advanced coatings to significantly extend the service life of rubber materials in demanding environments.

Marine Heatwaves Exacerbate the Toxic Effects of Tire Particle Leachate on Microalgae

Additives leached from tire particles (TPs) after entering the marine environment inevitably interact with marine life. Marine heatwaves (MHWs) would play a more destructive role than ocean warming during the interaction of pollutants and marine life. To evaluate the potential risks of TPs leachate under MHWs, the physiological and nutrient metabolic endpoints of microalgae Isochrysis galbana were observed for 7 days while being exposed to TPs leachate at current or predicted concentrations under MHWs. TPs leachate mainly contained Zn and 6-PPD, which could be absorbed by microalgae mostly, especially under MHWs. Additionally, TPs leachate increased the reactive oxygen species content, activated the antioxidant system, impaired photosynthesis and glycolysis, and decreased sugar and protein content. 10 mg/L TPs leachate increased the lipid content and saturation. Meanwhile, microalgae under such TPs leachate were biased toward the synthesis of long-chain fatty acids and Δ8 desaturation pathway. MHWs promoted the positive effects of TPs leachate on microalgae growth at the current concentration but exacerbated the negative effects at the predicted concentration. Our study emphasizes the potential risks of TPs leachate to marine primary production systems, especially if accompanied by the increasing intensity and frequency of extreme climate events.

Hydrolysis of p-Phenylenediamine Antioxidants: The Reaction Mechanism, Prediction Model, and Potential Impact on Aquatic Toxicity

While p-phenylenediamine antioxidants (PPDs) pose potential risks to aquatic ecosystems, their environmental persistence and transformation remain ambiguous due to the undefined nature of PPD C-N bond hydrolysis. Here, we investigated the hydrolysis patterns of PPDs by analyzing their hydrolysis half-lives, hydrolysis products around neutral pH (pH 6.0-7.7), and the role of atoms within the C-N bonds in PPDs. Hydrolysis preferentially targets the aromatic secondary amine N with the strongest proton affinity and the C atom of C-N with the highest nucleophilic-attack reactivity. The hydrolysis half-life (t1/2) shortens when the maximum proton affinity of N increases. These results are supported by theoretical calculations, demonstrating a hydrolysis reaction propelled by proton transfer from water to N and complemented by aromatic nucleophilic substitution of N in C-N by water hydroxyl. With the experimental results and the atom reactivity-based predictive model, the t1/2 around neutral pH for 60 PPDs (monitored in environment, commercially available, or under investigation) is determined, showing variations ranging from 2.2 h to 47 days. The model prediction of primary C-N hydrolysis is confirmed through typical PPDs. With the elucidated mechanism and developed model, this research provides new insights into PPD hydrolysis, underscoring its significance in delineating environmental impacts.

Machine learning helps reveal key factors affecting tire wear particulate matter emissions

Tire wear particles (TWPs) are generated with every rotation of the tire. However, obtaining TWPs under real driving conditions and revealing key factors affecting TWPs are challenging. In this study, we obtained a TWPs dataset by simulating tire wear process under real driving conditions using a tire wear simulator and custom-designed test conditions. This study shows that tire wear PM2.5 accounts for about 65 % of PM10. The response relationship between TWP emissions (both PM2.5 and PM2.5-10) and factors (the radial force, the lateral force, the tangential force, speed, driving torque, tire contact area, total contour length and tire tread temperature) was obtained by machine learning (ML) method. The random forest (RF) model was developed and displayed good prediction performance with an R2 of 0.84 and 0.78 for PM2.5 and PM2.5-10 on the test set, respectively. Model-related (similarity network graph) and model-unrelated (partial dependence plots and centered-individual conditional expectation plots) explainability methods were used to break the black box of ML. Model explainability results show that the feature parameters-emission response relationships for tire wear PM2.5 and PM2.5-10 are different. Avoiding strenuous driving behaviors (TTF < 400 N, TLF < 400 N), reducing tread temperature (T < 45℃), and minimizing the number of small tread patterns are feasible ways to reduce TWPs.

Development of a straightforward direct injection UHPLC-MS/MS method for quantification of plastic additive chemicals in roadside retention ponds

There is growing interest in road pollution that enters surface waters. Additive chemicals used in the manufacture of plastics, including tyre rubber, are mobile pollutants that pose a threat to aquatic life. Therefore, an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was developed to measure 25 plastic additive chemicals in road runoff and water of retention ponds used to manage road runoff. A straightforward direct injection methodology was adopted to minimise sample handling and risk of contamination. Using this approach, the method quantitation limits (MQLs) ranged from 4.3 × 10-3 to 13 µg/L. These were adequate to determine most chemicals at or below their freshwater predicted no-effect concentration (PNEC). Method trueness ranged from 18 to 148% with most chemicals being within 80-120%. The method was applied to water from four retention ponds in series to measure additive chemicals entering the ponds (i.e., in road runoff) and passing through each pond. Greatest concentrations were observed in road runoff during heavy rainfall following dry weather. Here, 1,3-diphenylguanidine (DPG) exceeded its current PNEC of 1.05 µg/L. Notably, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-quinone) was determined at 0.13 µg/L which is greater than its lowest acute toxicity threshold (0.095 µg/L). Similarity in additive chemical concentrations throughout the retention ponds during steady flow suggests little or no removal occurs. However, further studies are needed to assess the fate and removal of plastic additive chemicals in retention ponds and the risk posed to aquatic environments. Such research can be facilitated by this newly developed UHPLC-MS/MS method.

Occurrence, Emission, and Transport of Tire and Road Wear Particles across Four Environmental Compartments along Ring Road Networks in Beijing

Tire and road wear particles (TRWPs) are an appreciable source of microplastics (MPs); however, knowledge of their large-scale occurrence and mass flux based on robust sampling and quantification is limited. Herein, the first city-wide survey of TRWPs across environmental compartments (road dust, snowbank, water, and sediment from rivers and lakes) along four ring roads (beltways) in Beijing was performed. TRWP concentrations (n = 74) were quantified using bonded-sulfur as a marker to reveal the city-wide spatial distributions and adopted to establish a framework estimating TRWP emission factors (EFs) and mass flux from generation to remote atmospheric, terrestrial, and aquatic transport. The TRWP concentrations were 0.46 × 104-3.55 × 104 μg/g (road dust), 0.65-46.18 mg/L (water), 0.28 × 104-1.79 × 104 μg/g (sediment), and 9.46-19.12 mg/L (snowbank) and were highly related to nearby traffic conditions. Based on total EFs (34.4-288.5 mg/vKT) and airborne EFs (6.2-17.2 mg/vKT) calculated from the preceding concentrations, the TRWP emissions in Beijing were determined as 1.28 × 104 t/a. Among them, 61.3% was eventually disposed of in landfills owing to frequent road sweeping and high runoff treatment efficiency and 18.1% was stranded on the roadside; nevertheless, 11.9% escaped to freshwater systems and 5.7 and 3.0% airborne transported to remote land and ocean, respectively. This study provides new insights into the emissions and fate of TRWPs.

Environmental occurrence, fate, human exposure, and human health risks of p-phenylenediamines and their quinones

P-phenylenediamine antioxidants (PPDs) are widely used in the rubber industry and their release and transformation in the environment has become one of the current environmental research hotspots. PPDs are readily oxidized in the environment to form quinone transformation products (PPD-Qs), some of which (e.g. 6PPD-Q) have been shown to be highly toxic and persistent in the environment, posing a potential threat to aquatic organisms and ecosystems. The present study provides an overview of the physicochemical properties, environmental distribution, and potential human exposure and toxicological effects of PPDs and PPD-Qs. PPDs and PPD-Qs are found in water, air, dust and soil around the world, and humans are inevitably exposed to them by inhaling, ingesting and through dermal contact. There is growing evidence indicates that PPDs and PPD-Qs are present in human body fluids and tissues, where they are subject to metabolic and transformational processes in the liver and blood. Furthermore, PPDs and PPD-Qs have the potential to induce adverse health effects, including digestive, respiratory, neurotoxic and reproductive toxicity. Nevertheless, there is a paucity of evidence concerning the direct effects of PPDs and PPD-Qs on human health. Consequently, future research should concentrate on this area in order to provide quantitative support for the assessment of the risk posed by PPDs and PPD-Qs to human health.

Comparative growth inhibition of 6PPD and 6PPD-Q on microalgae Selenastrum capricornutum, with insights into 6PPD-induced phototoxicity and oxidative stress

Widespread environmental detection of tire additive N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its toxic metabolite 6PPD-Q has raised great concerns for their potential impact on aquatic biota. This study investigated the effects of 6PPD and 6PPD-Q on the model green microalgae (Selenastrum capricornutum). Results showed that 6PPD at the concentrations of 1-5 mg·L-1 stimulated S. capricornutum growth, while higher concentrations (10-50 mg·L-1) inhibited growth with an IC50(96 h) of 8.78 mg·L-1. However, at concentrations up to 10 mg·L-1, no toxicity was observed for S. capricornutum exposed to 6PPD-Q. Under the stress of 6PPD, S. capricornutum exhibited increased cellular membrane permeability and cell wall rupture, indicating structural damage to the algae cell. Microalgal oxidative stress was induced through the accumulation of reactive oxygen species (ROS), reaching levels of 1.65-5.29 times higher than the non-exposure cells, which altered enzymatic activities including superoxide dismutase (SOD) and catalase. Exposure to 6PPD at concentrations of 10-50 mg·L-1 resulted in photosynthetic toxicity as evidenced by decreased Chlorophyll a (Chl a) content and adverse effects on chlorophyll fluorescence parameters, such as maximum photochemical quantum yield (Fv/Fm), PSII (photosystem II) effective quantum yield [Y(II)], and photosynthetic electron transfer rate (ETR). While the concentrations employed may be higher than those typically found in the environment, this study uncovers a significant finding that 6PPD may demonstrate even greater toxicity to microalgae than its derivative, 6PPD-Q. This underscores the need for further investigation into the ecological risks of 6PPD, particularly in the context of primary producers like microalgae.

Priorities to inform research on tire particles and their chemical leachates: A collective perspective

Concerns over the ecological impacts of urban road runoff have increased, partly due to recent research into the harmful impacts of tire particles and their chemical leachates. This study aimed to help the community of researchers, regulators and policy advisers in scoping out the priority areas for further study. To improve our understanding of these issues an interdisciplinary, international network consisting of experts (United Kingdom, Norway, United States, Australia, South Korea, Finland, Austria, China and Canada) was formed. We synthesised the current state of the knowledge and highlighted priority research areas for tire particles (in their different forms) and their leachates. Ten priority research questions with high importance were identified under four themes (environmental presence and detection; chemicals of concern; biotic impacts; mitigation and regulation). The priority research questions include the importance of increasing the understanding of the fate and transport of these contaminants; better alignment of toxicity studies; obtaining the holistic understanding of the impacts; and risks they pose across different ecosystem services. These issues have to be addressed globally for a sustainable solution. We highlight how the establishment of the intergovernmental science-policy panel on chemicals, waste, and pollution prevention could further address these issues on a global level through coordinated knowledge transfer of car tire research and regulation. We hope that the outputs from this research paper will reduce scientific uncertainty in assessing and managing environmental risks from TP and their leachates and aid any potential future policy and regulatory development.

Intensive Spatiotemporal Characterization of the Tire Wear Toxin 6PPD Quinone in Urban Waters

6PPDQ is a tire-derived contaminant toxic to coho salmon (LC50 = 41-95 ng/L) found widely distributed in urban environments. Most monitoring efforts have relied on relatively few discrete samples collected at select locations across rain events. Early work has revealed that 6PPDQ concentrations vary widely over time and space, raising questions about when and where to collect samples. Here, we employ condensed phase membrane introduction mass spectrometry, a high-throughput analysis approach to characterize spatiotemporal variability of 6PPDQ in urban streams. Analytical method detection limits of 0.3-8 ng/L and a duty cycle of 2.5 min/sample enabled high-throughput adaptive sampling. Temporal sampling revealed dynamic 6PPDQ concentrations, with significant changes occurring over minutes during peak rainfall. Spatial variability was characterized at multiple sites along three watercourses during the first significant precipitation of autumn 2023 on central Vancouver Island, B.C., Canada. Site-specific concentrations suggest attenuation of 6PPDQ after point source inputs by some combination of physical (dilution, sorption) or chemical (degradation) processes. This is the first report of an intensive sampling campaign describing the spatiotemporal distribution of 6PPDQ, highlighting the need for careful consideration of sampling strategies to evaluate the risk and impact of 6PPDQ in urban waterways.

Occurrence, sources, and human exposure assessment of amine-based rubber additives in dust from various micro-environments in South China

Despite the ubiquitous use and potential health effects of amine-based rubber additives, information regarding their occurrences in indoor environments remains scarce and is basically investigated in traffic-related environments. In this study, a total of 140 dust samples collected from eight indoor micro-environments were analyzed for twelve amine-based rubber additives. Overall, 1,3-diphenylguanidine (DPG), dicyclohexylamine (DCHA), N-(1,3-dimethylbutyl)-N'-phenyl-p-penylenediamine (6PPD), 6PPD-quinone (6PPDQ), and hexa(methoxymethyl)melamine (HMMM) were frequently detected across all micro-environments with detection frequencies of 97 %, 51 %, 71 %, 99 %, and 77 %, respectively. The highest total concentration of amine-based rubber additives was found in parking lots (median 10,300 ng/g), indicating heavier emission sources of these compounds in vehicle-related indoor environments. Despite this, amine-based rubber additives were also frequently detected in various non-vehicle-related environments, such as markets, cinemas, and hotels, probably due to the widespread use of consumer products and more frequent air exchanges with outdoor environments. Further tracking of tire rubber products and paint particles from flooring materials in parking lots revealed that paint particles might be an overlooked contributor to amine-based rubber additives in indoor environments. Finally, the highest estimated daily intakes (EDIs) of all amine-based rubber additives via dust ingestion at home were observed for toddlers (3.48 ng/kg bw/d). This research provides a comprehensive overview of human exposure to a variety of amine-based rubber additives in various indoor environments. ENVIRONMENTAL IMPLICATION: This study highlights the presence of high concentrations of amine-based additives in indoor dust from both traffic-related and non-traffic-related indoor environments. Additional efforts are needed to identify potential sources of amine-based rubber additives indoors, beyond just tire rubber. This is critical because the widespread presence of rubber products in indoor settings could pose a risk to human health.

Response of Ceratophyllum demersum L. and its epiphytic biofilms to 6PPD and 6PPD-Q exposure: Based on metabolomics and microbial community analysis

The emerging contaminant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its ozone conversion product N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) pose a threat to aquatic ecosystems. Aquatic animals and plants exhibit vigorous responses at very low ambient concentrations. However, studies of submerged macrophytes, key producers in aquatic ecosystems, are limited and the full extent of their toxic effects and feedback mechanisms is unknown. To investigate the phytotoxicity of 6PPD and 6PPD-Q, we modeled plant responses to abiotic stress using Ceratophyllum demersum L. (C. demersum) as a representative submerged plant. Our findings indicate that 6PPD and 6PPD-Q disrupt physiological and biochemical processes in C. demersum, encompassing growth inhibition, reduction in photosynthetic pigments, induction of oxidative damage, and metabolic alterations. Moreover, unfavorable modifications to biofilms induced were also discernible supported by confocal laser scanning microscopy (CLSM) images and microbial community profiling. More importantly, we found a robust correlation between differentially expressed metabolites (DEMs) and dominant genera, and 6PPD and 6PPD-Q significantly altered their correlation. Overall, our results imply that even though C. demersum is a resilient submerged macrophyte, the toxic effects of 6PPD and 6PPD-Q cannot be disregarded.

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.

Unveiling the environmental impact of tire wear particles and the associated contaminants: A comprehensive review of environmental and health risk

This review offers a novel perspective on the environmental fate and ecotoxicological effects of tire wear particles (TWPs), ubiquitous environmental contaminants ranging in size from micrometers to millimeters (averaging 10-100 micrometers). These particles pose a growing threat due to their complex chemical composition and potential toxicity. Human exposure primarily occurs through inhalation, ingesting contaminated food and water, and dermal contact. Our review delves into the dynamic interplay between TWP composition, transformation products (TPs), and ecological impacts, highlighting the importance of considering both individual chemical effects and potential synergistic interactions. Notably, our investigation reveals that degradation products of certain chemicals, such as diphenylguanidine (DPG) and diphenylamine (DPA), can be more toxic than the parent compounds, underscoring the need to fully understand these contaminants' environmental profile. Furthermore, we explore the potential human health implications of TWPs, emphasizing the need for further research on potential respiratory, cardiovascular, and endocrine disturbances. Addressing the challenges in characterizing TWPs, assessing their environmental fate, and understanding their potential health risks requires a multidisciplinary approach. Future research should prioritize standardized TWP characterization and leachate analysis methods, conduct field studies to enhance ecological realism, and utilize advanced analytical techniques to decipher complex mixture interactions and identify key toxicants. By addressing these challenges, we can better mitigate the environmental and health risks associated with TWPs and ensure a more sustainable future.

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

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

Evidence for the formation of 6PPD-quinone from antioxidant 6PPD by cytochrome P450

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) as a rubber antioxidant has attracted global concern, since its ozone-oxidation product 6PPD-quinone (6PPDQ) was found to be the primary toxicant responsible for urban runoff mortality syndrome in coho salmon. However, the biotransformation fate and associated toxicological mechanism of 6PPD have not received much study yet. In this work, the in vitro assays showed 6PPD can be transformed into 6PPDQ by cytochromes P450 (CYP450) in human liver microsomes (HLMs) with 0.98 % production rate, and the adducts of 6PPDQ with calf thymus DNA and the N-N coupling product between 6PPD and 6PPDQ were further identified after 6PPD incubation in HLMs. Further evidence for the 6PPDQ formation can be obtained from the in vivo assays that the 6PPDQ-DNA adducts and 6PPD-N-N-6PPDQ dimer were detected in mice by oral gavage with 6PPD, and the latter dimer species was detected as well in 6PPD exposure to zebrafish larvae. Especially, the bioaccumulation property and high reactivity of 6PPDQ result in the continuous formation of the significant DNA adducts and 6PPD-N-N-6PPDQ dimer even in case of low production rate of biotransformation of 6PPD to 6PPDQ, which may provide potentially effective biomarkers for such process. DFT computations revealed the formation mechanism of 6PPDQ is the (N)H-abstraction of 6PPD by CYP450, followed by amino radical rebound at the nearby ortho-carbon, yielding a quinol intermediate due to spin delocalization, that might readily undergo further oxidation by CYP450 into 6PPDQ.

Unveiling spatiotemporal distribution, partitioning, and transport mechanisms of tire additives and their transformation products in a highly urbanized estuarine region

Numerous tire additives are high-production volume chemicals that are used extensively worldwide. However, their presence and partitioning behavior remain largely unknown, particularly in marine environments. This study is the first to reveal the spatiotemporal distribution, multimedia partitioning, and transport processing of 22 tire additives and their transformation products (TATPs) in a highly urbanized estuary (n = 166). Nineteen, 18, and 20 TATPs were detectable in water, suspended particulate matter (SPM), and sediments, respectively, with total levels of 59.7-2021 ng/L, 164-6935 ng/g, and 4.66-58.4 ng/g, respectively. The multimedia partitioning mechanisms of TATPs are governed by their molecular weight, hydrophobicity, and biodegradation rate. Mass inventories coupled with model simulations have revealed that substantial quantities of TATPs accumulate within estuarine environments, and these compounds can be continuously transported into the ocean, particularly during the wet season. According to the multi-criteria evaluation approach, four and three TATPs were identified as high-priority pollutants during the dry and wet seasons, respectively. Unexpectedly, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone was only listed as a medium-priority pollutant. This study underscores the importance of marine surveillance and advocates for particular attention to these ubiquitous but underexplored TATPs in future studies.

Exposure of RAW264.7 macrophages to exhaust emissions (gases and PAH) and non-exhaust emissions (tire particles) induces additive or synergistic TNF-α production depending on the tire particle size

Road traffic is a major contributor to air pollution and consequently negatively affects human health. Car pollution originates both from exhaust emissions (EE) and non-exhaust emissions (NEE, such as tire and brake wear particles, erosion of road surfaces and resuspension of road dust). While the toxicity of EE and NEE has been characterized separately, their combined effects are poorly documented. However, we are constantly exposed to a mixture of pollutants and their interactions should not be neglected as they may significantly impact their toxicological profile resulting in additive, synergistic or antagonistic effects. To fill this gap, we investigated in vitro the combined toxicity of exhaust gases and benzo[a]pyrene (representative of EE) and tire particles (representative of NEE). Macrophages from the RAW264.7 cell line were exposed for 24 h to tire particles (TP) of variable size (6-113 µm), alone or in combination with exhaust gases (CO2, CO, NO, NO2) and benzo[a]pyrene (B[a]P) as an archetype of polycyclic aromatic hydrocarbon (PAH). The cell response was assessed in terms of cytotoxicity, proinflammatory response and oxidative stress. TP, gases and B[a]P, alone or in combination triggered neither cytotoxicity nor oxidative stress. On the contrary, a proinflammatory response was elicited with two different profiles depending on the size of the TP: TNF-α production was either slightly (with the finest TP) or strongly (with coarse TP) increased in the presence of gases and B[a]P, suggesting that the effects of TP, gases and B[a]P were either additive or synergistic, depending on TP size.

Toxicological mechanisms and molecular impacts of tire particles and antibiotics on zebrafish

Tire microplastics (TMPs) and antibiotics are emerging pollutants that widely exist in water environments. The coexistence of these pollutants poses severe threats to aquatic organisms. However, the toxicity characteristics and key molecular factors of the combined exposure to TMPs in aquatic organisms remain unknown. Therefore, the joint toxicity of styrene-butadiene rubber TMPs (SBR-TMPs) and 32 antibiotics (macrolides, fluoroquinolones, β-lactams, sulfonamides, tetracyclines, nitroimidazoles, highly toxic antibiotics, high-content antibiotics, and common antibiotics) in zebrafish was investigated using a full factorial design, molecular docking, and molecular dynamics simulation. Sixty-four combinations of antibiotics were designed to investigate the hepatotoxicity of the coexistence of SBR-TMPs additives and antibiotics in zebrafish. Results indicated that low-order effects of antibiotics (e.g., enoxacin-lomefloxacin and ofloxacin-enoxacin-lomefloxacin) had relatively notable toxicity. The van der Waals interaction between additives and zebrafish cytochrome P450 enzymes primarily affected zebrafish hepatotoxicity. Zebrafish hepatotoxicity was also affected by the ability of SBR-TMPs to adsorb antibiotics, the relation between antibiotics, the affinity of antibiotics docking to zebrafish cytochrome P450 enzymes, electronegativity, atomic mass, and the hydrophobicity of the antibiotic molecules. This study aimed to eliminate the joint toxicity of TMPs and antibiotics and provide more environmentally friendly instructions for using different chemicals.