Tyre additive chemicals, tyre road wear particles and high production polymers in surface water at 5 urban centres in Queensland, Australia

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.

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.

Low-dose tire wear chemical 6PPD-Q exposure elicit fatty liver via promoting fatty acid biosynthesis in ICR mice

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) as a major metabolite of tire wear chemical 6PPD has been demonstrated to be an emerging burden of exposure in human populations, via contamination from drinking water, air particulate matter and food sources. Whilst increasing attention has been moved toward its adverse effect, the potential hepatotoxicity of 6PPD-Q in mammals at realistic dose remains unknown. Here, the toxic effects of 6PPD-Q at environmentally relevant dose on the liver of adult mice and its underlying mechanism were investigated through an integrative approach combining transcriptomic and lipidomic analyses. We found that 6PPD-Q exposure induced excessive lipid deposition following three weeks of exposure, ultimately contributing to the pathogenesis of fatty liver disease. Mechanistically, 6PPD-Q exposure caused a remarkable increase in the contents of fatty acids within the hepatic tissue of mice by enhancing their biosynthesis, thereby facilitating lipid deposition. In summary, this study provides a new understanding on the endocrine disrupting effects of 6PPD-Q on hepatic lipid metabolism and how it may contribute to elevated risk of fatty liver disease. Our findings call for a potential public health attention on the risk assessment of 6PPD-Q, particularly towards the risk of chronic metabolic diseases.

Effects of salinity on the adsorption of cadmium and zinc to tire and road wear particles in water - Significance for river systems and road runoff treatment

Tire wear particles (TWP) are potential pollutants of emerging concern. Therefore, the EU is set to regulate the TWP emissions under the new Euro 7 emission standard. For Germany it is estimated that up to 20,000 t TWP reach the aquatic environment. Main transport pathways are via road runoff and separate sewage systems. Studies indicate that, apart from ecotoxicological concerns, the negatively charged surface of TWP can adsorb heavy metals like Cr, Ni, Zn, Cd and Pb, potentially deteriorating the chemical water quality of rivers. As rivers usually undergo a salt gradient from their source to the sea this may change the adsorption of heavy metals. We investigated the influence of salinity on the heavy metal adsorption on TWP using water samples from the Freiberger Mulde (Saxony, Germany), enriched with NaCl to simulate the salinity representative of different rivers in the Elbe catchment area, and additional water samples (Elbe, Saale, Bode, Schlenze). The adsorption of Cd and Zn appear to be highly salt-dependent. Above 12 mg L-1 Cl-, no significant adsorption was observed. It is assumed that both metals form [MCl4]2- complexes which are repelled from the negative surface of TWP. The potential in building these complexes is high enough to dissolve previously adsorbed Cd from TWP. These findings are important for assessing water quality of river systems as well as runoff filtration and water retention systems. In winter, for instance, when de-icing salt is applied, Cd and Zn bound on TWP may be mobilized entering water systems.

p-Phenylenediamines and their derived quinones: A review of their environmental fate, human exposure, and biological toxicity

p-Phenylenediamines (PPDs) are widely used as antioxidants in numerous rubber products to prevent or delay oxidation and corrosion. However, their derived quinones (PPD-Qs), generated through reactions with ozone, are ubiquitous in the environment and raise significant health and toxicity concerns. This review summarizes the current state of knowledge on environmental distribution and fate, human exposure, and biological toxicity of PPDs and PPD-Qs, and makes recommendations for future research directions. Although PPDs and PPD-Qs have been monitored in a variety of environmental matrices, studies on soil, sediment, and organisms remain limited. This shortcoming hinders our understanding of their distribution patterns and migration mechanisms in these specific environments. These contaminants can enter the human body through various exposure routes, but toxicological studies have not yielded sufficient results to derive risk thresholds for the assessment of human health. Most studies examining biological and toxicological effects have focused on acute exposure scenarios, which do not accurately reflect the long-term interactions that occur in natural settings. The toxic effects of PPDs and PPD-Qs on zebrafish, nematodes, and mammals include neurobehavioral changes, reproductive dysfunction, and digestive damage, which are linked to mitochondrial stress, DNA adduct formation, and disrupted lipid metabolism, respectively. However, the underlying toxicological mechanisms remain poorly understood. Future research should prioritize the investigation of the impacts of PPDs and PPD-Qs on various organizational levels within biota to provide a scientific basis for developing effective risk management measures.

Toxicity of tire rubber-derived pollutants 6PPD-quinone and 4-tert-octylphenol on marine plankton

The impacts of tire wear particles and their associated chemicals on the aquatic systems are a major environmental concern. In this study, we investigated the acute toxicity of two pollutants derived from tire rubber, 6PPD-quinone and 4-tert-octylphenol, on marine plankton. Specifically, we determined the acute effects of these pollutants on various organisms within the plankton food web: the microalgae Rhodomonas salina, the adult copepod Acartia tonsa, and the early life stages of the echinoderms Arbacia lixula and Paracentrotus lividus and the fish Sparus aurata. Exposure to 6PPD-quinone did not affect the microalgae growth, copepod survival, or fish embryo viability after 48 h of exposure at concentrations up to 1000 µgL-1. However, 6PPD-quinone significantly inhibited the growth of early developmental stages of both echinoderm species, with median effective concentrations of 7 and 8 µgL-1. Conversely, 4-tert-octylphenol was toxic to all studied organisms, with median lethal and effective concentrations ranging from 21 to 79 µgL-1 depending on the species and endpoints. The most sensitive planktonic organisms to 4-tert-octylphenol were echinoderm embryos and copepods, which exhibited negative effects at concentrations as low as 1 and 25 µgL-1, respectively. Our results demonstrate that acute exposure to 6PPD-quinone and 4-tert-octylphenol can cause harmful effects on key planktonic organisms at environmentally relevant concentrations. Overall, our findings highlight the need for develop ecologically safer tire rubber additives and reduce traffic-related tire particle emissions to mitigate their entry and potential impacts on aquatic ecosystems.

Exploring potential targets and mechanisms of renal tissue damage caused by N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6-PPDQ) through network toxicology and animal experiments: A case of chronic kidney disease

6-PPDQ is a new type of environmental contaminant contained in tire rubber. No studies have been reported on the potential targets and mechanisms of action of 6-PPDQ on renal tissue damage. In the present study, we used CKD as an example to explore the potential targets and biological mechanisms of renal injury caused by 6-PPDQ using Network toxicology and animal experiments. A total of 1361 6-PPDQ-related target genes were obtained from the CTD database. 17,296 CKD-related target genes were obtained through the GeneCards database. After intersecting the two, a total of 908 intersecting genes were obtained. Next, we constructed a PPI protein interaction network. Using different algorithms in Cytoscape software and "Logistic regression analysis", five key target genes were finally identified as NOTCH1, TP53, TNF, IL1B and IL6. We constructed a diagnostic model using five key target genes, and the ROC curves, calibration curves and DCA curves proved that the model has good diagnostic value. Molecular docking demonstrated high affinity between 6-PPDQ and five key target gene proteins. In animal experiments, repeated intraperitoneal injections of 6-PPDQ using different concentration gradients for 28 days revealed that the expression levels of five key target genes in renal tissues increased progressively with the increase of the concentration, and the damage to renal tissues was also aggravated. ssGSEA and animal experiments revealed a key role for activation of the MAPK signaling pathway. Finally, we also identified a significant correlation between five key target genes and the level of infiltration of multiple immune cells. In conclusion, these findings suggest that 6-PPDQ can cause damage to renal tissue and that the level of damage progressively increases with increasing concentration. Among them, NOTCH1, TP53, TNF, IL1B and IL6 may be its potential targets of action. Activation of the MAPK signaling pathway is a potential mechanism of action.

Long-Term Exposure to Tire-Derived 6-PPD Quinone Causes Neurotoxicity and Neuroinflammation via Inhibition of HTR2A in C57BL/6 Mice

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6-PPDQ), a novel contaminant derived from tire wear, has raised concerns due to its potential neurotoxicity, yet its long-term effects on mammalian neurological health remain poorly understood. This study investigates the neurotoxic and neuroinflammatory impacts of prolonged 6-PPDQ exposure using male C57BL/6 mice. Behavioral assessments revealed significant cognitive deficits, while biochemical analyses demonstrated increased levels of reactive oxygen species, apoptosis, and blood-brain barrier (BBB) disruption. Elevated pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) and activation of microglial cells were observed, indicating a robust neuroinflammatory response. Network pharmacology and molecular docking identified serotonin receptor HTR2A as a key target through which 6-PPDQ mediates its toxic effects. Activation of HTR2A by the agonist DOI (2,5-dimethoxy-4-iodoamphetamine) mitigated these effects, suggesting a potential therapeutic strategy. These findings provide the first evidence of 6-PPDQ-induced neurotoxicity in mammals, underscoring the need for preventive measures to protect neurological health.

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.

Tire microplastic particles and warming inhibit physiological functions of the toxic microalga Alexandrium pacificum

Previous studies have confirmed that the tire microplastic particles (TMPs) have a variety of toxic biological effects. However, the potential toxic mechanisms of TMPs remain to be elucidated, especially in the interaction between particle behavior and seawater warming. In this study, we investigated the effects of three different concentrations of TMPs suspensions (0 mg/L, 1 mg/L, and 500 mg/L) on Alexandrium pacificum in both the presence and absence of warming. Our results revealed significant differences in toxicity among different concentrations of TMPs towards A. pacificum, i.e., low concentrations promoting but high concentrations inhibiting, furthermore, warming exacerbated these toxicological responses. Specifically, under elevated temperature, high concentrations TMPs could inhibit photosynthetic pigment and chlorophyll fluorescence parameter, as well as the nutrient absorption, and induced oxidative stress. Furthermore, TMPs could adsorb onto microalgae surfaces and thus, forming heterogeneous aggregates through agglomeration with extracellular secretions. This is strongly correlated with biomarker response. Overall, these findings highlight the influence of warming on the toxicity of TMPs and provide valuable data for risk assessment.

Potential human health risk of the emerging environmental contaminant 6-PPD quinone

The tire antioxidant 6-PPD has been widely used to enhance tire performance and extend tire lifespan. 6-PPD quinone (6-PPDQ), a quinone derivative derived from 6-PPD in the presence of ozone, has been recognized an emerging environmental contaminant. In addition to causing acute lethality to coho salmon, 6-PPDQ exhibits toxic effects on other aquatic species and mammals. Based on the existing evidence, we provide a critical overview on the human internal exposure, potential adverse effects on health, and prediction of human health risk of 6-PPDQ. 6-PPDQ could be detected in human samples, including human urine, blood, and cerebrospinal fluid. Human exposure to 6-PPDQ in the environment is inevitable and may lead to adverse health effects, including hepatotoxicity, enterotoxicity, pulmonary toxicity, neurotoxicity, reproductive toxicity, and cardiotoxicity. Additionally, potential human health risk to 6-PPDQ through exposure routes and human samples were predicted. This review is helpful to identify the existing knowledge gaps and future research directions regarding the human health effects of 6-PPDQ.

Are eco-friendly "green" tires also chemically green? Comparing metals, rubbers and selected organic compounds in green and conventional tires

Tires are a major source of synthetic and natural rubber particles, metals and organic compounds, in which several compounds are linked to negative environmental impact. Recent advances in material technology, coupled with focus on sustainability, have introduced a new range of tires, sold as "green, sustainable, and eco-friendly". Although these "green" tires may have lower impact on the environment on a global scale, there is no current knowledge about the chemical composition of "green" tires, and whether they are more eco-friendly when considering the release of tire wear particles or tire-associated chemicals. Here we have investigated the chemical composition of nine "green" vehicle tires, one "green" bike tire and seven "conventional" vehicle tires. No significant difference was found between "green" and "conventional" tires tested in this study. For N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), the average concentration in "green" tires were higher (16 ± 7.8 µg/mg) compared to "conventional" tires (8.7 ± 4.5 µg/mg). The relationship between metals, selected organic compounds and rubbers demonstrated large variation across brands, and lower variability between tires grouped according to their seasonal use. This study indicates that more work is needed to understand how the shift towards sustainable tires might change the chemical composition of tires.

Emerging N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and 6PPD quinone in paired human plasma and urine from Tianjin, China: Preliminary assessment with demographic factors

With increasing concerns about N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and 6PPD-quinone (6PPD-Q), relevant environmental investigations and toxicological research have sprung up in recent years. However, limited information could be found for human body burden assessment. This work collected and analyzed 200 samples consisting of paired urine and plasma samples from participants (50 male and 50 female) in Tianjin, China. Low detection frequencies (DF, <15 %) were found except for urinary 6PPD-Q (86 %), which suggested the poor residue tendency of 6PPD and 6PPD-Q in blood. The low DFs also lead to no substantial association between two chemicals. Data analysis based on urinary 6PPD-Q showed a significant difference between males and females (p < 0.05). No significant correlation was found for other demographic factors (Body Mass Index (BMI), age, drinking, and smoking). The mean values of daily excretion (ng/kg bw/day) calculated using urinary 6PPD-Q for females and males were 7.381 ng/kg bw/day (female) and 3.360 ng/kg bw/day (male), and apparently female suffered higher daily exposure. Further analysis with daily excretion and ALT (alanine aminotransferase)/TSH (thyroid stimulating hormone)/ blood cell analysis indicators found a potential correlation with 6PPD-Q daily excretion and liver/immune functions. Considering this preliminary assessment, systematic research targeting the potential organs at relevant concentrations is required.

Neurotoxicity from long-term exposure to 6-PPDQ: Recent advances

The recent acceleration of industrialization and urbanization has brought significant attention to N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6-PPDQ), an emerging environmental pollutant from tire wear, due to its long-term effects on the environment and organisms. Recent studies suggest that 6-PPDQ can disrupt neurotransmitter synthesis and release, impact receptor function, and alter signaling pathways, potentially causing oxidative stress, inflammation, and apoptosis. This review investigates the potential neurotoxic effects of prolonged 6-PPDQ exposure, the mechanisms underlying its cytotoxicity, and the associated health risks. We emphasize the need for future research, including precise exposure assessments, identification of individual differences, and development of risk assessments and intervention strategies. This article provides a comprehensive overview of 6-PPDQ's behavior, impact, and neurotoxicity in the environment, highlighting key areas and challenges for future research.

Assessment of fine and coarse tyre wear particles along a highway stormwater system and in receiving waters: Occurrence and transport

Tyre wear has been identified as a major road-related pollutant source, with road runoff transporting tyre wear particles (TWP) to adjacent soil, watercourses, or further through stormwater systems. The aim of this study was to investigate the occurrence and transport of TWP along a stormwater system. Water and sediment have been sampled at selected points (road runoff, gully pots, wells, outlet to a ditch, and stream) through a stormwater system situated along a highway in Sweden during November and December 2022, and March 2023. As there is limited data on the size distribution of TWP in different environmental media, especially in the size fraction <20 μm, the samples were fractioned into a fine (1.6-20 μm) and a coarse (1.6-500 μm) size fraction. The samples were analysed using a combination of marker compounds (benzene, α-methylstyrene, ethylstyrene, and butadiene trimer) for styrene-butadiene rubbers with PYR-GC/MS from which TWP concentration was calculated. Suspended solids were analysed in the water samples, and organic content was analysed in the sediment samples. TWP was found at nearly all locations, with concentrations up to 17 mg/L in the water samples and up to 40 mg/g in the sediment samples. In the sediment samples, TWP in the size fraction 1.6-20 μm represented a significant proportion (20-60%). Correlations were found between TWP concentration and suspended solids in the water samples (r = 0.87) and organic content in the sediment samples (r = 0.72). The results presented in this study demonstrate that TWP can be transported to the surrounding environment through road runoff, with limited retention in the studied stormwater system.

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.

Particle sizes crucially affected the release of additives from tire wear particles during UV irradiation and mechanical abrasion

In the environment, tire wear particles (TWPs) could release various additives to induce potential risk, while the effects of particle size on the additive release behavior and ecological risk from TWPs remain unknown. This study investigated the effects and mechanisms of particle sizes (>2 mm, 0.71-1 mm, and <0.1 mm) on the release behavior of TWPs additives under mechanical abrasion and UV irradiation in water. Compared to mechanical abrasion, UV irradiation significantly increased the level of additives released from TWPs. Especially, the additive releasing characteristics were critically affected by the particle sizes of TWPs, manifested as the higher release in the smaller-size ones. After 60 d of UV irradiation, the concentration of antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) reached 10.79 mg/L in the leachate of small-sized TWPs, 2.78 and 5.36 times higher than that of medium-sized and large-sized TWPs. The leachate of the small-sized TWPs also showed higher cytotoxicity. •OH and O2•- were identified as the main reactive oxygen species (ROS), which exhibited higher concentrations and dramatic attack on small-sized TWPs to cause pronounced fragmentation and oxidation, finally inducing the higher release of additives. This paper sheds light on the crucial effects and mechanism of particle sizes in the release behavior of TWPs additives, provides useful information to assess the ecological risk of TWPs.

Tracking Aromatic Amines from Sources to Surface Waters

This review examines the environmental occurrence and fate of aromatic amines (AAs), a group of environmental contaminants with possible carcinogenic and mutagenic effects. AAs are known to be partially responsible for the genotoxic traits of industrial wastewater (WW), and AA antioxidants are acutely toxic to some aquatic organisms. Still, there are gaps in the available data on sources, occurrence, transport, and fate in domestic WW and indoor environments, which complicate the prevention of adverse effects in aquatic ecosystems. We review key domestic sources of these compounds, including cigarette smoke and grilled protein-rich foods, and their presence indoors and in aquatic matrices. This provides a basis to evaluate the importance of nonindustrial sources to the overall environmental burden of AAs. Appropriate sampling techniques for AAs are described, including copper-phthalocyanine trisulfonate materials, XAD resins in solid-phase extraction, and solid-phase microextraction methods, which can offer insights into AA sources, transport, and fate. Further discussion is provided on potential progress in the research of AAs and their behavior in an aim to support the development of a more comprehensive understanding of their effects and potential environmental risks.

First Evidence of the Bioaccumulation and Trophic Transfer of Tire Additives and Their Transformation Products in an Estuarine Food Web

The discovery of the significant lethal impacts of the tire additive transformation product N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) on coho salmon has garnered global attention. However, the bioaccumulation and trophic transfer of tire additives and their transformation products (TATPs) within food webs remain obscure. This study first characterized the levels and compositions of 15 TATPs in the Pearl River Estuary, estimated their bioaccumulation and trophic transfer potential in 21 estuarine species, and identified priority contaminants. Our observations indicated that TATPs were prevalent in the estuarine environment. Eight, six, seven, and 10 TATPs were first quantified in the shrimp, sea cucumber, snail, and fish samples, with total mean levels of 45, 56, 64, and 67 ng/g (wet weight), respectively. N,N'-Diphenyl-p-phenylenediamine (DPPD) and N,N'-bis(2-methylphenyl)-1,4-benzenediamine (DTPD) exhibited high bioaccumulation. Significant biodilution was only identified for benzothiazole, while DPPD and DTPD displayed biomagnification trends based on Monte Carlo simulations. The mechanisms of bioaccumulation and trophodynamics of TATPs could be explained by their chemical hydrophobicity, molecular mass, and metabolic rates. Based on a multicriteria scoring technique, DPPD, DTPD, and 6PPD-Q were characterized as priority contaminants. This work emphasizes the importance of biomonitoring, particularly for specific hydrophobic tire additives.

Occurrence and partitioning of p-phenylenediamine antioxidants and their quinone derivatives in water and sediment

p-Phenylenediamine antioxidants (PPDs) and PPDs-derived quinones (PPDQs) may pose a threat to the river ecosystem. However, the knowledge on the occurrence and environmental behaviors of PPDs and PPDQs in the natural river environment remains unknown. In this study, we collected paired water (n = 30) and sediment samples (n = 30) from Jiaojiang River, China and analyzed them for nine PPDs and seven PPDQs. Our results showed that target PPDs and PPDQs are frequently detected in water samples, with the dominance of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD; mean 12 ng/L, range 4.0-72 ng/L) and 6PPD-derived quinone (6PPDQ; 7.0 ng/L, Collapse

Key Words

• PPDQs
• PPDs
• Partitioning
• Sediment
• Water

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Affiliation(s)

Jianqiang Zhu Department of Environmental Engineering, Taizhou University, Taizhou, Zhejiang 318000, 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 310032, 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 310032, PR China
Shengtao Jiang Department of Environmental Engineering, Taizhou University, Taizhou, Zhejiang 318000, 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 310032, PR China; Innovation Research Center of Advanced Environmental Technology, Eco-Industrial Innovation Institute ZJUT, Quzhou, Zhejiang 324400, PR China.

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Quantitative analysis of nanoplastics in environmental and potable waters by pyrolysis-gas chromatography-mass spectrometry

Nanoplastics are emerging environmental contaminants, but their presence in environmental and potable water remains largely understudied due to the absence of quantitative analytical methods. In this study, we developed and validated a pretreatment method that combines hydrogen peroxide digestion and Amicon® Stirred Cell ultrafiltration (at 100 kDa, approximately 10 nm) with subsequent detection by pyrolysis gas chromatography-mass spectrometry (Pyr-GC/MS). This method allows for the simultaneous identification and quantification of nine selected nanoplastic types, including poly(ethylene terephthalate) (PET), polyethylene (PE), polycarbonate (PC), polypropylene (PP), poly(methyl methacrylate) (PMMA), polystyrene (PS), polyvinylchloride (PVC), nylon 6, and nylon 66, in environmental and potable water samples based on polymer-specific mass concentration. Limits of quantification ranged from 0.01 to 0.44 µg/L, demonstrating the method's ability to quantitatively detect nanoplastics in environmental and potable water samples. Most of the selected nanoplastics were detected at concentrations of between 0.04 and 1.17 µg/L, except for PC, which was consistently below the limit of detection (<0.44 µg/L). The prevalent polymer components in the samples were PE (0.10 - 1.17 µg/L), PET (0.06 - 0.91 µg/L), PP (0.04 - 0.79 µg/L), and PS (0.06 - 0.53 µg/L) nanoplastics. The presented analytical method offers an accurate means to identify, quantify, and monitor nanoplastics in complex environmental and potable water samples. It fills gaps in our understanding of nanoplastic pollution levels, providing a valuable methodology and crucial reference data for future studies.

Ascertaining appropriate measuring methods to determine tire wear particle pollution on driving school grounds in China

Tire wear particles (TWPs) are garnering increasing attention due to their potential adverse environmental impacts. However, precisely ascertaining TWPs content is challenging due to the complexity and variability of the tire components used in the environment, indicating that more reliable methods to accurately determine TWPs are necessary. In this study, driving school grounds were used as a case study to ascertain an appropriate and reliable method to determine TWPs levels based on a comprehensive comparison between different analytical results using styrene butadiene rubber (SBR), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), and zinc (Zn) as analytical markers. Thermogravimetric analysis-Gas chromatography mass spectrometry (TGA-GC-MS) method reliability using SBR was verified and applied to measure TWPs levels on driving school grounds. By reliably converting SBR content to TWPs content, the average TWPs content on driving school grounds was measured at 190.13 ± 101.89 mg/g. The highest TWPs content was 281.83 ± 171.44 mg/g under the reverse stall parking driving programs, while the slope start and stop driving programs was lower at 208.36 ± 124.11 mg/g. Our findings highlight the importance of accurately determining TWPs content within specific environments while comprehensively exploring associated patterns of change to better understand the environmental risks of TWPs.

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

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

Unraveling the Marine Microplastic Cycle: The First Simultaneous Data Set for Air, Sea Surface Microlayer, and Underlying Water

Microplastics (MP) including tire wear particles (TWP) are ubiquitous. However, their mass loads, transport, and vertical behavior in water bodies and overlying air are never studied simultaneously before. Particularly, the sea surface microlayer (SML), a ubiquitous, predominantly organic, and gelatinous film (<1 mm), is interesting since it may favor MP enrichment. In this study, a remote-controlled research catamaran simultaneously sampled air, SML, and underlying water (ULW) in Swedish fjords of variable anthropogenic impacts (urban, industrial, and rural) to fill these knowledge gaps in the marine-atmospheric MP cycle. Polymer clusters and TWP were identified and quantified with pyrolysis-gas chromatography-mass spectrometry. Air samples contained clusters of polyethylene terephthalate, polycarbonate, and polystyrene (max 50 ng MP m-3). In water samples (max. 10.8 μg MP L-1), mainly TWP and clusters of poly(methyl methacrylate) and polyethylene terephthalate occurred. Here, TWP prevailed in the SML, while the poly(methyl methacrylate) cluster dominated the ULW. However, no general MP enrichment was observed in the SML. Elevated anthropogenic influences in urban and industrial compared to the rural fjord areas were reflected by enhanced MP levels in these areas. Vertical MP movement behavior and distribution were not only linked to polymer characteristics but also to polymer sources and environmental conditions.

Urine Excretion, Organ Distribution, and Placental Transfer of 6PPD and 6PPD-Quinone in Mice and Potential Developmental Toxicity through Nuclear Receptor Pathways

The rubber antioxidant 6PPD has gained significant attention due to its highly toxic transformation product, 6PPD-quinone (6PPDQ). Despite their detection in urines of pregnant women, the placental transfer and developmental toxicity of 6PPD and 6PPDQ are unknown. Here, we treated C57Bl/6 mice with 4 mg/kg 6PPD or 6PPDQ to investigate their urine excretion and placental transfer. Female and male mice exhibited sex difference in excretion profiles of 6PPD and 6PPDQ. Urine concentrations of 6PPDQ were one order of magnitude lower than those of 6PPD, suggesting lower excretion and higher bioaccumulation of 6PPDQ. In pregnant mice treated with 6PPD or 6PPDQ from embryonic day 11.5 to 15.5, 6PPDQ showed ∼1.5-8 times higher concentrations than 6PPD in placenta, embryo body, and embryo brain, suggesting higher placental transfer of 6PPDQ. Using in vitro dual-luciferase reporter assays, we revealed that 6PPDQ activated the human retinoic acid receptor α (RARα) and retinoid X receptor α (RXRα) at concentrations as low as 0.3 μM, which was ∼10-fold higher than the concentrations detected in human urines. 6PPD activated the RXRα at concentrations as low as 1.2 μM. These results demonstrate the exposure risks of 6PPD and 6PPDQ during pregnancy and emphasize the need for further toxicological and epidemiological investigations.

Transformation Products of Tire Rubber Antioxidant 6PPD in Heterogeneous Gas-Phase Ozonation: Identification and Environmental Occurrence

6PPD, a tire rubber antioxidant, poses substantial ecological risks because it can form a highly toxic quinone transformation product (TP), 6PPD-quinone (6PPDQ), during exposure to gas-phase ozone. Important data gaps exist regarding the structures, reaction mechanisms, and environmental occurrence of TPs from 6PPD ozonation. To address these data gaps, gas-phase ozonation of 6PPD was conducted over 24-168 h and ozonation TPs were characterized using high-resolution mass spectrometry. The probable structures were proposed for 23 TPs with 5 subsequently standard-verified. Consistent with prior findings, 6PPDQ (C18H22N2O2) was one of the major TPs in 6PPD ozonation (∼1 to 19% yield). Notably, 6PPDQ was not observed during ozonation of 6QDI (N-(1,3-dimethylbutyl)-N'-phenyl-p-quinonediimine), indicating that 6PPDQ formation does not proceed through 6QDI or associated 6QDI TPs. Other major 6PPD TPs included multiple C18H22N2O and C18H22N2O2 isomers, with presumptive N-oxide, N,N'-dioxide, and orthoquinone structures. Standard-verified TPs were quantified in roadway-impacted environmental samples, with total concentrations of 130 ± 3.2 μg/g in methanol extracts of tire tread wear particles (TWPs), 34 ± 4 μg/g-TWP in aqueous TWP leachates, 2700 ± 1500 ng/L in roadway runoff, and 1900 ± 1200 ng/L in roadway-impacted creeks. These data demonstrate that 6PPD TPs are likely an important and ubiquitous class of contaminants in roadway-impacted environments.

Exposure to 6-PPD Quinone at Environmentally Relevant Concentrations Causes Abnormal Locomotion Behaviors and Neurodegeneration in Caenorhabditis elegans

6-PPD quinone (6-PPDQ) can be transformed from 6-PPD through ozonation. Nevertheless, the potential neurotoxicity of 6-PPDQ after long-term exposure and the underlying mechanism are largely unclear. In Caenorhabditis elegans, we here observed that 0.1-10 μg/L of 6-PPDQ caused several forms of abnormal locomotion behaviors. Meanwhile, the neurodegeneration of D-type motor neurons was observed in 10 μg/L of 6-PPDQ-exposed nematodes. The observed neurodegeneration was associated with the activation of the Ca²⁺ channel DEG-3-mediated signaling cascade. In this signaling cascade, expressions of deg-3, unc-68, itr-1, crt-1, clp-1, and tra-3 were increased by 10 μg/L of 6-PPDQ. Moreover, among genes encoding neuronal signals required for the control of stress response, expressions of jnk-1 and dbl-1 were decreased by 0.1-10 μg/L of 6-PPDQ, and expressions of daf-7 and glb-10 were decreased by 10 μg/L of 6-PPDQ. RNAi of jnk-1, dbl-1, daf-7, and glb-10 resulted in the susceptibility to 6-PPDQ toxicity in decreasing locomotory ability and in inducing neurodegeneration, suggesting that JNK-1, DBL-1, DAF-7, and GLB-10 were also required for the induction of 6-PPDQ neurotoxicity. Molecular docking analysis further demonstrated the binding potential of 6-PPDQ to DEG-3, JNK-1, DBL-1, DAF-7, and GLB-10. Together, our data suggested the exposure risk of 6-PPDQ at environmentally relevant concentrations in causing neurotoxicity in organisms.

Widespread Occurrence and Transport of p-Phenylenediamines and Their Quinones in Sediments across Urban Rivers, Estuaries, Coasts, and Deep-Sea Regions

p-Phenylenediamines (PPDs) are widely used as antioxidants in tire rubber, and their derived quinone transformation products (PPD-Qs) may pose a threat to marine ecosystems. A compelling example is N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)-derived quinone, called 6PPD-Q, as the causal toxicant for stormwater-linked acute mortality toward coho salmon. However, the knowledge of the co-occurrences of PPDs and PPD-Qs and their transport from freshwater to oceanic waterbodies on a large geographical scale remains unknown. Herein, we performed the first large-scale survey of these chemicals in sediments across urban rivers, estuaries, coasts, and deep-sea regions. Our results demonstrated that seven PPDs and four PPD-Qs are ubiquitously present in riverine, estuarine, and coastal sediments, and most of them also occur in deep-sea sediments. The most dominant chemicals of concern were identified as 6PPD and 6PPD-Q. Total sedimentary concentrations of PPDs and PPD-Qs presented a clear spatial trend with decreasing levels from urban rivers (medians: 39.7 and 15.2 ng/g) to estuaries (14.0 and 5.85 ng/g) and then toward coasts (9.47 and 2.97 ng/g) and deep-sea regions (5.24 and 3.96 ng/g). Interestingly, spatial variation in the ratios of 6PPD to 6PPD-Q (R_6PPD/6PPD-Q) also presented a clear decreasing trend. Our field measurements implied that riverine outflows of PPDs and PPD-Qs may be an important route to transport these tire rubber-derived chemicals to coastal and open oceans.

Rubber Antioxidants and Their Transformation Products: Environmental Occurrence and Potential Impact

Antioxidants are prevalently used during rubber production to improve rubber performance, delay aging, and extend service life. However, recent studies have revealed that their transformation products (TPs) could adversely affect environmental organisms and even lead to environmental events, which led to great public concern about environmental occurrence and potential impacts of rubber antioxidants and their TPs. In this review, we first summarize the category and application of rubber antioxidants in the world, and then demonstrate the formation mechanism of their TPs in the environment, emphasizing their influence on the ozone oxidative degradation. The potential toxic effects of antioxidants and their TPs are further reviewed to improve understanding of their biological health impact and environmental risks. Finally, the environmental occurrences of antioxidants and their TPs are summarized and their environmental impacts are demonstrated based on the recent studies. Due to the currently limited understanding on the toxic and biological effects of these compounds, further studies are required in order to better assess various TPs of these antioxidants and their environmental impact. To our knowledge, this is the first review on antioxidants and their TPs in the environment, which may elevate the environmental risk awareness of rubber products and their TPs in the near future.