Photoaged Tire Wear Particles Leading to the Oxidative Damage on Earthworms (Eisenia fetida) by Disrupting the Antioxidant Defense System: The Definitive Role of Environmental Free Radicals

6PPD-quinone exposure induces oxidative damage and physiological disruption in Eisenia fetida: An integrated analysis of phenotypes, multi-omics, and intestinal microbiota

The environmental prevalence of the tire wear-derived emerging pollutant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) has increasingly raised public concern. However, knowledge of the adverse effects of 6PPD-Q on soil fauna is scarce. In this study, we elucidated its impact on soil fauna, specifically on the earthworm Eisenia fetida. Our investigation encompassed phenotypic, multi-omics, and microbiota analyses to assess earthworm responses to a gradient of 6PPD-Q contamination (10, 100, 1000, and 5000 μg/kg dw soil). Post-28-day exposure, 6PPD-Q was found to bioaccumulate in earthworms, triggering reactive oxygen species production and consequent oxidative damage to coelomic and intestinal tissues. Transcriptomic and metabolomic profiling revealed several physiological perturbations, including inflammation, immune dysfunction, metabolic imbalances, and genetic toxicity. Moreover, 6PPD-Q perturbed the intestinal microbiota, with high dosages significantly suppressing microbial functions linked to metabolism and information processing (P < 0.05). These alterations were accompanied by increased mortality and weight loss in the earthworms. Specifically, at an environmental concentration of 6PPD-Q (1000 μg/kg), we observed a substantial reduction in survival rate and physiological disruptions. This study provides important insights into the environmental hazards of 6PPD-Q to soil biota and reveals the underlying toxicological mechanisms, underscoring the need for further research to mitigate its ecological footprint.

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.

Soil properties explain the variability in tire wear particle effects in soil based on a laboratory test with 59 soils

Tire wear particles (TWPs) are among the most prevalent microplastics in the environment, with potential detrimental effects on ecosystem health and functionality. While little is known how the effects of TWPs on soil physicochemical and microbial properties vary across different soil types, and if so, which factors contribute to this variability. To address this knowledge gap, we conducted a laboratory experiment involving soils from 59 grassland plots across two sampling regions in Germany, each experienced varying land-use intensities. These soils were treated with (at a concentration of 10 mg g-1) and without TWPs. At harvest, we measured soil water-stable aggregates (WSA), pH, respiration, and decomposition rate. Our results revealed that TWPs negatively, neutrally, or positively impacted these parameters depending on soil types. Random forest analysis indicated that the variability in TWP effects was significantly explained by grazing frequency for WSA (14.5 %), by clay content for pH (9 %), by bulk density for respiration (7.9 %), and by silt content for decomposition rate (12 %). Partial dependence analysis and piecewise regression further suggested that low-intensity grazing (∼0.7-1.2) reduced TWP effects on WSA; clay content (420-550 g kg-1) increased TWP effects on pH; bulk density (0.75-0.88) decreased TWP effects, and silt content (460-620 g kg-1) enhanced TWP effects on decomposition rate, with the identified thresholds of 1.45, 353 g kg-1, 0.84, and 327 353 g kg-1, respectively. These results highlighted the context-dependent nature of TWP pollution, with significant variability observed across different sampling points. Additionally, our findings suggest that TWP pollution is particularly of concern in soils with high clay, silt, high bulk density, and areas with intensive land-use intensity. Our study contributes to a better understanding of the mechanisms by which TWPs impact soil, and how these effects are regulated by environmental factors.

Interactions between Nanoplastics and Antibiotics: Implications for Nanoplastics Aggregation in Aquatic Environments

Nanoplastics and antibiotics frequently co-occur in aquatic environments, and their interactions could alter nanoplastics' surface properties, affecting nanoplastics aggregation, fate, and ecotoxicity. However, the mechanisms driving antibiotics-induced nanoplastics aggregation under environmentally relevant conditions remain unclear. This study investigated the effects of ciprofloxacin (CIP) and sulfamethoxazole (SMX) on the aggregation of four environmentally relevant nanoplastics (pristine and aged polystyrene, polyethylene, and polypropylene). At pH 5.0, both CIP and SMX significantly promoted nanoplastics aggregation, with CIP being more potent. CIP enhanced nanoplastics aggregation through charge shielding driven by electrostatic attraction, hydrogen bonding (HB), and charge-assisted HB (CAHB), whereas SMX promoted aggregation solely through molecular bridging involving HB and CAHB. At pH 7.0, only CIP facilitated aggregation, while neither antibiotic induced aggregation at pH 9.0. Aged polystyrene aggregated more readily than pristine polystyrene due to increased surface functional groups. Polyethylene and polypropylene showed weaker aggregation due to fewer surface functional groups. High organic matter (OM) levels (1.65 mg/L TOC) inhibited antibiotics-induced aggregation, whereas low OM levels (16.5 μg/L TOC) were more conducive. These findings highlight that antibiotic characteristics, pH, OM levels, plastic types, and environmental aging collectively influence nanoplastics aggregation, and improve the understanding of the fate and risk of nanoplastics in natural waters.

Co-exposure to enrofloxacin and atrazine enhances the hepatotoxicity in Larimichthys crocea by targeting the hypothalamic-pituitary-thyroid and gut-liver axes

Enrofloxacin (ENR) and atrazine (ATZ) are common co-contaminants in marine environments. Although the immunosuppressive effects of ENR and the endocrine-disrupting properties of ATZ are well established, the combined effects of these pollutants on hepatotoxicity, particularly concerning the regulation of the hypothalamic-pituitary-thyroid (HPT) and gut-liver axes, remain poorly understood. In this study, Larimichthys crocea was exposed to ENR and ATZ at environmentally relevant concentrations, individually and in combination, to investigate the hepatotoxicity. Liver cell swelling, necrosis, oxidative stress, and elevated liver injury markers were observed, indicating hepatic damage, with co-exposure exacerbating liver injury. Decreased levels of thyrotropin-releasing hormone and thyroid-stimulating hormone, increased triiodothyronine and thyroxine, and altered expression of HPT axis-related genes demonstrated enhanced disruption of the HPT axis under co-exposure, which was strongly associated with oxidative stress and liver dysfunction. Molecular docking confirmed that ENR and ATZ inhibited thyroid hormone binding to target proteins, likely provoking the enhanced hepatotoxicity. Additionally, ATZ significantly intensified the intestinal bacterial disturbances induced by ENR, further aggravating hepatotoxicity through the gut-liver axis. This study is the first to reveal the increased risk associated with ENR and ATZ co-exposure, highlighting the need for attention to such co-contaminants.

Tire Rubber Antioxidant 6PPD and 6PPD-quinone Disrupt the Energy Supply and Lipid Metabolism of Earthworms

With the increase in traffic due to urbanization, tire wear particles (TWPs) derived compounds persistently accumulate in the soil environment. This study addresses critical knowledge gaps regarding the ecotoxicological effects of TWP-derived contaminants, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its precursor, 6PPD-quinone (6PPD-Q), on soil-dwelling organisms. The findings demonstrated that 6PPD-Q accumulated at a higher concentration (6.77 ± 0.124 ng/g) in earthworms (Eisenia fetida) compared to 6PPD (5.41 ± 0.002 ng/g), triggering more severe oxidative stress and cellular homeostatic imbalance. Specifically, 100 ng/g of 6PPD-Q in soil significantly elevated reactive oxygen species (ROS) levels by 180.77% and suppressed acetylcholinesterase (AchE) and Ca2+-ATPase activities by 17.14% and 44.70%, respectively. Notably, 6PPD-Q uniquely disrupted the nitrogen balance and disturbed energy supply by strongly inhibiting fatty acid degradation and peroxisome proliferator-activated receptor (PPAR) signaling pathways. Additionally, 6PPD-Q profoundly altered the abundance of key microbes and microbial network stability, affecting intestinal microbial functions such as bile secretion, hormone synthesis, and lipid digestion, thus exacerbating the energy metabolic imbalance in earthworms. This study deciphers the molecular toxicity mechanisms of TWP-derived contaminants in earthworms, providing crucial insights for developing risk assessment frameworks and mitigation strategies in soil ecosystems.

Impacts of environmentally persistent free radicals on the denitrification toxicity of photoaged tire wear particles in estuarine sediments

The widespread detection of tire wear particles (TWPs) in estuaries has raised concerns about their potential environmental hazards. However, knowledge of photoaging-induced environmentally persistent free radicals (EPFRs) formation on TWPs in estuarine environments and their impact on sediment denitrification remains limited. This study investigated the formation of EPFRs on TWP during photoaging in estuarine environments and evaluated their effects on sediment denitrification and nitrous oxide (N2O) accumulation. Sixty days of illumination increased EPFR concentration on TWPs by 373 %, with the generated EPFRs persisting in sediments for over 20 days. Exposure to pristine TWP (PTWP) reduced denitrification rates by 10.3 ± 5.6 % and increased N2O accumulation by 18.3 ± 4.5 %. Further exposure to photoaged TWP (ATWP) under 10-60 days of illumination expanded denitrification suppression and N2O accumulation to 28.1 ± 7.1-42.5 ± 6.6 % and 18.8 ± 4.3-31.7 ± 4.6 %, respectively. EPFRs exacerbated the accumulation of reactive nitrogen species in sediment and compromised the antioxidant systems. Structural equation modeling confirmed that EPFRs indirectly suppressed denitrification rates by directly impairing microbial processes involved in carbon metabolism and electron transfer. This study is the first to report that the formation of EPFRs enhances the negative effects of ATWP on the sediment's nitrogen cycle, offering valuable insights for assessing the ecological risks associated with TWP.

Behavioral and molecular neurotoxicity of thermally degraded polystyrene in Caenorhabditis elegans

Microplastics are pervasive environmental contaminants found across diverse ecosystems, inducing toxic effects in a wide range of organisms. However, the neurotoxic effects of thermally degraded polystyrene (T-PS) and its underlying mechanisms remain poorly unexplored. In this study, Caenorhabditis elegans was exposed to environmentally relevant concentrations of T-PS (0.1-100 μg/L), and endpoints including locomotion behaviors, neuronal development, neurotransmitter levels, and gene expression were assessed. Significant alterations in morphology, crystallinity, elemental composition, and functional groups were observed in T-PS compared to virgin polystyrene (V-PS), indicating that thermal degradation modifies the physicochemical properties of V-PS. Exposure to 10-100 μg/L T-PS resulted in a more pronounced decrease in head thrashes, body bends, forward turns, and backward turns compared to V-PS. In transgenic nematodes, T-PS exposure significantly impacted fluorescence intensity and the percentage of worms exhibiting neurodegeneration in serotonergic, cholinergic, dopaminergic, and γ-aminobutyric acid (GABA) neurons. Correspondingly, marked reductions were observed in the levels of dopamine, serotonin, GABA, and choline neurotransmitters, alongside significant declines in neurotransmitter-related gene expression (e.g., dat-1, tph-1, unc-30, and cha-1). Pearson's correlation analysis revealed a significant positive association between these genes and locomotion behaviors. Furthermore, the absence of locomotion behavior impairment in dat-1 (ok157), tph-1 (mg280), unc-30 (e191), and cha-1 (e1152) mutants highlights the pivotal roles of these genes in mediating T-PS-induced neurotoxicity in C. elegans. This study enhances our understanding of the neurotoxic mechanisms of T-PS at environmental concentrations, providing valuable insights into its potential environmental health risks.

Amplification of benzo[a]pyrene toxicity persistence in earthworms by polystyrene nanoplastics: From organismal health to molecular responses

Typically, nanoplastics (NPs) are contaminated before entering soil, and the impact of NPs on the biotoxicity of Persistent Organic Pollutants (POPs) they carry remains unclear. This study simulated two environmentally relevant scenarios: singular exposure of benzo[a]pyrene (BaP) in soil and exposure via NPs loading (NP-BaP). Correlation analysis and machine learning revealed that injury in earthworms exposed for 28 days was significantly associated with NPs. Moreover, when the soil exposure concentration of BaP was 4 mg/kg, the NP-BaP group exhibited 10.67 % greater pigmentation than the BaP-only group. Despite the lower biota soil accumulation factor (BSAF) of earthworms in the NP-BaP group, the concentration of BaP in the soil remained at higher levels in the late stages of exposure. This led to NP-BaP inducing a stronger trend of oxidative damage compared to BaP alone. Furthermore, molecular-level studies indicated that the differential preferences of NPs and BaP for damaging antioxidant enzymes were linked to individual oxidative stress responses. This study confirmed that NPs, at non-toxic concentrations, could increase the persistence of BaP's biological toxicity after prolonged exposure, highlighting the potential safety risks of NPs as carriers of POPs to soil organisms.

Assessing the distribution and human health risks of cationic surface-active agents in honey from China

Cationic surface-active agents (CSAAs) can persist in ambient water, be ingested by bees, and contaminate honey. Residues of CSAAs in honey remains unknown. This study measured the residual levels of five CSAAs in 271 honey samples from China using ultrahigh-performance liquid chromatography coupled with triple-quadrupole tandem mass spectrometry. Residual benzalkonium chloride-C12 (BAC-C12), BAC-C14, BAC-C16, chlorhexidine (CHG), and 4-chloraniline levels were 0.0098-2.1468, 0.0061-1.7492, 0.0012-1.6305, 0.1576-0.8401, and 0.0019-0.0234 μg kg-1, respectively. CHG and all BAC were detected in 100 % of Z. jujuba, V. negundo var. heterophylla, wildflower, L. chinensis, and D. longan Lour honey; T. tuan honey had the lowest detection rate of any CSAAs. BAC-C16 had the highest residual level among all BAC tested in Central, North China. CHG levels were detected in 91.38 % of samples in North China and 100 % in East China. BAC-C12 was significantly higher in A. cerana versus A. mellifera honey (P < 0.001). Hazard quotient and Hazard index values indicate that CSAAs residuals in honey do not pose a health risk. Correlation analysis revealed a positive correlation between BACs resides in honey and surrounding environment. The findings suggest that continuous monitoring of CSAAs in honey is imperative to ensure its safety for human consumption, while also serving as an effective matrix to assess the environmental pollution of a given region.

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.

Differential inhibition of tire wear particles on sludge dewatering by aging modes

The study assessed the acute toxicities of tire wear particles (TWPs) on activated sludge, comparing cryogenically ground TWPs (C-TWPs) with photo-aged (PA-TWPs), ozone-aged (OA-TWPs), and Fenton-aged (FA-TWPs) variants over 96 h. At 0.1 mg/L, TWPs showed no significant effects on sludge respiration or purification. However, at 50 mg/L, significant impacts on respiration, decontamination capacity, and microbial community structure were observed, particularly in aged TWPs. Specifically, aged TWPs, especially FA-TWPs, are prone to inducing necrosis by generating non-cellular reactive oxygen species (ROS) catalyzed by persistent free radicals, leading to an increase in lactate dehydrogenase release ranging from 215 % to 284 %. Conversely, C-TWPs tend to trigger apoptosis via intracellular ROS accumulation, leading to a 358 % increase in intracellular ROS. Aged TWPs exhibited higher affinities for proteins and polysaccharides, while C-TWPs preferred phospholipids. All TWPs adversely affected sludge dewatering, with strong correlations found between specific resistance to filtration (SRF) and total protein (r = 0.981, p < 0.001) and between bound water and early cell apoptosis (r = 0.961, p < 0.01). Additionally, a correlation between SRF and cellular necrosis (r = 0.956, p < 0.01) was noted, linked to increased protein and extracellular polymeric substance levels. These results emphasize substantial influence of aged TWPs on sludge dewatering efficiency via diverse bacterial cell death mechanisms.

Stress of soil moisture and temperature exacerbates the toxicity of tire wear particles to soil fauna: Tracking the role of additives through host microbiota

Tire wear particles (TWPs) are considered as an emerging threat to soil fauna. However, how TWP toxicity to soil fauna responds to the stress of soil moisture and temperature remains unclear. We assessed the toxicity of environmentally relevant TWPs to the soil model species Enchytraeus crypticus under three soil moisture and two temperature gradients. Typical thermoplastic polypropylene (PP) was selected for comparison. Results showed that compared with PP, TWPs exerted stronger toxicity, including decreasing the worm growth, survival and reproduction rates, disturbing the soil and worm gut microbiota, and leaching more diverse and higher contents of additives. Stress of soil moisture and temperature exacerbated TWP toxicity mainly through affecting the leaching and transformation of additives. Fourteen mediated additives significantly contributed to the shift of the gut microbiota under soil moisture and temperature stress, among which 1,3-diphenylguanidine, N,N'-bis(methylphenyl)-1,4-benzenediamine quinone, N-tert-butyl-2-benzothiazolesulfenamide, and 2-aminobenzothiazole were identified as the main drivers. In addition, this study provided the first clear evidence that increased soil moisture and temperature promoted the transformation of additives in the soil. Our study revealed the non-negligible aggravated toxicity of TWPs to soil fauna under stress of soil moisture and temperature, providing novel insights into the environmental behavior of additives.

Soil moisture-dependent tire wear particles aging processes shift soil microbial communities and elevated nitrous oxide emission on drylands

Tire wear particles (TWPs) have been an emerging threat to the soil ecosystem, while impact of the TWPs aging on soil microbial communities remains poorly understood. This study investigated the dynamic responses of soil microbial communities to the TWPs aging under both wet and flooded conditions. We found that different soil moisture conditions resulted in distinct microbial community structures. Soil bacteria were more sensitive to wet conditions, while soil fungi were more sensitive to flooded conditions. The family Symbiobacteraceae was predominant in the TWP-sphere under both wet and flooded conditions after 60 days, followed by Brevibacillaceae. Notably, we observed that TWPs input significantly increased nitrous oxide (N2O) emission from dryland soil. Several taxa including Cyanobacteriales, Blastocatellaceae and Pyrinomonadaceae were identified as TWP-biomarkers in soils and potentially played significant roles in N2O emissions from drylands. Their responses to the TWPs input correlated closely with changes in the relative abundance of genes involved in ammonia oxidation (amoA/B), nitrite reduction (nirS/K) and N2O reduction (nosZ) in drylands. Our results demonstrate that soil moisture-dependent TWP aging influences N2O emission by altering both the associated microbial communities and the relevant genes.

Impact of Pristine and Aged Tire Wear Particles on Ipomoea aquatica and Rhizospheric Microbial Communities: Insights from a Long-Term Exposure Study

Tire wear particles (TWPs), generated from tire abrasion, contribute significantly to environmental contamination. The toxicity of TWPs to organisms has raised significant concerns, yet their effects on terrestrial plants remain unclear. Here, we investigated the long-term impact of pristine and naturally aged TWPs on water spinach (Ipomoea aquatica) and its rhizospheric soil. The results indicated that natural aging reduced the toxicity of TWPs, as evidenced by decreased levels of polycyclic aromatic hydrocarbons (PAHs) in soil and TWPs themselves. Consequently, aged TWPs were found to enhance the plant growth and chlorophyll content, whereas pristine TWPs increased the plant stress. Furthermore, aged TWPs improved soil organic matter (SOM) and total organic carbon (TOC), thereby boosting the microbial enzymes involved in nitrogen cycling. Metabolomic analysis revealed that aged TWPs upregulated key pathways related to carbon and nitrogen metabolism, enhancing plant growth and stress responses. Additionally, rhizosphere bacterial diversity was higher under aged TWPs, favoring nutrient-cycling taxa such as Acidobacteriota and Nitrospirota. Pristine TWPs may lead to overproliferation of certain dominant species, thereby reducing microbial diversity in soil, which could ultimately compromise the soil health. These findings contribute to a deeper understanding of the mechanisms underlying TWP toxicity in plants and highlight the necessity for further research on the impact of aged TWPs across various plant species over different exposure durations for comprehensive risk assessment.

Accumulation and depuration of tire wear particles in zebrafish (Danio rerio) and toxic effects on gill, liver, and gut

The toxic effects of tire wear particles (TWPs) in the environment are a growing concern for a variety of aquatic organisms. However, studies about TWPs toxicity on aquatic organisms are limited. This study investigated the accumulation and depuration of TWPs in zebrafish at three different concentrations (5 mg/L, 10 mg/L, and 20 mg/L), as well as the toxic effects on the gill, liver, and gut. We found that TWPs could accumulate in the gill and gut for a long time, and the number of TWPs at the high-concentration (20 mg/L) was higher than at the low-concentration (5 mg/L). TWPs induced oxidative stress in the gill and liver. The liver transcriptome profiles indicated that the high concentration of TWPs tended to up-regulate metabolic processes, whereas the low concentration of TWPs was inclined to down-regulate cellular processes. The high-concentration treatment significantly increased xenobiotic biodegradation and metabolism, and lipid metabolism-related pathways, whereas the low-concentration treatment distinctly altered amino acid metabolism-related pathways. The expression of gstt1b, ugt1a1, mgst3b, miox, hsd17b3, and cyp8b1 gene was up-regulated in all TWPs treatments. In addition, Gemmobacter and Shinella enriched in the high-concentration treatment were closely correlated with the degradation of TWPs. These findings provided objective evidence for the toxicity evaluation of TWPs on zebrafish.

Insights into the controlling factors of the transport of tire wear particles in saturated porous media: The facilitative role of aging and fulvic acid

The widespread distribution and potential adverse effects of tire wear particles (TWPs) on soil and groundwater quality pose a growing environmental concern. This study investigated the transport behavior of TWPs in saturated porous media and elucidated the underlying mechanisms influenced by environmental factors. Additionally, the effects of key environmental factors, such as aging, ionic strength, cation species, medium type, and natural organic matter (NOM), on the transport of TWPs were evaluated. The results showed that aging processes simulated through O3 and UV irradiation altered the physicochemical properties of TWPs, increased the mobility of TWPs at low ionic strengths. However, the high ionic strengths and the presence of Ca2+ significantly inhibited the mobility of TWPs due to enhanced aggregation. The transport mechanism of the original and aged TWPs shifted from blocking to ripening under favorable retention conditions (i.e., high ionic strengths, divalent cations, and fine sands). Interestingly, the presence of fulvic acid (FA) inhibited the ripening of the three TWPs, significantly promoting their transport through a spatial site resistance mechanism. The two-site kinetic attachment model (TSKAM), extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and colloid filtration theory (CFT) were applied to describe the transport behavior of the TWPs. The study provided a comprehensive understanding of the transport behavior of TWPs in groundwater environments, highlighting the environmental risks associated with their widespread distribution.

Photoaged tire wear particles hinder the transport of Pb(II) in urban soils under acid rain: Experimental and numerical investigations

Rapid urbanization brought lots of serious environmental contamination, including the accumulation of heavy metals, acid rain, and the emission of tire wear particles (TWPs), with detrimental effects for terrestrial ecosystems. Nevertheless, how naturally aged TWPs affect the mobilization of heavy metals in soils under acid rain is still unclear. Here, we investigate the adsorption and transport mechanisms of Pb(II) co-existing with acid rainwater in soil-TWP mixtures via batch experiments, column experiments and modeling. Results showed that photoaged TWP significantly prolonged the Pb(II) adsorption equilibrium time (1 to 16 h) and enhanced the Pb(II) adsorption capacity of soils. Soil column profiles confirmed that TWP effectively boosted the initial accumulation of lead in the topsoil and thus impeded the downward transport of lead. The retardation factor (R) estimated by the linear two-site sorption model (TSM) fitting the Pb(II) breakthrough curves gradually increased from 1.098 to 16.38 in soils with TWP (0-10 %). Comparative results of linear or nonlinear TSM suggested nonlinear sorption replacing linear sorption as the main Pb(II) sorption mechanism under 1 % and 10 % TWP. This research provides significant insights into the implications of TWP on the Pb(II) retention behaviors and highlights the severer potential remobilization risks of Pb(II) in urban soils under different acid rain environments.

Acute inhibitory effects of tire wear particles on the removal of biological phosphorus：The critical role of aging in improving environmentally persistent free radicals

A comparative study explored how photoaging, ozonation aging, and Fenton aging affect tire wear particles (TWPs) and their phosphorus (P) removal in activated sludge. Aging altered TWPs' properties, increasing surface roughness, porosity, and generating more small particles, especially environmental persistent free radicals (EPFRs) in ozonation and Fenton aging. Post-aging TWPs (50 mg/L) inhibited sludge P removal significantly (p < 0.05), with rates of 44.3% and 59.6% for ozonation and Fenton aging, respectively. In addition, the metabolites involved in P cycling (poly-β-hydroxyalkanoates: PHA and glycogen) and essential enzymes (Exopolyphosphatase: PPX and Polyphosphate kinase: PPK) were significantly inhibited (p < 0.05). Moreover, TWPs led to a decrease in microbial cells within the sludge and altered the community structure, a situation exacerbated by the aging of TWPs. P-removing bacteria decreased (e.g., Burkholderia, Candidatus), while extracellular polymeric substance-secreting bacteria increased (e.g., Pseudomonas, Novosphingobium). Pearson correlation analysis highlighted EPFRs' role in TWPs' acute toxicity to microbial cells, yet, emphasizing particle size's impact on the sludge system's purification and community structure.

Biochar alters the soil fauna functional traits and community diversity: A quantitative and cascading perspective

With the widespread use of biochar, the cascading effects of biochar exposure on soil fauna urgently require deeper understanding. A meta-analysis quantified hierarchical changes in functional traits and community diversity of soil fauna under biochar exposure. Antioxidant enzymes (24.1 %) did not fully mitigate the impact of MDA (13.5 %), leading to excessive DNA damage in soil fauna (21.2 %). Concurrently, reproduction, growth, and survival rates decreased by 20.2 %, 8.5 %, and 21.2 %, respectively. Due to a 39.7 % increase in avoidance behavior of soil fauna towards biochar, species richness ultimately increased by 80.2 %. Compared to other feeding habits, biochar posed a greater threat to the survival of herbivores. Additionally, macrofauna were the most sensitive to biochar. The response of soil fauna also depended on the type, size, concentration, and duration of biochar exposure. It should be emphasized that as exposure concentration increased, the damage to soil fauna became more severe. Furthermore, the smaller the biochar sizes, the greater the damage to soil fauna. To mitigate the adverse effects on soil fauna, this study recommens applying biochar at appropriate times and selecting large sizes in low to medium concentrations. These findings confirm the threat of biochar to soil health from the perspective of soil fauna.

Effects of environmental concentrations of 6PPD and its quinone metabolite on the growth and reproduction of freshwater cladoceran

The widespread occurrence and accumulation of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its quinone metabolite, 6PPD quinone (6PPD-Q), have been globally recognized as a critical environmental issue. However, knowledge on the adverse effects of 6PPD and 6PPD-Q on freshwater invertebrates is limited. This study investigated the effects of 6PPD and its oxidative byproduct, 6PPD-Q, on the growth and reproduction of Daphnia pulex. Through 21-day exposure experiments, we measured the uptake of 0.1, 1, and 10 μg/L 6PPD and 6PPD-Q by D. pulex and assessed the effects on growth and fecundity of D. pulex. While 6PPD and 6PPD-Q did not affect the mortality rate of D. pulex, 6PPD-Q exposure inhibited the growth of D. pulex, indicating potential ecological risks. In particular, the reproductive capacity of D. pulex remained unaffected across the tested concentrations of 6PPD and 6PPD-Q, suggesting specific toxicological pathways that warrant further investigation. This study underscored the importance of evaluating the sublethal effects of emerging contaminants such as 6PPD and 6PPD-Q on aquatic invertebrates, and highlighted the need for comprehensive risk assessments to better understand their environmental impacts.

Waste rubber - Black pollution reframed as a global issue: Ecological challenges and sustainability initiatives

In contrast to "white pollution" originating from waste plastics, waste rubber is often referred to as "black pollution." The quantity and variety of waste rubber are increasing at an alarming rate, with a considerable fraction entering the global ecosystem via various pathways. This study presents the first critical review of waste rubber research with a focus on the risks associated with toxicant discharge and existing problems in waste rubber disposal, management, and recycling practices. We aim to obtain a comprehensive understanding of current research, particularly regarding the ecological impacts of these wastes, highlight major gaps, and propose the most significant research directions. A total of 192 studies published in journals were critically analysed. The importance of conducting long-term and large-scale experiments and developing efficient waste rubber recycling systems is also emphasised. This study highlights the need to address the challenges posed by waste rubber pollution and offers insights and references for undertaking ecological risk assessments and understanding the mechanisms underlying toxicant behaviour. Suggestions and countermeasures are proposed with ecosystem sustainability as the ultimate goal. Further long-term, comprehensive, and systematic research in this area is required.

Generation of environmentally persistent free radicals on photoaged tire wear particles and their neurotoxic effects on neurotransmission in Caenorhabditis elegans

Tire wear particles (TWP) are a prevalent form of microplastics (MPs) extensively distributed in the environment, raising concerns about their environmental behaviors and risks. However, knowledge regarding the properties and toxicity of these particles at environmentally relevant concentrations, specifically regarding the role of environmentally persistent free radicals (EPFRs) generated during TWP photoaging, remains limited. In this study, the evolution of EPFRs on TWP under different photoaging times and their adverse effects on Caenorhabditis elegans were systematically investigated. The photoaging process primarily resulted in the formation of EPFRs and reactive oxygen species (O2•-, ⋅OH, and 1O2), altering the physicochemical properties of TWP. The exposure of nematodes to 100 μg/L of TWP-50 (TWP with a photoaging time of 50 d) led to a significant decrease in locomotory behaviors (e.g., head thrashes, body bends, and wavelength) and neurotransmitter contents (e.g., dopamine, glutamate, and serotonin). Similarly, the expression of neurotransmission-related genes was reduced in nematodes exposed to TWP-50. Furthermore, the addition of free-radical inhibitors significantly suppressed TWP-induced neurotoxicity. Notably, correlation analysis revealed a significantly negative correlation between EPFRs levels and the locomotory behaviors and neurotransmitter contents of nematodes. Thus, it was concluded that EPFRs on photoaged TWP induce neurotoxicity by affecting neurotransmission. These findings elucidate the toxicity effects and mechanisms of EPFRs, emphasizing the importance of considering their contributions when evaluating the environmental risks associated with TWP.