Dysbiosis in the Gut Microbiota of Soil Fauna Explains the Toxicity of Tire Tread Particles

Effects of tire particles on earthworm (Eisenia andrei) fitness and bioaccumulation of tire-related chemicals

Tire and Road Wear Particles (TRWP) are produced during the wear of tire rubber on the road pavement and contain various chemicals originating from the road environment and from the rubber. Toxic effects of TRWP and their associated chemicals on soil organisms remain poorly characterized. In a series of laboratory experiments, this study investigated the bioaccumulation kinetics of several common tire-related chemicals in the earthworm species Eisenia andrei using Cryogenically Milled Tire Tread (CMTT), as a surrogate for environmental TRWP. Effects on survival, growth, reproductive output and behaviour were determined. Average biota-soil accumulation factors ranged from 0.8 to 4.7 indicating low to moderate bioaccumulation of the tire-related chemicals. Toxicokinetics showed both high uptake (0.0 - 13.2 days-1) and elimination rates (0.0 - 6.3 days-1) in E.andrei. Still, the uptake of tire-related chemicals in earthworms' tissues and ingestion of tire particles could lead to trophic transfer to preys feeding on earthworms and requires further investigated. No significant effects on survival and growth were recorded after exposure to 0.05 and 5% CMTT. In the reproduction test, a slight increase of the reproductive output with increasing CMTT concentration and a slight decrease of the weight of the juveniles were observed. Moreover, a strong and significant avoidance behaviour was observed for worms exposed to 5% CMTT. This work highlights that soil highly contaminated with tire particles can negatively impact habitat function due to changes in texture and/or chemical stressors, lead to uptake of tire-related additives by earthworms and that high concentrations can impact organism's fitness.

Tire Wear Particles Exposure Enhances Denitrification in Soil by Enriching Labile DOM and Shaping the Microbial Community

Tire wear particles (TWP) are emerging contaminants in the soil environment due to their widespread occurrence and potential threat to soil health. However, their impacts on soil biogeochemical processes remain unclear. Here, we investigated the effects of TWP at various doses and their leachate on soil respiration and denitrification using a robotized continuous-flow incubation system in upland soil. Fourier transform ion cyclotron resonance mass spectrometry and high-throughput sequencing were employed to elucidate the mechanisms underpinning the TWP effects. We show that TWP increased soil CO2, N2, and N2O emissions, which were attributed to the changes in content and composition of soil dissolved organic matter (DOM) induced by TWP and their leachate. Specifically, the labile DOM components (H/C ≥ 1.5 and transformation >10), which were crucial in shaping the denitrifying community, were significantly enriched by TWP exposure. Furthermore, the abundances of denitrification genes (nirK/S and nosZ-I) and the specific denitrifying genera Pseudomonas were increased following TWP exposure. Our findings provide new insights into impacts of TWP on carbon and nitrogen cycling in soil, highlighting that TWP exposure may exacerbate greenhouse gas emissions and fertilizer N loss, posing adverse effects on soil fertility in peri-urban areas and climate change mitigation.

Survival and reproduction effects of microplastics from three agricultural mulching films on Folsomia candida, Sinella curviseta, Heteromurus nitidus and Ceratophysella denticulata (Collembola)

An estimated 467 kt of plastic used in agriculture annually end up in European soils, potentially breaking down into secondary microplastics (MPs). Not much is known about the possible effects of these MPs on organisms residing in the soil. To properly assess their environmental risk, experimental data is needed on the toxicity of MPs to the survival and reproduction of model organisms. This study aimed at assessing the toxicity of three MP types derived from commonly used agricultural plastics to different Collembola species, representing an important and highly diverse class of soil arthropods. Starch- polybutadiene adipate terephthalate blend (starch-PBAT blend) MPs were produced from mulching films that were artificially aged by mechanical recycling. MPs were also made from virgin low density polyethylene (LDPE) mulching films and from linear low density polyethylene (LLDPE) films that underwent the same mechanical recycling process as the starch-PBAT blend films. Four Collembola species were tested: Folsomia candida, Sinella curviseta, Heteromurus nitidus and Ceratophysella denticulata, representing epedaphic, hemiedaphic and euedaphic, as well as sexually reproducing and parthenogenetic species. Each species was exposed in Lufa 2.2 soil spiked with nine MP concentrations: 0.0016, 0.008, 0.04, 0.2, 1, 2, 3, 4 and 5 % (w/w dry soil) and a control without additional MPs added to the soil. No dose-dependent effects were found for any of the exposed organisms, to any of the MPs tested. The results of this study suggest that the MPs used in this study, derived from commonly applied agricultural plastics, do not pose an immediate hazard to Collembola.

The Effect of Tyre and Road Wear Particles on the Terrestrial Isopod Armadillidium pallasii

(1) Car tyre microplastic particles (TMPs) significantly contribute to global microplastic pollution, with an estimated annual production of 6 million tonnes. However, the impact of TMPs, particularly tyre and road wear particles (TRWPs), resulting from tyre abrasion on the road on terrestrial organisms, is poorly understood. This study investigated the effects of TMPs and TRWPs on the growth, immune response, behaviour, and cognition of the woodlouse Armadillidium pallasii over 30 days; (2) TMPs and TRWPs were mixed together in the first experiment and provided at different concentrations of 1.25%, 2.5%, 5%, and 10% (w/w), and with soil at 5% and 10% (w/w) concentrations in the second experiment. (3) No differences in survival or immune responses were observed in both experiments. However, isopods exposed to TRWPs showed significant weight gain at lower concentrations but no gain at higher levels. Behavioural tests revealed increased vigilance in TRWP-exposed animals. Micro-FTIR analysis showed that the number of TMPs and TRWPs in the isopods correlated with soil concentrations, and particle size decreased during the experiment. (4) The study highlights the physiological and behavioural effects of TRWPs and the role of detritivorous species in the biofragmentation of TMPs and TRWPs, contributing to the biogeochemical plastic cycle.

Impact of freeze-thaw cycles on the remobilization behaviors of microplastics in natural soils

Freeze-thaw (FT) cycle would greatly influence the fate of plastic particles (one of emerging contaminants with great concerns) in soils, yet its impacts and mechanisms remain unclear. The vertical migration/release behaviors of plastic particles (with diameters of 0.2 μm and 1 μm) in two natural soils and one model soil (i.e. quartz sand) without/with FT treatments (1 and 3 cycles) were examined. Owing to the presence of Fe/Al oxide minerals, finer pore structure, and uneven surfaces of natural soils, the breakthrough ratio of plastics in two natural soils was over 25% lower than in quartz sand. However, regardless of porous media type, FT processes (increasing cycles) significantly promoted the remobilization of plastics initially retained in three media during the subsequent water flushing processes. Via theoretical calculation, tracer experiments, and visible chamber experiments, the mechanisms driving plastics release from natural soils subjected to FT treatments during the water elution processes were determined to be different from those from pure quartz sand. The change of sand local configuration (the rearrangement of local sand pore spaces) during FT process mainly drove to plastics released from quartz sand columns. While the alteration in local soil configuration, the formation of preferential pathways, and increased release of soil particles contributed to plastics remobilization from soil columns subjected to FT. Clearly, FT processes significantly increased the vertical migration of plastics in soils potentially to groundwater, enhancing environmental risks of plastics.

Microplastics regulate soil microbial activities: Evidence from catalase, dehydrogenase, and fluorescein diacetate hydrolase

Soil microbiomes drive many soil processes and maintain the ecological functions of terrestrial ecosystems. Microplastics (MPs, size <5 mm) are pervasive emerging contaminants worldwide. However, how MPs affect soil microbial activity has not been well elucidated. This review article first highlights the effects of MPs on overall soil microbial activities represented by three soil enzymes, i.e., catalase, dehydrogenase, and fluorescein diacetate hydrolase (FDAse), and explores the underlying mechanisms and influencing factors. Abundant evidence confirms that MPs can change soil microbial activities. However, existing results vary greatly from inhibition to promotion and non-significance, depending on polymer type, degradability, dose, size, shape, additive, and aging degree of the target MPs, soil physicochemical and biological properties, and exposure conditions, such as exposure time, temperature, and agricultural practices (e.g., planting, fertilization, soil amendment, and pesticide application). MPs can directly affect microbial activities by acting as carbon sources, releasing additives and pollutants, and shaping microbial communities via plastisphere effects. Smaller MPs (e.g., nanoplastics, 1 to <1000 nm) can also damage microbial cells through penetration. Indirectly, MPs can change soil attributes, fertility, the toxicity of co-existing pollutants, and the performance of soil fauna and plants, thus regulating soil microbiomes and their activities. In conclusion, MPs can regulate soil microbial activities and consequently pose cascading consequences for ecosystem functioning.

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.

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.

Effects of tire particles and associated-chemicals on the Pacific oyster (Magallana gigas) physiology, reproduction and next-generation

By 2040, tire particles (TP) are expected to dominate marine plastic contamination, raising concerns about their effects on marine animals. This study employed a multidisciplinary and multigenerational approach on the Pacific oyster Magallana gigas to investigate the effects of TP and their leachates (LEA). Effects were analyzed at the individual scale, from cellular, molecular, and microbiota changes to reproductive outputs and offspring performance. Microbiota characterization revealed potential dysbiosis in oysters treated with high concentration of both TP and LEA. RNA-seq analyses highlighted the activation of energy metabolism and stress responses in the LEA treatment. Additionally, transcriptional changes in oocytes and the reduction of motile spermatozoa suggested potential effects on gamete quality. Notably, possible oyster resilience was pointed out by the lack of significant ecophysiological modifications in adults and impacts on the growth and reproductive outputs of the offspring. Overall, the implications of the observed oyster resilience under our experimental setting are discussed in relation to available toxicity data and within a comprehensive view of coastal ecosystems, where a higher diversity of plastic/rubber materials and harsher environmental conditions occur.

Nanocolloids in the soil environment: Transformation, transport and ecological effects

Nanocolloids (Ncs) are ubiquitous in natural systems and play a critical role in the biogeochemical cycling of trace metals and the mobility of organic pollutants. However, the environmental behavior and ecological effects of Ncs in the soil remain largely unknown. The accumulation of Ncs may have detrimental or beneficial effects on different compartments of the soil environment. This review discusses the major transformation processes (e.g., agglomeration/aggregation, absorption, deposition, dissolution, and redox reactions), transport, bioavailability of Ncs, and their roles in element cycles in soil systems. Notably, Ncs can act as effective carriers for other pollutants and contribute to environmental pollution by spreading pathogens, nutrients, heavy metals, and organic contaminants to adjacent water bodies or groundwater. Finally, the key knowledge gaps are highlighted to better predict their potential risks, and important new directions include exploring the geochemical process and mechanism of Ncs's formation; elucidating the transformation, transport, and ultimate fate of Ncs, and their long-term effect on contaminants, organisms, and elemental cycling; and identifying the impact on the growth and quality of important crops, evaluating its dominant effect on agro-ecosystems in the soil environment.

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.

Effect of UV exposure and natural aging on the in vitro PAHs bioaccessibility associated with tire wear particles in soil

Tire wear particles (TWP), as an emerging type of microplastics, are a significant source of contaminants in roadside soils due to their high concentration of pollutants, including polycyclic aromatic hydrocarbons (PAHs). This study explored the impact of ultraviolet (UV) exposure and natural aging on the in vitro bioaccessibility of PAHs associated with TWP in soil on a China-wide scale. Our findings suggested that UV exposure amplified the negative charge of TWP by 75 % and increased the hydrophobic groups on the particle surface. The bioaccessibility of 3- and 4-ring PAHs in TWP was significantly (p < 0.05) heightened by UV exposure. After 20 types of soils containing 2 % UV-exposed TWP underwent natural aging, the bioaccessibility of PAHs saw a significant decrease (p < 0.05) to 16-48 %, compared to 28-96 % in the unaged group. Soil pH and electrical conductivity (EC) were the two primary soil properties positively influencing the reduction of in vitro PAHs concentration and PAHs bioaccessibility. According to the prediction results, soils in southern China presented the highest potential region for the release of bioaccessible PAHs from TWP, highlighting the regional specificity of environmental impact. Our study provides valuable insights into the biological impact of PAHs associated with TWP on a regional scale, and offers scientific evidence for targeted soil risk management strategies.

Adverse effect of TWPs on soil fungi and the contribution of benzothiazole rubber additives

Tire wear particles (TWPs) pollution is widely present in soil, especially in areas severely affected by traffic. Herein, regular variation of fungal biomass with TWPs was found in soils with different distances from the highway. In addition, the concentrations of benzothiazole compounds (BTHs), an important class of rubber vulcanization accelerators, were found to be positively correlated to the TWPs abundance. Sixty days' soil microcosm experiments were conducted to further confirm the adverse effect of TWPs and BTHs on soil fungi. TWPs spiking at 1000 mg/kg, a detectable level in the roadside, resulted in significant reduction of biomass and significant changes of soil fungal community structure, with Eurotium and Polyporales being the sensitive species. BTH+ 2-hydroxybenzothiazole (OHBT) (the dominant BTHs in soil) spiking at 200 ng/kg, the dose equivalent to 1000 mg/kg TWPs pollution, also caused a similar magnitude of soil fungal biomass reduction. Adonis demonstrated no significant difference of fungal community structure between TWPs and BTH+OHBT spiked soil, suggesting the adverse effect of TWPs on soil fungi may be explained by the act of BTHs. Pure culture using the representative soil fungi Eurotium and Polyporales also confirmed that BTHs were the main contributors to the adverse effect of TWPs on soil fungi.

A review of tire wear particles: Occurrence, adverse effects, and control strategies

Tire wear particles (TWPs), common mixed particulate emerging contaminants in the environment, have global per capita emissions accounting for 0.23-1.9 kg/year, attracting global attention recently due to their wide detection, small size, mobility, and high toxicity. This review focuses on the occurrence characteristics of TWPs in multiple environmental media, adverse effects on organisms, potential toxicity mechanisms, and environmental risk prevention and control strategies of TWPs. The environmental fate of TWPs throughout the entire process is systematically investigated by the bibliometric analysis function of CiteSpace. This review supplements the gap in the joint toxicity and related toxicity mechanisms of TWPs with other environmental pollutants. Based on the risks review of TWPs and their additives, adverse impacts have been found in organisms from aquatic environments, soil, and humans, such as the growth inhibition effect on Chironomus dilutes. A multi-faceted and rationalized prevention and control treatment of "source-process-end" for the whole process can be achieved by regulating the use of studded tires, improving the tire additive formula, growing plants roadside, encouraging micro-degradation, and other methods, which are first reviewed. By addressing the current knowledge gaps and exploring prospects, this study contributes to developing strategies for reducing risks and assessing the fate of TWPs in multiple environmental media.

Plastic pollution in terrestrial ecosystems: Current knowledge on impacts of micro and nano fragments on invertebrates

The increasing accumulation of small plastic particles, in particular microplastics (>1 µm to 5 mm) and nanoplastics (< 1 µm), in the environment is a hot topic in our rapidly changing world. Recently, studies were initiated to better understand the behavior of micro- and nanoplastics (MNP) within complex matrices like soil, as well as their characterization, incorporation and potential toxicity to terrestrial biota. However, there remains significant knowledge gaps in our understanding of the wide-extent impacts of MNP on terrestrial invertebrates. We first summarized facts on global plastic pollution and the generation of MNP. Then, we focused on compiling the existing literature examining the consequences of MNP exposure in terrestrial invertebrates. The diversity of investigated biological endpoints (from molecular to individual levels) were compiled to get a better comprehension of the effects of MNP according to different factors such as the shape, the polymer type, the organism, the concentration and the exposure duration. The sublethal effects of MNP are acknowledged in the literature, yet no general conclusion was drawn as their impacts are highly dependent on their characteristic and experimental design. Finally, the synthesis highlighted some research gaps and remediation strategies, as well as a protocol to standardize ecotoxicological studies.

Effects of arsenic on the transport and attachment of microplastics in porous media

Understanding the impact of arsenic (As(III), inorganic pollutant widely present in natural environments) on microplastics (MPs, one type of emerging contaminants) mobility is essential to predict MPs fate and distribution in soil-groundwater systems, yet relevant research is lacking. This study explored the effects of As(III) copresent in suspensions (0.05, 0.5, and 5 mg/L) on MPs transport/attachment behaviors in porous media containing varied water contents (θ = 100 %, 90 %, and 60 %) under different ionic strengths (5, 10, and 50 mM NaCl) and flow rates (2, 4, and 8 m/day). Despite solution ionic strengths, flow rates, porous media water contents, sizes, and surface charges of MPs, with coexisting humic acid, and in actual water samples, As(III) of three concentrations increased MPs transport in quartz sand and natural sandy soil. The increased electrostatic repulsion between MPs and sand caused by the altered MPs surface charge via the adsorption of As(III) together with steric repulsion from As(III) in solution contributed to the promoted MPs mobility in porous media. The occupying attachment sites by As(III) partially contributed to the increased mobility of MPs with negative surface charge in porous media. Clearly, As(III) coexisting in suspensions would enhance MPs transport in porous media, increasing MPs environment risks.

Aging increases the particulate- and leachate-induced toxicity of tire wear particles to microalgae

The toxic effects of tire wear particles (TWPs) on organisms have attracted widespread concerns over the past decade. However, the underlying toxicity mechanism of TWPs, especially aged TWPs to marine microalgae remains poorly understood. This study investigated the physiological and metabolic responses of Phaeodactylum tricornutum to different concentrations of TWPs (Experiment 1), virgin and differently aged TWPs (Experiment 2) as well as their leachates and leached particles (Experiment 3). Results demonstrated that TWPs promoted the growth of microalgae at low concentrations (0.6 and 3 mg L-1) and inhibited their growth at high concentrations (15 and 75 mg L-1). Moreover, aged TWPs induced more profound physiological effects on microalgae than virgin TWPs, including inhibiting microalgae growth, decreasing the content of Chla, promoting photosynthetic efficiency, and causing oxidative damage to algal cells. Untargeted metabolomics analysis confirmed that aged TWPs induced more pronounced metabolic changes than virgin TWPs. This study represented the first to demonstrate that both particulate- and leachate-induced toxicity of TWPs was increased after aging processes, which was confirmed by the changes in the surface morphology of TWPs and enhanced release of additives. Through the significant correlations between the additives and the microalgal metabolites, key additives responsible for the shift of microalgal metabolites were identified. These results broaden the understanding of the toxicity mechanism of aged TWPs to microalgae at the physiological and metabolic levels and appeal for considering the effects of long-term aging on TWP toxicity in risk assessment of TWPs.

Interspecific interactions disrupted by roads

Roads have pervasive impacts on wildlife, including habitat loss and fragmentation, road mortality, habitat pollution and increased human use of habitats surrounding them. However, the effects of roads on interspecific interactions are less understood. Here we provide a synthesis of the existing literature on how species interactions may be disrupted by roads, identify knowledge gaps, and suggest avenues for future research and conservation management. We conducted a systematic search using the Web of Science database for each species interaction (predation, competition, mutualism, parasitism, commensalism and amensalism). These searches yielded 2144 articles, of which 195 were relevant to our topic. Most of these studies focused on predation (50%) or competition (24%), and less frequently on mutualism (17%) or, parasitism (9%). We found no studies on commensalism or amensalism. Studies were biased towards mammals from high-income countries, with most conducted in the USA (34%) or Canada (18%). Our literature review identified several patterns. First, roads disrupt predator-prey relationships, usually with negative impacts on prey populations. Second, new disturbed habitats created in road corridors often benefit more competitive species, such as invasive species, although some native or endangered species can also thrive there. Third, roads degrade mutualistic interactions like seed dispersal and pollination. Fourth, roads can increase parasitism rates, although the intensity of the alteration is species specific. To reduce the negative impacts of roads on interspecific interactions, we suggest the following management actions: (i) verges should be as wide and heterogenous as possible, as this increases microhabitat diversity, thus enhancing ecosystem services like pollination and seed dispersal; (ii) combining different mowing regimes can increase the complexity of the habitat corridor, enabling it to act as a habitat for more species; (iii) the use of de-icing salts should be gradually reduced and replaced with less harmful products or maintenance practices; (iv) wildlife passes should be implemented in groups to reduce animal concentrations inside them; (v) periodic removal of carcasses from the road to reduce the use of this resource by wildlife; and (vi) implementation of traffic-calming schemes could enhance interspecific interactions like pollination and avoid disruption of predator-prey relationships.

Where the rubber meets the road: Emerging environmental impacts of tire wear particles and their chemical cocktails

About 3 billion new tires are produced each year and about 800 million tires become waste annually. Global dependence upon tires produced from natural rubber and petroleum-based compounds represents a persistent and complex environmental problem with only partial and often-times, ineffective solutions. Tire emissions may be in the form of whole tires, tire particles, and chemical compounds, each of which is transported through various atmospheric, terrestrial, and aquatic routes in the natural and built environments. Production and use of tires generates multiple heavy metals, plastics, PAH's, and other compounds that can be toxic alone or as chemical cocktails. Used tires require storage space, are energy intensive to recycle, and generally have few post-wear uses that are not also potential sources of pollutants (e.g., crumb rubber, pavements, burning). Tire particles emitted during use are a major component of microplastics in urban runoff and a source of unique and highly potent toxic substances. Thus, tires represent a ubiquitous and complex pollutant that requires a comprehensive examination to develop effective management and remediation. We approach the issue of tire pollution holistically by examining the life cycle of tires across production, emissions, recycling, and disposal. In this paper, we synthesize recent research and data about the environmental and human health risks associated with the production, use, and disposal of tires and discuss gaps in our knowledge about fate and transport, as well as the toxicology of tire particles and chemical leachates. We examine potential management and remediation approaches for addressing exposure risks across the life cycle of tires. We consider tires as pollutants across three levels: tires in their whole state, as particulates, and as a mixture of chemical cocktails. Finally, we discuss information gaps in our understanding of tires as a pollutant and outline key questions to improve our knowledge and ability to manage and remediate tire pollution.

Reproductive cytotoxic and genotoxic impact of polystyrene microplastic on Paracentrotus lividus spermatozoa

In recent decades, industrialization, intensive agriculture, and urban development have severely impacted marine environments, compromising the health of aquatic and terrestrial organisms. Inadequate disposal results in hundreds of tons of plastic products released annually into the environment, which degrade into microplastics (MPs), posing health risks due to their ability to biomagnify and bioaccumulate. Among these, polystyrene MPs (PS-MPs) are significant pollutants in marine ecosystems, widely studied for their reproductive toxicological effects. This research aimed to evaluate the reproductive cytotoxic and genotoxic effects of PS-MPs on sea urchin (Paracentrotus lividus) spermatozoa in vitro. Results showed that PS-MPs significantly reduced sperm viability and motility without altering morphology, and induced sperm DNA fragmentation mediated by reactive oxygen species production. Furthermore, head-to-head agglutination of the spermatozoa was observed exclusively in the sample treated with the plastic agents, indicating the ability of microplastics to adhere to the surface of sperm cells and form aggregates with microplastics on other sperm cells, thereby impeding movement and reducing reproductive potential. These findings suggest that PS-MPs can adversely affect the quality of sea urchin sperm, potentially impacting reproductive events.

Effects of farmland residual mulch film-derived microplastics on the structure and function of soil and earthworm Metaphire guillelmi gut microbiota

Microplastics derived from polyethylene (PE) mulch films are widely found in farmland soils and present considerable potential threats to agricultural soil ecosystems. However, the influence of microplastics derived from PE mulch films, especially those derived from farmland residual PE mulch films, on soil ecosystems remains unclear. In this study, we analyzed the bacterial communities attached to farmland residual transparent PE mulch film (FRMF) collected from peanut fields and the different ecological effects of unused PE mulch film-derived microplastics (MPs) and FRMF-derived microplastics (MPs-aged) on the soil and earthworm Metaphire guillelmi gut microbiota, functional traits, and co-occurrence patterns. The results showed that the assembly and functional patterns of the bacterial communities attached to the FRMF were clearly distinct from those in the surrounding farmland soil, and the FRMF enriched some potential plastic-degrading and pathogenic bacteria, such as Nocardioidaceae, Clostridiaceae, Micrococcaceae, and Mycobacteriaceae. MPs substantially influenced the assembly and functional traits of soil bacterial communities; however, they only significantly changed the functional traits of earthworm gut bacterial communities. MPs-aged considerably affected the assembly and functional traits of both soil and earthworm gut bacterial communities. Notably, MPs had a more remarkable effect on nitrogen-related functions than the MPs-aged in numbers for both soil and earthworm gut samples. Co-occurrence network analysis revealed that both MPs and MPs-aged enhanced the synergistic interactions among operational taxonomic units (OTUs) of the composition networks for all samples. For community functional networks, MPs and MPs-aged enhanced the antagonistic interactions for soil samples; however, they exhibited contrasting effects for earthworm gut samples, as MPs enhanced the synergistic interactions among the functional contents. These findings broaden and deepen our understanding of the effects of FRMF-derived microplastics on soil ecosystems, suggesting that the harmful effects of aged plastics on the ecological environment should be considered.

Microbial-influenced pesticide removal co-occurs with antibiotic resistance gene variation in soil-earthworm-maize system

Within human-influenced landscapes, pesticides cooccur with a variety of antibiotic stressors. However, the relationship between pesticides removal process and antibiotic resistance gene variation are not well understood. This study explored pesticide (topramezone, TPZ) and antibiotic (polymyxin E, PME) co-contamination using liquid chromatography-tandem mass spectrometry (LC-MS/MS), bacterial-16 S rRNA sequencing and high-throughput quantitative polymerase chain reaction (HT-qPCR) in a soil-earthworm-maize system. After incubating soil for 28 days with TPZ and PME (10 mg kg-1 dry weight), earthworm weight-gain, mortality rates, and maize plant weight-gain only differed slightly, but height-gain significantly decreased. PME significantly increased TPZ-removal in the soil. Accumulation of TPZ in earthworm's tissues may pose potential risks in the food chain. Combined pollution altered the microbial community structure and increased the abundance of functional microorganisms involved in aromatic compound degradation. Furthermore, maize rhizosphere can raise resistance genes, however earthworms can reduce resistance genes. Co-contamination increased absolute abundance of mobile genetic elements (MGEs) in bulk-soil samples, antibiotic resistance genes (ARGs) in skin samples and number of ARGs in bulk-soil samples, while decreased absolute abundance of transposase gene in bulk-soil samples and number of ARGs in rhizosphere-soil samples. Potential hosts harbouring ARGs may be associated with the antagonistic effect during resistance and detoxification of TPZ and PMB co-occurrence. These findings provide insights into the mechanism underlining pesticide removal regarding occurrence of ARGs in maize agroecosystem.

Effects of partial reduction of polystyrene micro-nanoplastics on the immunity, gut microbiota and metabolome of mice

Microplastic (MP) and nanoplastic (NP) could cause gut microbiota alterations. Although micro/nanoplastic (MNP) degradation is attracting increasing scientific interest, the evaluation of MNP reduction in gut needs to be further investigated. This study aimed to determine whether partial reduction of polystyrene MNP in gut could affect the immunity, gut microbiota and metabolome of mice. Serum eotaxin/CCL11 was at a lower level in the mice exposed to 200 μg and 500 μg NP (i.e., 2NP and 5NP groups, respectively) compared to those exposed to 500 μg MP (i.e., 5 MP group), while serum IL-2 and IL-4 were both greater in the 5NP group compared to the 5 MP group. The gut bacterial alpha diversity, fungal diversity and evenness were all similar among the MNP and control groups. However, the gut fungal richness was greater in both the 5NP and 5 MP groups compared to the control group. The gut bacterial and fungal compositions were both different between the MNP and control groups. Multiple gut bacteria and fungi showed different levels between the 2NP and 5NP groups, as well as between the 2NP and 5 MP groups. Increased Staphylococcus and decreased Glomus were determined in the 2NP group compared to both the 5NP and 5 MP groups. A Lactobacillus phylotype was found as the sole gatekeeper in the bacterial network of the 2NP group, while a Bifidobacterium phylotype contributed most to the stability of the bacterial networks of both the 5NP and 5 MP groups. Multiple differential gut metabolic pathways were found between the 2NP and 5NP/5 MP groups, and mTOR signaling pathway was largely upregulated in the 2NP group compared to both the 5NP and 5 MP groups. The relevant results could help with the evaluation of partial reduction of MNP in gut.

Microplastic pollution in terrestrial ecosystems: Global implications and sustainable solutions

Microplastic (MPs) pollution has become a global environmental concern with significant impacts on ecosystems and human health. Although MPs have been widely detected in aquatic environments, their presence in terrestrial ecosystems remains largely unexplored. This review examines the multifaceted issues of MPs pollution in terrestrial ecosystem, covering various aspects from additives in plastics to global legislation and sustainable solutions. The study explores the widespread distribution of MPs worldwide and their potential antagonistic interactions with co-occurring contaminants, emphasizing the need for a holistic understanding of their environmental implications. The influence of MPs on soil and plants is discussed, shedding light on the potential consequences for terrestrial ecosystems and agricultural productivity. The aging mechanisms of MPs, including photo and thermal aging, are elucidated, along with the factors influencing their aging process. Furthermore, the review provides an overview of global legislation addressing plastic waste, including bans on specific plastic items and levies on single-use plastics. Sustainable solutions for MPs pollution are proposed, encompassing upstream approaches such as bioplastics, improved waste management practices, and wastewater treatment technologies, as well as downstream methods like physical and biological removal of MPs. The importance of international collaboration, comprehensive legislation, and global agreements is underscored as crucial in tackling this pervasive environmental challenge. This review may serve as a valuable resource for researchers, policymakers, and stakeholders, providing a comprehensive assessment of the environmental impact and potential risks associated with MPs.

Aging in soil increases the disturbance of microplastics to the gut microbiota of soil fauna

Microplastics (MPs) in the soil environment inevitably experience aging processes. However, how aging in soil affects MP toxicity to soil fauna remains poorly understood. In this study, two types of widely distributed MPs (polypropylene and tire wear particles) were aged in different soils, and their surface properties, morphology, leaching features of additives, biofilm colonization and toxicity to the typical soil fauna Enchytraeus crypticus were investigated. Results showed that aging in soil slightly changed the surface properties and morphology for both types of MPs, but significantly affected the release of additives, especially for those MPs aged in soil amended with manure. Moreover, a distinct and less diverse microbial community than the surrounding soils was formed on the surface of MPs, and MP type was a determinant of the biofilm microbial community. Exposure experiments indicated that aged MPs, especially those aged in soil with manure significantly affected the reproduction of soil worms with a more obvious disturbance to their gut microbiota, and biofilm features and changes in the leaching properties of MPs during aging were the main factors for these shifts. This study is the first attempt to reveal the role of aging in soil in MP toxicity to soil fauna.

Integrating metabolomics and high-throughput sequencing to investigate the effects of tire wear particles on mung bean plants and soil microbial communities

Tire wear particles (TWPs) generated by vehicle tires are ubiquitous in soil ecosystems, while their impact on soil biota remains poorly understood. In this study, we investigated the effects of TWPs (0.1%, 0.7%, and 1.5% of dry soil weight) on the growth and metabolism of mung bean (Vigna radiata) plants over 32 days in soil pots. We found that TWPs-treated soils had high levels of heavy metals and polycyclic aromatic hydrocarbons (PAHs). However, there was no significant impact of TWPs exposure on plant growth, suggesting that mung bean plants have a degree of tolerance to TWPs. Despite the lack of impact on plant growth, exposure to TWPs had significant effects on soil enzyme activities, with a decrease of over 50% in urease and dehydrogenase activity. Furthermore, TWPs exposure resulted in marked changes in the plant metabolite profile, including altered levels of sugars, carboxylic acids, and amino acids, indicating altered nitrogen and amino acid-related metabolic pathways. TWPs exposure also disrupted the rhizospheric and bulk soil microbiota, with a decrease in the abundance of bacterial (Blastococcus) and fungal (Chaetomium) genera involved in nitrogen cycles and suppressing plant diseases. In summary, our study provides new insights into the effects of TWPs on plants and soil, highlighting the potential ecological consequences of TWPs pollution in terrestrial ecosystems and underscoring the need for further research in this area.

Responses of soil and collembolan (Folsomia candida) gut microbiomes to 6PPD-Q pollution

The potential risk of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) to soil organisms remains poorly understood. Here we showed that 6PPD-Q pollution inhibited the survival of collembolans (Folsomia candida) with the chronic median lethal concentration (LC50) of 16.31 μg kg-1 in a 28-day soil culture. The microbe-microbe interactions between abundant taxa in soil and collembolan gut helped alleviate the negative impact of 6PPD-Q on soil microbial community, while rare taxa contributed to maintaining microbial network complexity and stability under 6PPD-Q stresses. Gammaproteobacteria, Alphaproteobacteria and Actinobacteria in the gut of both adult and juvenile collembolans were identified as potential indicators for 6PPD-Q exposure. Such responses were accompanied by increases in the relative abundances of genes involved in nutrient cycles and their interactions between soil and collembolan gut microbiomes, which enhanced nitrogen and carbon turnover in 6PPD-Q polluted soil, potentially alleviating the stresses caused by 6PPD-Q. Overall, this study sheds new light on the toxicity of 6PPD-Q to soil organisms and links 6PPD-Q stresses to microbial responses and soil functions, thus highlighting the urgency of assessing its potential risk to the terrestrial ecosystem.

Stress response mechanism of wastewater biological nitrogen removal systems to environmentally realistic concentrations of tire wear particles: Contribution of leachable additives

The study quantified the biological nitrogen removal performance, microbial metabolism, microbial community structure, and antioxidant system in a sequencing batch reactor under long-term exposure to 0.1 and 1 mg/L tire wear particles (TWPs), and determined the contribution of leachable additives to the biotoxicity of TWPs. The results showed that long-term exposure to 0.1 and 1 mg/L TWPs inhibited both the nitrification and denitrification processes, reducing ammonia nitrogen (NH4+-N) and total nitrogen (TN) removal efficiency. The TWP leachate (TWPL) primarily contributed to the denitrification inhibition by TWPs, potentially due to the high concentration of zinc ions in the leachable additive. Furthermore, both TWP and TWPL inhibit nitrogen conversion, with TWP inhibiting the generation and transfer of electrons, while TWPL only negatively affects the electron transfer process. This study presents novel insights into the impact of TWPs on biological nitrogen removal, underscoring its broader implications for the geochemical nitrogen cycle.

Coupling multifactor dominated the biochemical response and the alterations of intestinal microflora of earthworm Pheretima guillelmi due to typical herbicides

The excessive application of herbicides on farmlands can substantially reduce labor costs and increase crop yields, but can also have undesirable effects on terrestrial ecosystems. To evaluate the ecological toxicity of herbicides, metolachlor and fomesafen, two typical herbicides that are extensively used worldwide were chosen as target pollutants, and the endogeic earthworm Pheretima guillelmi, which is widely distributed in China, was selected as the test organism. A laboratory-scale microcosmic experiment was set, and energy resources, enzymes, and the composition and connections of intestinal microorganisms in earthworms were determined. Both herbicides depleted the energy resources of the earthworms, especially glycogen contents; increased the levels of antioxidant enzymes; and inhibited acetylcholinesterase. Moreover, the richness and diversity of the intestinal bacterial community of the earthworms were suppressed. Additionally, the bacterial composition at the genus level changed greatly and the connections between dominant bacteria increased dramatically. Most interactions among the bacterial genera belonging to the same and different phyla showed mutualism and competition, respectively. Importantly, metolachlor with higher toxicity had a transitory effect on these indicators in earthworms, whereas fomesafen, with lower toxicity but stronger bioaccumulation potential, exerted a sustaining impact on earthworms. Collectively, these results indicate that the toxic effects of herbicides on terrestrial organisms should be comprehensively considered in combination with biological toxicity, persistence, bioaccumulation potential, and other factors.

The forgotten impacts of plastic contamination on terrestrial micro- and mesofauna: A call for research

Microplastics (MP) and nanoplastics (NP) contamination of the terrestrial environment is a growing concern worldwide and is thought to impact soil biota, particularly the micro and mesofauna community, by various processes that may contribute to global change in terrestrial systems. Soils act as a long-term sink for MP, accumulating these contaminants and increasing their adverse impacts on soil ecosystems. Consequently, the whole terrestrial ecosystem is impacted by microplastic pollution, which also threatens human health by their potential transfer to the soil food web. In general, the ingestion of MP in different concentrations by soil micro and mesofauna can adversely affect their development and reproduction, impacting terrestrial ecosystems. MP in soil moves horizontally and vertically because of the movement of soil organisms and the disturbance caused by plants. However, the effects of MP on terrestrial micro-and mesofauna are largely overlooked. Here, we give the most recent information on the forgotten impacts of MP contamination of soil on microfauna and mesofauna communities (protists, tardigrades, soil rotifers, nematodes, collembola and mites). More than 50 studies focused on the impact of MP on these organisms between 1990 and 2022 have been reviewed. In general, plastic pollution does not directly affect the survival of organisms, except under co-contaminated plastics that can increase adverse effects (e.g. tire-tread particles on springtails). Besides, they can have adverse effects at oxidative stress and reduced reproduction (protists, nematodes, potworms, springtails or mites). It was observed that micro and mesofauna could act as passive plastic transporters, as shown for springtails or mites. Finally, this review discusses how soil micro- and mesofauna play a key role in facilitating the (bio-)degradation and movement of MP and NP through soil systems and, therefore, the potential transfer to soil depths. More research should be focused on plastic mixtures, community level and long-term experiments.

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

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

A framework for systematic microplastic ecological risk assessment at a national scale

Microplastic pollution is widespread in terrestrial and aquatic environments; however, a systematic assessment of the ecological risks of microplastics is lacking. This study collected research studies on microplastics in soil, aquatic and sediment environments, and screened 128 articles including 3459 sites to assess the ecological risks posed by microplastics in China following a literature quality assessment. We developed a systematic ecological risk assessment framework for microplastics in terms of spatial characterization, biotoxicity and anthropogenic impacts. The results of the pollution load index indicated that 74% and 47% of the soil and aquatic environments studied, respectively, faced a medium or higher level of pollution. Comparing predicted no effect concentrations (PNEC) and measured environmental concentrations (MECs), revealed that soil (97.70%) and aquatic (50.77%) environmental studies were at serious ecological risk from microplastics. The results of the pressure-state-response model showed that the microplastic pollution in Pearl River Delta was in a high-risk state. In addition, we found that ultraviolet radiation and rainfall exacerbate soil microplastic pollution, and higher river runoff may carry large amounts of microplastic from the source. The framework developed in this study will help assess the ecological risks of microplastics in the region to promote the mitigation of plastic pollution.

Understanding the ecological effects of the fungicide difenoconazole on soil and Enchytraeus crypticus gut microbiome

Increasing knowledge of the impacts of pesticides on soil ecological communities is fundamental to a comprehensive understanding of the functional changes in the global agroecosystem industry. In this study, we examined microbial community shifts in the gut of the soil-dwelling organism Enchytraeus crypticus and functional shifts in the soil microbiome (bacteria and viruses) after 21 d of exposure to difenoconazole, one of the main fungicides in intensified agriculture. Our results demonstrated reduced body weight and increased oxidative stress levels of E. crypticus under difenoconazole treatment. Meanwhile, difenoconazole not only altered the composition and structure of the gut microbial community, but also interfered with the soil-soil fauna microecology stability by impairing the abundance of beneficial bacteria. Using soil metagenomics, we revealed that bacterial genes encoding detoxification and viruses encoding carbon cycle genes exhibited a dependent enrichment in the toxicity of pesticides via metabolism. Taken together, these findings advance the understanding of the ecotoxicological impact of residual difenoconazole on the soil-soil fauna micro-ecology, and the ecological importance of virus-encoded auxiliary metabolic genes under pesticide stress.

Diesel exhaust particles alter gut microbiome and gene expression in the bumblebee Bombus terrestris

Insect decline is a major threat to ecosystems around the world as they provide many important functions, such as pollination or pest control. Pollution is one of the main reasons for the decline, alongside changes in land use, global warming, and invasive species. While negative impacts of pesticides are well-studied, there is still a lack of knowledge about the effects of other anthropogenic pollutants, such as airborne particulate matter, on insects. To address this, we exposed workers of the bumblebee Bombus terrestris to sublethal doses of diesel exhaust particles (DEPs) and brake dust, orally or via air. After 7 days, we looked at the composition of the gut microbiome and tracked changes in gene expression. While there were no changes in the other treatments, oral DEP exposure significantly altered the structure of the gut microbiome. In particular, the core bacterium Snodgrassella had a decreased abundance in the DEP treatment. Similarly, transcriptome analysis revealed changes in gene expression after oral DEP exposure, but not in the other treatments. The changes are related to metabolism and signal transduction, which indicates a general stress response. Taken together, our results suggest potential health effects of DEP exposure on insects, here shown in bumblebees, as gut dysbiosis may increase the susceptibility of bumblebees to pathogens, while a general stress response may lower available energy resources. Those effects may exacerbate under natural conditions where insects face a multiple-stressor environment.

Chemical toxicity screening of tire particle leachates from vehicles and their effects on organisms across three trophic levels

Tire particles (TPs) generated on roads are a main contributor to microplastic environmental pollution. In this study, TP leachates from three vehicle types (bicycle, car, and electric scooter) were prepared. TP leachate toxicity impacts on three organisms (Vigna radiata, Daphnia magna, and Danio rerio) were analyzed, in addition to their chemical compositions. Zinc and benzothiazole were the most commonly detected compounds in all three leachate types. Growth inhibition of V. radiata, mortality of D. magna, and abnormality in D. rerio were observed as toxicological impacts. Overall, the lethal effects of TP leachates showed a significant, positive relationship with zinc and benzothiazole concentration. The results confirmed that TPs are complex contaminants, which release chemicals into the environment that affect both soil and aquatic organisms. These findings highlight the need for stricter control measures and environmental regulations to mitigate the ecotoxic effects of TPs and related contaminants across ecosystems and trophic levels.

Silent Contamination: The State of the Art, Knowledge Gaps, and a Preliminary Risk Assessment of Tire Particles in Urban Parks

Tire particles (TPs) are one of the main emission sources of micro- and nano-plastics into the environment. Although most TPs are deposited in the soil or in the sediments of freshwater and although they have been demonstrated to accumulate in organisms, most research has focused on the toxicity of leachate, neglecting the potential effects of particles and their ecotoxicological impact on the environment. In addition, studies have focused on the impact on aquatic systems and there are many gaps in the biological and ecotoxicological information on the possible harmful effects of the particles on edaphic fauna, despite the soil ecosystem becoming a large plastic sink. The aim of the present study is to review the environmental contamination of TPs, paying particular attention to the composition and degradation of tires (I), transport and deposition in different environments, especially in soil (II), the toxicological effects on edaphic fauna (III), potential markers and detection in environmental samples for monitoring (IV), preliminary risk characterization, using Forlanini Urban Park, Milan (Italy), as an example of an urban park (V), and risk mitigation measures as possible future proposals for sustainability (VI).

Exposure to cypermethrin pesticide disturbs the microbiome and disseminates antibiotic resistance genes in soil and the gut of Enchytraeus crypticus

Worldwide, pyrethroids, such as cypermethrin, are the second most applied group of insecticides, however, their effects on the soil microbiome and non-target soil fauna remain largely unknown. Herein, we assessed the change of bacterial communities and antibiotic resistance genes (ARGs) of soil and in the gut of the model soil species Enchytraeus crypticus using a combination of 16S rRNA gene amplicon sequencing, and high-throughput qPCR of ARGs. Results indicate that cypermethrin exposure enriches potential pathogens (e.g. Bacillus anthracis) in the soil and gut microbiome of E. crypticus, heavily disrupting the latter's microbiome structure, and even disrupts activities of the E. crypticus immune system. The co-occurrence of potential pathogens (e.g. Acinetobacter baumannii), ARGs, and mobile genetic elements (MGEs) revealed the increased risk of pathogenicity as well as antibiotic resistance in potential pathogens. Moreover, structural equation modeling demonstrated that the dissemination of ARGs was not only promoted by MGEs, but also by the ratio of the core to non-core bacterial abundance. Collectively, these results provide an in-depth view of the previously unappreciated environmental risk of cypermethrin on the dissemination of ARGs in the soil and non-target soil fauna.

Deciphering roles of microbiota in arsenic biotransformation from the earthworm gut and skin

Biotransformation mediated by microbes can affect the biogeochemical cycle of arsenic. However, arsenic biotransformation mediated by earthworm-related microorganisms has not been well explored, especially the role played by earthworm skin microbiota. Herein, we reveal the profiles of arsenic biotransformation genes (ABGs) and elucidate the microbial communities of the earthworm gut, skin, and surrounding soil from five different soil environments in China. The relative abundance of ABGs in the earthworm skin microbiota, which were dominated by genes associated with arsenate reduction and transport, was approximately three times higher than that in the surrounding soil and earthworm gut microbiota. The composition and diversity of earthworm skin microbiota differed significantly from those of the soil and earthworm gut, comprising a core bacterial community with a relative abundance of 96% Firmicutes and a fungal community with relative abundances of 50% Ascomycota and 13% Mucoromycota. In addition, stochastic processes mainly contributed to the microbial community assembly across all samples. Moreover, fungal genera such as Vishniacozyma and Oomyces were important mediators of ABGs involved in the biogeochemical cycle of arsenic. This is the first study to investigate earthworm skin as a reservoir of microbial diversity in arsenic biotransformation. Our findings broaden the current scientific knowledge of the involvement of earthworms in the arsenic biogeochemical cycle.

Biochar surface properties and chemical composition determine the rhizobial survival rate

Biochar may be potentially used as a rhizobial carrier due to its specific chemical compositions and surface properties, but the relationship between these properties and rhizobial survival rate is largely unknown. Here, we analysed the physicochemical characteristics and carrier potential of six types of biochars made from various feedstocks at 600 °C using slow pyrolysis method, and results were compared with conventional carrier material peat. Liquid suspension of Bradyrhziobium japonicum CB1809 was used to inoculate all the carrier materials. Shelf life and survival rate was determined via colony forming unit (CFU) method for up to 90 days under two storage temperature conditions (28 °C and 38 °C). The determined physicochemical characteristics of biochars were categorized into major elements, trace elements, relative ratios, surface morphology, functional groups, and key basic properties; and their interaction to shelf life was analysed using hypothesis-oriented structure equation modelling (path analysis). Results revealed that different types of biochars had different capacity to impact on shelf life due to their different physicochemical properties. Among all biochars pine wood BC was the most suitable carrier with the highest counts of 10.11 Log 10 CFU g^-1 and 9.76 Log 10 CFU g^-1 at the end of 90 days at 28 °C and 38 °C storage, respectively. Path analysis revealed that rhizobial shelf life was largely explained by total carbon (TC), manganese (Mn), specific surface area (SSA), pore size, CO (ketonic carbon), and O-CO (carboxyl carbon) functional groups, and all these indicators exhibited positive direct impact on shelf life. Pinewood BC showed the highest values of Mn, SSA, pore size and functional groups (CO and O-CO), contributing to its highest rhizobial shelf life and survival rate among other biochars and peat tested.

Soil Storage Conditions Alter the Effects of Tire Wear Particles on Microbial Activities in Laboratory Tests

In this study, we focused on the fact that soil storage conditions in the laboratory have never been considered as a key factor potentially leading to high variation when measuring effects of microplastics on soil microbial activity. We stored field-collected soils under four different conditions [room-temperature storage, low-temperature storage (LS), air drying (AD), and heat drying] prior to the experiment. Each soil was treated with tire wear particles (TWPs), and soil microbial activities and water aggregate stability were investigated after soil incubation. As a result, microbial activities, including soil respiration and three enzyme activities (β-glucosidase, N-acetyl-β-glucosaminidase, and phosphatase), were shown to depend on soil storage conditions. Soil respiration rates increased with the addition of TWPs, and the differences from the control group (no TWPs added) were more pronounced in the AD TWP treatment than in soils stored under other conditions. In contrast, phosphatase activity followed an opposing trend after the addition of TWPs. The AD soil had higher phosphatase activity after the addition of TWPs, while the LS soil had a lower level than the control group. We suggest that microplastic effects in laboratory experiments can strongly depend on soil storage conditions.

Microplastic pollution in soils, plants, and animals: A review of distributions, effects and potential mechanisms

Increasing production of synthetic plastics and poor management of plastic wastes have dramatically increased the amount of plastics in the environment. In 2014, at the first United Nations Environment Assembly, marine plastic waste pollution was listed as one of the 10 most pressing environmental issues. In addition, there is much plastic waste in terrestrial ecosystems due to substantial residues from agricultural mulching and packing. As a recently recognized pollutant, microplastics (MPs) have attracted significant attention from the public and various governments. Concentrations of MPs in the environment vary among locations, from <100 to >1 × 10⁶ particles per cubic meter. Many studies have addressed the impacts and potential mechanisms of MPs on the environment and organisms. Humans and other organisms can ingest or carry MPs in a variety of passive ways and these MPs can have a range of negative effects on metabolism, function, and health. Additionally, given their large surface area, MPs can sorb various pollutants, including heavy metals and persistent organic pollutants, with serious implications for animals and human wellbeing. However, due to their complexity and a lack of accurate determination methods, the systematic impacts of MP pollution on whole foodwebs are not clearly established. Therefore, this review summarizes current research advances in MP pollution, particularly the impact of MPs on soils, plants, and animals, and proposes potential future research prospects to better characterize MPs.

Domestic refrigerators: An overlooked breeding ground of antibiotic resistance genes and pathogens

Domestic refrigerator is a widely used appliance to keep food fresh and retard food spoilage in household. However, our understanding of microbial health risk associated with food under such circumstance still remains very poor. Here, typical types of food (vegetable, fish, and pork) were kept in a domestic refrigerator at 4 °C for 3-30 days. Temporal dynamics of antibiotic resistome, pathogens, bacterial and fungal communities during this period were investigated via high-throughput quantification and Illumina sequencing technologies. Results showed that a large number (21-134) of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) were detected across the three food types, including 10.06 % of high-risk ARGs classified by their risk ranks. Moreover, four bacterial pathogens (i.e., Bacillus cereus, Cronobacter spp., Klebsiella pneumoniae and Staphylococcus aureus) targeted by marker genes including the pathogen-specific genes or virulence factor genes, and some potential fungal pathogens (e.g., Fusarium, Candida, and Aspergillus) were detected, indicating the occurrence of microbial risk even at the normally regarded safe storage temperature. Among all food types, the total bacterial density and ARG abundances in fish rapidly increased after only 3 days, much faster than vegetable and pork after 10 days. In addition, fish samples contained the highest ARG and pathogen abundances, indicating its potentially higher health risk than other food types. Finally, the shifts of ARG pattern were mainly contributed by bacterial communities and MGEs. This study highlights that food preserved in refrigerator at 4 °C could still be an unneglected microbial risk, and raises awareness of improving food safety in domestic environment.

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.

Leachable Additives of Tire Particles Explain the Shift in Microbial Community Composition and Function in Coastal Sediments

Massive microplastics are deposited in the coastal zone. Tire particles (TPs) are an important microplastic source, but little is known about how TPs affect the microbial community composition and function in coastal sediments and the role leachable additives play in TP toxicity. Here, a microcosm experiment was performed using coastal sediments amended with different doses of TPs and with their leachable additives to investigate their effects on the sediment microbial community composition and function. Environmentally relevant concentrations of TPs can change the microbial community structure, decrease community diversity, and inhibit nutrient cycling processes, including carbon fixation and degradation, nitrification, denitrification, and sulfur cycling in sediments. Notably, the raw TP and leachate treatments showed consistent effects. A variety of additives were found in the pore water of sediment, and they could explain over 90% of the variations of the community structure. Further modeling revealed that leachable additives not only directly influenced community function but also indirectly affected community diversity and function by shifting the community structure. In addition, rare taxa could be crucial mediators of ecological functions of sediment microbial community. Combined, this study provides novel insights into the role of TPs' leachable additives in affecting sediment microbial community and function.

Toxicity assessment of tire particles released from personal mobilities (bicycles, cars, and electric scooters) on soil organisms

Tire particles are generated by the abrasion of tire treads on roads and are major contributors to microplastics in soil environments. Contamination by tire wear particles worsens annually as the use of personal mobilities increases. Tire particles (112-541 µm) were obtained from three types of personal mobility tires (bicycle, car, and electric scooter) and exposed to plants (Vigna radiata) and springtails (Folsomia candida) for 28 d to assess the toxicity of each tire-particle type. The laboratory-generated tire particles exhibit adverse effects depending on the origin of the tire or test species. Particles from bicycle or electric-scooter tires changed the soil's bulk density and water holding capacity and adversely affected plant growth. Car tire particles had leached various organic compounds and induced detrimental effects on springtails (adult and offspring growth). We concluded that laboratory-generated tire particles (frow new tires) can affect the soil environment by changing soil properties and leaching chemicals; thus, causing adverse effects on soil organisms. Since this study found tire particle toxicity on soil organisms, it would be possible to compare the various contamination levels in areas near road soil and other clean soils.

Temporal variation of antibiotic resistome and pathogens in food waste during short-term storage

The massive food wastes pose a growing health concern for spreading of antibiotic resistance and pathogens due to food spoilage. However, little is known about these microbial hazards during collection, classification, and transportation before eventual treatment. Here, we profiled the temporal variations of antibiotic resistance genes (ARGs), pathogens, bacterial and fungal communities across four typical food wastes (vegetable, fish, meat, and rice) during storage at room temperature in summer (maximum 28-29 °C) of typical southeast city in China. A total of 171 ARGs and 32 mobile genetic elements were detected, and the absolute abundance of ARGs significantly increased by up to 126-fold with the storage time. Additionally, five bacterial pathogens containing virulence factor genes were detected, and Klebsiella pneumoniae was persistently detected throughout the storage time in all food types except rice. Moreover, fungal pathogens (e.g., Aspergillus, Penicillium, and Fusarium) were also frequently detected. Notably, animal food wastes were demonstrated to harbor higher abundance of ARGs and more types of pathogens, indicating a higher level of hazard. Mobile genetic elements and food types were demonstrated to mainly impact ARG profiles and pathogens, respectively. This work provides a comprehensive understanding of the microbial hazards associated with food waste recycling, and will contribute to optimize the food waste management to ensure biosecurity and benefit human health.

Calling for comprehensive explorations between soil invertebrates and arbuscular mycorrhizas

Arbuscular mycorrhizal (AM) fungi and soil invertebrates represent a large proportion of total soil biomass and biodiversity and are vital for plant performance, soil structure, and biogeochemical cycling. However, the role of soil invertebrates in AM fungi development remains elusive. In this opinion article, we summarize the ecological importance of AM fungi and soil invertebrates in the plant-soil continuum and highlight the effects of soil invertebrates on AM fungal hyphae development and functioning. In a context of global change, we envision that better mechanistic understanding of the complex feedback via chemical signaling pathways across the interactions between soil invertebrates and AM fungi is critical to predict their ecological consequences and will open new avenues for promoting ecosystem resilience and sustainability.