Fate and abundance of antibiotic resistance genes on microplastics in facility vegetable soil

Sources, interactions, influencing factors and ecological risks of microplastics and antibiotic resistance genes in soil: A review

Microplastics (MPs) and antibiotic resistance genes (ARGs) are gaining increasing attention as they pose a threat to the ecological environment and human health as emerging contaminants. MPs has been proved to be a hot spot in ARGs, and although it has been extensively studied in water environment, the results of bibliometrics statistical analysis in this paper showed that relevant studies in soil ecological environment are currently in the initial stage. In view of this, the paper provides a systematic review of the sources, interactions, influencing factors, and ecological risks associated with MPs and ARGs in soil environments. Additionally, the mechanism and influencing factors of plastisphere formation and resistance are elaborated in detail. The MPs properties, soil physicochemical properties, soil environmental factors and agricultural activities are the primarily factors affecting the interaction between MPs and ARGs in soil. Challenges and development directions of related research in the future are also prospected. It is hoped that the review could assist in a deeper comprehension and exploration of the interaction mechanism between MPs and ARGs in soil as well as the function of MPs in the transmission process of ARGs among diverse environmental media and organisms, and provide theory basis and reference for the MPs and ARGs pollution control and remediation in soil.

Polystyrene microplastics as carriers for nano-hydroxyapatite particles: Impact of surface functionalization and mechanistic insights

The potential of microplastics (MPs) to act as carriers for contaminants or engineered nanomaterials is of rising concern. However, directly determining the vector effect of polystyrene (PS) MPs towards nano-hydroxyapatite (nHAP) particles, a typical nano phosphorus fertilizer and soil remediation material, has been rarely studied. In this study, the interaction of differentially surface functionalized PS MPs with nHAP were investigated through batch experiments under different solution chemistry conditions. The results demonstrated that nHAP had the highest attachment/adsorption affinity onto carboxyl-functionalized PS, followed by bare PS and amino-functionalized PS under near-neutral pH conditions. Adsorption of nHAP exhibited a strong pH-dependent behavior with PS MPs, increasing under acidic-neutral pH (3-7) and decreasing at higher pH values. The presence of humic acid and NaCl hindered the adsorption of nHAP onto MPs. Scanning electron microscopy observations revealed a rod-like morphology for adsorbed nHAP, which was randomly distributed on MPs surface. Surface complexation and cation-π interaction were mainly responsible for the adsorption of nHAP as revealed by multiple spectroscopic analyses. These results provide mechanistic insights into nHAP-PS interactions and expound the effect of surface functionalization of PS on binding mechanisms, and thus bring important clues for better understanding the vector effects of MPs towards nanoparticles.

Effect of polyethylene microplastics on antibiotic resistance genes: A comparison based on different soil types and plant types

Microplastics (MPs) and antibiotic resistance genes (ARGs) are two types of contaminants that are widely present in the soil environment. MPs can act as carriers of microbes, facilitating the colonization and spread of ARGs and thus posing potential hazards to ecosystem safety and human health. In the present study, we explored the microbial networks and ARG distribution characteristics in different soil types (heavy metal (HM)-contaminated soil and agricultural soil planted with different plants: Bidens pilosa L., Ipomoea aquatica F., and Brassica chinensis L.) after the application of MPs and evaluated environmental factors, potential microbial hosts, and ARGs. The microbial communities in the three rhizosphere soils were closely related to each other, and the modularity of the microbial networks was greater than 0.4. Moreover, the core taxa in the microbial networks, including Actinobacteriota, Proteobacteria, and Myxococcota, were important for resisting environmental stress. The ARG resistance mechanisms were dominated by antibiotic efflux in all three rhizosphere soils. Based on the annotation results, the MP treatments induced changes in the relative abundance of microbes carrying ARGs, and the G1-5 treatment significantly increased the abundance of MuxB in Verrucomicrobia, Elusimicrobia, Actinobacteria, Planctomycetes, and Acidobacteria. Path analysis showed that changes in MP particle size and dosage may indirectly affect soil enzyme activities by changing pH, which affects microbes and ARGs. We suggest that MPs may provide surfaces for ARG accumulation, leading to ARG enrichment in plants. In conclusion, our results demonstrate that MPs, as potentially persistent pollutants, can affect different types of soil environments and that the presence of ARGs may cause substantial environmental risks.

Ecological effect of microplastics on soil microbe-driven carbon circulation and greenhouse gas emission: A review

Soil organic carbon (SOC) pool, the largest part of terrestrial ecosystem, controls global terrestrial carbon balance and consequently presented carbon cycle-climate feedback in climate projections. Microplastics, (MPs, <5 mm) as common pollutants in soil ecosystems, have an obvious impact on soil-borne carbon circulation by affecting soil microbial processes, which play a central role in regulating SOC conversion. In this review, we initially presented the sources, properties and ecological risks of MPs in soil ecosystem, and then the differentiated effects of MPs on the component of SOC, including dissolved organic carbon, soil microbial biomass carbon and easily oxidized organic carbon varying with the types and concentrations of MPs, the soil types, etc. As research turns into a broader perspective, greenhouse gas emissions dominated by the mineralization of SOC coming into view since it can be significantly affected by MPs and is closely associated with soil microbial respiration. The pathways of MPs impacting soil microbes-driven carbon conversion include changing microbial community structure and composition, the functional enzyme's activity and the abundance and expression of functional genes. However, numerous uncertainties still exist regarding the microbial mechanisms in the deeper biochemical process. More comprehensive studies are necessary to explore the affected footprint and provide guidance for finding the evaluation criterion of MPs affecting climate change.

Microplastics as carriers of antibiotic resistance genes and pathogens in municipal solid waste (MSW) landfill leachate and soil: a review

Landfill leachate contains antibiotic resistance genes (ARGs) and microplastics (MPs), making it an important reservoir. However, little research has been conducted on how ARGs are enriched on MPs and how the presence of MPs affects pathogens and ARGs in leachates and soil. MPs possess the capacity to establish unique bacterial populations and assimilate contaminants from their immediate surroundings, generating a potential environment conducive to the growth of disease-causing microorganisms and antibiotic resistance genes (ARGs), thereby exerting selection pressure. Through a comprehensive analysis of scientific literature, we have carried out a practical assessment of this topic. The gathering of pollutants and the formation of dense bacterial communities on microplastics create advantageous circumstances for an increased frequency of ARG transfer and evolution. Additional investigations are necessary to acquire a more profound comprehension of how pathogens and ARGs are enriched, transported, and transferred on microplastics. This research is essential for evaluating the health risks associated with human exposure to these pollutants.

Graphical Abstract

Expanding the focus of the One Health concept: links between the Earth-system processes of the planetary boundaries framework and antibiotic resistance

The scientific community warns that our impact on planet Earth is so acute that we are crossing several of the planetary boundaries that demarcate the safe operating space for humankind. Besides, there is mounting evidence of serious effects on people's health derived from the ongoing environmental degradation. Regarding human health, the spread of antibiotic resistant bacteria is one of the most critical public health issues worldwide. Relevantly, antibiotic resistance has been claimed to be the quintessential One Health issue. The One Health concept links human, animal, and environmental health, but it is frequently only focused on the risk of zoonotic pathogens to public health or, to a lesser extent, the impact of contaminants on human health, i.e., adverse effects on human health coming from the other two One Health "compartments". It is recurrently claimed that antibiotic resistance must be approached from a One Health perspective, but such statement often only refers to the connection between the use of antibiotics in veterinary practice and the antibiotic resistance crisis, or the impact of contaminants (antibiotics, heavy metals, disinfectants, etc.) on antibiotic resistance. Nonetheless, the nine Earth-system processes considered in the planetary boundaries framework can be directly or indirectly linked to antibiotic resistance. Here, some of the main links between those processes and the dissemination of antibiotic resistance are described. The ultimate goal is to expand the focus of the One Health concept by pointing out the links between critical Earth-system processes and the One Health quintessential issue, i.e., antibiotic resistance.

Effects of microplastics on soil microorganisms and microbial functions in nutrients and carbon cycling - A review

The harmful effects of microplastics (MPs) pollution in the soil ecosystem have drawn global attention in recent years. This paper critically reviews the effects of MPs on soil microbial diversity and functions in relation to nutrients and carbon cycling. Reports suggested that both plastisphere (MP-microbe consortium) and MP-contaminated soils had distinct and lower microbial diversity than that of non-contaminated soils. Alteration in soil physicochemical properties and microbial interactions within the plastisphere facilitated the enrichment of plastic-degrading microorganisms, including those involved in carbon (C) and nutrient cycling. MPs conferred a significant increase in the relative abundance of soil nitrogen (N)-fixing and phosphorus (P)-solubilizing bacteria, while decreased the abundance of soil nitrifiers and ammonia oxidisers. Depending on soil types, MPs increased bioavailable N and P contents and nitrous oxide emission in some instances. Furthermore, MPs regulated soil microbial functional activities owing to the combined toxicity of organic and inorganic contaminants derived from MPs and contaminants frequently encountered in the soil environment. However, a thorough understanding of the interactions among soil microorganisms, MPs and other contaminants still needs to develop. Since currently available reports are mostly based on short-term laboratory experiments, field investigations are needed to assess the long-term impact of MPs (at environmentally relevant concentration) on soil microorganisms and their functions under different soil types and agro-climatic conditions.

Climate warming, environmental degradation and pollution as drivers of antibiotic resistance

Antibiotic resistance is a major challenge to public health, but human-caused environmental changes have not been widely recognized as its drivers. Here, we provide a comprehensive overview of the relationships between environmental degradation and antibiotic resistance, demonstrating that the former can potentially fuel the latter with significant public health outcomes. We describe that (i) global warming favors horizontal gene transfer, bacterial infections, the spread of drug-resistant pathogens due to water scarcity, and the release of resistance genes with wastewater; (ii) pesticide and metal pollution act as co-selectors of antibiotic resistance mechanisms; (iii) microplastics create conditions promoting and spreading antibiotic resistance and resistant bacteria; (iv) changes in land use, deforestation, and environmental pollution reduce microbial diversity, a natural barrier to antibiotic resistance spread. We argue that management of antibiotic resistance must integrate environmental goals, including mitigation of further increases in the Earth's surface temperature, better qualitative and quantitative protection of water resources, strengthening of sewage infrastructure and improving wastewater treatment, counteracting the microbial diversity loss, reduction of pesticide and metal emissions, and plastic use, and improving waste recycling. These actions should be accompanied by restricting antibiotic use only to clinically justified situations, developing novel treatments, and promoting prophylaxis. It is pivotal for health authorities and the medical community to adopt the protection of environmental quality as a part of public health measures, also in the context of antibiotic resistance management.

Antibiotics and microplastics in manure and surrounding soil of farms in the Loess Plateau: Occurrence and correlation

The wide use of animal manure in farmland operations is a source of soil nutrients. However, the return of manure affected antibiotics and microplastics in the soil, thus the potential ecological risks cannot be overlooked. This study investigated the distribution of different antibiotics and microplastics and their correlation. It was found that multiple classes of veterinary antibiotics and microplastics could be detected simultaneously in most manure and soil. In manure, the average concentration of tetracycline antibiotics was higher than fluoroquinolones and sulfonamides. A much lower concentration of antibiotics was found in the soil samples relative to manure. The abundance of microplastics ranged from 21,333 to 88,333 n/kg in manure, and the average abundance was 50,583 ± 24,318 n/kg. The average abundance was 3056 ± 1746 n/kg in the soil. It confirmed that applying organic fertilizer to agricultural soil and the application of plastic mulch in farmlands introduced microplastics. Moreover, microplastics were found to be significantly correlated with antibiotics (r = 0.698, p < 0.001). The correlation between microplastics and antibiotics in soil was significantly weaker than that in manure. Farms could be the hotspot for the co-spread of microplastics and antibiotics. These findings highlighted the co-occurrence of antibiotics and microplastics in agricultural environments.

The critical role of microplastics in the fate and transformation of sulfamethoxazole and antibiotic resistance genes within vertical subsurface-flow constructed wetlands

Constructed wetlands (CWs) are reservoirs of microplastics (MPs) in the environment. However, knowledge about the impact of MPs on antibiotic removal and the fate of antibiotic resistance genes (ARGs) is limited. We focused on sulfamethoxazole (SMX) as a representative compound to examine the effects of MPs on SMX removal and the proliferation and dissemination of two SMX-related ARGs (sul1 and sul2) in vertical subsurface-flow CW (VFCW) microcosm. The presence of MPs in the substrate was found to enhance the proliferation of microorganisms owing to the large specific surface area of the MPs and the release of dissolved organic carbon (DOC) on MP surfaces, which resulted in a high SMX removal ranging from 97.80 % to 99.80 %. However, the presence of MPs promoted microbial interactions and the horizontal gene transfer (HGT) of ARGs, which led to a significant increase in the abundances of sul1 and sul2 of 68.47 % and 17.20 %, respectively. It is thus imperative to implement rigorous monitoring strategies for MPs to mitigate their potential ecological hazards.

Microplastisphere antibiotic resistance genes: A bird's-eye view on the plastic-specific diversity and enrichment

The microplastisphere is a dense consortium of metabolically active microorganisms that develops on the surface of microplastics. Since the discovery that it harbors antibiotic resistance genes (ARGs), there has been a quest to decipher the relationship between ARG occurrences and selective enrichment with plastic types, which is important to understand their fate in diverse environmental settings. Nonetheless, it remains a neglected topic, and this developing field of microplastics research could benefit from a comprehensive review to acquire a deeper understanding of the most recent advances and drive scientific progress. Accordingly, the goal of this review is to critically discuss and provide an in-depth assessment of the evidence of ARGs' global nature in microplastispheres, as well as explore factors that influence them directly and indirectly, highlighting important concerns and knowledge gaps throughout the article. By comprehensively covering them, we underscore the potential environmental implications associated with microplastisphere ARGs. From our analysis, it emerged that microplastisphere ARGs are likely to be impacted not only by differences in microplastic types and characteristics but also by how their environments are shaped by other agents such as physiochemical properties, socioeconomic factors, and contaminants coexistence, influencing ARG subtype, incidence, abundance, and selective enrichment. The intricate relationship of microplastisphere ARGs to environmental conditions and plastic types calls for multilevel investigations to clearly assess the environmental fate of microplastics. We anticipate that this review could assist researchers in strengthening their foundation and identifying efforts to advance knowledge in this research field.

The soil plastisphere

Understanding the effects of plastic pollution in terrestrial ecosystems is a priority in environmental research. A central aspect of this suite of pollutants is that it entails particles, in addition to chemical compounds, and this makes plastic quite different from the vast majority of chemical environmental pollutants. Particles can be habitats for microbial communities, and plastics can be a source of chemical compounds that are released into the surrounding environment. In the aquatic literature, the term 'plastisphere' has been coined to refer to the microbial community colonizing plastic debris; here, we use a definition that also includes the immediate soil environment of these particles to align the definition with other concepts in soil microbiology. First, we highlight major differences in the plastisphere between aquatic and soil ecosystems, then we review what is currently known about the soil plastisphere, including the members of the microbial community that are enriched, and the possible mechanisms underpinning this selection. Then, we focus on outlining future prospects for research on the soil plastisphere.

Selection for antimicrobial resistance in the plastisphere

Microplastics and antimicrobials are widespread contaminants that threaten global systems and frequently co-exist in the presence of human or animal pathogens. Whilst the impact of each of these contaminants has been studied in isolation, the influence of this co-occurrence in driving antimicrobial resistance (AMR)1 in microplastic-adhered microbial communities, known as 'the Plastisphere', is not well understood. This review proposes the mechanisms by which interactions between antimicrobials and microplastics may drive selection for AMR in the Plastisphere. These include: 1) increased rates of horizontal gene transfer in the Plastisphere compared with free-living counterparts and natural substrate controls due to the proximity of cells, co-occurrence of environmental microplastics with AMR selective compounds and the sequestering of extracellular antibiotic resistance genes in the biofilm matrix. 2) An elevated AMR selection pressure in the Plastisphere due to the adsorbing of AMR selective or co-selective compounds to microplastics at concentrations greater than those found in surrounding mediums and potentially those adsorbed to comparator particles. 3) AMR selection pressure may be further elevated in the Plastisphere due to the incorporation of antimicrobial or AMR co-selective chemicals in the plastic matrix during manufacture. Implications for both ecological functioning and environmental risk assessments are discussed, alongside recommendations for further research.

Microplastics and potentially toxic elements: A review of interactions, fate and bioavailability in the environment

In recent years, microplastics (MPs) have obtained growing public concern due to widespread distribution and harmful impacts. Their distinctive features including porous structure, small size, as well as large specific surface area render MPs to be carriers for transporting other pollutants in the environment, especially potentially toxic elements (PTEs). Considering the hot topic of MPs, it is of great significance to comb the reported literature on environmental behaviors of co-occurrence of MPs and PTEs, and systematically discuss their co-mobility, transportation and biotoxicity to different living organisms in diverse environmental media. Therefore, the aim of this work is to systematically review and summarize recent advances on interactions and co-toxicity of MPs and PTEs, in order to provide in-depth understanding on the transport behaviors as well as environmental impacts. Electrostatic attraction and surface complexation mainly govern the interactions between MPs and PTEs, which are subordinated by other physical sorption processes. Besides, the adsorption behaviors are mainly determined by physicochemical properties regarding to different MPs types and various condition factors (e.g., ageing and PTEs concentrations, presence of substances). Generally speaking, recently published papers make a great progress in elucidating the mechanisms, impact factors, as well as thermodynamic and kinetic studies. Bioavailability and bioaccumulation by plant, microbes, and other organisms in both aquatic and terrestrial environment have also been under investigation. This review will shed novel perspectives on future research to meet the sustainable development goals, and obtain critical insights on revealing comprehensive mechanisms. It is crucial to promote efficient approaches on environmental quality improvement as well as management strategies towards the challenge of MPs-PTEs.

The effect of bulk-biochar and nano-biochar amendment on the removal of antibiotic resistance genes in microplastic contaminated soil

Biochar amendment has significant benefits in removing antibiotic resistance genes (ARGs) in the soil. Nevertheless, there is little information on ARGs removal in microplastic contaminated soil. Herein, a 42-day soil microcosm experiment were carried out to study how two coconut shell biochars (bulk- and nano-size) eliminate soil ARGs with/without microplastic presence. The results showed that microplastic increased significantly the numbers and abundances of ARGs in soil at 14d of cultivation. And, two biochars amendment effectively inhibited soil ARGs spread whether or not microplastic was present, especially for nano-biochar which had more effective removal compared to bulk-biochar. However, microplastic weakened soil ARGs removal after applying same biochar. Two biochars removed ARGs through decreasing horizontal gene transfer (HGT) of ARGs, potential host-bacteria abundances, some bacteria crowding the eco-niche of hosts and promoting soil properties. The adverse effect of microplastic on ARGs removal was mainly caused by weakening mobile genetic elements (MGEs) removal, and by changing soil properties. Structural equation modeling (SEM) analysis indicated that biochar's effect on ARGs profile was changed by its size and microplastic presence through altering MGEs abundances. These results highlight that biochar amendment is still an effective method for ARGs removal in microplastic contaminated soil.

Distribution and major driving elements of antibiotic resistance genes in the soil-vegetable system under microplastic stress

Microplastics (MPs) and antibiotic resistance genes (ARGs) are both enriched in soil-vegetable systems as a consequence of the prolonged use of agricultural mulches. MPs can form unique bacterial communities and provide potential hosts for ARGs. Therefore, MPs stress may promote the spread of ARGs from soil to crops. Increasing ARGs pollution in soil-vegetable system. In our research, we investigated the distribution and major driving elements of antibiotic resistance genes in the soil-vegetable system under microplastic stress. The results showed that MPs treatment decreased the relative abundance of ARGs in non-rhizosphere soil. High concentrations of MPs promoted the enrichment of tetracycline antibiotic resistance genes in rhizosphere soil. MPs treatment promoted the enrichment of ARGs and mobile genetic elements (MGEs) in lettuce tissues, and the overall abundance of ARGs in root after 0.5 %, 1 %, and 2 % (w/w, dry weight) polyethylene (PE) administration was considerably higher compared to that in the untreated group (p < 0.05). At the same time, high PE concentrations promoted the spread of sulfa ARGs from root to leaf. MPs also impacted the bacterial communities in the soil-plant system, and the changes in ARGs as well as MGEs in each part of the soil-vegetable system were significantly correlated with the bacterial diversity index (p < 0.05). Correlation analysis and network analysis showed that bacterial communities and MGEs were the main drivers of ARGs variation in soil-lettuce systems.

Microplastics as an emerging contaminant of concern to our environment: a brief overview of the sources and implications

Over the years, it has become evident that microplastics are one of the most important contaminants of concern requiring significant attention. The large abundance of microplastics that are currently in the environment poses potential toxicity risks to all organisms that are exposed to them. Microplastics have been found to affect the physiological and biological processes in marine and terrestrial organisms. As well as being a contaminant of concern in itself, microplastics also have the ability to act as vectors for other contaminants. The potential for microplastics to carry pollutants and transfer them to other organisms has been documented in the literature. Microplastics have also been linked to hosting antibiotic resistant bacteria and antibiotic resistance genes which poses a significant risk to the current health system. There has been a significant increase in research published surrounding the topic of microplastics over the last 5 years. As such, it is difficult to determine and find up to date and relevant information. This overview paper aims to provide a snapshot of the current and emerging sources of microplastics, how microplastics can act as a contaminant and have toxic effects on a range of organisms and also be a vector for a large variety of other contaminants of concern. The aim of this paper is to act as a tool for future research to reference relevant and recent literature in this field.

Alteration of microbial mediated carbon cycle and antibiotic resistance genes during plastisphere formation in coastal area

Microorganisms can attach on the surface of microplastics (MPs) through biological fouling process to form a diverse community called the "plastisphere", which has attracted extensive attention. Although the microbial structure and composition of biofilm have been studied, the knowledge of its microbial function and ecological risk is still limited. In this study, we investigated how the surface properties of MPs affect the biofilm communities and metabolic features under different environmental conditions, and explored the biofilm enrichment of antibiotic resistance genes (ARGs). The results showed that the incubation time, habitat and MPs aging state significantly influenced the structure and composition of biofilm microbial communities, and a small amount of pathogens have been found in the MPs-attached biofilm. The microbial carbon utilization capacity of the biofilm in different incubation habitats varies greatly with highest metabolism capacity appear in the river. The utilization efficiency of different carbon sources is polymer > carbohydrate > amino acid > carboxylic acids > amine/amide, which indicates that the biofilm communities have selectivity between different types of carbon sources. More importantly, ARGs were detected in all the MPs samples and showed a trend of estuary > river > marine. The aged MPs can accumulate more ARGs than the virgin items. In general, MPs in the aquatic environment may become a carrier for pathogens and ARGs to spread to other environment, which may enhance their potential risks to the ecosystem and human health.

Current studies on the degradation of microplastics in the terrestrial and aquatic ecosystem

Soil and water are two important basic ecosystems for the survival of different organisms. The excessive microplastic pollutants in soil have been directly discharged into the terrestrial ecosystems. Microplastic pollutants (MPs) constitute a ubiquitous global menace due to their durability, flexibility, and tough nature. MPs posed threat to the sustainability of the ecosystem due to their small size and easy transportation via ecological series resulting in the accumulation of MPs in aquatic and terrestrial ecosystems. After being emitted into the terrestrial ecosystem, the MPs might be aged by oxidative degeneration (photo/thermal), reprecipitation (bioturbation), and hetero-accumulation. The mechanism of adsorption, degradation, and breakdown of MPs into unaffected plastic debris is accomplished by using several biological, physical, and chemical strategies. This review presents the importance of ecosystems, occurrence and sources of MPs, its toxicity, and the alteration in the ecology of the ecosystems. The inhibitory impact of MPs on the ecosystems also documents to unveil the ecological hazards of MPs. Further research is required to study the immobilization and recovery efficiency of MPs on a larger scale.

Long-distance responses of ginger to soil sulfamethoxazole and chromium: Growth, co-occurrence with antibiotic resistance genes, and consumption risk

The coexistence of antibiotics and heavy metals in agroecosystems is nonnegligible, which permits the promotion of antibiotic resistance genes (ARGs) in crops, thus posing a potential threat to humans along the food chain. In this study, we investigated the bottom-up (rhizosphere→rhizome→root→leaf) long-distance responses and bio-enrichment characteristics of ginger to different sulfamethoxazole (SMX) and chromium (Cr) contamination patterns. The results showed that ginger root systems adapted to SMX- and/or Cr-stress by increasing humic-like exudates, which may help to maintain the rhizosphere indigenous bacterial phyla (i.e., Proteobacteria, Chloroflexi, Acidobacteria and Actinobacteria). The root activity, leaf photosynthesis and fluorescence, and antioxidant enzymes (SOD, POD, CAT) of ginger were significantly decreased under high-dose Cr and SMX co-contamination, while a "hormesis effect" was observed under single low-dose SMX contamination. For example, CS100 (co-contamination of 100 mg/L SMX and 100 mg/L Cr) caused the most severe inhibition to leaf photosynthetic function by reducing photochemical efficiency (reflected on PAR-ETR, φPSII and qP). Meanwhile, CS100 induced the highest ROS production, in which H2O2 and O2·- increased by 328.82% and 238.00% compared with CK (the blank control without contamination). Moreover, co-selective stress by Cr and SMX induced the increase of ARG bacterial hosts and bacterial phenotypes containing mobile elements, contributing to the high detected abundance of target ARGs (sul1, sul2) up to 10-2∼10-1 copies/16S rRNA in rhizomes intended for consumption.

Effects of freeze-thaw dynamics and microplastics on the distribution of antibiotic resistance genes in soil aggregates

This is the first study investigating the effects of freeze-thaw (FT) and microplastics (MPs) on the distribution of antibiotic resistance genes (ARGs) in soil aggregates (i.e., soil basic constituent and functional unit) via microcosm experiments. The results showed that FT significantly increased the total relative abundance of target ARGs in different aggregates due to the increase in intI1 and ARG host bacteria. However, polyethylene MPs (PE-MPs) hindered the increase in ARG abundance caused by FT. The host bacteria carrying ARGs and intI1 varied with aggregate size, and the highest number of hosts was observed in micro-aggregates (<0.25 mm). FT and MPs altered host bacteria abundance by affecting aggregate physicochemical properties and bacterial community and enhanced multiple antibiotic resistance via vertical gene transfer. Although the dominant factors affecting ARGs varied with aggregate size, intI1 was a co-dominant factor in various-sized aggregates. Furthermore, other than ARGs, FT, PE-MPs, and their integration promoted the proliferation of human pathogenic bacteria in aggregates. These findings suggested that FT and its integration with MPs significantly affected ARG distribution in soil aggregates. They amplified antibiotic resistance environmental risks, contributing to a profound understanding of soil antibiotic resistance in the boreal region.

Interaction of Microbes with Microplastics and Nanoplastics in the Agroecosystems-Impact on Antimicrobial Resistance

Microplastics (MPs) and nanoplastics (NPs) are hotspots for the exchange of antimicrobial resistance genes (ARGs) between different bacterial taxa in the environment. Propagation of antimicrobial resistance (AMR) is a global public health issue that needs special attention concerning horizontal gene transfer (HGT) under micro-nano plastics (MNPs) pressure. Interactions between MNPs and microbes, or mere persistence of MNPs in the environment (either water or soil), influence microbial gene expressions, affecting autochthonous microbiomes, their resistomes, and the overall ecosystem. The adsorption of a range of co-contaminants on MNPs leads to the increased interaction of pollutants with microbes resulting in changes in AMR, virulence, toxin production, etc. However, accurately estimating the extent of MNP infestation in agroecosystems remains challenging. The main limitation in estimating the level of MNPs contamination in agroecosystems, surface and subsurface waters, or sediments is the lack of standardized protocols for extraction of MPs and analytical detection methods from complex high organic content matrices. Nonetheless, recent advances in MPs detection from complex matrices with high organic matter content are highly promising. This review aims to provide an overview of relevant information available to date and summarize the already existing knowledge about the mechanisms of MNP-microbe interactions including the different factors with influence on HGT and AMR. In-depth knowledge of the enhanced ARGs propagation in the environment under the influence of MNPs could raise the needed awareness, about future consequences and emergence of multidrug-resistant bacteria.

Effects of long-term microplastic pollution on soil heavy metals and metal resistance genes: Distribution patterns and synergistic effects

Heavy metals (HMs) and microplastics (MPs) are two emerging factors threatening global food security. Whether long-term MPs pollution will affect the distribution of HMs and their resistance genes (MRGs) in soil is unknown. Here, metagenomic approach was used to decipher the fate of MRGs in cropland soils with long-term film MPs residues. Similar distribution pattern of MRGs was formed in long-term film MPs contaminated soil. A total of 202 MRG subtypes were detected, with resistance genes for Multimetal, Cu, and As being the most prevalent type of MRGs. MRGs formed a modular distribution of five clusters centered on MRGs including ruvB in long-term film MPs contaminated soil. MRGs also formed tight co-occurrence networks with mobile genetic elements (MGEs: integrons, insertions and plasmids). Redundancy analysis showed that HMs together with microbial communities and MGEs affected the distribution of MRGs in soil. Thirteen genera including Pseudomonas were identified as potential hosts for MRGs and MGEs. The research provides preliminary progress on the synergistic effect of HMs and MPs in affecting soil ecological security. The synergistic effect of MPs and HMs needs to be considered in the remediation of contaminated soils.

Single and combined effect of tetracycline and polyethylene microplastics on two drought contrasting cultivars of Oryza sativa L. (Rice) under drought stress

Co-exposure of tetracycline (TC) and polyethylene microplastic (MP-PE) pollution might result in more intricate effects on rice growth and grain quality. In present study, two different rice cultivars of contrasting drought tolerance, Hanyou73 (H73, drought-resistant) and Quanyou280 (Q280, drought-sensitive) were grown on MP-PE and TC-contaminated soils under drought. It was found that drought stress had different influence on TC accumulation in the two rice cultivars. H73 accumulated more TC in leaves and grains without drought stress while Q280 accumulated more TC under drought stress. Furthermore, metabolomics results demonstrated that under drought stress, about 80% of metabolites in H73 and 95% in Q280 were down-regulated as compared to non-drought treatments. These findings provide insights into the effects of TC and MP-PE with and without drought stress on potential risks to rice growth and grain quality, which has implications on rice production and cultivar election under multiple-stress conditions.

Microplastics exacerbate co-occurrence and horizontal transfer of antibiotic resistance genes

Microplastic pollution is a rising environmental issue worldwide. Microplastics can provide a niche for the microbiome, especially for antibiotic-resistant bacteria, which could increase the transmission of antibiotic resistance genes (ARGs). However, the interactions between microplastics and ARGs are still indistinct in environmental settings. Microplastics were found to be significantly correlated with ARGs (p < 0.001), based on the analysis of samples taken from a chicken farm and its surrounding farmlands. Analysis of chicken feces revealed the highest abundance of microplastics (14.9 items/g) and ARGs (6.24 ×10⁸ copies/g), suggesting that chicken farms could be the hotspot for the co-spread of microplastics and ARGs. Conjugative transfer experiments were performed to investigate the effects of microplastic exposure for different concentrations and sizes on the horizontal gene transfer (HGT) of ARGs between bacteria. Results showed that the microplastics significantly enhanced the bacterial conjugative transfer frequency by 1.4-1.7 folds indicating that microplastics could aggravate ARG dissemination in the environment. Potential mechanisms related to the up-regulation of rpoS, ompA, ompC, ompF, trbBp, traF, trfAp, traJ, and down-regulation of korA, korB, and trbA were induced by microplastics. These findings highlighted the co-occurrence of microplastics and ARGs in the agricultural environment and the exacerbation of ARGs' prevalence via rising the HGT derived from microplastics.

Co-existence of polyethylene microplastics and tetracycline on soil microbial community and ARGs

Microplastics are plastic particles with particle size less than 5 mm in the environment. As an emerging organic pollutant, the presence of microplastics in the soil environment has been widely noticed. Secondly, due to the overuse of antibiotics, a large amount of antibiotics that cannot be fully absorbed by humans and livestock enter the soil environment in the form of urine or manure, making the soil suffer from serious antibiotic contamination problems. To address the environmental problems of microplastics and antibiotic contamination in soil, this study was conducted to investigate the effects of PE microplastics on antibiotic degradation, microbial community characteristics and ARGs in tetracycline-contaminated soils. The results showed that the addition of PE microplastics inhibited the degradation of tetracycline, and significantly increased the organic carbon content and decreased the neutral phosphatase activity. The addition of PE microplastics significantly reduced the alpha diversity of soil microbial community. Compared to the single tetracycline contamination. In addition, combined contamination with PE microplastics and tetracycline significantly affected bacterial genera such as Aeromicrobium, Rhodococcus, Mycobacterium and Intrasporangium. Metagenome sequencing studies revealed that the addition of PE microplastics inhibited the dissipation of ARGs in tetracycline-contaminated soils. There were strong positive correlations between Multidrug, Aminoglycoside and Clycopeptide resistance genes and Chloroflexi and Proteobacteria in tetracycline contaminated soils, and there was a strong positive correlation between Aminoglycoside resistance genes and Actinobacteria in combined contamination of PE microplastics and tetracycline. This study will provide some data support for the current environmental risk assessment of the coexistence of multiple contaminants in soil.

Microplastics as vectors of chemical contaminants and biological agents in freshwater ecosystems: Current knowledge status and future perspectives

Microplastics (MPs) are becoming ubiquitous, and their environmental fate is becoming an issue of concern. Our review aims to synthesize current knowledge status and provide future perspectives regarding the vector effect of MPs for chemical contaminants and biological agents. The evidence in the literature indicates that MPs are a vector for persistent organic pollutants (POPs), metals and pharmaceuticals. Concentrations of chemical contaminant in orders of six-fold higher on MPs surfaces than in the surrounding environmental waters have been reported. Chemical pollutants such as perfluoroalkyl substances (PAFSs), hexachlorocyclohexane (HCHs) and polycyclic aromatic hydrocarbons (PAHs), exhibiting polarities in the range of 3.3-9 are the commonest chemicals reported on MP surfaces. Regarding metals on MPs including chromium (Cr), lead (Pb), cobalt (Co), the presence of C-O and N-H in MPs promote a relatively high adsorption of these metals onto MP surfaces. Regarding pharmaceuticals, not much has been done, but a few studies indicate that commonly used drugs such as ibuprofen, ibuprofen, diclofenac, and naproxen have been associated with MPs. There is sufficient evidence supporting the claim that MPs can act as vectors for viruses, bacterial and antibiotic-resistant bacteria and genes, and MPs act to accelerate horizontal and vertical gene transfer. An area that deserves urgent attention is whether MPs can act as vectors for invertebrates and vertebrates, mainly non-native, invasive freshwater species. Despite the ecological significance of invasive biology, little research has been done in this regard. Overall, our review summarises the state of the current knowledge, identifies critical research gaps and provides perspectives for future research.

Antibiotic sorption onto microplastics in water: A critical review of the factors, mechanisms and implications

Microplastics as vectors for contaminants in the environment is becoming a topic of public interest. Microplastics have been found to actively adsorb heavy metals, per-fluorinated alkyl substances (PFAS), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceuticals and personal care products (PPCPs) and polybrominated diethers (PBDs) onto their surface. Particular interest in microplastics capacity to adsorb antibiotics needs further attention due to the potential role this interaction plays on antibiotic resistance. Antibiotic sorption experiments have been documented in the literature, but the data has not yet been critically reviewed. This review aims to comprehensively assess the factors that affect antibiotic sorption onto microplastics. It is recognised that the physico- chemical properties of the polymers, the antibiotic chemical properties, and the properties of the solution all play a crucial role in the antibiotic sorption capacity of microplastics. Weathering of microplastics was found to increase the antibiotic sorption capacity by up to 171%. An increase in solution salinity was found to decrease the sorption of antibiotics onto microplastics, in some instances by 100%. pH also has a substantial effect on sorption capacity, illustrating the significance of electrostatic interactions on the sorption of antibiotics onto microplastics. The need for a uniform experimental design when testing antibiotic sorption is highlighted to remove inconsistencies in the data currently presented. Current literature examines the link between antibiotic sorption and antibiotic resistance, however, further studies are still required to fully understand this emerging global crisis.

A discussion of microplastics in soil and risks for ecosystems and food chains

Microplastics are among the major contaminations in terrestrial and marine environments worldwide. These persistent organic contaminants composed of tiny particles are of concern due to their potential hazards to ecosystem and human health. Microplastics accumulates in the ocean and in terrestrial ecosystems, exerting effects on living organisms including microbiomes, fish and plants. While the accumulation and fate of microplastics in marine ecosystems is thoroughly studied, the distribution and biological effects in terrestrial soil call for more research. Here, we review the sources of microplastics and its effects on soil physical and chemical properties, including water holding capacity, bulk density, pH value as well as the potential effects to microorganisms and animals. In addition, we discuss the effects of microplastics in combination with other toxic environmental contaminants including heavy metals and antibiotics on plant growth and physiology, as well as human health and possible degradation and remediation methods. This reflect is an urgent need for monitoring projects that assess the toxicity of microplastics in soil and plants in various soil environments. The prospect of these future research activities should prioritize microplastics in agro-ecosystems, focusing on microbial degradation for remediation purposes of microplastics in the environment.

Environmental drivers and interaction mechanisms of heavy metal and antibiotic resistome exposed to amoxicillin during aerobic composting

The environmental accumulation and spread of antibiotic resistance pose a major threat to global health. Aerobic composting has become an important hotspot of combined pollution [e.g., antibiotic resistance genes (ARGs) and heavy metals (HMs)] in the process of centralized treatment and resource utilization of manure. However, the interaction mechanisms and environmental drivers of HMs resistome (MRGs), antibiotic resistance (genotype and phenotype), and microbiome during aerobic composting under the widely used amoxicillin (AMX) selection pressure are still poorly understood. Here, we investigated the dynamics of HMs bioavailability and their MRGs, AMX-resistant bacteria (ARB) and antibiotic resistome (ARGs and intI1), and bacterial community to decipher the impact mechanism of AMX by conducting aerobic composting experiments. We detected higher exchangeable HMs and MRGs in the AMX group than the control group, especially for the czrC gene, indicating that AMX exposure may inhibit HMs passivation and promote some MRGs. The presence of AMX significantly altered bacterial community composition and AMX-resistant and -sensitive bacterial structures, elevating antibiotic resistome and its potential transmission risks, in which the proportions of ARB and intI1 were greatly increased to 148- and 11.6-fold compared to the control group. Proteobacteria and Actinobacteria were significant biomarkers of AMX exposure and may be critical in promoting bacterial resistance development. S0134_terrestrial_group was significantly negatively correlated with bla_TEM and czrC genes, which might play a role in the elimination of some ARGs and MRGs. Except for the basic physicochemical (MC, C/N, and pH) and nutritional indicators (NO₃ ^--N, NH₄ ⁺-N), Bio-Cu may be an important environmental driver regulating bacterial resistance during composting. These findings suggested the importance of the interaction mechanism of combined pollution and its synergistic treatment during aerobic composting need to be emphasized.

Tracking antibiotic resistance genes in microplastic-contaminated soil

Agricultural soils and microplastics (MPs) are hotspots for antibiotic resistance genes (ARGs). Plastic mulch is the most important source of MPs in agricultural soil. ARGs, mobile genetic elements (MGEs), and their host profiles in long-term mulch MP-exposed soils remain unclear. In the present study, metagenomics was used to investigate the distribution patterns of ARGs and MGEs in eight Chinese provinces with a long history of plastic mulch use. A total of 204 subtypes of ARGs and thousands of MGEs (14 integrons, 28 insertions, and 2993 plasmids) were identified. A similar diversity of ARGs was found among MPs film-contaminated sites. The types of ARGs with a high abundance were more concentrated, and multidrug resistance genes were the dominant ARGs. Soils from regions with a longer history of plastic film use (such as Xinjiang province) had a higher abundance of ARGs and MGEs. The distribution of ARGs and MGEs exhibited a modular network distribution pattern. A total of 27 ARG subtypes and 29 MGEs showed co-occurrence network relationships. More than 10 common hosts of ARGs and MGEs, such as Pseudomonas, were found, and their abundances were highest in three provinces, including Xinjiang. This study may help elucidate the impact mechanism of long-term MP residues on the occurrence and spread of ARGs in soil.

Size-dependent effects of microplastics on antibiotic resistance genes fate in wastewater treatment systems: The role of changed surface property and microbial assemblages in a continuous exposure mode

Microplastics (MPs) were continuously transported to wastewater treatment systems and accumulated in sludge constantly, potentially affecting systems function and co-occurrent contaminants fate. However, previous studies were based on acute exposure of MPs, which could not reflect the dynamics of MPs accumulation. Herein, this study firstly raised a more realistic method to evaluate the practical impacts of MPs on systems purification efficiency and antibiotic resistance genes (ARGs) fate. Continuous exposure of MPs did not pose negative effects on nutrients removal, but significantly changed the occurrence patterns of ARGs. ARGs abundances increased by 42.8 % and 54.3 % when exposed to millimeter-size MPs (mm-MPs) polyamide and polyethylene terephthalate, but increased by 31.3 % and 39.4 % to micron-size MPs (μm-MPs), respectively. Thus, mm-MPs posed severer effects on ARGs than μm-MPs. Further, mm-MPs surface properties were obviously altered after long-term exposure (higher specific surface area and O-containing species), which benefited microbes attachment. More importantly, more taxa linkages and changed topological properties (higher average degree and average weight) of co-occurrent network were observed in sludge with mm-MPs than with μm-MPs, as well as totally different potential host bacteria of ARGs. Rough surface of MPs and closer relations between ARGs and bacteria taxa contributed to the propagation of ARGs, which accounted for the observed higher ARGs abundances of mm-MPs. This study demonstrated that long-term accumulation of MPs in wastewater treatment systems affected ARGs fate, and mm-MPs caused severer risk due to their enrichment of ARGs. The results would promote the understanding of MPs real environmental behavior and influences.

Microplastics in urban waters and its effects on microbial communities: a critical review

Microplastic (MP) pollution is one of the emerging threats to the water and terrestrial environment, forcing a new environmental challenge due to the growing trend of plastic released into the environment. Synthetic and non-synthetic plastic components can be found in rivers, lakes/reservoirs, oceans, mountains, and even remote areas, such as the Arctic and Antarctic ice sheets. MPs' main challenge is identifying, measuring, and evaluating their impacts on environmental behaviors, such as carbon and nutrient cycles, water and wastewater microbiome, and the associated side effects. However, until now, no standardized methodical protocols have been proposed for comparing the results of studies in different environments, especially in urban water and wastewater. This review briefly discusses MPs' sources, fate, and transport in urban waters and explains methodological uncertainty. The effects of MPs on urban water microbiomes, including urban runoff, sewage wastewater, stagnant water in plumbing networks, etc., are also examined in depth. Furthermore, this study highlights the pathway of MPs and their transport vectors to different parts of ecosystems and human life, particularly through mediating microbial communities, antibiotic-resistant genes, and biogeochemical cycles. Overall, we have briefly highlighted the present research gaps, the lack of appropriate policy for evaluating microplastics and their interactions with urban water microbiomes, and possible future initiatives.

Microplastic/nanoplastic toxicity in plants: an imminent concern

The toxic impact of microplastics/nanoplastics (MPs/NPs) in plants and the food chain has recently become a top priority. Several research articles highlighted the impact of MPs/NPs on the aquatic food chain; however, very little has been done in the terrestrial ecosystem. A number of studies revealed that MPs/NPs uptake and subsequent translocation in plants alter plant morphological, physiological, biochemical, and genetic properties to varying degrees. However, there is a research gap regarding MPs/NPs entry into plants, associated factors influencing phytotoxicity levels, and potential remediation plans in terms of food safety and security. To address these issues, all sources of MPs/NPs intrusion in agroecosystems should be revised to avoid these hazardous materials with special consideration as preventive measures. Furthermore, this review focuses on the routes of accumulation and transmission of MPs/NPs into plant tissues, related aspects influencing the intensity of plant stress, and potential solutions to improve food quality and quantity. This paper also concludes by providing an outlook approach of applying exogenous melatonin and introducing engineered plants that would enhance stress tolerance against MPs/NPs. In addition, an overview of inoculation of beneficial microorganisms and encapsulated enzymes in soil has been addressed, which would make the degradation of MPs/NPs faster.

Factors promoting and limiting antimicrobial resistance in the environment - Existing knowledge gaps

The dissemination of multidrug-resistant bacteria strains and genes carrying antibiotic resistance is currently considered to be one of the most important global problem. The WHO calls for the need to contain the spread of Antimicrobial Resistance (AMR) from all possible sources. There have been many international actions grouping scientists studying this phenomenon, and quite a lot of scientific projects devoted to this problem have already been carried out. As well, so far several strategies have been developed that can inhibit the AMR spread. In this mini-review, we highlight overlooked aspects that seem to be crucial for creating a comprehensive picture of AMR, especially in the context of One Health approach.

Distribution, sources, migration, influence and analytical methods of microplastics in soil ecosystems

Microplastics are ubiquitous in soil ecosystems all over the world through source and migration. It is even estimated that the content of microplastics in terrestrial ecosystems exceeds the number of microplastics entering sea ecosystems. However, compared with the research on microplastics in marine ecosystems, the research and discussion on microplastics in soil ecosystems are still less. Transportation, film mulching and sewage sludge are three main sources of soil microplastics. The abundance, polymer type, size and shape of the microplastics are related to the source and they help to clarify the source. The characteristics of microplastics, farming measures, soil animal activities and other factors promote the migration of microplastics, which bring new challenges to the soil ecosystems and humans. This article summarizes the latest research findings on the effects of soil microplasticity on soil properties, plants, animals and microorganisms. The analysis methods of microplastics in soil can refer to the analysis methods of microplastics of aquatic sediments, because soil and aquatic sediments are similar, both of which are complex solid substrates. At present, the development of analytical methods is limited due to the complex matrix of soil and the small volume of microplastics, which requires continuous development and innovation. Through the summary and analysis of related articles, this article reviews the distribution, sources, migration, influence and analysis methods of soil microplastics. This article also critically analyzes the deficiencies in the studies of microplastics in the soil ecosystems, and made some suggestions for future work. The microplastics in soil ecosystems need further research and summary, which will help people further understand the potential hazards of microplastics.

Antibiotic resistant bacteria and genes in wastewater treatment plants: From occurrence to treatment strategies

This study aims to discuss the following: (1) occurrence and proliferation of antibiotic resistance in wastewater treatment plants (WWTPs); (2) factors influencing antibiotic resistance bacteria and genes in WWTPs; (3) tools to assess antibiotic resistance in WWTPs; (4) environmental contamination of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from WWTPs; (5) effects of ARB and ARGs from WWTPs on human health; and (6) treatment strategies. In general, resistant and multi-resistant bacteria, including Enterobacteriaceae, Pseudomonas aeruginosa, and Escherichia coli, exist in various processes of WWTPs. The existence of ARB and ARGs results from the high concentration of antibiotics in wastewater, which promote selective pressures on the local bacteria present in WWTPs. Thus, improving wastewater treatment technology and avoiding the misuse of antibiotics is critical to overcoming the threat of proliferation of ARBs and ARGs. Numerous factors can affect the development of ARB and ARGs in WWTPs. Abiotic factors can affect the bacterial community dynamics, thereby, affecting the applicability of ARB during the wastewater treatment process. Furthermore, the organic loads and other nutrients influence bacterial survival and growth. Specifically, molecular methods for the rapid characterization and detection of ARBs or their genes comprise DNA sequencing, real-time PCR, simple and multiplex PCR, and hybridization-based technologies, including micro- and macro-arrays. The reuse of effluent from WWTPs for irrigation is an efficient method to overcome water scarcity. However, there are also some potential environmental risks associated with this practice, such as increase in the levels of antibiotic resistance in the soil microbiome. Human mortality rates may significantly increase, as ARB can lead to resistance among several types of antibiotics or longer treatment times. Some treatment technologies, such as anaerobic and aerobic treatment, coagulation, membrane bioreactors, and disinfection processes, are considered potential techniques to restrict antibiotic resistance in the environment.

The formation of specific bacterial communities contributes to the enrichment of antibiotic resistance genes in the soil plastisphere

Soil serves as a major reservoir of both antibiotic resistance genes (ARGs) and microplastics. However, the characteristics of the antibiotic resistome in the soil plastisphere remain largely unknown. In this study, we used metagenomic approaches to reveal the changing patterns of ARGs and the bacterial community and their associations in response to three types of microplastics (light density polyethylene, LDPE; polypropylene, PP; polystyrene, PS) using particles 550 µm or 75 µm in diameter. The total ARG abundances significantly increased in the plastisphere and varied across plastic types. The LDPE plastisphere had the highest ARG total abundance and lowest Shannon diversity index, indicating that this plastic had the most severe negative impact on soil bacterial diversity. The PP plastisphere contained higher relative abundances of the pathogenic bacteria Acinetobacter johnsonii and Escherichia coli, demonstrating the higher pathogenic risk of the microbial communities enriched in the plastisphere. Specifically, multidrug resistance genes (ceoB and MuxB) co-existed with more than four microbial taxa, increasing the potential risk of ARG spread in pathogenic bacteria. These findings implied that the plastisphere acts as a hotspot for acquiring and spreading antibiotic resistance and may have long-term negative effects on the soil ecosystem and human health.

Recent advances in toxicological research and potential health impact of microplastics and nanoplastics in vivo

As emerging pollutants, direct and indirect adverse impacts of micro(nano)plastics (MPs/NPs) are raising an increasing environmental concern in recent years due to their poor biodegradability and difficulty in recycling. MPs/NPs can act as carriers of bacteria, viruses, or pollutants (such as heavy metals and toxic organic compounds), and may potentially change the toxicity and bioavailability of pollutants. Ingested or attached MPs/NPs can also be transferred from low-trophic level organisms to high-nutrient organisms or even the human body through the food chain transfer process. This article reviews the emerging field of micro- and nanoplastics on organisms, including the separate toxicity and toxicity of compound after the adsorption of organic pollutants or heavy metals, as well as possible mechanism of toxicological effects and evaluate the nano- and microplastics potential adverse effects on human health. The inherent toxic effects MPs/NPs mainly include the following: physical injury, growth performance decrease and behavioral alteration, lipid metabolic disorder, induced gut microbiota dysbiosis and disruption of the gut's epithelial permeability, neurotoxicity, damage of reproductive system and offspring, oxidative stress, immunotoxicity, etc. Additionally, MPs/NPs may release harmful plastic additives and toxic monomers such as bisphenol A, phthalates, and toluene diisocyanate. The vectors' effect also points out the potential interaction of MPs/NPs with pollutants such as heavy metals, polycyclic aromatic hydrocarbons, organochlorine pesticides, polychlorinated biphenyls, perfluorinated compounds, pharmaceuticals, and polybrominated diphenyl ethers. Nevertheless, these potential consequences of MPs/NPs being vectors for contaminants are controversial.

Soil plastisphere: Exploration methods, influencing factors, and ecological insights

Microplastic (MP), an emerging contaminant, is globally prevalent and poses potential environmental threats and ecological risks to both aquatic and terrestrial ecosystems. When MPs enter into natural environments, they may serve as artificial substrates for microbial colonization and plastisphere formation, providing new ecological niches for microorganisms. Recent studies of the plastisphere have focused on aquatic ecosystems. However, our understanding of the soil plastisphere e.g. its formation process, microbial ecology, co-transport of organic pollutants and heavy metals, and effects on biogeochemical processes is still very limited. This review summarizes latest methods used to explore the soil plastisphere, assesses the factors influencing the microbial ecology of the soil plastisphere, and sheds light on potential ecological risks caused by the soil plastisphere. The formation and succession of soil plastisphere communities can be driven by MP characteristics and soil environmental factors. The soil plastisphere may affect a series of ecological processes, especially the co-transport of environmental contaminants, biodegradation of MPs, and soil carbon cycling. We aim to narrow the knowledge gap between the soil and aquatic plastisphere, and provide valuable guidance for future research on the soil plastisphere in MP-contaminated soils.

Varying characteristics and driving mechanisms of antibiotic resistance genes in farmland soil amended with high-density polyethylene microplastics

The differential effects of microplastics and phthalates released from microplastics on antibiotic resistance genes in soil remain unknown. This study aims to analyze the varying characteristics and driving mechanisms of antibiotic resistance genes in soils amended with high-density polyethylene microplastics (with and without phthalates) through a 60-day microcosm experiment. The results indicate that the amended high-density polyethylene microplastics (containing phthalates) enhanced the abundance of antibiotic resistance genes in the soil, a phenomenon that markedly increased with the amendment period. Nevertheless, the addition of high-density polyethylene microplastics (without phthalates) mitigated the abundance of antibiotic resistance genes, which was less significant with increasing amendment period. Furthermore, addition of high-density polyethylene microplastics altered the soil properties, especially porosity. The phthalates released from high-density polyethylene microplastics and the changes in the soil properties transformed soil bacterial communities, resulting in increased abundance of bacterial hosts harboring antibiotic resistance genes (Calditrichaeota, Candidate division CPR1, Candidatus Delongbacteria, Candidatus Kapabacteria, Candidatus Spechtbacteria, Candidatus Wildermuthbacteria, and Ignavibacteriae), thereby enhancing the abundance of antibiotic resistance genes. These findings suggest that compared to microplastics, the phthalates released from microplastics considerably affect the antibiotic resistance genes in soils, thereby promoting the propagation of antibiotic resistance genes in agricultural environments.

A critical review of microplastics in the soil-plant system: Distribution, uptake, phytotoxicity and prevention

Microplastics (MPs) are creating an emerging threat on the soil ecosystems and are of great global concern. However, the distribution in soil-plant system, as well as the phytotoxicity and impact mechanisms of MPs remain largely unexplored so far. This study introduced the diverse sources of MPs and showed the significant spatial variation in the global geographic distribution of MPs contamination based on data collected from 116 studies (1003 sampling sites). We systematically discussed MPs phytotoxicity, such as plant uptake and migration to stems and leaves, delaying seed germination, impeding plant growth, inhibiting photosynthesis, interfering with nutrient metabolism, causing oxidative damage, and producing genotoxicity. We further highlighted the alterations of soil structure and function by MPs, as well as their self and load toxicity, as potential mechanisms that threaten plants. Finally, this paper provided several preventive strategies to mitigate soil MPs pollution and presented research gaps in the biogeochemical behavior of MPs in soil-plant systems. Meanwhile, we recommended that methods for the quantitative detection of MPs accumulated in plant tissues should be explored and established as soon as possible. This review will improve the understanding of the environmental behavior of MPs in soil-plant systems and provide a theoretical reference to better assess the ecological risk of MPs.

The dissemination of antibiotics and their corresponding resistance genes in treated effluent-soil-crops continuum, and the effect of barriers

Irrigation with treated effluent is expanding as freshwater sources diminish, but hampered by growing concerns of pharmaceuticals contamination, specifically antibiotics and resistance determinants. To evaluate this concern, freshwater and effluent were applied to an open field that was treated with soil barriers including plastic mulch together with surface and subsurface drip irrigation, cultivating freshly eaten crops (cucumbers or melons) for two consecutive growing seasons. We hypothesized that the effluent carries antibiotics and resistance determinants to the drip-irrigated soil and crops regardless of the treatment. To test our hypothesis, we monitored for antibiotics abundance (erythromycin, sulfamethoxazole, tetracycline, chlortetracycline, oxytetracycline, amoxicillin, and ofloxacin) and their corresponding resistance genes (ermB, ermF, sul1, tetW, tetO, bla_TEM and qnrB), together with class 1 integron (intl1), and bacterial 16S rRNA, in water, soil, and crop samples taken over two years of cultivation. The results showed that an array of antibiotics and their corresponding resistance genes were detected in the effluent but not the freshwater. Yet, there were no significant differences in the distribution or abundance of antibiotics and resistance genes, regardless of the irrigation water quality, or crop type (p > 0.05), but plastic-covered soil irrigated with effluent retained the antibiotics oxytetracycline and ofloxacin (p < 0.05). However, we could not detect significant correlations between the detected antibiotics and the corresponding resistance genes. Overall, our findings disproved our hypothesis suggesting that treated effluent may not carry antibiotics resistance genes to the irrigated soil and crops yet, plastic mulch covered soil retain some antibiotics that may inflict long term contamination.

Soil plastispheres as hotpots of antibiotic resistance genes and potential pathogens

In the Anthropocene, increasing pervasive plastic pollution is creating a new environmental compartment, the plastisphere. How the plastisphere affects microbial communities and antibiotic resistance genes (ARGs) is an issue of global concern. Although this has been studied in aquatic ecosystems, our understanding of plastisphere microbiota in soil ecosystems remains poor. Here, we investigated plastisphere microbiota and ARGs of four types of microplastics (MPs) from diverse soil environments, and revealed effects of manure, temperature, and moisture on them. Our results showed that the MPs select for microbial communities in the plastisphere, and that these plastisphere communities are involved in diverse metabolic pathways, indicating that they could drive diverse ecological processes in the soil ecosystem. The relationship within plastisphere bacterial zero-radius operational taxonomic units (zOTUs) was predominantly positive, and neutral processes appeared to dominate community assembly. However, deterministic processes were more important in explaining the variance in ARGs in plastispheres. A range of potential pathogens and ARGs were detected in the plastisphere, which were enriched compared to the soil but varied across MPs and soil types. We further found that the addition of manure and elevation of soil temperature and moisture all enhance ARGs in plastispheres, and potential pathogens increase with soil moisture. These results suggested that plastispheres are habitats in which an increased potential pathogen abundance is spatially co-located with an increased abundance of ARGs under global change. Our findings provided new insights into the community ecology of the microbiome and antibiotic resistome of the soil plastisphere.

Meta-analysis reveals differential impacts of microplastics on soil biota

Contamination of microplastics (MPs) is a global environmental issue that has received much attention from the scientific and public communities due to ecological concerns in recent decades. Comparing with aquatic ecosystems, soil systems, regardless of the high importance and complexity, have been less studied under widely existing and increasing MP contamination. This review, combined with data assimilation and meta-analysis methods, has summarized current contamination conditions of soil MPs across different sites reported in earlier studies. While performing this meta-analysis, we investigated the effects of MPs on soil biota including their numbers, biomass, diversity, and physiological properties. The results showed that abundance of soil MPs ranged from 0.34 to 410958.9 items kg-1 and concentration ranged from 0.002 to 67500 mg kg-1 across sites, with agricultural soils containing significantly lower abundance and concentration of MPs than others. Presence of MPs significantly decreased the individual number of soil biota, operational taxonomic unit, diversity index (Simpson), movement index and reproduction rate, whereas the mortality rate was significantly increased by the soil MPs. Despite these significant effects, MPs did not significantly alter the biomass of soil biota, which could be due to a counteraction of their negative and positive effects on different groups of soil organisms. Moreover, we observed that soil MPs could significantly increase the Chao1 index, suggesting that MPs may act as a food resource for the soil rare biosphere. Based on the existing knowledge, we suggest that future studies should focus on research areas that include but are not limited to methodological improvements, intensive field investigations, risk assessment from the perspective of soil food web and bioaccumulation, MPs induced antibiotic resistance, and restoration strategies to reduce their concentrations in soil.

Interactions of microplastics, antibiotics and antibiotic resistant genes within WWTPs

Microplastics (MPs) have been detected in atmosphere, soil, and water and have been characterized as contaminants of emerging concern. When exposed to these environments, MPs interact with the chemical compounds as well as the (micro)organisms inhabiting these ecosystems. This paper overviews the interactions and significant factors influencing the sorption process of antibiotics on MPs since distinct interactions are developed between MPs and antibiotics. The interplay between the MPs and the antibiotic resistant genes (ARGs) microbial hosts is presented and the important factors that may shape the plastisphere resistome are discussed. The interactions of MPs, antibiotics and antibiotic resistant bacteria (ARB) and ARGs in wastewater treatment plants (WWTPs) were discussed with the aim to provide a perspective for better understanding of the role of WWTPs in bringing together MPs, antibiotics and ARB/ARGs and further as release points of MPs carrying antibiotics, and ARB/ARGs.

Bacterial Community under the Influence of Microplastics in Indoor Environment and the Health Hazards Associated with Antibiotic Resistance Genes

Selectively colonized microbial communities and enriched antibiotic resistance genes (ARGs) in (micro)plastics in aquatic and soil environments make the plastisphere a great health concern. Although microplastics (MPs) are distributed in indoor environments in high abundance, information on the effect of MPs on a microbial community in an indoor environment is lacking. Here, we detected polymers (containing MPs and natural polymers), bacterial communities, and 18 kinds of ARGs in collected indoor dust samples. A significant correlation by Procrustes analysis between bacterial community composition and the abundance of MPs was observed, and correlation tests and redundancy analysis identified specific associations between MP polymers and bacterial taxa, such as polyamide and Actinobacteria. In addition, the abundance of MPs showed a positive correlation with the relative abundance of the ARGs (to 16S RNA), while natural polymers, such as cellulosics, showed positive correlations with the absolute abundance of ARGs and 16S rRNA. Simulated experiments verified that significantly higher bacterial biomasses and ARGs were observed on the surface of cotton, hair, and wool than on MPs, while a higher relative abundance of ARGs was detected on MPs. However, a significantly higher amount of ARG was found on MPs of poly(lactic acid), the biodegradable plastics with the highest yield. In addition to the plastisphere in water and soil environments, MPs in an indoor environment may also affect the bacterial community and specifically enrich ARGs. Moreover, degradable MPs and nondegradable MPs may result in different health hazards due to their distinct effects on bacterial community.

Phytotoxic effects of plastic pollution in crops: what is the size of the problem?

Plastic pollution is one of the most impactful human interferences in our planet. Fragmentation of plastic leads to nano- and microplastics (NP/MP) formation, which accumulate in agricultural lands, representing an increasing risk for crop production and food safety. It has been shown that MP promote damage in plant tissues by several direct and indirect ways, and that NP can enter the tissues/cells and accumulate in edible organs. Investigation of the phytotoxic effects of NP/MP in plants started only in 2016, with most of the studies performed with crops. Since contradictory results are often observed, it is important to review the literature in order to identify robust effects and their possible mechanisms. In this review, we discuss the potential of NP/MP in damaging crop species, with focus on the physiological changes described in the literature. We also performed scientometrics analyses on research papers in this field during 2016-2021, to reveal the research situation of phytotoxic effects of plastic pollution in crops. Our review is as a starting point to help identify gaps and future directions in this important, emerging field.

Microplastics pollution in the ocean: Potential carrier of resistant bacteria and resistance genes

Microplastics pollution in marine environments is concerning. Microplastics persist and accumulate in various sections of the ocean where they present opportunity for micropollutant accumulation and microbial colonisation. Even though biofilm formation on plastics was first reported in the 1970's, it is only in recent years were plastic associated biofilms have gained research attention. Plastic surfaces pose a problem as they are a niche ready for colonisation by diverse biofilm assemblages, composed of specific bacterial communities and putative pathogens prone to acquiring ARGs and resistance in the biofilm. However, the nature of antibiotic resistance on aquatic plastic debris is not yet fully understood and remains a concern. Given the inevitable increase of plastic production and waste generation, microplastics released into the environment may prove to be problematic. This review explores microplastic waste in the ocean and possible concerns that may arise from the presence of microplastics in conjunction with favourable conditions for the development and dispersal of antibiotic resistance in the ocean and food web.

Recent advances on ecological effects of microplastics on soil environment

The mass production and wide application of plastics and their derivatives have led to the release of a large number of discarded plastic products into the natural environment, where they continue to accumulate due to their low recycling rate and long durability. These large pieces of plastic will gradually break into microplastics (<5 mm), which are highly persistent organic pollutants and attract worldwide attention due to their small particle size and potential threats to the ecosystem. Compared with the aquatic system, terrestrial systems such as soils, as sinks for microplastics, are more susceptible to plastic pollution. In this article, we comprehensively summarized the occurrence and sources of microplastics in terrestrial soil, and reviewed the eco-toxicological effects of microplastics in soil ecosystems, in terms of physical and chemical properties of soil, soil nutrient cycling, soil flora and fauna. The influence of microplastics on soil microbial community, and particularly the microbial community on the surface of microplastics, were examined in detail. The compound effects of microplastics and other pollutants, e.g., heavy metals and antibiotics, were addressed. Future challenges of research on microplastics include development of new techniques and standardization for the extraction and qualitative and quantitative analysis of microplastics in soils, toxic effects of microplastics at microbial or even molecular levels, the contribution of microplastics to antibiotic resistance genes migration, and unraveling microorganisms for the degradation of microplastics. This work provides as a better understanding of the occurrence, distribution and potential ecological risks of microplastics in terrestrial soil ecosystems.