Response of soil enzyme activities and bacterial communities to the accumulation of microplastics in an acid cropped soil

Microplastics in the soil-water-food nexus: Inclusive insight into global research findings

Nuisance imposed by biotic and abiotic stressors on diverse agroecosystems remains an area of focus for the scientific fraternity. However, emerging contaminants such as microplastics (MP) have imposed additional dimension (alone or in combinations with other stressors) in agroecosystems and keep escalating the challenges to achieve sustainability. MP are recognized as persistent anthropogenic contaminants, fetch global attention due to their unique chemical features that keeps themselves unresponsive to the decaying process. This review has been theorized to assess the current research trends (along with possible gap areas), widespread use of MP, enhancement of the harshness of heavy metals (HMs), complex interactions with physico-chemical constituents of arable soil, accumulation in the edible parts of field crops, dairy products, and other sources to penetrate the food web. So far, the available review articles are oriented to a certain aspect of MP and lack a totality when considered from in soil-water-food perspective. In short, a comprehensive perspective of the adverse effects of MP on human health has been assessed. Moreover, an agro-techno-socio-health prospective-oriented critical assessment of policies and remedial measures linked with MP has provided an extra edge over other similar articles in influential future courses of research.

Water-dependent effects of biodegradable microplastics on arsenic fractionation in soil: Insights from enzyme degradation and synchrotron-based X-ray analysis

The abundance of biodegradable microplastics (BMPs) is increasing in soil due to the widespread use of biodegradable plastics. However, the influence of BMPs on soil metal biogeochemistry, especially arsenic (As), under different water regimes is still unclear. In this study, we investigated the effects of two types of BMPs (PLA-MPs and PBAT-MPs) on As fractionation in two types of soils (black soil and fluvo-aquic soil) under three water regimes including drying (Dry), flooding (FL), and alternate wetting and drying (AWD). The results show that BMPs had limited indirect effects on As fractionation by altering soil properties, but had direct effects by adsorbing and releasing As during their degradation. Enzyme degradation experiments show that the degradation of PLA-MPs led to an increased desorption of 4.76 % for As(III) and 15.74 % for As(V). Synchrotron-based X-ray fluorescence (μ-XRF) combined with micro-X-ray absorption near edge structure (μ-XANES) analysis show that under Dry and AWD conditions, As on the BMPs primarily bind with Fe hydrated oxides in the form of As(V). Conversely, 71.57 % of As on PBAT-MP under FL conditions is in the form of As(III) and is primarily directly adsorbed onto its surface. This study highlights the role of BMPs in soil metal biogeochemistry.

Differential impacts of polyethylene microplastic and additives on soil nitrogen cycling: A deeper dive into microbial interactions and transformation mechanisms

The impact of microplastics and their additives on soil nutrient cycling, particularly through microbial mechanisms, remains underexplored. This study investigated the effects of polyethylene microplastics, polyethylene resin, and plastic additives on soil nitrogen content, physicochemical properties, nitrogen cycling functional genes, microbial composition, and nitrogen transformation rates. Results showed that all amendments increased total nitrogen but decreased dissolved total nitrogen. Polyethylene microplastics and additives increased dissolved organic nitrogen, while polyethylene resin reduced it and exhibited higher microbial biomass. Amendments reduced or did not change inorganic nitrogen levels, with additives showing the lowest values. Polyethylene resin favored microbial nitrogen immobilization, while additives were more inhibitory. Amendment type and content significantly interacted with nitrogen cycling genes and microbial composition. Distinct functional microbial biomarkers and network structures were identified for different amendments. Polyethylene microplastics had higher gross ammonification, nitrification, and immobilization rates, followed by polyethylene resin and additives. Nitrogen transformation was driven by multiple functional genes, with Proteobacteria playing a significant role. Soil physicochemical properties affected nitrogen content through transformation rates, with C/N ratio having an indirect effect and water holding capacity directly impacting it. In summary, plastic additives, compared to polyethylene microplastics and resin, are less conducive to nitrogen degradation and microbial immobilization, exert significant effects on microbial community structure, inhibit transformation rates, and ultimately impact nitrogen cycling.

Effects of polypropylene films and leached dissolved organic matters on bacterial community structure in mangrove sediments

Over the past decades, the accumulation of plastics in mangrove ecosystems has emerged as a significant environmental concern, primarily due to anthropogenic activities. Polypropylene (PP) films, one of the plastic types with the highest detection rate, tend to undergo intricate aging processes in mangrove ecosystems, leading to the release of dissolved organic matter (DOM) that may further influence the local bacterial communities. Yet, the specific effects of new and weathered (aged) plastic films and the associated leached DOM on bacterial consortia in mangrove sediments remain poorly understood. In this study, an incubation experiment was conducted to elucidate the immediate effects and mechanisms of the new and relatively short-term (45 or 90 days) aged PP films, as well as their leached DOM (PDOM), on characteristics of DOM and the bacterial community structure in mangrove sediments under different tidal conditions. Surface morphology and functional group analyses showed that both new and aged PP films exhibited comparable degradation profiles under different tidal conditions over the incubation period. As compared to the new PP film treatments, the introduction of the short-term aged PP films significantly affected the content of humic-like compounds in sediments, and such effects were partially ascribed to the release of PDOM during the incubation. Although the addition of PP films and PDOM showed minor effects on the overall diversity and composition of bacterial communities in the sediments, the abundance of some dominant phyla exhibited a growth or reduction tendency, possibly changing their ecological functions. This study was an effective attempt to investigate the relationship among plastic surface characteristics, sedimentary physicochemical properties, and bacterial communities in mangrove sediments. It revealed the ecological ramifications of new and short-term plastic pollution and its leachates in mangrove seedtimes, enhancing our understating of their potential impacts on the health of mangrove ecosystems.

Polyvinyl chloride and polybutylene adipate microplastics affect peanut and rhizobium symbiosis by interfering with multiple metabolic pathways

Microplastics (MPs), widely presented in cultivated soil, have caused serious stresses on crop growth. However, the mechanism by which MPs affect legumes and rhizobia symbiosis is still unclear. Here, peanut seedlings were inoculated with Bradyrhizobium zhanjiangense CCBAU 51778 and were grown in vermiculite with 3 %/5 % (w/w) addition of PVC (polyvinyl chloride)-MPs/PBAT (polybutylene adipate)-MPs. PVC-MPs and PBAT-MPs separately decreased nodule number by 33-100 % and 2.62-80.91 %. Transcriptome analysis showed that PVC-MPs affected more DEGs (differentially expressed genes) than PBAT-MPs, indicating PVC-MPs were more devastating for the symbiosis than PBAT-MPs. Functional annotation revealed that PVC-MPs and PBAT-MPs enriched DEGs related to biosynthesis pathways such as flavonoid, isoflavonoid, and phenylpropanoid, in peanut. And when the dose increased from 3 % to 5 %, PVC-MPs mainly enriched the pathways of starch and sucrose metabolism, alanine, aspartate and glutamate metabolism, diterpenoid biosynthesis, etc.; PBAT-MPs enriched cysteine and methionine metabolism, photosynthesis, MAPK signaling, and other pathways. These significantly enriched pathways functioned in reducing nodule number and promoting peanut tolerance to MPs stresses. This study reveals the effect of PVC-MPs and PBAT-MPs on peanut and rhizobium symbiosis, and provides new perspectives for legume production and environmental safety.

Sources, environmental fate, and impacts of microplastic contamination in agricultural soils: A comprehensive review

The pervasive presence of microplastics has emerged as a pressing global environmental concern, posing threats to food security and human health upon infiltrating agricultural soils. These microplastics primarily originate from agricultural activities, including fertilizer inputs, compost-based soil remediation, irrigation, and atmospheric deposition. Their remarkable durability and resistance to biodegradation contribute to their persistent presence in the environment. Microplastics within agricultural soils have prompted concerns regarding their potential impacts on agricultural practices. Functioning as significant pollutants and carriers of microcontaminants within agricultural ecosystems, microplastics and their accompanying contaminants represent ongoing challenges. Within these soil ecosystems, the fate and transportation of microplastics can detrimentally affect plant growth, microbial communities, and, subsequently, human health via the food chain. Specifically, microplastics interact with soil factors, impacting soil health and functionality. Their high adsorption capacity for hazardous microcontaminants exacerbates soil contamination, leading to increased adverse effects on organisms and human health. Due to their tiny size, microplastic debris is easily ingested by soil organisms and can transfer through the food chain, causing physiological and/or mechanical damage. Additionally, microplastics can affect plant growth and have the potential to accumulate and be transported within plants. Efforts to mitigate these impacts are crucial to safeguarding agricultural sustainability and environmental health. Future research should delve into the long-term impacts of environmental aging processes on microplastic debris within agricultural soil ecosystems from various sources, primarily focusing on food security and human beings.

High-density polyethylene microplastics in agricultural soil: Impact on microbes, enzymes, and carbon-nitrogen ratio

Microplastics (MPs), recognized as emerging pollutants, pose a significant threat to diverse organisms and have adverse effects on agricultural soil. High-density polyethylene (HDPE) holds a prominent position among prevalent forms of MPs. In the current investigations, the impact of HDPE was assessed at four different concentrations (0.25%, 0.5%, 0.75%, and 1.0%) on agricultural soil, microbial population, exoenzymes activities including amylase, cellulase, and invertase, and alteration in carbon-to-nitrogen (C/N) ratio. Both bacterial and fungal populations exhibited a non-concentration-dependent response to different concentrations of HDPE over time. In this study, we refer to the concentrations of 0.25%, 0.5%, 0.75%, and 1.0% as HT1, HT2, HT3, and HT4, respectively. Initial MP application significantly reduced bacterial colony counts for HT1, HT2, and HT4, while HT3 showed no significant change. On the 60th day, HT1 and HT3 exhibited a higher bacterial colony count compared to the control. On the other hand, fungal populations increased to maximum on day 1 but displayed no distinct time-dependent trend from days 15 to 60. Furthermore, enzyme activities decreased with increasing concentrations of MPs over an extended period. Molecular docking studies suggest that HDPE can hinder enzyme activity by forming hydrogen bonds with enzymes. The C/N ratio was found to be significantly higher in MP-treated soils on the 60th day relative to control, suggesting relatively slower degradation of carbon compounds in the MP-treated soils.

Characteristics of microplastics and their abundance impacts on microbial structure and function in agricultural soils of remote areas in west China

As an emergent pollutant, microplastics (MPs) are becoming prevalent in the soil environment. However, the characteristics of MPs and the response of microbial communities to the abundance of MPs in agricultural soils in West China still need to be elucidated in detail. This study utilized the Agilent 8700 Laser Direct Infrared (LDIR) to analyze the characteristics of small-sized MPs (20-1000 μm) in soils from un-mulched and mulched agricultural fields in West China, and illustrated their correlation with microbial diversity. The results revealed a higher abundance of MPs in mulched soil ((4.12 ± 2.13) × 105 items kg-1) than that in un-mulched soil ((1.04 ± 0.26) × 105 items kg-1). The detected MPs were dominated by fragments, 20-50 μm and Polyamide (PA). High-throughput sequencing analysis indicated that alpha diversity (Chao1 and Shannon indices) in the plastisphere was lower compared to that in soil, and varied significantly with MPs abundance in soil. As the abundance of MPs increased, the proportion of soil about the degradation of organic matte and photoautotrophic taxa increased, which showed enrichment in the plastisphere. Functional predictions further indicated that MPs abundance affected potential soil functions, such as metabolic pathways associated with the C and N cycling. The plastisphere showed higher functional abundance associated with organic matter degradation, indicating higher potential health risks compared to soil environments. Based on the RDA analyses, it was determined that environmental physicochemical properties and MPs abundance had a greater impact on fungal communities than on bacterial communities. In general, the abundance of MPs affected the microbial diversity composition and potentially influenced the overall performance of soil ecosystems. This study offers empirical data on the abundance of MPs in long-term mulched agricultural fields and new insights for exploring the ecological risk issues associated with MPs.

Nonbiodegradable microplastic types determine the diversity and structure of soil microbial communities: A meta-analysis

As an emerging contaminant, microplastics (MPs) have received considerable attention for their potential threat to the soil environment. However, the response of soil bacterial and fungal communities to MPs exposure remains unclear. In this study, we conducted a global meta-analysis of 95 publications and 2317 observations to assess the effects of nonbiodegradable MP properties and exposure conditions on soil microbial biomass, alpha and beta diversity, and community structure. Our results indicate that MPs increased (p < 0.05) soil active microbial biomass by 42%, with the effect varying with MPs type, exposure concentration, exposure time and soil pH. MPs concentration was identified as the most important factor controlling the response of soil microbial biomass to MPs. MPs addition decreased (p < 0.05) the soil bacterial Shannon and Chao1 indices by 2% and 3%, respectively, but had limited effects (p > 0.05) on soil fungal Shannon and Chao1 indices. The type of MPs and exposure time determined the effects of MPs on bacterial Shannon and Chao1 indices, while the type of MPs and soil pH controlled the response ratios of fungal Shannon and Chao1 indices to MPs. Specifically, soil organic carbon (SOC) was the major factor regulating the response ratio of bacterial alpha diversity index to MPs. The presence of MPs did not affect soil bacterial community structure and beta diversity. Our results highlight that MPs reduced bacterial diversity and richness but increased the soil active microbial biomass, suggesting that MPs could disrupt biogeochemical cycles by promoting the growth of specific microorganisms.

Microplastics in heavy metal-contaminated soil drives bacterial community and metabolic changes

Microplastic (MP) and heavy metal pollution in soil are global issues. When MPs invade the soil, they combine with heavy metals and adversely affect soil organisms. Six common MPs-polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and polytetrafluoroethylene-were selected for this study to examine the effects of various concentrations and MP types on the physicochemical properties, bacterial community, and soil metabolism of heavy metal-contaminated soil. MP enhanced predation and competition among heavy metal-contaminated soil bacteria. Heavy metal-MPs alter metabolites in lipid metabolism, other pathways, and the bacterial community. MP treatment promotes energy production and oxidative stress of soil bacteria to resist the toxicity of heavy metals and degrade MP pollution. In conclusion, MP treatment changed the metabolism of the microbiome in heavy metal-contaminated soil and increased the abundance of Proteobacteria that responded to MPs and heavy metal pollution by 11.54 % on average. This study explored bacteria for the ecological regeneration and provided ideas for MPs and heavy metal-contaminated soil remediation.

Differential impacts of microplastics on carbon and nitrogen cycling in plant-soil systems: A meta-analysis

Microplastics (MPs) are widely present in terrestrial ecosystems. However, how MPs impact carbon (C) and nitrogen (N) cycling within plant-soil system is still poorly understood. Here, we conducted a meta-analysis utilizing 3338 paired observations from 180 publications to estimate the effects of MPs on plant growth (biomass, nitrogen content, nitrogen uptake and nitrogen use efficiency), change in soil C content (total carbon (TC), soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC)), C losses (carbon dioxide (CO2) and methane), soil N content (total nitrogen, dissolved organic nitrogen, microbial biomass nitrogen, total dissolve nitrogen, ammonium, nitrate (NO3--N) and nitrite) and nitrogen losses (nitrous oxide, ammonia (NH3) volatilization and N leaching) comprehensively. Results showed that although MPs significantly increased CO2 emissions by 25.7 %, they also increased TC, SOC, MBC, DOC and CO2 by 53.3 %, 25.4 %, 19.6 % and 24.7 %, respectively, and thus increased soil carbon sink capacity. However, MPs significantly decreased NO3--N and NH3 volatilization by 14.7 % and 43.3 %, respectively. Meanwhile, MPs significantly decreased plant aboveground biomass, whereas no significant changes were detected in plant belowground biomass and plant N content. The impacts of MPs on soil C, N and plant growth varied depending on MP types, sizes, concentrations, and experimental durations, in part influenced by initial soil properties. Overall, although MPs enhanced soil carbon sink capacity, they may pose a significant threat to future agricultural productivity.

Traversing the prevalence of microplastics in soil-agro ecosystems: Origin, occurrence, and pollutants synergies

The ubiquity of plastics in modern life has made them a significant environmental concern and a marker of the Anthropocene era. The degradation of plastics results in the formation of microplastics (MPs), which measure 5 mm or less. The coexistence of MPs with other pollutants found in sludge, water treatment plant effluents, surface water, and groundwater, shapes the environmental landscape together. Despite extensive investigation, the long-term implications of MPs in soils remain uncertain, underscoring the importance of delving into their transportation and interactions with soil biota and other contaminants. The present article provides a comprehensive overview of MPs contamination in soil, encompassing its sources, prevalence, features, and interactions with soil flora and fauna, heavy metals, and organic compounds. The sources of MPs in soil agroecosystems are mulching, composting, littering, sewage sludge, irrigation water, and fertilizer application. The concentration of MPs reported in plastic mulch, littering, and sewage sludge is 503 ± 2760 items per kg-1, 4483 ± 2315 MPs/kg, and 11,100 ± 570 per/kg. The transport of MPs in soil agroecosystems is due to their horizontal and vertical migration including biotic and abiotic mobility. The article also highlighted the analytical process, which includes sampling planning, collection, purification, extraction, and identification techniques of MPs in soil agroecosystems. The mechanism in the interaction of MPs and organic pollutants includes surface adsorption or adhesion cation bridging, hydrogen bonding, charge transfer, ligand exchange, van der Waals interactions, and ion exchange.

Effects of biodegradable (PBAT/PLA) and conventional (LDPE) mulch film residues on bacterial communities and metabolic functions in different agricultural soils

Soil health is a crucial aspect of sustainable agriculture and food production, necessitating attention to the ecological risks associated with substantial amounts of mulch film residues. Biodegradable mulch films (BDMs) carry the same risk of mulch film residues formation as low-density polyethylene (LDPE) mulch films during actual use. More information is needed to elucidate the specific impacts of mulch film residues on the soil environment. Integrated 16S rRNA gene sequencing and non-targeted metabolomics, this study revealed the response patterns of bacterial communities, metabolites, and metabolic functions in the soil from three different agricultural regions to the presence of mulch film residues. LDPE mulch film residues negatively impacted the bacterial communities in the soils of Heilongjiang (HLJ) and Yunnan (YN) and had a lesser impact on the metabolic spectrum in the soils of HLJ, YN, and Xinjiang (XJ). BDM residues had a greater negative impact on all three soils in terms of both the bacterial communities and metabolites. The impact of BDM treatment on the soils of HLJ, YN, and XJ increased sequentially in that order. It is recommended that, when promoting the use of biodegradable mulch films, a fuller assessment should be made, accounting for local soil properties.

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.

Ecotoxicological effects of polyethylene microplastics and lead (Pb) on the biomass, activity, and community diversity of soil microbes

Microplastics and heavy metals are ubiquitous and persistent contaminants that are widely distributed worldwide, yet little is known about the effects of their interaction on soil ecosystems. A soil incubation experiment was conducted to investigate the individual and combined effects of polyethylene microplastics (PE-MPs) and lead (Pb) on soil enzymatic activities, microbial biomass, respiration rate, and community diversity. The results indicate that the presence of PE-MPs notably reduced soil pH and elevated soil Pb bioavailability, potentially exacerbated the combined toxicity on the biogeochemical cycles of soil nutrients, microbial biomass carbon and nitrogen, and the activities of soil urease, sucrase, and alkaline phosphatase. Soil CO2 emissions increased by 7.9% with PE-MPs alone, decreased by 46.3% with single Pb, and reduced by 69.4% with PE-MPs and Pb co-exposure, compared to uncontaminated soils. Specifically, the presence of PE-MPs and Pb, individually and in combination, facilitated the soil metabolic quotient, leading to reduced microbial metabolic efficiency. Moreover, the addition of Pb and PE-MPs modified the composition of the microbial community, leading to the enrichment of specific taxa. Tax4Fun analysis showed the effects of Pb, PE-MPs and their combination on the biogeochemical processes and ecological functions of microbes were mainly by altering amino acid metabolism, carbohydrate metabolism, membrane transport, and signal transduction. These findings offer valuable insights into the ecotoxicological effects of combined PE-MPs and Pb on soil microbial dynamics, reveals key assembly mechanisms and environmental drivers, and highlights the potential threat of MPs and heavy metals to the multifunctionality of soil ecosystems.

Microplastic pollution promotes soil respiration: A global-scale meta-analysis

Microplastic (MP) pollution likely affects global soil carbon (C) dynamics, yet it remains uncertain how and to what extent MP influences soil respiration. Here, we report on a global meta-analysis to determine the effects of MP pollution on the soil microbiome and CO2 emission. We found that MP pollution significantly increased the contents of soil organic C (SOC) (21%) and dissolved organic C (DOC) (12%), the activity of fluorescein diacetate hydrolase (FDAse) (10%), and microbial biomass (17%), but led to a decrease in microbial diversity (3%). In particular, increases in soil C components and microbial biomass further promote CO2 emission (25%) from soil, but with a much higher effect of MPs on these emissions than on soil C components and microbial biomass. The effect could be attributed to the opposite effects of MPs on microbial biomass vs. diversity, as soil MP accumulation recruited some functionally important bacteria and provided additional C substrates for specific heterotrophic microorganisms, while inhibiting the growth of autotrophic taxa (e.g., Chloroflexi, Cyanobacteria). This study reveals that MP pollution can increase soil CO2 emission by causing shifts in the soil microbiome. These results underscore the potential importance of plastic pollution for terrestrial C fluxes, and thus climate feedbacks.

Mitigating microplastic stress on peanuts: The role of biochar-based synthetic community in the preservation of soil physicochemical properties and microbial diversity

Tire-derived rubber crumbs (RC), as a new type of microplastics (MPs), harms both the environment and human health. Excessive use of plastic, the decomposition of which generates microplastic particles, in current agricultural practices poses a significant threat to the sustainability of agricultural ecosystems, worldwide food security and human health. In this study, the application of biochar, a carbon-rich material, to soil was explored, especially in the evaluation of synthetic biochar-based community (SynCom) to alleviate RC-MP-induced stress on plant growth and soil physicochemical properties and soil microbial communities in peanuts. The results revealed that RC-MPs significantly reduced peanut shoot dry weight, root vigor, nodule quantity, plant enzyme activity, soil urease and dehydrogenase activity, as well as soil available potassium, and bacterial abundance. Moreover, the study led to the identification highly effective plant growth-promoting rhizobacteria (PGPR) from the peanut rhizosphere, which were then integrated into a SynCom and immobilized within biochar. Application of biochar-based SynCom in RC-MPs contaminated soil significantly increased peanut biomass, root vigor, nodule number, and antioxidant enzyme activity, alongside enhancing soil enzyme activity and rhizosphere bacterial abundance. Interestingly, under high-dose RC-MPs treatment, the relative abundance of rhizosphere bacteria decreased significantly, but their diversity increased significantly and exhibited distinct clustering phenomenon. In summary, the investigated biochar-based SynCom proved to be a potential soil amendment to mitigate the deleterious effects of RC-MPs on peanuts and preserve soil microbial functionality. This presents a promising solution to the challenges posed by contaminated soil, offering new avenues for remediation.

Toxicity assessment of animal manure composts containing environmental microplastics by using earthworms Eisenia andrei

Nowadays, animal manure composting constitutes a sustainable alternative for farmers to enhance the level of nutrients within soils and achieve a good productivity. However, pollutants may be present in manures. This study focuses on the detection of environmental microplastics (EMPs) into composts, as well as on the assessment of their potential toxicity on the earthworm Eisenia andrei. To these aims, animals were exposed to two types of compost, namely bovine (cow) and ovine (sheep) manure, besides to their mixture, for 7 and 14 days. The presence and characterization of EMPs was evaluated in all the tested composts, as well as in tissues of the exposed earthworms. The impact of the tested composts was assessed by a multi-biomarker approach including cytotoxic (lysosomal membrane stability, LMS), genotoxic (micronuclei frequency, MNi), biochemical (activity of catalase, CAT, and glutathione-S-transferase, GST; content of malondialdehyde, MDA), and neurotoxic (activity of acetylcholinesterase, AChE) responses in earthworms. Results indicated the presence of high levels of EMPs in all the tested composts, especially in the sheep manure (2273.14 ± 200.89 items/kg) in comparison to the cow manure (1628.82 ± 175.23 items/kg), with the size <1.22 μm as the most abundant EMPs. A time-dependent decrease in LMS and AChE was noted in exposed earthworms, as well as a concomitant increase in DNA damages (MNi) after 7 and 14 days of exposure. Also, a severe oxidative stress was recorded in animals treated with the different types of compost through an increase in CAT and GST activities, and LPO levels, especially after 14 days of exposure. Therefore, it is necessary to carefully consider these findings for agricultural good practices in terms of plastic mitigation in compost usage, in order to prevent any risk for environment health.

Effects of biodegradable microplastics and straw addition on soil greenhouse gas emissions

Large pieces of plastic are transformed into microplastic particles through weathering, abrasion, and ultraviolet radiation, significantly impacting the soil ecosystem. However, studies on biodegradable microplastics replacing traditional microplastics as agricultural mulching films to drive the biogeochemical processes influenced by GHG are still in their initial stages, with limited relevant reports available. This study sought to investigate the effects of microplastic and straw addition on CO2 and N2O emissions in different soils. Herein, yellow-brown soil (S1) and fluvo-aquic soil (S2) were utilized, each treated with three different concentrations of PLA (polylactic acid) microplastics (0.25%, 2%, and 7% w/w) at 25 °C for 35 days, with and without straw addition. The results showed that straw (1% w/w) significantly increased soil CO2 by 4.1-fold and 3.2-fold, respectively, and N2O by 1.8-fold and 1.8-fold, respectively, in cumulative emissions in S1 and S2 compared with the control. PLA microplastics significantly increased CO2 emissions by 71.5% and 99.0% and decreased N2O emissions by 30.1% and 24.7% at a high concentration (7% w/w, PLA3) in S1 and S2 compared with the control, respectively. The same trend was observed with the addition of straw and microplastics together. Structural equation modeling and redundancy analysis confirmed that soil physiochemical parameters, enzyme and microbial activities are key factors regulating CO2 and N2O emissions. The addition of microplastics is equivalent to the addition of carbon sources, which can significantly affect DOC, MBC, SOC and the abundance of carbon-associated bacteria (CbbL), thereby increasing soil CO2 emissions. The addition of microplastics alone inhibited the activity of nitrogen cycling enzymes (urease activity), increasing the abundance of denitrifying microbes. However, adding a high amount of microplastics and straw together released plastic additives, inhibiting microbial abundance and reducing the nitrogen cycle. These effects decreased NH4+-N and increased NO3--N, resulting in decreased N2O emissions. This study indicates that biodegradable microplastics could reduce soil plastic residue pollution through degradation. However, their use could also increase CO2 emissions and decrease N2O emissions. Consequently, this research lays the groundwork for further investigation into the implications of utilizing biodegradable microplastics as agricultural mulch, particularly concerning soil geochemistry and GHG emissions.

Effects of combined microplastics and heavy metals pollution on terrestrial plants and rhizosphere environment: A review

Microplastics (MPs) can enter the soil environment through industry, agricultural production and daily life sources. Their interaction with heavy metals (HMs) poses a significant threat to a variety of terrestrial ecosystems, including agricultural ones, thereby affecting crop quality and threatening human health. This review initially addresses the impact of single and combined contamination with MPs and HMs on soil environment, including changes in soil physicochemical properties, microbial community structure and diversity, fertility, enzyme activity and resistance genes, as well as alterations in heavy metal speciation. The article further explores the effects of this pollution on the growth characteristics of terrestrial plants, such as plant biomass, antioxidant systems, metabolites and photosynthesis. In general, the combined contaminants tend to significantly affect soil environment and terrestrial plant growth, i.e., the impact of combined contaminants on plants weight ranged from -87.5% to 4.55%. Similarities and differences in contamination impact levels stem from the variations in contaminant types, sizes and doses of contaminants and the specific plant growth environments. In addition, MPs can not only infiltrate plants directly, but also significantly affect the accumulation of HMs in terrestrial plants. The heavy metals concentration in plants under the treatment of MPs were 70.26%-36.80%. The co-occurrence of these two pollution types can pose a serious threat to crop productivity and safety. Finally, this study proposes suggestions for future research aiming to address current gaps in knowledge, raises awareness about the impact of combined MPs + HMs pollution on plant growth and eco-environmental security.

A bibliometric perspective on the occurrence and migration of microplastics in soils amended with sewage sludge

The land application of sewage sludge from wastewater treatment plants has been recognized as a major source of microplastic contamination in soil. Nevertheless, the fate and behavior of microplastics in soil remain uncertain, particularly their distribution and transport, which are poorly understood. This study does a bibliometric analysis and visualization of relevant research publications using the CiteSpace software. It explores the limited research available on the topic, highlighting the potential for it to emerge as a research hotspot in the future. Chinese researchers and institutions are paying great attention to this field and are promoting close academic cooperation among international organizations. Current research hot topics mainly involve microplastic pollution caused by the land application of sewage sludge, as well as the detection, environmental fate, and removal of microplastics in soil. The presence of microplastics in sludge, typically ranging from tens of thousands to hundreds of thousands of particles (p)/kg, inevitably leads to their introduction into soil upon land application. In China, the estimated annual accumulation of microplastics in the soil due to sludge use is approximately 1.7 × 1013 p. In European countries, the accumulation ranges from 8.6 to 71 × 1013 p. Sludge application has significantly elevated soil microplastic concentrations, with higher application rates and frequencies resulting in up to several-fold increases. The primary forms of microplastics found in soils treated with sludge are fragments and fibers, primarily in white color. These microplastics consist primarily of components such as polyamide, polyethylene, and polypropylene. The vertical transport behavior of microplastics is influenced by factors such as tillage, wind, rainfall, bioturbation, microplastic characteristics (e.g., fraction, particle size, and shape), and soil physicochemical properties (e.g., organic matter, porosity, electrical conductivity, and pH). Research indicates that microplastics can penetrate up to 90 cm into the soil profile and persist for decades. Microplastics in sewage sludge-amended soils pose potential long-term threats to soil ecosystems and even human health. Future research should focus on expanding the theoretical understanding of microplastic behavior in these soils, enabling the development of comprehensive risk assessments and informed decision-making for sludge management practices. PRACTITIONER POINTS: Microplastics in sewage sludge range from tens to hundreds of thousands per kilogram. Sludge land application contributes significantly to soil microplastic pollution. The main forms of microplastics in sludge-amended soils are fragments and fibers. Microplastics are mainly composed of polyamide, polyethylene, and polypropylene. Microplastics can penetrate up to 90 cm into the soil profile and persist for decades.

Insights into the influence of polystyrene microplastics on the bio-degradation behavior of tetrabromobisphenol A in soil

Soil contamination by emerging pollutants tetrabromobisphenol A (TBBPA) and microplastics has become a global environmental issue in recent years. However, little is known about the effect of microplastics on degradation of TBBPA in soil, especially aged microplastics. In this study, the effect of aged polystyrene (PS) microplastics on the degradation of TBBPA in soil and the mechanisms were investigated. The results suggested that the aged microplastics exhibited a stronger inhibitory effect on the degradation of TBBPA in soil than the pristine microplastics, and the degradation efficiency of TBBPA decreased by 21.57% at the aged microplastic content of 1%. This might be related to the higher TBBPA adsorption capacity of aged microplastics compared to pristine microplastics. Aged microplastics strongly altered TBBPA-contaminated soil properties, reduced oxidoreductase activity and affected microbial community composition. The decrease in soil oxidoreductase activity and relative abundance of functional microorganisms (e.g., Bacillus, Pseudarthrobacter and Sphingomonas) caused by aged microplastics interfered with metabolic pathways of TBBPA. This study indicated the importance the risk assessment and soil remediation for TBBPA-contaminated soil with aged microplastics.

Do Added Microplastics, Native Soil Properties, and Prevailing Climatic Conditions Have Consequences for Carbon and Nitrogen Contents in Soil? A Global Data Synthesis of Pot and Greenhouse Studies

Microplastics threaten soil ecosystems, strongly influencing carbon (C) and nitrogen (N) contents. Interactions between microplastic properties and climatic and edaphic factors are poorly understood. We conducted a meta-analysis to assess the interactive effects of microplastic properties (type, shape, size, and content), native soil properties (texture, pH, and dissolved organic carbon (DOC)) and climatic factors (precipitation and temperature) on C and N contents in soil. We found that low-density polyethylene reduced total nitrogen (TN) content, whereas biodegradable polylactic acid led to a decrease in soil organic carbon (SOC). Microplastic fragments especially depleted TN, reducing aggregate stability, increasing N-mineralization and leaching, and consequently increasing the soil C/N ratio. Microplastic size affected outcomes; those <200 μm reduced both TN and SOC contents. Mineralization-induced nutrient losses were greatest at microplastic contents between 1 and 2.5% of soil weight. Sandy soils suffered the highest microplastic contamination-induced nutrient depletion. Alkaline soils showed the greatest SOC depletion, suggesting high SOC degradability. In low-DOC soils, microplastic contamination caused 2-fold greater TN depletion than in soils with high DOC. Sites with high precipitation and temperature had greatest decrease in TN and SOC contents. In conclusion, there are complex interactions determining microplastic impacts on soil health. Microplastic contamination always risks soil C and N depletion, but the severity depends on microplastic characteristics, native soil properties, and climatic conditions, with potential exacerbation by greenhouse emission-induced climate change.

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.

The impact of arbuscular mycorrhizal fungi and endophytic bacteria on peanuts under the combined pollution of cadmium and microplastics

It remains unclear how symbiotic microbes impact the growth of peanuts when they are exposed to the pollutants cadmium (Cd) and microplastics (MPs) simultaneously. This study aimed to investigate the effects of endophytic bacteria Bacillus velezens SC60 and arbuscular mycorrhizal fungus Rhizophagus irregularis on peanut growth and rhizosphere microbial communities in the presence of Cd at 40 (Cd40) or 80 (Cd80) mg kg-1 combined without MP or the presence of low-density polyethylene (LDPE) and poly butyleneadipate-co-terephthalate (PBAT). This study assessed soil indicators, plant parameters, and Cd accumulation indicators. Results showed that the application of R. irregularis and B. velezens significantly enhanced soil organic carbon and increased Cd content under the conditions of Cd80 and MPs co-pollution. R. irregularis and B. velezens treatment increased peanut absorption and the enrichment coefficient for Cd, with predominate concentrations localized in the peanut roots, especially under combined pollution by Cd and MPs. Under treatments with Cd40 and Cd80 combined with PBAT pollution, soil microbes Proteobacteria exhibited a higher relative abundance, while Actinobacteria showed a higher relative abundance under treatments with Cd40 and Cd80 combined with LDPE pollution. In conclusion, under the combined pollution conditions of MPs and Cd, the co-treatment of R. irregularis and B. velezens effectively immobilized Cd in peanut roots, impeding its translocation to the shoot.

Effects of combined microplastic and cadmium pollution on sorghum growth, Cd accumulation, and rhizosphere microbial functions

The interaction between microplastics (MPs) and cadmium (Cd) poses a threat to agricultural soil environments, and their effects on plant growth and rhizosphere microbial community functions are not yet clear. In this study, energy sorghum was used as a test plant to investigate the effects of two types of MPs, polystyrene (PS) and polyethylene (PE), at different particle sizes (13 μm, 550 μm) and concentrations (0.1%, 1% w/w), and Cd, as well as their interactions, on the growth of sorghum in a soil-cultivation pot experiment. The results showed that the combined effects of MP and Cd pollution on the dry weight and Cd accumulation rate in sorghum varied depending on the type, concentration, and particle size of the MPs, with an overall trend of increasing stress from combined pollution with increasing Cd content and accumulation. High-throughput sequencing analysis revealed that combined MP and Cd pollution increased bacterial diversity, and the most significant increase was observed in the abundance-based coverage estimator (ACE), Shannon, and Sobs indices in the 13 μm 1% PS+Cd treatment group. Metagenomic analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways revealed that 19 groups of metabolic pathways, including microbial metabolism and methane metabolism, differed significantly under combined MP and Cd pollution. Hierarchical clustering results indicated that Cd treatment and combined MP and Cd treatment affected the abundances of sorghum rhizosphere soil nitrogen (N) and phosphorus (P) cycling genes and that the type of MP present was an important factor affecting N and P cycling genes. The results of this study provide a basis for exploring the toxic effects of combined MP and Cd pollution and for conducting soil environmental risk assessments.

Short-term impacts of polyethylene and polyacrylonitrile microplastics on soil physicochemical properties and microbial activity of a marine terrace environment in maritime Antarctica

Evidence of microplastic (MP) pollution in Antarctic terrestrial environments reinforces concerns about its potential impacts on soil, which plays a major role in ecological processes at ice-free areas. We investigated the effects of two common MP types on soil physicochemical properties and microbial responses of a marine terrace from Fildes Peninsula (King George Island, Antarctica). Soils were treated with polyethylene (PE) fragments and polyacrylonitrile (PAN) fibers at environmentally relevant doses (from 0.001% to 1% w w-1), in addition to a control treatment (0% w w-1), for 22 days in a pot incubation experiment under natural field conditions. The short-term impacts of MPs on soil physical, chemical and microbial attributes seem interrelated and were affected by both MP dose and type. The highest PAN fiber dose (0.1%) increased macro and total porosity, but decreased soil bulk density compared to control, whereas PE fragments treatments did not affect soil porosity. Soil respiration increased with increasing doses of PAN fibers reflecting impacts on physical properties. Both types of MPs increased microbial activity (fluorescein diacetate hydrolysis), decreased the cation exchange capacity but, especially PE fragments, increased Na+ saturation. The highest dose of PAN fibers and PE fragments increased total nitrogen and total organic carbon, respectively, and both decreased the soil pH. We discussed potential causes for our findings in this initial assessment and addressed the need for further research considering the complexity of environmental factors to better understand the cumulative impacts of MP pollution in Antarctic soil environments.

Exploring correlations between microplastics, microorganisms, and water quality in an urban drinking water source

The microplastic pollution in freshwater system is gradually becoming more severe, which has led to increasing attention on the distribution and potential harmful effects of microplastics. Moreover, microplastics may have an impact on river ecology and pose risks to ecosystems. Therefore, it is important to reveal this process. This study aimed to explore correlations between microplastics and free-living microorganisms in an urban drinking water source of Xiangjiang River by using multivariate statistical analysis. The results indicated that the abundance of microplastics (size 50 μm to 5 mm) in surface water and sediments ranged from 0.72 to 18.6 (mean ± SD: 7.32 ± 2.36) items L-1 and 26.3-302 (150 ± 75.6) items kg-1 dry weight (dw), respectively, suggesting potential microplastic pollution despite the protected status as a drinking water source. Higher microplastic abundances were observed in urban areas and the downstream of wastewater plants, with mostly granular shape, transparent and black color as well as 50-100 μm in size. The multivariate statistical analysis presented that the abundance of microplastics is not significantly correlated with water indicators, due to the complexity of the abundance data. The water indicators showed an obvious correlation with microplastics in colors of transparent and black, and smaller sizes of 50-100 μm. This is also true for microplastics and microorganisms in water and sediment. Proteobacteria was the main prokaryote in water and sediments, being positively correlated with 50-100 μm microplastics; while Chloroplastida was the dominated eukaryotes, presenting a weak correlation with smaller-size microplastics. Overall, when considering the properties of microplastics such as shape, color and size, the potential correlations with water indicators and microorganisms were more evident than abundance. This study provides new insights into the multivariate statistical analysis, explaining the potential correlations among microplastic properties, microorganisms and environmental factors in a river system.

A red seaweed Kappaphycus alvarezii-based biostimulant (AgroGain®) improves the growth of Zea mays and impacts agricultural sustainability by beneficially priming rhizosphere soil microbial community

The overuse of chemical-based agricultural inputs has led to the degradation of soil with associated adverse effects on soil attributes and microbial population. This scenario leads to poor soil health and is reportedly on the rise globally. Additionally, chemical fertilizers pose serious risks to the ecosystem and human health. In this study, foliar sprays of biostimulant (AgroGain/LBS6) prepared from the cultivated, tropical red seaweed Kappaphycus alvarezii increased the phenotypic growth of Zea mays in terms of greater leaf area, total plant height, and shoot fresh and dry weights. In addition, LBS6 improved the accumulation of chlorophyll a and b, total carotenoids, total soluble sugars, amino acids, flavonoids, and phenolics in the treated plants. LBS6 applications also improved the total bacterial and fungal count in rhizospheric soil. The V3-V4 region of 16S rRNA gene from the soil metagenome was analyzed to study the abundance of bacterial communities which were increased in the rhizosphere of LBS6-treated plants. Treatments were found to enrich beneficial soil bacteria, i.e., Proteobacteria, especially the classes Alphaproteobacteria, Cyanobacteria, Firmicutes, Actinobacteriota, Verrucomicrobiota, Chloroflexi, and Acidobacteriota and several other phyla related to plant growth promotion. A metagenomic study of those soil samples from LBS6-sprayed plants was correlated with functional potential of soil microbiota. Enrichment of metabolisms such as nitrogen, sulfur, phosphorous, plant defense, amino acid, co-factors, and vitamins was observed in soils grown with LBS6-sprayed plants. These results were further confirmed by a significant increase in the activity of soil enzymes such as urease, acid phosphatase, FDAse, dehydrogenase, catalase, and biological index of fertility in the rhizosphere of LBS6-treated corn plant. These findings conclude that the foliar application of LBS6 on Z. mays improves and recruits beneficial microbes and alters soil ecology in a sustainable manner.

Microplastics affect soil-plant system: Implications for rhizosphere biology and fitness of sage (Salvia officinalis L.)

A mesocosm experiment was set-up to investigate the effects of low-density polyethylene (LDPE) fragments deriving from plastic film on soil ecology, rhizosphere and plant (Salvia officinalis L.) fitness. The internal transcribed spacer (ITS) and 16S metagenomic analysis was adopted to evaluate taxonomic and functional shifts of both soil and rhizosphere under the influence of microplastics (MPs). Photosynthetic parameters and enzymes involved in oxidative stress were assessed to unveil the plant physiological state. MP fragments were analysed by scanning electron microscope (SEM) and metagenomics to investigate the plastisphere. Microbial biomarkers of MPs pollution were identified in soil and rhizosphere, reinforcing the concept of molecular biomonitoring. Overall, Bacillus, Nocardioides and Streptomyces genera are bacterial biomarkers of MPs pollution in soil whereas Aspergillus, Fusarium and Trichoderma genera, and Nectriaceae family are fungal biomarkers of MPs polluted soil. The data show that the presence of MPs promotes the abundance of taxa involved in the soil N cycle, but simultaneously reduces the endophytic interaction capability and enhances pathogen related functions at the rhizosphere level. A significant decrease in chlorophyll levels and increase of oxidative stress enzymes was observed in plants grown in MPs-polluted soil. The SEM observations of MPs fragments revealed a complex colonisation, where bacteria (Bacillus in MPSo and Microvirga in MPRz) and fungi (Aspergillus in MPSo and Trichoderma in MPRz) represent the main colonisers. The results demonstrate that the presence of MPs causes changes in the soil and rhizosphere microbial community and functions leading to negative effects on plant fitness.

Impacts of polypropylene microplastics on the distribution of cadmium, enzyme activities, and bacterial community in black soil at the aggregate level

Microplastics (MPs) can co-occur widely with heavy metals in soil. This study intended to investigate the influences of the co-exposure of polyethylene MPs (0.5 %, w/w) and cadmium (Cd) in black soil on the Cd distribution, enzyme activities, and bacterial communities in both bulk soil and different sized soil aggregates (> 1, 0.50-1, 0.25-0.50, and < 0.25 mm aggregates) after a 90-day incubation. Our results showed that the existence of MPs increased the distributions of Cd in >1 mm and < 0.25 mm soil aggregates and decreased its distributions in 0.50-1 mm and 0.25-0.50 mm soil aggregates. About 12.15 %-17.65 % and 9.03 %-11.13 % of Cd were distributed in the exchangeable and oxidizable forms in bulk soil and various sized soil aggregates after the addition of MPs which were higher than those in the only Cd-treated soil (11.17 %-14.72 % and 8.66 %-10.43 %, respectively), while opposite tendency was found for Cd in the reducible form. Urease and β-glucosidase activities in the Cd-treated soils were 1.14-1.18 and 1.07-1.31 times higher than those in the Cd-MPs treated soils. MPs disturbed soil bacterial community at phylum level and increased the bacteria richness in bulk soil. The levels of predicted functional genes which are linked to the biodegradation and metabolism of exogenous substances and soil C and N cycles were altered by the co-exposure of Cd and MPs. The findings of this study could help deepen our knowledge about the responses of soil properties, especially microbial community, to the co-occurrence of MPs and heavy metals in soil.

Dosage and exposure time effects of two micro(nono)plastics on arbuscular mycorrhizal fungal diversity in two farmland soils planted with pepper (Capsicum annuum L.)

As emerging environmental pollutants, micro(nano)plastics (MPs) like polyethylene terephthalate (PET) and low-density polyethylene (LDPE) have adverse effects on terrestrial biota and ecosystem function. However, the performance and roles of soil arbuscular mycorrhizal (AM) fungi in MPs-contaminated vegetable fields are poorly understood. Thus, a 120-day pot experiment was conducted to test the impacts of two input levels of either PET (~13 μm) or LDPE (~500 nm) on AM fungal diversity and pepper (Capsicum annuum L.) growth in two farmland soils collected from Nanjing (NJ) and Chongqing (CQ), respectively. In the vast majority of cases, 1 % rather than 0.1 % of both MPs greatly decreased the observed richness, Shannon and Simpson's indices, and Pielou's evenness of AM fungi, and decreased mycorrhizal colonization, root and shoot biomasses, fruit yield, and leaf superoxide dismutase, peroxidase, and catalase activities of pepper, while increased leaf malondialdehyde content. From day 40 to 120, the inhibition of either diversity or vitality of AM fungi by 1 % and 0.1 % of MPs gradually increased and weakened, respectively. Compared with PET, LDPE with substantially smaller particle size was more toxic to mycorrhization at day 40, but no longer at day 120. Almost all plant parameters significantly correlated to mycorrhizal colonization, which significantly correlated to both Shannon and Simpson's indices of AM fungi, and soil pH, available P and K concentrations, and alkaline phosphatase activity. All diversity indices of AM fungi clearly negatively correlated to soil pH from 4.4 to 5.6 for the NJ soil and from 5.3 to 6.5 for the CQ soil, and also positively to mineral N and negatively to available P concentrations for the NJ and CQ soils, respectively. Thus, the study emphasized that high input of MPs significantly inhibited soil AM fungal diversity and vitality and thereby vegetable growth via changing soil pH and major nutrient availability.

Potential synergy of microplastics and nitrogen enrichment on plant holobionts in wetland ecosystems

Wetland ecosystems are global hotspots for environmental contaminants, including microplastics (MPs) and nutrients such as nitrogen (N) and phosphorus (P). While MP and nutrient effects on host plants and their associated microbial communities at the individual level have been studied, their synergistic effects on a plant holobiont (i.e., a plant host plus its microbiota, such as bacteria and fungi) in wetland ecosystems are nearly unknown. As an ecological entity, plant holobionts play pivotal roles in biological nitrogen fixation, promote plant resilience and defense chemistry against pathogens, and enhance biogeochemical processes. We summarize evidence based on recent literature to elaborate on the potential synergy of MPs and nutrient enrichment on plant holobionts in wetland ecosystems. We provide a conceptual framework to explain the interplay of MPs, nutrients, and plant holobionts and discuss major pathways of MPs and nutrients into the wetland milieu. Moreover, we highlight the ecological consequences of loss of plant holobionts in wetland ecosystems and conclude with recommendations for pending questions that warrant urgent research. We found that nutrient enrichment promotes the recruitment of MPs-degraded microorganisms and accelerates microbially mediated degradation of MPs, modifying their distribution and toxicity impacts on plant holobionts in wetland ecosystems. Moreover, a loss of wetland plant holobionts via long-term MP-nutrient interactions may likely exacerbate the disruption of wetland ecosystems' capacity to offer nature-based solutions for climate change mitigation through soil organic C sequestration. In conclusion, MP and nutrient enrichment interactions represent a severe ecological risk that can disorganize plant holobionts and their taxonomic roles, leading to dysbiosis (i.e., the disintegration of a stable plant microbiome) and diminishing wetland ecosystems' integrity and multifunctionality.

The impacts of microplastics on the cycling of carbon and nitrogen in terrestrial soil ecosystems: Progress and prospects

As contaminants of emerging concern, microplastics (MPs) are ubiquitously present in almost all environmental compartments of the earth, with terrestrial soil ecosystems as the major sink for these contaminants. The accumulation of MPs in the soil can trigger a wide range of effects on soil physical, chemical, and microbial properties, which may in turn cause alterations in the biogeochemical processes of some key elements, such as carbon and nitrogen. Until recently, the effects of MPs on the cycling of carbon and nitrogen in terrestrial soil ecosystems have yet to be fully understood, which necessitates a review to summarize the current research progress and propose suggestions for future studies. The presence of MPs can affect the contents and forms of soil carbon and nitrogen nutrients (e.g., total and dissolved organic carbon, dissolved organic nitrogen, NH4+-N, and NO3--N) and the emissions of CH4, CO2, and N2O by altering soil microbial communities, functional gene expressions, and enzyme activities. Exposure to MPs can also affect plant growth and physiological processes, consequently influencing carbon fixation and nitrogen uptake. Specific effects of MPs on carbon and nitrogen cycling and the associated microbial parameters can vary considerably with MP properties (e.g., dose, polymer type, size, shape, and aging status) and soil types, while the mechanisms of interaction between MPs and soil microbes remain unclear. More comprehensive studies are needed to narrow the current knowledge gaps.

Effects of polystyrene, polyethylene, and polypropylene microplastics on the soil-rhizosphere-plant system: Phytotoxicity, enzyme activity, and microbial community

The widespread presence of soil microplastics (MPs) has become a global environmental problem. MPs of different properties (i.e., types, sizes, and concentrations) are present in the environment, while studies about the impact of MPs having different properties are limited. Thus, this study investigated the effects of three common polymers (polystyrene, polyethylene, and polypropylene) with two concentrations (0.01% and 0.1% w/w) on growth and stress response of lettuce (Lactuca sativa L.), soil enzymes, and rhizosphere microbial community. Lettuce growth was inhibited under MPs treatments. Moreover, the antioxidant system, metabolism composition, and phyllosphere microbiome of lettuce leaves was also perturbed. MPs reduced phytase activity and significantly increased dehydrogenase activity. The diversity and structure of rhizosphere microbial community were disturbed by MPs and more sensitive to polystyrene microplastics (PSMPs) and polypropylene microplastics (PPMPs). In general, the results by partial least squares pathway models (PLS-PMs) showed that the presence of MPs influenced the soil-rhizosphere-plant system, which may have essential implications for assessing the environmental risk of MPs.

Quantitative distribution and quantized ecological threat of microplastics in farmland: Shanghai as an example

The occurrence of microplastics (MPs) in farmlands poses a threat to soil health and crop yield. There needs to be more research on the role of cropping patterns in the accumulation of MPs and quantizing the threat of MPs on soil health and crop yield. In this study, a field study was carried out to explore the role of cropping patterns in the accumulation of MPs in agricultural soil in Shanghai, China. Furthermore, the specific effect and importance of MPs and each soil physicochemical indicator to soil health and crop yield were clarified, and the threat of MPs in reducing soil health and crop yield was quantized. Relative lower MPs abundance was detected in Shanghai. MPs abundance in vegetable fields was significantly higher than that in orchards. The broad source of MPs, the acceleration of plastics breaking under artificial disturbance and warmer temperatures, and the block of MPs exchange could account for the quicker accumulation of MPs in vegetable fields. MPs have a negligible effect on microbial diversity and metabolic activity which plays a role in soil enzyme activity. Besides, MPs served as one of the critical factors for rice yield reduction.

Effect of microplastics on urban wastewater disinfection and impact on effluent reuse: Sunlight/H2O2 vs solar photo-Fenton at neutral pH

The interference of three types of microplastics (MPs) on the inactivation of Escherichia coli (E. coli) by advanced oxidation processes (AOPs) (namely, sunlight/H2O2 and solar photo-Fenton (SPF) with Ethylenediamine-N,N'-disuccinic acid (EDDS)), in real secondary treated urban wastewater was investigated for the first time. Inactivation by sunlight/H2O2 treatment decreased as MPs concentration and H2O2 dose were increased. Noteworthy, an opposite behaviour was observed for SPF process where inactivation increased as MPs concentration was increased. Biofilm formation and microbial attachment on surfaces of post-treated MPs were observed on polyethylene (PE) and polyvinyl chloride (PVC) MPs by field emission scanning electron microscopy. In presence of PE MPs, a complete inactivation of E. Coli was achieved by SPF with EDDS (Fe:EDDS = 1:2) after 90 min treatment unlike of sunlight/H2O2 treatment (∼4.0 log reduction, 40 mg/L H2O2 dose, 90 min treatment). The lower efficiency of sunlight/H2O2 process could be attributed to the blocking/scattering effect of MPs on sunlight, which finally reduced the intracellular photo Fenton effect. A reduced E. coli regrowth was observed in presence of MPs. SPF (Fe:EDDS = 1:1) with PE MPs was less effective in controlling bacterial regrowth (∼120 CFU/100 mL) than sunlight/H2O2 (∼10 CFU/100 mL) after 48 h of post-treatment. These results provide useful information about possible interference of MPs on urban wastewater disinfection by solar driven AOPs and possible implications for effluent reuse.

Responses of methane production and methanogenic pathways to polystyrene nanoplastics exposure in paddy soil

Nanoplastics (NPs) have attracted increasing attention within terrestrial ecosystems. However, our understanding of their impacts on the intricate anaerobic methanogenesis processes occurring in paddy soils microbial communities remains limited with respect to nanoplastics shape, function, and metabolic effects. Herein, we explored the effects of polystyrene nanoplastics (PS-NPs) and microplastics (PS-MPs) on anaerobic methanogenesis in a typical paddy soil. The results show that PS-NPs delayed methane production and the time to reach peak acetate content in incubation process of paddy soils, and the methanogenic rate increased rapidly after 13 days, with a maximum increase of 87.97%. However, PS-MPs had no marked effect on CH4, CO2 and acetate production. In addition, PS-NPs affected soil physicochemical properties by reducing pH and increasing electrical conductivity. Acetoclastic methanogens were enriched and the relative abundance of the genes ackA, pta, ACSS, cdhC, cdhD and cdhE in the acetoclastic pathways were significantly increased under PS-NPs exposure. In addition, PS-MPs had significant effect on the microbial community structure but no effect on methanogenic pathways of the paddy soils. This study provides important insights into the response of key microorganisms, functional genes and methanogenesis pathways to NPs during anaerobic methanogenesis in paddy soils.

Phosphorus fertiliser application mitigates the negative effects of microplastic on soil microbes and rice growth

Soil microplastics (MPs) have attracted widespread attention recently. Most studies have explored how soil MPs affect the soil's physicochemical parameters, matter circulation, and soil microbial community assembly. Similarly, a key concern in agricultural development has been the use of phosphorus (P) fertiliser, which is essential for plant health and development. However, the relationship between MPs and phosphate fertilisers and their effects on the soil environment and plant growth remains elusive. This study assessed the influence of adding low-density polyethylene MPs (1%) with different phosphate fertiliser application rates on microbial communities and rice biomass. Our results showed that MPs changed the structure of soil bacterial and phoD-harbouring microbial communities in the treatment with P fertiliser at the same level and suppressed the interactions of phoD-harbouring microorganisms. In addition, we found that MPs contamination inhibited rice growth; however, the inclusion of P fertiliser in MP-contaminated soils reduced the inhibitory action of MPs on rice growth, probably because the presence with P fertiliser promoted the uptake of NO3--N by rice in MP-contaminated soils. Our results provide further insights into guiding agricultural production, improving agricultural management, and rationally applying phosphate fertilisers in the context of widespread MPs pollution and global P resource constraints.

Nanoplastics promote the dissemination of antibiotic resistance genes and diversify their bacterial hosts in soil

The wide application of plastics has led to the ubiquitous presence of nanoplastics and microplastics in terrestrial environments. However, few studies have focused on the mechanism underlying the effects of plastic particles on soil microbiomes and resistomes, especially the differences between nanoplastics and microplastics. This study investigated the microbiome and resistome in soil exposed to polystyrene microplastics (mPS) or nanoplastics (nPS) through 16S rRNA and shotgun metagenomic sequencing. Distinct microbial communities were observed between mPS and nPS exposure groups, and nPS exposure significantly changed the bacterial composition even at the lowest amended rate (0.01%, w/w). The abundance of antibiotic resistance genes (ARGs) in nPS exposure (1%) was 0.26 copies per cell, significantly higher than that in control (0.21 copies per cell) and mPS exposure groups (0.21 copies per cell). It was observed that nanoplastics, bacterial community, and mobile genetic elements (MGEs) directly affected the ARG abundance in nPS exposure groups, while in mPS exposure groups, only MGEs directly induced the change of ARGs. Streptomyces was the predominant host for multidrug in the control and mPS exposure, whereas the primary host was changed to Bacillus in nPS exposure. Additionally, exposure to nPS induced several bacterial hosts to exhibit possible multi-antibiotic resistance characteristics. Our results indicated that the effects of plastic particles on the soil microbial community were size-dependent, and nano-sized plastic particles exhibited more substantial impacts. Both microplastics and nanoplastics promoted ARG transfer and diversified their bacterial hosts. These findings bear implications for the regulation of plastic waste and ARGs.

Microplastics alter the equilibrium of plant-soil-microbial system: A meta-analysis

Microplastics (MPs) are widely identified as emerging hazards causing considerable eco-toxicity in terrestrial ecosystems, but the impacts differ in different ecosystem functions among different chemical compositions, morphology, sizes, concentrations, and experiment duration. Given the close relationships and trade-offs between plant and soil systems, probing the "whole ecosystem" instead of individual functions must yield novel insights into MPs affecting terrestrial ecosystems. Here, a comprehensive meta-analysis was employed to reveal an unambiguous response of the plant-soil-microbial system to MPs. Results showed that in view of plant, soil, and microbial functions, the general response patterns of plant and soil functions to MPs were obviously opposite. For example, polyethylene (PE) and polyvinyl chloride (PVC) MPs highly increased plant functions, while posed negative effects on soil functions. Polystyrene (PS) and biodegradable (Bio) MPs decreased plant functions, while stimulating soil functions. Additionally, low-density polyethylene (LDPE), PE, PS, PVC, Bio, and granular MPs significantly decreased soil microbial functions. These results clearly revealed that MPs alter the equilibrium of the plant-soil-microbial system. More importantly, our results further revealed that MPs tended to increase ecosystem multifunctionality, e.g., LDPE and PVC MPs posed positive effects on ecosystem multifunctionality, PE, PS, and Bio MPs showed neutral effects on ecosystem multifunctionality. Linear regression analysis showed that under low MPs size (<100 µm), ecosystem multifunctionality was gradually reduced with the increased size of MPs. The response of ecosystem multifunctionality showed a concave shape pattern along the gradient of experimental duration which was lower than 70 days. More importantly, there was a threshold (i.e., 5% w/w) for the effects of MPs concentration on ecosystem multifunctionality, i.e., under low concentration (< 5% w/w), ecosystem multifunctionality was gradually increased with the increased concentration of MPs, while ecosystem multifunctionality was gradually decreased under high concentration (i.e., > 5% w/w). These findings emphasize the importance of studying the effects of MPs on plant-soil-microbial systems and help us identify ways to reduce the eco-toxicity of MPs and maintain environmental safety in view of an ecology perspective.

Regulation of ARGs abundance by biofilm colonization on microplastics under selective pressure of antibiotics in river water environment

Interactions of microplastics (MPs) biofilm with antibiotic resistance genes (ARGs) and antibiotics in aquatic environments have made microplastic biofilm an issue of keen scholarly interest. The process of biofilm formation and the degree of ARGs enrichment in the presence of antibiotic-selective pressure and the impact on the microbial community need to be further investigated. In this paper, the selective pressure of ciprofloxacin (CIP) and illumination conditions were investigated to affect the physicochemical properties, biomass, and extracellular polymer secretion of polyvinyl chloride (PVC) microplastic biofilm. In addition, relative copy numbers of nine ARGs were analyzed by real-time quantitative polymerase chain reaction (qPCR). In the presence of CIP, microorganisms in the water and microplastic biofilm were more inclined to carry associated ARGs (2-3 times higher), which had a contributing effect on ARGs enrichment. The process of pre-microplastic biofilm formation might have an inhibitory effect on ARGs (total relative abundance up to 0.151) transfer and proliferation compared to the surrounding water (total relative abundance up to 0.488). However, in the presence of CIP stress, microplastic biofilm maintained the abundance of ARGs (from 0.151 to 0.149) better compared to the surrounding water (from 0.488 to 0.386). Therefore, microplastic biofilm act as abundance buffer island of ARGs stabilizing the concentration of ARGs. In addition, high-throughput analyses showed the presence of antibiotic-resistant (Pseudomonas) and pathogenic (Vibrio) microorganisms in biofilm under different conditions. The above research deepens our understanding of ARGs enrichment in biofilm and provides important insights into the ecological risks of interactions between ARGs, antibiotics, and microplastic biofilm.

Wheat (Triticum aestivum L.) seedlings performance mainly affected by soil nitrate nitrogen under the stress of polyvinyl chloride microplastics

Microplastics are exotic pollutants and are increasingly detected in soil, but it remains poorly understood how microplastics impact soil and plant systematically. The present study was conducted to evaluate the effects of polyvinyl chloride microplastics (PVC-MPs) on wheat seedlings performance and soil properties. Under the stress of PVC-MPs, no new substance and functional groups were generated in soil by X-ray diffraction and the fourier transform infrared spectroscopy analyses, whereas the diffraction and characteristic peaks and of soil was affected by PVC-MPs. Wheat seedlings shoot biomass and soil nitrate nitrogen were significantly inhibited by PVC-MPs. Chlorophylls were not significant affected by PVC-MPs. Superoxide dismutase, catalase, and peroxidase activities in wheat seedlings increased, while malondialdehyde and proline contents decreased significantly. Redundancy analysis displayed that wheat seedlings traits can be largely explained by soil nitrate nitrogen. Our results indicate that PVC-MPs have more significant influence on soil structure than on soil substance composition. Moreover, even though antioxidant enzyme activities were improved to respond the stress of PVC-MPs, wheat seedlings are not severely impacted by PVC-MPs. Besides, soil nitrate nitrogen is the main factor on wheat seedlings performance and wheat seedlings are prone to ensure the root growth under the stress of PVC-MPs.

Independent and combined effects of microplastics pollution and drought on soil bacterial community

Global terrestrial ecosystems are simultaneously threatened by multiple environmental pressures, with microplastics (MPs) pollution and drought possibly being the most pressing, both of which may have unanticipated effects on soil organisms. Here, we investigated the responses of diversity, composition and functions of soil bacterial community to MPs pollution (including two MPs types: polyethylene (PE) and polylactic acid (PLA); two MPs sizes: < 20 μm and <300 μm) and drought in microcosms. We found that only 20 μm PLA MPs significantly decreased soil bacterial diversity by 17.4 % and altered soil bacterial community composition, while PE MPs and 300 μm PLA MPs had no significant effects. The copiotrophic bacteria (i.e., Proteobacteria and Firmicutes) were enriched in the 20 μm PLA MPs pollution soils due to the enhanced dissolved organic carbon contents. Moreover, our results showed that the 20 μm PLA MPs also affected the potential phenotypes and functions of soil bacterial community, increasing the potentially pathogenic, stress-tolerant, containing mobile elements and forming biofilms phenotypes, and promoting membrane transport and signal transduction pathways. These results suggested that the effects of MPs on soil bacterial community varied depending on MPs types and sizes. However, drought significantly increased soil bacterial diversity by 10.3 % and affected soil bacterial community composition in the 20 μm PLA MPs pollution soils. We also found that drought inhibited the levels of potentially pathogenic, containing mobile elements and forming biofilms phenotypes in the 20 μm PLA MPs pollution soils. Taken together, these findings reveal that drought may alleviate the adverse effects of MPs pollution on soil bacterial community, which enhances our understanding of the interactive effects of multiple global change factors on agroecosystem functions.

Effect of microplastics on soil greenhouse gas emissions in agroecosystems: Does it depend upon microplastic shape and soil type?

Microplastics have emerged as a significant pollutant in terrestrial ecosystems, with their accumulation in agricultural fields influencing soil greenhouse gas emissions. Nevertheless, the specific impact of microplastics, particularly in relation to their varying shapes, and how this effect manifests across diverse soil types, remains largely unexplored. In this study, a 56-day incubation experiment was conducted to assess the influence of microplastic shapes (fibers, films, and spheres) on CO2 and N2O emissions in three types of soils (Chernozems, Luvisols, and Ferralsols), while also investigating potential associations with the compositional and functional characteristics of soil bacterial communities. When compared to the control group, the introduction of microplastic fibers resulted in an increase of 21.7 % in cumulative CO2 emissions and a 31.4 % rise in cumulative N2O emissions in Ferralsols. This increase was closely linked to the proliferation of the Actinobacteria and Bacilli classes and the orders of Catenulisporales, Bacillales, Streptomycetales, Micrococcales, and Burkholderiales within the bacterial communities of Ferralsols, alongside an observed elevation in N-acetyl-glucosaminidase enzyme activity. The inclusion of microplastic fibers did not result in significant alterations in greenhouse gas emissions within Chernozems and Luvisols. This is likely attributed to the inherent buffering capacity of these soils, which helps stabilize substrate and nutrient availability for microbial communities. These findings highlight that the response of greenhouse gas emissions to microplastic additions is contingent upon the shape of the microplastics and the specific soil types.

The environmental impact of mask-derived microplastics on soil ecosystems

During the COVID-19 pandemic, a significant increased number of masks were used and improperly disposed of. For example, the global monthly consumption of approximately 129 billion masks. Masks, composed of fibrous materials, can readily release microplastics, which may threaten various soil ecosystem components such as plants, animals, microbes, and soil properties. However, the specific effects of mask-derived microplastics on these components remain largely unexplored. Here, we investigated the effects of mask-derived microplastics (grouped by different concentrations: 0, 0.25, 0.5, and 1 % w/w) on soil physicochemical properties, microbial communities, growth performance of lettuce (Lactuca sativa L. var. ramosa Hort.) and earthworm (Eisenia fetida) under laboratory conditions for 80 days. Our findings suggest that mask-derived microplastics reduced soil bulk density while increasing the mean weight diameter of soil aggregates and modifying nutrient levels, including organic matter, potassium, nitrogen, and phosphorus. An increase in the abundance of denitrification bacteria (Rhodanobacteraceae) was also observed. Mask-derived microplastics were found to reduce lettuce germination, and a hormesis effect of low-concentration stimulation and high-concentration inhibition was observed on biomass, chlorophyll, and root activity. While the mortality of earthworms was not significantly affected by the mask-derived microplastics, but their growth was inhibited. Collectively, our results indicate that mask-derived microplastics can substantially impact soil properties, plant growth, and earthworm health, with potential implications for soil ecosystem functionality.

A global review on the abundance and threats of microplastics in soils to terrestrial ecosystem and human health

Soil is the source and sink of microplastics (MPs), which is more polluted than water and air. In this paper, the pollution levels of MPs in the agriculture, roadside, urban and landfill soils were reviewed, and the influence of MPs on soil ecosystem, including soil properties, microorganisms, animals and plants, was discussed. According to the results of in vivo and in vitro experiments, the possible risks of MPs to soil ecosystem and human health were predicted. Finally, in light of the current status of MPs research, several prospects are provided for future research directions to better evaluate the ecological risk and human health risk of MPs. MPs concentrations in global agricultural soils, roadside soils, urban soils and landfill soils had a great variance in different studies and locations. The participation of MPs has an impact on all aspects of terrestrial ecosystems. For soil properties, pH value, bulk density, pore space and evapotranspiration can be changed by MPs. For microorganisms, MPs can alter the diversity and abundance of microbiome, and different MPs have different effects on bacteria and fungi differently. For plants, MPs may interfere with their biochemical and physiological conditions and produce a wide range of toxic effects, such as inhibiting plant growth, delaying or reducing seed germination, reducing biological and fruit yield, and interfering with photosynthesis. For soil animals, MPs can affect their mobility, growth rate and reproductive capacity. At present epidemiological evidences regarding MPs exposure and negative human health effects are unavailable, but in vitro and in vivo data suggest that they pose various threats to human health, including respiratory system, digestive system, urinary system, endocrine system, nervous system, and circulation system. In conclusion, the existence and danger of MPs cannot be ignored and requires a global effort.

Interactive impacts of microplastics and arsenic on agricultural soil and plant traits

The ability of microplastics (MPs) to interact with environmental pollutants is currently of great concern due to the increasing use of plastic. Agricultural soils are sinks for multipollutants and the safety of biodegradable MPs in field conditions is questioned. However, still few studies have investigated the interactive effects between MPs and metals on the soil-plant system with agricultural soil and testing crops for human consumption. In this work, we tested the effect on soil and plant parameters of two common MPs, non-degradable plastic low-density polyethylene and biodegradable polymer polylactic acid at two different sizes (<250 μm and 250-300 μm) in association with arsenic (As). Lettuce (Lactuca sativa L.) was used as a model plant in a small-scale experiment lasting 60 days. Microplastics and As explained 12 % and 47 % of total variance, respectively, while their interaction explained 21 %, suggesting a higher toxic impact of As than MPs. Plant growth was promoted by MPs alone, especially when biodegradable MPs were added (+22 %). However, MPs did not affect nutrient concentrations in roots and leaves. The effect of MPs on enzyme activities was variable depending on the time of exposure (with larger effects immediately after exposure), the type and size of the MPs. On the contrary, the co-application of MP and As, although it did not change the amount of bioavailable As in soil in the short and medium term, it resulted in a significant decrease in lettuce biomass (-19 %) and root nutrient concentrations, especially when polylactic acid was applied. Generally, MPs in association with As determined the plant-soil toxicity. This work provides insights into the risk of copollution of MPs and As in agricultural soil and its phytotoxic effect for agricultural crops. However, the mechanisms of the joint effect of MP and As on plant toxicity need further investigation, especially under field conditions and in long-term experiments.

Microplastics as carriers of toxic pollutants: Source, transport, and toxicological effects

Microplastic pollution has emerged as a new environmental concern due to our reliance on plastic. Recent years have seen an upward trend in scholarly interest in the topic of microplastics carrying contaminants; however, the available review studies have largely focused on specific aspects of this issue, such as sorption, transport, and toxicological effects. Consequently, this review synthesizes the state-of-the-art knowledge on these topics by presenting key findings to guide better policy action toward microplastic management. Microplastics have been reported to absorb pollutants such as persistent organic pollutants, heavy metals, and antibiotics, leading to their bioaccumulation in marine and terrestrial ecosystems. Hydrophobic interactions are found to be the predominant sorption mechanism, especially for organic pollutants, although electrostatic forces, van der Waals forces, hydrogen bonding, and pi-pi interactions are also noteworthy. This review reveals that physicochemical properties of microplastics, such as size, structure, and functional groups, and environmental compartment properties, such as pH, temperature, and salinity, influence the sorption of pollutants by microplastic. It has been found that microplastics influence the growth and metabolism of organisms. Inadequate methods for collection and analysis of environmental samples, lack of replication of real-world settings in laboratories, and a lack of understanding of the sorption mechanism and toxicity of microplastics impede current microplastic research. Therefore, future research should focus on filling in these knowledge gaps.

Metals and microorganisms in a Maar lake sediment core indicating the anthropogenic impact over last 800 years

A closed Maar lake, receiving mostly atmospheric deposition, offers a unique setting for investigating the impact of human activities on the environment. In this study, we aimed to investigate the historical record of metals in core sediments of Maar Lake in Huguangyan (HGY), Southeast China, and elucidate the possible microbial responses to anthropogenic metal stress. Five stages were divided according to the historical record of metals and corresponding distribution of microbial community, among which Pb and Sn showed a peak value around 1760 CE, indicating the ancient mining and smelting activities. Since the 1980s, a substantial enrichment of metals such as Zn, As, Mo, Cd, Sn, Sb, and Pb was observed, due to the rapid industrial growth in China. In terms of microorganisms, Chloroflexi phylum, particularly dominated by Anaerolineales, showed significant correlations with Pb and Sn, and could potentially serve as indicator species for mining and smelting-related contamination. Desulfarculales and Desulfobacterales were found to be more prevalent in recent period and exhibited positive correlations with anthropogenic metals. Moreover, according to the multivariate regression modeling and variance decomposition analysis, Pb and Sn could regulate Anaerolineales and further pose impact on the carbon cycle; while sulfate-reducing bacteria (SRB) could response to anthropogenic metals and influence sulfur cycle. These findings provide new insights into the interaction between metals and microbial communities over human history.