Effects of Microplastics in Soil Ecosystems: Above and Below Ground

Development of Enzyme-Based Approaches for Recycling PET on an Industrial Scale

Pollution by plastics such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyurethane (PUR), polyamide (PA), polystyrene (PS), and poly(ethylene terephthalate) (PET) is now gaining worldwide attention as a critical environmental issue, closely linked to climate change. Among them, PET is particularly prone to hydrolysis, breaking down into its constituents, ethylene glycol (EG) and terephthalate (TPA). Biorecycling or bioupcycling stands out as one of the most promising methods for addressing PET pollution. For dealing with pollution by the macrosize PET, a French company Carbios has developed a pilot-scale plant for biorecycling waste PET beverage bottles into new bottles using derivatives of thermophilic leaf compost cutinase (LCC). However, this system still provides significant challenges in its practical implementation. For the micro- or nanosize PET pollution that poses significant human health risks, including cancer, no industrial-scale approach has been established so far, despite the need to develop such technologies. In this Perspective, we explore the enhancement of the low activity and thermostability of the enzyme PETase to match that of LCC, along with the potential application of microbes and enzymes for the treatment of waste PET as microplastics. Additionally, we discuss the shortcomings of the current biorecycling protocols from a life cycle assessment perspective, covering aspects such as the diversity of PET-hydrolyzing enzymes in nature, the catalytic mechanism for crystallized PET, and more. We also provide an overview of the Ideonella sakaiensis system, highlighting its ability to operate and grow at moderate temperatures, in contrast to high-temperature processes.

Connecting the Dots: Livestock Animals as Missing Links in the Chain of Microplastic Contamination and Human Health

Plastic pollution is a global diffuse threat, especially considering its fragmentation into microplastics (MPs) and nanoplastics (NPs). Since the contamination of the aquatic environment is already well studied, most studies have now focused on the soil. Moreover, the number of studies on the exposure routes and toxic effects of MNPs in humans is continuously increasing. Although MNPs can cause inflammation, cytotoxicity, genotoxicity and immune toxicity in livestock animals, which can accumulate ingested/inhaled plastic particles and transfer them to humans through the food chain, research on this topic is still lacking. In considering farm animals as the missing link between soil/plant contamination and human health effects, this paper aims to describe their importance as carriers and vectors of MNP contamination. As research on this topic is in its early stages, there is no standard method to quantify the amount and the characteristics of MNPs in different matrices. Therefore, the creation of a common database where researchers can report data on MNP characteristics and quantification methods could be helpful for both method standardization and the future training of an AI tool for predicting the most abundant/dangerous polymer(s), thus supporting policy decisions to reduce plastic pollution and perfectly fitting with One Health principles.

Discrepant responses of bacterial community and enzyme activities to conventional and biodegradable microplastics in paddy soil

The prevalence of microplastics in soil ecosystems has raised concerns about their potential effects on soil properties. As promising alternatives to conventional plastics, biodegradable plastics have been increasingly applied in agricultural activities, which may release microplastics into the soil due to incomplete degradation. Compared to conventional microplastics, biodegradable microplastics in soil may induce different impacts on soil microbial properties, which have yet to be well studied. Through a 41-day microcosm experiment, we evaluated the differential effects of conventional (polypropylene, PP) and biodegradable (polylactic acid, PLA) microplastics on the geochemical properties, enzyme activities, and microbial community structure in paddy soil. Adding PLA or PP microplastics into soil significantly increased pH values and altered the contents of carbon and nitrogen nutrients. Exposure to microplastics significantly increased the activity of fluorescein diacetate hydrolase, but had varying effects on the activities of urease, sucrase, and alkaline phosphatase depending on microplastic types and doses. The addition of microplastics also influenced the structure of soil bacterial community, with Proteobacteria, Actinobacteriota, and Acidobacteriota being the dominant phyla. Significant differences in the genera of Pseudarthrobacter, Acidothermus, Bacillus, Aquisphaera, and Massilia were observed between treatments. Results of structural equation modeling (SEM) demonstrated that changes in soil carbon and nitrogen nutrients and pH values positively affected the bacterial community, while soil bacterial community as a whole exerted a negative impact on enzyme activities. FAPRPTAX analysis showed that the addition of microplastics altered the relative abundances of functional genes related to the metabolism of cellulose decomposition and ureolysis in paddy soil. Findings of this study clearly suggest that microplastic impacts on soil geochemical and microbial properties should be an integral part of future risk assessment and that to evaluate microplastic impacts, both the concentration and polymer type must be taken into account.

Photo-oxidation of Micro- and Nanoplastics: Physical, Chemical, and Biological Effects in Environments

Micro- and nanoplastics (MNPs) are attracting increasing attention due to their persistence and potential ecological risks. This review critically summarizes the effects of photo-oxidation on the physical, chemical, and biological behaviors of MNPs in aquatic and terrestrial environments. The core of this paper explores how photo-oxidation-induced surface property changes in MNPs affect their adsorption toward contaminants, the stability and mobility of MNPs in water and porous media, as well as the transport of pollutants such as organic pollutants (OPs) and heavy metals (HMs). It then reviews the photochemical processes of MNPs with coexisting constituents, highlighting critical factors affecting the photo-oxidation of MNPs, and the contribution of MNPs to the phototransformation of other contaminants. The distinct biological effects and mechanism of aged MNPs are pointed out, in terms of the toxicity to aquatic organisms, biofilm formation, planktonic microbial growth, and soil and sediment microbial community and function. Furthermore, the research gaps and perspectives are put forward, regarding the underlying interaction mechanisms of MNPs with coexisting natural constituents and pollutants under photo-oxidation conditions, the combined effects of photo-oxidation and natural constituents on the fate of MNPs, and the microbiological effect of photoaged MNPs, especially the biotransformation of pollutants.

Machine learning prediction and interpretation of the impact of microplastics on soil properties

The annual microplastic (MP) release into soils is 4-23 times higher than that into oceans, significantly impacting soil quality. However, the mechanisms underlying how MPs impact soil properties remain largely unknown. Soil-MP interactions are complex because of soil heterogeneity and varying MP properties. This lack of understanding was exacerbated by the diverse experimental conditions and soil types used in this study. Predicting changes in soil properties in the presence of MPs is challenging, laborious, and time-consuming. To address these issues, machine learning was applied to fit datasets from peer-reviewed publications to predict and interpret how MPs influence soil properties, including pH, dissolved organic carbon (DOC), total P, NO3--N, NH4+-N, and acid phosphatase enzyme activity (acid P). Among the developed models, the gradient boost regression (GBR) model showed the highest R2 (0.86-0.99) compared to the decision tree and random forest models. The GBR model interpretation showed that MP properties contributed more than 50% to altering the acid P and NO3--N concentrations in soils, whereas they had a negligible impact on total P and 10-20% impact on soil pH, DOC, and NH4+-N. Specifically, the size of MPs was the dominant factor influencing acid P (89.3%), pH (71.6%), and DOC (44.5%) in soils. NO3--N was mainly affected by the MP type (52.0%). The NH4+-N was mainly affected by the MP dose (46.8%). The quantitative insights into the impact of MPs on soil properties of this study could aid in understanding the roles of MPs in soil systems.

Polyethylene microplastic can adsorb phosphate but is unlikely to limit its availability in soil

In plant growth experiments, the presence of microplastics (MPs) often reduces plant growth. We conducted laboratory experiments to investigate the potential of microplastics to adsorb the major soil nutrient phosphate; adsorption to MPs was then compared to adsorption to soil. Adsorption experiments used two contrasting soils, pristine high density polyethylene and artificially weathered material (the same material but exposed to 185 nm UV light for 420 h over 105 days), phosphate solutions (dissolved KH2PO4) ranging from 0.2 to 200 mg L-1 and a solid (g) to liquid (mL) ratio of 1: 150 at different values of pH (2-12) and different concentrations of background electrolyte (0.00-0.10 M NaNO3). The adsorption data were best fitted to linear and Freundlich isotherms. In initial experiments where pH was not fixed and with a background electrolyte of 0.10 M NaNO3, Kd values ranged from 3.37 to 27.65 L kg-1, log Kf from 1.21 to 1.96 and 1/n from 0.36 to 0.84. Exposure of the MP to 185 nm UV radiation led to the appearance of a C=O functional group in the MP; the partition coefficient Kd, calculated from the linear isotherm did not increase but the logKf value derived from fits to the Freundlich isotherm increased by a factor of 1.5. Kd values for soils were 3-7.5 times greater than those for MPs and log Kf values 1.1-1.7 greater. In the experiments in which initial pH and ionic strength were varied, adsorption was similar across all treatments with adsorption parameters for the higher organic content soil sometimes having the highest values and the pristine microplastic the lowest. In the desorption experiments most of the adsorbed phosphate desorbed. Overall our findings indicate that despite their ability to adsorb phosphate, MPs are unlikely to control the fate and behaviour of phosphate in soil.

Soil plastisphere interferes with soil bacterial community and their functions in the rhizosphere of pepper (Capsicum annuum L.)

With a growing number of research reports on microplastics (MPs), there is increasing concern regarding MPs-induced contamination in soil ecological systems. Notwithstanding, the interaction between the plastisphere and rhizosphere microbial hotspots in soil-plant systems, as well as the diversity and composition of plastisphere microbial communities in such systems, remain largely unexplored. This study evaluated the response of rhizosphere bacterial communities to MPs at three growth stages of pepper and examined the bacterial communities present on MPs (plastisphere). The 16 S rRNA revealed that, under the stress of MPs, the Chao1 and Shannon index of the pepper soil bacterial community decreased. Meanwhile the relative abundance of Actinobacteriota was decreased, and that of Proteobacteria was increased. Furthermore, the plastisphere serves as a unique microbial habitat (niche) that recruits the colonization of specific bacterial groups, including potential plastic-degrading bacteria and potential pathogens (e.g., Massilia and Pseudomonas). Simultaneously, the plastisphere recruits specific bacteria that may impact the rhizosphere soil bacterial communities, thus indirectly affecting plant growth. Functional prediction using PICRUSt2 revealed higher activity in the plastisphere for Metabolism of terpenoids and polyketides, Human diseases, and Xenobiotics biodegradation and metabolism. Notably, the human diseases metabolic pathway exhibited increased activity, suggesting potential ecological risks associated with pathogens. These results highlighted that the plastisphere serves as a unique microbial habitat (niche) in the soil ecological systems, recruiting specific bacteria and potentially interfering with the surrounding soil microbial community, thereby influencing the functional characteristics of the soil ecological systems.

Responses of lettuce (Lactuca sativa L.) growth and soil properties to conventional non-biodegradable and new biodegradable microplastics

Residual plastic films in soils are posing a potential threat to agricultural ecosystem. However, little is known about the impacts of microplastics (MPs) derived from biodegradable and non-biodegradable plastic films on plant-soil systems. Here, we carried out a pot experiment using soil-cultivated lettuce treated by two types of MPs, degradable poly(butylene adipate-co-terephthalate) (PBAT-MPs) and non-biodegradable polyethylene (PE-MPs). MPs resulted in different degrees of reduction in shoot biomass, chlorophyll content, photosynthetic parameters, and leaf contents of nitrogen (N), phosphorus (P), and potassium (K), accelerated accumulation of hydrogen peroxide and superoxide, and increased malondialdehyde content in lettuce leaves. Moreover, MPs obviously decreased contents of total N, nitrate, ammonium, and available K in soils, and increased available P, thus altering soil nutrient availability. MPs also significantly decreased proportions of macroaggregates, and decreased soil electrical conductivity and microbial activity. PBAT-MPs had significantly greater impacts on oxidative damage, photosynthetic rate, soil aggregation, microbial activity, and soil ammonium than those of PE-MPs. Our results suggested that MPs caused oxidative damages, nutrient uptake inhibition, soil properties alteration, ultimately leading to growth reduction, and PBAT-MPs exhibited stronger impacts. Therefore, it is urgent to further study the ecological effects of MPs, especially biodegradable MPs, on soil-plant systems.

A bibliometric analysis of global research hotspots and progress on microplastics in soil‒plant systems

Plastic pollution has become a global and persistent challenge, posing threats to ecosystems and organisms. In recent years, there has been a rapid increase in scientific research focused on understanding microplastics in the soil‒plant system. This surge is primarily driven by the direct impact of microplastics on agricultural productivity and their association with human activities. In this study, we conducted a comprehensive bibliometric analysis to provide an overview of the current research on microplastics in soil‒plant systems. We systematically analysed 192 articles and observed a significant rise in research interests since 2017. Notably, China has emerged as a leading contributor in terms of published papers, closely followed by Germany and the Netherlands. Through co-authorship network analysis, we identified 634 different institutions that participated in publishing papers in this field, with the Chinese Academy of Sciences having the most collaborations. In the co-occurrence keyword network, we identified four clusters focusing on the diversity of microplastics within the agroecosystem, transportation, and quantification of microplastics in soil, analysis of plastic contamination type and impact, and investigation of microplastic phytotoxicity. Furthermore, we identified ten research priorities, categorized into the effects of microplastics in "soil" and "plant". The research hotspots were found to be the effect of microplastics on soil physicochemical properties and the synergistic phytotoxicity of microplastics with other pollutants. Overall, this bibliometric analysis holds significant value, serving as an important reference point and offering valuable suggestions for future researchers in this rapidly advancing field.

A case on source to soil to solutions: Distribution characteristics of microplastics in farmland soil of the largest vegetable base in Northwest China

The wide application of facility agriculture accelerated the rapid development of agriculture. However, microplastics pollution in the soil caused by long-term residual agricultural film posed a significant threat to the soil ecosystem and human health. Jingyang County of Shaanxi Province was the largest vegetable planting base in northwest China. Soil samples of facility agriculture and non-facility agriculture were collected to investigate the distribution characteristics and risks of microplastics. The abundance of microplastics in Jingyang County ranged from 200.00 to 4733.33 n·kg-1, and the mean abundance was 1955.00 n·kg-1. Microplastics abundance in facility agriculture soil was higher than that in non-facility agriculture soil, and it increased with the growth of planting years. In general, the size of soil microplastics was mainly <100 μm and the abundance was negatively correlated with particle size. There were 30 types of chemical constituents in the microplastics detected, and PE (47.03 %) and PET (11.48 %) were the main ones. In addition, the types of microplastics in soil were identical with those detected in irrigation water and fertilizer, which provided another source of soil microplastics. All the sampling sites were ecological risk category I, and there was no carcinogenic risk to human health at present. In the future, the government should advocated and encouraged farmers to improve mulch recycling efficiency. Correspondingly, more positive action should be taken to the management on mulch recycling and the standards on placement of waste agricultural inputs. This study would provide foundation data for the research of microplastics pollution in farmland and the risk assessment of ecosystem and human health.

Organic amendment in climate change mitigation: Challenges in an era of micro- and nanoplastics

As a global strategy for mitigating climate change, organic amendments play critical roles in restoring stocks in carbon (C) depleted soils, preserving existing stocks to prevent further soil organic carbon (SOC) loss, and enhancing C sequestration. However, recent emerging evidence of a significant proportion of micro- and nanoplastics (M/NPs) occurrence in most organic substrates (e.g., compost manure, farmyard manure, and sewage sludge) compromises its role in climate change mitigation. Given the predicted surge of soil M/NPs proliferation in the coming years, we argued whether organic amendment remains a reliable climate change mitigation strategy. Toxicity effects of M/NPs influx within the soil matrix disrupt plants and their associated key microbial taxa responsible for crucial biogeochemical processes and restructuring of SOC, leading to increasing emissions of potent greenhouse gases (GHGs, e.g., CO2, CH4, and N2O) that feedback to aggravate the rapidly changing climate. Here, we summarize evidence based on literature that the discovery of M/NPs in organic substrates compromises its role in the climate change mitigation strategy. We briefly discuss the overview of synthetic fertilizers and their impact on SOC and atmospheric emissions. We discuss the role of organic amends in climate change mitigation and the emergence of M/NPs in it. We discuss M/NPs-induced damages to SOC and subsequent emissions of GHGs. We briefly highlight management approaches to clean organic substrates of M/NPs to improve their use in agrosystems and provide recommendations for future research studies. We found that organic amendment plays pivotal role in modulating the biotic and abiotic drivers responsible for climate mitigation. However, M/NPs in organic amendments weaken the regulatory mechanisms of organic amendments in plant-soil systems. We conclude that organic amendments of soils are critical for restoring SOC and mitigating the rapidly changing climate; yet, the discovery of M/NPs in organic substrates put their usage in a dilemma.

Uptake and transport of micro/nanoplastics in terrestrial plants: Detection, mechanisms, and influencing factors

The pervasive dispersion of micro/nanoplastics in various environmental matrices has raised concerns regarding their potential intrusion into terrestrial ecosystems and, notably, plants. In this comprehensive review, we focus on the interaction between these minute plastic particles and plants. We delve into the current methodologies available for detecting micro/nanoplastics in plant tissues, assess the accumulation and distribution of these particles within roots, stems, and leaves, and elucidate the specific uptake and transport mechanisms, including endocytosis, apoplastic transport, crack-entry mode, and stomatal entry. Moreover, uptake and transport of micro/nanoplastics are complex processes influenced by multiple factors, including particle size, surface charge, mechanical properties, and physiological characteristics of plants, as well as external environmental conditions. In conclusion, this review paper provided valuable insights into the current understanding of these mechanisms, highlighting the complexity of the processes and the multitude of factors that can influence them. Further research in this area is warranted to fully comprehend the fate of micro/nanoplastics in plants and their implications for environmental sustainability.

Microplastic pollution in terrestrial ecosystems: Global implications and sustainable solutions

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

Polystyrene microplastics accumulation in lab-scale vertical flow constructed wetlands: impacts and fate

Microplastics (MPs) are ubiquitous pollutants that significantly threaten organisms and ecosystems. Constructed wetlands (CWs), a nature-based treatment technology, can effectively remove MPs from wastewater. However, the responses of CWs when exposed to MPs remain unclear. In this study, lab-scale vertical flow constructed wetlands (VFCWs) were installed for receiving polystyrene (PS) MPs at concentrations of 100 μg/L and 1000 μg/L. The results showed that exposure to PS-MPs has no effects on COD and TP removal in VFCWs, but TN removal decreased by 3.69-5.37 %. Further investigation revealed that PS-MPs significantly impacted microbial communities and metabolic functions. The abundances of predominant nitrifiers (Nitrospira and Nitrosomonas) and denitrifiers (Nakamurella, Bradyrhizobium, and Bacillus) in VFCWs were significantly reduced, aligning with the responses of key enzymes. The presence of PS-MPs also decreased nitrogen removal by plant uptake, leading to decreased plant biomass and chlorophyll by 39.32-48.75 % and 5.92-32.19 %, respectively. Notably, > 90 % removal rates were observed for PS-MPs within VFCWs. In addition to PS-MPs interception by VFCWs substrate, the increase of released benzenes indicated that the PS-MPs biodegradation occurred. Such insights are vital for developing sustainable solutions to mitigate MPs' adverse effects on ecosystems.

Soils in distress: The impacts and ecological risks of (micro)plastic pollution in the terrestrial environment

Plastics have revolutionised human industries, thanks to their versatility and durability. However, their extensive use, coupled with inadequate waste disposal, has resulted in plastic becoming ubiquitous in every environmental compartment, posing potential risks to the economy, human health and the environment. Additionally, under natural conditions, plastic waste breaks down into microplastics (MPs<5 mm). The increasing quantity of MPs exerts a significant burden on the soil environment, particularly in agroecosystems, presenting a new stressor for soil-dwelling organisms. In this review, we delve into the effects of MP pollution on soil ecosystems, with a specific attention to (a) MP transport to soils, (b) potential changes of MPs under environmental conditions, (c) and their interaction with the physical, chemical and biological components of the soil. We aim to shed light on the alterations in the distribution, activity, physiology and growth of soil flora, fauna and microorganisms in response to MPs, offering an ecotoxicological perspective for environmental risk assessment of plastics. The effects of MPs are strongly influenced by their intrinsic traits, including polymer type, shape, size and abundance. By exploring the multifaceted interactions between MPs and the soil environment, we provide critical insights into the consequences of plastic contamination. Despite the growing body of research, there remain substantial knowledge gaps regarding the long-term impact of MPs on the soil. Our work underscores the importance of continued research efforts and the adoption of standardised approaches to address plastic pollution and ensure a sustainable future for our planet.

Plastic residues alter soil microbial community compositions and metabolite profiles under realistic conditions

Wide usage of plastic coupled with mismanagement has created a humongous environmental hazard threatening entire ecosystems. To date, the potential effects of plastic debris-induced soil nutrition substance changes and the relevant microbial metabolic behavior remain unclear. Here, we studied the effect of plastic films polyethylene and polylactic acid in differential soil environments (farmland, woodland, and wetland) for 120 days. Soil enzyme activities (urease, neutral phosphatase, and catalase) and nutrition substance (NH4+-N, available P, available K, and soil organic matter) present obvious variations in polylactic acid groups compared to polyethylene-treated samples. 16S rRNA gene sequencing indicates that several bacteria abundance such as Bacteroidales, Actinobacteriota, Nitrososphaeraceae, Pyrinomonadalcs, Muribaculaceae, exhibited obvious up-regulation or down-regulation, and simultaneously, the carbon, nitrogen, and phosphorus cycling relevant species Bryobacter, Bradyrhizobium, and Sphingomonas, expressed wider margin of down-regulation in abundance in plastic treatment soil samples. As a result, the abundance of metabolites including sugar, amino acid, and fatty acids, which may associated with nutrition substance metabolic pathways, were significantly altered in the stress of plastic. These findings provide valuable information on the environmental effects of plastics, and the relationships of subsequent nutrition substance changes and microbial metabolic behavior.

Alleviation of microplastic toxicity in soybean by arbuscular mycorrhizal fungi: Regulating glyoxalase system and root nodule organic acid

Microplastic accumulation in the soil-plant system can stress plants and affect products quality. Currently, studies on the effect of microplastics on plants are not consistent and underlying molecular mechanisms are yet unknown. Here for the first time, we performed a study to explore the molecular mechanism underlying the growth of soybean plants in soil contaminated with various types of microplastics (PS and HDPE) and arbuscular mycorrhizal fungi (AMF) (presence/absence). Our results revealed that a dose-dependent decline was observed in plant growth, chlorophyll content, and yield of soybean under MPs stress. The addition of MPs resulted in oxidative stress closely related to hydrogen peroxide generation (H2O2), methylglyoxal (MG) levels, lipid peroxidation (MDA), and lipoxygenase (LOX). In contrast, MPs addition enhanced mycorrhizal colonization and dependency relative to control while the rubisco and root activity declined. All the genes (GmHMA13 and GmHMA19) were downregulated in the presence of MPs except GmHMA18 in roots. AMF inoculation alleviated MPs-induced phytotoxic effects on colonization, rubisco activity, root activity and restored the growth of soybean. Under MPs exposure, AMF inoculation induced plant defense system via improved regulation of antioxidant enzymes, ascorbate, glutathione pool, and glyoxalase system. AMF upregulated the genes responsible for metals uptake in soybean under MPs stress. The antioxidant and glyoxalase systems coordinated regulation expressively inhibited the oxidative and carbonyl stress at both MPs types. Hence, AMF inoculation may be considered an effective approach for minimizing MPs toxicity and its adverse effects on growth of soybean grown on MPs-contaminated soils.

Biochar Mitigates the Negative Effects of Microplastics on Sugarcane Growth by Altering Soil Nutrients and Microbial Community Structure and Function

Microplastic pollution in sugarcane areas of China is severe, and reducing the ecological risks is critical. Biochar has been widely used in soil remediation. This study aims to explore the effects and mechanisms of microplastics combined with or without biochar on sugarcane biomass, soil biochemical properties in red soil through a potted experiment. The results show that, compared with control (CK), treatments with microplastics alone reduced the dry biomass of sugarcane, soil pH, and nitrogen (N) and phosphorus (P) contents by an average of 8.8%, 2.1%, 1.1%, and 2.0%, respectively. Interestingly, microplastics combined with biochar could alleviate the negative effects of microplastic accumulation on sugarcane growth and soil quality. There were significant differences in the bacterial community alpha diversity indices and compositions among different treatments. Compared with CK, treatments with microplastics alone obviously decreased the observed operational taxonomic units (OTUs) and the Chao1 and Shannon indices of soil total bacteria (16S rRNA gene-based bacteria) while increasing them in phoD-harboring bacteria. Microplastics combined with biochar treatments significantly increased the abundance of Subgroup_10 for the 16S rRNA gene and treatments with microplastics alone significantly increased the relative abundance of Streptomyces for the phoD gene compared to CK. Moreover, compared with microplastics alone, the treatments with microplastics combined with biochar increased the relative abundance of Subgroup_10, Bacillus, Pseudomonas in soil total bacteria, and Amycolatopsis and Bradyrhizobium in phoD-harboring bacteria, most of which can inhibit harmful bacteria and promote plant growth. Additionally, different treatments also changed the abundance of potential microbial functional genes. Compared to CK, other treatments increased the abundance of aerobic ammonia oxidation and denitrification but decreased the abundance of nitrate respiration and nitrogen respiration; meanwhile, these four functional genes involved in N cycling processes were obviously higher in treatments with microplastics combined with biochar than in treatments with microplastics alone. In conclusion, microplastics combined with biochar could alleviate the negative effects of microplastic accumulation on sugarcane biomass by altering soil nutrients and microbial community structure and function.

Nano-Iron Oxide (Fe3O4) Mitigates the Effects of Microplastics on a Ryegrass Soil-Microbe-Plant System

To understand microplastic-nanomaterial interactions in agricultural systems, a randomized block 90-day pot experiment was set up to cultivate ryegrass seedings in a typical red sandy soil amended with compost (1:9 ratio). Polyvinyl chloride (PVC) and polyethylene (PE) microplastic (MP) contaminants were added into pot soils at 0.1 and 10%, whereas nano-Fe3O4 (as nanoenabled agrochemicals) was added at 0.1% and 0.5% in comparison with chemical-free controls. The combination of nano-Fe3O4 and MPs significantly increased the soil pH (+3% to + 17%) but decreased the total nitrogen content (-9% to - 30%; P < 0.05). The treatment group with both nano-Fe3O4 and PE had the highest total soil C (29 g kg-1 vs 20 g kg-1 in control) and C/N ratio (13 vs 8 in control). Increased rhizosphere nano-Fe3O4 concentrations promoted ryegrass growth (+42% dry weight) by enhancing the chlorophyll (+20%) and carotenoid (+15%) activities. Plant leaf and root peroxidase enzyme activity was more significantly affected by nano-Fe3O4 with PVC (+15%) than with PE (+6%). Nano-Fe3O4 significantly changed the ryegrass bacterial community structure from belowground (the rhizoplane and root endosphere) to aboveground (the phylloplane). Under MP contamination, the addition of nano-Fe3O4 increased bacterial diversity (+0.35%) and abundance (+30%) in the phylloplane and further intensified the connectivity of ryegrass aboveground bacterial networks (positive association increased 17%). The structural equation model showed that the change in the plant microbiome was associated with the rhizosphere microbiome. Overall, these findings imply the positive influences of nano-Fe3O4 on the soil-microbe-plant system and establish a method to alleviate the harmful effects of MP accumulation in soils.

Microplastics sequestered in the soil affect the turnover and stability of soil aggregates: A review

Plastic products have become ubiquitous in society, and entered various ecosystems due to the massive scale of production. The United Nations Environment Program (UNEP) has listed microplastics (MPs), which form when plastic remnants degrade, as a global emerging pollutant, and the association between soil pollution and MPs has become a popular research topic. This paper systematically reviews research focusing on MP-related soil pollution from the past 10 years (2012-2022), with the identified papers demonstrating that interactions between MPs and soil aggregates has become a research frontier in the field. The presented research provides evidence that soil aggregates are important storage sites for MPs, and that storage patterns of MPs within soil aggregates are influenced by MP characteristics. In addition, MPs affect the formation, turnover, and stability of soil aggregates through the introduction of fracture points along with diverse physicochemical characteristics such as composition and specific surface area. The current knowledge base includes certain issues and challenges that could be addressed in future research by extending the spatial and temporal scales over which microplastic-soil aggregate interactions are studied, unifying quantitative and qualitative methods, and tracing the fates of MPs in the soil matrix. This review contributes to enriching our understanding of how terrestrial MPs interact with soil aggregates, and whether they pose a risk to soil health.

Advances on micro/nanoplastics and their effects on the living organisms: A review

Micro/nanoplastics (MPs) are attracting increasing attention owing to the potential threats they pose to the sustainability of the environment and the health of living organisms. Thus, a comprehensive understanding of the influence of MPs on living organisms is vital for developing countermeasures. We conducted an extensive literature search to retrieve the articles related to MPs via the Web of Science. Accordingly, 152 articles published in the last decade and in influential journals were selected to analyze the effects of MPs on plants, animals, microorganisms, and humans as well as the current status, hotspots, and trends of studies on MPs. The results showed that owing to the special characteristics of MPs and anthropogenic activities, MPs have become ubiquitous worldwide. MPs are ingested by plants and animals and enter the human body through various pathways, resulting in numerous adverse effects, such as growth inhibition, oxidative stress, inflammation, organ damage, and germ cell lesions. Moreover, they affect microorganisms by reshaping the structure and function of microbial communities and changing the spread pathway. However, microorganisms can also contribute to the degradation of MPs. With increasing evidence of the adverse effects of MPs on biota, coping with MP pollution and mitigating harmful outcomes have emerged as major challenges. This review focuses on (1) the main effects of MPs on living organisms, ranging from microorganisms to humans, (2) the current status and hotspots of studies related to MPs, and (3) the challenges and prospects of further studies on MPs.

A critical review of the recent trends in source tracing of microplastics in the environment

Microplastics are found across the globe because of their size and ability to transport across environments. The effects of microplastics on the micro- and macro-organisms have brought out concern over the potential risk to human health and the need to regulate their distribution at the source. Control of microplastic pollution requires region-specific management and mitigation strategies which can be developed with the information on sources and their contributions. This review provides an overview of the sources, fate, and distribution of microplastics along with techniques to source-trace microplastics. Source-tracing approaches provide both qualitative and quantitive information. Since better outcomes have been produced by the integration of techniques like backward trajectory analysis with cluster analysis, the significance of integrated and multi-dimensional approaches has been emphasized. The scope of the plastisphere, heavy metal, and biofilm microbial community in tracing the sources of microplastics are also highlighted. The present review allows the researchers and policymakers to understand the recent trends in the source-tracing of microplastics which will help them to develop techniques and comprehensive action plans to limit the microplastic discharge at sources.

Chemical features and biological effects of degradation products of biodegradable plastics in simulated small waterbody environment

A plethora of research has focused on the biosafety of biodegradable plastics (BPs), including their microplastic formation and additives leaching; however, relatively fewer studies have explored biodegradation products. This study aims to investigate the biological effects and chemical features of degradation products from three kinds of BPs, namely polyglycolic acid (PGA), poly (butylene adipate-co-terephthalate) (PBAT), and the blends of PGA/PBAT without the addition of additives, in a simulated small waterbody environment with extracted soil solution for three months. Results showed that exposure to the whole degradation remnants of three BPs had no lethal effects on zebrafish at the current BP environmental concentrations (from 0.24 to 12.72 mg plastic/L) in small waterbodies. However, from the calculated BPs environmental concentrations (from 0.57 to 43.82 mg plastic/L) in 2026, PGA and PGA/PBAT blends may cause adverse effects on the cardiovascular system such as heartbeat rate suppression in zebrafish embryos, and also lead to reduced body length and pericardial edema and spinal curvature in fish larvae. We further qualitatively analyzed the composition of degradation products, and quantitatively measured four dominant degradation monomers (glycolic acid (GA), adipic acid (A), 1,4-butanediol (B), and terephthalic acid (T)) in the degradation remnants. It was found that the observed toxicities were probably due to the presence of GA, A, and T monomers, and their concentrations can reach 0.776, 0.034, and 0.6 mg/L under the calculated future scenario, respectively. It is worth mentioning that either GA or T monomers at the above concentrations were found to cause suppressed heartbeat rate in zebrafish embryos. Collectively, though the degradation products of BPs are temporarily safe at current environmental concentrations, they may lead to non-negligible toxicity with increasing production and continual improper recycling and/or BP waste management.

A review of the occurrence and degradation of biodegradable microplastics in soil environments

The use of plastics for manufacturing of products and packaging has become ubiquitous. This is because plastics are cheap, pliable, and durable. However, these characteristics of plastics have also led to their disposal in landfill, where they persist. To overcome the environmental challenge posed by conventional plastics (CPs), biodegradable plastics (BDPs) are increasingly being used. However, BDPs form residual microplastics (MPs) at a rate that far exceeds that of CPs, and MPs have negative impacts on the soil environment. This review aimed to evaluate whether the move away from CPs to BDPs is having an overall positive impact on the environment considering the formation of MPs. Topics focused on in this review include the degradation of BDPs in the soil environment and the impacts of MPs originating from BDPs on soil physical and chemical properties, microbial communities, animals, and plants. The information collated in this review can provide scientific guidance for sustainable development of the BDPs industry.

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

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

Elicitation of E-waste (acrylonitrile-butadiene styrene) enriched soil bioremediation and detoxification using Priestia aryabhattai MGP1

Given the rise in both usage and disposal of dangerous electronics, there is a catastrophic rise in assemblage of electronic waste (e-waste). E-waste including various plastic resins are among the most frequently discarded materials in electronic gadgets. In current digital era, managing e-waste has become universal concern. From the viewpoint of persisting lacuna of e-waste managing methods, the current study is designed to fabricate an eco-friendly e-waste treatment with native soil bacteria employing an enrichment culture method. In the presence of e-waste, indigenous soil microbes were stimulated to degrade e-waste. Microbial cultures were isolated using enrichment medium containing acrylonitrile-butadiene styrene (ABS) as the primary carbon source. Priestia aryabhattai MGP1 was found to be the most dominant e-polymer degrading bacterial isolate, as it was reported to degrade ABS plastic in disposed-off television casings. Furthermore, to increase degradation potential of MGP1, Response Surface Methodology (RSM) was adopted which resulted in optimized conditions (pH 7, shaking-speed 120 rpm, and temperature 30 °C), for maximum degradation (18.88%) after 2 months. The structural changes induced by microbial treatment were demonstrated by comparing the findings of Field emission scanning electron microscopy (FESEM) images and Fourier Transform Infrared (FTIR) spectra confirming the disappearance of ≡ C─H peaks along with C-H, C=C and C ≡N bond destabilization following degradation. Energy-dispersive X-ray (EDX) analyzers of the native and decomposed e-polymer samples revealed a considerable loss in elemental weight % of oxygen by 8.4% and silica by 0.5%. Magnesium, aluminium and chlorine which were previously present in the untreated sample, were also removed after treatment by the bacterial action. When seeds of Vigna radiata were screened using treated soil in the presence of both e-waste and the chosen potent bacterial strain, it was also discovered that there was reduced toxicity in terms of improved germination and growth metrics as a phytotoxicity criterion.

Microplastics reduced bioavailability and altered toxicity of phenanthrene to maize (Zea mays L.) through modulating rhizosphere microbial community and maize growth

Due to its large specific surface area and great hydrophobicity, microplastics can adsorb polycyclic aromatic hydrocarbons (PAHs), affecting the bioavailability and the toxicity of PAHs to plants. This study aimed to evaluate the effects of D550 and D250 (with diameters of 550 μm and 250 μm) microplastics on phenanthrene (PHE) removal from soil and PHE accumulation in maize (Zea mays L.). Moreover, the effects of microplastics on rhizosphere microbial community of maize grown in PHE-contaminated soil would also be determined. The results showed that D550 and D250 microplastics decreased the removal of PHE from soil by 6.5% and 2.7% and significantly reduced the accumulation of PHE in maize leaves by 64.9% and 88.5%. Interestingly, D550 microplastics promoted the growth of maize and enhanced the activities of soil protease and alkaline phosphatase, while D250 microplastics significantly inhibited the growth of maize and decreased the activities of soil invertase, alkaline phosphatase and catalase, in comparison with PHE treatment. In addition, microplastics changed the rhizosphere soil microbial community and reduced the relative abundance of PAHs degrading bacteria (Pseudomonas, Massilia, Proteobacteria), which might further inhibit the removal of PHE from soil. This study provided a new perspective for evaluating the role of microplastics on the bioavailability of PHE to plants and revealing the combined toxicity of microplastics and PHE to soil microcosm and plant growth.

Dose-dependent toxicity of polyethylene microplastics (PE-MPs) on physiological and biochemical response of blackgram and its associated rhizospheric soil properties

Microplastic contamination in terrestrial ecosystem is emerging as a global threat due to rapid production of plastic waste and its mismanagement. It affects all living organisms including plants. Hence, the current study aims at understanding the effect of polyethylene microplastics (PE-MPs) at different concentrations (0, 0.25, 0.50, 0.75, and 1.00% w/w) on the plant growth and yield attributes. With blackgram as a test crop, results revealed that a maximum reduction in physiological traits like photosynthetic rate; chlorophyll a, b; and total chlorophyll by 5, 14, 10, and 13% at flowering stage; and an increase in biochemical traits like ascorbic acid, malondialdehyde, proline, superoxide dismutase, and catalase by 11, 29.7, 16, 22, and 30% during vegetative stage was observed with 1% PE-MP application. Moreover, a reduction in growth and yield attributes was also observed with increasing concentration of microplastics. Additionally, application of 1% PE-MPs decreased the soil bulk density, available phosphorus, and potassium, whereas the EC, organic carbon, microbial biomass carbon, NO3-N, and NH4-N significantly increased. Moreover, the presence of PE-MPs in soil also had a significant influence on the soil enzyme activities. Metagenomic analysis (16 s) reveals that at genus level, Bacillus (19%) was predominant in control, while in 1% PE-MPs, Rubrobacter (28%) genus was dominant. Microvirga was found exclusively in T5, while the relative abundance of Gemmatimonas declined from T1 to T5. This study thus confirms that microplastics exert a dose-dependent effect on soil and plant characteristics.

Micro (nano) plastics uptake, toxicity and detoxification in plants: Challenges and prospects

Plastic pollution has emerged as a global challenge affecting ecosystem health and biodiversity conservation. Terrestrial environments exhibit significantly higher plastic concentrations compared to aquatic systems. Micro/nano plastics (MNPs) have the potential to disrupt soil biology, alter soil properties, and influence soil-borne pathogens and roundworms. However, limited research has explored the presence and impact of MNPs on aquaculture systems. MNPs have been found to inhibit plant and seedling growth and affect gene expression, leading to cytogenotoxicity through increased oxygen radical production. The article discusses the potential phytotoxicity process caused by large-scale microplastics, particularly those unable to penetrate cell pores. It also examines the available data, albeit limited, to assess the potential risks to human health through plant uptake.

Shifting enzyme activity and microbial composition in sediment coregulate the structure of an aquatic plant community under polyethylene microplastic exposure

It has been shown that microplastics (MPs) interfere with critical biological processes (including development, growth and fitness); however, there is no information about the impact of MPs on plant productivity and community structure in freshwater ecosystems. Here, we investigated the effects of two sizes (MIC: 20-300 μm, MAC: 2-3 mm) and three concentrations (0.03 %, 0.3 %, and 0.6 %) of low-density polyethylene MPs on submerged plant communities. The results showed that plant responses to MPs were species specific, which can affect plant community structure. For canopy-forming species (Hydrilla verticillata), total biomass increased by 4 %-46 % and relative abundance increased by 23 %-34 % under MP exposure, while rosette-forming species (Vallisneria natans) decreased by 44 %-67 % in total biomass and relative abundance decreased by 54 %-71 %. Myriophyllum spicatum growth was largely unaffected by MPs. Community diversity was negatively correlated with MAC treatments, and the community root to shoot ratio decreased by 40 %, while community productivity increased by 41 % at a 0.6 % MAC concentration. Although MPs did not change the microbial community composition, alpha diversity was reduced at the 0.6 % concentration. It is worth noting that 0.6 % is a higher concentration than most field sediment investigations. During the experiment, the activity of functional enzymes related to carbon and nitrogen increased under most MP treatments. Structural equation modelling showed that MIC changed the community structure mainly by driving sediment enzyme activity, while MAC changed the community structure mainly by driving plant growth. The results implied that MPs may affect sediment enzymatic activities, microbial alpha diversity and aquatic plant growth, potentially altering the diversity and stability of aquatic ecosystems.

Microplastic accumulation in bivalves collected from different coastal areas of Vietnam and an assessment of potential risks

Microplastic (MP) pollution is an emerging problem in many areas around the world and in coastal areas of Vietnam, requiring more studies dedicated to the accumulation of this pollutant in the food chain as well as its potential risk to human health. This study investigated MP levels in tissues of five common bivalve species collected from aquaculture areas along the coast of Vietnam. MPs were found in all bivalve samples, with average values of 10.84 ± 2.61 items/individual or 2.40 ± 1.34 items/g wet weight. Impacts of feeding habits of bivalves showed influences on MP abundance in the samples. Fibers were the dominant shape of MPs recorded, most of which accumulated in the gills and digestive glands of all bivalve samples, with the majority falling within the size range of 300-2000 µm. MPs found in all studied species had relatively similar chemical compositions, mainly composed of polypropylene (PP) and polyethylene (PE). In this study, a diverse diet consisting of different bivalve species and detailed data on the consumption rate of these species were used to assess the human health risk of MPs dedicated to the coastal communities of Vietnam. The results suggested a significant part of MP uptake by human could be via bivalve consumption, in which removing viscera and proper depuration should be applied prior to eating, thereby reducing the risk.

Nano-microplastic and agro-ecosystems: a mini-review

Plastics' unavoidable and rampant usage causes their trash to be extensively dispersed in the atmosphere and land due to its numerous characteristics. Because of extensive plastic usage and increased manufacturing, there is insufficient recycling and a large accumulation of microplastics (MPs) in the environment. In addition to their wide availability in the soil and atmosphere, micro- and nanoplastics are becoming contaminants worldwide. Agro-ecosystem functioning and plant development are being negatively impacted in several ways by the contamination of the environment and farmland soils with MPs (<5 mm) and nanoplastics (<1 µm). The contributions of some recyclable organic waste and plastic film mulching and plastic particle deposition in agroecosystems may be substantial; therefore, it is crucial to understand any potentially hazardous or undesirable impacts of these pollutants on agroecosystems. The dissolution of bioplastics into micro- and nano-particles (MBPs and NBPs) has not been considered in recent studies, which focus primarily on agro-ecosystems. It is essential to properly understand the distribution, concentration, fate, and main source of MPs, NPS, MBPs, and NBPs in agroecosystems. Based on the limited findings, understanding the knowledge gap of environmental impact from micro and nanoplastic in farming systems does not equate to the absence of such evidence. It reveals the considerations for addressing the gaps to effectively protect global food safety and security in the near future.

Nutrient enrichment mediates the effect of biodegradable and conventional microplastics on macroinvertebrate communities

There is growing concern regarding the lack of evidence on the effects bioplastics may have on natural ecosystems, whilst their production continues to increase as they are considered as a greener alternative to conventional plastics. Most research is limited to investigations of the response of individual taxa under laboratory conditions, with few experiments undertaken at the community or ecosystem scale, either investigating microplastics independently or in combination with other pollutants, such as nutrient enrichment. The aim of this study is to experimentally compare the effects of oil-based (high density polyethylene - HDPE) with those of bio-based biodegradable (polylactic acid - PLA) microplastics and their interaction with nutrient enrichment on freshwater macroinvertebrate communities under seminatural conditions. There were no significant differences in total abundance, alpha and beta diversities, or community composition attributable to the type of microplastics, their concentration, or nutrient enrichment compared with the control. However, there was a significant difference in macroinvertebrate alpha diversity between high concentrations of both microplastic types under ambient nutrient conditions, with lower diversity in communities exposed to HDPE compared with PLA. Nutrient enrichment mediated the effect of microplastic type, such that the diversity of macroinvertebrate communities exposed to HDPE were similar to those communities exposed to PLA. These findings suggest that the effects of microplastic pollution on macroinvertebrate communities are very weak at large-scale settings under seminatural conditions and that these effects might be mediated by the nutrient status of freshwater ecosystems. More research under large-scale, long-term, seminatural settings are needed in order to elucidate the impact of both conventional plastics and bioplastics on natural environments and their interactive effect with other occurring stressors and pollutants.

Ecological risks of microplastics contamination with green solutions and future perspectives

The rise of plasticulture as mulching material in farming systems has raised concerns about microplastics (MPs) in the agricultural landscape. MPs are emerging pollutants in croplands and water systems with significant ecological risks, particularly over the long term. In the soil systems, MPs polymer type, thinness, shape, and size induces numerous effects on soil aggregates, dissolved organic carbon (C), rapidly oxidized organic C, microbial biomass C, microbial biomass nitrogen (N), microbial immobilization, degradation of organic matter, N cycling, and production of greenhouse gas emissions (GHGs), thereby posing a significant risk of impairing soil physical and biochemical properties over time. Further, toxic chemicals released from polyethylene mulching (PMs) might indirectly harm plant growth by affecting soil wetting-drying cycles, releasing toxic substances that interact with soil matrix, and suppressing soil microbial activity. In the environment, accumulation of MPs poses a risk to human health by accelerating emissions of GHGs, e.g., methane and carbon dioxide, or directly releasing toxic substances such as phthalic acid esters (PAEs) into the soils. Also, larger sizes MPs can adhere to root surface and block stomata could significantly change the shape of root epidermal cells resulting in arrest plant growth and development by restricting water-nutrient uptake, and gene expression and altering the biodiversity of the soil pollutants. In this review, we systematically analyzed the potential risks of MPs to the soil-plant and human body, their occurrence, abundance, and migration in agroecosystems. Further, the impacts of MPs on soil microbial function, nutrient cycling, soil C, and GHGs are mechanistically reviewed, with emphasis on potential green solutions such as organic materials amendments along with future research directions for more eco-friendly and sustainable plastic management in agroecosystems.

Unveiling the effect of microplastics on agricultural crops - a review

Microplastics (MPs), ever since they were identified as a potential and widely distributed persistent contaminant, the number of studies highlighting their impacts on various terrestrial ecosystems have been increasing. Recently, the effect of MPs on the agricultural ecosystem has gained momentum. Hence, the present review examines the impact of microplastics on agricultural crop systems and the mechanism underlying its toxicity. The current review revealed that most of the studies were conducted at a laboratory scale and under controlled conditions. Additionally, it was observed that polystyrene (PS) followed by polyethylene (PE) are the most studied polymer type, while the most studied plants are wheat and maize. Hitherto, literature studies suggest that the microplastics' influence on plant growth can be negative or sometimes neutral; while in some cases it exerts a hormetic effect which depends on other factors determining plant growth. Notably, the main mechanisms through which microplastics influence plant growth are mechanical damage, alteration of soil properties, or by leaching of additives. Overall, with burgeoning research interest in this aspect, the current review has significant implications for the toxicity of MPs on plants and throws light on the need to develop novel guidelines toward the sustainable use of plastics in agricultural sector. However, realistic field-level studies and estimating the MPs concentration at various region are essential to develop remediation approaches. Future studies should also focus on translocation and accumulation of micron sized MPs in edible portion of crops and their effect on food safety.

Accumulation and migration of microplastics and its influencing factors in coastal saline-alkali soils amended with sewage sludge

Coastal saline-alkali soil can be transformed to agricultural soil with sewage sludge amendment. However, sewage sludge contains a large number of microplastics (MPs), and the fate of MPs in sludge-treated saline-alkali soil needs to be studied. Therefore, we investigated the accumulation and migration of MPs, and their influencing factors in saline-alkali soil after one-time sewage sludge application (0, 25, 50, 100 and 200 t ha-1 SSA). The results indicated that sewage sludge input contributed to MP accumulation in soil, and the MP abundance in 20-40 cm soil was significantly lower than that in 0-20 cm soil. Fragments and fibers were the most abundant MPs in soil, and the proportions of fragments and 50-200 µm MPs in 20-40 cm soil were lower than those in 0-20 cm soil, while the < 50 µm MP proportion was higher than that in 0-20 cm soil. Correlation analysis showed that MP accumulation rate (0-40 cm) and migration rate (20-40 cm) were negatively correlated with soil organic matter (SOM) content and SSA, but positively correlated with soil pH. Stepwise regression analysis further showed that SOM and SSA were the main factors affecting MP accumulation rate, which explained 47.7% and 46% of its variation, respectively, while pH was the crucial factor affecting the migration rate of MPs, followed by EC and SSA. In conclusion, SSA caused MP accumulation in saline-alkali soil, and SSA primarily affected the MP abundance, while soil OM, pH and EC directly affected MP migration in soil.

Status, characteristics, and ecological risks of microplastics in farmland surface soils cultivated with different crops across mainland China

Microplastics (MPs) in agricultural soils could affect the safety of food crops. However, most relevant studies have paid scant attention to the crop fields and focused more on MPs in farmlands with or without film mulching in different regions. To detect MPs, we investigated farmland soils with >30 typical crop species from 109 cities in 31 administrative districts across mainland China. The relative contributions of different MP sources in different farmlands were estimated in detail based on a questionnaire survey, and we also assessed the ecological risks of MPs. Our results indicated the order of MP abundances in farmlands with different crop types, namely fruit fields > vegetable fields > mixed crop fields > food crop fields > cash crop fields. For the detailed sub-types, the highest MP abundance was detected in grape fields, which was significantly higher than that in solanaceous & cucurbitaceous vegetable fields (ranked second, p < 0.05), whereas the MP abundance was lowest in cotton and maize fields. The total contributions of three potential sources, namely livestock and poultry manure, irrigation water, and atmospheric deposition to MPs, varied depending on the crop types in the farmlands. Owing to exposure to MPs, the potential ecological risks to agroecosystems across mainland China were not negligible, particularly in fruit fields. The results of the current study could provide basic data and background information for future ecotoxicological studies and relevant regulatory strategies.

Sulfurization alters phenol-formaldehyde resin microplastics redox property and their efficiency in mediating arsenite oxidation

Microplastics weathering by various types of oxidants in the oxic environment and their interaction with environmental contaminants have drawn numerous scientific attention. However, the environmental fate of microplastics under a reducing environment has been largely unresolved. Herein, the change of physicochemical and redox properties of microplastics during the weathering under a sulfate-reducing environment and the interaction with arsenite were addressed. The sulfurization of phenol-formaldehyde resin microplastics under a sulfate-reducing environment generated smooth and porous particles with the induction of organic S species. Multiple spectroscopic results demonstrated thioether and thiophene groups formed by the substitute removal of O-containing functional groups. Moreover, the sulfurization process induced the reduction of carbonyl groups and oxidation of phenolic hydroxyl groups and resulted in the formation of semiquinone radicals. The O-containing functional groups contributed to microplastics redox property and As(III) oxidation while S-containing functional groups showed no obvious effect. The sulfurized microplastics had lower efficiency in mediating arsenite oxidation than the unsulfurized counterparts due to the decreased electron donating capacity. Producing hydrogen peroxides by electron-donating phenol groups and semiquinone radicals and the direct semiquinone radicals oxidation could mediate arsenite oxidation. The findings of this study help us understand the fate of microplastics in redox fluctuation interfaces.

Negative effects of EPDM microplastic and cork granules on plant growth are mitigated by earthworms and likely caused by their structural properties

Soil microplastic pollution can have negative effects on organisms, including plants, but the underlying mechanisms are not fully understood. We tested whether structural or chemical properties of a microplastic cause its effects on plant above- and belowground growth and whether these effects can be influenced by earthworms. We conducted a factorial experiment in a greenhouse with seven common Central European grassland species. Microplastic granules of the synthetic rubber ethylene propylene diene monomer (EPDM),1 a frequently used infill material of artificial turfs, and cork granules with a comparable size and shape to the EPDM granules were used to test for structural effects of granules in general. To test for chemical effects, EPDM-infused fertilizer was used, which should have contained any leached water-soluble chemical components of EPDM. Two Lumbricus terrestris individuals were added to half of the pots, to test whether these earthworms modify effects of EPDM on plant growth. EPDM granules had a clear negative effect on plant growth, but since cork granules had a negative effect of similar magnitude, with an average decrease in biomass of 37 % in presence of granules, this is likely due to the structural properties of granules (i.e., size and shape). For some belowground plant traits, EPDM had a stronger effect than cork, which shows that there must be other factors playing into the effects of EPDM on plant growth. The EPDM-infused fertilizer did not have any significant effect on plant growth by itself, but it had in interaction with other treatments. Earthworms had an overall positive effect on plant growth and mitigated most of the negative effects of EPDM. Our study shows that EPDM microplastic can have negative effects on plant growth, and that these might be more related to its structural than to its chemical properties.

Naturally aged polylactic acid microplastics stunted pakchoi (Brassica rapa subsp. chinensis) growth with cadmium in soil

Biodegradable microplastics (BMPs) and cadmium (Cd) are posing threats to agro-systems especially to plants and current studies mostly used virgin BMPs to explore their ecological effects. However, effects of naturally aged BMPs and their combined effects with Cd on pakchoi are yet to be unraveled. Therefore, this study incubated naturally aged polylactic acid (PLA) MPs through soil aging process and investigated the single and combined effects of Cd and PLA MPs (virgin and aged) on pakchoi (Brassica rapa subsp. chinensis) morphology, antioxidant systems and soil microbial activities. Our results found that after being deposited in soil for six months, aged PLA (PLAa) MPs formed with a fractured surface, demonstrating more detrimental effects on pakchoi than virgin ones. PLA/PLAa MPs and Cd stunted pakchoi growth, caused oxidative stress and altered the biophysical environment in soil, separately. Moreover, co-existence of PLA/PLAa MPs and Cd caused greater damages to pakchoi than applied alone. The co-presence of PLAa MPs and Cd inhibited pakchoi biomass accumulation rate by 92.2 % compared with the no-addition group. The results unraveled here emphasized BMPs, especially aged BMPs, could trigger negative effects on agro-systems with heavy metals. These findings will give reference to future holistic assessments of BMPs' ecological effects.

Microplastics affect soil bacterial community assembly more by their shapes rather than the concentrations

Polyethylene film mulching is a key technology for soil water retention in dryland agriculture, but the aging of the films can generate a large number of microplastics with different shapes. There exists a widespread misunderstanding that the concentrations of microplastics might be the determinant affecting the diversity and assembly of soil bacterial communities, rather than their shapes. Here, we examined the variations of soil bacteria community composition and functioning under two-year field incubation by four shapes (ball, fiber, fragment and powder) of microplastics along the concentration gradients (0.01%, 0.1% and 1%). Data showed that specific surface area of microplastics was significantly positively correlated with the variations of bacterial community abundance and diversity (r=0.505, p<0.05). The fragment- and fiber-shape microplastics displayed more pronounced interfacial continuity with soil particles and induced greater soil bacterial α-diversity, relative to the powder- and ball-shape ones. Strikingly, microplastic concentrations were not significantly correlated with bacterial community indices (r=0.079, p>0.05). Based on the variations of the βNTI, bacterial community assembly actually followed both stochastic and deterministic processes, and microplastic shapes significantly modified soil biogeochemical cycle and ecological functions. Therefore, the shapes of microplastics, rather than the concentration, significantly affected soil bacterial community assembly, in association with microplastic-soil-water interfaces.

Impacts of Micro(nano)plastics on Terrestrial Plants: Germination, Growth, and Litter

Micro(nano)plastics (MNP) are pervasive in various environmental media and pose a global environmental pollution issue, particularly in terrestrial ecosystems, where they exert a significant impact on plant growth and development. This paper builds upon prior research to analyze and consolidate the effects of MNP on soil properties, seed germination, plant growth, and litter decomposition. The objective is to elucidate the environmental behavior of MNP and their mechanisms of influence on the plant life cycle. The unique physicochemical and electrical properties of MNP enable them to modify soil structure, water retention capacity, and pH. They can potentially act as "electron shuttles" or disrupt natural "electron shuttles" in litter decomposition, thereby interfering with nutrient transport and availability in the soil. Furthermore, MNP can physically obstruct nutrient and water channels within plants, impacting nutrient and water absorption. Once infiltrating plant tissues, MNP can form eco-coronas with plant proteins. Together with MNP adsorbed on the plant's surface and within its tissues, they disrupt normal physiological processes, leading to changes in photosynthesis, biomass, cellular toxicity, genetics, nutrient uptake, and gene expression. These changes, in turn, influence seed germination and plant growth and development. As a burgeoning research field, future studies should delve deeper into various aspects of these changes, such as elucidating the pathways and mechanisms through which MNP enter plant tissues, assessing their intensity and mechanisms of toxicity on different plant species, and exploring the relationship between micro(nano)plastics and "electron shuttles". These endeavors will contribute to establishing a more comprehensive theoretical framework for understanding the environmental behavior of MNP and their impact on plants.

Response of peanut plant and soil N-fixing bacterial communities to conventional and biodegradable microplastics

Microplastics (MPs) occur and distribute widely in agroecosystems, posing a potential threat to soil-plant systems. However, little is known about their effects on legumes and N-fixing microbes. Here, we explored the effects of high-density polyethylene (HDPE), polystyrene (PS), and polylactic acid (PLA) on the growth of peanuts and soil N-fixing bacterial communities. All MPs treatments showed no phytotoxic effects on plant biomass, and PS and PLA even increased plant height, especially at the high dose. All MPs changed soil NO3--N and NH4+-N contents and the activities of urease and FDAse. Particularly, high-dose PLA decreased soil NO3--N content by 97% and increased soil urease activity by 104%. In most cases, MPs negatively affected plant N content, and high-dose PLA had the most pronounced effects. All MPs especially PLA changed soil N-fixing bacterial community structure. Symbiotic N-fixer Rhizoboales were greatly enriched by high-dose PLA, accompanied by the emergence of root nodulation, which may represent an adaptive strategy for peanuts to overcome N deficiency caused by PLA MPs pollution. Our findings indicate that MPs can change peanut-N fixing bacteria systems in a type- and dose-dependent manner, and biodegradable MPs may have more profound consequences for N biogeochemical cycling than traditional MPs.

Earthworm activity effectively mitigated the negative impact of microplastics on maize growth

Microplastic pollution can have detrimental effects on soil environments and inhibit crop growth. Earthworms, known as soil engineers, promote crop growth, but their role and impact on the amelioration of microplastic-polluted soil is not yet clear. In this study, we investigated the impact and pathways of earthworm activity on microplastic-contaminated soil by introducing varying densities (without earthworm:0, low-density: 1, medium-density: 2, high-density: 5 ind column-1) of earthworms (epi-endogeic) into soil contaminated with two types of microplastics: polyethylene and polyvinyl chloride. Our results showed that earthworms all survived in soil polluted with two types of microplastics. Meanwhile, earthworm activity increased nutrient content and enzyme activity by 0.2-36.1% and 2.9-34.3%, respectively, and significantly increased soil microbial biomass and community diversity index. Earthworm activity also decreased antioxidant enzyme activity and promoted maize plant growth, including agronomic traits such as plant height, biomass, root length, and root surface area. Furthermore, the nutrient content of maize organs increased by 1.1-29.7%. Partial least squares models confirmed that earthworm activity alleviated the stress effect of microplastic pollution on plant growth by improving soil structure, fertility, and microbial abundance and diversity. The greatest effect on maize growth was observed with the improvement of soil physical-chemical properties. Our results suggest that medium densities of earthworms have the greatest soil improvement effect and provide an important basis for bioremediation of farmland contaminated by microplastics and promoting green and efficient development in agriculture.

Microplastics in cultivated soil environment: Construction of toxicity grading evaluation system, development of priority control checklist, and toxicity mechanism analysis

The present study aimed to comprehensively evaluate the toxicological effects of microplastics (MPs) on cultivated soil quality. Based on improved G1 evaluation method, we first constructed a grading evaluation system comprising of the indicators of toxicological effects of cultivated soil quality under MPs exposure, while focusing on types of MPs that had significant/non-significant toxicity effects. Furthermore, we verified reliability of screening results of significance-links at each level, using several data processing methods. Then, using natural breakpoint classification method, a priority control checklist of toxicological effects of 18 types of MPs on cultivated soil was developed to determine the types of MPs having significant toxicity risks and cultivated soil quality links significantly affected by the toxicity of MPs exposure. Finally, quantum-mechanics/molecular-mechanics (QM/MM) methods were used to carry out the differential toxicity mechanism analysis. The results showed that MPs with higher non-polar surface area may lead to stronger toxicity effect to the cultivated soil quality. Notably, the MPs that have abundant binding sites enhance the binding affinity, and less polar MPs bind more strongly to the non-polar amino acids of target receptors. Our study provides a new theoretical perspective for multi-dimensional analysis toxicological effects of different MPs exposure on cultivated soil quality.

Are biodegradable mulch films a sustainable solution to microplastic mulch film pollution? A biogeochemical perspective

Mulch film residue contributes significantly to global plastic pollution, and consequently biodegradable mulch films (BDMs) are being adopted as a solution. BDMs decompose relatively quickly, but their complete biodegradation requires suitable conditions that are difficult to achieve in nature, causing biodegradable microplastics (bio-MPs) to be more likely to accumulate in soil than traditional microplastics (MPs). If BDMs are to be considered as a sustainable solution, long-term and in-depth studies to investigate the impact of bio-MPs on the biogeochemical processes are vital to agroecosystems operation and ecosystem services supply. Although bio-MP-derived carbon can potentially convert into biomass during decomposition, its contribution to soil carbon stocks is insignificant. Instead, given their biodegradability, bio-MPs can result in greater alterations of soil biodiversity and community composition. Their high carbon-nitrogen ratios may also significantly regulate various processes involved in the natural decomposition and transformation of soil organic matter, including the reduction of nutrient availability and increase in greenhouse gas emissions. Soil ecosystems are complex organic entities interconnected by disturbance-feedback mechanisms. Given the prevailing knowledge gaps regarding the impact of bio-MPs on soil biogeochemical cycles and ecosystem balance, this study emphasized the safety and sustainability assessment of bio-MPs and the prevailing comprehensive challenges.

Effect of different types and shapes of microplastics on the growth of lettuce

The presence of microplastics in agricultural soils has emerged as a significant environmental concern due to their persistent nature. Microplastics of different properties (i.e., types, shapes, size, concentration) are present in the environment, but the studies on the effect of microplastics having different properties are limited. Thus, this study investigated the effects of different microplastics (low-density polyethylene (LDPE) fragments, polyvinyl chloride (PVC) fragments, and LDPE fiber) in soil on the growth of lettuce (Lactuca sativa L.). Pot tests were carried out to study the effect of a range of microplastic concentrations and different shapes and types of microplastics in soil on the lettuce growth. The different growth parameters such as lettuce weight, lengths, and chlorophyll contents were measured and compared. The results showed that the adverse effects of the microplastics on the lettuce growth increased with increasing microplastic concentration. The effects of LDPE fragments and fibers on the root weights and the chlorophyll contents were microplastic shape-dependent. Also, the effects of LDPE fragments and PVC fragments on the shoot and root weights and the chlorophyll contents were microplastic type-dependent. Among the three microplastics studied, LDPE fragments tend to have greater effects on the lettuce growth than the other microplastics. Overall, the results show that the effects of microplastics on different growth parameters of lettuce can be shape- and/or type-dependent. The presence of microplastics having different properties make the understanding the effects of microplastics on plants difficult, and this necessitates further studies.

Change in the chemical, mechanical and physical properties of plastics due to UVA degradation in different water matrices: A study on the recyclability of littered plastics

To move towards a circular society, the recyclability potential of littered plastics should be explored to provide potential value for a product that is typically destined for landfill or incineration. This study aims to understand the changes in physical, mechanical, and chemical properties of four types of plastics (polyethylene terephthalate (PET), polypropylene (PP), polycarbonate (PC) and polylactic acid (PLA) after simulated environmental degradation. Plastic samples were subjected to different water matrices (in an attempt to simulate terrestrial, ocean, and river environments) to understand the role the environment plays on plastic degradation. Significant physical, mechanical, and chemical changes were observed for the PET, PP and PLA samples. Flakes and cracks were noted during the scanning electron microscopy (SEM) analysis of PET, PP and PLA illustrating the surface degradation that had occurred. Colour scanning of the samples provided complementary information about their suitability for upcycling or downcycling. Both PET and PP had visual colour changes, making them unsuitable for upcycling purposes. PLA had a significant decrease in its tensile strength in all environmental conditions, alongside significant chemical and surface change as revealed by Fourier-transform infrared (FTIR) and SEM analysis, respectively. PC had little to no changes in its chemical, mechanical, and physical properties due to high resistance to solar (UVA) degradation in presence of salt and natural organic matter in the form of humic acid. Therefore, out of the four types of plastics tested, PC was the only plastic determined to have good upcycling potential if collected from the environment. However, PET and PP could still be recycled into lower value products (i.e., construction materials).

Effect of polylactic acid microplastics and lead on the growth and physiological characteristics of buckwheat

Microplastics (MPs) and heavy metals are common, often co-existing pollutants, that threaten crop growth and productivity worldwide. We analysed the adsorption of lead ions (Pb2+) to polylactic acid MPs (PLA-MPs) and their single factor and combined effects on tartary buckwheat (Fagopyrum tataricum L. Gaertn.) in hydroponics by measuring changes in the growth characteristics, antioxidant enzyme activities and Pb2+ uptake of buckwheat in response to PLA-MPs and Pb2+. PLA-MPs adsorbed Pb2+, and the better fitting second-order adsorption model implied that Pb2+ was adsorbed by chemisorption. However, the similar Pb2+ contents in the plants treated with Pb2+ only and those treated with the combined PLA-MPs-Pb2+ suggested that the adsorption played no role in the uptake of Pb2+. Low concentrations of PLA-MPs promoted shoot length. At high concentrations of both PLA-MPs and Pb2+, buckwheat growth was inhibited, and leaf peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) activities and malondialdehyde (MDA) contents were higher than in the control. No significant differences were observed in seedling growth between exposure to Pb2+ only and combined exposure to PLA-MPs with Pb2+, implying that PLA-MPs did not increase the toxicity of Pb2+ at macroscopic level. POD activity was higher and chlorophyll content was lower with PLA-MPs in the low Pb2+ dose treatments, suggesting that PLA-MPs may increase the toxicity of naturally occurring Pb2+. However, the conclusions must be verified in controlled experiments in natural soil conditions over the whole cultivation period of buckwheat.

Impact and mitigation of lead, cadmium and micro/nano plastics in fragrant rice

Heavy metals (HMs) and micro(nano)plastics (MNPs), represent a significant risk to global food supply as well as a potential risk to humankind. Over 50% of the worldwide population eat rice every day, and rice aroma is a significant qualitative trait that is highly valued by consumers and fetches premium prices in the global market. Despite the huge commercial importance of fragrant rice, limited studies were directed to investigate the influence of HMs and MNPs on yield related traits and 2-Acetyl-1-pyrroline (2-AP) compound, mainly responsible for aroma production in fragrant rice. In this review, we found that the interaction of HMs and MNPs in fragrant rice is complex and accumulation of HMs and MNPs was higher in root as compared to the grains. Nutrients and phytohormones mediated mitigation of HMs and MNPs were most effective sustainable strategies. In addition, monitoring the checkpoints of 2-AP biosynthesis and its interaction with HMs and MNPs is challenging. Finally, we explained the potential challenges that fragrant rice faces considering the continuous rise in environmental pollutants and discussed the future avenues of research to improve fragrant rice's yield and qualitative traits.