Identification of factors influencing the microplastic distribution in agricultural soil on Hainan Island

Methods to optimize the collection, pretreatment, extraction, separation, and examination of microplastics in soil, groundwater, and human samples

Microplastics (MPs) in soil, groundwater, and human (SGH) present a significant global challenge due to their ecological and human health impacts. However, current protocols for detecting MPs in these environments and humans are limited, inconsistently applied, and vary significantly, particularly during the pretreatment stages of MP analysis. Moreover, no study has investigated the impact of methodological flaws on MP detection. This study conducted a thorough global assessment of the existing soil and groundwater (SG) pretreatment methods, using statistical tests to evaluate their effectiveness. It also reviewed filtration and analytical techniques for MPs in SGH samples. The analysis included research articles from PubMed, Google Scholar, Scopus, and Web of Science published between 2015 and 2024. Findings show that pretreatment using more than 100 g of soil can impact MP quantification, likely due to soil heterogeneity, while groundwater volume did not significantly affect MP quantification, likely due to the homogeneity of groundwater. During SGH pretreatment, various salts (e.g., ZnCl2 and NaCl) can be used for density flotation. Fenton's reagent was found to be a better choice than H2O2 for organic material removal because less heat was released. Post treatment MPs in SGH samples can be analyzed using various instruments and resolutions such as FTIR down to 1-5 µm, ATR-FTIR down to 2 µm, micro-Raman down to 500 nm, and LDIR down to 1 µm. This study lays the foundation for developing an effective MP analysis in SGH.

Polyethylene microplastics impair chicken growth through gut microbiota-induced hepatic fatty acid metabolism dysfunction

Microplastics (MPs) negatively impact various terrestrial animals, but their comprehensive effects on Gallus gallus domesticus, key agricultural and ecological species connecting people and the environment, are not well-documented. This study investigates the effects of polyethylene (PE) MPs and phthalate esters (PAEs) on chicken growth, liver metabolism, and gut microbiota using multi-omics and 16S rRNA sequencing technology. Results show that PE MPs, particularly those containing PAEs, significantly reduced body weight gain and hepatic triglyceride levels by up to 71.2 % and 50.1 %, respectively (p < 0.05). The clean MPs affected energy metabolism, while PAE-spiked MPs disrupted fatty acid metabolism and triggered immune and inflammatory responses in the liver. Key genes related to fatty acid metabolism such as FAN, SCD and ELOVL5 were significantly downregulated, leading to imbalances in lipid metabolism. These disruptions in PAE-spiked MPs exposure were associated with the altered gut microbiota balance, including increased Firmicutes/Bacteroidetes ratios and changes in Actinobacteriota and Proteobacteria abundance. Totally, the study highlights a "Trojan Horse" effect, where MPs act as carriers for PAEs, intensifying toxicity through gut-liver axis interactions. The findings emphasize the role of gut microbiota in mediating liver dysfunction and impaired growth.

Microplastics in agricultural soils: sources, impacts on soil organisms, plants, and humans

Agricultural land has long been regarded as a resource for food production, but over time, the effects of climate change have reduced the ability of soil to produce food efficiently. Nowadays, farmers have moved from traditional to modern techniques of farming. Across the globe, plastic mulching has become widely used on farmlands. According to a few studies, the breakdown of plastic mulches releases microplastics (MPs) into the soil. Despite studies reporting the presence of MPs in soils, there are limited studies on the sources and impacts on soil organisms, plant growth, fruits, and human health. This study evaluated research articles collected from the Web of Science to assess the origin of MP in soil and crops and its effects on soil organisms, plants, and humans. It was observed that MPs come from different sources such as waste water, organic fertilizer, irrigation water, sewage, and sludge. Plastic mulching, which can spread across agricultural fields at varying depths, is the dominant source. Furthermore, it was observed that MPs alter crop quality, reduce the leaf count of wheat, and decrease the root length of crops such as maize, water spinach, black gram, and garden cress. MP can decrease the abundance of soil microarthropods and nematodes, damage the intestinal walls of earthworms, and reduce the feeding and excretion of snails. MP causes liver damage, inflammation, respiratory irritation, and immunological issues. Ultimately, these contaminants (MPs) can transfer and have been detected in fruits and vegetables, which pose adverse effects on human health.

Retention and migration of microplastics in stepped paddy fields: A study on microplastic dynamics in the special irrigation system

The stepped paddy fields (SPFs) are important for food security and sustainable development. The unique spatial structure and complex hydrological processes in this system make it difficult to understand the migration of pollutants. In this study, microplastic pollution was investigated in the water and soil from Ziquejie SPFs, China. Samples were taken according to different stages of rice cultivation, different altitudes, and soil depths. Before rice planting, the average abundance in the water and soil samples was 1.3 ± 1.1 items/L and 292.2 ± 260.8 items/kg, respectively. After rice harvesting, the average abundance in soil increased to 495.37 ± 175.46 items/kg. More microplastics were found in depths of 0-15 cm than that of 15-30 cm, but the difference was not significant. Major microplastics were small (<1 mm) polyethylene (PE) and polypropylene (PP) fibers, with the main color of blue and transparent. The study found that SPFs hindered the migration of microplastics in irrigation water and hydraulic conditions affected the accumulation of microplastics. The edge areas in paddy fields where the water flowed slowly and were prone to vortices made it easier for microplastics to stay. Most of the microplastics accumulated in the upper SPF. After rice harvesting, the overall abundance of microplastics in the SPFs increased. Fibers and fragments exhibited different characteristics in migration. This study attempts to draw attention to the ecological risks caused by microplastic pollution in SPFs, especially in the upper paddy field and the effluent. The results are helpful for the protection of the SPF ecosystem and provide valuable references for future research.

Microplastic effects on soil nitrogen cycling enzymes: A global meta-analysis of environmental and edaphic factors

Microplastic accumulation in soil ecosystems poses significant environmental concerns, potentially impacting nitrogen cycling processes and ecosystem health. This meta-analysis of 147 studies (1138 data points) assessed the impact of microplastics (MPs) on soil nitrogen-acquisition enzymes. We found that MPs exposure significantly increased soil urease (UE) and leucine aminopeptidase activities by 7.6 % and 8.0 %, respectively, while N-acetyl-β-D-glucosaminidase activity was not significantly affected. Biodegradable MPs showed more pronounced effects compared to conventional MPs. Enzyme activities were influenced by MPs properties (e.g., polymer type, size, concentration), experimental conditions (e.g., field or laboratory setting, temperature, nitrogen fertilization), and soil properties (e.g., clay content, pH, organic carbon, total nitrogen). For instance, acidic soils enhanced UE activity, while neutral soils reduced it. These findings emphasize the complex interactions between MPs and soil ecosystems, highlighting the need for context-specific environmental management strategies and policy-making approaches to mitigate the impacts of MPs pollution on soil health.

Assessment of microplastic ecological risk and environmental carrying capacity of agricultural soils based on integrated characterization: A case study

Microplastic pollution in agricultural soils poses a significant threat to soil quality and environmental sustainability. This study investigated the composition, abundance, distribution, ecological risk, and environmental carrying capacity of microplastic pollution in the Tarim River Basin (TRB), China. The risk quotient combined with soil environmental carrying capacity (SECC) approaches was proposed to evaluate ecological risks and soil sustainability. Microplastic abundances ranged from 0 to 4000 items/kg (average = 570 items/kg), with polyethylene (PE) polytetrafluoroethylene (PTFE) and polypropylene (PP) as dominant polymers. In addition, various factors affecting the occurrence of microplastics were analyzed. Agricultural mulching and drip irrigation were associated with higher microplastic levels. The risk assessment showed that among the different shapes, size ranges and categories of microplastics, fragmented (film), large-sized microplastics and PE had the highest risk, respectively. While current levels are within SECC limits, early warning model predicts PE and PP may reach threshold limits in recent years. This study provides crucial insights for managing microplastic pollution in agricultural regions, emphasizing the need for targeted mitigation strategies to maintain soil ecology sustainability.

Microplastics influence nutrient content and quality of salt-affected agricultural soil under plastic mulch

Northeast China is an important food production base and plays a crucial role in national food security. However, the increase in salt-affected soils poses a challenge to agricultural production in this region. Plastic mulching is an effective technique for saline cropland improvement, and although it has increased crop yields in the short term, its long-term application may have introduced the problem of contamination by microplastics (MPs). The distribution of MPs in salt-affected cropland, along with the effects on soil nutrients, remains largely unknown. Accordingly, the presented research selected salt-affected cropland as the research object, after which MPs were quantified from 46 soil samples from currently mulched and unmulched fields. MPs abundance in the sampled soils ranging from 4.10 × 103∼1.50 × 104 particles per kilogram of dry soil. The detected MP polymers were mainly high-density polyethylene (46%), polypropylene (22%) and polyvinyl chloride (20%). The MP particles most commonly fell under the size ranges of 50∼100 μm (35%) and 100-200 μm (28%), both of which are small particle sizes. The most commonly detected MP shapes were film (34%) and fragment (31%). The mulched samples from salt-affected cropland generally showed higher soil nutrient contents than the unmulched samples. Moreover, MP abundance, type, size, and shape all demonstrated strong correlations with soil organic carbon and total nitrogen. MP type is a major factor determining soil nutrient content. Plastic mulching serves as an important source of MPs in salt-affected cropland, with these contaminants affecting nutrient content. Future research should be broader in scope and include ecological benefits and policy implications, with a view to optimizing the problem of MPs contamination due to mulching.

Environmental fate of microplastics and common polymer additives in non-biodegradable plastic mulch applied agricultural soils

Numerous studies have been conducted to investigate the impact of microplastics on soil eco-system, yet little attention has been given to the specific effects of mulch microplastics and the leaching of plastic additives from mulch films. This review inspects the propensity of commonly used plastic additives in mulch films, such as Di(2-ethylhexyl) phthalate (DEHP), bisphenol A (BPA), and benzophenones (BPs), to migrate into soils and pose potential risks to soil biota. Further, we highlight the degradation of non-biodegradable plastic mulch films over time, which leads to an increase in the release of plastic additives and microplastics into agricultural soils. DEHP has been detected in high concentrations for example 25.2 mg/kg in agricultural soils, indicating a potential risk of uptake, translocation and accumulation in plants, ultimately altering soil physicochemical properties and affecting soil microflora and invertebrates. The review also explores how exposure to ultraviolet (UV) radiation and microbial activities accelerates the weathering of mulch films. Moreover, the resultant plastic additives and mulch microplastics can lead to genotoxicity and growth inhibition in earthworms (Eisenia fetida) and negatively impact the soil microbiome. Despite the significant implications, there has been a lack of comprehensive reviews comparing the effects of non-biodegradable mulch film additives on agricultural soil flora and fauna. Therefore, this review addresses the knowledge gaps providing a bibliometric analysis and eco-toxicological evaluation, discussing the challenges and future perspectives regarding mulch plastic additives and microplastics, thus offering a comprehensive understanding of their impact.

Unveiling the mechanism of the effect of polyethylene microplastics on phenanthrene degradation in agricultural soils through DNA-based stable isotope probing

Polyethylene microplastics (MPs) derived from plastic mulch films are ubiquitous in agricultural soils. However, the mechanism underlying the effect of MPs on the degradation of polyaromatic hydrocarbons remains unclear. In this study, we investigated the influence of MPs amendment on the profiles of active microbes involved in phenanthrene (PHE) degradation in agricultural soils using DNA-based stable isotope probing (SIP) combined with high-throughput sequencing. Results showed that biodegradation dominated the removal of PHE, and MPs promoted the PHE degradation rate from 79.0 % to 92.3 % in agricultural soils. The addition of MPs could stimulate and prolong the activities of original active microbes responsible for PHE degradation including the genera Flavisolibacter and Nocardioides. Furthermore, the presence of MPs could also recruit novel active microbes, including Gaiella, Methylopila, JGI_0001001-H03, and unclassified Intrasporangiaceae, to participate in PHE degradation. Notably, Flavobacterium, Methylopila, Lysobacter, and unclassified Blastocatellaceae were directly linked with PHE degradation for the first time by SIP. This study provides novel insights into the mechanism underlying the effect of MPs on PHE degradation and enhances our comprehensive understanding of the co-contamination of MPs and PHE in agricultural soils.

Global distribution, drivers, and potential hazards of microplastics in groundwater: A review

Since microplastics (MPs) were first detected in groundwater, an increasing number of studies have focused on groundwater pollution by MPs. However, knowledge of the global properties of groundwater MPs: distribution, concentration, composition, and morphology remains limited, while potential factors regulating their transport and distribution in groundwater, especially the hydrogeological background and climate warming conditions, have been omitted from most analyses. Furthermore, previous field investigations did not assess the risks posed by groundwater MPs to the environment and to human health, a necessary preliminary to remediation. In this work, to promote future MP pollution studies and remediation policies, we assimilated and synthesized the current knowledge on this topic. We reviewed current data on global groundwater pollution by MPs, analyzed the driving factors of their transport and distribution, and summarized the ecological and health hazards posed by MPs, before discussing current knowledge limits and suggesting perspectives for future work.

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.

Microplastic accumulation and oxidative stress in sweet pepper (Capsicum annuum Linn.): Role of the size effect

Microplastics (MPs), which are widely dispersed in terrestrial environments, threaten crop growth and human food security. However, plant accumulation and phytotoxicity related to the size effects of MPs remain insufficiently explored. This study investigated the accumulation and toxicity of two sizes of MPs on Capsicum annuum Linn. (C. annuum) through fluorescence tracing and antioxidant defense system assessment. The results revealed that the size of MPs significantly impacts their accumulation characteristics in C. annuum roots, leading to variations in toxic mechanisms, including oxidative stress and damage. Smaller MPs and higher exposure concentrations result in more pronounced growth inhibition. C. annuum roots have a critical size threshold for the absorption of MPs of approximately 1.2 μm. MPs that enter the root tissue exhibit an aggregated form, with smaller-sized MPs displaying a greater degree of aggregation. MP exposure induces oxidative stress in root tissues, with high concentrations of smaller MPs causing lipid peroxidation. Analysis of the IBR values revealed that C. annuum roots utilize ascorbic acid (ASA) to prevent oxidative damage caused by larger MPs. Conversely, smaller MPs primarily induce superoxide dismutase (SOD) and glutathione (GSH). These results emphasize the significant impact of MP size on plant antioxidant defense response mechanisms, laying the foundation for further investigating the implications for human health.

Using machine learning to reveal drivers of soil microplastics and assess their stock: A national-scale study

The issue of microplastic (MP) contamination in soil is a significant concern. However, due to limited large-scale studies and stock assessments, our understanding of the drivers of their distribution and fate remains incomplete. To address this, we conducted a comprehensive study in China, collected MP data from 621 sites, and utilized machine learning techniques for analysis. Our findings revealed 9 key factors influencing the distribution of soil MPs, highlighting their nonlinear influence processes. Among these factors, atmospheric deposition emerged as the most dominant driver, while wind and precipitation could lead to the transformation of soil from a sink to a source of MPs. MP concentrations in Chinese soils vary from 1.4 to 4333.1 particles/kg, with human activities significantly affecting their distribution, resulting in higher concentrations in the east and lower concentrations in the west. The estimated MP stock in Chinese soils is 1.92 × 1018 particles, equivalent to a mass of 2.11-8.64 million tonnes. This stock alone surpasses that found in global oceans, making global soil the largest reservoir of MPs. Overall, this study enhances our understanding of the environmental behavior of MPs and provides valuable data and theoretical support for the prevention, control, and management of this contamination.

Agricultural plastic pollution reduces soil function even under best management practices

Soil plastic contamination is considered a threat to environmental health and food security. Plastic films-which are widely used as soil mulches-are the largest single source of agricultural plastic pollution. Growing evidence indicates that high concentrations of plastic negatively affect critical soil functions. However, the relationships between agricultural plastic accumulation and its biogeochemical consequences in regions with relatively low levels of soil plastic pollution remain poorly characterized. We sampled farms across the California Central Coast (a region of global agricultural importance with extensive plastic mulch-based production) to assess the degree and biogeochemical consequences of plastic pollution in fields subject to "best practice" plastic mulching application and removal practices over multiple years. All farms exhibited surface soil plastic contamination, macroplastic positively correlated with microplastic contamination levels, and macroplastic accumulation was negatively correlated with soil moisture, microbial activity, available phosphate, and soil carbon pool size. These effects occurred at less than 10% of the contamination levels reported to degrade field soils, but were relatively subtle, with no detectable relationship to microplastic concentration. Identifying declines in soil quality with low levels of macroplastic fragment accumulation suggests that we must improve best management plasticulture practices to limit the threat to soil health and agricultural productivity of unabated plastic accumulation.

Nationwide meta-analysis of microplastic distribution and risk assessment in China's aquatic ecosystems, soils, and sediments

Microplastic (MP) accumulation has recently become a pressing global environmental challenge. As a major producer and consumer of plastic products, China's MP pollution has garnered significant attention from researchers. However, accurate and comprehensive investigations of national-level MP pollution are still lacking. In this study, we systematically collated a national MP pollution dataset consisting of 7766 water, soil, and sediment sampling sites from 544 publicly published studies, revealing the spatiotemporal distribution and potential risks of MP pollution in China. The results indicate that MP distribution is influenced by various regional factors, including economic development level, population distribution, and geographical environment, exhibiting considerable range and complexity. MP concentrations are generally higher in economically prosperous areas, but the degree of pollution varies significantly across different environmental media. Given the uncertainty and lack of standardized data in traditional microplastic risk assessment methods, this article highlights the urgency of developing a comprehensive big data and artificial intelligence (AI)-based regulatory framework. This work provides a substantial amount of accurate MP pollution data and offers a fresh perspective on leveraging AI for microplastic pollution regulation.

Influencing factors and risk assessment of phthalate ester pollution in the agricultural soil on a tropical island

Phthalate esters (PAEs) are widely prevalent in agricultural soil and pose potential risks to crop growth and food safety. However, the current understanding of factors influencing the behavior and fate of PAEs is limited. This study conducted a large-scale investigation (106 sites in 18 counties with 44 crop types) of 16 types of PAEs on a tropical island. Special attention was given to the impacts of land use type, soil environmental conditions, agricultural activity intensity, and urbanization level. The health risks to adults and children from soil PAEs via multiple routes of exposure were also evaluated. The results showed that the mean concentration of PAEs was 451.87 ± 284.08 μg kg-1 in the agricultural soil. Elevated agricultural and urbanization activities contributed to more pronounced contamination by PAEs in the northern and southern regions. Land use type strongly affected the concentration and composition of PAEs in agricultural soils, and the soil PAE concentration decreased in the order of vegetable fields, orchards, paddy fields, and woodlands. In paddy fields, di-isobutyl phthalate and di-n-butyl phthalate made more substantial contributions to the process through which the overlying water inhibited volatilization. Soil microplastic abundance, pesticide usage, crop yield, gross domestic product, and distance to the nearest city were calculated to be the major factors influencing the concentration and distribution of PAEs. Soil pH, organic matter content, microplastic abundance and the fertilizer application rate can affect the adsorption of PAEs by changing the soil environment. A greater risk was detected in the northern region and paddy fields due to the higher soil PAE concentrations and the dietary structure of the population. This study reveals important pathways influencing the sources and fate of PAE pollution in agricultural soils, providing fundamental data for controlling PAE contamination.

Non-negligible impact of microplastics on wetland ecosystems

There has been much concern about microplastic (MP) pollution in marine and soil environments, but attention is gradually shifting towards wetland ecosystems, which are a transitional zone between aquatic and terrestrial ecosystems. This paper comprehensively reviews the sources of MPs in wetland ecosystems, as well as their occurrence characteristics, factors influencing their migration, and their effects on animals, plants, microorganisms, and greenhouse gas (GHG) emissions. It was found that MPs in wetland ecosystems originate mainly from anthropogenic sources (sewage discharge, and agricultural and industrial production) and natural sources (rainfall-runoff, atmospheric deposition, and tidal effects). The most common types and forms of MPs identified in the literature were polyethylene and polypropylene, fibers, and fragments. The migration of MPs in wetlands is influenced by both non-biological factors (the physicochemical properties of MPs, sediment characteristics, and hydrodynamic conditions) and biological factors (the adsorption and growth interception by plant roots, ingestion, and animal excretion). Furthermore, once MPs enter wetland ecosystems, they can impact the resident microorganisms, animals, and plants. They also have a role in global warming because MPs act as unique exogenous carbon sources, and can also influence GHG emissions in wetland ecosystems by affecting the microbial community structure in wetland sediments and abundance of genes associated with GHG emissions. However, further investigation is needed into the influence of MP type, size, and concentration on the GHG emissions in wetlands and the underlying mechanisms. Overall, the accumulation of MPs in wetland ecosystems can have far-reaching consequences for the local ecosystem, human health, and global climate regulation. Understanding the effects of MPs on wetland ecosystems is essential for developing effective management and mitigation strategies to safeguard these valuable and vulnerable environments.

Effects of soil properties and land use patterns on the distribution of microplastics: A case study in southwest China

Microplastic pollution in the soil environment is of great concern. However, the current research on microplastics (MPs) in Southwest China mainly focuses on their distribution characteristics and sources in soil, making the understanding of the soil properties and land use patterns influencing soil MPs insufficient. In this study, the abundance and distribution characteristics of MPs in the soil of different land use patterns in Guizhou Province were determined. The results revealed that the average abundance of MPs in soils was 2936 items/kg, ranging from 780 to 9420 items/kg. The MPs were mainly small particle size (0-0.5 mm), granular, and black, accounting for 87.5%, 36.6%, and 82.2%, respectively. The most common polymer types of MPs were polypropylene, polyethylene terephthalate, and polyethylene, which accounted for 20.4%, 16.8%, and 16.4%, respectively. As soil bulk density increased, microplastic abundance and small particle size decreased. Soil microplastic abundance slightly decreased with increasing soil porosity. The abundance of MPs increased with the increase in soil pH, but no significant correlation was observed between soil organic matter content and microplastic abundance. pH was the major factor that affected the microplastic distribution, which accounted for 32.5%. This study provides insight into the distribution and influencing factors of soil MPs and also provides a theoretical basis for subsequent research on soil microplastic pollution.

Health assessment based on exposure to microplastics in tropical agricultural soil

Microplastic (MP) pollution of agricultural soils has caused global alarm over its widespread distribution and potential risks to terrestrial ecosystems and human health. This study assessed human health based on exposure to soil MPs through a comprehensive investigation of the factors influencing their occurrence and spatial distribution on Hainan Island, South China. The results showed that the abundance of soil MPs was 1128.6 ± 391.5 items·kg-1, whereas the normalized abundance of MPs based on using a power-law function was 19,261.4 items·kg-1. Regarding the extent of population exposure to agricultural soil MPs, the average daily exposure dose (pADD) model revealed that using mass as an indicator to assess the health risks associated with MP intake is more reliable than using abundance. However, abundance-based exposure assessments are also relevant because MPs with smaller particle sizes are more harmful to human health. Moreover, for adults, the normalized pADD values based on abundance and mass were 1.68E-02 item MPs·kg BW-1·d-1 and 7.23E-02 mg MPs·kg BW-1·d-1, respectively. Although the multidimensionality of MPs should be further aligned and quantified, the preliminary findings of this study contribute to the development of human health risk assessment frameworks for soil MPs.

Farmland Microhabitat Mediated by a Residual Microplastic Film: Microbial Communities and Function

How the plastisphere mediated by the residual microplastic film in farmlands affects microhabitat systems is unclear. Here, microbial structure, assembly, and biogeochemical cycling in the plastisphere and soil in 33 typical farmland sites were analyzed by amplicon sequencing of 16S rRNA genes and ITS and metagenome analysis. The results indicated that residual microplastic film was colonized by microbes, forming a unique niche called the plastisphere. Notable differences in the microbial community structure and function were observed between soil and plastisphere. Residual microplastic film altered the microbial symbiosis and assembly processes. Stochastic processes significantly dominated the assembly of the bacterial community in the plastisphere and soil but only in the plastisphere for the fungal community. Deterministic processes significantly dominated the assembly of fungal communities only in soil. Moreover, the plastisphere mediated by the residual microplastic film acted as a preferred vector for pathogens and microorganisms associated with plastic degradation and the nitrogen and sulfur cycle. The abundance of genes associated with denitrification and sulfate reduction activity in the plastisphere was pronouncedly higher than that of soil, which increase the potential risk of nitrogen and sulfur loss. The results will offer a scientific understanding of the harm caused by the residual microplastic film in farmlands.

Occurrence characteristics and risk assessment of microplastics in agricultural soils in the loess hilly gully area of Yan' an, China

Large amounts of microplastics accumulated in the soil of agricultural fields with the rapid development of mulch agriculture. The enrichment of microplastics endangered the growth of crops and food security, and it also posed ecological risks. In this study, we investigated microplastics in a typical agriculture area of Yan' an City, in the loess hilly gully area of China. The characteristics of microplastics including their abundances, sizes, and types were measured through laser direct infrared spectrometer. The potential sources of microplastics were analyzed and the risk of soil microplastic pollution was evaluated. It was elaborated that the average abundances of microplastics in soil, water, and fertilizer were 4505 ± 435 n·kg-1, 91 ± 27 n·L-1, and 39,629 ± 10,114 n·kg-1, respectively. Microplastics with particle sizes < 100 μm accounted for >90 %. The smaller the particle size, the higher the content of microplastics. The top three polymers were polyethylene (PE, 37.4 %), polyethylene terephthalate (PET, 15.0 %), and ethylene vinyl acetate (EVA, 8.9 %), respectively. Agricultural mulch, plastic film, domestic waste, surface water irrigation, and organic compost were probably the potential sources of soil microplastics. The ecological risk evaluation showed that overall sampling sites had a minor ecological risk of microplastic pollution based on their abundance, while the polymer type showed a relatively high ecological risk for the investigated agricultural soils. Polyvinylchloride (PVC) and polymethylmethacrylate (PMMA) contribute considerably to the ecological risk, and their inputs to the farmland environment should be strictly limited. There was no significant carcinogenic risk to humans. This study would provide the basic reference for the current situation and risk assessment of farmland soil microplastics pollution in the loess hilly gully area of China.

Microplastics in soils: Production, behavior process, impact on soil organisms, and related toxicity mechanisms

In recent years, microplastics (MPs) pollution has become a hot ecological issue of global concern and MP pollution in soil is becoming increasingly serious. Studies have shown that MPs have adverse effects on soil biology and ecological functions. Although MPs are evident in soils, identifying their source, abundance, and types is difficult because of the complexity and variability of soil components. In addition, the effects of MPs on soil physicochemical properties (PCP), including direct effects such as direct interaction with soil particles and indirect effects such as the impact on soil organisms, have not been reported in a differentiated manner. Furthermore, at present, the soil ecological effects of MPs are mostly based on biological toxicity reports of their exudate or size effects, whereas the impact of their surface-specific properties (such as environmentally persistent free radicals, surface functional groups, charge, and curvature) on soil ecological functions is not fully understood. Considering this, this paper reviews the latest research findings on the production and behavioral processes of MPs in soil, the effects on soil PCP, the impacts on different soil organisms, and the related toxic mechanisms. The above discussion will enhance further understanding of the behavioral characteristics and risks of MPs in soil ecosystems and provide some theoretical basis for further clarification of the molecular mechanisms of the effects of MPs on soil organisms.

Evaluation of niche, diversity, and risks of microplastics in farmland soils of different rocky desertification areas

The occurrence, sources, effects, and risks of microplastics (MPs) in farmland soils have attracted considerable attention. However, the pollution and ecological characteristics of MPs in farmland soils at different levels of rocky desertification remain unclear. We collected and analyzed farmland soil samples from rocky desertification areas in Guizhou, China, ranging from no to heavy risks. We explored differences and migration of MPs across these areas, unveiled the relationship between diversity, niche, and risks of MPs, and determined influencing factors. The average abundance of soil MPs was 8721 ± 3938 item/kg, and the abundance and contamination factor (CF) of MPs escalated with the increase in rocky desertification level. Diversity, niche, and risk of soil MPs in different rocky desertification areas were significantly different. Rocky desertification caused both MP community differences and linked MP communities at different sites. Diversity and niche significantly affected MP risk (p < 0.05). Environmental factors with significant correlations (p < 0.05) with the abundance and ecological characteristics of MPs varied significantly in soils of different rocky desertification areas. This study advances our comprehension of MP pollution in farmland soils within rocky desertification areas, offering essential data and theoretical insights for the development of control strategies.

Occurrence of microplastics in agricultural soils in ecologically fragile areas of China

The pollution caused by microplastics (MPs), an emerging pollutant, has been receiving continuous concern. However, the distribution characteristics of MPs in ecologically fragile areas (EFAs), which are sensitive to environmental change and pollution, are still unclear. Here, the abundance and pollution characteristics of MPs in agricultural soils in four typical EFAs in China, namely semiarid farming-pastoral area (SFPA), desert-oasis interlaced area (DOIA), plateau composite erosion area (PCEA) and southwest karst area (SWKA) were investigated. MPs were detected in all agricultural soil samples with a mean abundance of 2685 ± 938 n/kg. DOIA (3193 ± 630 n/kg) had the largest abundance of MPs in agricultural soils, followed by SWKA (2948 ± 819 n/kg), SFPA (2920 ± 935 n/kg), and PCEA (1680 ± 320 n/kg). MPs in four EFAs were mostly small size (0-0.49 mm), accounted for 81.71 %. Fragmented and pelleted MPs were the main shapes, occupying for 51.26 % and 28.53 %, respectively. In addition, Fourier transform infrared (FTIR) was applied to determine the polymer types of MPs and to assess the pollution risk of MPs, which ranged from 157 to 938, indicating a moderate to high risk. The results revealed that EFAs located in remote inland areas were considerably polluted by MPs, close to the developed coastal areas. This study provided systematic data on MPs pollution of EFAs, which is crucial in preventing further environmental degradation and promoting ecological restoration.

Vertical distribution and characteristics of soil microplastics under different land use patterns: A case study of Shouguang City, China

Soil microplastic pollution is ubiquitous, but the vertical distribution characteristics of microplastics in different land use types are unclear. In this study, the microplastic abundance, particle size, shape, color, and polymer type in 0-20 cm, 20-40 cm, and 40-60 cm soil layers of seven land use types (woodland, grassland, maize, wheat, cotton, polytunnel, and greenhouse) were systematically investigated in Shouguang City, a typical agricultural city in China. The results showed that the average microplastic abundance from top to deep for the three soil layers of Shouguang City were 1948.1 ± 992.5, 1349.4 ± 654, and 670.1 ± 341.6 items kg-1. In the top soil layer (0-20 cm), the abundance of microplastics in facility soils was significantly higher than in other land use types. In agricultural soils, microplastics were predominantly small size (<0.5 mm), films and fragments, PE and PP. The average microplastic abundance in deep soils (40-60 cm) of the seven land use types was 349.1 ± 62.8 (woodland), 284.9 ± 113.9 (grassland), 657.1 ± 127.1 (maize), 537.8 ± 137.4 (wheat), 851.4 ± 204.2 (cotton), 878.5 ± 295.7 (polytunnel), 1132.2 ± 304.5 (greenhouse) items kg-1, respectively, accounting for 11 % to 19 % in all three soil layers. The percentage of small size and pellet microplastics increased in deep soils (40-60 cm). Correlation analysis showed that soil environmental factors (pH, EC, total phosphorus, total nitrogen, and organic carbon) influenced to different extents the distribution, fragmentation, and transport of microplastics. The results of this study contribute to a better understanding of contamination and vertical distribution of soil microplastics in agricultural and non-agricultural soils, as well as provide important data for the development of preventive and management policies.

Impact of soil structure and texture on occurrence of microplastics in agricultural soils of karst areas

The impact of microplastics (MPs) on soil ecosystems has attracted widespread attention; however, the effects of soil structure and texture on the occurrence of MPs are not fully understood. In this study, we investigated the effects of soil structure and texture on the abundance of MPs and their potential mechanisms in agricultural soils of karst areas in Guizhou, China. The results showed the average abundance of MPs was 2948 items/kg. The soil texture in the study area can be categorized into seven types such as powdered-light clay, the range of total soil porosity was 39.05-69.22 % and the range of soil bulk density was 0.66-1.51 g/cm3. Soils with a powdered-light clay, low soil porosity, and low soil bulk density showed higher MPs pollution. The percentage of pellet MPs in agricultural soils with a powdered-light clay was 84 %, which was higher than that of the other soil textures. The direct effects of soil texture, soil porosity, and soil bulk density on MPs abundance were much lower than the indirect effects, with soil texture having the highest effect on MPs abundance. We speculated that karst geology may affect the accumulation and distribution of MPs in soil by affecting soil texture and structure, which, in turn, affects the fragmentation and migration of MPs. These findings will help to better understand the mechanisms of soil MPs pollution and provide a scientific basis for the development of relevant control strategies.

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.

Response of microplastic occurrence and migration to heavy rainstorm in agricultural catchment on the Loess plateau

Microplastics have received widespread attention as an emerging pollutant in recent years, but limited studies have explored their response to extreme weather. This study surveyed and analyzed the occurrence and distribution of microplastics in a typical agricultural catchment located on the Loess Plateau, focusing on their response to heavy rainstorms. Microplastics were detected in all soil samples with an abundance of 70-4020 items/kg, and particles less than 0.5 mm accounted for 81.61 % of the total microplastics. The main colors of microplastic were white, yellow, and transparent, accounting for 38.50 %, 32.90 %, and 21.05 % respectively, and the main shapes were film and fragment, accounting for 47.65 % and 30.81 %. Low density polyethylene was the main component of microplastics identified using Fourier transform infrared spectrometry. The extensive use of plastic mulch film is a major contributor to microplastic pollution in this catchment. The differences and connections observed in microplastics imply mutual migration and deposition within the catchment. A check dam at the outlet effectively intercepts microplastics during the rainstorm, reducing the microplastic by at least 6.1 × 1010 items downstream. This study provides a reference for the effects of rainstorms on the sources and pathways of MP pollution in regions prone to severe soil erosion.

Microplastic pollution in typical seasonal rivers in northern China: temporal variation and risk assessment

Rivers are important channels for the transport of microplastics (MPs) from land to sea. In this work, the temporal variation and risk assessment of MP pollution in the surface water of the Wei River, a typical seasonal river in northern China, were quantified. The number abundance of MPs in the dry season was significantly higher than that in the wet season (p < 0.05). Fiber was the most abundant type of MP in both dry and wet seasons. Infrared spectrometer and Raman spectroscopy identification showed that polypropylene (PP) and polyethylene (PE) were the major polymers found in both dry and wet seasons, and the mixture of different MP polymers was more diverse in the dry season. The risk assessment showed that the average pollution load index (PLI) and risk quotient (RQ) were 2.10 and 1.19 in the dry season, which significantly decreased to 1.25 and 0.74, respectively, in the wet season (p < 0.05). In total, the results from this study highlight the characteristics of seasonal rivers that influence the temporal distribution and risk assessment of microplastics, providing scientific reference for policymakers and river managers to effectively deal with MP pollution.