Minimal Impacts of Microplastics on Soil Physical Properties under Environmentally Relevant Concentrations

Mechanism of nanoplastics altering soil carbon turnover under freeze-thaw cycle

Nanoplastics (NPs) affect soil carbon (C) turnover, but their influence on this process through modifications in soil aggregate stability under freeze-thaw cycles remains unclear. In this study rare earth oxides (REOs) and C isotope (13C) labeling, combined with Soil Microstructure Scanning Computed Tomography (SMS-CT) and data modeling, were used to examine the relationship between soil aggregate turnover and C turnover under NPs. Compared with the control group, the total phase porosity and surface area of soil treated with NPs increased by 11.9 % and 30.9 %, respectively under freeze-thaw cycle. NPs exhibited a positive effect on the stability of soil aggregates, and the change in soil aggregate stability were attributed to shifts in aggregate composition. During the freeze-thaw cycle, the distribution of 13C in 0.5-1 mm aggregates decreased by 41.9 % compared with the control group, while it increased by 60.8 % in < 0.25 mm aggregates, indicating NPs redirected C toward microaggregates. Freeze-thaw cycles improved the connection between soil aggregates and C turnover, whereas NPs increased resistance of aggregate to freeze-thaw forces. This study provides new insights into the environmental effects of NPs on soil ecosystems and food security.

Microplastics in Agricultural Soils: Sources, Fate, and Interactions with Other Contaminants

Microplastics (MPs) are recognized as emerging soil contaminants. However, the potential risks of MPs to agroecosystems have not been fully revealed, especially the compound toxic effects of MPs with co-existing organic or inorganic pollutants (OPs/IPs) in agricultural fields. In this study, we quantified the contributions of different agronomic practices to the sources of MPs in soil and highlighted the important influences of long-term tillage and fertilization on the migration and aging of MPs in agricultural fields. In addition, the antagonistic and synergistic interactions between MPs and OPs/IPs in soil were explored. We emphasized that the degree of adsorption of MPs and soil particles to OPs/IPs is a key determinant of the co-toxicity of those contaminants in soil. Finally, several directions for future research are proposed, and these knowledge gaps provide an important basis for understanding the contamination process of MPs in agricultural soils.

Microplastic-induced alterations in growth and microecology of mulberry seedlings: Implications for sustainable forest-soil systems

This study investigated the ecotoxicological effects of polyethylene (PE) and polylactic acid (PLA) microplastics (MPs) on mulberry growth and soil-microbe interactions through controlled pot experiments (0.1 % and 1 % concentrations). PE exposure significantly increased mulberry height by 16 % (0.1 %) and 18 % (1 %) (p < 0.05), whereas PLA reduced total biomass by 12 % (0.1 %) and 66 % (1 %), highlighting polymer- and concentration-dependent responses. MPs differentially modulated soil biogeochemistry: PE decreased nitrate and ammonium nitrogen levels while enhancing nitrogen fixation (nifH) (from 0.9 × 107 to 6.1 × 107 copies/g) and denitrification (nirK) (from 1.0 × 108 to 1.9 × 108 copies/g) gene expression via Acidobacteriota enrichment, which was correlated with increased soil organic matter mobilisation and photosynthetic rates. PLA disrupted phosphorus cycling and destabilised structure of fungal communities critical for nutrient assimilation. Structural equation modelling identified direct microplastic-soil-plant linkages, with real-time polymerase chain reaction validating PE-driven suppression of nitrogen loss through microbial functional shifts. These findings illuminate the dual roles of microplastics as ecological stressors and modifiers, providing actionable insights for balancing agricultural productivity and soil health in MP-contaminated forest ecosystems.

Microplastics indirectly affect soil respiration of different-aged forest by altering microbial communities and carbon metabolism

This study explored how microplastics impact soil respiration processes in forests of varying ages by modulating the structure of microbial communities and carbon metabolic functions. The findings indicated that the abundance of microplastics in different aged forests was approximately 600-3858 items∙kg-1. The 10-year-old Pinus massoniana forest exhibited the lowest, and the 60-year-old forest had the highest microplastic abundance. The microplastics mainly consisted of fibers (26.57-38.38 %), particles sized 0-0.1 μm (40.28-70.19 %), and black particles (6.92-43.46 %). The soil respiration rate decreases with increasing forest age. However, the microplastics indirectly modified soil respiration by influencing total organic carbon (TOC) and soil pH. The functional prediction analysis showed that metabolic pathways such as formaldehyde assimilation, ribulose monophosphate pathway, and the hydroxypropionate-hydroxybutylate cycle, were significantly correlated with microplastic abundance. Structural equation model (SEM) results suggested that microplastics affected microbial carbon metabolic demands by altering microbial community structure (0.44) or directly influencing carbon metabolic pathways (0.68). Consequently, this impacts soil CO2 emissions. The findings provide new insights into the critical role of forest soils in mitigating carbon emissions caused by microplastics.

Water level regimes can regulate the influences of microplastic pollution on carbon loss in paddy soils: Insights from dissolved organic matter and carbon mineralization

The persistence of farmland microplastic (MP) pollution has raised significant concerns regarding its effects on soil organic carbon (SOC) pools in the context of soil pollution but also of global climate change. Nevertheless, the effect of MPs on SOC mineralization as well as dissolved organic carbon (DOC) transformation with different water levels in paddy soils remained uncertain. In this study, we investigated the effect of micro polyethylene (PE) on SOC decomposition in paddy soils under alternating wet and dry (AWD) and continuous flooding (CF) conditions through a 205-day microcosm experiment. Polyethylene addition reduced cumulative CO2 emissions by 5.1-14.8 % under both water conditions. The presence of PE influenced SOC mineralization under CF conditions by diminishing the activity of cellobiohydrolase enzymes and increasing the microbial community diversity. Conversely, at AWD the addition of PE impeded SOC mineralization by reducing the activity of polyphenol oxidase enzymes. However, PE addition resulted in higher DOC content and at low dose of PE addition (0.25 % w/w) increased DOM bioavailability. The most significantly positive effect was found with the addition of 1 % w/w PE, which increased DOC content by 37.2 % and 18.5 % compared to Control (CK) under AWD and CF conditions, respectively. The strong correlation observed between DOC and mineral-associated organic carbon (MAOC) concentrations might result from DOC adsorbed to mineral surfaces to form MAOC and then affect SOC mineralization. Accordingly, AWD is a more efficient management to attenuate the impact of MPs on SOC decomposition compared to CF. Our study is noteworthy in the development of sustainable agricultural practice management in plastic-contaminated soil-crop systems.

In-field degradation of polybutylene adipate-co-terephthalate (PBAT) films, microplastic formation, and impacts on soil health

Polybutylene adipate-co-terephthalate (PBAT) mulch films are potential alternatives to traditional polyethylene (PE) mulch films in agriculture. Here, we investigated the degradation rate and microplastic formation of PBAT films in an agricultural field and the impacts on soil health as well as maize yields. We compared two biodegradable films (PBAT clear film: BCF and PBAT black film: BBF) with two conventional films (PE clear film: PCF and PE black film: PBF) in a field experiment over three growing seasons. Biodegradable films consisted of >90% PBAT and 5% polylactic acid. After three years of mulching, more microplastics were detected for the BCF (1820 particles kg-1) and BBF (1560 particles kg-1) treatments than for PCF (840 particles kg-1) and PBF (747 particles kg-1). The majority (about 70%) of microplastics in BCF and BBF were <0.25 mm, while in PCF and PBF the fraction of microplastics <0.25 mm made up only 24-41%. Biodegradable films increased soil organic carbon, microbial biomass carbon, and nitrate nitrogen by 0.16-0.48 g kg-1, 5.5-33.8 mg kg-1, and 32.6-109.6 mg kg-1, respectively, compared to PE films. Yield was highest for BBF, exceeding that of non-film, PCF, PBF and BCF by 2550, 566, 960 and 367 kg ha-1, respectively. Overall, the biodegradable films had a positive impact on soil health and maize yields.

Microplastics in sandy soils: Alterations in thermal conductivity, surface albedo, and temperature

Rapid growth in plastic production has exacerbated disposal of plastic wastes in terrestrial ecosystems. Unfortunately, soils represent large reservoirs for disposal of microplastics (MPs). MPs infiltrate into the soil through various pathways and alter its intrinsic properties. Despite advances in understanding the impact of MPs on soil physical, biological, and hydrological processes, their influence on surface energy balance and soil temperature remains understudied. Such information is more necessary than ever, considering the ongoing changes to soil systems caused by climate variations and extremes. We conducted laboratory experiments on sandy soils to investigate how MPs with different characteristics impact soil temperature dynamics. The changes in the soil thermal conductivity and surface albedo, in the presence of polyethylene (PE) and polyvinylchloride (PVC) particles at various concentrations were measured. The results demonstrate that MPs, and particularly PVC, with amorphous characteristics may decrease effective thermal conductivity of sand by 38%. Moreover, the deposition of MPs at the surface of samples may increase surface albedo by 28% and 77% with addition of 5% PVC and 5% PE, respectively. Such effects are pronounced at higher soil moisture contents, facilitating migration and deposition of MPs on the surface. We ultimately examined the impact of changes in soil thermal and radiative properties on soil temperature dynamics by monitoring the thermal regime in drying sand columns. Our findings indicate that MPs significantly alter evaporative flux and subsurface temperature profile, hence providing insights into understanding the changes in soil energy balance due to the presence of MPs.

Potential impacts of microplastic pollution on soil-water-plant dynamics

This study was designed to assess the potential impact of microplastic (MP) pollution on soil hydrology, specifically in retaining and releasing moisture. Herein, High-Density Polyethylene (HDPE) MP of different sizes (i.e., 0.5-1, 1-3, and 3-5 mm) and shapes (i.e., fiber, film, and fragment) were evaluated for their effects on water retention curve (WRC) of sandy loam soil, chosen for its agricultural relevance and widespread environmental presence of HDPE. Nine contamination scenarios were simulated with a low MP pollution rate, 0.01% w/w. Van Genuchten models were used to assess plant available water (PAW), wilting point (WP), and water holding capacity (WHC). Results showed that studied MP could significantly affect WRC and PAW mainly by changing WHC rather than WP and that this effect varied with MP shape and size. According to the results, fragment MP had the greatest impact on soil WHC by increasing 36.3%, followed by fibers and films by 19.8% and 15.7%. MP particles significantly increased WHC, while WP remained relatively unchanged. An observed trend indicated that the impact on WHC increased with the size of the MP particles. These findings emphasize the need to manage soil MP pollution to protect plant growth, agriculture, and water dynamics.

Mechanisms of microplastic generation from polymer-coated controlled-release fertilizers (PC-CRFs)

Polymer-coated controlled-release fertilizers (PC-CRFs) are valued for nutrient efficiency, but concerns remain about the long-term impacts of their plastic coatings on soil health. This study investigates the physicochemical characteristics of two commercially available PC-CRFs, type A and B, and their changes during nutrient release. Accelerated nutrient release experiments were conducted for 25 d in ultrapure water (free water) and saturated soil with five wet-dry cycles. Total phosphorus and total nitrogen release were measured, with lower concentrations found in soil column effluent compared to water. Additionally, studying microplastic (MP) release from type A PC-CRFs during nutrient release showed that a significantly greater number of MPs were released in the soil column than in water. The results also indicated a preferential migration of smaller MPs to the deeper layers of the soil column. Microscopic pores and cracks were observed through surface morphology analysis, likely caused by osmotic pressure during nutrient release, potentially contributing to MP generation. Mechanical degradation of the type A PC-CRF microcapsules was assessed through surface wear and shear tests to simulate the forces exerted by soil particles and agricultural machinery. Our results showed that longer surface wear duration increased the number of generated MPs, while higher loading in surface wear experiments resulted in a larger median diameter of the MPs.

Effects of naturally aged microplastics on arsenic and cadmium accumulation in lettuce: Insights into rhizosphere microecology

Naturally aged microplastics (NAMPs) are commonly found in farmland soils contaminated with heavy metals (HMs), such as arsenic (As) and cadmium (Cd); yet their combined effects on soil-plant ecosystems remain poorly understood. In this study, we investigated the toxic effects of NAMPs and As-Cd on lettuce, considering the influence of earthworm activity, and examined changes in As-Cd bioavailability in the rhizosphere. Four experimental systems were established: soil-only, soil-lettuce, soil-earthworms, and soil-lettuce-earthworms systems, with four NAMPs concentrations (0, 0.1, 0.5, 1 %). Our results showed that exposure to 0.1 % NAMPs reduced As accumulation in lettuce shoots (0.17-0.25 mg kg-1) and roots (1.13-1.72 mg kg-1), while increasing biomass and enhancing root growth by alleviating toxicity. In contrast, the combined stress of higher NAMPs concentration (0.5 %/1 %) and As-Cd caused a 28.4-58.4 % reduction in root activity, which stimulated low-molecular-weight organic acid (LMWOA) secretion in the rhizosphere, increasing the bioavailability of As and Cd and enhancing their absorption by lettuce. Partial least squares path modeling (PLS-PM) revealed that co-exposure altered LMWOA content, soil enzyme activity, and microbial community stability in the rhizosphere, ultimately influencing the bioavailability and uptake of As and Cd by lettuce.

Smallest microplastics intensify maize yield decline, soil processes and consequent global warming potential

Microplastic pollution seriously affects global agroecosystems, strongly influencing soil processes and crop growth. Microplastics impact could be size-dependent, yet relevant field experiments are scarce. We conducted a field experiment in a soil-maize agroecosystem to assess interactions between microplastic types and sizes. Microplastics were added to soils used for maize cultivation: either polyethylene or polystyrene, of 75, 150, or 300 µm size. Overall, we found that microplastic contamination led to increased soil carbon, nitrogen and biogeochemical cycling. Polyethylene contamination was generally more detrimental than polystyrene. Smallest polyethylene microplastics (75 µm) were associated with two-fold raised CO2 and N2O emissions - hypothetically via raised microbial metabolic rates. Increased net greenhouse gases emissions were calculated to raise soil global warming potential of soils. We infer that MPs-associated emissions arose from altered soil processes. Polyethylene of 75 µm size caused the greatest reduction in soil carbon and nitrogen pools (1-1.5 %), with lesser impacts of larger microplastics. These smallest polyethylene microplastics caused the greatest declines in maize productivity (∼ 2-fold), but had no significant impact on harvest index. Scanning electron microscopy indicated that microplastics were taken up by the roots of maize plants, then also translocated to stems and leaves. These results raise serious concerns for the impact of microplastics pollution on future soil bio-geochemical cycling, food security and climate change. As microplastics will progressively degrade to smaller sizes, the environmental and agricultural impacts of current microplastics contamination of soils could increase over time; exacerbating potential planetary boundary threats.

Environmental release behavior, cell toxicity and intracellular distribution of novel biodegradable plastic materials

In response to the increasingly severe issue of plastic waste, biodegradable plastics have garnered extensive attention as a potential alternative to traditional plastics. Among these materials, biodegradable plastics hold a dominant position. The objective of this study was to assess the environmental risks of five commercially available biodegradable plastics: polyglycolic acid (PGA), polylactic acid (PLA), poly(butylene succinate) (PBS), poly(butylene carbonate) (PBC), and poly(butylene adipate-co-terephthalate) (PBAT). The evaluation included their physical properties, microplastic release behavior, and cytotoxicity. In addition, the effect of age process on the environmental behavior of biodegradable plastic materials was further investigated. The results revealed that PGA and PBS exhibited lower risks in terms of microplastic release, whereas PLA demonstrated higher environmental mobility. Further cytotoxicity experiments indicated that PLA and PBS exerted significant toxic effects on human cell lines, including human normal liver cells (LO2), human monocytic leukemia cells (THP-1), human umbilical vein endothelial cells (HUVECs), and human colon carcinoma cells (Caco-2). Additionally, this study utilized Nile Red labeling to observe the co-culture system of PGA with THP-1 cells, uncovering that THP-1 cells gradually engulfed and internalized PGA microplastics over time. This finding provides new insights into the potential mechanism by which microplastics promote cell proliferation. Moreover, we also found that the aging process partially reduced the cytotoxicity of PGA, but had little effect on environmental mobility. Considering the comprehensive research findings, PGA is considered an ideal material for large-scale applications due to its low cytotoxicity and environmental risks. In contrast, the environmental safety of other types of plastics requires more comprehensive risk assessment to determine their suitability. This study provides significant scientific evidence for the environmental impact assessment of biodegradable plastics and plays a crucial role in promoting the development of sustainable plastic alternatives.

Microplastics in agricultural soil: Unveiling their role in shaping soil properties and driving greenhouse gas emissions

Microplastics (MPs) contamination is pervasive in agricultural soils, significantly influencing carbon and nitrogen biogeochemical cycles and altering greenhouse gas (GHG) fluxes. This review examines the sources, status, mechanisms, and ecological consequences of MPs pollution in agricultural soils, with a focus on how MPs modified soil physicochemical properties and microbial gene expression, ultimately impacting GHG emissions. MPs were found to reduce soil water retention, decreasing soil respiration and increasing emissions of CO2, CH₄, and N2O. They also enhanced soil aggregate stability and influenced soil organic carbon (SOC) sequestration, contributing further to GHG emissions. MPs-induced increases in soil pH were associated with suppressed CH₄ and N2O emissions, whereas the abundance of genes encoding enzymes for cellulose and lignin decomposition (e.g., abfA and mnp) stimulated enzyme activity, intensifying N2O release. Additionally, a reduced soil C/N ratio promoted denitrification processes. Changes in microbial communities, including increases in Actinomycetes and Proteobacteria, were observed, with a rise in genes associated with carbon cycling (abfA, manB, xylA) and nitrification-denitrification (nifH, amoA, nirS, nirK), further exacerbating CO2 and N2O emissions. This review provides valuable insights into the complex roles of MPs in GHG dynamics in agricultural soils, offering perspectives for improving environmental management strategies.

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.

Effects of polyethylene and poly (butyleneadipate-co-terephthalate) contamination on soil respiration and carbon sequestration

To address plastic pollution in agricultural soils due to polyethylene plastic film mulch used, biodegradable film is being studied as a promising alternative material for sustainable agriculture. However, the impact of biodegradable and polyethylene microplastics on soil carbon remains unclear. The field experiment was conducted with Poly (butyleneadipate-co-terephthalate) debris (PBAT-D, 0.5-2 cm), low-density polyethylene debris (LDPE-D, 0.5-2 cm) and microplastic (LDPE-Mi, 500-1000 μm) contaminated soil (0% (control), 0.05%, 0.1%, 0.2%, 0.5%, 1% and 2% w:w) planted with soybean, to explore potential impacts on soil respiration (Rs), soil organic carbon (SOC) and carbon fractions (microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidizable carbon (EOC), particulate organic carbon (POC), mineral-associated organic carbon (MAOC)), and C-enzymes (β-glucosidase, β-xylosidase, cellobiohydrolase). Results showed that PBAT-D, LDPE-D and LDPE-Mi significantly inhibited Rs compared with the control during the flowering and harvesting stages (p < 0.05). SOC significantly increased in the PBAT-D treatments at both stages, and in the LDPE-Mi treatments at the harvesting stage, but decreased in the LDPE-D treatments at the flowering stage. In the PBAT-D treatments, POC increased but DOC and MAOC decreased at both stages. In the LDPE-D treatments, MBC, DOC and EOC significantly decreased but POC increased at both stages. In the LDPE-Mi treatments, MBC and DOC significantly decreased at the harvesting stage, while EOC and MAOC decreased but POC increased at the flowering stage. For C-enzymes, no significant inhibition was observed at the flowering stage, but they were significantly inhibited in all treatments at the harvesting stage. It is concluded that PBAT-D facilitates soil carbon sequestration, which may potentially alter the soil carbon pool and carbon emissions. The key significance of this study is to explore the overall effects of different forms of plastic pollution on soil carbon dynamics, and to inform future efforts to control plastic pollution in farmlands.

Comprehensive understanding of microplastics in compost: Ecological risks and degradation mechanisms

The introduction of microplastics (MPs) into soil ecosystems via compost application has emerged as a critical environmental concern. However, the ecological risks and degradation behavior of MPs in compost remain insufficiently understood. This review addresses these gaps by synthesizing recent findings on MPs in composting systems, focusing on their sources, impacts on compost quality, ecological risks, and degradation mechanisms. MP sources vary significantly across compost matrices-domestic waste, sludge, and agricultural waste‑leading to differences in their types and quantities. MPs adversely impact compost quality by disrupting its physical structure and impairing fertility, aeration, and water retention. Furthermore, their persistence after compost application can result in long-term environmental accumulation, posing risks to soil ecosystems and biological health. This review also explores the aging and degradation of MPs during composting, a complex process influenced by physical, chemical, and biological mechanisms. Finally, we propose future research directions, emphasizing the development of standardized methodologies to assess MP behavior in compost and strategies to mitigate associated risks. These insights contribute to advancing sustainable waste management and environmental protection practices.

Root traits of soybeans exposed to polyethylene films, polypropylene fragments, and biosolids

Biosolid use imports microplastics into the rhizosphere where they may interfere with root-soil-microbial interactions and cause morphological adaptations in crop root systems. Few studies have examined the response of crop roots to microplastics at documented soil concentrations, and many studies collect root traits using destructive techniques. Hence, there is little information on when and how microplastics effect the physical structure of root systems. Using the rhizobox method, soybeans (Glycine max) were grown in soil amended with biosolid microplastic mimics (polyethylene film or polypropylene fragments at 2,000 and 15,000 particles/kg dry soil) or biosolids and imaged weekly until maturity (11 weeks) using a custom scanner system. Plant biomass increased in the polyethylene treatments and decreased in the high concentration polypropylene treatment. Relative to the Control, polyethylene treatments had larger root length, reduced root diameters, reached maturity faster, had deeper root systems, and had a greater number of lateral roots. In contrast, polypropylene treatments had a mixed response, with high concentrations eliciting a lower root length, fewer laterals, and a more vertical root orientation. Segmented linear regression revealed that root growth in the Control and Biosolid treatments continued through the course of the experiment, while the microplastic treatments reached maturity up to two weeks earlier. Imagery revealed that microplastics elicited deeper rooting depth within the first week and differences in all root traits were evident by the development of the first trifoliate leaflets. Microplastic effects on root traits at early life stages suggest soil physiological drivers, while increased branching frequency and lower lateral elongation are suggestive of changes in soil nitrogen availability. The minimal difference in root traits in the biosolid treatment may be attributable to differences in microplastic properties or counteractive effects by other biosolid constituents.

Rapid on-site analysis of soil microplastics using miniaturized NIR spectrometers: Key aspect of instrumental variation

Contamination by microplastics, a global environmental concern, demands effective monitoring. While current methods focus on characterizing the smallest particles, their low throughput hinders practical assessment. Miniaturized near-infrared (NIR) spectroscopy offers high-throughput capabilities and rapid on-site analysis, potentially filling this gap. However, diverse sensor characteristics result in significant differences among handheld NIR spectrometers. This study characterizes the analytical performance of these instruments for identifying soil microplastics, comparing miniaturized devices MicroNIR 1700ES, NeoSpectra Scanner, microPHAZIR, nanoFTIR-NIR, NIR-S-G1, and SCiO sensor against a reference benchtop instrument, the NIRFlex N-500. Detection of common polymers, ABS, EVAC, HDPE, LDPE, PA6, PMMA, POM, PET, PS, PTFE, and SBR, at low concentrations (0.75 % w/w) was possible without sample preparation. Sensor selection proved crucial; FT instruments N-500 and NeoSpectra Scanner provided the most accurate analysis, while other handheld instruments faced various challenges. Covariance analysis, Principal Component Analysis (PCA), and mid-level data fusion revealed that miniaturized NIR spectrometers can successfully screen microplastics on-site. However, the ability of each sensor to discriminate certain groups of polymers strongly depends on its spectral characteristics. This study demonstrates the importance of sensor selection in the development of portable NIR spectroscopy for environmental monitoring of microplastics.

A state-of-the-art review of environmental behavior and potential risks of biodegradable microplastics in soil ecosystems: Comparison with conventional microplastics

As the use of biodegradable plastics becomes increasingly widespread, their environmental behaviors and impacts warrant attention. Unlike conventional plastics, their degradability predisposes them to fragment into microplastics (MPs) more readily. These MPs subsequently enter the terrestrial environment. The abundant functional groups of biodegradable MPs significantly affect their transport and interactions with other contaminants (e.g., organic contaminants and heavy metals). The intermediates and additives released from depolymerization of biodegradable MPs, as well as coexisting contaminants, induce alterations in soil ecosystems. These processes indicate that the impacts of biodegradable MPs on soil ecosystems might significantly diverge from conventional MPs. However, an exhaustive and timely comparison of the environmental behaviors and effects of biodegradable and conventional MPs within soil ecosystems remains scarce. To address this gap, the Web of Science database and bibliometric software were utilized to identify publications with keywords containing biodegradable MPs and soil. Moreover, this review comprehensively summarizes the transport behavior of biodegradable MPs, their role as contaminant carriers, and the potential risks they pose to soil physicochemical properties, nutrient cycling, biota, and CO2 emissions as compared with conventional MPs. Biodegradable MPs, due to their great transport and adsorption capacity, facilitate the mobility of coexisting contaminants, potentially inducing widespread soil and groundwater contamination. Additionally, these MPs and their depolymerization products can disrupt soil ecosystems by altering physicochemical properties, increasing microbial biomass, decreasing microbial diversity, inhibiting the development of plants and animals, and increasing CO2 emissions. Finally, some perspectives are proposed to outline future research directions. Overall, this study emphasizes the pronounced effects of biodegradable MPs on soil ecosystems relative to their conventional counterparts and contributes to the understanding and management of biodegradable plastic contamination within the terrestrial ecosystem.

Wet-dry or freeze-thaw alternation can regulate the impacts of farmland plastic pollution on soil bacterial communities and functions

The persistence of farmland plastic pollution has raised significant concerns regarding its potential long-term impacts on soil health in the context of global climate change. However, there are still gaps in the understanding of the impacts of plastic residues on soil microbial communities and functions in agricultural environments under unstable and extreme climatic conditions. In this study, the effects of plastic residues (two types and three shapes) on farmland soil bacterial communities and functions across varying environmental conditions were investigated through microscopic experiments. The results revealed that plastic residues subjected to wet-dry or freeze-thaw alternations exhibited greater degradation compared to those under natural conditions. The effects of plastic residue types and shapes on soil bacterial diversity and function were regulated by environmental factors. The plastic residues significantly reduced the stability of the bacterial network under natural condition (P < 0.05), whereas the opposite phenomenon was observed under wet-dry or freeze-thaw alternating conditions. Compared to under natural condition, lower numbers of bacterial functional pathways exhibiting significant differences due to plastic residues were observed under wet-dry or freeze-thaw alternating conditions. Significant associations were observed between soil bacterial communities and functions and various soil physicochemical properties under natural conditions (P < 0.05), and most of these associations were attenuated in the wet-dry or freeze-thaw alternations. This study demonstrated the potential impacts of plastic pollution on farmland soil microbiomes, which could be modulated by both residue characteristics and climatic conditions. Specifically, extreme environments could mitigate plastic-pollution-driven influences on soil microbiomes.

Multifaceted effects of microplastics on soil-plant systems: Exploring the role of particle type and plant species

Microplastics have emerged as a global environmental concern, yet their impact on terrestrial environments, particularly agricultural soils, remains underexplored. Agricultural soils, due to intensive farming, may serve as significant sinks for microplastics. This study investigated the effects of different types of microplastics-polyester microfibers, polyethylene terephthalate microfragments, and polystyrene microspheres-on soil properties and radish growth, while a complementary experiment examined the impact of polyester microfibers on the growth of lettuce and Chinese cabbage. Through both horizontal and vertical comparisons, this research comprehensively evaluated the interactions between microplastic particles and plant species in soil-plant systems. The results showed that polyester microfibers significantly affected soil bulk density, with effects varying based on planting conditions (p < 0.01). Polyethylene terephthalate microfragments and polystyrene microspheres reduced the proportion of small soil macroaggregates under radish cultivation (p < 0.01). Additionally, polystyrene microspheres significantly altered the total organic carbon stock in radish-growing soil, potentially affecting the microclimate (p < 0.01). Interestingly, polyester microfibers promoted lettuce seed germination and significantly enhanced the root biomass of Chinese cabbage (p < 0.05). Overall, the environmental effects of microplastic exposure varied depending on the type of particle and plant species, suggesting that microplastics are not always harmful to soil-plant systems and may even offer benefits in certain scenarios. Given the crucial role of soil-plant systems in terrestrial ecosystems, and their direct connection to food safety, human health, and global change, further research should explore both the positive and negative impacts of microplastics on agricultural practices.

Co-exposure to microplastics and soil pollutants significantly exacerbates toxicity to crops: Insights from a global meta and machine-learning analysis

Environmental contamination of microplastics (MPs) is ubiquitous worldwide, and co-contamination of arable soils with MPs and other pollutants is of increasing concern, and may lead to unexpected consequences on crop production. However, the overall implications of this combined effect, whether beneficial or detrimental, remain a subject of current debate. Here, we conducted a global meta and machine-learning analysis to evaluate the effects of co-exposure to MPs and other pollutants on crops, utilizing 3346 biological endpoints derived from 68 different studies. Overall, compared with control groups that only exposure to conventional soil contaminants, co-exposure significantly exacerbated toxicity to crops, particularly with MPs intensifying adverse effects on crop morphology, oxidative damage, and photosynthetic efficiency. Interestingly, our analysis demonstrated a significant reduction in the accumulation of pollutants in the crop due to the presence of MPs. In addition, the results revealed that potential adverse effects were primarily associated with crop species, MPs mass concentration, and exposure duration. Our study reaffirms the substantial consequences of MPs as emerging pollutants on crops within the context of integrated pollution, providing novel insights into improving sustainability in agro-ecosystems.

Deciphering the role of nonylphenol adsorption in soil by microplastics with different polarities and ageing processes

In the soil environment, microplastics (MPs) commonly coexist with organic pollutants such as nonylphenol (NP), affecting the migration of NP through adsorption/desorption. However, few studies have focused on the interaction between NP and MPs in soil, especially for MPs of different types and ageing characteristics. In this study, non-polar polypropylene (PP) and polar polyamide (PA) MPs were aged either photochemically (144 h) or within soil (60 days), then used to determine the effect of 5 % MPs on the adsorption behaviour of NP (0.1-4.0 mg/L) in soil. Results showed that both ageing processes significantly promoted the conversion of -CH3 groups to C-O and CO on the surface of PPMPs, while PAMPs exhibited amide groups changes and a reduction in average particle size due to ageing. Additionally, both ageing processes promoted the adsorption of NP by soil containing PPMPs, due to an increase in oxygen-containing functional groups and specific surface area. In contrast, the NP adsorption capacity of soil containing PAMPs decreased by 15.4 % following photochemical ageing due to hydrolysis of amide groups, but increased by 21.15 % after soil ageing due to reorganization of amide groups, respectively. The soil-PAMPs systems exhibited a stronger affinity for NP compared to the soil-PPMPs systems, which was primarily attributed to the dominant role of hydrogen bonding. NP was found to be distributed mainly on soil particles in the soil-PPMPs systems, while it tended to be adsorbed by MPs in the soil-PAMPs systems, especially in the soil aged MPs system. This study provides a comprehensive analysis of the complex effects of MPs on coexisting pollutants in soil environments, highlighting the effect of MP characteristics on the adsorption of organic pollutants, which is essential for understanding the transport behaviour of organic pollutants.

Rapid Generation of Microplastics and Plastic-Derived Dissolved Organic Matter from Food Packaging Films under Simulated Aging Conditions

In this study, we show that low-density polyethylene films, a prevalent choice for food packaging in everyday life, generated high numbers of microplastics (MPs) and hundreds to thousands of plastic-derived dissolved organic matter (DOM) substances under simulated food preparation and storage conditions. Specifically, the plastic film generated 66-2034 MPs/cm2 (size range 10-5000 μm) under simulated aging conditions involving microwave irradiation, heating, steaming, UV irradiation, refrigeration, freezing, and freeze-thaw cycling alongside contact with water, which were 15-453 times that of the control (plastic film immersed in water without aging). We also noticed a substantial release of plastic-derived DOM. Using ultrahigh-resolution mass spectrometry, we identified 321-1414 analytes with molecular weights ranging from 200 to 800 Da, representing plastic-derived DOM containing C, H, and O. The DOM substances included both degradation products of polyethylene (including oxidized forms of oligomers) and toxic plastic additives. Interestingly, although no apparent oxidation was observed for the plastic film under aging conditions, plastic-derived DOM was more oxidized (average O/C increased by 27-46%) following aging with a higher state of carbon saturation and higher polarity. These findings highlight the future need to assess risks associated with MP and DOM release from plastic wraps.

Global microplastics pollution: a bibliometric analysis and review on research trends and hotspots in agroecosystems

The prevalence of microplastics (MPs) in agricultural ecosystems poses a notable threat to dynamics of soil ecosystems, crop productivity, and global food security. MPs enter agricultural ecosystems from various sources and have considerable impacts on the physiochemical properties soil, soil organisms and microbial communities, and plants. However, the intensity of these impacts can vary with the size, shape, types, and the concentrations of MPs in the soil. Besides, MPs can enter food chain through consummation of crops grown on MPs polluted soils. In this study, we conducted a bibliometric analysis of 1636 publications on the effects of MPs on agricultural ecosystems from 2012 to May 2024. The results revealed a substantial increase in publications over the years, and China, the USA, Germany, and India have emerged as leading countries in this field of research. Social network analysis identified emerging trends and research hotspots. The latest burst keywords were contaminants, biochar, polyethylene microplastics, biodegradable microplastics, antibiotic resistance genes, and quantification. Furthermore, we have summarized the effects of MPs on various components of agricultural ecosystems. By integrating findings from diverse disciplinary perspectives, this study provides a valuable insight into the current knowledge landscape, identifies research gaps, and proposes future research directions to effectively tackle the intricate challenges associated with MPs pollution in agricultural environments.

Impact of microplastics on strength parameters of clayey, Sandy, silty soil: A comparative assessment

The comparative assessment of a variety of microplastic contamination on various soil types hasn't been extensively explored in existing literature. The present study focuses on the comparative analysis of the impact of environmentally relevant concentrations of LDPE, HDPE, and PVC microplastic contamination (2 %, 4 %, and 6 %) on index properties and strength parameters of sandy, silty and clayey soil types at varying observation days 5,10,15,20,25, and 30 days. Extensive experimental investigations are carried out to understand the effect of contamination on moisture content, specific gravity, liquid limit, plastic limit, plasticity index, optimum moisture content, maximum dry density, and shear strength parameters of the respective soil type. It is observed that the depletion in Atterberg's limits is found more in the case of clayey soil as compared to silty soil because clayey soils consist of large specific surface areas leading to van der Waals force of attraction being the predominant force between particles, compared with silty soil which is affected by microplastic addition leading to decrease in net attractive forces. In the case of clayey soil maximum depletion of liquid limit up to 168 %, plastic limit up to 33 %, plasticity index (136 %), and optimum moisture content (9.04 %) is observed for PVC microplastic. The deduction in maximum dry density values is observed more for sandy soil (0.59 g/cc) followed by silty soil (0.21 g/cc) and clayey soil (0.12 g/cc). The maximum depletion of moisture content(delta-8 %), shear strength (delta-0.89 kg/cm2), and maximum dry density (delta-0.44 g/cc) is observed in the case of sandy soil for PVC and LDPE microplastic contamination. Significant depletion in optimum moisture content is observed in the case of clayey soil (9.57 %) compared to sandy (5.62 %) and silty soil (5.3 %). An increase in cohesion is observed for sandy soil (0.09 kg/cm2) and a decrease for clayey (0.19 kg/cm2) and silty soil (0.19 kg/cm2). The angle of internal friction is reduced in the case of clayey soil (∆-14.380) followed by silty soil (∆-11.230) and sandy soil (∆-11.020). For silty soil maximum depletion of specific gravity(delta-1.06) and cohesion (0.192 kg/cm2) is observed for LDPE and HDPE microplastic. The sandy soil type is most affected due to microplastic contamination irrespective of the type of microplastic contamination followed by clayey soil and the silty soil type is least affected. The maximum overall shear strength is reduced due to microplastic contamination in all the soil types.

Mitigating the detrimental impacts of low- and high-density polyethylene microplastics using a novel microbial consortium on a soil-plant system: Insights and interactions

The accumulation of polyethylene microplastics (PE-MPs) in soil has raised considerable concerns; however, the effects of their persistence and mitigation on agroecosystems have not been explored. This study aimed to assess the detrimental effects of PE-MPs on a soil-plant system and evaluate their mitigation using a novel microbial consortium (MC). We incorporated low-density polyethylene (LDPE) and high-density polyethylene (HDPE) at two different concentrations, along with a control (0 %, 1 %, and 2 % w/w) into the sandy loam soil for a duration of 135 days. The samples were also treated with a novel MC and incubated for 135 days. The MC comprised three bacterial strains (Ralstonia pickettii (MW290933) strain SHAn2, Pseudomonas putida strain ShA, and Lysinibacillus xylanilyticus XDB9 (T) strain S7-10F), and a fungal strain (Aspergillus niger strain F1-16S). Sunflowers were subsequently cultivated, and physiological growth parameters were measured. The results showed that adding 2 % LDPE significantly decreased soil pH by 1.06 units compared to the control. Moreover, adding 2 % HDPE resulted in a more significant decrease in soil electrical conductivity (EC) relative to LDPE and the control. A dose-dependent increase in dissolved organic carbon (DOC) was observed, with the highest DOC found in 2 % LDPE. The addition of higher dosages of LDPE reduced soil bulk density (BD) more than HDPE. The addition of 2 % HDPE increased the water drop penetration time (WDPT) but decreased the mean weight diameter of soil aggregates (MWD) and water-stable aggregates (WSA) compared to LDPE. The results also revealed that higher levels of LDPE enhanced soil basal respiration (BR) and microbial carbon biomass (MBC). The interaction of MC and higher MP percentages considerably reduced soil pH, EC, BD, and WDPT but significantly increased soil DOC, MWD, WSA, BR, and MBC. Regarding plant growth, incorporating 2 % PE-MPs significantly reduced physiological responses of sunflower: chlorophyll content (Chl; -15.2 %), Fv/Fm ratio (-25.3 %), shoot dry weight (ShD; -31.3 %), root dry weight (RD; -40 %), leaf area (LA; -38.4 %), and stem diameter (StemD; -25 %) compared to the control; however, the addition of novel MC considerably reduced and ameliorated the harmful effects of 2 % PE-MPs on the investigated plant growth responses.

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

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

Microplastics alter soil structural stability as quantified by high-energy moisture characteristics

Microplastics (MiPs) can potentially influence soil structural stability, with impacts likely dependent on their chemistry, concentration, size, and degradation in soil. This study used high-energy moisture characteristics (HEMC; water retention at matric suctions from 0 to 50 hPa) to quantify the effects of these MiP properties on soil structure stabiltiy. The HEMCs of soil samples contaminated with polypropylene (PP) or polyethylene (PE) were measured and modelled. Greater MiP concentrations (2 % and 7 % w w-1) increased the volume of drainable pores (VDP). At smaller MiP concentrations (0.5 % and 1 % w w-1), larger MiP fibres (3 and 5 mm) exhibited higher VDP values compared to a smaller size (1.6 mm) across a range of concentrations. Both PE and PP MiPs increased the modal matric suction (hmodal). The impacts on VDP and hmodal were more pronounced for fast than slow wetting, likely due to MiPs fibres entangling around soil aggregates, and MiPs pores filling after aggregate slaking, respectively. Soil structural index (SI) and stability ratio (SR) values increased following MiP incorporation. Our findings revealed the detrimental impacts of MiPs on soil aggregates and pores, demonstrating that MiPs significantly influence HEMC parameters due to combined impacts on structure stability and pore distribution. ENVIRONMENTAL IMPLICATION: Microplastics have emerged as a major anthropogenic hazardous material in the soil environment, with secondary impacts on soil structure and aggregate stability. Our study indicates that MiPs alter water retention, pore distribution, and soil hydraulic properties, affecting soil's ability to retain and supply water. The introduction of MiPs leads to the destruction of soil aggregates and pores, compromising soil health and productivity. By characterising structural stability and pore structure dynamics using HEMC, this study highlights the sensitivity of MiP impacts, emphasizing the need for comprehensive assessment and strategies to preserve soil ecosystem functioning in the face of increasing MiP pollution.

Micro/nanoplastics pollution poses a potential threat to soil health

Micro/nanoplastic (MNP) pollution in soil ecosystems has become a growing environmental concern globally. However, the comprehensive impacts of MNPs on soil health have not yet been explored. We conducted a hierarchical meta-analysis of over 5000 observations from 228 articles to assess the broad impacts of MNPs on soil health parameters (represented by 20 indicators relevant to crop growth, animal health, greenhouse gas emissions, microbial diversity, and pollutant transfer) and whether the impacts depended on MNP properties. We found that MNP exposure significantly inhibited crop biomass and germination, and reduced earthworm growth and survival rate. Under MNP exposure, the emissions of soil greenhouse gases (CO2, N2O, and CH4) were significantly increased. MNP exposure caused a decrease in soil bacteria diversity. Importantly, the magnitude of impact of the soil-based parameters was dependent on MNP dose and size; however, there is no significant difference in MNP type (biodegradable and conventional MNPs). Moreover, MNPs significantly reduced As uptake by plants, but promoted plant Cd accumulation. Using an analytical hierarchy process, we quantified the negative impacts of MNP exposure on soil health as a mean value of -10.2% (-17.5% to -2.57%). Overall, this analysis provides new insights for assessing potential risks of MNP pollution to soil ecosystem functions.

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

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

Regulatory path for soil microbial communities depends on the type and dose of microplastics

To reveal the feedbacks and regulating mechanisms of microplastic types and doses on microbial community, a microcosm experiment was carried out with two non-degradable microplastics [polyethylene (PE) and polyvinyl chloride (PVC)] and four biodegradable microplastics [poly(butylene succinate) (PBS), polyhydroxyalkanoates (PHA), poly(butyleneadipate-co-terephthalate) (PBAT), and polypropylene carbonate (PPC)] at different levels (1 %, 7 %, and 28 %). As a result, the content of total carbon (TC), soil organic carbon (SOC), and microbial biomass carbon (MBC) (expect MBC in PBS soil) increased with increasing doses of microplastics, and increased at the lowest PE dose rate. Biodegradable microplastics created a more active ecological niche while enriching more pathogens than non-degradable microplastics. Structural equation modeling indicated that microbial diversities were in a type-dependent assembly, whereas microbial compositions were more profoundly affected by the microplastic doses, ultimately. The standardized total effect coefficient of microplastic types on bacterial and fungal diversities was - 0.429 and - 0.282, and that of doses on bacterial and fungal compositions was 0.487 and 0.336, respectively. Both microplastic types and doses significantly impacted pH, electrical conductivity, total nitrogen, TC, SOC, and MBC, subsequently inhibiting microbial diversities and stimulating microbial compositions with particular pathways. The results provide a comprehensive understanding for evaluating the potential risk of microplastics.

Earthworms improve the rhizosphere micro-environment to mitigate the toxicity of microplastics to tomato (Solanum lycopersicum)

Microplastics (MPs) are widespread in agricultural soil, potentially threatening soil environmental quality and plant growth. However, toxicological research on MPs has mainly been limited to individual components (such as plants, microbes, and animals), without considering their interactions. Here, we examined earthworm-mediated effects on tomato growth and the rhizosphere micro-environment under MPs contamination. Earthworms (Eisenia fetida) mitigated the growth-inhibiting effect of MPs on tomato plant. Particularly, when exposed to environmentally relevant concentrations (ERC, 0.02% w/w) of MPs, the addition of earthworms significantly (p < 0.05) increased shoot and root dry weight by 12-13% and 13-14%, respectively. MPs significantly reduced (p < 0.05) soil ammonium (NH4+-N) (0.55-0.69 mg/kg), nitrate nitrogen (NO3--N) (7.02-8.65 mg/kg) contents, and N cycle related enzyme activities (33.47-42.39 μg/h/g) by 37.7-50.9%, 22.6-37.2%, and 34.2-48.0%, respectively, while earthworms significantly enhanced (p < 0.05) inorganic N mineralization and bioavailability. Furthermore, earthworms increased bacterial network complexity, thereby enhancing the robustness of the bacterial system to resist soil MPs stress. Meanwhile, partial least squares modelling showed that earthworms significantly influenced (p < 0.01) soil nutrients, which in turn significantly affected (p < 0.01) plant growth. Therefore, the comprehensive consideration of soil ecological composition is important for assessing MPs ecological risk.

Comprehensive Review of Geotechnical Engineering Properties of Recycled Polyethylene Terephthalate Fibers and Strips for Soil Stabilization

The waste management of plastic has become a pressing environmental issue, with polyethylene terephthalate (PET) being one of the major contributors. To address this challenge, the utilization of recycled PET fibers and strips in geotechnical engineering applications for soil stabilization has gained considerable attention. This review aims to provide a comprehensive study of the geotechnical engineering properties of recycled-PET-reinforced soils. The review examines various factors influencing the performance of PET-reinforced soils, including PET percent content, fiber length, and aspect ratio. It evaluates the mechanical properties, like shear strength, compressibility, bearing capacity, hydraulic behavior, and durability of recycled-PET-reinforced soils. The findings reveal PET reinforcement enhances shear strength, reduces settlement, and increases the bearing capacity and stability of the soil. However, it is observed that the incorporation of recycled PET fibers and strips does not lead to a significant impact on the dry density of the soil. Finally, an environmental and cost comparison analysis of recycled PET fibers and strips was conducted. This review serves as a valuable resource for researchers, engineers, and practitioners involved in the field, offering insights into the geotechnical properties of PET-reinforced soils and outlining future research directions to maximize their effectiveness and sustainability.

Impact of long-term conventional and biodegradable film mulching on microplastic abundance, soil structure and organic carbon in a cotton field

Biodegradable film mulching has attracted considerable attention as an alternative to conventional plastic film mulching. However, biodegradable films generate transitory microplastics during the film degradation. How much of this transitory microplastics is being formed and their impact on soil health during long-term use of biodegradable plastic film are not known. Here, we quantified the amounts of microplastics (0.1 to 5 mm in size) in the topsoil (0-20 cm) of two cotton fields with different mulching cultivations: (1) continuous use of conventional (polyethylene, PE) film for 23 years (Plot 1), and (2) 15 years use of conventional film followed by 8 years of biodegradable (polybutylene adipate-co-terephthalate, PBAT) film (Plot 2). We further assessed the impacts of the microplastics on selected soil health parameters, with a focus on soil carbon contents and fluxes. The total amount of microplastics was larger in Plot 2 (8507 particles kg-1) than in Plot 1 (6767 particles kg-1). The microplastics (0.1-1 mm) were identified as derived from PBAT and PE in Plot 2; while in Plot 1, the microplastics were identified as PE. Microplastics > 1mm were exclusively identified as PE in both plots. Soil organic carbon was higher (27 vs. 30 g C kg-1 soil) but dissolved organic carbon (120 vs. 74 mg C kg-1 soil) and microbial biomass carbon were lower (413 vs. 246 mg C kg-1 soil) in Plot 2 compared to the Plot 1. Based on 13C natural abundance, we found that in Plot 2, carbon flow was dominated from micro- (<0.25 mm) to macroaggregates (0.25-2 and >2 mm), whereas in Plot 1, carbon flow occurred between large and small macroaggregates, and from micro- to macroaggregates. Thus, long-term application of biodegradable film changed the abundance of microplastics, and organic carbon accumulation compared to conventional polyethylene film mulching.

Effects of tire wear particles on the water retention of soils with different textures in the full moisture range

Tire wear particles (TWPs) are significant contributors to microplastic pollution in the environment, yet there is limited scientific information concerning their impact on soil hydraulic properties. This study aimed to investigate the impact of TWPs at different concentrations (1, 4, 8, and 16% of the air-dried mass of packed soil samples, w/w) on the water retention curves (WRC) of southern California soils with five different textures (clay, clay loam, silt loam, sandy loam, and loamy sand). The concentrations of 8% and 16% were selected to represent extreme pollution scenarios that might occur near highway corridors. High-resolution water retention data, spanning from saturation to oven dryness, were generated using HYPROP™ and WP4C dew point meter instruments. We also developed WRC scaling equations based on the quantity of TWPs. The bulk density of the samples decreased as the TWP concentration in soils increased. The inclusion of very high concentrations of TWPs (8% and 16% w/w) led to a significant reduction in soil moisture content in the intermediate and dry ranges across various soil textures. However, at the same moisture range, adding 1% TWPs had a minimal impact on soil moisture reduction, while the influence of the 4% TWPs concentration treatment was noticeable only in loamy sand and partially in clay loam soils. Additionally, the overall plant available water decreased with increasing TWP concentrations, except for the clay soil. The texture-specific scaling models exhibited promising performance, with RMSE values ranging from 0.0061 to 0.0120 cm3 cm-3. When bulk density was included as an additional input predictor to construct a single scaling model for all textures, the RMSE increased. Nevertheless, it still indicated a good fit ranging from 0.007 to 0.024 cm3 cm-3, highlighting the suitability of simple scaling for identifying WRC in TWPs-polluted soils, particularly for practical purposes. The findings of this study can contribute to a better understanding and quantification of the impact of TWPs on soil hydrology.

Impact of microplastics on microbial-mediated soil sulfur transformations in flooded conditions

As emerging environmental pollutants, microplastics have become a crucial focus in environmental science research. Despite this, the impact of microplastics on soil in flooding conditions remains largely unexplored. Addressing this gap, our study examined the influence of polystyrene (PS) and polyphenylene sulfide (PPS) on the microbial populations in black soil, meadow soil, and paddy soil under flooded conditions. Given the significant regulatory influence exerted by microorganisms on sulfur transformations, our study was primarily focused on evaluating the microbial contributions to alterations in soil sulfur species. Our findings revealed several notable trends: In black soil, both PS and PPS led to a marked increase in the abundance of γ-proteobacteria and Subgroup_6, while reducing Clostridia. Ignavibacteria were found to be lower under PPS compared to PS. In meadow soil, the introduction of PPS resulted in increased levels of KD4-96 and γ-proteobacteria, while α-proteobacteria decreased. Chloroflexia under PPS was observed to be lower than under PS conditions. In paddy soil, our study identified a significant rise in Bacteroidia and Ignavibacteria, accompanied by a decrease in α-proteobacteria and γ-proteobacteria. γ-proteobacteria levels under PPS were notably higher than those under PS conditions. These shifts in microbial communities induced by both PS and PPS had a direct impact on adenosine 5'-phosphosulfate reductase, sulfite reductase, and polysulfide dioxygenase. Consequently, these changes led to soil organic sulfur decrease and sulfide increase. This study not only offers a theoretical framework but also provides empirical evidence for understanding the effects of microplastics on soil microorganisms and their role in regulating nutrient cycling, particularly in flood-prone conditions. Furthermore, this study underscores the importance of ensuring an adequate supply of sulfur in agricultural practices, such as rice and lotus root cultivation, to support optimal crop growth in the presence of microplastic pollution.

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

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

Co-exposure of microplastics and polychlorinated biphenyls strongly influenced the cycling processes of typical biogenic elements in anoxic soil

The co-exposure of microplastics (MPs) and polychlorinated biphenyls (PCBs) in soil is inevitable, but their combined effect on cycles of typical biogenic elements (e.g. C, N, Fe, S) is still unclear. And the co-exposure of MPs and PCBs caused more severe effects than single exposure to pollution. Therefore, in this study, a 255-day anaerobic incubation experiment was conducted by adding polyethylene microplastics (PE MPs, including 30 ± 10 μm and 500 μm) and PCB138. The presence of PE MPs inhibited the PCB138 degradation. Also, PE MPs addition (1%, w/w) enhanced the methanogenesis, Fe(Ⅲ) reduction, and sulfate reduction while inhibited nitrate reduction and the biodegradation of PCB138. And PCB138 addition (10 mg·kg-1) promoted the methanogenesis and Fe(Ⅲ) reduction, but inhibited sulfate reduction and nitrate reduction. Strikingly, the presence of PE MPs significantly reduced the impact of PCB138 on the soil redox processes. The abundance changes of special microbial communities, including Anaeromyxobate, Geobacter, Bacillus, Desulfitobacterium, Thermodesulfovibrio, Metanobacterium, etc., were consistent with the changes in soil redox processes, revealing that the effect of PE MPs and/or PCB138 on the cycle of typical biogenic elements was mainly achieved by altering the functional microorganisms. This study improves the knowledge of studies on the impact of MPs and combined organic pollutants to soil redox processes, which is greatly important to the stabilization and balance of biogeochemical cycling in ecology.

Effects of naturally aged microplastics on the distribution and bioavailability of arsenic in soil aggregates and its accumulation in lettuce

Naturally aged microplastics (NAMPs) and arsenic (As) have been reported to coexist in and threaten potentially to soil-plant ecosystem. The research explored the combined toxic effects of NAMPs and As to lettuce (Lactuca sativa L.) growth, and the distribution, accumulation and bioavailability of As in soil aggregates. The As contaminated soil with low, medium and high concentrations (L-As, M-As, H-As) were treated with or without NAMPs, and a total of six treatments. The results displayed that, in comparison to separate treatments of L-As and M-As, the presence of NAMPs increased the total biomass of lettuce grown at these two As concentrations by 68.9 % and 55.4 %, respectively. Simultaneous exposure of NAMPs and L-As or M-As led to a decrease in As content in shoot (0.45-2.17 mg kg-1) and root (5.68-14.66 mg kg-1) of lettuce, indicating an antagonistic effect between them. In contrast, co-exposure to H-As and NAMPs showed synergistic toxicity, and the leaf chlorophyll and nutritional quality of lettuce were also reduced. NAMPs altered the ratio of different soil aggregate fractions and the distribution of bioavailable As within them, which influenced the absorption of As by lettuce. In conclusion, these direct observations assist us in enhancing the comprehend of the As migration and enrichment characteristics in soil-plant system under the influence of NAMPs.

The environmental impact of mask-derived microplastics on soil ecosystems

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

Effects of microplastic contamination on the hydraulic, water retention, and desiccation crack properties of a natural clay exposed to leachate

Microplastic (MP) can significantly affect soil behaviour and the ecosystem. This paper presents an experimental study to investigate the effects of MP contamination and leachate exposure on the desiccation cracks, hydraulic conductivity, and water retention properties of the natural black clay. The leachate was from a landfill in Australia. The black clay was incorporated with up to 2.0% MPs by weight (w/w) with diverse dimensions and mixed with water/leachate. The measured properties include saturated hydraulic conductivity (ksat), soil-water characteristic curves, moisture evaporation rates, and crack intensity factors. The results suggest that the inclusion of MPs significantly increases ksat, and this increase is more obvious for soils with larger dimensions and contents of MPs, e.g., ksat of the black clay with 2.0% of 500 μm MP increases significantly by 206% (p < 0.05). The black clay exposed to leachate exhibits a slight increase in ksat due to the low viscosity of leachate. The existence of MPs decreases the residual moisture contents and air-entry pressures, and so does the water retention capacity (v/v %) of the black clay. The exposure to leachate increases the air-entry pressures by 6.0%-15.8% of the clay. The evaporation rates increase with the dimensions and concentrations of MPs. The highest evaporation rate (0.96 g/h) can be observed in samples exposed to 2.0% 500 μm MP with water addition. For all samples, the crack intensity factors increase when MP content is between 0.2% and 1.0% and decreases slightly after that. After being exposed to leachate, the evaporation rates and crack intensity factors of the black clay are decreased by 2.4%-12.6% and 3.6%-13.7%, respectively.

Non-invasive 3D analysis of microplastic particles in sandy soil - Exploring feasible options and capabilities

Increasingly, environmental research efforts seek to understand how the continuous input of microplastics into terrestrial environments alters soil physicochemical properties and affects plants and other soil biota. However, fundamental understanding is hampered by the destructive nature of current analytical techniques, which typically require the disruption of soil samples and often the removal of soil organic matter. This results in the irretrievable loss of essential information about soil microstructure and the spatial distribution of microplastic particles. We showed that the non-invasive approach of dual neutron and X-ray tomography is capable of detecting and localizing microplastics embedded in soil environments with organic components, here tested with peat, charcoal, and bark mulch additions. We explored how the number of microplastic particles can be determined on intact samples, even accompanied by add-on information on the size, shape and distribution of microplastic particles. For some combinations of plastic types and organic material amendments, the basic approach was not successful, but could be enhanced by soaking the sample in hydrogen peroxide solution while largely preserving the integrity of the microstructure, or by including shape parameters into the image analysis. By segmenting images using region growing, we were able to identify all microplastic particles without false positives, even in the presence of organic material. We also succeeded in analyzing small-sized microplastic particles, such as film or fibers, embedded in natural sandy soil. 3D visualization of plastic film fragments together with the soil matrix made it obvious that larger fragments can have a significant impact on soil hydraulic properties. It has also been shown that a group of microplastic fibers can induce a planar crack in the soil matrix. Finally, roots and microplastics could be differentiated and visualized in a soil sample, demonstrating the leeway for the non-invasive study of potential interactions between roots and microplastics.

Assessing stress responses in potherb mustard (Brassica juncea var. multiceps) exposed to a synergy of microplastics and cadmium: Insights from physiology, oxidative damage, and metabolomics

Both microplastics (MPs) and cadmium (Cd) are common contaminants in farmland systems, is crucial for assessing their risks for human health and environment, and little research has focused on stress responses mechanisms of crops exposed to the combined pollution. The present study investigated the impact of polyethylene (PE) and polypropylene (PP) microplastics (MPs), in combination with Cd, on the physiological and metabolomic changes as well as rhizosphere soil of potherb mustard. Elevated levels of PEMPs and PPMPs were found to impede nutrient uptake in plants while promoting premature flowering, and the concomitant effect is lower crop yields. The substantial improvement in Cd bioavailability facilitated by MPs in rhizosphere soil, especially in high concentrations of MPs, then elevated bioavailability of Cd contributed to promoted Cd accumulation in plants, with distinct effects depending on the type and concentration of MPs. The presence of MPs Combined exposure to high concentrations of MPs and Cd resulted in alterations in plant physiology and metabolomics, including decreased biomass and photosynthetic parameters, elevated levels of reactive oxygen species primarily H2O2, increased antioxidant enzyme activities, and modifications in metabolite profiles. Overall, our study assessed the potential impact on food security (the availability of cadmium to plant) and crops stress responses regarding the contamination of MPs and Cd, providing new insights for future risk assessment in agriculture.

Occurrence and characteristics of microplastics in soils from greenhouse and open-field cultivation using plastic mulch film

There is a major knowledge gap concerning the extent of microplastic pollution in agronomic regions of China, which represent a plastic use hotspot. In order to clarify the amendment of agronomic region and plastic film mulching mode to microplastics distribution, the characteristics of microplastics distributed in agricultural soils from three typical regions (Beijing (BJ), Shandong (SD), and Xinjiang (XJ)) with two plastic film mulching modes (greenhouse (G) and conventional field-based film mulching (M)) in China were investigated. Microplastics weight and their response to planting regions were also evaluated in this study. The result showed that the average abundance of microplastics in soils from BJ, SD, and XJ was 1.83 × 104 items kg-1, 4.02 × 104 items kg-1, and 3.39 × 104 items kg-1, and the estimated weight of microplastics per kg of dry soils was 3.12 mg kg-1, 5.63 mg kg-1, and 7.99 mg kg-1, respectively. Microplastics in farmland were mainly of small particle size (50 to 250 μm), with their abundance decreasing with increasing particle size. Among the microplastics detected, polyethylene and polypropylene were the two dominant types present, accounting for 50.0% and 19.7%, respectively. The standard total effect of planting regions on microplastic number and weight was 31.8% and 32.3%, and plastic film mulching modes (G vs. M) could explain 34.4% of the total variation of microplastic compositions with a contribution rate of 65.6% in this study. This research provides key data for an assessment of the environmental risk of microplastics and supports the development of guidelines for the sustainable use of agricultural plastic film. Further, it is necessary to quantify and assess the contribution of other different plastic sources to microplastics in soil. Big data technologies or isotope tracer techniques may be promising approaches.

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.

Effects of Microplastics on the Transport of Soil Dissolved Organic Matter in the Loess Plateau of China

Microplastics (MPs) pollution and dissolved organic matter (DOM) affect soil quality and functions. However, the effect of MPs on DOM and underlying mechanisms have not been clarified, which poses a challenge to maintaining soil health. Under environmentally relevant conditions, we evaluated the major role of polypropylene particles at four micron-level sizes (20, 200, and 500 μm and mixed) in regulating changes in soil DOM content. We found that an increase in soil aeration by medium and high-intensity (>0.5%) MPs may reduce NH4+ leaching by accelerating soil nitrification. However, MPs have a positive effect on soil nutrient retention through the adsorption of PO43- (13.30-34.46%) and NH4+ (9.03-19.65%) and their leached dissolved organic carbon (MP-leached dissolved organic carbon, MP-DOC), thereby maintaining the dynamic balance of soil nutrients. The regulating ion (Ca2+) is also an important competitor in the MP-DOM adsorption system, and changes in its intensity are dynamically involved in the adsorption process. These findings can help predict the response of soil processes, especially nutrient cycling, to persistent anthropogenic stressors, improve risk management policies on MPs, and facilitate the protection of soil health and function, especially in future agricultural contexts.

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.

Water retention and hydraulic properties of a natural soil subjected to microplastic contaminations and leachate exposures

The influences of microplastics (MPs) contamination on soils have been extensively studied recently. Most of previous studies focus on saturated hydraulic conductivities and water retention of loose soils under laboratory conditions. The effects of MPs on the hydraulic properties of compacted soils for engineering purposes have not been well understood. This paper presents the laboratory investigation of water retention capacity, saturated (ksat) and unsaturated (kθ) hydraulic conductivities of a compacted natural soil contaminated by MPs and exposed to fresh, medium-aged, and stabilized leachates. The saturated (kg) and unsaturated air conductivities (kgθ) are calculated. The MPs with maximum particle sizes of 500, 150 and 50 μm were added to soils to obtain samples with mass ratios of 0.5, 1.0, 2.0, and 5.0 %, respectively. Under similar ranges of dry densities, permeation of fresh leachates decreases ksat of the compacted soils by 30 % while exposure to stabilized leachates increases ksat by 10 %, due to the viscosities of liquids. The flow channel properties of the compacted soils contaminated with different sizes and concentrations of MPs vary. The most complex flow channel can be found in samples with 5 % 50 μm MPs. The inclusions of MPs decrease residual moisture contents of the compacted soils regardless of MP sizes and percentages. The effects of MPs on air-entry pressures and parameter n depend on the sizes of MPs. The kθ (kgθ) of compacted soils with MPs depend on the combined effects of ksat (kg) and tortuosity parameter (l). Though l ranges from -0.85 to 2.12 with different levels of MP exposures, it does not have a significant influence on the relative hydraulic (kθ/ksat) and air conductivities (kgθ/kg) of the compacted soils. Future studies can focus on the long-term hydraulic properties of soils under MP contamination.

Study of soil microplastic pollution and influencing factors based on environmental fragility theory

Soil microplastics (MPs) pollution is a global concern, but the distribution of MPs and the factors affecting the distribution of MPs in different ecologically fragile karst areas remain poorly understood. Here, we investigated the spatial distribution, characteristics, and composition of MPs in different ecologically fragile karst areas of Guizhou Province and explored the relationship between ecosystem fragility and MPs. Structural equation models combined with robust random forest (RF) models were used to clarify the effects of karst soil properties on MPs and quantify their relative contributions. The abundance of soil MPs in ecologically fragile karst areas was 2949 item kg-1, and the risk of MPs contamination was highest in medium-fragile areas. The robust RF models precisely predicted the abundance of soil MPs in different fragile areas, and the mean root mean square error and R2 were 0.21 and 0.93, respectively. The contribution of karst soil properties to the abundance of MPs was estimated. Some soil chemical properties had a significant effect (p < 0.05) on MPs pollution in ecologically fragile karst areas. The results of our study suggest that the fragile ecological environment may exacerbate MPs pollution. Our study also contributes to establish a scientific theoretical foundation for the utilization of plastics and the prevention and control of microplastics pollution in karst ecosystems.