Plastic particles present in soil are exposed to soil solutions containing a mixture of microbial metabolites, dissolved organic matter, mineral and organic colloids, as well as inorganic ions. These components can interact with plastic particles in different ways that may alter their surface properties and environmental behavior. In this study, we examined how soil solution affects the aggregation kinetics and colloidal stability of nanoplastics made from a soil-biodegradable plastic (poly(butylene adipate-co-terephthalate), PBAT) and a conventional plastic (polyethylene). Without the soil solution, both PBAT and polyethylene nanoplastics aggregated more readily in CaCl2 than in NaCl, with critical coagulation concentrations of 344 and 284 mM in NaCl and 31 and 36 mM in CaCl2, respectively. The addition of the soil solution promoted the aggregation of both nanoplastics, as evidenced by the larger aggregate sizes, despite that the critical coagulation concentrations did not decrease correspondingly. Such an increase in aggregate sizes was induced not only by the formation of an eco-corona on nanoplastics, which enhanced aggregation through polymer bridging and attractive patch-charge interactions, but also by the heteroaggregation between nanoplastics and colloids present in the soil solution. These results suggest that interaction with soil solution can promote the aggregation of nanoplastics through eco-corona formation and heteroaggregation, underlining the role of the complex interactions between nanoplastics and their surrounding matrices on the environmental behavior of nanoplastics.

Polyethylene (PE) mulch is widely used in specialty crop production because it suppresses weeds, conserves soil moisture, modifies soil temperature, and enhances crop yield and quality. However, PE mulch generates substantial end-of--season waste, incurs removal and disposal costs, and can leave persistent plastic residues in agricultural soils. Soil-biodegradable plastic mulch films (BDMs) provide agronomic benefits comparable to PE mulches while allowing for end-of-life incorporation into soil, thereby reducing labor requirements, landfilled plastic, and overall environmental burden. Over the past decade, research has expanded from short-term performance trials to multiyear field studies evaluating BDM degradation dynamics, soil impacts, and environmental tradeoffs. Meta-analyses show that BDMs generally provide agronomic benefits comparable to PE mulch across many specialty crops. Multiyear studies report limited or transient effects of BDMs on soil physical and biological indicators under realistic management, while also demonstrating that degradation rates vary by site and micro-and nanoplastics can form during deterioration. Consequently, credible evaluation requires integration of standardized laboratory biodegradation tests with field-relevant monitoring of degradation and residue fate. Standards and certification frameworks such as EN 17033 and ISO 23517 define requirements and test methods, biodegradation thresholds, and ecotoxicity safeguards for BDMs and are used by third-party certification programs. The US National Organic Program (NOP) added 100% biobased BDMs to their list of allowed synthetic substances in 2014, and further required that no genetically modified organisms be used in their feedstocks or fermentation. However, no commercially available BDMs are currently approved for use in US-certified organic production, although many BDM products meet laboratory-based biodegradability criteria ($90% biodegradation within 2 years). Knowledge regarding BDM feedstocks, additives, degradation mechanisms, and assessment methods will help identify research and policy priorities needed to support responsible adoption of BDMs in sustainable specialty crop production systems.

Nanoplastics in soil are exposed to soil solution, which is a mixture of microbial metabolites, dissolved organic matter, mineral and organic colloids, as well as inorganic ions. These components can interact with nanoplastics, thereby altering their surface properties and environmental behavior. Here, we examined how soil solution affects the aggregation kinetics and colloidal stability of nanoplastics made from a soil-biodegradable plastic (poly(butylene adipate-co-terephthalate), PBAT) and a conventional plastic (polyethylene). We found that both PBAT and polyethylene nanoplastics formed bigger aggregates in the presence of a soil solution extracted from a sandy loam soil, suggesting that the soil solution promoted the aggregation of both nanoplastics, thereby reducing their colloidal stability. Fluorescent excitation–emission spectroscopy revealed that microbial biomass in the soil solution dominantly adsorbed onto nanoplastics, followed by humic acid, forming an eco-corona that induced polymer bridging and attractive patch-charge interactions. Despite the observed bigger aggregates, the critical coagulation concentrations did not decrease correspondingly for either PBAT or polyethylene nanoplastics, which is likely due to the uncertainties of the critical coagulation concentrations as well as the hetero-aggregation between nanoplastics and colloids present in the soil solution. These results indicate that interactions with soil solution can decrease the colloidal stability of nanoplastics via eco-corona formation and hetero-aggregation, underlining the role of the complex interactions between nanoplastics and their surrounding matrices on the environmental behavior of nanoplastics.

Abstract Background Growing evidence suggests that many ecological systems exhibit tipping points, thresholds at which small changes in stressors can trigger critical shifts in ecosystem properties. Whether such responses also occur in soils exposed to microplastics remains largely unexplored. Using a published dataset, we re-examined how microplastics affect soil physical properties, focusing on potential threshold concentrations at which those responses shift abruptly. Findings We identified statistically supported threshold concentrations under which soil physical properties responded abruptly to microplastics incorporation by comparing linear, nonlinear, and piecewise models using Akaike Information Criterion (AIC). Unlike previous assumptions, our analysis of the investigated dataset indicated that abrupt effects can emerge at concentrations far lower than those typically used in classic dose-effect experiments, with threshold concentrations shifting depending on polymer type, particle shape, and ageing condition, and occurring at microplastic concentrations around 0.06%, 0.12%, 0.24% and 0.30% w/w. This study introduces a novel framework for detecting non-linear soil responses and identifying potential tipping points, suggesting that even low microplastic concentrations can alter soil physical properties. Conclusions Given the dataset size and scope, these threshold estimates must be viewed as preliminary, pointing to candidate critical tipping concentrations rather than validated tipping points, and may depend on the chosen model representation. Future studies should incorporate fine low-dose gradients to confirm breakpoints, assess threshold types, and investigate soil compensatory processes and regime shifts in response to microplastic pollution.

The Sustainability Nexus Analytics, Informatics, and Data (AID) Programme of the United Nations University (UNU), aims to provide information, data, computational, and analytical tools to support the sustainable management and long-term security of natural resources using a nexus approach. This paper introduces the Soil Health Module of the Sustainability Nexus AID Programme. Healthy soil is crucial for life on Earth, and it is essential for ecosystem services and functioning, access to clean water, socioeconomic structure, biodiversity, and food security for the growing population of the world. Healthy soils contribute to mitigating the effects of climate change and reduce the consequences of extreme events such as flooding and drought. Healthy soils influence the hydrologic cycle by regulating transpiration, water infiltration, and soil water evaporation affecting land–atmosphere interactions. The Soil Health Module of the UNU Sustainability Nexus AID Programme aims to evolve into the ultimate focal point, supporting a diverse array of stakeholders with state-of-the-art data and tools that are essential for soil health monitoring and projection. This paper discusses the importance of adopting a nexus approach for ensuring soil health, explores the AID tools currently at our disposal for quantifying and predicting soil health, and concludes with recommendations for future effort and direction within the Sustainability Nexus AID Programme concerning 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.

Soil compaction and soil organic matter (SOM) are critical factors influencing crop growth and soil health, yet their interaction and impact on plant-available water (PAW) remain underexplored. To address this, we investigated a 26-year field experiment on fine sandy loam soil in Washington State, USA, involving three biosolids application rates (0, 4.7, and 10.0 Mg ha-1) applied every four years in a winter wheat-fallow rotation. Compacted and uncompacted strips were created using field-traffic, with additional intact soil cores from uncompacted strips compacted in the laboratory. Intact cores from uncompacted, field-compacted and lab-compacted treatments were analyzed for saturated hydraulic conductivity (Ksat), soil moisture release curves, and bulk density (rho b). The change in rho b after compaction (Delta rho b) and rebound (Delta epsilon) were assessed for lab-compacted cores. Disturbed soil samples were analyzed for Proctor maximum bulk density (rho bmax), critical water content (CWC), and contact angle (alpha). Biosolids application generally reduced rho b and rho bmax, increased CWC, volumetric water content at saturation (theta SAT), Ksat, and alpha but did not affect volumetric water content at field capacity (theta FC), permanent wilting point (theta PWP), or PAW. Compaction reduced theta SAT and Ksat while increasing rho b, theta FC, theta PWP, and PAW. While compaction impacted soil physical and hydraulic properties, biosolids had limited effects under the study conditions. Contrary to our expectations, no interaction between biosolids application and compaction treatments was observed. Despite numerous benefits of increased SOM with biosolids application, increased resistance to and recovery from soil compaction does not appear to be one of them in this study.

Plant uptake of micro- and nanoplastics can lead to contamination of food with plastic particles and subsequent human consumption of plastics. There is evidence that plant roots can take up...

The increasing threat from plastic pollution has promoted the widespread application of biodegradable plastic. In agriculture, biodegradable plastic, mainly in the form of biodegradable plastic mulch, has received a lot of attention due to its in-situ degradability and satisfying agronomical performances. However, biodegradable plastic mulches do not degrade instantaneously but rather fragment into micro- and nanoplastics, and these micro- and nanoplastics could reside in soil or even migrate along soil profiles. Here, we investigated the mobility of pristine and weathered polybutylene adipate co-terephthalate (PBAT) nanoplastics in sand columns under unsaturated flow conditions. We further studied the effect of proteins on the mobility of PBAT nanoplastics with both negatively charged bovine serum albumin and positively charged lysozyme. We found that (1) the pristine and the weathered PBAT nanoplastics were mobile with or without the presence of proteins; (2) the positively charged lysozyme inhibited the transport of PBAT nanoplastics; and (3) lower water saturation inhibited the transport of PBAT nanoplastics via physical straining. These results suggest that biodegradable nanoplastics generated from biodegradable plastic mulches are mobile and may transport readily along soil profiles.

The use of biodegradable mulch (BDM) instead of a conventional plastic mulch film has the potential to reduce the accumulation of legacy plastic in agroecosystems. The fate of BDM polymer carbon (C) in soil, however, remains poorly understood, especially the fraction of polymer-C that enters microbial catabolic (mineralization) versus anabolic (immobilization) pathways. We present a novel approach that allows tracking of polymer-C into CO2, macro- and microplastic residues, living microbial biomass, and soil organic matter (SOM) through the combination of CO2 emission, 13C- and 14C-phospholipid fatty acid (PLFA) analysis, and plastic polymer analysis. After exposing a clear BDM piece (2 cm × 2 cm) in an agricultural soil for up to 1 year, we found that 22 ± 9% (mean and standard deviation) of the polymer-C remained as macroplastic residues (>1 mm), 19 ± 3% was present in microplastic particles (<1 mm), 22 ± 1% was emitted as CO2, 0.9 ± 0.1% was present in living microbial biomass, and 37 ± 9% was present in microbial necromass or SOM. Similar values were observed for black BDM (21 ± 3%, 10 ± 2%, 21 ± 4%, 0.8 ± 0.0%, and 47 ± 6%, respectively). Our findings indicate that, within 1 year of soil incubation, a fraction of the macroscopic BDM pieces fragmented into microplastics, while a fraction of polymer-C was mineralized and emitted as CO2, and another substantial fraction transferred into SOM. Our research advances knowledge on reducing reliance on polyethylene-based plastics and offers practical implications for improving agroecosystem sustainability.

Reflective agricultural films are widely used in vegetable production and orchards to repel pests, accelerate fruit ripening, and boost yields. These films, composed of a plastic base metallized with aluminum (Al), degrade over time in soil, releasing Al and microplastics. This study investigated the aging and weathering of Al-coated reflective films (polyethylene terephthalate, PET-based) under UV radiation, simulated rainfall, and soil burial for up to 120 days, assessing the effects of released Al and microplastics on soil chemistry and microbial communities. Weathering was confirmed by the formation of C-O/CO functional groups, an increasing carbonyl index, and the oxidation of Al to Al₂O₃, as shown by Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Faster Al-coated shedding and PET oxidation were observed in the soil environment. Microplastics (0.5 % w/w) from the films reduced soil micronutrient availability (Fe, Mn, Cu), suppressed functional genes involved in carbon, nitrogen, and phosphorus cycling, and shifted microbial communities towards oligotrophic bacteria enrichment (e.g., RB41, Candidatus_Udaeobacter, Gemmatimonadetes, and Chloroflexi) while reducing copiotrophic bacteria (e.g., Sphingomonas, Ellin6067, Dongia, Puia, and Flavisolibacter). Therefore, these findings highlight that reflective film weathering strongly alters soil nutrient content and microbial community composition, with potential implications for soil health and agricultural sustainability.

Microplastic pollution of soils has raised concerns on how microplastics impact soil properties and functions. Impacts of microplastics on soil properties is usually studied by amending soils with microplastics at various concentrations, but little attention has been given on how to compact soils after microplastic incorporation and how microplastics affect soil compressibility. Here, we used the uniaxial compression test to investigate the effects of microplastic type (i.e., granular polyethylene and fibrous polypropylene), size (i.e., 20, 200, 1000 mu m for granular polyethylene and 3000 and 5000 mu m for fibrous polypropylene) and concentration (i.e., 0.0 %, 0.5 %, 1 % and 2 %) on compression characteristics of a silt loam soil, followed by the evaluation of soil structure, water holding characteristics, and water and gas permeability. Soil compression was significantly affected by microplastic types, size, and concentrations. Granular microplastics increased the void ratio uniformly within the applied stress whereas fibrous microplastics increased the void ratio much more at low stress than at high stress. As a result, fibrous microplastics significantly increased the compression index (Cc) with increasing microplastics concentration. Granular microplastics decreased the swelling index (Cs), making soil less resilient against compaction. However, soil structure, water holding characteristics, and water and gas permeability were not significantly affected, except for the 5000 mu m fibrous polypropylene at a concentration of 2 %, where soil porosity increased and soil water holding capacity decreased. These findings highlight the importance in considering soil compressibility, especially for laboratory incubation experiments, when evaluating microplastic effects.

The vadose zone—the variably saturated, near‐surface environment that is critical for ecosystem services such as food and water provisioning, climate regulation, and infrastructure support—faces increasing pressures from both anthropogenic and natural factors, including changing climatic conditions. A more comprehensive understanding of vadose zone processes and interactions is imperative to effectively address these challenges and safeguard water and soil resources. This review outlines selected key issues, knowledge gaps, and research opportunities across six thematic sections. Each section presents a problem statement, a summary of recent innovations, and a compilation of emerging challenges and study opportunities. The selected topics include scaling and modeling of vadose zone properties and processes, soil moisture monitoring initiatives, surface energy balance, interplay between preferential water flow paths and biogeochemical processes, interactions between fires and vadose zone dynamics, and emerging contaminants and their fate in the vadose zone. This overview is intended to serve as a compendium of vadose zone science that encompasses both insights gained from prior research and anticipated needs for the coming years.

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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 (0.1-5 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 > 1 mm 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 C-13 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.

Plastic mulching is a critical agricultural practice for food production, which provides multiple benefits, including water conservation, weed control, and increased crop yield and quality. However, the application of conventional polyethylene mulch films has led to plastic pollution in the terrestrial environment because mulch residues in fields are difficult to remove and recycle. To address this issue, soil-biodegradable plastic mulch (BDM) films have been introduced to replace conventional polyethylene mulch films, as BDM films are designed to provide desired agronomic outcomes as well as in-situ disposal and degradation. Thus, increasing interests have been expressed toward BDM films in both research and application areas. In this review, we summarize and synthesize current knowledge about BDM films, regarding the history, definition and use, in-field degradation, agronomic performance, environmental impacts, and economic feasibility. In-field research suggests that BDMs show satisfactory agronomical performance but vary considerably in biodegradability among different products and environmental conditions, and generally do not impair soil health. However, laboratory studies indicate that BDMs may negatively impact terrestrial and aquatic ecosystems. Overall, current data indicate that BDMs are a promising alternative of conventional polyethylene mulch films. Questions remain about in-field biodegradation, potential accumulation of BDM residues in soils, release of nonbiodegradable additives, and off-site transport of biodegradable plastic residues (including micro- and nanoplastics) to air and water. We provide recommendations to address these questions and challenges to ensure safe and sustainable use of BDM films in agriculture.

Soil-biodegradable plastic has been increasingly used as mulches in agriculture, which provides not only agronomical benefits but also in situ disposal and biodegradation options.

Biodegradable plastics have been proposed as an alternative to conventional plastics for many applications, such as single-use plastic bags, disposable cutleries and tablewares, and agricultural plastic mulch films. However, concerns have arisen about environmental sustainability of biodegradable plastics, especially regarding degradability, generation of biodegradable micro- and nanoplastics, and release of additives. Here, we critically evaluate literature on the degradation and ecotoxicity of biodegradable plastics with the consideration of environmentally relevant concentrations. Our evaluation suggests that, provided with proper disposal and full biodegradation, biodegradable plastics, including biodegradable micro- and nanoplastics, would not accumulate substantially in the environment and would be far from reaching concentrations at which negative impacts on ecosystems can be expected. In addition, we highlight existing regulatory efforts to prevent adverse ecotoxicity of biodegradable plastics. To ensure timely biodegradation under various disposal conditions, we propose to calibrate the actual biodegradability in disposal environments against the intrinsic biodegradability in standards. Further, we recommend to supplement biodegradability certificates on biodegradable plastics with clear disposal instructions, to ensure proper end-of-life management. With proper testing, comprehensive labeling, and effective management, we believe that, for certain applications, biodegradable plastics are a promising substitute for conventional plastics.