Although plastic mulch enhances crop yield, its removal and disposal present significant challenges, contributing to macro- and microplastic pollution in agricultural soils. The adverse effects of this pollution on soil and plant health are not fully understood but may stem from the plastic particles or the toxicity of leached chemical additives. This study assessed the impact of macro- and microplastics from nondegradable LDPE-based (LDPEb) and biodegradable PBAT-based (PBATb) mulch films, along with their leachates, on the germination of three plant species. After seven days of incubation, PBAT mulch leached compounds that significantly inhibited Arabidopsis germination, while cotton and tomato exhibited notable tolerance. Notably, PBATb mulch released a higher concentration of compounds, whereas LDPEb mulch exhibited a greater diversity of leached chemicals. Microplastic particles alone did not hinder seed germination, indicating that plastic toxicity primarily arises from the leachates. Many of these leached compounds lack global regulation and hazard information, underscoring the urgent need for further investigation into their environmental impacts and the development of appropriate regulatory frameworks to mitigate the potential toxicity of chemicals from conventional and biodegradable mulches.

Advances in molecular techniques have recently uncovered microbial communities associated with plastic debris. The term ‘plastisphere’, was originally used for microbial communities on marine plastic. In terrestrial systems, this term has been extended to the plastic-soil interface, encompassing microbes from the surrounding soil. Although some studies have revealed differences in microbial composition and diversity between plastisphere and bulk soil, high-resolution spatial analyses of microbial communities on the immediate plastic surface (plasticplane) and in the attached soil (plastisphere-soil), are still lacking. In this study, a methodology was developed to disentangle the bacterial populations associated with the plastisphere-soil of weathered plastic mulch from agricultural fields from those on the plasticplane by using culture-based and High-Throughput sequencing approaches. A significantly higher number of colony-forming units were cultured from the plastisphere-soil compared to the plasticplane. Main genera isolated from the plasticplane by culturing included Arthrobacter, Pseudarthrobacter, Priestia, Massilia, Microbacterium, Bacillus, and Kocuria genera, some of which are known plastic-degraders. High-throughput sequencing analysis revealed higher bacterial richness in plastisphere-soil, while beta diversity showed main significant differences among field plots. Core taxa significantly associated to the plasticplane included Bacillus, Sphingomonas, Nocardioides, and Solirubrobacter. This study provides a pioneering description of a methodology to differentially analyze microbial communities at different soil-plastic interfaces, particularly on a small spatial scale using samples from plastic mulch residues in agricultural soils. This methodology may lay a foundation for future research to isolate and identify microbial plastic degraders, contributing to efforts against mitigating plastic pollution.

Soil microbial activity is a key indicator of soil health, traditionally assessed using methods like enzymatic activity, community-level physiological profiling (CLPP), microbial biomass, and soil respiration. This study introduces isothermal microcalorimetry assessed with the CalScreener™ system as a novel tool for evaluating soil activity and validates its use in assessing the impact of anthropogenic pollutants like microplastics. Soil samples were exposed to microplastic particles from conventional and biodegradable plastic mulches, one of the main sources of microplastic pollution in agricultural soils. Microbial activity was assessed after short-term (10 days) and long-term (12 months) microplastic exposure using respirometry, isothermal microcalorimetry, and microbial CLPP. Isothermal microcalorimetry's effectiveness to assess microbial activity was validated by observing distinct thermograms between active and autoclaved soil, and differences between treatments under basal and glucose-amended conditions. Both respirometry and microcalorimetry showed similar results, revealing higher basal activity in soils with biodegradable microplastics after long-term exposure, compared to conventional microplastics and unamended soil. Isothermal microcalorimetry offers advantages over traditional methods, including shorter assessment periods and the need for smaller soil sample amounts. While CLPP did not detect significant differences in overall soil activity among treatments, it may be a useful technique for characterizing microbial functional traits. This study provides, for the first time, insights into the use of isothermal microcalorimetry as a novel methodological approach to evaluate the potential impact of microplastics on soil biological activity.

Plastic pollution in terrestrial environments is a global issue due to its adverse effects on soil health, with negative impacts on ecosystem services and food production. However, the enormous heterogeneity of both plastic and soil characteristics complicate the assessment of the impact and overall trends in plastic-induced changes in soil properties beyond experimental conditions. In this work, we have carried out a systematic and in-depth review of the existing literature on the impact of plastics on soil physical properties. To this end, we have quantified the effects of macro- (MaP, >5000 μm) and micro-plastics (MiP, <5000 μm) on soil bulk density, soil porosity, water-stable aggregates (WSAs), saturated hydraulic conductivity, and soil moisture at field capacity (FC), based on four characteristics of plastics: polymer types, shapes and sizes of plastic particles, and plastic concentrations in soil. Results showed that MaPs and MiPs significantly modified the values of the analyzed soil physical properties compared to the control without plastic in over 50% of the experimental dataset, albeit with a large variability, from a reduction to an increase in values, depending on the specific experimental conditions and the soil physical property. Depending on the plastic concentration, soil bulk density and porosity decreased moderately (4%-6%) with MiP and MaP. MiP reduced WSA by an average of 20%, ranging from a 40% decrease to a 20% increase depending on the shapes and concentration of MiP. Saturated hydraulic conductivity changed depending on the polymer types, shapes, and concentrations of MaP and MiP, varying from a 70% decrease to a 40% increase. Soil water content at FC varied depending on the soil texture, and concentration and sizes distribution of conventional MiP, decreasing from 10% to 65%. However, biodegradable plastic increased soil water content at FC. The few studies available provide evidence that not enough attention is being paid to soil physical properties influenced by plastic input. It is recommended to consider the wide range of characteristics of MaP and MiP and their effects on soil physical properties in future studies, for an advance understanding of the impact of MiP and MaP on soil health in the medium-long term under different environmental conditions., This research was carried out within the SOPLAS project financed by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement Number 955334. A M acknowledged the financial support of the COST ACTION PRIORITY (CA20101) for participation in the 'Microplastic Workshop for Early Career Researchers: Best Practices and Expert Insight' held in June 2022 in Athens, Greece., Peer reviewed

TUdi - Transforming Unsustainable management of soils in key agricultural systems in EU and China. Developing an integrated platform of alternatives to reverse soil degradation. Referencia del proyecto: 101000224. Partner/Coordinador principal: José Alfonso Gómez Calero – Instituto de Agricultura Sostenible IAS- CSIC., Soil is polluted with plastic waste from macro to submicron level. Our understanding of macroplastics (> 5 mm) occurrence and behavior has remained comparatively elusive, mainly due to a lack of a tracing mechanism. This study set up a methodology to trace macroplastic displacement, which combined magnetic iron oxide-tagged soil and macroplastic pieces tagged by an adhesive passive radiofrequency identification transponder. By utilizing these techniques, a field study was carried out to analyze the effect of tillage implement and plastic sizes on plastic displacement, to understand the fate of macroplastics in arable land. Results indicated that the displacement of macroplastics did not depend upon plastic sizes but did depend upon the tillage implement used. The mean macroplastics displacement per tillage pass was 0.36 ± 0.25 m with non-inversion chisel tillage and 0.15 ± 0.13 m with inversion disk tillage, which was similar to bulk soil displacement. However, only inversion disk tillage caused fragmentation (41 %) of macroplastics and generated microplastics (< 5 mm). In contrast, both tillage implements drove to similar burial of surface macroplastics into the tilled layer (74 % on average). These results highlight that tillage is a major process for macroplastics fate in arable soils, being one of the first studies to investigate it., European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie SOPLAS project (GA 955334). Horizon 2020 TUdi project (GA 101000224). Open Access cost covered by CSIC agreement with Elsevier., Peer reviewed

Although plastic mulch enhances crop yield, its removal and disposal present significant challenges, contributing to macro- and microplastic pollution in agricultural soils. The adverse effects of this pollution on soil and plant health are not fully understood but may stem from the plastic particles or the toxicity of leached chemical additives. This study assessed the impact of macro- and microplastics from nondegradable LDPE-based (LDPEb) and biodegradable PBAT-based (PBATb) mulch films, along with their leachates, on the germination of three plant species. After seven days of incubation, PBAT mulch leached compounds that significantly inhibited Arabidopsis germination, while cotton and tomato exhibited notable tolerance. Notably, PBATb mulch released a higher concentration of compounds, whereas LDPEb mulch exhibited a greater diversity of leached chemicals. Microplastic particles alone did not hinder seed germination, indicating that plastic toxicity primarily arises from the leachates. Many of these leached compounds lack global regulation and hazard information, underscoring the urgent need for further investigation into their environmental impacts and the development of appropriate regulatory frameworks to mitigate the potential toxicity of chemicals from conventional and biodegradable mulches., We would like to acknowledge the financial support from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement No 955334. We also thank Wendy Beekman-Lukassen and Patrick Hendrickx for their prompt support for our urgent freeze-drying step., Peer reviewed

Microplastic particles are an emerging pollutant that can be transported through preferential pathways, such as macropores. Agricultural soils, prone to microplastic contamination, often have macroporosity due to biological activity, natural formation of soil aggregates, desiccation cracks, or no-till practices. However, little is known about the factors controlling microplastic leaching through soil macropores. In this study, artificial soil-like macroporosity (2.5% v/v) was developed in packed soil columns to investigate the effect of macropore size, that is, 2, 3 and 4 mm, on the leaching of microplastics of three sizes, that is, 53–63, 75–90 and 125–150 μm, and the influence of both factors on the vertical mobilisation of soil particles. Under artificial rainfall (30.6 mm h⁻¹ for 30 min), microplastics were preferentially leached, with over 50% of the 75–90 μm and 125–150 μm particles transported, regardless of macropore size. Macropores without microplastics leached a significant amount of soil particles. Macropore characteristics, including pore diameter, number, and surface area, were strongly correlated with vertical soil particle transport. Microplastics increased vertical soil particle transport through macropores by a factor of about 1.6. A conceptual framework was developed to explain the observed mechanisms, emphasising the collisional forces exerted by microplastic particles detaching soil particles. Our results suggest that microplastic flow induced additional stress on macropore walls, intensifying soil particle mobilisation. This study also highlights that macropores (i.e., biopores) might be an underestimated driver of microplastic transport in the vadose zone and their role in intensifying vertical displacement of surface soil to subsurface layers. Given the environmental implications, further research will be needed to study these processes under field conditions., This work was supported by the SOPLAS project financed by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement Number 955334., Peer reviewed

Green and biowaste, processed within large facilities into compost, is a key fertilizer for agricultural and horticultural soils. However, due to improper waste disposal of plastic, its residues often remain or even lead to the formation ofmicroplastics (1 µm - 5 mm, MiPs) in the final compost product. To better understand the processes, we first quantified 'macroplastics' (> 20 mm, MaPs) input via biowaste collection into an industrial composting plant, and, then determined MiP concentrations at five stages during the composting process (before and after shredding and screening processes), and in the water used for irrigation. The total concentrations of MaPs in the biowaste collected from four different German districts ranged from 0.36 to 1.95 kg ton-1 biowaste, with polyethylene (PE) and polypropylene (PP) representing the most abundant types. The "non-foil" and "foil" plastics occurred in similar amounts (0.51 ± 0.1 kg ton-1 biowaste), with an average load of 0.08 ± 0.01 items kg-1 and 0.05 ± 0.01 items kg-1, respectively. Only 0.3 ± 0.1 kg MaP t-1 biowaste was biodegradable plastic. Compost treatment by shredding tripled the total number of MaPs and MiPs to 33 items kg-1, indicating an enrichment of particles during the process and potential fragmentation. Noticeably, a substantial amount of small MiPs (up to 22,714 ± 2,975 particles L-1) were found in the rainwater used for compost moistening, being thus an additional, generally overlooked plastic source for compost. Our results highlight that reducing plastic input via biowaste is key for minimizing MiP contamination of compost., his work was funded by the European Union’s Horizon 2020, ITN SOPLAS, with grant agreement No. 955334 to the main author., Peer reviewed

Advances in molecular techniques have recently uncovered microbial communities associated with plastic debris. The term ‘plastisphere’, was originally used for microbial communities on marine plastic. In terrestrial systems, this term has been extended to the plastic-soil interface, encompassing microbes from the surrounding soil. Although some studies have revealed differences in microbial composition and diversity between plastisphere and bulk soil, high-resolution spatial analyses of microbial communities on the immediate plastic surface (plasticplane) and in the attached soil (plastisphere-soil), are still lacking. In this study, a methodology was developed to disentangle the bacterial populations associated with the plastisphere-soil of weathered plastic mulch from agricultural fields from those on the plasticplane by using culture-based and High-Throughput sequencing approaches. A significantly higher number of colony-forming units were cultured from the plastisphere-soil compared to the plasticplane. Main genera isolated from the plasticplane by culturing included Arthrobacter, Pseudarthrobacter, Priestia, Massilia, Microbacterium, Bacillus, and Kocuria genera, some of which are known plastic-degraders. High-throughput sequencing analysis revealed higher bacterial richness in plastisphere-soil, while beta diversity showed main significant differences among field plots. Core taxa significantly associated to the plasticplane included Bacillus, Sphingomonas, Nocardioides, and Solirubrobacter. This study provides a pioneering description of a methodology to differentially analyze microbial communities at different soil-plastic interfaces, particularly on a small spatial scale using samples from plastic mulch residues in agricultural soils. This methodology may lay a foundation for future research to isolate and identify microbial plastic degraders, contributing to efforts against mitigating plastic pollution., We would like to acknowledge the financial support from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 955334 SOPLAS and the Qualifica Project QUAL21-023IAS, Consejeria de Universidad, Investigación y Inovación-Junta de Andalucía., Peer reviewed

Agricultural soils, particularly those utilizing plastic products for crop production, are increasingly recognized as sources of microplastics (MPs) to aquatic ecosystems. In this research, we investigate the transport of polyethylene MPs of three different size ranges (53-63 μm, 125-150 μm and 425-500 μm) in an agricultural soil during a plot-based rainfall simulation. Using a combination of fluorescent particles and high-frequency photography, we tracked the number of MPs on the soil surface throughout the rainfall simulation, measured the depth MPs migrated into the soil profile and the number of MPs which were transported in surface runoff. Our results show that MPs had dynamic movement on the soil surface throughout the rainfall simulation. Approximately 20% of MPs sized 125-150 μm and 425-500 μm were exported from the plot in surface runoff with the remaining 80% of MPs thought to be retained in the soil. No significant differences were found in the number of MPs transported in surface runoff between MPs sized 125-150 μm and 425-500 μm. Microplastics were found to be enriched in eroded sediments. Microplastics of all sizes 53-63 μm, 125-150 μm and 425-500 μm were found in soil as deep as 8 cm with the majority of MPs found in the 0-2 cm soil depth. Results from this research not only indicate that MPs are quite mobile both vertically and laterally during rainfall events but also show that soils effectively retain and accumulate a sizeable proportion of MPs during heavy rainfall events., This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 955334., Peer reviewed

Microplastics, both biodegradable and conventional, are becoming ubiquitous in terrestrial ecosystems, posing potential risks to soil health and ecosystem functioning. Although biodegradable polymers are promoted as environmentally friendly alternatives to persistent plastics such as polyethylene, their effects on critical soil physical properties and processes remain poorly understood, creating a major knowledge gap. We conducted a controlled experimental study by incorporating two types of microplastics, polybutylene adipate terephthalate (PBAT, biodegradable) and low-density polyethylene (LDPE, conventional), into soil at five concentrations (0.1, 0.5, 1.0, 3.0, and 5.0% of w/w). The study used a size mixture to reflect environmentally relevant microplastic distributions: 4000–2000 µm (4.25%), 2000–650 µm (8%), 650–400 µm (8%), 400–250 µm (15%), 250–100 µm (26%), 100–50 µm (21%), and < 50 µm (17.75%). We then employed a mechanistic framework to evaluate the effects of microplastics on key soil physical processes, such as aggregate stability, and their influence on splash erosion dynamics (particle detachment, soil consolidation, and surface roughness), encompassing the effects on soil hydraulic properties (water repellency, hydraulic conductivity, and water retention). Results of the linear regression analysis showed a negative relationship with saturated hydraulic conductivity (Ks) and a positive relationship with soil water retention (SWR) at matric potential (hPa), water-stable aggregate (WSA), and splash erosion under simulated rainfall, with increasing microplastics concentrations. Furthermore, increasing microplastic concentration did not affect soil water repellency, bulk density, or surface roughness as characterized by photogrammetry. Moreover, a monotonic response of microplastic concentration on soil properties was observed: WSA increased by up to 58% and 53%, splash erosion by 39% and 44%, and SWR by up to 30%, while Ks decreased by 44% and 53% for conventional and biodegradable microplastics, respectively, compared to the plastic-free control. PBAT, a biodegradable microplastic, and LDPE, a conventional microplastic, showed comparable effects on soil physical properties, challenging the presumed functional divergence between them. The study also established concentration thresholds above which microplastics begin to alter soil functions in the tested soil type., European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie SOPLAS project (GA 955334) and EU-China Flagship initiative TUdi (GA 101000224). Funding was also provided by the Spanish State Research Agency, through the Severo Ochoa and María de Maeztu Program for Centers and Units of Excellence in R&D (Ref. CEX2019-000968-M). The CSIC agreement with Elsevier covers the Open Access cost., With funding from the Spanish government through the "Maria de Maeztu Centre of Excellence" accreditation (CEX2019-000968-M)., Peer reviewed

The impact of microplastics (MPs) on soil organisms is still a growing field, yet very little is known about the
exposure of ultraviolet (UV) aging of MPs to soil organisms. In this study, we explored the response of the epigeic
earthworm Eisenia andrei to pristine and UV-aged polyethylene (PE-MP) exposure at a wide range of environmentally relevant concentrations (0, 0.2, 2, 20, 200 and 2000 mg kg− 1
) in an organic farm soil for 56d and
assessed changes in reproduction, ingestion, egestion and gut microbiome. Results showed that exposure to 20
mg kg− 1 pristine PE-MP significantly increased earthworm reproduction by 39 % but the same concentration
decreased reproduction by 29 % when they were exposed to UV-aged PE-MP. Ingestion of PE was verified by
staining the whole worm body and their casts after 48h of starvation. The amounts of PE-MP found in the body
and the casts were positively correlated with PE-MP concentrations in the soil, however only significantly so with
pristine PE-MP. A decline in E. andrei gut microbiome alpha diversity and a significantly different community
composition were observed in UV-aged PE-MP exposures compared to pristine PE-MP. Relative to the control
treatments, Proteobacteria increased up to 135 %, Actinobacteria increased up to 35 %, and Firmicutes decreased
up to 38 % under UV-aged PE-MP exposure, whereas Cyanobacteria increased up to 19 times in the pristine PEMP treatments. These results confirm the negative effect of UV-aged PE-MP on earthworms even at low concentrations and could have important implications in the well-functioning of agricultural soils.

Wariness is increasing about resident times of microplastics (MPs) in soils; however, limited knowledge is available on ultraviolet (UV) light exposure of MPs to soil fauna. This study investigated the effects of virgin and photoaged polyethylene microplastics (PE MPs) on soil mesofauna (enchytraeids and collembolans) at environmentally relevant concentrations in a microcosm incubation experiment. Ten individuals of each Enchytraeus crypticus and Folsomia candida and twenty Proisotoma minuta were exposed separately to virgin and photoaged PE MPs (40–48 μm) admixed in agricultural soil (0.2–2000 mg/kg) to evaluate reproduction and survival. After 28 d of exposure to photoaged PE MPs, there was a moderate survival reduction but reproduction promotion of E. crypticus. Contrastingly, F. candida exhibited an opposite trend, with survival enhancement and reproduction depression rates when exposed to both PE MP contaminated soils. However, P. minuta was the only species with significant apical endpoint changes after PE MP exposure; at 20 mg/kg photoaged and 2000 mg/kg virgin PE MP exposure, there was a 34% and 31% decrease in survival, respectively, and at 200 mg/kg photoaged PE MP exposure, an increase of 39% for reproduction. PE MPs had contrasting impacts on soil mesofauna species, which highlights the need to account for these variable results when understanding the repercussions of MP pollution on community assemblage and population dynamics in soils.