# Migration dynamics of PE and PVC microplastics in soil: An experimental column-based investigation on the effects of drip irrigation

Khaoula En-Nejmy, Bouchra El Hayany, Eric Record, Mohamed Hafidi, Loubna El Fels

<figure><img src="image_1.png" /></figure>

## To cite this version:

Khaoula En-Nejmy, Bouchra El Hayany, Eric Record, Mohamed Hafidi, Loubna El Fels. Migration dynamics of PE and PVC microplastics in soil: An experimental column-based investigation on the effects of drip irrigation. Journal of Hazardous Materials Advances, 2026, 21, pp.100962. 10.1016/j.hazadv.2025.100962. hal-05525629

HAL Id: hal-05525629

https://hal.inrae.fr/hal-05525629v1

Submitted on 24 Feb 2026

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
<figure><img src="image_3.png" /></figure>

# Migration dynamics of PE and PVC microplastics in soil: An experimental column-based investigation on the effects of drip irrigation

Khaoula En-Nejmy<sup>a</sup>, Bouchra El Hayany<sup>a,b</sup>, Eric Record<sup>c,*</sup>, Mohamed Hafidi<sup>a</sup>, Loubna El Fels<sup>a,*</sup>

## ARTICLE INFO

### Keywords:

Agricultural pollution

Drip irrigation

Groundwater risk

Microplastics

Migration

Soil contamination

## ABSTRACT

Migration patterns of microplastics (MPs) in agricultural soil remain unclear due to a lack of scientific data. In this study, a soil column experiment was conducted using polyethylene (PE) and polyvinyl chloride (PVC) particles of different sizes under simulated drip irrigation. The MPs were collected and analysed after different irrigation time intervals (4, 8, 12, and 16 weeks) to track their migration over time.

Results showed that simulated drip irrigation triggered a time-dependent migration of MPs through soil matrices. After 16 weeks, the maximum migration depth of MP particles reached 15–20 cm. Moreover, we further revealed that the migration of MPs in sandy loam soil was influenced by both the size/type of the particles and the duration of irrigation. Comparatively, small-sized MPs, particularly those <0.5 mm, showed higher mobility compared to larger-sized MPs. A difference in mobility between the two types of MPs was also observed, with PVC exhibiting a higher mobility than PE (6.6 % of recovered PVC compared to 4 % of PE from 20 cm soil depth). This study is one of the first to simulate quantitatively and temporally (16 weeks) the migration of MPs (PE and PVC) in agricultural soil under drip irrigation. Given that MPs are hazardous materials whose transfer must be assessed, our study quantifies the critical impact of MP size and polymer type on their vertical mobility in soils, providing essential data for assessing and modelling the risks of contaminant transfer to groundwater resources.

## Introduction

Global plastic production reached a record of 1.038 billion tonnes between 2017 and 2019 (Dey et al., 2023). Current projections indicate an alarming increase of 33 billion tonnes by 2050, underlining the need for urgent action (Dey et al., 2023). Inappropriate management and disposal result in 70 % of the world's plastic production being released into the environment as waste (Geyer et al., 2017). Microplastic (MPs) pollution is a major challenge as it is present across all environments. While plastic pollution in marine and freshwater ecosystems is well documented, contamination of agricultural soils, accounting for 14 % of

global plastic pollution, has only recently begun to receive attention (Wanner, 2021). Soil contamination by plastics arises from various sources, including the application of sewage sludge, fragmentation of agricultural plastic films, poor management of plastic waste, tire abrasion, atmospheric fallout, and run-off water (En-Nejmy et al., 2024; Nguyen et al., 2025). The persistent degradation of plastics in the soil environment leads to the release of micro and nanoplastics, exacerbating widespread plastic contamination (Hanun et al., 2021). The accumulation of MPs in the terrestrial environment has disastrous implications, as it alters soil properties, including enzymatic activity, and reduces the soil's capacity to infiltrate and retain water, ultimately

**Abbreviations:** dMP, Microplastic particle diameter; dsand, Sand particle diameter; EC, Electrical conductivity; FTIR, Fourier Transform Infrared Spectroscopy; H₂O₂, Hydrogen peroxide; MPs, Microplastics; NaCl, Sodium chloride; PE, Polyethylene; PET, Polyethylene Terephthalate; PP, Polypropylene; PVC, Polyvinyl chloride; SOM, Soil organic matter; ZnCl₂, Zinc chloride.

* Corresponding authors.

E-mail addresses: eric.record@inrae.fr (E. Record), loubna.elfels@uca.ac.ma, loubna.elfels@gmail.com, loubna.elfels@uca.ac.ma (L. El Fels).

<footnote><sup>a</sup> Cadi Ayyad University (UCA), Faculty of Sciences-Semlalia, Laboratory of Water Sciences, Microbial Biotechnologies, and Natural Resources Sustainability (AQUABIOTECH), Unit of Microbial Biotechnologies, Agrosciences, and Environment (BIOMAGE)-CNRST Labeled Research Unit N° 4, PO Box 2390, Marrakesh, Morocco</footnote>

<footnote><sup>b</sup> Higher Institute of Nursing Professions and Health Techniques, Essaouira-Marrakech, Morocco</footnote>

<footnote><sup>c</sup> INRAE, Aix Marseille Univ, BBF, Biodiversité et Biotechnologie Fongiques, Marseille, France</footnote>
affecting plant productivity (Hasan and Tarannum, 2025; Xu et al., 2025).

Furthermore, MPs can be absorbed by plants, potentially entering the human food chain (Ansar et al., 2025). By attaching to plant roots, MPs can disrupt growth parameters and interfere with the metabolic functioning of plants (Zong et al., 2021). Soil acts both as a potential reservoir for MPs and as a pathway through which they can reach groundwater, engendering greater environmental and ecological impacts and thereby making remediation more complex (Chia et al., 2021). MPs in soil have detrimental effects on soil fauna, including earthworms (Tian et al., 2024), springtails (Kwak et al., 2024) and nematodes (X. Zhang et al., 2025), impacting their growth and reproduction. Additionally, they serve as vectors for other pollutants, such as heavy metals and pesticides (J. Liu and Zheng, 2025), thereby amplifying the risks to ecosystems. Their accumulation in the soil ultimately leads to contamination of groundwater through both lateral and vertical transport (Balestra et al., 2023). To evaluate the risk and the repercussions related to groundwater contamination, it is crucial to understand the factors that govern the vertical transport of MPs in the soil. This migration is influenced by various elements, such as MP characteristics (size, shape, density, and roughness), soil properties (porosity, texture, and pH), soil biodiversity, and agricultural activities (Luo et al., 2024). Irrigation is a major factor that amplifies preferential or macropore flow, thus becoming a critical transport mechanism for MPs. This process occurs when the injected water does not infiltrate uniformly, but rather takes the high-permeability pathways in the soil (macropores). By concentrating in these channels, water allows MPs to bypass the soil matrix where they would normally be trapped and retained. As a result, irrigation significantly increases the speed and depth of MP migration, including large MP, which is crucial for assessing the risk of rapid groundwater contamination.

Numerous studies have examined the presence and movement of MPs in soils, but significant gaps remain in our comprehensive understanding of their migration under relevant environmental conditions. The fate of MPs in soils is still poorly understood, particularly when considering the combination of the following key factors: (1) the impact of different types of polymers and different size categories on MPs mobility, rather than limiting the analysis to a single particle type; (2) the influence of exposure time to irrigation that simulate prolonged agricultural and environmental scenarios; and (3) the distinction between specific transport mechanisms based on the nature and dimensions of MPs. These uncertainties hinder the development of accurate process-based predictive models to assess the risk of groundwater contamination by MPs. O'Connor et al. (2019) investigated MP migration on sand (size < 2 mm), by adding two types of MPs (PP and PE) separately to better control the factors influencing their migration. Unlike studies using sand, which does not mimic typical agricultural soils, Zhang et al. (2022) examined the migration of MPs in real agricultural soils. This study considered the size and shape of MPs, as well as simulated and natural precipitation, to approximate real environmental conditions. However, the study did not include temporal monitoring to assess the migration of MPs over different time scales. We hypothesize that the vertical migration of MPs in agricultural soils is significantly affected by both the physicochemical properties of the particles—such as polymer type and size—and the duration of irrigation exposure. Therefore, our study focuses on assessing the vertical migration of MPs through sandy-loam soil directly collected from an agricultural soil under simulated drip irrigation conditions over different time intervals. This preliminary approach aims to overcome the lack of information and seeks to address the existing gap in knowledge regarding the behaviour of MPs in agricultural soils, particularly regarding irrigation practices and temporal monitoring. To address these gaps, this study aims to determine how MP migration is influenced by polymer type (PE, red PVC, and grey PVC), particle size (four categories), and duration of exposure to irrigation, based on a column experiment with an analysis of the effluent water to verify the presence of MPs.

This research is distinguished by the use of an experimental soil column methodology that accurately simulates drip irrigation conditions, a widely used but rarely studied method of water supply in the context of MPs migration. By focusing on the temporal monitoring of migration (over 16 weeks) for MPs of varying nature and size (PE and PVC), this work provides original and crucial quantitative data on the long-term fate of these pollutants. The results obtained are essential for more accurately assessing the ecological risk associated with MPs contamination of agricultural soils and for clarifying environmental and agricultural management strategies.

## Material and methods

### Soil sampling and characterization

Soil samples were collected from the upper 30 cm of agricultural land located in the suburbs of Marrakech city-Morocco (31°40'54.6 "N 8°11'07.6 "W). Plant residues and debris were manually removed to ensure the purity of the soil. Transported to the laboratory, the soil samples were air-dried, ground, and then sieved at 5 mm to obtain a uniform particle size for subsequent analysis.

The physico-chemical analysis of the soil sample, carried out according to the methodology described by El Fels et al. (2014) and El Hayany et al. (2021), showed the following results: pH was 8.51 ± 0.22, organic matter content was 2.52 ± 0.08 %, the total organic carbon was 1.4 ± 0.05 %, the bulk density was 1.43 ± 0.28 %, the porosity was 47 %, and the humidity rate was 2.28 ± 0.88 %. Granulometric analysis revealed a sandy-loam texture with a particle distribution of 34.88 % silt, 50.23 % sand, and clay about 14.89 %. Soil samples were collected from areas free of plastic debris. Moreover, an extraction test was conducted to check for the presence of MPs particles in this soil to ensure their absence.

### Microplastic samples preparation

The microplastic (MP) samples used in the experiment were two types of plastics: polyethylene (PE) ($C_2H_4)_n$ and polyvinyl chloride (PVC) ($C_2H_3Cl)_n$, with densities of 0.948 g/cm³ and 1.442 g/cm³, respectively. MPs into various size categories: [1–2 mm], [0.5–1 mm[, [0.2–0.5 mm[, and [0.05–0.2 mm[ were used. To ensure easier identification and differentiation, the microplastic particles were distinctly colored with red PVC, grey PVC, and black PE selected for distinct visual recognition. The different microplastic particles were mixed homogeneously in the following proportions: red PVC (34.98 %), grey PVC (36.17 %), and black PE (28.85 %). These percentages are based on weight, taking into account the difference in polymer densities. Since PVC is denser than PE, it represents a higher percentage by mass, although an equal number of particles (1000 units) from each type was used. The MPs mixture was added in the corresponding quantities to the soil column according to the quantities mentioned in Table 1. The top layer of soil (0–2 cm) was mixed with MPs at a concentration of 0.11 % (w/w). Surface roughness parameters were determined from scanning electron microscopy (SEM) images using ImageJ software (Fig. 1B). To

<table><caption>**Table 1**

Quantities of the microplastics used in this study.</caption><thead><tr><th rowspan="2"></th><th rowspan="2"></th><th colspan="4">Size categories (mm)</th></tr><tr><th>[0.05 - 0.2[ (400 particles)</th><th>[0.2 - 0.5[ (300 particles)</th><th>[0.5 - 1[ (200 particles)</th><th>[1 - 2] (100 particles)</th></tr></thead><tbody><tr><td rowspan="4">Microplastic content (mg)</td><td>PE</td><td>1.3 ± 0.02</td><td>3 ± 0.21</td><td>9.8 ± 0.9</td><td>27.3 ± 0.5</td></tr><tr><td>Grey</td><td>1.9 ± 0.13</td><td>3.3 ± 0.21</td><td>12.4 ± 0.18</td><td>34.3 ± 0.25</td></tr><tr><td>PVC</td><td></td><td></td><td></td><td></td></tr><tr><td>Red</td><td>1.6 ± 0.21</td><td>3.2 ± 0.07</td><td>11.2 ± 0.26</td><td>34.2 ± 0.07</td></tr><tr><td></td><td>PVC</td><td></td><td></td><td></td><td></td></tr></tbody></table>
confirm their identity, the spectral properties of the MP particles were analysed using Fourier Transform Infrared Spectroscopy (FTIR, Bruker Tenson 27), which allowed for the precise identification of PE and PVC particles based on their characteristic absorption bands (Fig. 1A) (Fig. 1B).

## Experiment set-up description

To assess the vertical mobility of the two types of MPs, six cylinders were connected to create the soil column. Each cylinder is 5 cm in length and 10 cm in diameter (Fig. 2). During the assembly process, when sealing the cylinders, waterproof adhesive tape was used to seal the joints, effectively preventing water from seeping through and ensuring the column remained watertight.

Polyester gauze was placed and securely fixed to the underside of the column to avoid soil loss. The column was then held vertically by an iron support. During the filling process, each cylinder was gradually filled with the appropriate dry soil to each depth layer by layer from 0 to 30 cm, as observed in the field, by maintaining a high apparent density of the soil at depth relative to the surface. MPs were thoroughly mixed with the soil at a concentration of 0.11 % (w/w) and added to the uppermost layer of the soil column (0–2 cm). To simulate drip irrigation, additional finely perforated cylinders were mounted atop the support structure, allowing water to be added at a controlled intensity of 1423 mL per day. This irrigation rate was selected to maintain field capacity until the column reached saturation. The infiltrated water was systematically collected at weekly intervals to detect and monitor the presence of MPs, thereby enabling an assessment of their vertical migration through the soil column. Experimental replicates were carried out in the same conditions.

Four soil columns were installed and the experiment lasted a total of 16 weeks. Each month, a column was taken out and the distribution of MPs was analyzed. The soil samples were stored in sealed containers and kept in boxes in the fridge until further analysis.

## Microplastics extraction and analysis

At the end of the experiment, for each column according to the time-dependence, the setup was meticulously dismantled, taking into account the cylinders associated with each depth. To assess the extent of MP migration within the soil. The MPs were extracted from different transversal sections of the column, taking into account the different

<figure><img src="image_4.png" /><figcaption>Fig. 1A. FTIR spectra of microplastic polymers.</figcaption></figure>

depths. After allowing the soil in the various cylinders to air dry, samples were taken from each layer to extract the MPs. A pretreatment consisting of organic matter digestion was carried out before starting the extraction of microplastics using H₂O₂ (30 % (w/w); Merck KGaA, Darmstadt, Germany) for both the digestion of organic matter and the separation of soil aggregates (Lv et al., 2019). Two extraction solutions were used for flotation and density separation: a saturated sodium chloride (NaCl: Purity ≥ 99 % Merck KGaA, Darmstadt, Germany) solution with a density of 1.19 g/cm³ and zinc chloride (ZnCl₂: Purity ≥ 98 %; Loba Chemie Pvt. Ltd., Mumbai, India) solution with a density of 1.7 g/cm³. This method capitalized on the density differences, as PVC has a higher density than the saturated NaCl solution, enabling effective separation of the two types of MPs (Zhou et al., 2019). The samples were stirred in the corresponding solutions for 15 min, followed by a settling period of 4 h. The supernatant was then vacuum filtered to isolate floating particles containing MPs, using grid membrane filters (cellulose nitrate filter, pore size 0.45 µm) that provide a scale for measurement of MP size (El Hayany et al., 2021). This extraction step was repeated several times until no particles were found in the supernatant. During the filtration step, each beaker was carefully rinsed with saturated NaCl solution to remove any remaining debris. The observation of the filter was carried out using a stereomicroscope (Nikon SMZ-1 Zoom Stereomicroscope, USED). To ensure that all particles were observed, the microscope was carefully maneuvered in a 'zigzag' pattern, moving from left to right across the entire filter. For easier counting, a needle was used to separate potential microplastic particles from each other.

Statistical analysis was performed using analysis of variance (ANOVA), followed by Tukey's post hoc test, with a 95 % confidence interval and a significance level of *p* < 0.05, using SPSS Statistics software version 26 (Windows 11).

## Results and discussion

### Temporal and depth variation in microplastic concentration

The microplastics were extracted from the different layers, time-dependent, to quantify them at each penetration depth. Every 4 weeks, one of the columns was opened and the microplastics were analyzed according to their size and type. The extraction of MPs from soil matrices is a technically challenging process, particularly for smaller particles. However, the extraction method used in our study proved to be highly efficient. This has been illustrated by the recovery rate of the particles reaching almost 100 % for all the particles in all size ranges except the (0.05-0.2 mm), which showed a recovery rate of about 96 % ±0.63 for PE, 97 % ±1.13 for PVC (grey) and 97 % ±0.515 for PVC (red) (Fig. 3).

The results, which display the MP count at each depth over 4 weeks intervals are shown in Fig. 4. A logarithmic decrease in microplastic quantity was observed with increasing column depth (Fig. 4). The majority of the particles were predominantly retained in the top layer (0-5 cm), with only a few particles possibly penetrating deeper into the column.

The deposition of MPs on the various layers exhibits temporal variation. Over the first 8 weeks, MPs migrated until they reached the 10–15 cm layer. The number of MPs extracted from the (10–15 cm) layer was 50 ± 15 and 108 ± 31 particles after 4 and 8 weeks, respectively. After 12 weeks, the penetration depth of 65 ± 10 particles reached 20 cm. By 16 weeks, the number of MPs was extended to 171 ± 4 in the 15–20 cm layer. The observed penetration depth is less than that reported by Ranjan et al. (2023). This discrepancy is mainly attributed to the duration of the experiment, soil type, and the size of MPs used. Ranjan et al. (2023) found that particles smaller than 50 µm reached penetration depths of up to 30 cm. In addition, the column was made of sand and the experiment lasted 180 days. In our study, no particles were extracted from the deep layers (20 to 30 cm), and the filtered water did not contain any particles. This proves that MP particles did not migrate
<figure><img src="image_5.png" /></figure>

<table><thead><tr><th>Slice</th><th>Rq</th><th>Ra</th><th>Rsk</th><th>Rku</th><th>Rv</th><th>Rp</th><th>Rt</th><th>Rc</th><th>FPO</th><th>MFOV</th><th>FAD</th><th>MRV</th><th>SA</th></tr></thead><tbody><tr><td>1</td><td>20.1854</td><td>11.7588</td><td>-1.1637</td><td>3.0720</td><td>-68.4131</td><td>6.6731</td><td>75.0862</td><td>-0.1795</td><td>4.7321</td><td>16.9923</td><td>82.9845</td><td>0.8975</td><td>1.1029</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>Fig. 1B. SEM Images and surface roughness of microplastic polymers.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 2. Schematic representation of the experimental setup.</figcaption></figure>

to reach the deeper layers nor were they infiltrated. Many studies have shown that soil can not only serve as a sink for those particles but also as a practical entry passage to deeper horizons, posing a risk of ground-water contamination, especially under the conditions of high irrigation runoff or rainfall (Ren et al., 2021; Samandra et al., 2022).

Soil structure and texture have a major impact on the migration of microplastics (S. Zhang et al., 2023). Fine-textured soils, with a high proportion of clay and silt, have low porosity and smaller pores, which tend to limit infiltration and therefore the vertical movement of microplastics. Conversely, sandy soils, with a coarse texture and high

<figure><img src="image_8.png" /><figcaption>Fig. 3. Recovery rates of MPs for various sizes and types.</figcaption></figure>

porosity, facilitate the movement of microplastics towards the depths of the profile (S. Zhao et al., 2022). Given the characteristics of our soil, the migration of MPs will be greatly facilitated. The sandy-loam texture with a predominance of sand (50.23 %) and high porosity (47 %) ensures large flow channels and low bulk density, facilitating vertical mobility and reducing filtration retention for the smallest MPs. Chemically, the alkaline pH (8.51) tends to give MP and clay minerals a negative charge, which increases electrostatic repulsion and inhibits physicochemical attachment (adsorption), thereby enhancing particle mobility in the aqueous phase. Although organic matter (2.52 %) can potentially retain hydrophobic MPs, the combination of physical (open structure) and chemical (strong repulsion) factors suggests that the soil presents a high
<figure><img src="image_9.png" /><figcaption>Fig. 4. Temporal variation of total MPs distribution at different soil depths.</figcaption></figure>

risk of transport and groundwater contamination by MPs.

At the field level, under real conditions, the movement of soil fauna, such as earthworms and springtails, can significantly contribute to the dispersion of MPs by ingesting and excreting them at different depths (Rillig et al., 2017; Kim and An, 2020). In addition, plant root growth can create channels and fissures in the soil, facilitating the migration of MPs to deeper layers (H. Li et al., 2021; Tumwet et al., 2024). These bioturbation processes and root structure interact with soil properties to determine the fate of MPs in the terrestrial environment.

### Polymer type influence on microplastic migration

The vertical movement of the different types of MPs (PE, red PVC, and grey PVC) was investigated over different time intervals (4, 8, 12, and 16 weeks) to track their migration (Fig. 5). In various depths, the presence of MPs particles was detected, and their types were easily identified based on their color differences. Identification was performed using FTIR analysis, with the absorption peaks used for their characterization are presented in Fig. 1A. Comparing the results obtained for grey and red PVC, as expected, the color difference had no significant impact on migration. However, the variation in MP types revealed meaningful differences in their migration patterns (Fig. 5).

After 4 weeks, MPs were detected in the 10 - 15 cm layer, at respective rates of 1 % for PE, 1.8 % for grey PVC, and 2.2 % for red PVC. After 8 weeks, the microplastics did not penetrate beyond 15 cm. However, the proportion of migrated microplastics increased over this period, reaching 2.7 % for PE, 3.9 % for grey PVC, and 4.2 % for red PVC.

Between weeks 12 and 16, the migration rates of MPs, confined to a layer of 15 to 20 cm, increased to two-threefold, reaching 4 %, 6.3 % and

6.8 % respectively for PE, grey PVC and red PVC, compared to 1.9 %, 2.2 % and 2.4 % twelve weeks earlier. At the end of the experiment, no type of MPs was detected beyond a depth of 20 cm. Our study highlights a statistically significant difference in migration phenomena between PE and PVC. This heterogeneity is interpreted as reflecting the distinct structural properties of the two polymers, particularly their density and surface roughness. We observe that PE, with its lower density, has a higher surface roughness (11.76 nm) than PVC (9.34 nm), allowing for significant migration of PVC compared to PE (Fig. 1B).

The findings during a study that examined the migration of Polypropylene (PP) and Polyethylene (PE) through a sand column showed that the mobility of PE particles exhibited significantly greater mobility within the column, while PP particles experienced a notable reduction in mobility in the subsurface (O'Connor et al., 2019).

In the same context, sand column experiments were conducted under artificial rainfall conditions to assess the vertical migration of a microplastic mixture consisting of PP, PE, and polyethylene terephthalate (PET). After an incubation period of 180 days, the results revealed a clear difference in mobility between the different types of MPs. PE proved to be the most mobile polymer, being found at all depths of the column. PET also showed significant vertical transport capacity, reaching a maximum depth of 6 cm. PP, on the other hand, proved to be the least mobile of the three polymers; its migration is limited to the first 3 cm of the column profile (Ranjan et al., 2023). Both studies lead towards the same conclusion, that PE is the polymer that migrates most easily in sand, followed by PET and PP, which is the least mobile. The results of these studies revealed that the mobility of microplastics (PE, PET, PVC and PP) strongly correlates with their physico-chemical properties. Density, in particular, plays a significant role: PP, with a density of 0.848 g/cm³, is 8.32 % less dense than PE, 40.85 % less dense
<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /><figcaption>**Fig. 5.** Time-based distribution of different microplastic types and colors across soil depth.</figcaption></figure>

than PET, and 70.05 % less dense than PVC. The direct consequence of this difference in density is that PP particles are more buoyant, limiting their penetration into the soil matrices. In addition, the surface roughness of PP (28.18 nm) is significantly higher than that of PET (14.46 nm), PE (11.68 nm) and PVC (9.35 nm). This morphological characteristic results in increased friction with the sand particles, further slowing down the migration of PP. These physical properties support our experimental finding that PVC was more mobile than PE in the sandy-loam soil column migration experiment. The buoyancy of low-density microplastics has a critical influence on their interactions in the soil. By undergoing upward vertical migration or prolonged suspension, they are retained in the surface layers of the soil, particularly the rhizosphere. This area is crucial because it is where the most intense microbial and enzymatic activity occurs. Prolonged presence of MPs in this biologically active environment can accelerate their aging (chemical modification of surfaces) and potentially their partial degradation, as the biofilms that develop there and the enzymes released are more likely to initiate these transformation processes than in the deeper, less active layers of the subsoil.

## Particle size influence on microplastic vertical mobility

The influence of the size of the MPs on their vertical migration in the soil column was studied. The results represented in Fig. 6 show the

distribution of particles of different sizes at various soil depths in different time intervals. After 8 weeks, only microplastics having size between 0.05 and 0.2 mm were found in the 10–15 cm layer. The MPs with a size between 0.5 to 2 mm did not migrate deeper and were trapped in the surface layer up to 5 cm. After 12 weeks, the migration reached the 15–20 cm layer and only the small particles were found with a size between 0.05 and 0.2 mm. After 16 weeks, the migration did not exceed the (15–20 cm) layer, however, the particles with a size range between 0.2 and 0.5 mm were also found.

Fig. 7, illustrating the size distribution of MPs in the different soil layers after 16 weeks, reveals that the size of the microplastics is the primary factor influencing their ability to penetrate the soil (Fig. 7). All the MPs used in this migration study, regardless of size, were found in the two uppermost soil layers, between 0 and 10 cm deep. The maximum concentration of MPs, measured as particles per layer, decreased with increasing penetration depth. Large MPs (0.5–2 mm) have limited penetration capacity, reaching depths of no >10 cm. Only MPs smaller than 0.5 mm were able to penetrate to depths beyond 10 cm and up to 20 cm. Results of studies conducted by Ranjan et al. (2023) and Zhang et al. (2022) have provided evidence for the increased mobility of small particles. MP migration may be influenced by soil porosity, a hypothesis confirmed by previous research conducted on sandy soils, notably by Gao et al. (2021) and O'Connor et al. (2019). Infiltration, also known as ‘straining’, occurs when the pores in a medium are too small for particles
<figure><img src="image_14.png" /><figcaption>Fig. 6. Temporal distribution of different microplastic sizes according to soil depth.</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Fig. 7. Size distribution of microplastics in the different sandy loam soil layers after 16 weeks.</figcaption></figure>

to pass through (Tarbuck J and Lutgens K, 2017).

On the other hand, the ratio of microplastic particle diameter to sand diameter has been studied as a factor influencing the vertical migration of microplastics (Gao et al., 2021). Three different infiltration scenarios

were used to analyze microplastic penetration depths. In the first scenario, when dMP/dsand < 0.11 free movement along the column depth was observed. The second scenario, with 0.11 < dMP/dsand < 0.32, showed mixed particle mobility, resulting in both free and restricted
movement. The third scenario, where dMP/dsand > 0.32 involved large MP ratios and showed restricted particle penetration or surface deposition on the sand. Despite the free movement of smaller particles, they were also present in all layers due to their agglomeration during the infiltration process. Another study conducted column experiments using different natural sediments (gravel, coarse sand, finer sediments) and microplastics of different sizes (ranging from 10 µm to 150 µm) (W. Li et al., 2024). The study shows that the size of MPs and the grain size of the sediment strongly control their transport and retention. The efficiency of MP retention increases (less migration) as the sediment grain size decreases (finer sediments). The smallest MP (10–20 µm) showed the greatest mobility, with >85 % found in the effluent for the gravel and coarse sand columns. The largest MP (125–150 µm) were almost entirely retained (100 %) in the coarse sand column (W. Li et al., 2024).

Due to size-dependent migration, MPs can be irregularly distributed throughout the soil profile, potentially infiltrate into deep soil layers or reach groundwater. This increases the potential for them to be ingested or absorbed by soil flora and fauna (W. Li et al., 2020; B. Huang et al., 2021). Small-sized MPs have an increased potential for interaction with soil microorganisms due to their greater mobility and their ability to remain suspended in the interstitial liquid phase for longer periods. Their small size allows them to pass through finer pores and reach "micro-sites" inaccessible to larger MPs, increasing the specific contact surface area available per unit mass for microbial colonization. This prolonged and extensive interaction facilitates the formation of biofilms on the surface of MP, which can potentially alter microbial communities in the soil, serve as a vector for the transport of pathogens or resistance genes, and influence fundamental biogeochemical processes, such as the nutrient cycle, while accelerating the degradation of the particles themselves. In addition, MPs can have a significant impact on soil structure, soil enzymes, and crop biomass, as shown by large-scale studies on the distribution of MPs in agricultural soils and the associated analysis of environmental impacts (En-Nejmy et al., 2024; Hu et al., 2022).

## Influence of irrigation and soil texture on soil microplastic vertical dispersion

Unlike pesticides and heavy metals, MPs exhibit low chemical reactivity in soil. However, they are subject to physical transport processes, particularly in the presence of cracks and pores in the soil. These structures can be further enhanced by water, which degrades soil structure as a result of factors such as drought and logging (Majdalani et al., 2008). These disturbances can make the soil more susceptible to degradation and affect how microplastics move through the soil. Irrigation then plays a critical role in the degradation of soil structure, leading to an increase in flow in the macropores to the detriment of water diffusion in the soil. A study showed that the irrigation volume has a negligible effect on the transport of MPs (O'Connor et al., 2019). It has also been indicated that an upward migration of microplastics is allowed when the pore spaces are saturated due to their low specific density. This reverse migration could explain the lower concentrations of microplastics in deeper soil profiles associated with the application of higher infiltration volumes. Another study analysed the transport of microplastics (MP) in soil columns (disturbed and undisturbed) subjected to irrigation and drying cycles (Yang et al., 2025), showing extremely high MP retention, with >80 % remaining in the top 5 cm even after intensive irrigation (120 cm of water over seven cycles). Although undisturbed columns showed slightly higher transport via fractures, the overall behaviour remained similar, with low vertical mobility (detection beyond 40 cm only after seven cycles). The analysis revealed a strong correlation between MP concentrations in the soil matrix and in the fractures, suggesting a mainly diffusive transport mechanism and that strong slowing down (retention) is dominant in both areas (Yang et al., 2025). These findings are consistent with our results, which also showed high MP retention in the upper soil layers [0–5 cm], with 93.57 %, 88.07 %, 68.84 %, and 52.04 % remaining after 4, 8, 12, and 16 weeks, respectively.

In accordance with previous studies (Koutnik et al., 2022; Z. Zhao et al., 2022), our results indicate that irrigation contributes to the migration of microplastics into the deeper layers of the soil. MP concentrations showed significant variation as a function of soil depth and irrigation duration (Fig. 3). An increase in irrigation time led to a gradual increase in MP concentrations in the deeper layers, and the surface layers showed a decrease in microplastic content. At the end of the experiment (16 weeks), the quantity of microplastics was reduced by 48.21 % in the surface layer (0–5 cm). At the same time, 5.78 % of microplastics were found in the deep layer (15–20 cm), compared with 2.2 % after 12 weeks. However, the maximum depth attained in our study was 20 cm, which is shallower than the depth reported by Zhao et al. (2022), where a greater depth of 50 cm was achieved. Nevertheless, our finding was deeper than those obtained by Koutnik et al. (2022) and O'Connor et al. (2019) who observed a maximum depth of only about 15 and 8 cm.

This difference can be attributed to the particularities of the experimental set-up used as well as the types of soil matrices employed in each study. Given their homogeneity and low aggregation, quartz sand used by Koutnik et al. (2022) and construction sand used in the study of O'Connor et al. (2019) are materials that promote high hydraulic conductivity and uniform infiltration. In our study, we used sandy-loam soil, which, despite its higher hydraulic conductivity and rapid infiltration due to larger pore spaces, is less susceptible to damage such as disaggregation and cracking. In contrast, the structural fragility of the clay loam soil during wetting and drying cycles used by Zhao et al. (2022), leading to its high susceptibility to disintegration and cracking, increased preferential transport of microplastics to deeper profiles.

Irrigation introduces complex feedback mechanisms that alter soil structure over time, thereby influencing the transport of MPs. Repeated cycles of wetting and drying induced by irrigation affect soil aggregation and pore connectivity. In the long term, these structural changes can evolve in two opposite directions: either they reinforce preferential flow by accentuating differences in pore size, thus allowing rapid migration of MP, or they cause pore clogging due to erosion, accumulation of fine particles, or increased deposition of organic matter. This gradual alteration of available migration pathways is crucial, as it means that MP transport dynamics are not static but evolve with agricultural practices and the degradation or stabilization of soil structure.

Moreover, variations in water supply and soil moisture are likely to have a more pronounced effect on microplastic migration. The structure of clay soils makes macropore flow more vulnerable to changes in soil moisture and irrigation volume than in sand and sandy loam soils, explaining the migration of microplastics to deeper soil profiles.

The sandy loam soil in our study (34.88 % silt, 50.23 % sand, clay 14.89 %) is a mixture composed of a sandy component that ensures good macroporosity and, therefore, relatively high permeability, allowing water to infiltrate easily, and a loamy component that offers microporosity and slightly more water retention capacity than sand alone. Loam can also increase physical filtration in deeper layers.

In general, sandy loam soil is characterized by medium to high conductivity (Jabro et al., 2023), and the flow velocity is sufficient to transport MPs. The interaction between irrigation duration and soil hydraulic conductivity determines the speed and extent of vertical transport of MPs. Hydraulic conductivity, which is the soil's ability to transmit water, is mainly dictated by soil texture and structure. Water infiltrates and flows quickly. This promotes the rapid and deep transport of MPs in the soil profile.

Furthermore, the duration or intensity of irrigation controls the water flow and the hydraulic load applied to the column. The rapid movement of water, which keeps the column under high hydraulic load for a long period of time, combined with the sustained flow, causes the MPs to be transported deep underground through a leaching phenomenon.
The water flow is maintained for a long time, saturating most of the pores. The water then acts like a piston (called convection flow), carrying the MP beyond the surface filtration zones and towards the deeper horizons. The duration of irrigation is therefore the limiting (or propulsion) factor for deep migration and maximum leaching risk. Long irrigation times on highly permeable soil maximise the risk of groundwater contamination, as the volume of water pumped provides the kinetic energy needed to prevent filtration and adhesion of MPs to soil particles (Wei et al., 2024). The findings indicate that the migration of MPs is influenced not only by irrigation but also by the texture and structure of the soils, particularly those susceptible to disaggregation and cracking. Consequently, soils contaminated by MPs and exposed to disintegration and cracking require careful irrigation to limit the negative impact on the environment.

## Factors influencing microplastic migration and environmental repercussions

Our study investigates the vertical movement of MPs in the soil under the influence of simulated drip irrigation. The influence of microplastic properties (type and size) on their vertical migration was evaluated in a relatively porous matrix (sandy loam soil). Besides microplastic properties, soil's physico-chemical properties influence the migration of microplastics (Sadri et al., 2017). It was reported that high soil electrical conductivity (EC) increases the deposition of microplastics (Kobayashi et al., 2009) and soil organic matter (SOM), which, by interacting with colloids, forms aggregates (H. Li et al., 2021). Soil aggregates, which are the fundamental components of the soil and have an important role in soil porosity, also impact MP migration. MPs are captured by soil aggregates, but the intensity of this incorporation varies according to the size and shape of the MPs: fibers adhere better to aggregates than fragments due to their strong hydrophobic interaction and large contact angles (Guo et al., 2020). Soil organic matter, loam fraction, and particle size heterogeneity strongly influence microplastic transport and retention through mechanisms such as cationic bridging, hydrophobic interactions, and physical adsorption (Chanda and Bathi, 2026). While the hydrophobic nature of microplastics favors their adsorption to soil organic matter, this can either hinder transport via trapping and chemical interactions or, if dissolved, enhance mobility by reducing surface hydrophobicity (Ivanic et al., 2023; Chanda and Bathi, 2026). In addition, microplastics act as vectors for heavy metals, which can modulate microplastic-SOM interactions and surface charge, thereby affecting their transport behaviour (B. Liu et al., 2024). Gravitational force is the main driver of downward transport, but its effect is constantly modulated by water volume (infiltration and runoff) and the physical properties of the column, including height/elevation and soil texture (sandy-loam grain size), which influence porosity and preferential flow paths, where greater height provides more opportunities for interactions and retention through physical trapping in pores (Yang et al., 2025).

The deposition of colloidal particles (including MP, often likened to large colloids) is governed by surface interactions, mainly described by DLVO theory (Derjaguin-Landau-Verwey-Overbeek), which combines two forces: van der Waals attraction and electrostatic repulsion. Indeed, the increase in soil electrical conductivity, which is directly linked to the increase in the ionic strength of the interstitial medium, mechanistically explains the promotion of MP deposition. According to DLVO theory, the increased presence of dissolved ions causes compression of the electric double layer surrounding both MP and soil surfaces. This compression drastically reduces the electrostatic repulsion energy barrier between particles. As a result, the van der Waals force of attraction, which is effective at very short ranges, becomes predominant, allowing MP to cross the weak residual barrier and irreversibly attach to the grains of the porous medium, resulting in higher retention rates. Other factors can influence MP migration, such as water infiltration and biological activity. Plants and soil fauna, such as earthworms, create cracks and pores

in the soil, leading to a modification of microplastic transport pathways. The infiltrated water contributed to MP migration into deeper soil layers. However, once cracks and pores are filled with water, the buoyancy effect increases, causing a reverse (upward) transport (H. Li et al., 2021; O'Connor et al., 2019). The surface layers of soil, particularly the rhosphere, are areas of vital importance due to their high enzymatic and microbial activity. When microplastics (MP) remain there for a long time, this intensive exposure to active biological processes—via biofilms and enzymes—significantly increases the probability of their chemical aging and partial degradation, phenomena that are less pronounced in deeper soil zones where biological activity is reduced.

Integrating field relevance and risk assessment into the study of MPs migration requires a shift from ideal laboratory conditions to the realities of heterogeneous soils and irrigation systems. Laboratory results, often obtained on uniform soil columns and with constant flows, provide fundamental mechanisms (adhesion, filtration) but must be adjusted to account for spatial heterogeneity (macropores, cracks) and actual intermittent irrigation cycles, which can create preferential pathways (short-circuiting) for rapid MP transport. A recent study conducted by Wei et al. (2024) highlights that the results of MP migration observed in soil columns often cannot be explained by conventional advection-dispersion models alone. The development of a coupled dispersion-drag force model, calibrated using experimental data from laboratory and field-scale studies, has enabled robust simulation of the vertical migration dynamics of MPs. The integration of dispersion proved to be fundamental, as it induces a significant increase in the maximum particle velocity (Vmaxp) and, correlatively, in the concentration of MPs in the aquifer, confirming that advection alone is insufficient to characterise transport. From a hydrodynamic perspective, the increase in irrigation flow significantly intensifies the migration of MPs from the soil to saturated aquifer formations. Critically, the intrinsic properties of MPs exert a predominant control over mobility: (Vmaxp) exhibits a non-linear relationship with particle size, reaching a transport peak for diameters of approximately 8 µm, followed by a gradual decrease for larger sizes (20–100 µm) due to increased steric hindrance within the porous medium (Wei et al., 2024).

Furthermore, a study concluded that the retention of large microplastics (10–20 µm) in saturated porous media is dominated by size exclusion filtration, supplemented by adsorption. The attachment and detachment of MP are strongly influenced by the size of the particles (larger ones being more easily trapped) and by the chemistry of the water, particularly the pH and ionic strength (low electrostatic repulsion favouring attachment). In addition, high flow velocity can cause trapped MP to detach, while a higher MP size ratio and an increase in salinity (up to 25 mmol/L) significantly reduced mobility by promoting attachment. The data confirmed the importance of the desorption phenomenon, requiring the use of an Attachment-Detachment Model (ADM) to accurately simulate the gradual detachment of MP from the soil during the clear water rinsing phase, where the desorption coefficient decreased to only 31.6 % of its initial value after prolonged rinsing. Understanding these mechanisms, often modelled kinetically by distinguishing between reversible and irreversible attachment, is essential for assessing groundwater contamination (Qi et al., 2022).

The retention in the porous medium is not static but influenced by time-dependent kinetic mechanisms such as physical trapping (straining), desorption, and re-mobilisation of particles in response to changes in hydrodynamic or chemical conditions (e.g., ionic strength or pH). Therefore, if the experimental results show unexpected behaviour (such as MP release after a period of stability or faster than expected migration), this can be attributed to the limitations of traditional filtration models and the need to consider the flexibility and heterogeneity of MPs in models, a major challenge in predicting their environmental fate.

In terms of risk assessment, MP migration raises serious implications: their mobility through these preferential pathways threatens groundwater safety through leaching, while MP accumulation in the rhosphere or their potential for uptake by crops (especially nanoparticles
from degradation) poses a risk to the food chain. Furthermore, their long-term interaction with microbes and soil structure may compromise soil fertility and overall health.

On one hand, these particles act as concentrators of toxic pollutants, increasing the sorption of these harmful substances within the soil (S. Zhang et al., 2023; Zhou et al., 2019). On the other hand, their migration through the different soil strata presents a major risk of contamination of groundwater, including aquifers (Dey et al., 2023). The global effects of this migration are likely to generate severe ecological imbalances, affecting biodiversity and the health of ecosystems (En-Nejmy et al., 2024; Mondol et al., 2024). The presence of microplastics in the soil disrupts the complex interactions between fauna (Rillig et al., 2017), flora (Khalid et al., 2020) and micro-organisms (Aralappanavar et al., 2024), which are essential for soil fertility and stability. It is also imperative to consider the interactions of microplastics with the soil-root system, which can alter plant growth and development. Faced with these challenges, in-depth research is needed to assess the long-term risks and develop effective prevention and remediation strategies.

## Conclusion

In this study, we conducted a soil column experiment to examine the transport of microplastics through sandy loam soil under simulated drip irrigation. The research focused on the migration of three types of MPs—PE, red PVC, and grey PVC—with four size categories during different irrigation time intervals. The main findings showed that with increasing time of irrigation, MPs was progressively transported to deeper soil layers with a notable presence in the 15–20 cm soil depth after 16-week experiment. We further revealed that simulated drip irrigation affects the migration of MPs differently depending on their size and type. In particular, particles smaller than 0.5 mm exhibited significantly higher mobility than larger particles. Furthermore, PVC particles showed relatively high mobility compared to PE, with colour having no effect on migration behaviour. The vertical movement of MPs can be influenced by different parameters including the characteristics of the MPs themselves (their density, polymer type, size and shape) as well as the properties of the environment (slope length), soil characteristics, amount of organic matter, ionic strength of infiltrating water and flow velocity.

By providing an original temporal monitoring of MPs mobility (PE and PVC) under simulated drip irrigation conditions, this work makes a significant contribution to understanding the long-term fate of microplastics in the environment. These results provide an essential basis for the development of predictive models and sustainable management strategies for agricultural soils. Future research must therefore focus on studying the interactions between crop roots, the characteristics of microplastics (size, type of polymer, ageing) and their migration in the soil.

The urgent need to mitigate soil contamination by MPs requires both a preventive and curative approach, opening up crucial prospects for research. One promising approach is the targeted inactivation of MPs reactivity, in particular through the development of surface coatings or pre-treatments aimed at minimising their adsorption of concomitant pollutants (heavy metals, xenobiotics) and modulating their interactions with soil matrix components. At the same time, harnessing the potential for in situ enzymatic degradation by soil microorganisms requires in-depth exploration of specialised microbial consortia and optimal environmental conditions to accelerate the biodegradation of dominant polymers. Finally, future mitigation measures will need to rely on Nature-Based Solutions (NbS), such as ecological soil management, ecosystem restoration and the use of biochar or functional organic amendments, to strengthen soil resilience to microplastics, requiring long-term field studies to validate their effectiveness and integrate them into sustainable land management policies.

## Funding

Not applicable.

## Ethical approval

Not applicable.

## Consent to participate

Not applicable.

## Consent to publish

Not applicable.

## CRediT authorship contribution statement

Khaoula En-Nejmy: Writing – original draft, Methodology, Formal analysis, Conceptualization. Bouchra El Hayany: Writing – original draft, Methodology, Conceptualization. Eric Record: Visualization, Validation, Investigation. Mohamed Hafidi: Visualization, Validation, Investigation. Loubna El Fels: Writing – review & editing, Supervision, Methodology, Conceptualization.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Data availability

Data will be made available on request.

## References

Ansar, S.S., Balasubramanian, B., Chaudhary, A., Pushparaj, K., Gopalakrishnan, N.K., Kamyab, H., Chelliapan, S., Pappuswamy, M., 2025. Microplastics distribution and potential health implications of food and food products. J. Food Compos. Anal. 139 (December 2024), 107098. https://doi.org/10.1016/j.jfca.2024.107098.

Aralappanavar, V.K., Mukhopadhyay, R., Yu, Y., Liu, J., Bhatnagar, A., Praveena, S.M., Li, Y., Paller, M., Adyel, T.M., Rinklebe, J., Bolan, N.S., Sarkar, B., 2024. Effects of microplastics on soil microorganisms and microbial functions in nutrients and carbon cycling – a review. Sci. Total Environ. 924 (October 2023). https://doi.org/10.1016/j.scitotenv.2024.171435.

Balestra, V., Vigna, B., De Costanzo, S., Bellopede, R., 2023. Preliminary investigations of microplastic pollution in karst systems, from surface watercourses to cave waters. J. Contam. Hydrol. 252 (November 2022), 104117. https://doi.org/10.1016/j.jconhyd.2022.104117.

Chanda, M., Bathi, J.R., 2026. media : effect of physicochemical properties. Environ. Pollut. Manag. 3 (September 2025), 52–58. https://doi.org/10.1016/j.epm.2025.09.005.

Chia, R.W., Lee, J.Y., Kim, H., Jang, J., 2021. Microplastic pollution in soil and groundwater: a review. Environ. Chem. Lett. 19 (6), 4211–4224. https://doi.org/10.1007/s10311-021-01297-6.

Dey, U., Raj, D., Mondal, M., Roy, P., Mukherjee, A., Mondal, N.K., Das, K., 2023. Microplastics in groundwater: an overview of source, distribution, mobility constraints and potential health impacts during the anthropocene. Groundw. Sustain. Dev. 23 (November), 101036. https://doi.org/10.1016/j.gsd.2023.101036.

El Fels, L., Zamama, M., El Asli, A., Hafidi, M., 2014. Assessment of biotransformation of organic matter during co-composting of sewage sludge-lignocellulosic waste by chemical, FTIR analyses, and phytotoxicity tests. Int. Biodeterior. Biodegrad. 87, 128–137. https://doi.org/10.1016/j.ibiod.2013.09.024.

El Hayany, B., El Fels, L., Dignac, M.F., Quenea, K., Rumpel, C., Hafidi, M., 2021. Pyrolysis-GCMS as a tool for maturity evaluation of compost from sewage sludge and green waste. Waste Biomass Valorization 12 (5), 2639–2652. https://doi.org/10.1007/s12649-020-01184-1.

El Hayany, B., El Fels, L., Quenea, K., Dignac, M-F., Rumpel, C., Gupta, V-K., Hafidi, M., 2021. Microplastics from lagooning sludge to composts as revealed by Fluorescent staining- Image analysis, Raman spectroscopy and Pyrolysis-GC/MS. J. Environ. Manag. 275, 111249. https://doi.org/10.1016/j.jenvman.2020.111249 (IF: 5,647).

En-Nejmy, K., El Hayany, B., Al-Alawi, M., Jemo, M., Hafidi, M., El Fels, L., 2024. Microplastics in soil: a comprehensive review of occurrence, sources, fate, analytical
techniques and potential impacts. Ecotoxicol. Environ. Saf. 288 (October), 117332. https://doi.org/10.1016/j.ecoenv.2024.117332.

Gao, J., Pan, S., Li, P., Wang, L., Hou, R., Wu, W.M., Luo, J., Hou, D., 2021. Vertical migration of microplastics in porous media: multiple controlling factors under wet-dry cycling. J. Hazard. Mater. 419 (June), 126413. https://doi.org/10.1016/j.jhazmat.2021.126413.

Geyer, R., Jambeck, J.R., Law, K.L., 2017. Production, use, and fate of all plastics ever made [Producción, uso y destino de todos los plásticos jamás fabricados]. Sci. Adv. 3 (7), e1700782. https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.1700782.

Guo, J.J., Huang, X.P., Xiang, L., Wang, Y.Z., Li, Y.W., Li, H., Cai, Q.Y., Mo, C.H., Wong, M.H., 2020. Source, migration and toxicology of microplastics in soil. Environ. Int. 137 (September 2019), 105263. https://doi.org/10.1016/j.envint.2019.105263.

Hanun, J.N., Hassan, F., Jiang, J.J., 2021. Occurrence, fate, and sorption behavior of contaminants of emerging concern to microplastics: influence of the weathering/aging process. J. Environ. Chem. Eng. 9 (5), 106290. https://doi.org/10.1016/j.jece.2021.106290.

Hasan, M.M., Tarannum, M.N., 2025. Adverse impacts of microplastics on soil physicochemical properties and crop health in agricultural systems. J. Hazard. Mater. Adv. 17 (August 2024), 100528. https://doi.org/10.1016/j.hazadv.2024.100528.

Hu, B., Guo, P., Han, S., Jin, Y., Nan, Y., Deng, J., He, J., Wu, Y., Chen, S., 2022. Distribution characteristics of microplastics in the soil of mangrove restoration wetland and the effects of microplastics on soil characteristics. Ecotoxicology 31 (7), 1120-1136. https://doi.org/10.1007/s10646-022-02561-3.

Huang, B., Sun, L., Liu, M., Huang, H., He, H., Han, F., Wang, X., Xu, Z., Li, B., Pan, X., 2021. Abundance and distribution characteristics of microplastic in plateau cultivated land of Yunnan Province, China. Environ. Sci. Pollut. Res. 28 (2), 1675-1688. https://doi.org/10.1007/s11356-020-10527-3.

Ivanic, F.M., Guggenberger, G., Woche, S.K., Bachmann, J., Hoppe, M., Carstens, J.F., 2023. Soil organic matter facilitates the transport of microplastic by reducing surface hydrophobicity. Colloids Surf. A. Physicochem. Eng. Asp. 676 (Part B), 132255. https://doi.org/10.1016/j.colsurf.a.2023.132255.

Jabro, J.D., Stevens, W.B., Iversen, W.M., Sainju, U.M., & Allen, B.L. (2023). *Saturated hydraulic conductivity of a sandy loam under No-till and intensive tillage in a corn – Soybean rotation*.

Khalid, N., Aqeel, M., Noman, A., 2020. Microplastics could be a threat to plants in terrestrial systems directly or indirectly. Environ. Pollut. 267, 115653. https://doi.org/10.1016/j.envpol.2020.115653.

Kim, S.W., An, Y.J., 2020. Edible size of polyethylene microplastics and their effects on springtail behavior. Environ. Pollut. 266, 115255. https://doi.org/10.1016/j.envpol.2020.115255.

Kobayashi, M., Nanaumi, H., Muto, Y., 2019. Initial deposition rate of latex particles in the packed bed of zirconia beads. Colloids Surf. A: Physicochem. Eng. Asp. 347 (1-3), 2-7. https://doi.org/10.1016/j.colsurf.a.2008.09.054.

Koutnik, V.S., Leonard, J., Brar, J., Cao, S., Glasman, J.B., Cowger, W., Ravi, S., Mohanty, S.K., 2022. Transport of microplastics in stormwater treatment systems under freeze-thaw cycles: critical role of plastic density. Water Res. 222 (July), 118950. https://doi.org/10.1016/j.watres.2022.118950.

Kwak, J.Ji, Kim, L., An, Y.J., 2024. Microplastics promote the accumulation of negative fungal groups and cause multigenerational effects in springtails. J. Hazard. Mater. 466 (January), 133574. https://doi.org/10.1016/j.jhazmat.2024.133574.

Li, H., Lu, X., Wang, S., Zheng, B., Xu, Y., 2021. Vertical migration of microplastics along soil profile under different crop root systems. Environ. Pollut. 278, 116833. https://doi.org/10.1016/j.envpol.2021.116833.

Li, W., Brunetti, G., Zafiu, C., Kunaschk, M., Debreczeby, M., Stumpp, C., 2024. Experimental and simulated microplastics transport in saturated natural sediments: impact of grain size and particle size. J. Hazard. Mater. 468 (February), 133772. https://doi.org/10.1016/j.jhazmat.2024.133772.

Li, W., Wufuer, R., Duo, J., Wang, S., Luo, Y., Zhang, D., Pan, X., 2020. Microplastics in agricultural soils: extraction and characterization after different periods of polythene film mulching in an arid region. Sci. Total Environ. 749. https://doi.org/10.1016/j.scitotenv.2020.141420.

Liu, B., Zhao, S., Qiu, T., Cui, Q., Yang, Y., Li, L., 2024. Science of the Total environment interaction of microplastics with heavy metals in soil: mechanisms, influencing factors and biological effects. Sci. Total Environ. 918 (October 2023), 170281. https://doi.org/10.1016/j.scitotenv.2024.170281.

Liu, J., Zheng, L., 2025. Microplastic migration and transformation pathways and exposure health risks. Environ. Pollut. 368 (January), 125700. https://doi.org/10.1016/j.envpol.2025.125700.

Luo, H., Chang, L., Ju, T., Li, Y., 2024. Factors influencing the vertical migration of microplastics up and down the soil profile. ACS Omega. https://doi.org/10.1021/acsomega.4c04083.

Lv, W., Zhou, W., Lu, S., Huang, W., Yuan, Q., Tian, M., Lv, W., He, D., 2019. Microplastic migration in rice-fish co-culture system: a report of three farmland stations in Shanghai, China. Sci. Total Environ. 652, 1209-1218. https://doi.org/10.1016/j.scitotenv.2018.10.321.

Majdalani, S., Michel, E., Di-Pietro, L., Angulo-Jaramillo, R., 2008. Effects of wetting and drying cycles on in situ soil particle mobilization. Eur. J. Soil Sci. 59 (2), 147-155. https://doi.org/10.1111/j.1365-2389.2007.00964.x.

Mondol, M., Angon, P.B., Roy, A., 2024. Effects of microplastics on soil physical, chemical and biological properties. Nat. Hazards Res. https://doi.org/10.1016/j.nhres.2024.02.002. January.

Nguyen, M., Jahan, R., Hwangbo, M., Kim, J., 2025. Journal of Hazardous Materials advances microplastic accumulation in soils: unlocking the mechanism and biodegradation pathway. J. Hazard. Mater. Adv. 17 (January), 100629. https://doi.org/10.1016/j.jhazadv.2025.100629.

O'Connor, D., Pan, S., Shen, Z., Song, Y., Jin, Y., Wu, W.M., Hou, D., 2019. Microplastics undergo accelerated vertical migration in sand soil due to small size and wet-dry cycles. Environ. Pollut. 249, 527-534. https://doi.org/10.1016/j.envpol.2019.03.092.

Qi, S., Song, J., Shentu, J., Chen, Q., Lin, K., 2022. Chemosphere attachment and detachment of large microplastics in saturated porous media and its influencing factors. Chemosphere 305 (April), 135322. https://doi.org/10.1016/j.chemosphere.2022.135322.

Ranjan, V.P., Joseph, A., Sharma, H.B., Goel, S., 2023. Preliminary investigation on effects of size, polymer type, and surface behaviour on the vertical mobility of microplastics in a porous media. Sci. Total Environ. 864 (December 2022), 161148. https://doi.org/10.1016/j.scitotenv.2022.161148.

Ren, Z., Gui, X., Xu, X., Zhao, L., Qiu, H., Cao, X., 2021. Microplastics in the soil-groundwater environment: aging, migration, and co-transport of contaminants - A critical review. J. Hazard. Mater. 419 (March), 126455. https://doi.org/10.1016/j.jhazmat.2021.126455.

Rillig, M.C., Ziersch, L., Hempel, S., 2017. Microplastic transport in soil by earthworms. Sci. Rep. 7 (1), 1-6. https://doi.org/10.1038/s41598-017-01594-7.

Sadri, B., Pernitsky, D., Sadrzadeh, M., 2017. Aggregation and deposition of colloidal particles: effect of surface properties of collector beads. Colloids Surf. A: Physicochem. Eng. Asp. 530 (July), 46-52. https://doi.org/10.1016/j.colsurf.a.2017.07.041.

Samandra, S., Johnston, J.M., Jaeger, J.E., Symons, B., Xie, S., Currell, M., Ellis, A.V., Clarke, B.O., 2022. Microplastic contamination of an unconfined groundwater aquifer in Victoria, Australia. Sci. Total Environ. 802, 149727. https://doi.org/10.1016/j.scitotenv.2021.149727.

Tarbuck, J.E., Lutgens, K.F., 2017. Earth: An introduction to Physical Geology. Pearson, p. 32.

Tian, H., Zheng, C., Huang, X., Qi, C., Li, B., Du, Z., Zhu, L., Wang, J., Wang, J., 2024. Effects of farmland residual mulch film-derived microplastics on the structure and function of soil and earthworm Metaphire guillelmi gut microbiota. Sci. Total Environ. 915 (January), 170094. https://doi.org/10.1016/j.scitotenv.2024.170094.

Tumwet, F.C., Richter, A., Kleint, T., Scheytt, T., 2024. Vertical movement of microplastics by roots of wheat plant (Triticum aestivum) and the plant response in sandy soil. Microplastics Nanoplastics 4 (1). https://doi.org/10.1186/s43591-024-00092-8.

Wanner, P., 2021. Plastic in agricultural soils – a global risk for groundwater systems and drinking water supplies? – A review. Chemosphere 264, 128453. https://doi.org/10.1016/j.chemosphere.2020.128453.

Wei, Y., Chen, Y., Cao, X., Yeh, T-cJ, Zhang, J., Zhan, Z., Cui, Y., Li, H., 2024. Modeling of microplastics migration in soil and groundwater: insights into dispersion and particle property effects. Environ. Sci. Technol. 58 (34), 15224-15235.

Xu, Z., Deng, X., Lin, Z., Wang, L., Lin, L., Wu, X., Wang, Y., Li, H., Shen, J., Sun, W., 2025. Microplastics in agricultural soil: unveiling their role in shaping soil properties and driving greenhouse gas emissions. Sci. Total Environ. 958 (December 2024), 177875. https://doi.org/10.1016/j.scitotenv.2024.177875.

Yang, X., Chen, R., Tang, D.W.S., 2025. Minimal preferential transport of microplastics through macropores in irrigated disturbed and undisturbed soil columns. Agric. Water Manag. 318 (May). https://doi.org/10.1016/j.agwat.2025.109751.

Zhang, S., Wang, W., Yan, P., Wang, J., Yan, S., Liu, X., Aurangzeib, M., 2023. Microplastic migration and distribution in the terrestrial and aquatic environments: a threat to biotic safety. J. Environ. Manage 333 (February), 117412. https://doi.org/10.1016/j.jenvman.2023.117412.

Zhang, X., Chen, Y., Li, X., Zhang, Y., Gao, W., Jiang, J., Mo, A., He, D., 2022. Size/shape-dependent migration of microplastics in agricultural soil under simulative and natural rainfall. Sci. Total Environ. 815, 152507. https://doi.org/10.1016/j.scitotenv.2021.152507.

Zhang, X., Menzel, R., Ruess, L., 2025. The impact of microplastic on nematodes: soil type, plastic amount and aging as determinants for the fitness of Caenorhabditis elegans. Appl. Soil Ecol. 206 (July 2024), 105883. https://doi.org/10.1016/j.apsoil.2025.105883.

Zhao, S., Zhang, Z., Chen, L., Cui, Q., Cui, Y., Song, D., Fang, L., 2022a. Review on migration, transformation and ecological impacts of microplastics in soil. Appl. Soil Ecol. 176 (April), 104486. https://doi.org/10.1016/j.apsoil.2022.104486.

Zhao, Z., Zhao, K., Zhang, T., Xu, Y., Chen, R., Xue, S., Liu, M., Tang, D., Yang, X., Giessen, V., 2022b. Irrigation-facilitated low-density polyethylene microplastic vertical transport along soil profile: an empirical model developed by column experiment. Ecotoxicol. Environ. Saf. 247 (July), 114232. https://doi.org/10.1016/j.ecoenv.2022.114232.

Zhou, Y., Liu, X., Wang, J., 2019. Characterization of microplastics and the association of heavy metals with microplastics in suburban soil of central China. Sci. Total Environ. 694. https://doi.org/10.1016/j.scitotenv.2019.133798.

Zong, X., Zhang, J., Zhu, J., Zhang, L., Jiang, L., Yin, Y., Guo, H., 2021. Effects of polystyrene microplastic on uptake and toxicity of copper and cadmium in hydroponic wheat seedlings (Triticum aestivum L.). Ecotoxicol. Environ. Saf. 217. https://doi.org/10.1016/j.ecoenv.2021.112217.