Plastic nanoparticles, widely used in various consumer products, have become a significant contributor to soil pollution, making it essential to understand their transport in soils, where organic substances are prevalent. This study aimed to investigate the influence of low-molecular-weight organic acids (LMWOAs) on the transport of polystyrene nanoparticles (PS-NPs) through saturated quartz sand. The focus was on seven specific organic acids: three dibasic acids—malonic acid (MA1), malic acid (MA2), and tartaric acid (TA)—and four monobasic acids—formic acid (FA), acetic acid (AA), propanoic acid (PA), and glycolic acid (GA). The effects were evaluated across a range of pH levels (4.0, 5.5, and 7.0) and in the presence of two cations, Na⁺ and Ca²⁺. The results showed that, in the presence of Na⁺, dibasic acids significantly enhanced the transport of PS-NPs, with TA being the most effective, followed by MA2 and MA1. This enhancement was attributed to the adsorption of LMWOAs onto the PS-NPs and quartz sand, leading to a more negative ζ-potential. This negative shift increased electrostatic repulsion between the particles, reducing their deposition and facilitating transport. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory further explained that higher pH levels increased the energy barrier, which reduced PS-NPs deposition by stabilizing them in the suspension. In contrast, the monobasic acids—apart from GA—exhibited minimal impact on PS-NP transport. These acids slightly diminished the hydrophilicity of the PS-NPs, as evidenced by a minor increase in the water contact angle, which in turn reduced their mobility. However, GA, with its additional hydroxyl group, acted similarly to dibasic acids, promoting both enhanced hydrophilicity and increased transport of PS-NPs. When Ca²⁺ was present, the transport enhancement was similar to that observed with Na⁺. The complexation and bridging effects of Ca²⁺ with the organic acids and PS-NPs contributed to this effect. Overall, these findings offer valuable insights into the factors influencing the mobility of PS-NPs in soils, which is crucial for understanding their environmental behavior and potential ecological impacts.

How to cite: Lu, T., He, J., and Yang, M.: Impact of Low-Molecular-Weight Organic Acids on the Transport of Polystyrene Nanoplastics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-512, https://doi.org/10.5194/egusphere-egu25-512, 2025.

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

How to cite: Jiang, R. and Wang, K.: Impact of long-term conventional and biodegradable film mulching on microplastic abundance and soil organic carbon in a cotton field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1849, https://doi.org/10.5194/egusphere-egu25-1849, 2025.

Soil aggregates play a pivotal role in soil organic carbon dynamics and microbial activity. However, their influence on the pressing issue of microplastic (MP) contamination in soils remains poorly understood. This lack of attention may be attributed to the inherent complexity and heterogeneity of soil, which renders plastic isolation and identification in soil is particularly challenging. This study aims to investigate MPs redistribution among soil aggregate fractions during the process of soil aggregation. Two soil textures (silt loam and sandy loam) were amended with organic matter (OM) to promote aggregation during a two-month incubation period,  with 0.1 % microplastics powder added to the soils. A self-made pristine and aged LDPE and PET microplastics (<50 µm) were used in this experiment. Subsequently, physical fractionation were implemented to separate the soils into aggregate fraction (macro-aggregate, micro-aggregates and within associated fractions and silt+clay fractions). Organic matter was removed via oxidation to prevent interference with MP analysis. MPs were subsequently extracted through density separation, filtration, and examined using a Keyence VH-Z500 digital microscope. Unexpectedly, even small amounts of MPs significantly influenced soil aggregation, with effects varying by polymer type, weathering state, and soil texture. LDPE was predominantly retained in the micro-aggregate fractions in both soil textures, except for aged LDPE in loam soil, where over 60% accumulated in the silt+clay fraction. Conversely, PET was primarily retained in the macro-aggregates of silt loam soils and the micro-aggregates of sandy loam soils. Furthermore, the redistribution of MPs during soil aggregation exhibited notable differences, with silt loam soils demonstrating the highest degree of MP redistribution. These findings are relevant as soil aggregates provide different levels of physical protection against degradation and mobility, influencing the bioavailability of microplastics and their potential transfer to other environmental compartments.

How to cite: Kusumawardani, P. N., Amaya, D. P. T., Krekelbergh, N., Liu, Y., Sleutel, S., Skirtach, A., and De Neve, S.: The Re-distribution of Pristine and Aged Microplastics (<50 µm) in Soil Aggregate Fractions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5584, https://doi.org/10.5194/egusphere-egu25-5584, 2025.

The presence of NPs in drinking water has raised wide concerns due to their potential impacts on human health. Riverbank filtration (RBF), a natural water treatment process that involves the passage of water through soil, is employed by some Dutch drinking water companies that source water from rivers. Given the emergence of NPs as pollutants, it is essential to understand their transport and removal behavior during riverbank filtration to ensure the safety and quality of drinking water.

The deposition of NPs in porous media is strongly influenced by the physicochemical properties of aquifer grain surfaces. Natural biofilms, consisting of complex communities of bacteria and other microorganisms, typically form on these surfaces and alter their properties. During RBF, biofilm-associated microbial activity leads to rapid oxygen consumption due to the degradation of organic matter, resulting in the formation of localized anoxic and anaerobic zones. However, the impact of this spatial heterogeneity of biofilms on the removal of NPs remains unclear. In this study, we aim to investigate how biofilm spatial heterogeneity influences NP deposition during RBF.

We constructed several long columns (90 cm in length), each composed of ten short columns (9 cm in length, 2 cm in diameter), packed with technical sand (particle size: 0.4–0.6 mm). River water sourced from an RBF site was pumped through the columns at a flow rate of 0.1 mL/min (0.054 m/h) to facilitate biofilm growth over periods of 1, 3, and 6 months. After biofilm formation, columns were segmented into ten short columns to assess NP transport behavior by analyzing breakthrough and retention curves at different biofilm depths. Europium-doped polystyrene NPs (30 mg/L) suspended in synthetic river water with a similar ionic composition to natural river water were used as tracers to evaluate NP transport and retention at an increased flow rate of 0.75 mL/min.

So far, we have obtained breakthrough curves for NP transport in columns with 1- and 3-month biofilms. Preliminary results indicate that site blocking contributed to the concentration- and time-dependent deposition of NPs. The inherent surface roughness of the technical sand created heterogeneous sites that contributed to multi-site NP deposition. Compared to the original sand grains, biofilms exhibited a less negative surface charge, facilitating stronger interaction with NPs. It suggest that biofilms created more favorable heterogeneous sites, enhancing both irreversible and reversible deposition of NPs. The maximum retention capacity of sand grains decreased with depth, with the shallow biofilm layers, which had the highest biomass, greatly enhancing NP retention. Additionally, biofilms grown for 3 months demonstrated a stronger capacity to retain NPs compared to those grown for 1 month.

The remaining experiments are expected to be completed by May next year. This study will enhance the understanding of NP deposition mechanisms during RBF, with a particular focus on the critical role of the spatial heterogeneity of natural biofilms. The findings will provide valuable insights into the potential removal efficiency of NPs in RBF systems, as well as the associated risks of NP exposure in downstream environments and drinking water sources.

How to cite: Xu, Y., van der Hoek, J. P., Liu, G., and Maren Lompe, K.: Biofilm heterogeneity affects the mobility of nanoplastics during riverbank filtration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10477, https://doi.org/10.5194/egusphere-egu25-10477, 2025.

How to cite: Schneidewind, U., Krause, S., Kelleher, L., Reiss, J., Perkins, D., Barrett, N., and Robertson, A.: Microplastic particles in groundwater systems worldwide, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11153, https://doi.org/10.5194/egusphere-egu25-11153, 2025.

Microplastics (MPs) have emerged as a significant environmental concern, particularly due to their pervasive presence in various ecosystems, including soil and groundwater. These small plastic particles, often resulting from the degradation of larger plastic items, pose serious risks to ecological health and human safety. Their infiltration into groundwater systems is alarming, especially in agricultural practices utilizing mulching techniques, where microplastics can permeate porous media and potentially disrupt soil health and crop productivity. Despite the growing body of research on microplastics, most studies have focused on uniform soil matrices or sediments, neglecting the complexities of layered and heterogeneous aquifer systems. This study investigates the dynamics of polyethylene microplastics within soil column tests, specifically examining their transport behavior through stratified layers of coarse sand and small gravel. We utilized medium-sized microplastics (25 microns) embedded within a layered column consisting of coarse sand (500-1000 microns) and small gravel (4-8 mm), packed uniformly to simulate real-world conditions. Groundwater was injected into the columns at a flow rate of 12 mm per minute for 360 minutes. Water samples were collected at intervals of 5, 10, and 20 minutes for microplastic quantification using fluorescence microscopy after filtration. Post-experiment, sediment layers were sequentially removed every 6 cm to isolate and count microplastics using density separation methods. Results indicated a significantly faster movement of microplastics through gravel compared to sand, with the highest concentrations detected in the outflow from gravel columns. In mixed columns where gravel was positioned below sand, a greater number of microplastic particles were observed compared to when sand was below. This suggests that while gravel facilitates rapid transport, the arrangement of layers plays a critical role in determining the concentration of microplastics in the outflow. Additionally, entrapment of microplastics was most pronounced in the sand layers, while minimal retention occurred in gravel. Notable variations in microplastic counts were observed at the interface between gravel and sand in mixed sediment columns, highlighting the influence of layer interactions on transport dynamics. In conclusion, this study underscores the critical need to consider soil layering when assessing microplastic transport in agricultural settings. The findings reveal that microplastic dynamics are significantly affected by substrate composition and layering, which could have profound implications for groundwater quality and ecosystem health in agricultural landscapes. Further research is essential to explore the long-term effects of microplastic contamination on soil biota and crop systems, as well as to develop effective management strategies to mitigate their impact on environmental health.

Keywords: Microplastics, Soil layering, Transport dynamics, Groundwater contamination

How to cite: Dehbandi, R., Alqrinawi, F., Singh, J., Schneidewind, U., and Krause, S.: Impact of Layering and Heterogeneity on the Transport Dynamics of Microplastics in Soil Columns: Implications for Groundwater Contamination, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15142, https://doi.org/10.5194/egusphere-egu25-15142, 2025.

While there have been advances in understanding the above ground plastic cycle, there is still a substantial lack of understanding the sources and activation mechanisms of plastic pollution affecting the entry, fate, transport, transformation and impact of microplastics into soils, riverbeds, sediment and groundwater aquifers.

We here present the initial outcomes of integrated field and laboratory analytical experimental approaches and mathematical modelling studies to provide mechanistic understanding of the overall magnitude as well as hot spots (and hot moments) of microplastic entry into subsurface ecosystems and their transport and transformation pathways. Our model results highlight that a large proportion (>95%) of all mismanaged plastic waste emitted since the 1950s is temporarily stored in river basins and able to enter subsurface ecosystems in the long-term. Using multi-scale modelling studies in combination with artificial river simulators (flumes) and laboratory column experiments we evidence that hyporheic exchange represents a preferential input mechanism for smaller and lighter microplastics into streambed sediments and underlying groundwater ecosystems. This finding maps directly onto field experimental findings from our global monitoring programmes which identified distinct hotspots of microplastic accumulation. Soil and streambed sediment columns were deployed to explore the controls on microplastic transport once they have entered the subsurface, highlighting that in particular intermittent pulsed hydraulic forcing increases the potential for fast particle transport.

How to cite: Krause, S., Schneidewind, U., Alqrinawi, F., Chen, Z., Fraga, B., Dehbandi, R., Gomez Velez, J., Mecaj, P., Cardoza Pedroza, L., Simon, L., Mermillod Blondin, F., Mourier, B., Volatier, L., Lassabatiere, L., Kelleher, L., Comer-Warner, S., Quinones, Z., Lynch, I., Singh, J., and Yadav, B.: The plastic underground – Exploring the mechanisms controlling the fate and transport of microplastics in the subsurface, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21555, https://doi.org/10.5194/egusphere-egu25-21555, 2025.

Microplastics (MPs) are ubiquitous environmental contaminants that not only accumulate in sediments and biota but also act as vectors for toxic substances, facilitating the transport and dispersion of hazardous chemicals within ecosystems. Their environmental impact is exacerbated by their propensity to adsorb pollutants from their surroundings, a process influenced by the physicochemical properties of both the polymers and the contaminants. While MPs typically exhibit limited surface porosity, exposure to natural environmental factors, such as weathering, abrasion, and photo-oxidation, significantly alters their surface characteristics. These transformations result in structural modifications, including the incorporation of oxygen-containing functional groups, sulfhydryl groups, and persistent free radicals. Such alterations lead to the generation of negatively charged surfaces, which enhance the adsorption of metal cations and other pollutants, thereby amplifying their environmental persistence and toxicity.

This study aimed to investigate the distribution of MPs and their interactions between surface water (SW) and groundwater (GW) systems, with a particular focus on understanding how redox potential (ORP), and surface modifications influence their structural transformations, pollutant adsorption mechanisms, and role as carriers of hazardous substances within natural ecosystems. SW and GW samples were collected from various locations across Uttarakhand, India. In-situ parameters, including pH, conductivity, TDS, DO, temperature, salinity, pressure, ORP, turbidity, and alkalinity, were measured using a portable multiparameter probe (HANNA-HI9829-01201). The average concentration of MPs in the GW and SW samples was found to be 34 MPs/L and 29 MPs/L, respectively. In SW, the relationship between MPs and ORP appears less direct but is still influenced by ionic parameters such as conductivity and TDS, reflecting the potential for pollutant adsorption in regions with high redox activity. In GW, MPs exhibit a moderate correlation with ORP and alkalinity, suggesting that redox conditions may play a significant role in their behavior or interaction with other pollutants. Notably, pH and ORP were clustered together in both GW and SW, suggesting a link between acidity/alkalinity and redox conditions driven by shared environmental or geochemical processes. This research provides key insights into MPs' behavior, aiding strategies to combat water pollution and guide policies to protect ecosystems and public health.

Keywords: microplastics; redox; emerging contaminants; transport; interactions.

How to cite: Dogra, K.: Microplastic-Facilitated Transport of Emerging Contaminants in Redox-Active Environments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17448, https://doi.org/10.5194/egusphere-egu25-17448, 2025.