Hannes Laermanns

Microplastic (MP) contamination in soil ecosystems is a growing concern because MPs can accumulate in soils and interact with soil biota. Microbial biofilms forming on MP surfaces modify their physicochemical properties, influence transport and bioavailability, and potentially contribute to microbial degradation of the particles. This study investigates bacterial and fungal colonization on polystyrene MPs incubated in floodplain soil under controlled laboratory and natural field conditions over 4, 8, and 16 weeks. Using scanning electron microscopy and biofilm assays, we observed progressive biofilm formation, with higher biomass under laboratory conditions after 16 weeks compared to natural incubation. Metabarcoding analysis (16S rRNA genes for bacteria and ITS genes for fungi) showed distinct temporal shifts in bacterial communities under natural incubation (R2 = 0.316, p = 0.0001) compared to laboratory conditions, demonstrating that environmental dynamics strongly influence early biofilm succession. In contrast, fungal communities, dominated by Ascomycota and Basidiomycota, showed more comparable patterns between incubation conditions. Genera with known PS degradation potential, such as Pseudomonas, Bacillus, and Penicillium spp., were detected, suggesting potential microbial involvement in MP decomposition. This study shows the early-stage processes of colonization of microorganisms on irregularly shaped MPs. Our findings highlight the importance of natural incubations for understanding MP–microbe interactions in soils and call for longer-term, polymer-diverse studies to better assess MP fate.

Microplastic (MP) contamination in soil ecosystems is a growing concern because MPs can accumulate, interact with soil biota, and have negative impact on soil functioning. Microbial biofilms forming on MP surfaces modify their physicochemical properties, potentially influence the transport and bioavailability of MPs, and possibly contribute to microbial degradation of the particles. While many studies have examined how MPs affect soil organisms, less attention has been given to how soil biota, particularly microbial biofilms, influence MPs in soils. This study investigates bacterial and fungal colonization on polystyrene MPs incubated in two parallel experiments in floodplain soil in the field as well as under controlled laboratory conditions over 4, 8, and 16 weeks. Using scanning electron microscopy and biofilm biomass assays, we observed progressive biofilm formation. We found higher biomass on MPs under laboratory conditions compared to natural incubation after 16 weeks. Metabarcoding analysis (16S rRNA genes for bacteria and ITS genes for fungi) showed that bacterial communities on MPs exhibited distinct dynamics under laboratory and natural conditions, with Acidobacteriota and Proteobacteria dominating and indicating temporal succession in natural conditions. In contrast, fungal communities, dominated by Ascomycota and Basidiomycota, remained more stable in composition across both conditions over time. Genera with known PS degradation potential, such as Pseudomonas, Bacillus, and Penicillium, were also detected, suggesting potential microbial involvement in MP breakdown. Our findings underscore the significance of natural incubations in elucidating MP-microbe interactions in soils, with a particular focus on bacterial and fungal communities. This study also calls for longer-term, polymer-diverse studies to better assess MP fate in soil ecosystems.

Microplastics (MPs) are increasingly recognized as persistent contaminants in soils and groundwater systems worldwide. Polystyrene MPs are highly hydrophobic and show strong homoaggregation, which affects their mobility in porous media. Most laboratory transport studies therefore use chemical dispersants, such as Tween 20, to achieve a uniform distribution of particles during transport experiments. However, these additives coat plastic surfaces and alter plastic–soil interactions, making it difficult to assess environmentally realistic transport behavior. Here, we introduce a surfactant-free approach based on controlled radio-frequency oxygen plasma treatment to modify MP surface properties. Oxygen plasma-treated polystyrene particles (

Floodplains are highly dynamic systems and can accumulate large quantities of microplastics (MPs), yet the mechanisms controlling their vertical redistribution after deposition remain poorly constrained. We investigate MP infiltration and transport in undisturbed Rhine floodplain soils using intact 0–20 cm cores subjected to a controlled flooding scenario. A particle mix of polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) (20–75 µm), cryomilled and pre-incubated in Rhine water to allow biofilm formation, was applied to the soil surface prior to flooding. Particles were labelled with Rhodamine-B and metal oxides to enable complementary optical and elemental tracing. Water flow and tracer transport were monitored using D₂O breakthrough curves and continuous gravimetric measurements.After freezing, soil columns were sectioned into 2 cm layers, and MPs were quantified by fluorescence microscopy, µ-XRF, and AI-assisted particle recognition. Results indicate rapid MP infiltration and vertical transport within the soil. MP breakthrough was observed in all columns, although breakthrough timing and concentrations varied among replicates. Vertical transport was strongly governed by spatial heterogeneity and preferential flow paths, particularly biogenic macropores, whereas saturated hydraulic conductivity alone did not reliably predict MP movement. These findings highlight the dominant role of soil structural controls in floodplain MP transport and challenge the use of bulk hydraulic parameters for predicting MP redistribution during flooding events.

Floodplains are increasingly recognised as important sinks for microplastics (MPs) at the interface between terrestrial and aquatic systems, yet their role in the long-term retention, redistribution, and vertical transport of MPs in soils remains poorly understood. While rivers are known pathways for microplastics to marine environments, floodplain soils may act as intermediate storage compartments where hydrological dynamics, sediment properties, and biological activity jointly control plastic fate.Here, we investigate the spatial and vertical distribution of microplastics in floodplain soils along the Rhine River, combining field observations, depth-resolved soil analyses, and hydrodynamic flood modelling. Soil profiles were sampled across multiple transects spanning contrasting floodplain topographies and flooding frequencies. Microplastic abundance and mass concentrations were quantified using FTIR spectroscopy and pyrolysis GC/MS. To assess controls on vertical redistribution, top soils and one selected soil profile were studied, supported by physico-chemical analyses and dating. In parallel, a hydrodynamic flood model was used to relate observed microplastic patterns to flood frequency and inundation dynamics.Our results reveal pronounced spatial heterogeneity in MP distribution across floodplains. Highest concentrations consistently occur in topographic depressions characterised by frequent inundation and enhanced sediment deposition. Vertically, microplastics are predominantly enriched in upper soil horizons but are also detected at depth, indicating downward transport beyond simple surface accumulation. Associations with finer-grained horizons suggest a role of soil physical structure in regulating retention, while deviations from this pattern point to the modifying influence of biological activity and soil mixing processes.These findings highlight floodplains as dynamic and heterogeneous microplastic sinks, where hydrological connectivity, local topography, and soil properties interact to control transport and long-term fate.

Floodplains are recognized as significant sinks for sediments and pollutants transported by rivers, particularly during flood events which mobilize and redistribute contaminants like microplastics (MPs). This study investigates the role of floodplain vegetation and rough surfaces in the retention of microplastics and fine sediments during overbank flow, and the subsequent fate of these particles within the soil profile.The research combined column experiments and field observations to quantify particle deposition. We found that vegetation characteristics are a primary driver for the retention of suspended particles. Specifically, plant biomass and structural diversity were positively correlated with the amount of sediment deposited on the vegetation surface. This suggests that denser and more structurally complex vegetation enhances the capture of both sediments and microplastics from the water column. To differentiate the effects of biological surfaces from purely physical ones, deposition on vegetation was compared with deposition on metal sheets of varying surface areas. The deposition results potentially reveal the impact of surface areas and roughness on microplastic retention.Following the initial retention process, microplastics can infiltrate into the floodplain soil. The analysis of flood simulated soil column experiments confirm a heterogenous and rapid microplastic breakthrough. Additionally, under field conditions soil profiles confirms that floodplains act as major sinks, with the highest concentrations of MPs found in the upper 38-45 cm of soil depth. However, MPs are not permanently sequestered at the surface. The vertical distribution of microplastics is influenced by particle characteristics such as size and shape and soil properties. Smaller, spherical particles tend to infiltrate deeper into the soil compared to larger fragments and fibers. This downward translocation can be facilitated by processes such as preferential flow through soil structure and biopores.In conclusion, floodplain vegetation plays a critical role in intercepting microplastics during floods, initiating their transfer from the aquatic to the terrestrial environment. The retention efficiency is closely linked to vegetation biomass and structure. Our findings highlight that vegetation structure is one factor for MP sedimentation from flooding, while soil structure and biopores control infiltration and vertical transport of MP into the soil matrix. Subsequent infiltration and distribution in the soil profile are governed by a complex interplay between MP particle traits, soil texture, and biological activity. These findings highlight the importance of floodings, vegetation cover, soil structure in the transport of microplastics at the interface of aquatic and terrestrial ecosystems.

Microplastics in rivers originate from various sources and can be transported by river water. During their time in the river, the properties of microplastics may change leading to a temporary deposition and accumulation in the riverbed. In particular, during floodings, stronger flow velocities occur and can remobilize microplastics and sediments, transporting them further downstream and to adjacent floodplains. Floodplains represent dynamic and vegetation-rich environments, where the vegetation increases the floodplains’ roughness, resulting in slower flow velocities during floods and potentially enhance deposition of sediments and microplastics. While previous research has shown that factors such as local topography and flood frequency influence microplastic distribution in floodplains, however, the role of vegetation in microplastic filtering during floods has not been studied. This study investigates the retention of microplastics and natural sediments by floodplain grassland vegetation during a major river flood. Directly after the flood event in July 2021, we sampled vegetation from a formerly flooded Rhine floodplain north of Cologne, Germany. For comparison we sampled vegetation from an adjacent non-flooded grassland, which was only affected by atmospheric microplastic deposition. After rinsing the deposits from the vegetation, we used ZnCl₂ density separation to extract microplastics, followed by enzymatic-oxidative purification to remove organic material and µ-FPA-FTIR imaging for microplastic analysis. Our findings show that microplastics from fluvial and atmospheric origin differ in terms of their numbers, shapes, sizes, and polymer types. Concerning the samples from flooded vegetation, higher vegetation biomass was associated with increased deposition of both natural sediments and small microplastics. However, we observed distinct deposition patterns for natural sediments and microplastics. Our results provide valuable insights into the role of floodplain vegetation in the retention, accumulation, and distribution of microplastics at the interface between aquatic and terrestrial ecosystems.

Microplastics (MPs), ubiquitous in terrestrial environments, are usually covered by an eco-corona (EC) under natural conditions. When mistakenly ingested by soil organisms, MPs could harm their development, reproduction, and survival rates. The EC, a natural layer on MP surfaces, contains organic matter like carbohydrates, proteins, DNA, and compounds like humic and fulvic acids. It strongly influences the transport and behaviour of MPs, by altering their surface properties, thereby affecting their adsorption efficiency. While limited research on EC formation on MP in aquatic environments exists, our understanding of typical ECs in soils is limited. Therefore, the present study aims to evaluate the identification, formation, and variation of EC on MPs in floodplain soils, and the physico-chemical changes induced on MP surfaces under different incubation conditions. Polystyrene MPs (600-1000 microns) were incubated with soil samples in cylindrical chambers (mesh size 500 microns) for 4, 8, and 16 weeks in both field (Northern floodplains in Cologne, Germany) and laboratory settings. Laboratory-incubated samples were controlled for temperature and moisture, while the field incubations were left to natural conditions. Additional soil parameters including pH, CN content, grain size, and elemental composition were also measured. After each incubation period, MPs were extracted manually and were analyzed, employing 16S-V4 and ITS1 for metabarcoding and sequencing for attached ECs (bacteria and fungi), ATR-FTIR spectroscopy for polymer-level analysis, and the SEM imaging for visual inspection along with EDS for identifying potential heavy metal attachments on MPs. While the degree of change in the lab samples stayed low, the DNA results in the field samples demonstrated that various bacterial communities formed on MP surfaces during the incubation periods. This communal change could be attributed to the variation in the environmental condition of the incubations. Both incubation settings resulted in intricate fungal structures on MP surfaces, which were also visible during SEM imaging. Potential attachments of heavy metals like Ti, Mn, Zr, Th, and Ag were also identified on incubated MP surfaces. Our findings help uncover the influence of soil organisms on environmental MPs and clarify the formation of EC in soil ecosystems, providing insights into the ecological impacts of MPs.

Microplastics (MPs) have emerged as contaminants of global concern due to their ubiquity and potential ecological risks. Understanding MP transport, behavior, and fate in soils is crucial for assessing their interactions with soil organisms and for conducting environmental risk assessments. Most studies on MP transport are conducted in laboratory settings, often using soil column experiments. These experiments typically examine MP mobility by assessing the retention of MPs in different soil types under varying flow conditions. To ensure consistent MP application over time or volume, dispersants are frequently added to MP suspensions, particularly when targeting floating or highly hydrophobic MPs. However, dispersants may alter both the behavior of MPs and their interactions with soil particles, potentially introducing biases when attempting to understand natural MP transport—a critical aspect that remains underexplored.Therefore, this study developed an improved soil column experiment protocol that excludes dispersants while maintaining consistent MP application through a low-liquid-level, continuously stirred suspension. The Coefficient of Variation (< 5%) for this improved experimental design is found to be statistically acceptable.Based on this improved method, MP transport was investigated in soil column experiments with quartz and natural sandy soil as matrices. Rhodamine B-stained polystyrene (RhB-PS) particles (D90 < 10 µm) were intermittently pumped upward into the columns, with and without the dispersant (0.25% v/v Tween 20). Drainage samples were collected after each RhB-PS application and during intermittent flushing with artificial rainwater. Fluorescence microscopy was used to quantify RhB-PS concentrations in the drainage samples on haematocrit plates.The analysis of drainage samples revealed that dispersants significantly enhanced MP mobility, allowing more MPs to bypass soil retention. The clay and organic matter in natural sandy soil, through their fine particles and surface charges, may potentially enhance the interaction between microplastics and soil, thereby reducing their movement within the natural sandy soil, regardless of whether dispersants were used. These results suggest that existing transport studies and related models, which are based on dispersant-assisted experiments, may not accurately reflect the natural behavior of MPs in soils.

In the midlatitudes of the planet, we are facing the imminent disappearance of one of our best high-resolution (pre)historic climate and anthropogenic pollution archives, namely the loss of glacial ice, through accelerated global warming. To capture these records and interpret these vanishing archives, it is imperative that we extract ice-cores from midlatitude regions where glaciers still survive and analyse them within frameworks of inter-disciplinary research. In this paper, we focus on Georgia, part of the Greater Caucasus. Results of ice-core analyses from the region have never, to date, been integrated with its other abundant palaeo-environmental, archaeological and historical sources. We review the results of international projects on palaeo-environmental/geoarchaeological sediment archives, the archaeology of metal economies and preliminary ice-core data in Georgia. Collectively, we show that the different strands need to be integrated to fully explore relationships between climate/landscape change and human societal transformations. We then introduce an inclusive interdisciplinary framework for ongoing research on these themes, with an ultimate future goal of using data from the past to inform societal resilience strategies in the present.