HS1.3.5 | Small-scale transport processes of plastics in the aquatic environment: From laboratory experiments to advanced modeling
EDI
Small-scale transport processes of plastics in the aquatic environment: From laboratory experiments to advanced modeling
Convener: Uwe Schneidewind | Co-conveners: Antonia Praetorius, Daniel Valero, Mário J Franca, Kryss WaldschlägerECSECS
Orals
| Mon, 15 Apr, 14:00–15:45 (CEST), 16:15–18:00 (CEST)
 
Room 2.44
Posters on site
| Attendance Tue, 16 Apr, 16:15–18:00 (CEST) | Display Tue, 16 Apr, 14:00–18:00
 
Hall A
Posters virtual
| Attendance Tue, 16 Apr, 14:00–15:45 (CEST) | Display Tue, 16 Apr, 08:30–18:00
 
vHall A
Orals |
Mon, 14:00
Tue, 16:15
Tue, 14:00
This session is dedicated to the comprehensive investigation of small-scale transport processes governing the movement of plastics (ranging from nano- to macroplastics) within the aquatic environment. While we aim to place special emphasis on laboratory experiments and modeling approaches, we also welcome presentations employing additional methodologies such as field work, and contributions focused on theoretical concepts.

The presentations will revolve around understanding and characterizing plastic movement, considering influential factors like particle size, shape, density, and environmental conditions such as temperature, salinity, flow velocities, water turbulence and suspended sediment concentrations. Additionally, relevant biological and chemical processes will be taken into account. Key processes to be addressed include sedimentation, resuspension, biofouling, aggregation and fragmentation, along with other interactions between plastics and the environment that may influence the transport and ultimate fate of plastic pollutants.

Beyond the presentation of research findings, this session will also focus on advancements in laboratory and modelling techniques, highlighting improvements in accuracy, complexity, and spatial-temporal resolution. Cutting-edge modelling approaches tailored to simulate the intricate transport dynamics of plastics in aquatic environments will be showcased.

Through engaging discussions, the session aims to enhance our comprehension and predictive capabilities, while also identifying unresolved questions and paving the way for future research endeavors in this vital area of study.

Session assets

Orals: Mon, 15 Apr | Room 2.44

Chairpersons: Daniel Valero, Antonia Praetorius, Kryss Waldschläger
14:00–14:05
14:05–14:15
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EGU24-131
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ECS
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On-site presentation
James Lofty, Pablo Ouro, and Catherine Wilson

The settling velocity of a plastic particle is a crucial descriptor for plastic transport in rivers. When a plastic particle is introduced into the riverine environment, the plastic’ surface provides a medium that enables the attachment, accumulation and growth of microorganisms, known as biofouling. While the settling velocity has been extensively studied for pristine plastics, the influence of biofouling on settling velocity and transport dynamics of plastics needs to be fully understood. Biofouling can alter a plastic particle's size, shape, weight, and buoyancy, potentially leading to an increase in settling velocity of up to 130% compared to the same pristine plastic. However, the effect of an uneven particle weight distribution, caused by heterogeneous biofilm growth, on the plastic’s settling orientation, vertical trajectory and subsequent settling velocity has yet to be investigated.

 

This study aims to quantify the impact of biofouling on the settling orientation of a plastic particle and describe its subsequent effect on settling velocity and pattern. To achieve this, we conducted experiments using a synchronised multi-camera setup and a three-dimensional particle reconstruction to characterise particle trajectories and settling orientations. Two sets of the same negatively buoyant PTFE plastic fragments and spheres were tested, namely: i) pristine plastics, and ii) plastics subjected to biofilm colonisation in laboratory conditions. The tested plastics were fragments in sizes 1 x 10 x 10 mm and 1 x 20 x 10 mm, as well as spheres with a diameter of 5 mm. These experiments will have significant implications for the description of the settling velocity of plastics which will aid in informing future field campaigns aimed at quantifying riverine plastic transport.

How to cite: Lofty, J., Ouro, P., and Wilson, C.: A plastic tipping point: The influence of biofouling on the settling orientation of plastics., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-131, https://doi.org/10.5194/egusphere-egu24-131, 2024.

14:15–14:25
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EGU24-3779
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ECS
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On-site presentation
Marco La Capra and Sven Frei

Microplastics (MPs) are a major pollutant of the modern world, being dubbed “the lead of our generation”. Even though their potential danger to life on Earth is understood, their transport in water bodies remains an area with open questions, specifically their transport in rivers and streams. Such contaminants can be divided into three categories: spherical, irregular and fiber MPs. While research has been done on the fluvial transport of spherical MPs and their interaction with the hyporheic zone, the transport mechanisms that govern Microplastic Fibers (MPFs) are still unknown. State of the art models suggest a marked difference between the transport and settling of MPFs compared to spherical and irregular MPs, thus the need to confirm these models in a laboratory setting. The difference between the fluvial transport of spherical MPs, irregular MPs and MPFs is thereby researched here. Similarly sized fluorescent MPs and MPFs will be compared in an experimental flume, continuously logging the concentration in the water head and that in the hyporheic zone at the flume interface.

How to cite: La Capra, M. and Frei, S.: Comparing the interaction of differently shaped Microplastics with the Hyporheic zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3779, https://doi.org/10.5194/egusphere-egu24-3779, 2024.

14:25–14:35
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EGU24-6625
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ECS
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On-site presentation
Arianna Varrani, Massimo Guerrero, Magdalena Mrokowska, and Paweł M. Rowiński

Transport processes involving both microplastics (MPs) and natural sediments are being marginally studied, for the high complexity of the system and the many factors requiring attention. Still, it is of high importance to understand the interactions between natural sediments and MPs transport, especially at the water-bed interface, a critical area for rivers’ ecology and biodiversity. To bridge this gap, we carried out flume (15-m long, 1.0-m wide and with 0.27 m water depth) experiments to study the interactions of a small bedform and a deposit of compact MPs. The compact-shaped MPs, consisting of Polyamide 6 particles with equivalent sphere diameter around 2.9 mm, were released at a low flow rate (around 20 l/s corresponding to a mean velocity of 0.1 m/s), for which deposit formed at the lee side of a 2-cm high and approximately 0.7-m long sand dune. A sudden increase of flow rate was then applied (up to 60 l/s corresponding to a mean velocity of 0.3 m/s), forcing erosion of the MPs. Measurements included velocity profiles and turbulent measurements via Acoustic Doppler instrumentation, videos and underwater photos of the small bedform. From Doppler measurements the mean flow characteristics were derived, as well as fluctuating terms of the velocity components up to 50Hz. Using Structure from Motion, a 3D model of the bedform and the MPs deposit was constructed. The erosional behaviour of deposited MPs was derived by estimating the total volume mobilised from the deposit by difference (prior and post erosion) via DEM. The MPs’ removal efficiency was then estimated, in three cases of MPs’ deposit initial volumes.  

How to cite: Varrani, A., Guerrero, M., Mrokowska, M., and Rowiński, P. M.: Bedforms effect on microplastics deposits erosion , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6625, https://doi.org/10.5194/egusphere-egu24-6625, 2024.

14:35–14:45
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EGU24-10392
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ECS
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On-site presentation
Giovanni Di Lollo, Luca Gallitelli, Claudia Adduce, Maria Rita Maggi, Beatrice Trombetta, and Massimiliano Scalici

Every day, millions of tons of plastic debris are poured into rivers from industrial and civil waste or due to social carelessness and transported to the ocean. Here they decompose into small fragments, compromising the health and growth of fauna and flora that ingest or absorb them. In recent years the idea of using vegetation to trap and extract plastic waste has developed to limit this phenomenon. The aim of this work is to experimentally quantify the ability of aquatic vegetation in trap plastic and understand whether different biotic factors, hydraulic conditions or debris type influence it. Three of the most abundant macrophytes in European and Asian rivers are tested in this study, Myriophyllum spicatum, Potamogeton crispus and Phragmites australis. Natural samples of vegetation, taken along the Tiber, Ninfa-Sisto and Aniene rivers, are positioned into a recirculating flume, where the flow rate and the water depth can be varied. Once stationary flow conditions are reached, a known quantity of polystyrene fragments of different sizes (macroplastics, mesoplastics and microplastics) is added in the upstream part of the channel. The ratio between the fragments retained in the green barrier and the total added during the experiment defines the species' capacity to retain plastics. A change in seasonality, simulated by changing the water depth and the number of stolons inserted into the flume, is tested and its effects on the trapping efficiency is analysed. Three plant’s densities and two water depths are tested for each species. All three plant species show to effectively retain large and medium-sized plastic debris. Only the Myriophyllum spicatum, whose needle-like leaves form a denser network than the other two species, is also found to be efficient in retaining microplastics. The density of the area occupied by vegetation affects the number of trapped fragments, which increases for all species as the number of inserted stolons increases. The change in water depth has no significant impact on the results obtained. In conclusion, the three macrophyte species analyzed in this work can be used to create a barrier to the transport of plastics from rivers to oceans. A more complex structure of the vegetation allows the trapping of microplastics. A larger density of the area occupied by vegetation induces larger trapping efficiency, while hydraulic conditions appear to have no significant influence for the values tested in this study.

How to cite: Di Lollo, G., Gallitelli, L., Adduce, C., Maggi, M. R., Trombetta, B., and Scalici, M.: Green barriers to plastic transport in rivers: an indoor study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10392, https://doi.org/10.5194/egusphere-egu24-10392, 2024.

14:45–14:55
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EGU24-494
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On-site presentation
Zi Wang, Devendra Pal, Abolghasem Pilechi, Maïline Fok Cheung, and Parisa Ariya

Maritime micro/nanoplastic research provides valuable insights into oceanic plastic waste remediation. Yet, there is a notable disparity, with micro/nanoplastic research in freshwater being ~ 85% less extensive than that in seawater. Observational studies suggest that over 1000 rivers contribute to ~ 80% of the global riverine plastic input into the oceans. Understanding the presence of micro/nanoplastics in freshwater systems is essential for unraveling the global micro/nanoplastic cycle.

In our laboratory, a cutting-edge nano-digital inline holographic microscope (nano-DIHM) was developed for real-time and in-situ micro- and nanoplastic research, including physicochemical characteristics, coatings, and dynamic behaviours in freshwater systems. The nano-DIHM data revealed distinct intensity and optical phase patterns of various types of single particles and clusters of micro/nanoplastics (PE, PP, PS, PET, PVC, and PUR), along with other organics (oleic acid), inorganics (magnetite), and biological materials (phytoplankton). We further incorporated a deep neural network functionality to nano-DIHM for rapid micro/nanoplastic detection in real-environmental waters. With its 4D (3D + time) tracking capability, we utilized nano-DIHM to measure the sedimentation (settling and floating) velocity of plastics in two size categories in water. The experimental results were subsequently integrated into a numerical model (CaMPSim-3D) developed at the National Research Council Canada to simulate the transport of plastic particles in Canadian rivers. Complementary modelling results demonstrated distinct distribution and accumulation patterns of macro-, micro-, and nanoplastic particles in aquatic systems, establishing nano-DIHM a powerful approach for plastic life-cycle analysis.

How to cite: Wang, Z., Pal, D., Pilechi, A., Fok Cheung, M., and Ariya, P.: In-situ and real-time detection of micro/nanoplastics in water: Combining laboratory experiments and modelling studies for plastic life cycle analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-494, https://doi.org/10.5194/egusphere-egu24-494, 2024.

14:55–15:05
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EGU24-20316
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ECS
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Virtual presentation
Isabel Jalon-Rojas, Adeline Lemaire-Coqueugniot, Guillaume Gomit, Alicia Romero-Ramírez, and Sébastien Jarny

This study aims to elucidate the erodability behavior of microplastics in muddy environments like lakes, rivers, estuaries, and deltas, quantifying their critical shear stress on muddy sediment beds. Microplastics of diverse compositions, densities, shapes, and sizes were tested in a hydraulic flume with smooth and synthetic cohesive sediment beds. As flow intensity gradually increased, leading to particle mobilization, friction velocities and critical shear stresses were calculated. Initial results on smooth beds reveal that particle shape was a dominant factor in mobilization (sphere > pellet > fiber > sheet), followed by density: for equivalent shapes, denser particles required higher friction velocities for mobilization. Results from tests with different particle sizes and orientations relative to the flow highlight the influence of the exposed surface area: larger surface areas facilitate easier particle mobilization. Comparative experiments on smooth and muddy surfaces revealed higher shear stresses on cohesive sediment beds, attributed to particles sinking. Particle Image Velocimetry (P.I.V.) analysis showcased roughness-induced turbulence, marked by acceleration peaks and depressions, as the primary mechanism facilitating particle detachment from sediment.

How to cite: Jalon-Rojas, I., Lemaire-Coqueugniot, A., Gomit, G., Romero-Ramírez, A., and Jarny, S.: Experimental Study on the Erodability of Microplastics in Muddy Environments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20316, https://doi.org/10.5194/egusphere-egu24-20316, 2024.

15:05–15:15
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EGU24-10930
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On-site presentation
Resolving the dynamics of microplastic transport and burial in rivers requires the incorporation of fluvial sedimentary processes
(withdrawn)
Shai Arnon
15:15–15:25
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EGU24-20585
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ECS
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On-site presentation
Catherine Russell, Roberto Fernandez, Daniel Parsons, and Florian Pohl

Plastic is ubiquitous in the landscape and rivers are increasingly important vectors for its transport. Some riverbeds exhibit bedforms including ripples and dunes, which are well understood, but understanding of plastic in bedforms is in its infancy. In this study, flume tank experiments show that when plastic particles are introduced to sandy riverbeds, bedforms change character and behaviour. We detail i) mechanisms of plastic incorporation and transport in riverbed dunes, ii) the topographic changes that occur on the riverbed, and iii) quantify plastic-induced changes in sand transport downstream. We find that plastic directly affects bed topography and locally increases the proportion of sand suspended in the water column, even at very low concentrations in the sand. In the wider environment, such changes have the potential to impact river ecosystems and wider landscapes. Different plastic types and shapes have different impacts, therefore the classification of plastic ought to be consistent and comparable to sediment. Considering plastic as a sediment, we present a classification scheme, to enable better comparison of plastic to sediment such that we can better understand their interaction with sediment as a sedimentary particle, and therefore why plastics accumulate where they do. This is importantly not just another classification scheme, but a philosophically grounded solution to a long-standing challenge that is set to be of increasing significance in increasingly contaminated contemporary settings. We set the framework to a suite of questions that will aid understanding of plastic routing and accumulation in the rivers and the wider landscape.

How to cite: Russell, C., Fernandez, R., Parsons, D., and Pohl, F.: The impact of plastic pollution in sandy riverbeds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20585, https://doi.org/10.5194/egusphere-egu24-20585, 2024.

15:25–15:35
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EGU24-3545
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On-site presentation
Eshel Peleg, Yoni Teitelbaum, and Shai Arnon

MP of all sizes and densities have been found deposited in streambeds. Several delivery processes were proposed to explain these observations, especially their dynamics, because most information was based on discrete sampling. Only a few studies have attempted to use a wide range of particle sizes to understand how MP moves in streams and rivers. At the same time, no experiments were conducted during bed motion due to the complexity of running such experiments. This study aimed to quantify the effect of streambed motion on the deposition and accumulation of MP in streambed sediments. We used a numerical model that predicts the flow and transport of particles in a moving streambed to quantify MP deposition. The model was run for streamwater velocities of 0.1- 0.5 m s-1 and median grain sizes of 0.15, 0.3, 0.45, and 0.6 mm. Streambed morphodynamics were estimated from empirical relationships. The flow conditions and sediment types resulted in ripple formation with celerities between 0-2000 cm hr-1. MP propensity to become trapped in porous media was simulated using a filtration coefficient. Various filtration coefficients (0.1-1 [1/cm]) were used in the simulations to predict the fate of particles in the sediment. The maximum deposition efficiency and deposition depth were found for sediment with high hydraulic conductivity and slow-moving stream water velocity conditions. Also, we found that the exchange of water and particles due to sediment motion leads to burial and potentially long-term deposition of MPs that initially were not expected to enter the bed due to size exclusion. However, increasing celerity reduces the depth of MP deposition in the streambed and reduces deposition efficiency due to resuspension. The burial of MP beneath the moving fraction of the bed provides a mechanism for long-term accumulation and may explain resuspension events characterized by high MP loads during floods. The modeling results could also assist in developing strategies for streambed sampling since a horizontal layer of particle deposit is expected to form below the moving fraction of the bed.

How to cite: Peleg, E., Teitelbaum, Y., and Arnon, S.: Understanding how sediment movement affects microplastic deposition in sandy streambeds: A modeling study., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3545, https://doi.org/10.5194/egusphere-egu24-3545, 2024.

15:35–15:45
Coffee break
Chairpersons: Uwe Schneidewind, Antonia Praetorius, Daniel Valero
16:15–16:25
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EGU24-8895
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On-site presentation
Lee Haverson, Lisa Mignanelli, Uwe Schneidewind, and Stefan Krause

In the last decade mismanaged plastic waste, specifically microplastics (1-5000 µm) have gained significant scientific and public interest with research from numerous disciplines highlighting the ubiquitous nature and potential harm microplastics can exert on both human and ecosystem health. Microplastics can now be found in all of Earth’s environmental compartments. Although a large level of knowledge has been obtained highlighting the sources (wastewater treatment plants, urban areas, agricultural fields etc), sinks (oceans, lakes, rivers, ground water, etc) and transport routes (rivers, air currents, ground water etc) of microplastics in the environment, our understanding of the processes that drive flux between systems is still limited. This is especially true in systems where environmental loading and activation events are less predictable, such as those found in diffuse source dominated catchments. Previous studies have highlighted storm events as significant drivers of microplastic flux in such catchments. However, little research has been conducted examining how microplastic concentrations, loading and characteristics change over the course of a storm hydrograph and also how the hydrometeorological conditions before and during an event interact with the microplastic supply dynamics.

This study aims to address this gap. In June 2022 a single light storm event (<2.5 mm/day) was sampled after a 10-day dry period (<0.2 mm/day) within a peri urban, headwater catchment located within Birmingham, UK. In total 34 surface water samples were collected covering discharge before, during and after the captured event. For each sample 100 L of surface water was collected from the main flow path of the Bourne Brook river and filtered through a 64 µm sieve. Collected particles were treated with H2O2 (30%) and Fenton to remove organics and stained with Nile red to aid quantification and characterisation of potential microplastics using fluorescent microscopy. Furthermore, >20% of the potential microplastics identified were analysed using Raman spectroscopy for polymer classification. Additionally, in-situ loggers collected level (to infer discharge, concentration and loading) and turbidity data. During baseflow (discharge = 58 to 99 L/s) immediately before the event, microplastic concentrations ranged from 0.01 to 0.17 MP/L (n = 7). In contrast, during the event microplastic concentrations ranged from 0.13 MP/L (discharge = 91 L/s) the statistically defined start of the storm hydrograph to 1.69 MP/L (discharge = 401 L/s), with microplastic concentrations being significantly higher in the ascending limb of the storm hydrograph than the descending limb. Hysteresis analysis indicated source limitation (Clockwise hysteric loop and hysteresis index >1 (2.05)) with microplastic concentration peaking before peak discharge suggesting microplastic supply depletion. Furthermore, it was estimated that during the sampled portion of the storm event (around 8 hours) about six million microplastic particles were exported from the catchment. In contrast, microplastic export during baseflow ranged from around 28,000 to around 368,000 particles for the same time frame, indicating the significance of such events when calculating annual MP flux. This study demonstrates how microplastic concentrations and characteristics change over the course of a single storm event, providing a mechanistic understanding of how hydrometeorological conditions interact with microplastic supply dynamics.

How to cite: Haverson, L., Mignanelli, L., Schneidewind, U., and Krause, S.: High frequency sampling during a storm hydrograph offers insights into the possible transport and source activation dynamics of microplastics within a peri urban stream. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8895, https://doi.org/10.5194/egusphere-egu24-8895, 2024.

16:25–16:35
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EGU24-20181
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On-site presentation
Jan Fleckenstein, Franz Dichgans, Jan-Pascal Boos, Ben Gilfedder, and Sven Frei

Microplastic (MP) pollution in the aquatic environment has become a problem of growing concern due to potential adverse effects on aquatic organisms and ecosystems. While MP transport and fate in marine systems has been researched to quite some extent relatively little is known about the transport mechanisms of MP particles in terrestrial surface waters and in saturated porous media like in groundwater or the hyporheic zone (HZ).

We investigated the transport and fate of small (1, 3 and 10 μm diameter) polystyrene MP particles in a rippled, sandy stream bed (D50 = 1.04 mm) using CFD simulations calibrated to a set of flume experiments. A novel detection system for fluorescent MP particles (Boos et al. 2021) was used to track and quantify particle movement in the turbulent open water and in the hyporheic sediments in the laboratory flume following a pulse injection of MP particles into the surface water compartment. A new, integrated CFD simulation scheme within the OpenFOAM suite of CFD solvers was implemented for the flume system for a seamless simulation of water flow and particle transport in the open water and in the hyporheic sediments (Dichgans et al. 2023). Additionally we simulated the transport and fate of a range of “virtual” particles in the open water for different channel geometries using a Lagrangian approach.

Simulations show that 1 μm MP particles are transported through the HZ like a solute, following the typical hyporheic flow cells below the bedforms. Transport and particle progression through the HZ could be adequately described with an advection-dispersion equation. Larger 10 µm MP particles instead showed retarded transport through the HZ, while retardation increased with travel distance in the sediments. Our results indicate that advective pumping across the streambed interface can transport very small MP particles through the HZ, while larger particles are increasingly retained. Distinct flow structures in the open water are found to be decisive for the fate of MP particles in the river channel.

References:

Dichgans, F., Boos, J.P., Ahmadi, P., Frei, S., Fleckenstein, J.H. (2023), Integrated numerical modeling to quantify transport and fate of microplastics in the hyporheic zone, Water Research, 243, https://doi.org/10.1016/j.watres.2023.120349

Boos, J.-P., Gilfedder, B. S., & Frei, S. (2021), Tracking microplastics across the streambed interface: Using laserinduced-fluorescence to quantitatively analyze microplastic transport in an experimental flume. Water Resources Research, 57, e2021WR031064.
https://doi.org/10.1029/2021WR031064

Boos, J.-P., Dichgans, F., Fleckenstein, J.H., Gilfedder, B. S., Frei, S. (2024) Assessing the Behavior of Microplastics in Fluvial Systems: Infiltration and Retention Dynamics in Streambed Sediments. Water Resources Research, accepted

How to cite: Fleckenstein, J., Dichgans, F., Boos, J.-P., Gilfedder, B., and Frei, S.: Microplastic transport in rivers and their hyporheic zone – combining modeling and experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20181, https://doi.org/10.5194/egusphere-egu24-20181, 2024.

16:35–16:45
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EGU24-1720
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On-site presentation
Hassan Elagami, Sven Frei, Jan-Pascal Boos, Gabriele Trommer, and Benjamin S. Gilfedder

Microplastic residence time in lakes is governed by complex and interrelated processes. In this work, we have used a series of in-lake mesocosm experiments combined with random walk modeling to understand microplastic residence times in the lake water column. Three size ranges of green fluorescent microplastic (1-5, 28-48, and 53-63 µm) were added to a 12m deep mesocosm and detected using fluorescence detectors. Experiments were conducted over one year capturing thermal stratification in summer as well as lake turnover in autumn. The measured residence times in summer ranged between ~1 and 24 days and depended mainly on particle size. The modeled residence time for the smallest particles (>200d) was considerably longer than the measured residence times in the mesocosm (~24d). This could be due to interactions between the small microplastic particles and existing particles in the lake. In contrast, during lake turnover large Rayleigh numbers showed that instabilities in the water column likely led to turbulent convective mixing and rapid sinking within the mesocosm.

How to cite: Elagami, H., Frei, S., Boos, J.-P., Trommer, G., and Gilfedder, B. S.: Quantifying microplastic residence times in lakes using mesocosm experiments and 1D random walk model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1720, https://doi.org/10.5194/egusphere-egu24-1720, 2024.

16:45–16:55
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EGU24-12749
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ECS
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On-site presentation
Three-dimensional Lagrangian microplastic transport simulations in the Gulf of Naples (Southern Tyrrhenian Sea)
(withdrawn)
Luigi Gifuni, Paola de Ruggiero, Daniela Cianelli, Stefano Pierini, and Enrico Zambianchi
16:55–17:05
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EGU24-10484
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On-site presentation
Vlad Giurgiu, Giuseppe Carlo Alp Caridi, Marco De Paoli, and Alfredo Soldati

We perform measurements to assess the influence of the wall-normal position of micro-
plastic fibres on their spinning and tumbling rates in wall-bounded turbulence. The exper-
iments are carried out in a turbulent water channel at a Shear Reynolds number of 720.
The used fibres are curved, 1.2mm long, and 10μm in diameter (aspect ratio 120). Their
length ranges between 4 and 12 Kolmogorov length scales. In the generated flow condi-
tions they are inertial-less, neutrally buoyant, and undeformable. We observe their motion
with six high-speed cameras focused in the near-wall region and channel centre. We employ
and improve upon an established methodology involving the tomographic reconstruction of
each fibre and subsequent tracking. Leveraging their curved shape, we uniquely identify the
temporal evolution of their orientation, enabling measurements of spinning and tumbling
rates. We discuss the uncertainty on the rotation rates based on their shape and angular
displacement between time-steps. Analysis of converged statistics revealed that the mean
and mean square spinning are higher than tumbling rates at both channel centre and near-
wall region. These results are novel, considering that previous experiments are restricted to
measurements of rotation rates of longer straight fibres in homogeneous isotropic turbulence
or to tumbling rates only.

How to cite: Giurgiu, V., Caridi, G. C. A., De Paoli, M., and Soldati, A.: Measurements of spinning and tumbling rates of micro-plastic fibres, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10484, https://doi.org/10.5194/egusphere-egu24-10484, 2024.

17:05–17:15
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EGU24-12168
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ECS
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On-site presentation
Sascha Müller, Edith Hammer, Tommy Cedervall, and Nathalie Tufenkji

Nanoplastic, as primary or secondary plastics, emerges as a contaminant across all environmental compartments. In terrestrial settings, the vadose zone is considered a plastic sink. Yet, leaching into deeper saturated subsurface areas and groundwater may occur via preferential flow paths, changing hydro-chemical conditions, or direct infiltration in low lying or recharge areas. Understanding transport and deposition behavior of nanoplastics in aquifer settings is crucial as it i) is expected to deviate from that of engineered nanoparticles (ENPs) due to its more complex physical and chemical properties, and ii) to be able to develop and inform numerical models to upscale nanoplastic contaminant transport when e.g., exploring groundwater resources.  Quartz-crystal microbalance with dissipation monitoring (QCM-D) was used to investigate the deposition behavior of various model polystyrene nanoparticles onto two of the most abundant mineral species on Earth: quartz and kaolinite under various chemical settings.Three types of polystyrene of ~ 100 nm were used herein: A non-functionalized spherical polystyrene (PLAIN), a spherical carboxyl functionalized polystyrene (CARBO) and a hexagonal secondary polystyrene (GRIND) produced by mechanical grinding of larger polystyrene beads. Furthermore, divalent ion concentrations in terrestrial environments are inducing larger effects on nanoplastic processes than monovalent ions and therefore only the effect of increasing Ca2+ concentration in solution was tested. Moreover, natural organic matter (NOM) in terrestrial environments is usually degraded with depth, thus its presence in saturated groundwater can be negligible, yet to consider even low concentrations, we also tested the effect of technical grade humic acid as a model NOM.   We found that deposition behavior differs between various particles and mineral surfaces as well as with Ca2+ concentration. For quartz surfaces, non-spherical particles showed the highest deposition rates, while with the increasing mineral complexity (kaolinite), this effect diminished, and other factors gained more importance. Kaolinite surfaces showed the highest deposition rates among all particle types. This suggests the involvement of surface charge driven processes, where positive Al-OH sites of the kaolinite more effectively attract negatively charged nanoplastics as compared to negatively charged quartz. Increasing the ionic strength increased the deposition behavior until a peak deposition observed at 15 mM Ca2+ due to a gradual charge decrease of particles and minerals. Beyond 15 mM, deposition decreases as a result of reduced particle stability, and consequently lowered convective-diffusive transport to the mineral surface. Surprisingly, highly carboxylated CARBO particles showed a large increase in deposition on kaolinite irrespective of Ca2+ concentration. This may be explained by the importance of Al-OH sites, which bind -COOH groups more effectively than Si-O sites.  Adding 1mg/L humic acid at 15 mM Ca2+ reduced the deposition behavior significantly at both mineral surfaces. Our results highlight important processes between nanoplastics and mineral surfaces and thereby also important impacts in understanding nanoplastic transport in subsurface terrestrial environments. Charge driven processes dominate in simple mineral settings (quartz), while with increasing mineral complexity, chemical processes and specific ion binding interactions will dominate nanoplastic deposition and transport.

How to cite: Müller, S., Hammer, E., Cedervall, T., and Tufenkji, N.: Investigating the deposition behavior of different polystyrene nanoplastics onto mineral surfaces using QCM-D, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12168, https://doi.org/10.5194/egusphere-egu24-12168, 2024.

17:15–17:25
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EGU24-17435
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ECS
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On-site presentation
Johanna Schmidtmann, Hannah Weishäupl, Luisa Hopp, and Stefan Peiffer

Microplastic (MP) particles are ubiquitous in aquatic environments. There they interact with naturally occurring particles and colloids. Processes like aggregation affect not only MP surface properties but also removal from the water column. Additionally, MP particles are exposed to UV radiation, which alters their surface properties and thus their interactions with environmental particles. We studied heteroaggregation and subsequent sedimentation of 1 µm polystyrene (PS) (pristine and UV-weathered) with ferrihydrite, an iron (oxy)hydroxide commonly found in nature. Pristine PS particles were highly negatively charged at pH 3-11. After reaction with ferrihydrite, at neutral pH values, strong heteroaggregation with ferrihydrite caused sedimentation of almost all PS particles. At acidic pH, negatively charged PS particles were coated with positively charged ferrihydrite leading to charge reversal. UV-weathering of PS led to lower negative surface charge, and particle size decreased with increasing weathering time. These changes in surface properties and particle size resulted in differences in aggregation behavior with ferrihydrite. With increasing weathering time, the isoelectric point (pHIEP) of samples with PS and ferrihydrite shifted from slightly alkaline pH to pH 3-4. Furthermore, we observed aggregation and subsequent sedimentation of weathered PS and ferrihydrite for larger pH ranges (3-7) compared to pristine PS. We attribute this to the fact that zeta potential values of the mixture of weathered PS and ferrihydrite were rather low in this pH range. Thus, particle repulsion was low, leading to aggregation. Overall, UV-weathering but also interactions of MP with environmental particles cause changes of MP surface properties, which influence its environmental behavior in water and contribute to removal from the water column.

How to cite: Schmidtmann, J., Weishäupl, H., Hopp, L., and Peiffer, S.: UV-weathering affects heteroaggregation and subsequent sedimentation of polystyrene microplastic particles with ferrihydrite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17435, https://doi.org/10.5194/egusphere-egu24-17435, 2024.

17:25–17:35
|
EGU24-12122
|
On-site presentation
Sophie Comer-Warner, John Scott, Jim Best, Keith Carr, and Stefan Krause

Microplastics are known to be ubiquitous throughout the Earth’s ecosystems, with plastics found everywhere from terrestrial soils to deep ocean trenches. Much of the research to date has focussed on microplastics typically found in, for example, plastics bags, disposable utensils and food containers, with a large focus on marine microplastics. Recently, tyres have been identified as major sources of microplastics to the environment, due to the synthetic rubber they contain. Currently, estimates of the tyre microplastic burden in the environment suggest up to a third of marine microplastics and a third of terrestrial microplastics are tyre wear particles. Despite an increase in tyre wear research we still lack knowledge and understanding of the fate, transport and dynamics of tyre wear particles in the environment. Here, we investigate the role of green infrastructure, specifically bioswales, on the fate of tyre wear from road runoff. We present data from bioswales constructed in 2010, which were subsequently sampled in 2011, 2015 and 2023, providing a temporal record of tyre wear in the bioswales. We analysed samples from two bioswales (wet versus dry) to determine if there is an advantage of different bioswale designs to act as a sink of tyre wear particles. Samples were taken within the bioswale from upstream of the culvert inflow pipe, at various points down the bioswale and upstream of the bioswale outflow. These sampling sites were selected to provide information on potential transport through the bioswale, including whether bioswales are acting as sinks for tyre wear particles and if areas of preferential settling upstream of check dams produce increased rates of settling and trapping of tyre wear particles compared to other areas. The total mass of styrene-butadiene rubber and natural rubber in the samples was analysed using pyrolysis-gas chromatography-mass spectrometry, particle count, size and morphology were determined using optical microscopy. This study aims to determine whether bioswales can be used to effectively remediate tyre wear pollution from road runoff and the best design for this potential storage.

How to cite: Comer-Warner, S., Scott, J., Best, J., Carr, K., and Krause, S.: Bioswales as potential sinks for tyre wear particle pollution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12122, https://doi.org/10.5194/egusphere-egu24-12122, 2024.

17:35–17:45
17:45–18:00

Posters on site: Tue, 16 Apr, 16:15–18:00 | Hall A

Display time: Tue, 16 Apr 14:00–Tue, 16 Apr 18:00
Chairpersons: Uwe Schneidewind, Antonia Praetorius, Daniel Valero
A.1
|
EGU24-850
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ECS
Bishwatma Biswas and Sudha Goel

Microplastics (MPs) are ubiquitous in all kinds of water matrices. The different properties of MPs facilitate their role as carriers of emerging contaminants like pesticides, pharmaceuticals, PFAS and surfactants. Hydrophobic pesticides have a high tendency to be adsorbed on non-polar substances such as MPs. The widespread use of atrazine has caused it to be omnipresent in the environment, leading to their concurrent presence with MPs. The partitioning and fate of atrazine sorbed MPs are governed by various environmental conditions and physicochemical characteristics of different matrices. The interaction of MPs with pesticides enables MPs to serve as vectors for the transport of pesticides in aquatic media. In this work, the sorption of atrazine on polyethylene MPs was investigated in batch adsorption studies. The characterization of MPs was conducted using FTIR, SEM and XRD. By examining the characteristics of MPs and atrazine, an adsorption mechanism is proposed. The sorption of atrazine on PS was mainly governed by van der Waals forces and pore-filling mechanism. The effect of contact time on the adsorption of ATZ on PS was examined. Contact time was used to compare the results of different experiments as it is necessary to establish an equilibrium time that can be used in all the experiments. It was found that the pseudo-second order model was a better fit than pseudo first order-model based on the highest R2 values obtained. Finally, the effects of salinity and pH were also measured and found to be relatively limited. The results of this study prove that MPs can act as carriers of pesticides like atrazine in aqueous medium.

How to cite: Biswas, B. and Goel, S.: Review and analysis of atrazine adsorption on different microplastics in aqueous solution. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-850, https://doi.org/10.5194/egusphere-egu24-850, 2024.

A.2
|
EGU24-1077
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ECS
Anuja Joseph, Bishwatma Biswas, and Sudha Goel

Microplastics can act as carriers for several organic pollutants like poly aromatic hydrocarbons, pesticides, polychlorinated biphenyls, and other persistent pharmaceutical pollutants. It is important to be noted that pharmaceuticals are bio-active substances, structurally modified to induce pharmacological changes in living organisms. These pharmaceuticals pose a threat to the ecosystem and the organisms living in it when not treated effectively. Antibiotic residues may enter the aquatic environment through effluents from sewage treatment plants, application in aquaculture, and other riverine inputs. The transport of one such antibiotic, Sulfamethoxazole (SMX), with the aid of microplastics was investigated in this study.

Surgical masks are made up of polypropylene fibers and they tend to degrade faster in the air as compared to sea-water when exposed to sunlight. Surgical masks are used for medical and personal care purposes and are often disposed of irresponsibly. In this study, the sorption mechanism of SMX onto the mask fibers was observed. The optimum adsorption capacity was analyzed for the microplastics. The effects of pH, salinity, microplastic dose, and SMX concentration were observed. Kinetic models were used to identify the sorption behavior and mechanism. The sorption pattern was then fitted onto linear and Freundlich isotherms. The van Der Waal interactions were probably responsible for the interaction between SMX (hydrophilic) and microplastics (hydrophobic). The results indicate that the microplastics can adsorb up to 15 % of the SMX concentration, when in seawater. The adsorption and desorption of SMX aided by the microplastics from the surgical masks can be interpreted into a transport model for SMX. Thus, this study confirms that aged microplastics when left near the seashore, gradually enter the aquatic ecosystem and act as carriers for pharmaceuticals like SMX. The ability of microplastics to desorb a certain amount of adsorbed contaminant can lead to major health concerns, as the organisms may consume the same, causing complications to health.

How to cite: Joseph, A., Biswas, B., and Goel, S.: Microplastics from surgical masks: A piggy-back ride for sulfamethoxazole in the sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1077, https://doi.org/10.5194/egusphere-egu24-1077, 2024.

A.3
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EGU24-17995
|
ECS
How to make nano-plastics standard materials
(withdrawn)
Linhan Zhang
A.4
|
EGU24-1433
Tao Cheng and Somayeh Saliminasab

In the environment, plastics are exposed to weathering processes such as mechanical cutting and abrasion, chemical and biological degradation, as well as UV radiation and heat. These processes breakdown larger plastics into smaller pieces and alter the physical and chemical properties of plastics. Most environment micro- and nano-plastics are generated via weathering of larger plastics. Micro- and nano-plastics are often more mobile, bioavailable, and toxic than their larger counterparts due to their smaller size. As a result, contamination of micro- and nano-plastics has become an increasing concern. Although many laboratory studies have been conducted on micro- and nano-plastics to understand their behavior in the environment, most studies were conducted using synthesized, mono-dispersed, polystyrene micro-spheres as surrogate for micro- and nano-plastics in the environment. The polystyrene micro-spheres, however, do not represent well the complex and diverse composition, size, shape, and other physiochemical properties of real-world micro- and nano-plastics. The objective of our research is to fill the gap by studying the micro- and nano-plastics released from macro-plastics including polystyrene (PS), high-density and low-density polyethylene (HDPE and LDPE), polypropylene (PP), and nylon under laboratory-controlled conditions. Plastic sheets or pellets were cut into small pieces, mixed with nano-pure water, heated, and filtered through 1 um membrane to collect fine plastics. Some macro-plastics were also “weathered” using UV radiation or high temperature. Particle concentration measurement showed that substantial quantities of fine plastics (~ 5*10^9 particles/mL) were released from PP and LDPE macro-plastics, moderate quantities were released from PS macro-plastics (~5*10^8 particles/mL), and practically no fine plastics were released from nylon or HDPE. SEM results indicated the fine plastic particles were of irregular shape and poly-dispersed with a size-range of ~100 to 400 nm, while the polystyrene micro-spheres were of spherical shape with a uniform diameter of 100 nm. Zeta-potential of LDPE fine plastics in 3 mM NaCl solution at pH 5 was ~-42 mV, more negative than those of polystyrene micro-spheres (~-25 mV). This study highlights the distinct properties of manufactured polystyrene micro-spheres and fine plastics released from macro-plastics. Results from our study suggest fine plastics released from macro-plastics may better represents the properties of micro- and nano-plastics in the environment.

How to cite: Cheng, T. and Saliminasab, S.: Release and characterization of micro- and nano-plastic particles from different types of macro-plastics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1433, https://doi.org/10.5194/egusphere-egu24-1433, 2024.

A.5
|
EGU24-18284
|
ECS
Ralph Stevenson-Jones, Tor Nordam, Raymond Nepstad, Frode Leirvik, Jenny Margareta Mørk, Shraddha Mehta, and Arsalan Mostaani

The understanding of processes governing the distribution of plastics pollution on beaches is currently an underdeveloped field of study but one with huge potential impact. Current models for plastics transport in the marine environment tend to use very simplified descriptions of the plastics-shoreline interaction. However, the stranding process is clearly a very important component of a model, both due to the direct interest in plastics on beaches and because of the impact on the overall transport due to beaching and resuspension.  Hence, experimental lab data and comparisons with observed beach litter is necessary for further understanding and model development for processes governing the distribution of plastics accumulation.

Here we investigate the mechanisms controlling the accumulation of plastic pollution upon an artificial beach.  Weakly buoyant plastic “nurdles” are placed within a linear wave flume with a sloping sandy beach. The water level is changed to emulate tides, and randomly generated waves are sent towards the beach. The distribution of particulates is imaged using a downward facing camera above the beach.  Image analysis is then used to determine the varying concentration of plastics, as a function of time, over varying wave and tide conditions.

How to cite: Stevenson-Jones, R., Nordam, T., Nepstad, R., Leirvik, F., Mørk, J. M., Mehta, S., and Mostaani, A.: SWAT (Shoreline plastics in Waves and Tides), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18284, https://doi.org/10.5194/egusphere-egu24-18284, 2024.

A.6
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EGU24-6714
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ECS
Nazife Oruc Baci, Félix Santiago-Collazo, and Jenna R Jambeck

The global issue of marine litter pollution, mainly from land-based sources, has gained significant attention in recent years due to its profound environmental and socio-economic impacts. Environmental impacts pose a significant threat to marine ecosystems, harming marine life through ingestion and entanglement, disrupting habitats, and even introducing harmful chemicals into the food chain. Socio-economically, it affects coastal communities and industries by reducing tourism revenues, damaging fisheries, and increasing cleanup costs, thereby undermining livelihoods and the overall well-being of communities. Furthermore, long-term consequences include potential economic burdens related to public health issues and the need for more extensive waste management systems. This review is a comprehensive overview of the state-of-the-art numerical modeling of land-to-ocean litter transport. It underscores the significance of an integrated approach in addressing this pressing environmental challenge. The focus of this study is exploring the evolving landscape of numerical modeling techniques in the context of hydrodynamics and the significance of fieldwork in enhancing their accuracy in litter transport. Numerical modeling techniques have emerged as powerful tools for simulating complex hydrodynamic processes responsible for litter movement in aquatic environments. For example, Particle Tracing Models (PTMs) have gained prominence in recent years as an effective approach for simulating the trajectory of individual litter particles in aquatic systems by considering various environmental factors, such as currents, tides, and winds. These models enable researchers to assess various scenarios, identify key drivers of litter transport, and develop targeted strategies for litter management and remediation by aiding in predicting their dispersion patterns and arrival locations. However, their effectiveness is significantly enhanced when informed and validated by real-world field data. Fieldwork complements numerical models by providing crucial data for model validation and calibration. It also offers a unique perspective on the real-world challenges and dynamics of land-to-ocean litter transport. Moreover, fieldwork helps identify hotspots of litter accumulation, assess the composition and sources of litter, and understand the influence of local conditions on transport pathways. By combining these approaches, researchers can accurately represent litter transport processes, ultimately aiding in effective litter management and policy development.

How to cite: Oruc Baci, N., Santiago-Collazo, F., and Jambeck, J. R.: Integrating Numerical Modeling and Fieldwork for Understanding Land-to-Ocean Litter Transport: A Comprehensive Review, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6714, https://doi.org/10.5194/egusphere-egu24-6714, 2024.

A.7
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EGU24-10148
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ECS
Jenny Margareta Mørk, Tor Nordam, and Øyvind Breivik

When modelling the transport of plastics in the marine environment it is common to use a Lagrangian modelling framework. The movement of the particles is governed primarily by advective and diffusive transport, but the plastics are also subjected to a number of other physical, chemical, and biological processes that affect their fate. For transport in coastal regions, one of the more important processes is the interaction between particles and the shoreline.

Currently, there is no consensus on how to handle shoreline interactions in particle tracking models, and many resort to over-simplified descriptions such as considering a particle to be permanently beached at the position where it first hits land, or not allowing for beaching of debris at all. However, it is well-known that a lot of floating marine litter ends up on beaches, and mark-recapture studies of plastic on beaches around the world show that there can be considerable turnover in the litter on a beach. Furthermore, these studies show that both beaching and resuspension rates vary both over different beaches, and over different seasons at the same beach, indicating that these processes depend on several different factors, such as wind and wave conditions, beach morphology, and likely also the shape, size, and density of the object. Thus, in order to accurately predict the accumulation sites for floating plastic debris in coastal regions, more care should be put into modelling shoreline interactions.

Here we investigate a toy model for beaching of floating plastic debris, implemented in an idealised Lagrangian framework with analytically defined current, spatially constant wind and diffusivity, and a domain bounded on one edge by a straight, homogeneous shoreline. We implement different strategies for handling the beaching and resuspension of debris and compare the resulting distribution of particles. There is currently insufficient experimental data on the extent to which the different factors affect the beaching and resuspension processes for different kinds of plastic objects, so the purpose of this work is not to reproduce actual conditions, but rather to investigate the effect of the choice of beaching and resuspension strategies on the simulation results. We investigate e.g. a simple resuspension model where particles have an average lifetime on the beach, as well as a wave-based model where the beaching and resuspension is affected by randomly generated wave heights. 

How to cite: Mørk, J. M., Nordam, T., and Breivik, Ø.: A simple model for beaching and resuspension of plastic debris, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10148, https://doi.org/10.5194/egusphere-egu24-10148, 2024.

A.8
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EGU24-8159
|
ECS
Daniel Valero, Stefan Felder, Frank Seidel, Antonio Moreno-Rodenas, and Mário J. Franca

Plastic transport experiments have been conducted under laboratory conditions over the past five-year period. The primary objective of these experiments is to obtain physical insights into the interactions among fluids, plastics, and solids. These insights aim to facilitate the upscaling of findings to riverine or maritime environments for predictive purposes. Despite the significant progress, challenges persist, notably in tracking plastic particles, potentially employing multi-camera setups. Traditional imaging methods, such as contrast-based detection or moving-object algorithms (based on selected computer vision or background differentiation techniques), can encounter several limitations. For instance, samples with low contrast relative to the background are more susceptible to errors, and the slow movement of samples can yield weaker signals compared to fluctuating light reflections in the area of interest. Additionally, 3D tracking can introduce compounded errors across multiple cameras, leading to amplified errors.

In response to these difficulties, our research introduces a novel colour-based contrast enhancement technique, based on a multi-colour water-proof coating for plastic samples. Our protocol leads to coating added masses remaining below 1%, while facilitating the precise detection of transparent and deformable plastics. We present the current limitations in detectability, including light dependency, and discuss the potential advancements enabled by our proposed methodology.

How to cite: Valero, D., Felder, S., Seidel, F., Moreno-Rodenas, A., and Franca, M. J.: Low-intrusive colour-enhanced pattern coating of plastics for fluid-mechanics laboratory experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8159, https://doi.org/10.5194/egusphere-egu24-8159, 2024.

A.9
|
EGU24-9356
Annie Ockelford, Xuxu Wu, and Daniel Parsons

Microplastic contamination of river sediments has been found to be pervasive at the global scale however, the physical controls governing the storage, remobilization and pathways of transfer in fluvial sediments remain largely unknown. The properties that make plastics useful - strength, flexibility, durability and resistance to degradation - also make their transport through the environment difficult to predict. Specifically, the risk profile associated with microplastic transfer is dynamic because their physical and chemical properties change over time as they persist in, or move through, the environment. For example, mechanical breakdown, due to abrasion, likely decreases the size of microplastic particles, increases their surface roughness and surface area to volume ratio, and influences the diversity and abundance of the microbial taxa that colonise them. However, the processes controlling the mechanical breakdown of plastic particles rivers by abrasion is poorly understood, particularly in gravel bed rivers where there are a range of grain sizes present with the bed sediment. Here we report a series of experiments designed to explicitly quantify the influence of sediment grain size on microplastic degradation and understand how this varies by microplastic type.

Four sediment beds ((i) 0.8mm uniform sand; (ii)10mm uniform gravel; (iii) 20mm uniform gravel and (iv) bimodal sand gravel mix D50 14mm)) were seeded with either Nylon pellets (d= 1.2 g/cm3), Polycarbonate fragments (d=1.2 g/cm3) or Nylon fibres (d = 1.15g/cm3) at 0.005% concentration by mass. The sediment and plastic were placed into a cement mixer with 20L of water and tumbled for 100 hours. During each experiment, the cement mixer was periodically stopped and a sample removed to assess microplastic abrasion.

Results indicate that fibres are abraded to the greatest degree in comparison to beads and fragments.  Results also indicate a clear relationship with sediment size where microplastic fragmentation rates increase with river sediment grain size. In all plastic types surface complexity increases with time which has implications for the ability of the plastics to potentially host microbial taxa.   

How to cite: Ockelford, A., Wu, X., and Parsons, D.: Controls on microplastic breakdown due to abrasion in gravel bed rivers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9356, https://doi.org/10.5194/egusphere-egu24-9356, 2024.

A.10
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EGU24-8953
|
ECS
Jaswant Singh, Reza Dehbandi, Neeraj Chauhan, Uwe Schneidewind, Lee Haverson, Brijesh K Yadav, and Stefan Krause

Microplastics (MPs) have emerged as a growing concern, posing potential risks to both marine and terrestrial environments. While surface soils are recognised as a primary sink for these particles, the vertical mobility of MPs in the subsurface remains uncertain due to a lack of comprehensive scientific data. Here, we conducted column experiments to study the transport behaviour of MPs through and retention in subsurface sediment. Two types of pre-stained MPs (median size 50.4 µm) with densities greater than (polystyrene) and smaller than (polyethylene) water were added to the top of large (110 cm) wet-packed fine gravel columns - the most common gravel found in the subsurface zone of the riverine environment. The concentration of deposited MPs was 50,000 particles per kilogram of sediment, derived from an extensive literature survey of polluted sites. Various scenarios, including continuous rain, wet-dry cycles, and dry conditions (characterised by a single rain event followed by a subsequent drying period), were implemented to simulate diverse rain events. 20 mL of water samples were systematically collected at specified intervals from different ports of the column at depths of 30, 50 and 70 cm. Additionally, continuous effluent collection took place at the bottom port (90 cm), which was connected to a pump that maintained a controlled flux at around 4.6 mL/min. At the end of the experiment, gravel samples were methodically collected from discrete sediment layers within the columns (0–5 cm (top of the source layer), 5–10 cm (source layer), 10–30 cm, 30–50 cm, 50–70 cm, 70–90 cm) to quantify the MP mass retained in the column. Results showed that the smallest PS-MPs with a continuous flow system exhibit the highest potential for transport due to higher density and less hydrophobicity compared to PE. With increasing rain events, MPs in the source sediment layer decreased, while MPs concentrations in deeper column layers increased significantly. Furthermore, an intriguing observation indicates that as these MPs undergo more wet-dry cycles, their penetration depth substantially increases. The results indicate that sediment may not only act as a sink for MPs but also as a possible entry point to subsurface receptors such as subterranean fauna and aquifers. This research underscores the intricate dynamics of MPs in sediment and raises awareness regarding the potential environmental consequences.

 

Keywords: Microplastics, Transport, Raining events, Density, Hydrophobicity

 

How to cite: Singh, J., Dehbandi, R., Chauhan, N., Schneidewind, U., Haverson, L., Yadav, B. K., and Krause, S.: Subsurface transport of microplastics in riverine sediment: Impacts of different rain events and particle density, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8953, https://doi.org/10.5194/egusphere-egu24-8953, 2024.

A.11
|
EGU24-3025
|
ECS
|
Verena Levy Sturm, Silvia Gobrecht, and Shai Arnon

Microplastic (MP) is ubiquitously found in aquatic environments and poses a significant environmental challenge. However, what controls MP deposition and burial in river networks is unclear, especially when sediments are in motion. This study addresses this gap by examining the impact of streambed motion and particle size on microplastic deposition in sandy streambeds. Experiments were conducted in a stainless-steel flume (650 cm x 20 cm) filled with 25 cm of silica sand (D50 = 0.6 mm) and water (depth = 12 cm). A centrifugal pump circulated the water and maintained a stream water velocity of 0.53 m/s. Polypropylene (PP) fibers at lengths of 25 μm, 100 μm, 200 μm, and 2000 μm, and carboxylated Polystyrene (PS) microspheres (diameter of 0.5 μm, 1 μm, and 5 μm) were added to the stream water and their concentration in the water was measured over three days. The deposition of the MP was inferred from the decline of MP in the streamwater. A control experiment was conducted by repeating the same experiments but without sediments. The flow in the flume generated ripples, which move at a speed of approximately 4 m/h. Bed motion dominated the exchange flux of streamwater and particles with the sediments. MP concentrations declined rapidly in the first two hours after the addition due to the exchange that led to a mixing of streamwater with particle-free pore water. After the relatively fast initial decline in MP, further reduction in MP concentrations in the water occurred due to deposition. Different deposition dynamics were observed for fibers and microspheres. Buried MP particles were partly resuspended during the scouring of the ripples during their movement. It was found that  PP fibers 25 μm and 0.5 μm spheres were more mobile in the sediment than longer fibers and larger spheres, respectively. We explain their higher deposition than larger particles by a potential advective movement through the porous media, leading to their transport below the scour zone. PP fibers ≥ 100 μm were immobile within the sediment, and thus, their deposition was only due to burial by the ripple motion. Our results highlight the significant influence of moving sediments on MP and the importance of considering MP size for catchment-scale modeling to predict MP fluxes to oceans. Deposition locations are also likely to be affected by bed motions and thus should be considered when developing effective sampling strategies.

How to cite: Levy Sturm, V., Gobrecht, S., and Arnon, S.: The effects of streambed movement and particle size on microplastic deposition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3025, https://doi.org/10.5194/egusphere-egu24-3025, 2024.

A.12
|
EGU24-8538
|
ECS
Betty John Kaimathuruthy, Isabel Jalon Rojas, and Damien Sous

Studying microplastic transport in estuaries is challenging due to the dynamic interplay between river and ocean, compounded by the diverse properties exhibited by these particles. Lagrangian particle-tracking numerical modelling is a relevant tool for investigating microplastic transport dynamics, dispersion patterns, and vertical distribution. However, these models oversimplify the parametrizations of crucial estuarine processes by ignoring the effect of varying water density or vertical diffusion coefficients. In this study, we implement a hydrodynamic and improved particle tracking model in the macrotidal Gironde estuary (SW France) to explore the relative importance of different physical processes (time-space varying vertical diffusivity and water density, beaching-refloating, bottom resuspension) and provide a better understanding of microplastic dispersion and potential trapping. The simulated particle trajectories and density distributions from our findings indicate a limited influence of the spatio-temporal variability of vertical turbulence on floating particles, with a notable impact observed for settling particles, showing its significance in particle resuspension. Despite the time-space-varying water density, the effect on the transport patterns of both floating and settling microplastics is relatively lower, while the phenomenon of beaching-refloating increases the particle's residence time within the upper estuary. The higher river discharge during the spring season flushes floating particles downstream, with a portion reaching the open sea, while settling particles persist within the estuary during both seasons. Notably, denser microplastic particles tend to accumulate in the upper estuary region during summer, where the estuarine turbidity maxima have been identified.

How to cite: Kaimathuruthy, B. J., Jalon Rojas, I., and Sous, D.: Modelling the transport of microplastics in the Gironde estuary: Sensitivity to physical processes and their parameterizations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8538, https://doi.org/10.5194/egusphere-egu24-8538, 2024.

A.13
|
EGU24-18209
|
ECS
Infiltration and Transport of PVC microplastic particles in saturated quartz sand columns
(withdrawn)
Faith Tumwet

Posters virtual: Tue, 16 Apr, 14:00–15:45 | vHall A

Display time: Tue, 16 Apr 08:30–Tue, 16 Apr 18:00
Chairpersons: Kryss Waldschläger, Daniel Valero
vA.1
|
EGU24-13565
|
ECS
Somayeh Saliminasab and Tao Cheng

Microplastics (MPs) and nanoplastics (NPs) have gained considerable attention as emerging contaminants that can pose potential risks to subsurface environments due to their widespread presence and persistence in the environment. They can act as carriers for other contaminants, such as heavy metals, by adsorbing onto their surfaces, potentially increasing their mobility and consequently causing toxicity to organisms and human health. MPs and NPs can enter groundwater through landfill leachate, agricultural mulches, and wastewater effluent. However, MPs’ and NPs’ behavior in porous media with complicated components has not been thoroughly examined. Therefore, further research is essential to identify the key factors such as aggregation (particles attaching to each other) and deposition (particles attaching to a transport medium), that may influence MPs' and NPs' behavior, fate, and transport mechanisms in soils and groundwater.

The purpose of our research is to investigate how plastic particle properties, pore water chemistry, as well as characteristics of the medium would influence the aggregation and deposition of MPs and NPs.

This study focuses on the attachment of low-density polyethylene micro- and nano-plastics (LDPE) released from macro-plastic pellets and synthesized polystyrene micro-spheres to quartz sand under controlled laboratory conditions. Batch experiments were performed to study the aggregation and deposition of LDPE and synthesized polystyrene micro-spheres onto quartz sand that allow for precise control over environmental variables, facilitating the observation of microplastic-sand interactions in varying background solutions. The influence of two common salts, sodium chloride (NaCl) and calcium chloride (CaCl2), on the attachment process is systematically investigated. The results from our experiments indicated that similar to polystyrene micro-spheres, the LDPE particles did not adsorb to quartz sand at pH 5 in 3 mM NaCl solution, while a substantial amount of LDPE adsorbed to quartz sand in 1 mM CaCl2 at pH 5. This could be attributed to the less negative zeta potential of LDPE (~-25 mV) and polystyrene micro-spheres (~-17 mV) in 1mM CaCl2 background solution as a result of lower electrostatic repulsion between particles.

Results from these experiments provide insights into the complex mechanisms governing MPs' and NPs' behavior in aquatic environments, aiding in the development of strategies to mitigate their impact on ecosystems.

How to cite: Saliminasab, S. and Cheng, T.: Deposition of synthetic polystyrene and low-density polyethylene to quartz sand in different background solutions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13565, https://doi.org/10.5194/egusphere-egu24-13565, 2024.