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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 (pH_IEP) 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.

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.