Seafloor sediment is an important sink for microplastics, and vertical profile of microplastic accumulation in a sediment core can provide historical pollution trend. However, microplastic pollution in coastal sediment has not been addressed well, and a few studies have investigated the trends of microplastic pollution in age-dated core sediments. In this study, the microplastics in surface sediments in urban, aquafarm and reference areas of South Korea were analyzed to evaluate the pollution characteristics of microplastic according to different sea area use patterns. In addition, the historical trend of microplastic pollution was investigated in core sediments in the urban and aquafarm areas. The abundance of microplastics in surface sediment were in order of urban area (6,887 ± 6,100 particles/kg d.w.), aquafarm area (5,121 ± 2,428 particles/kg d.w.), and reference area (2,474 ± 522 particles/kg d.w.). Polymer types were diverse in the urban area, and expanded polystyrene used for buoys was dominant in the aquafarm area. Fragment type microplastic was dominant in all three areas, and the proportion of fiber was higher in urban and aquafarm areas than in reference area. The polymer composition of fiber was different in urban (polyester 51% and polypropylene (PP) 29%) and aquafarm areas (PP 84% and polyamide 13%). These results support that the characteristics of microplastic pollution well reflect the sea area use patterns. Historical trend of microplastic pollution has increased since the 1980s and the increasing rate steeply increased around the early and mid-2000s in both the core samples. Their increasing trend reflected the influence of population or surrounding input sources (i.e. effluent discharge amount of a wastewater treatment plant). The clear increasing trend of historical microplastic pollution up to now indicates that more efforts is highly required to reduce the microplastic pollution. 

How to cite: Eo, S., Hong, S. H., Song, Y. K., Cho, Y., Han, G. M., and Shim, W. J.: Spatial distribution and historical trend of microplastic pollution in sediments from enclosed bays of South Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4586, https://doi.org/10.5194/egusphere-egu23-4586, 2023.

Increasing volumes of mismanaged plastic waste have resulted in millions of tons of plastics entering the environment. While recent research has made substantial progress in determining the fate and transport of microplastics (MP) in river systems and their subsequent discharge to the worlds oceans, much less is known about the subsurface fate of MP as they enter soils, (riverine) sediments and global groundwater resources. Initial studies have identified MP in selected groundwater samples and there is great interest to understand entry pathyways of MPs into soils, in particular through agricultural pathways. The mechanisms of MP release from agricultural sources such as seed and agrochemical encapsulations or sewage sludges as well as the total quantity, spatial distribution, residence time scales as well as the impact of MP on soils and subsequently groundwater ecosystems are completely unknown. There is hence a critical need to study the role of soils and groundwater systems as a long-term sink for plastic pollution, including the development of legacy risks.

Here we identify the significance of various entry pathways for MP into subsurface ecosystems, integrating experimental and model based quantifications of MP transport through streambed sediments with quantifications of MP inputs into agricultural soils through irrigation with river water. We present first results of MP impacts on the functioning of subsurface ecosystem services, by the particular example of MP exposure impacts on the behaviour of bioturbating invertebrates and the subsequent consequences for sediment biogeochemical cycling in order to draw attention to the potential risks for vital soil and groundwater ecosystem services.

We complement this site specific mechanistic process understanding with global estimates of mismanaged plastic waste accumulation in river basins to quantify MP catchment wide loads available for leakage into soils and present first results of our recently started participatory approach that aims to develop a baseline of MP pollution in aquifers across the world. Such baseline data is imperative to increase our understanding of MP fate and transport processes, MP uptake by groundwater organisms and the interaction of MP with nutrients and potential co-contaminants. Our specifically tailored protocol allows for standardized MP sampling in boreholes, springs or wells across a wide range of geological settings and land cover classes. We invite and encourage the community to contribute to this global effort in order to enable estimates of the magnitude and expected time scales of soil and groundwater MP contamination.

How to cite: Krause, S., Schneidewind, U., Wazne, M., Kukkola, A., Lynch, I., Haverson, L., Kelleher, L., Davies, G., Dendievel, A.-M., Mourier, B., Mermillod-Blondin, F., Quiñones-Rivera, Z., Simon, L., Reiss, J., Perkins, D., Robertson, A., and Gomez-Velez, J.: The Plastic Underground: Are Microplastics in the Subsurface a Ticking Time Bomb for Soil and Groundwater Ecosystems?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4405, https://doi.org/10.5194/egusphere-egu23-4405, 2023.

Soil is considered the largest sink of microplastics (MP) in terrestrial ecosystems. Among the expected effects of MP as hydrophobic surface addition is the likelihood that MP enhances soil water repellency. So, crucial for MP fate in soils is the interaction between MP and water. If MP is translocated by water flow and, vice versa, MP impacts water flow, to what extent? Water flow on the pore scale will be impacted with feedbacks on transport and retention of MP. However, we don’t know the extent of and conditions under which MP are transported through porous media and, if deposited, how they interplay with soil water dynamics. We hypothesize that: (i) isolated MP are displaced and translocated by air-water interfaces and (ii) local accumulation of MP is facilitated by bypassing water flow. To approach this question, neutron and x-ray imaging of MP and water in soils was utilized.

Dual neutron and x-ray imaging at the beamlines ICON (Paul-Scherrer-Institute) during repeated wetting-drying cycles was applied to trace MP-water interactions in aluminum cylinders filled with sand (0.7-1.2 mm) and MP (PET, 20-75 µm) in gravimetric contents of 0.35, 1.05 and 2.10%. The contents refer to static contact angle estimations of the mixtures resembling < 90°, 90° and > 90°. First, simultaneous neutron and x-ray tomography captured the initial dry MP configuration in samples. Subsequently, neutron radiographies of deuterated water flow through the sample of 1 ml min^-1 were recorded for 200s. After drying, repeated tomography gave insights into MP translocation.

Neutron and x-ray imaging results showed that regions of major MP content are water repellent. Water flow bypasses and MP is mainly retained. Resultant air entrapments lead to reduced water contents. In regions of minor MP content water can infiltrate. Here, the air-water interface collects isolated MP and shifts their distribution towards an enhanced accumulation.

Extrapolation of these results to natural soil systems suggests that vertical transport of MP can be limited especially at hotspots of high MP contents. Water bypasses here. This might limit the water dependent degradation processes of MP due to reductions in hydrolysis, coating and colonization by microorganisms even elongating the process of natural attenuation.

How to cite: Cramer, A., Benard, P., Anders, K., Zarebanadkouki, M., and Carminati, A.: Microplastic Interaction with Soil Water - Visualization and Quantification with Neutron and X-ray Imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1477, https://doi.org/10.5194/egusphere-egu23-1477, 2023.

Plastic has greatly changed modern society, and it has become an indispensable material in our daily lives. Microplastics are now regarded as the serious environmental threats due to the management limitations. Saltmarshes are one of the most productive ecosystems on earth and a high-efficiency blue carbon sink. As an emerging contaminant, the load, transport and fate of microplastics are largely neglected in saltmarshes. Here, we firstly measured the mass concentration of microplastics in the sediment cores of a multi-species saltmarsh by pressurized liquid extraction and modified double-shot pyrolysis gas chromatography-mass spectrometry. The major microplastics in saltmarsh sediments were polyethylene (PE), polyvinyl chloride (PVC), and polypropylene (PP). The microplastic mass concentration in the sediment of Scirpus mariqueter was greater than Phragmites australis and mudflat. As artificial carbon, carbon content of microplastics accounts for 1.15% of total organic carbon. Overall, the results suggest that saltmarsh vegetation can efficiently drive the microplastic settling and retention. Therefore, the microplastic distribution characteristics in saltmarsh can be effected by the vegetation types and their distribution pattern.

How to cite: Zhang, Y., Wang, Y., Chen, X., Zhu, P., Jing, S., and Li, L.: Microplastic distribution characteristics and storage in a multi-species saltmarsh, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5676, https://doi.org/10.5194/egusphere-egu23-5676, 2023.

Glacimarine sediment results from glaciers weathering the rock exporting silt and clay into the ocean. Such fine sediments are also exported from the Greenlandic Ice Sheet where new sources of plastic pollution like seasonal ice thawing may be releasing microplastics (MP) back to the environment. MP could be then transported to the seafloor via sediment burial and incorporated into the layers of the geological record. However, the purification and extraction of MP from such a fine-grain matrix is challenging, as the small grains remain in suspension and can form aggregates. In order to look for a footprint of the Anthropocene in Greenland, a sediment core was analyzed to generate a record of MP by comparing a pre- and post-plastic boom period. Using ²¹⁰Pb and ¹³⁷Cs dating, the chronology was established from 1861 to 2015 ±5 yrs bridging the plastic boom of the 1950s. Using a 4-step methodology developed for fine-grain matrices, MP particles were characterized via FT-IR imaging. QC/QA protocols were applied throughout the process to reduce the risk of contamination. More than 1000 particles were found in total ranging from 20 µm to 600 µm and going as far back as 1930. Nine polymer types were found, the most common being PE and PP accounting for 84% of all particles. This is the first sediment record of MP pollution in the Arctic, which shows that once thought pristine regions have in fact being polluted for a long time, which in turn implies that the impact might be greater than previously thought. In addition, this long-term accumulation in Greenlandic marine sediment could be compared to global horizons in the search for markers of the Anthropocene.

How to cite: Parga Martinez, K. B., Andersen, T. J., da Silva, V., Strand, J., and Posth, N. R.: Greenland in the Anthropocene: an archive of microplastic pollution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10534, https://doi.org/10.5194/egusphere-egu23-10534, 2023.

Biodiverse coastal ecosystems are vulnerable to microplastic (<5 mm) pollution due to inputs from riverine and shoreline sources which pose ecological threats and have repercussions for social ecosystem services. These ecosystems may contain an aquatic canopy covering the bed, such as seagrass meadows or coral reefs that can trap particles. Despite field measurements revealing the accumulation of plastic debris in a variety of aquatic canopies, the transport and dispositional processes that drive microplastic trapping within such canopies is barely understood. Here, we investigate for the first time the prevalence of biofilmed microplastic retention by sparse and dense branching coral canopies in a hydraulic flume under unidirectional flow. Corals were replicated through 3D-printing using a scan of a staghorn coral Acropora genus, a branching coral that encompasses one-fifth of extant reef-building corals, globally.

Trapping mechanisms by coral canopies were identified, and include: a) interception of particles with the coral acting as a barrier and microplastics and settling to the bed; b) settling of microplastics on the branches or within the structure of the coral and c) accumulation in the downstream region of individual corals. Trapping efficiency was found to depend on bulk velocity and canopy density, with up to 99% of microplastics retained across the duration of the experiments. Surprisingly, sparse reefs may be as vulnerable to microplastic trapping and contamination as denser canopies under certain flow velocities, with the latter found to retain only up to 18% more microplastics than in sparser conditions. Flow velocity profiles provide insights into the relationships between canopy hydrodynamics and microplastic trapping and distribution. The results indicate coral reefs may form areas of accumulation for microplastic pollution through their observed high trapping efficiency that may otherwise have been transported greater distances.

How to cite: Houseago, R., Mendrik, F., Hackney, C., and Parsons, D.: Transport and trapping of microplastics in coral reefs: a physical experimental investigation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14119, https://doi.org/10.5194/egusphere-egu23-14119, 2023.

Plastic mobilization, transport, and retention dynamics are influenced by hydrological processes and river catchment features (e.g. land-use, vegetation, and river morphology). Increased river discharge has been associated with higher plastic transport rates, although the exact relation between the two can vary over time and space. The precise role of an extreme discharge event on plastic transport is however still unknown. Here, we show that fluvial floods drive floating macroplastic transport and accumulation in river systems. We collected observational evidence during the (return period of 200 years) along the Dutch part of the Meuse. Upstream plastic transport multiplied by a factor of over 100 compared to non-flood conditions (3.3x10⁵ vs 2.3x10²), making the Meuse . Over one-third of the annual plastic transport was estimated to occur within the six-day period of extreme discharge (>3,200 m³/s). Towards the river mouth, plastic transport during the flood decreased by 90%, suggesting that the Plastic transport and accumulation on the riverbanks decreased significantly along the river, corroborating the river's function as a plastic reservoir, rather than conduit for plastic towards the ocean. We demonstrate the crucial role of floods as drivers of plastic transport and accumulation in river systems. Floods amplify the mobilization of plastics, but the effects are local and the river-scale dispersion is limited. We anticipate that our findings serve as a starting point for improving global estimates of river plastic transport, retention, and export into the sea. Moreover, our results provide essential insights for future large-scale and long-term quantitative assessments of river plastic pollution. Reliable observations and a fundamental understanding of plastic transport are key to designing effective prevention and reduction strategies.

Link to preprint

Tim van Emmerik, Roy Frings, Louise Schreyers et al. River plastic during floods: Amplified mobilization, limited river-scale dispersion, 08 August 2022, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-1909246/v1]

How to cite: van Emmerik, T., Frings, R., Schreyers, L., Hauk, R., de Lange, S., and Mellink, Y.: River plastic during floods: Amplified mobilization, limited river-scale dispersion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9164, https://doi.org/10.5194/egusphere-egu23-9164, 2023.

Following the discovery of microplastics (MPs) in river sediments, the number of MP studies on rivers and other freshwater systems has increased rapidly, revealing that MPs are omnipresent in all freshwater environments. The abundance of MPs in freshwater sediments seems to be affected by population density, urban centers, water flow velocity, water catchment size and position and type of sewage and waste management. However, not all of these relations are consistent. For example, while many studies report good correlations between MP source regions (highly populated and industrialized areas) and MP abundance in river sediments, others do not. This is in contrast to the concentrations in the water itself, for which better links with MP source areas were found. What all these studies have in common, is their large-scale approach, in which sediment samples are obtained over distances of tens to thousands of kilometers along the river; and at each site sediments are than retrieved either from the deepest part of the channel or from the river bank (depending on the study). Here, we study MP distribution in a section of the meandering Leie River, in a rural area, a few kilometers upstream of the city of Ghent (Belgium). Multibeam bathymetry and side-scan sonar images allowed selecting three undisturbed across-channel transects where surface sediments were retrieved. Sediment samples were analyzed for MP content, organic-matter content and grain size of the clastic fraction. Overall the MP concentrations are much (up to an order of magnitude) lower in the thalweg compared to samples near the river banks, resulting in an asymmetric distribution at the bend apex, where the thalweg approaches the outer banks. Furthermore, MP concentrations show strong correlations with the organic matter content and grain-size parameters as expected form hydrodynamic sorting. Exceptions to these correlations are the outer bank samples, where MP concentrations are lower than predicted from sedimentological characteristics. We attribute this to the more erosive character of the current in the thalweg near the outer banks, which inhibits MP deposition, but exposes fine-grained and organic-rich flood plain sediments. We highlight that the different hydrodynamic conditions across a river channel greatly influence MP distribution (with an order of magnitude), but in a sedimentologically predictable manner. Care should thus be taken in environmental studies, as local variability in MP concentration across a river bed may be larger then the large-scale variability.

How to cite: Van Daele, M., Van Bastelaere, B., Vercauteren, M., Meyer, I., and Asselman, J.: Depositional patterns of microplastics in a meandering river: a case study of the Leie River, Belgium, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16232, https://doi.org/10.5194/egusphere-egu23-16232, 2023.