Microplastics in turbidity currents: transport and sedimentation

The environmental pollution from plastics is steadily increasing, reaching 390.7 million tons in 2021 (Plastics Europe, 2022). Between 2% and 5 % of MPs produced worldwide, may ultimately find their way into the ocean, where they accumulate on the deep seafloor (Phuong et al., 2021), infiltrate into hyporheic zones (Mancini et al., 2023) or may remain in suspension in the water column (Zobkov et al. 2019). MPs have been reported not only in marine and coastal areas (Jung et al., 2021) but also in Marine Protected Areas (Zachello Nunes et al., 2023). Consequently, plastic pollution is recognized one of the most serious anthropogenic generated pollutants affecting aquatic ecosystems.MPs can be transported and deposited by turbidity currents from shallow waters to the deep ocean (Pohl et al., 2020). This study contributes to further knowledge about the transport and the depositional patterns of MPs by turbidity currents related to different factors:  the MP shape, the MP density and the sediments’ characteristics. To mimic turbidity currents transporting MPs, lock-exchange flume experiments were performed with sediment contaminated with three types of microplastics: PET fibers, PVC fragments, and melamine fragments. These MPs were selected to represent a range of densities and shapes. The study revealed distinct sedimentation patterns: higher sediment concentrations enhance MP transport, and turbidity currents with finer sediments transported MPs over greater distances, highlighting the important role of sediment in transporting MPs in the propagation of turbidity currents. Further, MP sedimentation patterns varied with MP-particle shape, size, and density, highlighting the crucial role of MP particle properties in determining MP distribution in turbidites. These findings enhance our understanding of the mechanisms controlling the spatial distribution of MPs in marine sedimentary-environments and underscores the importance of considering both hydrodynamic and particle-specific factors when addressing the complex behaviour of MPs.ReferencesPlastics Europe, 2022. Plastics- the Facts 2022. An analysis of European plastics production, demand and waste data.Phuong, N.N., Fauvelle, V., Grenz, C., Ourgaud, M., Schmidt, N., Strady, E., Sempéré, R., 2021. Highlights from a review of microplastics in marine sediments, STOTEN, 777.Mancini M., Francalanci S., Innocenti L., Solari L., 2023a. Investigations on microplastic infiltration within natural riverbed sediments. STOTEN, 904, 167256.Jung, J.W., Park, J.W., Eo, S., Choi, J., Song, Y.K., Choi, Y., Hong, S.H. and Shim, W.J. 2021. Ecological risk assessment of microplastics in coastal, shelf and deep sea waters with a consideration of environmentally relevant size and shape. Environmental Pollution. 270, 116217.Pohl, F., Eggenhuisen, J. T., Kane, I. A., Clare, M. A., 2020. Transport and Burial of Microplastics in Deep-Marine Sediments by Turbidity Currents. Environmental Science & Technology, 54(7), 4180–4189.Zachello Nunes, B., de Oliveira Soares, M., Zanardi-Lamardo, E., Braga Castro, I. 2023. Marine Protected Areas Affected by the most extensiveOil Spill on the Southwestern Atlantic coast. Ocean and Coastal Research, 71(2), e23028,Zobkov, M.B. , Esiukova, E.E. , Zyubin, A.Y. , Samusev, I.G., 2019. Microplastic content variation in water column: The observations employing a novel sampling tool in stratified Baltic Sea, Marine Pollution Bulletin, 138, 193-205.