Annotation of the results obtained in 2023
The project aims to study the pattern of contamination with microplastics particles (MPs) at the boundaries of the marine environment - in bottom sediments, on the coast, and in sea ice. The distribution of contamination is analyzed and the mechanisms responsible for its formation are considered. In 2023, the processing and analysis of bottom sediment samples (a total of 44 samples) collected during the 2022 expeditions was completed. The distribution of contamination on sections crossing areas of rapid changes in the granulometric composition of bottom sediments was analyzed. Many studies confirm that the observed spatial heterogeneity of the concentration of MPs particles in bottom sediments does not show a statistical connection with the type of sediment. This means that sediment grain size is not a determining factor in the distribution of MPs particles in bottom sediments. However, physical considerations indicate that the connection should still be present, since the grain size of the sediment affects both the characteristics of the flow in the bottom layer and the possibility of MPs particles getting stuck in the soil. A comparison of the results of the analysis of the pattern of contamination of bottom sediments by MPs particles with the conclusions of previously conducted laboratory experiments allows us to assume the formation of zones of accumulation of MPs particles in areas of sharp changes in the type of bottom sediment. The results obtained can be used to take measures to reduce marine pollution. A comprehensive analysis of (micro)plastic pollution on the sandy coasts of the south-eastern Baltic was carried out. As part of the project, various areas of the beach were studied, including the swash zone, current and storm surge lines, the berm, as well as marine debris patches formed as a result of storms. Different plastic size fractions were assessed using appropriate collection and sampling methods (frame method and its modifications, OSPAR method). As part of the analysis, a study was carried out of the MPs content (0.5-2 mm, including fibers) in the sands of the surf zone of the southern and southeastern coasts of the Baltic Sea. Data for the study were compiled from various sources, including data from the Curonian Spit, the Sambian Peninsula, the Vistula Spit, and the coasts of Poland and Germany. The results of the study showed that over more than 600 km of sandy beaches, the average contamination of surf zone sands in May was approximately 30 pieces of MPs per kilogram of dry weight of sediment on the German coast, 52 pieces per kilogram on the Curonian Spit and 60 pieces per kilogram on the Vistula Spit. Data collected on the Vistula Spit during the year showed that the level of MPs contamination changed only slightly and did not depend on wind wave conditions. This allows us to conclude that data on sand contamination in the sea surf zone can be used for long-term monitoring assessments. Sea ice is known to be heavily contaminated with MPs, with increased amounts of larger MPs particles, a deficiency of fibers, and a predominance of materials denser than the surrounding water. To find out the reasons for this pattern, a series of laboratory experiments were conducted: (1) on the formation of ice when cooling fresh and salt water with fragments and fibers of different sizes from heavy plastics, which were initially distributed along the bottom of the experimental volume and (2) on the influence of freezing/thawing cycles on the redistribution of MPs particles in the ice column. During the experiments, the vertical distribution of MPs particles and their mass, ice salinity (in experiments with salt water) and the vertical distribution of bubble concentration (in experiments with fresh water) were studied. It has been shown that the main reason for the capture of MPs particles by ice is the formation of bubbles on hydrophobic surfaces, while convection plays a secondary role in laboratory experiments. Vertical redistribution of MPs particles as a result of freezing/thawing cycles is observed in both directions, i.e. both from the bottom to the surface and in the opposite direction. Physical reasons have been found to justify the deficiency of small MPs particles, especially small fibers, observed in natural ice. Suggestions have been made about a method for assessing the hydrophobicity of the surface of real marine MPs particles, including particles covered with biofilms. Thus, the research carried out within the framework of this project reveals the features of the distribution of microplastic contamination at the boundaries of the marine environment and indicates the mechanisms influencing its formation. This provides a basis for developing practical solutions and measures to reduce microplastic contamination in the marine environment.

 

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Annotation of the results obtained in 2022
Contamination of all environments of the oceans with plastic waste has been confirmed by numerous studies to date. Microplastics (MPs, plastic particles less than 5 mm) are of particular concern due to potential threats to biological organisms and ecosystem balance. At the same time, even the basic regularities of the entry, transfer, and accumulation of MPs in various media are still very far from being understood. This project is devoted to the study of MPs contamination at the boundaries of the aquatic environment - in bottom sediments, on the coastline, in ice. This formulation of the problem is motivated by the obvious fact that there are no sources of plastic in the water column, therefore, its distribution is determined by the conditions at the boundaries and transport processes in the water column. As the results show, the highest concentrations of MPs particles are indeed observed at the boundaries of the marine environment - in bottom sediments, beach sediments, and sea ice. In 2022, the research team of the project (Laboratory for Marine Physics, IO RAS, Atlantic Branch, Kaliningrad) obtained a number of new scientific results and published 4 articles in high-ranking (Q1) international journals. The generalization of data from field studies of the distribution of MPs (0.2-5 mm) in bottom sediments of the Baltic Sea proper has been completed. MPs content varied between stations from 103 to 10,179 pcs/kg dw, with an average of 863±1371 pcs/kg dw. Fibers turned out to be the most common form of MT particles - 74.5%, films accounted for 19.8% and fragments - 5.7%. A statistically significant increase in the number of fibers with depth was confirmed. An analysis of the results of laboratory experiments on the transport/redeposition of MPs particles by a unidirectional flow along the bottom with a stepwise changing type of sediment made it possible to reveal the effect of the formation of relatively narrow zones of accumulation of plastic particles (having negative buoyancy) in zones of a sharp increase in sediment grain size. The effect was consistently observed for plastic particles of various shapes and sizes in a wide range of flow velocities, which makes it possible to expect its manifestation under natural conditions as well. To verify the results obtained, three field expeditions to the Baltic Sea and the Vistula Lagoon were planned and carried out this year, where a total of 73 samples of bottom sediment were taken in areas of a sharp change in its grain size. The study of the distribution of plastic contamination on the shoreline is continued. Based on the data of previous years of research by the team, it can already be quite confidently asserted that active sorting of not only natural material, but also plastic particles is taking place at the sea edge. Both the maximum and minimum levels of contamination are observed precisely in the area of the water's edge: the minimum - in the zone of wave run-up, the maximum - on the line of storm splash and in spots of post-storm emissions of marine debris. These results are important for organizing effective monitoring of plastic waste. Thus, the minimum concentrations in the wave run-up zone - about 30-60 MP particles 0.5-2 mm in size per kg of dry weight of sand, confirmed over 600 km of the shore of the South-Eastern Baltic, with minimal seasonal variations - can serve as a long-term indicator of plastic contamination. The release after storms of large patches of marine debris containing the highest concentrations of plastics can be used to organize effective measures to clean up the marine environment from plastic. The analysis was completed and the results of studying the distribution of MPs particles in cores of natural sea and freshwater ice – from the Novik bight (Peter the Great Bay, Sea of Japan) and Curonian Lagoon (Baltic Sea) were published. The dependence of the level of MPs (25–5000 µm) contamination on the salinity of the ice layer, which was expected for sea ice, is not reliably confirmed, but a noticeable deficit of MF in ice was found in the size range of 25–300 µm. A series of laboratory experiments was carried out to identify the mechanisms of ice capture of heavy MPs particles (sinking in water) during the formation of freshwater and saline ice. The conditions of convective mixing of thermal and haline nature during ice formation are analyzed. Correlation of the obtained distributions of MPs particles with salinity in the layer was also not found, but an obvious effect on the ascent of MPs particles was noticed from the formation of air bubbles on them. The hydrophobicity of the surface of typical plastics under natural conditions also favoures the formation of bubbles on it from gases dissolved in water, i.e. this mechanism obviously needs to be studied further. Next year, experiments will also be carried out on the effect of freeze/thaw cycles on the distribution of MPs particles, which will make it possible to assess the potential for MPs particles to be redelocated together with brine in the ice column. Thus, the work plan for 2022 has been completed, all the declared results have been obtained, and a solid foundation has been created for further steps of the research.

 

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