Plastic debris in coastal environments usually undergoes weathering due to various environmental conditions. However, the weathering effects on exposed and shaded sides of the same plastics are underexplored. In this study, 1573 plastic fragments were collected from 15 coastal sites worldwide between December 2021 and December 2022, and weathering experiments were conducted outdoors. The field investigation showed significant two-sided weathering differences of plastic fragments. The weathering morphology included biota, cracks, delamination, discoloration, etc. The weathering degree was assessed with three metrics, i.e., line density (0-58 mm/mm(2)), surface loss (0-92 %), and texture index (0-2). The 3D magnitudes of these three metrics revealed the two-sided weathering differences of plastic fragments. Specifically, 43 % of the samples had magnitudes > 5, indicating significant differences. Outdoor simulations suggested that sun-exposed sides developed more cracks, pores, and bubbles, while shaded sides remained smoother. After 12 months, the line density increased from 2.85 to 9.23 mm/mm(2) for polyethylene (PE) and 4.16-8.47 mm/mm(2) for polypropylene (PP) (p < 0.05). The carbonyl index increased from 0.50 to 1.70 (PE), from 0.18 to 1.10 (PP), and from 0.45 to 1.57 (polyvinyl chloride). This increase indicated oxidative degradation on sun-exposed sides. Our results highlighted the uneven degree of weathering on both sides of the same plastic fragment due to different environmental factors. The study provided critical insights for creating more accurate models to predict plastic degradation, which will help inform global strategies to reduce plastic pollution.

Estuaries are effective natural filters retaining a significant part of the sediments and contaminants transported by rivers towards the ocean. For these complex and dynamic environments, field studies are the key to reveal the most effective retention mechanisms. This review examines published field observations of microplastics (MPs) contamination in river/estuary/sea transitional areas worldwide from the perspective of the classical Marginal Filter concept. This general concept includes three mechanisms - gravitational sedimentation, sorption, and bio-assimilation, each including a number of contaminant-specific processes. The reviewed field studies on MPs confirm, though still incompletely and sometimes inconsistently, the importance of hydrodynamics, hetero-aggregation with environmental particles, and multifaceted interactions with biota. To obtain wider experimental basis, relevant in-situ, ex-situ, and laboratory studies were reviewed on coagulation of MPs with mineral particles under changing pH and salinity, entrapment in flocs of organic material, adhesion of smaller MPs to the surface of sand grains, co-precipitation with suspended matter. Estuarine MPs transport is suggested to be size and shape selective: millimeter-sized MPs and fibers appear to be more easily exported to the ocean. Time/scale analysis of MPs-related retention/deposition processes suggests that areas of weak hydrodynamics favor the formation of accumulation zones of MPs in all estuaries, while hetero-aggregation and interactions with biota require longer time/space scales and are sensitive to seasonal and event-specific variations of environmental conditions. Water currents, turbulence, salinity, pH, organic matter content, and biomass are the key environmental factors that are highly recommended for simultaneous measurements in future studies of MP distribution in estuaries.

Most of the plastic mass in the ocean is concentrated in coastal zones: large and small plastic items slowly circulate there for a long time, experiencing repeated episodes of beaching/recapture, fouling/defouling, sinking/resurfacing, aggregation, UV degradation, mechanical fragmentation, etc. In this chapter, physical and dynamical properties of marine microplastic particles (MPs, <5 mm) are summarized, with relevance to their behavior in the coastal zone. The density range, size classes, and typical particle shapes are presented, and their variation with time is considered. Results of laboratory experiments mimicking mechanical fragmentation of typical plastics in the swash zone are discussed and applied to oceanographically relevant cases. Relations between the mass and the number of generated MPs are experimentally obtained for four plastics typically found in marine environment. Dynamical behavior of MPs is discussed based on knowledge from classical hydrodynamics, marine sedimentology, and physical oceanography. Shape-dependent manner of the particle sinking and the value of the terminal settling velocity are considered, including the influence of vertical convection. Critical velocity of resuspension by a unidirectional flow is addressed, as well as motion of particles in an oscillatory flow under surface waves and in roll structures. Natural sorting of MPs at the shore face is highlighted, which suggests seaward export of smaller MPs, onshore transport of larger particles, and possible arresting of finer MPs below coarser sediment grains. The events of massive wash-outs of seaweed and plastics onto the beaches after severe storms are examined, and the potential of the machine learning methods in prediction of such events is highlighted. Importance of high surface waves, clastic shores, rocky headlands suggests that high-latitude coasts are effective generators of secondary MPs in the World Ocean.

Micro- (0.5-5mm) and meso-size (0.5-2.5cm) floating marine litter was collected in June 2022 in the southeastern part of the Baltic Sea using a manta trawl (mesh size 335µm). Plastic items, excluding fibers and paint flakes, accounted for approximately 90.1% of the total number of collected particles in fifteen surface water samples. The contamination level ranged from (0.33-23.90)×105 items/km2 (or 0.22-15.93 items/m3, or 5-1,779g/km2, or 0.03-11.86mg/m3). Foamed PS particles accounted for 49.2% of the total number of collected particles. The mass of paraffin in each sample was high, ranging from 1.4-3,750g/km2 (9.1×10-3-25.0mg/m3), which was comparable to or greater than the mass of plastic. This study suggests that plastic particles are retained at the water surface by paraffin stains left after washing tanks on transport ships. This finding highlights an unexpected aspect of the contribution of shipping to plastic pollution in the region.

The accumulation of marine litter on beaches has a detrimental impact on the environment, human health, and recreational activities. A total of 116 monitoring surveys were conducted along the shore of the Kaliningrad region between 2019 and 2023. Sampling of anthropogenic and plastic litter (>0.5 cm) was carried out under various meteorological conditions on eight sandy beaches. The greatest abundance and mass of plastic marine litter (mean ± SE: 13.75 ± 8.61 items/m2 and 19.97 ± 5.92 gDW/m2, correspondingly) were observed in the aftermath of storms within beach-cast accumulation stains at the shoreline, where it was intermixed with organic debris. This is two orders of magnitude greater than the plastic litter contamination obtained using the OSPAR methodology at the same beach during fine weather (0.11 ± 0.01 items/m2, 0.33 ± 0.02 gDW/m2). The results suggest that the most effective strategy for beach cleaning is to implement it in the post-storm period.

The distribution of plastic pollution in the marine environment is highly variable in time and space, making it difficult to assess pollution levels. This study shows that mixing and natural sorting of material in the wave runup zone of a sandy beach results in a relatively stable abundance of microplastics in the size range 0.5-2 mm (SMPs). Based on 175 samples collected over 14 months during 42 monitoring surveys at 6 stations along the shore of the Vistula Spit (Baltic Sea), the mean abundance of S-MPs was found to be 64 +/- 36 items/kg DW (98.6 % fibers), with a coefficient of variation of only 56 % over more than one year. Statistical tests confirmed its independence from current wind speed, significant wave height, mean sediment grain size, sediment sorting, percentage of certain sand fractions, month, season, or location along the shore. It can therefore be used as a suitable indicator for long-term monitoring of increasing plastic pollution in the marine environment.

Plastic and oil pollution are closely linked to our dependence on petroleum derivatives. Their excessive use and inefficiencies in their management, have led to negative impacts on marine ecosystems since their very introduction. Agglomerates of tar, plastic, paraffins, and other petrochemicals and oil derivatives with naturally occurring materials, are increasingly widespread in coastal environments, stalling as an iconic and readable sign of environmental degradation. Starting from a historical review of the available reports on the occurrence of similar aggregates dating back to 1971, we highlight how most of these observations are based on the morphological description of the petroleum residues with no chemical fingerprinting and are mainly related to materials stranded on the coastline, with few and unclear indications for the open sea. We discuss here a list of scientific questions and knowledge gaps, that need to be examined by future studies.

The most massive design on the Baltic shore used geosynthetic materials, the landslide protection construction in Svetlogorsk (1300 m long, 90,000 m2 area, South-Eastern Baltic, Kaliningrad Oblast, Russian Federation) comprises the geotextile and the erosion control geomat coating the open-air cliff slopes. Due to changes in elastic properties during long-term use in the open air, as well as due to its huge size, this structure can become a non-negligible source of microplastic pollution in the Baltic Sea. Weather conditions affected the functioning of the structure, so it was assessed that geosynthetic materials used in this outdoor (open-air) operation in coastal protection structures degraded over time. Samples taken at points with different ambient conditions (groundwater outlet; arid places; exposure to the direct sun; grass cover; under landslide) were tested on crystallinity and strain at break. Tests showed a 39–85% loss of elasticity of the polymer filaments after 3 years of use under natural conditions. Specimens exposed to sunlight are less elastic and more prone to fail, but not as much as samples taken from shaded areas in the grass and under the landslide, which were the most brittle.

The shores of the Kaliningrad Region (the Russian part of the South-Eastern Baltic Sea) are regularly exposed to extreme storms, which leads to intensive abrasion and flooding of the land. Based on archival data, meteorological monitoring, forecast and synoptic maps, an analysis of extreme storms observed in the autumn-winter periods of the early 21st century was done. The cyclone type was determined using the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model), which makes it possible to reconstruct the trajectory of the approach of the atmospheric vortex to the coast. The seasons with clusters of storms were identified, when deep cyclones affected the coasts of the Kaliningrad Region in a relatively short time. Regardless of the type of trajectory, storms cause destruction of both natural and infrastructure objects. But the shores of the northern exposure are most susceptible to destruction by “diving” cyclones, the wave regime of which has a high potential energy. Earlier it was noted that the frequency of cyclones with northerly winds increases. Clusters of northern cyclones are especially dangerous, as was in January 2022, when 4 atmospheric eddies affected the coast with an interval of several hours to 2–3 days. When the water level was high, the waves crashed on the coast, causing catastrophic damage. The coastal monitoring revealed numerous destruction of the banks, breakthroughs of the foredune, both flooding and collapse of forests, critical damage to coast protection and engineering structures, and infrastructure facilities. Dozens of hectares of coastal territories have been lost. There are environmental problems associated with numerous emissions into the marine environment of a huge amount of anthropogenic mega-, macro-, meso-, micro-garbage with a predominance of plastic after extreme storms.

The beach-cast material attracts more attention nowadays since it contains both organic wrack, considered as a natural resource, and plastic waste which is potentially dangerous for biota. The material resides on the beach for a short time, making the prediction of the beach-cast event important. With the idea to disclose hydrodynamics behind the appearance of these hazardous patches on the seashore, the likelihood methods were applied to the freely available surface-waves reanalysis data and the observations of beach-cast appearance on the northern shore of the Sambian peninsula (south-eastern part of the Baltic Sea) in 2011-2021. Significant wave height, peak wave period, and mean wave direction at the open-sea limit of the coastal zone were analyzed with the differentiation between the "freshly discovered" and "ordinary" beach-casts. The results were refined using different time-frames of sampling of surface-wave parameters and indicated the 3-day period as most suitable for the present analysis. The most important parameters for beach-cast appearance are large wave heights (>4 m) and long periods (>6 s) in the preceding period. Waves from the northern sector are especially favorable: they have the largest possible fetch for the region, and the studied shore is directly exposed to them. This suggests that a fully developed wave field after a storm with a long wave fetch is an essential condition for the appearance of a beach-cast. Wave periods and heights are interchangeable when analyzing the sea state before the beach-cast appearance. The results are in agreement with both present-day and long-term historical observations.

Sea ice is heavily contaminated with microplastics (MPs), with the repeatedly confirmed increased number of larger-sized particles, deficit of fibers, and prevalence of materials denser than the surrounding water. To get insight into the drivers behind such a specific pattern, sets of laboratory experiments were performed on the formation of ice by cooling from the surface of fresh and salty (NaCl, 34 g/L) water, with particles of different sizes from heavy plastics (HPP) distributed initially over the bottom of the experimental volume. After freezing, about 50-60 % of HPP were trapped in ice in all the runs. Vertical distribution of HPP, plastic mass distribution, ice salinity (in saltwater experi-ments), and bubble concentration (in freshwater experiments) were recorded. Formation of bubbles on hydrophobic surfaces was the main cause of the entrapment of HPP into ice, with convection playing a secondary role. Supplemen-tary bubble formation experiments with the same particles in water demonstrated that at larger fragments and fibers, several bubbles grow at the same time, so particle rising and residing at the surface is stable. Smaller HPP experience rising/sinking cycles with minimum time spent at the surface: one bubble is enough to cause a particle rising, but it is most often lost when colliding with the water surface. Application of the results to oceanic conditions is discussed. Oversaturation with gases due to various physical/biological/chemical processes and liberation of bubbles from meth-ane seeps and melting permafrost are common in Arctic waters. Convective water motions are able to relocate HPP in vertical. Based on applied research, the bubble nucleation and growth, the hydrophobicity of weathered surfaces, the effectiveness of flotation methods for plastic particles are discussed. Interaction of plastic particles with bubbles is an important feature, still completely overlooked in the context of MPs behavior in marine environment.

The database gives information on the contamination of the shore of the South-Eastern Baltic with the debris of geosynthetic materials for the period 2018–2020. This new type of coastal pollution enters the natural environment due to the destruction of coastal protection structures and construction activities. The database contains sections: (1) a list of types of geosynthetic material residues, their photographic images and photographs illustrating examples of finds in natural conditions [1 List_geosynthetic_debris_SEB], (2) monitoring data on the contamination of the beach strip with the debris of geotextiles, braids from gabions, geocontainers (big bags), geocells and geogrids for the beaches of the South-Eastern Baltic for the period 2018–2020 [2 Monitoring_geosynthetic_debris_SEB]; (3) statistical distributions of the found geosynthetic debris by size [3 Scales_geosynthetic_debris_SEB] and (4) results of test surveys on the shores of Lithuania and Poland adjacent to Kaliningrad Oblast. All data refer to the beaches of the Kaliningrad Oblast (Russia), including the Russian parts of the Vistula and Curonian Spits, but also contains information on a one-time assessment of the pollution of the beaches of the adjacent territories: the Polish shore from the Poland-Russia border on the Vistula Spit to the mouth of the Vistula River, the Lithuanian shore from the border Lithuania-Russia on the Curonian Spit to the border of Latvia-Lithuania. Materials were collected during field surveys within the ERANET-RUS_Plus joint project EI-GEO, ID 212 (RFBR 18-55-76002 ERA_a, BMBF 01DJ18005).

Investigations of natural factors leading to large wash-outs of marine debris to the shores of seas and oceans have become urgently needed due to the presence in its composition in the last decades of a significant amount of anthropogenic litter, potentially dangerous to living organisms and humans. This paper provides an analysis of meteorological and hydrophysical factors responsible for the wash-outs of marine debris to the shore of the Baltic Sea. A detailed review of 25 cases of emissions observed on the beach of the northern shore of the Sambian Peninsula. For each of the cases, the variations in time of the wind speed and direction (according to field measurements), the height and the direction of the significant waves (according to reanalysis data) during 10 days preceding the wash-out event are considered. The results of the analysis of the development of hydrophysical situations show that the largest influence on the wash-out of marine debris is exerted by surface waves (the height and direction of the significant waves) during the phase of the storm subsiding. The results obtained are important for the elaboration of a system for predicting massive marine debris wash-outs on the Baltic Sea shores for taking prompt measures to eliminate potentially dangerous contamination.

Beach cast is a material deposited on beaches after being washed up by storm (or tidal movement). The composition of beach cast usually includes seagrass or algae fragments, wracks of land plants and other materials of natural origin, (anthropogenic) marine litter, including plastic debris and microplastics. Beach casts monitoring is of current interest for beach management and maintenance of the sandy shores for recreational purposes, tracing marine litter transport and dispersion, evaluating environmental contamination by microplastiсs. Large patches of marine debris appear on beaches after stormy weather. However, little is known about the sea state that precedes the formation of beach casts. From an observer's point of view, beach casts occur at random locations along the coast at unpredictable times. They may even be washed back to the sea at some time later. This work aims to disclose characteristic features of temporal variations of surface wave field parameters, which lead to beach cast formation. Results of incidental surveys of the northern coast of the Sambia Peninsula, stretching from west to east in the southeastern part of the Baltic Sea, were analyzed. The presence of beach cast (at one or more locations) was observed during 234 days of 2011-2021. Some of the observations were performed during or shortly after the ending of the beaching process. Field information was collated with a freely available re-analysis database on surface waves (http://marine.copernicus.eu). Surface wave spectrum parameters were picked up from the database at the geographical point corresponding to the coastal zone's open-sea limit. Elements of Bayesian analysis were applied to overcome the lack of information on the very time of the beach casts formation and/or the unknown duration of the beaching process. The analysis shows the values of significant wave height, peak period, and wave direction, which occurred before the beach cast appearance more often than follows from the overall time statistics ("climate"). A separate analysis of only recently formed beach casts made it possible to determine the evolution of wave spectrum parameters during the beaching process. Data suggests that most of the beach cast events on this coast are preceded by waves caused by cyclone passages from the northern direction. Data analysis is carried out by I.I., with the support of the Russian Science Foundation, grant No 21-77-00027. Beach surveys are carried out by E.E. voluntarily and with partial support from IO RAS state assignment.

The paper provides information about the XXIX Coastal Conference, held in Kaliningrad in April 2022. The thematic directions of reports, round tables are reflected, statistical data are given on the number of speeches (232), on participating organizations (38) and cities (13). Additional events held within the framework of the conference (sessions, lectures, competitions, excursions) are described. The text is accompanied by illustrative materials – color photographs of participants taken directly during the conference. The decision of the conference notes that the practical development of new sections of the coasts, the construction of modern infrastructure facilities and the existing natural trends lead to increased coastal erosion in almost all coastal regions of Russia; that there is an urgent need to apply unified observation methods, division of work into research and monitoring and an interdisciplinary approach to jointly take into account physical, chemical and biological aspects (especially for coastal waters with limited or periodic connection with the marine area), that pollution by anthropogenic debris continues to grow, while the pollution pattern is extremely heterogeneous, and information on pollution by anthropogenic debris and microplastics of the marine environment and coasts of the Russian Federation is extremely fragmented. The conference recommends the introduction of amendments and additions to the federal and regional legislation on the regulation of the activities of nature users in the coastal zone, as well as the inventory of the natural resource potential of coastal territories and adjacent water areas with the compilation of a Coastal Registry for coastal ecosocio-economic systems of the Russian Federation. The participants highly appreciated the existing experience and results of coastal protection activities in the Kaliningrad Oblast, and also emphasized the lack of attention of the coastal community to the problems of inland waters (for example, the shores of Lake Baikal). Proposals on the venues of the conference in 2024 (Moscow) and 2026 (Lake Baikal) were announced.

An abundance of microplastics particles (0.2-5 mm, MPs) in bottom sediments is analyzed based on 53 samples (3 to 215 m deep) obtained in 8 cruises of research vessels across the Baltic Sea Proper in March-October 2015-2016. MPs content varied between stations from 103 up to 10,179 items kg-1 d.w., with the bulk mean of 863 ± 1371 items kg-1 d.w., showing a statistically significant increase with water depth. As many as 74.5% of MPs are of fibrous shape, followed by films (19.8%) and fragments (5.7%). The distributions of fibres, fragments, films, and different types of natural bottom sediments are significantly different, highlighting the specific behaviour of each of these kinds of bottom deposits. A statistically significant correlation between water depth and fibres content is found. Based on the analysis of oceanographic factors and sedimentological principles, an erosion/transition/accumulation pattern for fibres in the Baltic Sea Proper is outlined. Fibres can be considered as a specific type of "synthetic sediment", while principles of distribution of other MPs are not yet certain.

The chapter combines an overview of several studies of marine litter distribution on beaches and in sediments for two Russian parts of the Baltic Sea: the Gulf of Finland and the South-East Baltic for a period of 2016–2020. Various methods for sand sampling on beaches have been applied, including the OSPAR method, NOAA methodology, and IOW beach litter sampling methods (Frame and Sand Rake methods). The results of field research for the period of 2016–2020 showed both the applicability and some limitations of some methods. Results showed an overall high level of contamination with marine litter and its polymer components, microplastics in particular, of the Russian Baltic beaches – both regularly cleaned and “wild” isolated beaches. However, in comparison to the Neva Bay and beaches around the world the beaches of the South-East Baltic are quite clean and there is no obvious difference in the contamination of beaches with high (near resort cities) and low (less-visited coastal areas) anthropogenic load. The largest amount of litter of all fractions was found on the beaches of the inner part of the estuary in the Neva Bay. At the same type a high variability of types of litter was shown: the predominant type of litter in the South-East Baltic is foamed plastic (foam/polystyrene foam), together with paraffin, coming from the tank waters from ships, and a specific pollutant-geosynthetic materials that are a new contaminant emerging from coastal engineering protection activities. In the Gulf of Finland region, the most common litter items are plastic pellets, broken glass, cigarette butts, rusty metal, and pieces of building plaster, together with synthetic napkins and cotton bud sticks, that are not retained by the wastewater treatment facilities.

Geosynthetic materials are applied in measures for coastal protection. Weathering or any damage of constructions, as shown by a field study in Kaliningrad Oblast (Russia), could lead to the littering of the beach or the sea (marine littering) and the discharge of possibly harmful additives into the marine environment. The ageing behavior of a widely used geotextile made of polypropylene was studied by artificial accelerated ageing in water-filled autoclaves at temperatures of 30 to 80 °C and pressures of 10 to 50 bar. Tensile strength tests were used to evaluate the progress of ageing, concluding that temperature rather than pressure was the main factor influencing the ageing of geotextiles. Using a modified Arrhenius equation, it was possible to calculate the half-life for the loss of 50% of the strain, which corresponds to approximately 330 years. Dynamic surface leaching and ecotoxicological tests were performed to determine the possible release of contaminants. No harmful effects on the test organisms were observed.

Twelve seas with an integral coastline length of about 38,000 km wash upon the Russian coasts. They belong to the basins of the Atlantic, the Arctic, and the Pacific Oceans and stretch over temperate, subpolar, and polar climate zones. This review of 32 studies published between 2015 and August 2020 analyses the available peer-reviewed scientific publications related to the topic of plastic contamination. At present, plastic contamination of the marine environments is confirmed by field investigations in 7 out of 12 Russian seas. Pollution levels vary widely: from 0.6 to 336,000 items/m(3) for microplastics in water and from 1.3 to 10,179 items/kg (DW)-in sediments, while median macroplastics abundance is around 1.0 item/m(2) at the coast. One monitoring survey of the Barents Sea reported mean macroplastics concentration in the upper 60 m as 0.011 mg/m(3) and 2.9 kg/km(2) at the sea floor. The identification of the polymer types with spectroscopy techniques is performed only in 9 studies (28%); most researchers use visual identification which makes the results difficult to compare. Most projects aimed at the plastic contamination research use their own collection and extraction methods that poorly agree with other studies. Since the pollution levels in most of the areas are relatively low, sampling is inhomogeneous in space and time. The most extensively studied areas are the beaches of the Baltic Sea, while the least examined is the Arctic region. Our study highlights the need for a discussion on harmonizing sampling methodology and identification techniques among different studies.

The distribution of small (0.5-2 mm, S-MPs) and large (2-5 mm, L-MPs) microplastics and mesoplastic particles in 51 samples of surface beach sands at 7 locations along the southern shore of the Baltic Sea was investigated. MPs particles (3267 in total) were found at all the sites and in all the beach zones. The bulk mean MPs (0.5-5 mm) contamination is 68 +/- 117 (median 33) items/kg DW (n = 51). The results were confirmed by mu-Raman spectroscopy analysis. National park areas did not differ substantially from other beaches. Expanded polystyrene fragments accounted for about 38% of the total collected particles. Fibres were the predominant type of MPs (55%). The highest contamination was found within the current wrack line (60.1 +/- 36.6 items/kg DW of S-MPs). A consistent picture for S-MPs was observed at the beach face, where the mean values in different locations varied between 21.0 and 58.1 items/kg DW, with a bulk mean of 30.4 +/- 13.7 items/kg DW.