Annotation of the results obtained in 2021
Scientists from the Laboratory for Marine Physics of the IO RAS (Atlantic Branch, Kaliningrad) under the leadership of Dr. I. Chubarenko carried out a number of original works on the study of the transport and accumulation of microplastic (MP) particles in the marine environment. On the basis of field data and laboratory experiments, the behavior of MP particles during ice formation / melting in marine, brackish, and fresh waters, the distribution of MP particles in the ice mass, and the properties of MP particles captured by ice were investigated. It is shown that, due to the hydrophobicity of the material, the MP particles are not crystallization centers, and when ice forms on the plastic surface, the crystals tend to grow away from the surface. Based on the results of laboratory experiments, it is shown that in the ice mass, MP particles are found in association with air bubbles (in fresh ice) or between plates (in salt ice). A significant difference in the thermal properties of plastic (heat capacity, thermal conductivity) from the properties of ice under freezing / melting cycles leads to the melting of MP particles out from the ice. At temperatures typical of high latitudes, many plastics are brittle, which may explain the observed lack of large floating plastic debris in the Arctic by observers. The mechanisms that determine the vertical distribution and redistribution of MP particles in the ice are considered. Although it is theoretically possible to expect an increase in the number of MP particles in the surface and lower layers of ice, the variability of natural conditions during the formation of sea ice and its permeability should smooth out the distribution features. The hypothesis on the correlation of the distribution of MP particles and salinity in the ice is tested. For MP particles, the size of which is smaller than the characteristic diameter of the salt channels, migration in the ice mass along with the brine should obviously be observed, since they are hydrophobic and, like salt, are displaced from the ice. For larger particles, migration with the brine is mechanically impossible. Therefore, the analysis of the distribution of MP particles in the ice mass should be carried out separately for different size ranges. The laboratory experiments carried out to date on the formation of salty ice and the layer-by-layer analysis of its salinity and the content of MP particles have not yet provided any convincing indications of their relationship. Analysis of field data also does not yet allow us to confidently speak about the correlation between the number of MP particles and salinity in ice cores, since the data series is still very limited. The salinity profiles of the first-year sea ice in the Novik Bay cores of the Peter the Great Bay (obtained in the winter season of 2019/2020) show that the salinity in the lower ~ 10 cm of cores is significantly higher (by ~ 3 PSU) than in the central part. However, the processing of the layer-by-layer filters of these cores for the MP content is still far from complete. According to two analyzed cores - in the lower layer, indeed, the content of MP particles is higher than in the central part (by 83% in the size range of 0.3-5 mm and by 60% - for particles of 25-300 µm). The analysis of 14 filters obtained from two sea ice cores of the Peter the Great Bay for the content of MP particles (0.3-5 mm) has been carried out. The analysis showed that the concentration of MP particles in the range of 0.3-5 mm is of the order of 200-300 pcs / l, with a predominance of fibers. Analysis of the particle size distribution showed that the largest number of particles are 1–2 mm (37%). In the winter period 2020/2021, sampling of ice cores, sludge, snow, sub-ice water in fresh (Lower Lake and the Pregolya River) and brackish (Curonian and Vistula lagoons, the Baltic Sea) waters of the Kaliningrad region, and analyzed for the content of MP particles (0.3-5 mm) obtained including 76 filters. It was found that fibers are the predominant type of MP (95.4%). On average, the number of fibers for water was 53.7 pcs / l, for slush 116 pcs / l, for snow - 118.5 pcs / l, for ice - 138.9 pcs / l. The ice samples turned out to be the most contaminated with MP particles, and the least contaminated water. The most polluted were the samples from the river compared to other bodies of water. When studying the processes at the bottom for bottom sediments of the Baltic Sea proper, the content of MP particles was established. The analysis for the content of MP particles (0.3-5 mm) of a series of bottom sediment samples (53 samples from depths from 3 to 215 m), obtained in 8 cruises in the Baltic Sea proper in March-October 2015-2016, has been completed. It was found that the average content of MP particles was 863 ± 1371 pcs / kg dry weight and that fibers are the predominant type of MP (74.5%). The distributions of various forms of MP differ both from each other and from the distributions of natural bottom sediments, which leads to the conclusion that different types of MP particles can be considered as specific types of sediments, the distribution of which in bottom sediments does not correlate either with the characteristics of natural sediments or with other types of MP particles. Fibers are one of the characteristic types of "synthetic sediment", and their number increases rapidly with depth. There is still insufficient data to identify other characteristic types of anthropogenic precipitation. Based on the analysis of oceanological / hydrophysical factors and sedimentological processes, assumptions about the driving factors of turbidity / transfer / accumulation of fibers in the Baltic Sea proper are formulated. In the study of the processes of roiling, transfer, and accumulation of MP particles on the basis of laboratory experiments, the analysis of the transfer process of heterogeneous plastic waste and MP containing particles of various shapes with sizes (i) exceeding the grain size of the largest (of the used) sediment was carried out, (ii) of the order sediment grains, and (iii) substantially less sediment grain. A picture of the zones of transfer, temporary retention, and accumulation of plastic particles is revealed, and the possible reasons for their formation are analyzed. It turned out that the most mobile are large (in comparison with sediment grains) three-dimensional particles. Small particles (much smaller than the sediment grains) fall into the subsurface sediment layer and accumulate there over time. The mobility and manner of movement (rolling, sliding, saltation) of particles of intermediate sizes are largely determined by their shape. The most important and unexpected result of the analysis of the picture of the transfer of particles by a unidirectional flow was the formation of rather narrow zones of their accumulation, where plastic particles of all sizes and shapes stop most often. Thus, potential zones of their accumulation were found for non-spherical plastic particles of various shapes, and the effect of the ratio of the grain size of the sediment and MP particles on the mobility (threshold of the onset of movement) of the latter was experimentally confirmed. The experimental results also indicate the influence of the coefficient of friction (rolling, sliding) of plastic-soil on the mobility of relatively large particles. A review of approaches to the theoretical description of the onset of motion of bottom sediment particles and their applicability to the problem of transport of MP particles is carried out. The form of parametrization of the near-bottom transfer of MP in numerical models is refined. Since the accumulation zones are short and retain particles with different properties (size, shape), a probabilistic approach to the parameterization of the bottom transfer of MP seems to be more preferable for use in numerical models (for example, the probability of displacement of an MP particle on a coarser soil or the probability of moving when an increase in the flow rate). Thus, the use of probabilistic approaches (such as, for example, the Monte Carlo method for the sedimentation rates of MP particles) seems to be more effective for describing the processes of bottom transfer and accumulation of MP particles than the traditional approaches for bottom sediments based on the introduction of threshold values of flow rates or bottom shear stress. A study of the role of rooted bottom vegetation in retaining MP particles (based on expeditionary data) showed that rooted bottom vegetation actively retains microplastic particles (0.2-5 mm), and areas covered with macroalgae and macrophytes are more contaminated with microplastics than water and sediments in this area. The number of MP particles in water samples taken inside the thickets is, on average, 1.7 times higher than in water samples taken outside the thickets. Plant thalli are entangled in fibers, while filamentous algae retain 2-8 times more fibers than cartilaginous ones. It turned out that the dry mass of algae contains an order of magnitude more MP than the sands of the shoreline zone. The analysis of pollution by microplastic particles of the surf zone sands has been completed. It turned out that the level of pollution by MP particles (0.3-2 mm) of the surf zone sands is practically the same along the coast of the South Baltic for about 400 km, and the seasonal course of pollution is also small. The relationship between contamination by microplastics (0.3-2 mm) with the grain size distribution, the sorting of the sample material, the porosity, and the permeability of the soil has not yet been revealed. Thus, with the general heterogeneity and patchiness of plastic pollution of the marine environment, a convenient for monitoring and a rather conservative indicator of its general level was found. In the study of coastal plastic pollution, it was found that the maximum (both in quantity and mass) plastic pollution is observed in the spots of natural marine debris thrown out by storms on the coast. In 2021, an analysis of the meteorological and hydrophysical situation of 240 cases of the formation of such throws on the coast of the Sambia Peninsula was carried out, and a model structure based on an artificial neural network was proposed to predict the place and time of throws. The presence of such a system for predicting peak pollution will make it possible to more efficiently organize the cleaning of anthropogenic garbage thrown out by the sea. Thus, as a result of the research, scientifically grounded recommendations have been proposed for monitoring MP and marine debris in the coastal zone of the sea. In 2021, the team published a monograph in Russian, which included the research results. Links to information resources on the Internet (URL-addresses) dedicated to the project: http://lamp.ocean.ru/ http://lamp.ocean.ru/index.php/lab-video-archive/ https://www.researchgate.net/project/Boundary-conditions-for-problems-of-transport-and-fate-of-microplastics-particles-in-marine-environment-MARBLE-Boundaries

 

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Annotation of the results obtained in 2019
The widespread pollution of water, bottom sediments, shores of the oceans with the remnants of synthetic polymers (plastics) was a surprise to mankind. The presence in the oceans of fragments of plastic products, and especially microplastic particles (MP, <5 mm), has been documented to date not only in populated regions, but also in sediments of deep water depressions, in the ice of the Arctic, on deserted beaches of secluded islands, in waters of circumpolar currents in the Southern Ocean. Such a large-scale distribution of plastic around the planet in just half a century of the "plastic era" is amazing. At the same time, it is clear that, with the “lifetime” of plastic in the environment of the order of several hundred years, all the plastic produced is still with us, its entry into the ocean continues to grow rapidly, and many generations have to live side by side with this pollutant. What is fraught with such a neighborhood is not yet obvious, but it inevitability requires at least an understanding of the scale of the potential threat to humans, the balance of ecosystems, and the quality of the environment. At present, the processes of transport and accumulation of MP particles in the World Ocean cannot be mathematically described and predicted (including using the numerical simulation). The problem turned out to be complex, requiring both an interdisciplinary approach and new information about the “life” of synthetic polymer particles in natural conditions. In a marine environment, MP particles change their size over time (they are fragmented due to ultraviolet radiation, or mechanical stress) and the integral density (due to aging of the material, bio-fouling, action of factors of a chemical and biological nature, adhesion with organic / mineral particles, etc. ), they can be eaten, trapped in ice, or buried by bottom sediment. These changes are closely related to the (physical, chemical, biological) environmental conditions that a particular particle encountered as it was transported. For such objects, the currently used models using Lagrangian tracers or a conservative admixture can describe only a small part of the process. For example, the propagation of plastic particles floating on the surface is successfully predicted; but it is estimated that such particles are only 1% of the total mass of plastic in the ocean. The problem is compounded by the lack of experimental information on the physical behavior of MP particles in natural processes responsible for its transfer, accumulation, and change in properties. Obviously, there is no “production" of plastic in the waters of the World Ocean, and its distribution and transport mainly depend on the conditions at the borders and the properties (stratification, currents, biochemical conditions) of the marine environment. If the latter has been studied for a long time and is predicted quite successfully by numerical models, then there is practically no information on the generation / transformation / retention of MP particles at the boundaries of the marine environment. The research within the framework of this project is devoted to these issues: the goal is to experimentally research and develop parameterization options for numerical models of the following processes: (a) fragmentation of plastic objects / generation of secondary MP in the surf zone of the sea with various types of natural sediment, (b) stirring and holding MP particles of various shapes, sizes and densities at the bottom, covered with various types of natural sediment, and (c) the interaction of MP particles with ice during its formation / melting on the ocean, with brackish and freshwater areas. In 2019, results were obtained and published on the study of the process and mechanisms of fragmentation of plastic objects / generation of secondary MP in the surf zone of the sea with various types of natural sediment. A series of laboratory experiments was carried out on the fragmentation of the most common types of plastic (polyethylene film, polystyrenes and disposable tableware polypropylene; expanded polystyrene foam) under conditions simulating mixing with various types of natural bottom sediment in the surf zone of the sea. The experimental samples (2 cm x 2 cm) were made of plastic types / objects that are most often found on the sea coast: plastic bags, disposable tableware made of polypropylene and polystyrene, building insulation made of polystyrene foam. Four types of beach material for experiments - sand, granules, coarse and fine pebbles - were collected on the Baltic Sea coast. A comparison of the effectiveness of different types of sediment in plastic fragmentation clearly shows that the coarser the sediment, the faster the destruction; The conclusion is valid for all types of plastic used and does not depend on the buoyancy of particles. Such experiments on the wear / aging of materials are carried out without fail by their manufacturers and users - but only for the expected operating conditions. Since the presence / destruction of household plastic under the conditions (and under specific loads) of the marine environment is not expected in advance - there is no relevant information, and such experiments are already necessary when studying the consequences. As a result of statistical analysis of the obtained data, a unified dependence of the integral mass of MP particles (from 0.5 to 5 mm) on their quantity for the four most common types of plastic and four types of beach sediment is proposed. The obtained dependence is close to a similar dependence found for MP particles collected on the surface of the oceans. This suggests a significant role for coastal mechanical fragmentation in the generation of MP particles in the oceans. Actually, obtaining the dependence M (N) is important from a scientific and practical point of view: data on monitoring MP pollution are usually given in the number of MP particles (N pieces per linear, square, cubic meter, per kilogram), which is not a conservative value; numerical models, as a rule, work with conservative parameters (mass M, for example), which does not allow efficient use of monitoring data for calibration and verification. To study the process of stirring MP particles from the bottom, covered with various types of natural sediment, the PIV system was retrofitted and a laboratory setup was tested, which is a 10-meter channel with a unidirectional flow of variable speed. A facility was developed and assembled to study the processes of interaction between MP particles and the forming ocean / brackish / freshwater ice. Expeditionary studies were aimed at collecting data on the role of attached bottom vegetation in the retention of MP particles. The selection of bulk (20--100 l) water samples from macrophyte thickets with various types of thallus and outside of them made it possible to preliminary confirm the hypothesis of an increased concentration of MP particles in macrophyte thickets. The available information on the content of MP particles in the bottom sediments of the Baltic Sea is systematized. The methods for identifying MP particles by the method of Raman spectroscopy have been refined. To increase the intensity of the recorded weak signals of the material of MP particles, media were created and used to realize the effect of giant Raman scattering and to obtain an amplified Raman signal based on colloidal solutions of silver and gold, as well as nanostructured rough surfaces of gold and silver.

 

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Annotation of the results obtained in 2020
The pollution of the oceans with plastic waste raises concerns, primarily due to the unpredictability of the consequences. Plastic in the marine environment is practically eternal, but it appeared there relatively recently, having managed, nevertheless, to have already reached the both poles and the ocean floor. Small particles of plastic (microplastics, MP, <5 mm) are recognized as especially dangerous since they penetrate the food chains and climb up to the humans. The properties of MPs particles in the ocean differ significantly from the properties of both natural particles and other anthropogenic pollutants; therefore, neither the transport paths nor the areas of accumulation of MPs in the marine environment are clear. The use of standard numerical modeling techniques - Lagrangian tracers, conservative impurities, particles with certain properties - provide only a small part of the information, since the properties of MPs (a) are very diverse and (b) change over time. The purpose of this project is to study the processes occurring to MPs on the coastline, on the bottom, and on the ocean surface and formalize them for use in numerical modeling. In 2021, experiments were carried out on the behavior of MPs of various sizes, shapes, and densities in a unidirectional flow over the bottom covered with sediment of various grain sizes. An archive of videos on the behavior of MPs in various regimes during laboratory experiments is posted on the IORAS website (http://lamp.ocean.ru/index.php/lab-video-archive/). It is proposed to distinguish separate classes of MPs particles with sizes much larger and much smaller than the sediment grain size. Laboratory experiments have shown that in other cases, the division of particles by shape into the "one-dimensional", "two-dimensional", and "three-dimensional" can be refined depending on the observed intensity of the capture of MPs particles between the soil grains. As a variant of parameterizing the threshold for initiation of motion of MPs particles for numerical models, it is proposed to consider the critical bottom shear stress for MPs as proportional to that for the sediment. The proportionality coefficient should be determined according to the proposed division of the MP particles into classes. On the basis of field data, the distribution of MP particles in the deposits of sandy beaches of the Curonian Spit National Park was analyzed. The distribution of debris and MPs (0.5–5 mm) is extremely uneven, patchy both along and across the beach. However, an important regularity was revealed: the amount of small MPs (0.5–2 mm) on the swash zone of the beach is practically the same for all stations and in all replicates. Moreover, in the surf zone, which is characterized by the most vigorous processes of mixing, filtration, and sediment sorting, natural sorting of MP particles also takes place, for which the pore size of the natural sediment is the most important factor (and not the grain size). In the surf zone, there is minimal plastic contamination of the sediment: both on the beach and in bottom sediments it is orders of magnitude higher. Analysis of the content of MPs particles (0.3–5 mm) in 53 samples of bottom sediments of the Baltic Sea showed that contamination by MPs increases with depth, with a maximum in the deepest part of the sea, and about 75% of particles are fibers. For the first time, it is statistically confirmed using a single dataset that the deep sea is indeed the ultimate end for synthetic fibers. On the basis of statistical analyses, it has been shown that the MPs content is not directly related either to the type of sediment, or to the average grain size, or to the sorting of sediment. Rather, the distribution and accumulation of various types of MPs (fibers, films, fragments), as well as various fractions of natural bottom sediments, are associated with the intensity of hydrodynamic forcing. The following conclusions about the distribution of MPs in bottom sediments were formulated: (1) “MPs as a whole”, apparently, should be divided into a number of sets of particles of various specific types (just as it is customary for natural bottom sediments); (2) MPs particles of the same type have similar suspension / accumulation behavior, which, however, may differ from that for any sediment or other type of MPs; (3) fibers are one such specific type of MPs; their distribution in bottom sediments can be described in terms of zones of erosion / transit / accumulation (as is customary for small fractions of bottom sediments - silt, clay), but the boundaries between these zones for fibers are located at a greater depth. For fragments and films, statistical analysis does not indicate any correlation - neither with the properties of natural sediment nor with the distribution of fibers. This confirms the need for further experimental studies to identify the features of these particular types of "plastic deposits". A series of laboratory experiments were carried out to identify the main regularities in the distribution of MPs particles of various types in the ice cores at various combinations of the properties of water, MPs particles, and the freezing rate. The processing of filters obtained from melted segments of ice cores in the Peter the Great Bay (Sea of Japan) has begun. Among the particles obtained from the Novik Bay ice filtrate, fibers were the most common type of MPs. Among the fibers, the most common color was blue (33%). The bulk concentration of MPs particles in ice was 0.25 pcs / cm3 or 254 pcs / l. Sample collection and analysis for the content of MP particles in sediments, water, beach sands, macrophyte algae was continued. All stages of processing and extraction of MPs particles from two series of samples - macrophyte algae and sands on the shoreline - have been completed, allowing for further statistical analyses.

 

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