## 1 Introduction  
Contamination of the World Oceans by synthetic non-biodegradable litter has become a high-profile environmental concern. Of this debris, plastics make up the largest quantity, which is related to increased production of anthropogenic materials and growing dependence on plastic products [1]. Global production rates for 2003 were estimated at 299 million tons [2], while in 2018, this increased to more than 350 million tons [3]. According to recent forecasts, only 23% of plastic produced in 2020 will be recycled. Taken together, these numbers indicate the risk of increased plastic pollution. Plastics in the environment can be classified by size into macro- (over 25 mm), meso- (25-5 mm), and microplastics (<5 mm). Microplastics may enter the ocean directly as primary products such as granules, pellets, fibers, and powders or through the fragmentation of macroplastics under the influence of biological, chemical, and physical processes producing microplastics. This type of microplastic is often referred to as secondary microplastics [4]. It is important to establish the origin, trajectory, and fate of plastics in the environment in order to understand not only the sources but also consequences for the environment, including wildlife. At this stage, harmful effects of plastic pollution on wildlife have already been described, but further information is needed [5]. These effects can be very different depending on the size, shape, and chemical composition of the plastic. For example, it has been shown that daphnia can swallow microplastic particles from polyvinyl chloride [6], which leads to a decrease in offspring and in body size. There is also strong evidence of the harmful effects of especially meso plastics particles on fish, seabirds, and animals [1]. Marine animals often confuse such particles with food. Seabirds are known to swallow different mesoplastics, especially transparent and white particles but also fibers, which accumulate in the digestive system, and eventually could lead to death [7]. In addition, particles of meso- and microplastics in the ocean are often chemically contaminated (absorbing heavy metals, persistent organic pollutants), that is, enhanced by the degradation of plastic in the marine environment [8]. Research on meso- and macroplastics is often limited to visual identification. As an example, recent studies of microplastic pollution of the beaches and in surface waters [9] only used visual methods for the qualitative analysis of collected plastic particles. Resin identification codes (RIC) can aid with the identification of the type of plastic. All commercial plastic products have triangular symbols indicating the type of material (plastic polymer) from which the product is made (Table 1). This is helpful for the identification of large marine litter items without any special equipment. About 73% of produced plastic in 2018 was from category RIC 1-6 of unified product labeling system (Table 1). All other types of plastic placed in one category RIC 7. Results of beach cleaning programs show that 70-80% of collected items represent various packaging and are made from plastic with RIC 1-6 [1]. This is most likely due to the fact that about 60% of plastics are less dense than surface seawater and can float freely on the surface and be washed ashore [10]. Production of polymers with RIC 7 increases year by year and their share in worldwide plastic production becomes larger replacing those with RIC 1-6. From 2015 to 2018, the share of produced plastic with RIC 1-6 decreased from 85 to 73%. This will lead to higher pollution with more complex plastic polymers from category RIC 7, including a broad number of polymer types. RIC identification is not suitable for meso- and microparticles, as the RICs are not visible. Results of beach cleaning programs showed that more than 20% of found items are of unknown origin of polymer type, especially smaller fragments (meso- and microplastics), because they do not have RICs and only visual identification was performed.