# Microplastic Pollution on the Beaches of the Black Sea in Romania and Bulgaria
## 1 Introduction  
Microplastics in beach sand have become a growing environmental concern due to their persistence, potential to absorb toxic substances, and adverse impacts on marine ecosystems and coastal biodiversity, underscoring the need for comprehensive studies ontheir distribution, sources, and degradation processes [1]. Plastic materials are synthetic polymer-based products that have experienced a significant increase in use across various industries in recent decades, becoming an indispensable element of modern society [2]. Microplastics are small plastic particles present in the environment that have become a major problem, especially for the marine environment [3]. Plastic materials are of different types and shapes, comprising natural or modified polymers, thermosetting plastics, thermoplastics, and more recently, ecological plastics [4]. These can be biodegradable and biologically synthesized, with natural origins (plants, animals, microorganisms), from polyhydroxyalkanoates (PHAs), polylactic acid (PLA), starch, cellulose, and lignin [5]. Alternatively, plastics can be biodegradable and based on petroleum, such as polyglycolic acid (PGA), polybutylene succinate (PBS), polycaprolactone (PCL), polyvinyl alcohol (PVA, PVOH), and polybutylene adipate terephthalate (PBAT) [6]. The cheapest and most commercially used plastics are low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polyethylene terephthalate (PET) [7]. The occurrence of environmental pollution, including in the Black Sea area, is not only well known but is also deeply studied in all the components of an ecosystem [8]. Surface water pollution due to industrial, touristic, and domestic activities and population growth is a current concern for the whole world, with repercussions on human health [9; 10]. According to studies [11] conducted as early as 2014, approximately 4.2 tons of plastic are discharged into the Black Sea from the Danube River each day in Romania. Plastic microparticles have been identified by researchers in both Romanian rivers and the Black Sea [12]. The identified particles have primarily been fibers originating from clothing items and the construction industry and polypropylene from plastic waste, fishing nets, etc. Plastic fibers also enter wastewater through the cleaning of textiles, eventually reaching rivers or seas. Microplastics are additionally formed through the degradation of plastic waste caused by UV radiation or physical forces [13]. Textile or plastic waste thrown into water is ingested by fish and molluss, such as mussels [14]. Recent research has shown that in Romania, the amount of plastic found in running water increases by at least 10% annually. This plastic then flows towards the Black Sea, where it significantly contributes to marine pollution and impacts the biodiversity of the aquatic ecosystem [11; 15]. The Danube River flows through ten countries before emptying into the Black Sea, constituting the primary source of microplastics in this marine basin [16]. The results of one study [17] revealed the widespread presence of microplastics in the coastal waters of Bulgaria, with an average concentration measured at 7.3 \(\pm\) 4.9 particles per liter, highlighting the extent of plastic pollution in the region. Based on their sizes, microplastics on sand beaches can be divided into macroplastics (\(\geq\)5 mm), microplastics (<5 mm), and nanoplastics (<1000 nm) [18]. The microplastics in the water eventually end up in marine organisms, which constitute food for the population. These micro-fragments can change their structure during cooking and when consumed can become carcinogenic [19]. This study makes an important contribution by providing a comparative investigation of microplastic pollution on the beaches of Romania and Bulgaria--an underrepresented region in the scientific literature--using complementary analytical methods such as FT-IR, DSC, and microscopic examination.