## 1 Introduction
Additionally, mussels are benthic organisms with a selective mechanism of suspension feeding and the ability to easily excrete non-essential particulate matter [34; 35]. They filter substantial amounts of water during feeding, averaging 7.5 L of seawater per hour, thereby maximizing their exposure to any adverse materials present in the aquatic environment [36]. This can lead to the accumulation of various chemical pollutants, microorganisms, and MPs in their body tissue [14; 37; 38; 39; 40; 41]. Consequently, mussels offer an accurate reflection of the local environmental conditions [28]. Despite their ecological importance, they are globally harvested and cultured for human consumption [42]. The Mediterranean mussel, _Mytilus galloprovincialis_ [PERSON], 1819, holds significant commercial value in Slovenia and Croatia, particularly in the northern Adriatic Sea, leading to extensive mariculture practices [43]. To date, numerous studies worldwide have highlighted the widespread occurrence of MPs in mussels, proposing them as a sentinel species for detecting MP pollution in coastal areas [21; 32; 44; 45; 46; 47; 48; 49; 50]. [PERSON] et al. have gone even further and suggested the use of mussel species for the bioremediation of plastic contamination [51]. All the aforementioned studies have found a close relationship between MP abundance in field-collected mussels and human activity, providing evidence for a positive and quantitative correlation between MPs in mussels and the surrounding waters. _M. galloprovincialis_ was used previously in a study as the organism of interest for screening the occurrence of MPs in the northern Adriatic Sea. In the aforementioned study, 1.11 MPs/g wet weight of mussel tissue was recorded, fibers were identified as the mostly occurring MPs, and the color black (50-70%) was the most dominant color found inside the mussel tissue [51]. Moreover, it has been demonstrated that mussels are prone to the ingestion of MPs and smaller nanoplastics in their gut. This may lead to the accumulation of plastic items smaller than 10 mm in the digestive gland or in the hemolymph [7; 52; 53; 54; 55]. In a study conducted by [PERSON] et al. [56], microfibers were identified in the foot and mantle of mussels, with adherence accounting for approximately 50% of the MP uptake in mussels. Consequently, the study concluded that mussels may potentially absorb MPs through both adherence and ingestion, thus establishing new pathways for bioavailability, accumulation, and toxicity of MPs to aquatic animals. Microbeads (spherical MPs) were recorded on mussel gills after MP exposure, showing that plastic beads can be taken and ingested from the organism's surrounding environment [57; 58; 59]. Furthermore, several studies have observed a higher accumulation of MPs in the digestive gland of mussels [60; 61; 62; 63]. The detection of plastic in mussel tissues and organs indicates the potential for MPs to accumulate at higher trophic levels. This observation aligns with the findings on littoral crabs after they had been fed on mussels pre-exposed to plastic pollution [64]. A lot of research to date has stated a range of different adverse effects on mussels exposed to MPs leading to the disruption of mussel homeostasis. In particular, alterations in immunological responses, mean clearance rate alterations, decreased filtration rates, increased abnormality in gills (e.g., deciliation and hypertrophy) and digestive glands (e.g., atrophy and necrosis), an increase in oxidative stress (stress proteins elevation, peroxisomal proliferation; antioxidant system turns on), and genotoxicity (DNA damage and changes in gene expression) have been observed [21; 27; 63; 64; 65; 66; 67]. Furthermore, mussels are able to excrete foreign particles like MPs without them passing through their digestive system [68; 69; 70; 6].