## 3 Results and Discussion
### Abundance of Microl plastics Found in Mussel Digestive Glands
Altogether, these data further confirm the presence of MPs to be from 8 up to 32 pieces of MPs per mussel digestive gland at all six sampled locations. This number is notably high, but direct comparisons to previously published data are challenging. Many previous studies have reported the presence of a considerable number of MPs in mussels. A higher number of MPs was also recorded in the mussel _Perna perna_ from Guanabara Bay (southwestern Atlantic), and the number of MPs/mussels was up to 31.2 \(\pm\) 17.8 (size of MPs \(\geq\) 0.45 \(\upmu\)m) [69]. In another study, the number of MPs from the mussel _M. edulis_ collected along the coastline of China was also higher and varied from 1.5 to 7.6 items/individual [32]. Furthermore, it was noted that MP abundance was greater within the mussel _Perna viridis_ (2.8-14.7 items/individual) compared to the other two species from Hong Kong: _Brachidontes variabilis_ (0.2-0.7 items/individual) and _Xenostrobus securis_ (0.6-3.1 items/individual) [50]. These data suggest that not all bivalves can intake the same number of MPs and, thus, only some are suitable for the identification of higher concentrations of MPs in their surroundings. MPs were found along the Hong Kong coast, with an average of 1.60-14.7 particles per mussel (_P. viridis_) per site [97]. [PERSON] et al. have recorded 1.5 to 7.6 items/individual in mussels (_P. viridis_ and _P. perna_) and have further stated that the MP abundance in mussels reflected the abundance found in the water column [51]. The abundance of MPs varied among four cultured bivalve species, ranging from 0.5 to 3.3 items/individual or 0.3 to 20.1 items/g of wet weight in the digestive system. In the aforementioned study, significant differences were observed between species and regions, but no seasonal variations were detected [88]. In numerous studies, the quantity of MPs found per mussel was considerably lower. [PERSON] et al. have recorded the MP abundance in the mussel _P. perna_ from around New Zealand to be from 0 to 1.5 particles/mussel, and tissue MP concentrations ranged from 0 to 0.48 particles/g tissue (\(w/w\)) [98]. MPs were also recorded in mussels (_M. galloprovincialis_) from the Ionian Sea, and their abundance ranged from 1.7 to 2 items/individual [52]. In another study, MPs were present in _M. edulis_ sampled from the French-Belgian-Dutch coastline, and the number of MPs found per mussel was on average 0.2 \(\pm\) 0.3 MPs/g [99]. However, it is important to note that many studies employed digestion protocols, involving aggressive chemical extraction, subsequent filtration, and examination under a stereo microscope for MP quantification. During this long process, many smaller MP particlesmay have been lost or simply remained undetectable under a microscope. For instance, [PERSON] et al. have found an average of 0.18 \(\pm\) 0.14 items/g of wet weight for the acid mix method and 0.12 \(\pm\) 0.04 total items/g of wet weight using the nitric acid method in the field-collected mussels _M. galloprovincialis_ from three different \"hotspot\" locations in Europe (Po estuary, Italy; Tagus estuary, Portugal; Ebro estuary, Spain) [79]. The average amount of MPs found in mussels sold on the market in five Turkish cities was determined to be 0.6 \(\pm\) 0.1 MPs/mussel using chemical digestion and, further, \(\upmu\)-Raman spectroscopy [94]. Furthermore, the presence of MPs recorded in two commercially grown bivalves _Mytilus edulis_ and _Crassostrea gigas_ was found to be 0.36 \(\pm\) 0.07 particles/g \(w\)/w and 0.47 \(\pm\) 0.16 particles/g \(w\)/w, respectively [89]. In a study conducted on mussels from 23 different locations along the Turkish coast, only 48% of the sampled mussels were found to have MPs. The average MP abundance was quite low and consisted of 0.69 items/individual [32]. The protocol used in the aforementioned study consisted of the digestion of the mussel tissue with H\({}_{2}\)O\({}_{2}\), further determination of MPs under a stereomicroscope, and characterization by confirming with FTIR analyses.