## 3 Results and Discussion
### Color of Microlgistics Found in Mussel Digestive Glands  
The most abundant MPs by color found in mussels were white, while the least abundant particles were green particles (Figure 8). The majority of white particles (26.75 \(\pm\) 6.94) were found in the mussel digestive glands sampled at the ACI marina Rovinj, while the fewest were found in the mussels from St. Catherine Island (6.25 \(\pm\) 4.41). The second most abundant MP particles were orange and transparent in color and were found in mussel tissues from all investigated locations. Transparent MPs, along with the blue and red, were also recorded in the mussel _P. perua_ from Guanabara Bay (southwestern Atlantic) [54]. Contrary to our findings, in another study the predominant colors of MPs recorded by FT-IR analysis in mussels were blue (54.4%) and pink (29.4%); only some were black (4.4%), yellow (4.4%), or transparent (4%); and a few were green (1.4%) [52]. Also, in our study, a greater number of green MP particles was noted, but only in the mussels sampled from the Kopar location. In mussels from Hong Kong, the MPs found were either red (67%), transparent (16%), blue (9%), or black (6%), and the proportion of the MP colors found differed among species and sites [36]. [PERSON] et al. have demonstrated blue-colored MPs to be the most dominant color found in mussels, and they further explained in their conclusion that the fragments are usually blue, transparent, and black [51]. The higher occurrences of blue MPs identified in mussels originate from synthetic textiles and materials used for fishing (e.g., ropes, lines, and floating buoys). Films are mostly transparent. The prevalence of white items observed in this study could result from the increased presence of white MPs in seawater, greater contamination of mussel prey with white MPs, and/or mussels exhibiting a preference for actively ingesting white particles. It must also be noted that the white and transparent MP items detected in the mussel digestive glands could have been due to a weathering process happening in the environment that might have resulted in the loss of MP color. Figure 7: Different shapes of MP particles found in the digestive glands of mussels sampled at different locations: Katarina (native); Strunjan and Seča (cultured); and Kopar, Pula, and Rovinj (polluted—ACI marinas) in the northern Adriatic (N = 40 per sampling site). Data are reported as mean \(\pm\) standard deviation. Statistically significant differences between locations are marked with stars (*). Altogether, the direct comparison of our data with other studies that have researched the presence of MPs inside the mussel _M. galloprovincialis_ sampled from the northern Adriatic Sea is difficult since this was the first time that this methodology was used (FTIR analysis or different digestion protocols were used in previously published studies). Nonetheless, the previous studies all indicate the higher presence of MPs in the mussel tissue. The work conducted by [41] on the mussel _M. galloprovincialis_ sampled from the northern Adriatic Sea indicates the presence of 1.11 MPs/g \(w/w\) of mussels' tissue. This result is much lower if compared to our data, especially considering the highest number of MPs per mussel digestive gland was found at the ACI marina Rovinj location (32.85 MP/digestive gland). The differences could be attributed to different sampling locations and periods, but specifically also due to the differences in the used methodologies because the aforementioned study used filtration protocols where a significant number of MPs could be lost. Furthermore, in the same study, fragments consisted of 10-40% of all MP items, and this is contrary to our finding where fragments were found to be the dominant form of MPs in mussels. Fragments being the most dominant shape of MPs found in the mussels from the northern Adriatic Sea was also documented by [103]. As in our findings, [PERSON] et al., ref. [103], have also noted the prevalence of smaller sizes of MPs (20-40 \(\upmu\)m).