## 3 Results and Discussion  
### Identification and Quantification of MP Particles in Biota Samples Using Raman Spectroscopy  
The polymers identified in the present study are found everywhere in our lives. For instance, PE is commonly used in a variety of industrial products and has a significant global production, which results in high occurrence in aquatic environments. PE tends to float in water instead of settling in the bed, which makes it more available for fish [15; 55; 56]. Polyvinyl alcohol is a synthetic water-soluble biopolymer (WPS) that is generally prepared by the saponification of polyvinyl acetate and can be found in a wide range of items, including food packaging (31.4% of the demand), construction, electronics, coatings, printing, textile, cosmetics, paper, and fishing lines. Most of these materials can reach the aquatic environment, resulting in their ingestion by marine organisms [57]. Furthermore, PBMA and PVB polymers act as toughening agents to the brittle phenolic resins applied as coatings for metals [58; 59]. Recently, to overcome the lack of dissolved oxygen in high-density aquaculture water, a hydrogen peroxide acrylic resin inclusion complex with a sustained oxygen-releasing effect could be synthesized by emulsion polymerization of acrylic acid, methyl methacrylate, and butyl acrylate [60]. As a result, PVB and PBMA ingestion could also be attributed to such applications. Figure 1 shows the mean relative contribution of each size class and polymer type to sea bass samples. The following polymer types were identified: low-density polyethylene (LDPE), polyvinyl-butyral (PVB), and polybutyl methacrylate (PBMA). The most frequent type of polymer was PE (47.4%), followed by PVB (36.8%) and PBMA (15.8%). The average number of MPs in sea bass was 22 \(\pm\) 2.1 items per fish. MPs were also categorized according to their diameter and perimeter (Figure 1c,d), with an average size of 5.4 \(\upmu\)m diameter and 37.3 \(\upmu\)m perimeter. Finally, the results obtained from this study were expressed as an average number of MP items per gram wet weight of fish gastrointestinal content. More specifically, sea bass samples contained 0.81 ng of PE per gram wet weight, 1.2 ng g\({}^{-1}\) PBMA, and 1.61 ng g\({}^{-1}\) PVB. The Raman spectroscopic analysis showed representative distinct spectrum profiles belonging to the different polymers presented in Figure 2. PE polymers had four major peaks in the Raman fingerprint region, namely the peaks corresponding to the C=C backbone stretching at 1118-1200 cm\({}^{-1}\), CH\({}_{2}\) twisting at 1288 cm\({}^{-1}\), CH\({}_{2}\) bending mode at around 1432-1450 cm\({}^{-1}\) and CH\({}_{2}\) symmetric and antisymmetric stretching 2870-2950 cm\({}^{-1}\)[61]. PVB exhibits stretching at 2850 to 3000 cm\({}^{-1}\) (-CH, -CH\({}_{2}\) stretching), 1720 cm\({}^{-1}\) (C=O stretching), 1420 to 1500 cm\({}^{-1}\) (CH\({}_{2}\) bending), and 1250 to 1350 cm\({}^{-1}\) (C-O-C stretching). Finally, PBMA polymer presents two characteristic peaks: the band at 1648 cm\({}^{-1}\) is attributed to the combination band arising out of \(\upnu\)(C=C) and \(\upnu\)(C-COO) modes, and the band at 3100 cm\({}^{-1}\) is attributed to the first overtone involving (C=O) of C-COO [62; 63]. Figure 1: (**a**) Identified particles of sea bass sample on silicon filters; (**b**) mean relative contribution of each polymer type; (**c,d**) size (diameter and perimeter, respectively) of MPs extracted from sea bass samples. In the case of bream, MP particles, including LDPE, PVB, PBMA, ethylene-co-vinyl acetate (EVA), and polyvinyl alcohol (PVA), were detected. The most abundant polymer types were PE and EVA, with frequency of detection of 70% and 65%, respectively. The second common polymer type was PBMA, with 25%, followed by PVB (20%) and PVA (20%). The average number of MPs in sea bream was 40 \(\pm\) 3.9 items per fish. MPs were also classified according to their size (Figure 3c,d), with an average diameter of 5.5 \(\upmu\)m and 41 \(\upmu\)m perimeter.