## 3 Results and Discussion
### Surface Morphology and Elemental Analysis Using SEM-EDS  
The surface morphology of selected MPs (seawater and fish gut), whose plastic nature and polymer type were previously identified by ATR-FTIR and micro-Raman spectroscopies, were investigated via SEM, as it is a technique through which high-resolution and magnification images can be obtained. Figure 6: Representative examples of Raman spectra for microplastics detected in seawater samples with micro-Raman spectroscopy. In Figure 8, the SEM images of six selected MPs recovered from seawater are presented, which are representative of the six different classes of plastic materials (PE, PP, PS, PEO, EAA, EVA) that were, as previously mentioned, determined through the combined use of ATR-FTIR and micro-Raman spectroscopies. As can be observed from the micrographs of these MPs, their surfaces appear to be rough with small cracks and burrs, while cavities are also present on some of them (Figure 8b-d). By comparing these images with micrographs of standard PE [77], PP [78], and PS [79], whose surfaces appear to be mostly smooth without any cracks or holes, it appears that all the aforementioned morphological characteristics could be the results of environmental exposure. The results of various studies conducted in different seawaters around the world are in agreement with these findings, as  
Figure 7: Representative ATR-FTIR spectra of microplastics detected in seawater samples. From top to bottom: polystyrene (PS), polypropylene (PP), polyethylene (PE), ethylene-co-vinyl acetate (EVA), ethylene oxide (PEO), and ethylene-co-acrylic acid (EAA), each accompanied by the percent match to the corresponding library polymer spectrum. they detected MPs (PE, PP, PS, etc.) whose morphological features were quite similar to those reported in this work and attributed them to mechanical erosion as well as aging in the marine environment [80; 81; 82; 83]. Therefore, this general surface roughness of MPs could act as an indicator of their level of exposure to marine environmental conditions where various abiotic (e.g., mechanical abrasion, photodegradation) and biotic (e.g., bacterial degradation) processes capable of degrading plastic particles take place [84; 31]. Also, the aforementioned cracks, burrs, and cavities are of significant importance as they lead to an increase in the surface area of MPs, facilitating the adsorption of various contaminants on their surfaces [31]. As a consequence, the more weathered MPs could potentially pose a greater environmental risk. From the representative SEM images of MPs (i.e., F1-F6) recovered from fish guts (Figure 9), their average diameter was estimated to be about 7.5 \(\upmu\)m, which is consistent with  
Figure 8: SEM images of selected MPs recovered from seawater, which were previously identified as (**a**) PE, (**b**) PP, (**c**) PS, (**d**) EAA, (**e**) PEO, and (**f**) EVA. Images were acquired by applying an accelerating voltage of 15 kV under high vacuum (0.1 Pa), using both backscattered and secondary electron detectors (20:80). the micro-Raman spectroscopy results that showed an average diameter of about 5.4 \(\upmu\)m. The surface morphology of the selected MPs, as in other similar works [31; 85; 86], appears to be mostly rough, cracked, and uneven due to physical, chemical, and/or biological erosion of the materials in the marine environment [86]. Also, based on their structural characteristics, the fish-recovered MPs were distinguished into two categories, namely fibers and fragments [87], with the former being the largest. The abundance of fibers in the present work coincides with the findings of various studies that retrieved mostly fibrous MPs from the gastrointestinal tracts of other fish species and attributed this to the breakdown of plastic parts of fishing gear as well as recreational sailing equipment [88; 89; 90].