## 3 Results
### Distribution of Microplastic Categories and Correlation with Polymer Types  
The whole microplastics set comprised 86.8% of fragments, 9.2% of lines and 4.0% of films (Table 1). The abundance of microplastic categories, in each investigated ocean site, is reported in Figure 10. Fragments were the most common category across all analyzed samples, followed by lines and films. However, films were not detected at one site in the Mediterranean Sea (i.e., A06 NS) and in the Western Atlantic Ocean sample (i.e., E4 SARMIENTO). Additionally, lines were absent from another Mediterranean Sea site (i.e., A34 NS). An exception was the sampling site ETO16 in the Bay of Biscay, where lines were the most abundant category, followed by fragments and films. The abundance of lines in the Bay of Biscay was considerably higher, likely due to the relatively intense fishing activity in the area. Concerning the correlation between microplastic category and polymer type, it was found that PE was the most common polymer for fragments and lines, followed by PP and smaller amounts of EPS and PS. Films were mainly made up of PP, followed by PE and no other polymers (Figure 11). The correlation between microplastic category and polymer type for each investigated sampling site is shown in Figure 12. PE was confirmed the most common polymer for fragments in all sampling sites, followed by PP and by EPS, except for ETO16 in the Bay of Biscay in which fragments are all composed of PE, A06 NS in which EPS is more abundant than PP and A02 DS in which only PE and PP were found. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Rule** & **LVs** & & & **PE** & **EPS/PS/PP** \\ \hline \multirow{4}{*}{1} & \multirow{4}{*}{9} & Sensitivity Specificity & \multirow{2}{*}{Calibration} & 0.930 & 0.958 \\  & & Sensitivity Specificity & & 0.958 & 0.930 \\ \cline{2-5}  & & Sensitivity Specificity & & 0.931 & 0.958 \\  & & Sensitivity Specificity & & 0.958 & 0.931 \\ \hline \hline \multirow{4}{*}{2} & \multirow{4}{*}{6} & \multirow{4}{*}{Calibration} & EPS & PS & PP \\ \cline{1-1} \cline{3-5}  & & Sensitivity Specificity & & 0.999 & 0.997 & 1.000 \\ \cline{1-1} \cline{3-5}  & & Sensitivity Specificity & & 0.984 & 0.999 & 0.997 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Sensitivity and specificity values, in calibration (Cal) and cross-validation (CV), related to each rule of the implemented hierarchical PLS-DA model developed for the recognition of the microplastic particles. Figure 10: Abundance of microplastic categories in each analyzed sample. Figure 11: Percentage of polymer types in each analyzed marine microplastic category such as fragments, films and lines. Figure 12: Percentage abundance of polymer types at each sampling site, categorized by fragments, films and lines. The highest % of EPS fragments were found in the Mediterranean Sea, with the majority located in A06 NS, followed by A34 NS and A27 NS, followed by the Western Atlantic Ocean site (E4 SARMIENTO) and the NST41 site in the Bay of Biscay,  
PS fragments were detected in a tiny percentage (2%) only at the NST41 sample site in the Bay of Biscay. Films were mainly found at NST41 sampling site (i.e., 30 particles) and they are mostly composed of PP (i.e., 93%), followed by PE (7%). At other sites where films were detected (i.e., A02 DS, A27 NS, A34 NS), their quantities were very low (\(\leq\)5 particles), and they were all composed of PP. The ETO16 site is an exception, with two films found: one made of PP and the other of PE. PE was the most common polymer for lines, followed by PP in the NS41 sampling site, where most of this kind of microplastic category was found (65 out of 90 particles). At the ETO16 site, lines were predominantly made of PE (i.e., 4 particles), with smaller amounts of PP (i.e., 3 particles) and EPS (i.e., 1 particle), although only 8 lines were detected at this location. The E4 SARMIENTO site had only five lines, all composed of PE. At the Strait of Gibraltar (A02 DS), lines were equally split between PE and PP, with two lines made of each polymer.