## 3 Results and Discussion
### PAH Sources in the Adriatic Sea
Compared to the other three sources, the mixture emitted from Source 4 was enriched in PHE, ANT, ACE and F, which is similar to the composition of PAH mixtures in the heavier petroleum fractions but may also indicate weathered petroleum contamination. Thus, Source 4 may also be considered as a petrogenic source, but more related to accidental leakage of heavier petroleum fractions during vessel maintenance and weathered petroleum pollution [37]. Figure 7 shows the contribution of sources (factors) to the total concentration of PAH in the sediment of each studied station. According to the model results, the two most important sources in the coastal area were transportation, both inland and marine (Source 1), and weathered petroleum products (Source 4). Transport activities were the predominant PAH sources at the stations near the island of Pag (CS1), near Biograd (CS5), in the channel of Sibenik (CS6 and CS7) and in the port of Split (CS8), where Source 1 contributed with more than 50% to the total PAH pollution. At the other stations in the coastal zone, the main source of PAH pollution was Source 4, which can be attributed to accidental spills of fresh motor oil and other heavier petroleum distillates during vehicle maintenance. Source 4 was present at every site in the coastal zone, with contributions ranging from 27.02% to 96.06%. Source 3 was also present at stations CS2, CS9 and CS10, indicating recent petroleum pollution in these areas. These stations are in the canal areas (CS2 and CS9) and in the port area (CS10), which explains the higher contribution of recently spilled petroleum. The contribution of coke and biomass burning (Source 2) was not observed at any station in the coastal area, which can be explained by the absence of industrial activities in these areas. The contribution of fresh petroleum pollution (Source 3) to the total PAH concentration was the highest in the sediments of the stations along the mid-Adriatic transect, ranging from 34.85%, as determined at station TS4, to 75.07%, as determined at station TS6. In the transect area, a high contribution of Source 1 was also observed, especially at station TS4, which is located along the high-density traffic route from the Strait of Otranto to the northern Adriatic Sea. These results indicate that accidental leakage of unburned fossil fuels and traffic are the main PAH sources in the transect area. This agrees well with the literature data for the open sea areas, where the main PAH sources are associated with maritime traffic. Elevated contributions of coke and biomass burning (Source 2) were determined in the sediment from station TS1 (24.67%), which is located near the island of Brax. Since this area is not heavily industrialized, these results can be explained by the frequent forest fires on the island of Brax, which occur frequently during the summer season [35]. In Kastela Bay, the highest contribution to the sediment PAH concentration was determined for Source 4, ranging from 72.17% at KB3 in October, to 88.48% as observed at the same station in February. Seasonal differences in the contributions of each PAH source were observed only at station KB3, where the contribution of recently spilled petroleum was higher in February than in October. The highest contribution of Source 3 to the total concentrations of PAH in the sediment of Kastela Bay was observed at station KB3 in February. This station is located near the industrial port of Split and the shipyard area, suggesting that the high contribution of Source 2 may be due to accidental spillage of unburned petroleum during ship maintenance [37; 32]. The absence of Source 2, or minimal contributions from this source in the coastal area, Kastela Bay and most of the open-sea stations are likely due to the absence of industrial activities in these areas. In Sibenik Bay, a high contribution from Source 1 is observed at station SB1 in October.