## 3 Results and Discussion
### Chemical Characterization of Sediment  
As discussed in the previous section, the presence of PAHs and PCBs was observed in seawater. Hence, the analysis of sediment belonging to the same sea area is justified to assess whether a partition took place from the waters. Results are reported in Figure 2.  
Results showed that, as for seawater, PAHs containing the highest number of aromatic rings (i.e., DBA, BP and Ind) were not present (Figure 2), except for BbFl and BaP that were not previously detected in the water column.  
The total amount of PAHs in sediment was assessed to reach about 700 ug/Kg, with most of the contribution ascribed to higher molecular weight compounds (i.e., BaA (14 ug/Kg), Chr (73 ug/kg), BbFl (250 ug/Kg), BkFl (99 ug/Kg) and BaP (230 ug/Kg)). The  
Figure 2: Concentration of PAHs and PCBs detected in sediment. Analytical conditions are detailed in the Experimental section.  
concentration of these compounds accounted for almost 95% of the total PAH concentration. Upon comparing these latter results (Figure 2) with those previously presented for the water column (Figure 1), it was observed that the contribution of the compounds with higher molecular weight to the total PAH content measured higher in sediment rather than in water. Such differences remain in good agreement with the physicochemical properties of PAHs and may be ascribed to the different partitioning attitudes of the individual compounds. Indeed, the higher the molecular weight, the higher the octanol-water partition coefficients, thus enhancing the sorption on the organic matter present in the sediment [45]. In addition, it should be mentioned that neritie areas are highly subjected to sediment resuspension [46] which causes organic matter to rise temporarily in water and, hence, favoring the sorption of PAHs dissolved in water.  
As for seawater, the ratios between PAH congeners (see \"Chemical characterization of seawater\" section) confirm a pyrogenic origin of the PAHs detected in sediment (\(\Sigma\)LowPAHs/\(\Sigma\)HighPAHs = 0.04 and BaP/(BaP + Chr) = 0.76). Hence, detected contamination should be tentatively ascribed to industrial activities, as well as to maritime transport.  
Concerning PCBs, detected concentrations were about two orders of magnitude lower in comparison to PAHs (Figure 2), ranging from 1.2 \(\mu\)g/Kg (PCB167) to 3.3 \(\mu\)g/Kg (PCB101). Even if no congeners were detected in seawater, their presence in sediment at quantifiable concentrations could be ascribed to the sorption properties of sediment towards microorganic pollutants, as described for PAHs [47]. A similar behavior was also confirmed by studies performed in other marine areas, where PCBs were detected at fractions of ng/L in water and at \(\mu\)g/Kg in sediments [48].  
It should be mentioned that PAH concentrations detected in sediment exceeded the limit imposed by Italian and European regulations for BbFI (limit: 40 \(\mu\)g/Kg), BkFI (limit: 40 \(\mu\)g/Kg) and BaP (limit: 40 \(\mu\)g/Kg). As for the sum of PCB congeners (10.5 \(\mu\)g/Kg), this value partially exceeded the limit of 8 \(\mu\)g/Kg. However, similar values are not uncommonly found in the Mediterranean sea, due to the high impact of anthropic activities, as shown by other studies [44,49].