## 2 Material and Methods
### Determination of Polycyclic Aromatic Hydrocarbon in Sediment Samples  
Polycyclic aromatic hydrocarbons were collected from the research vessels BIOS DVA using the Van Ween sampling device. Sediment samples were transferred in the laboratory for biogeochemistry of organic contaminants (_Biogeochimie des Contaminants Organique_) at the French institute for exploration of the sea: Ifremer (Institut Francais de Recherche pour l'exploitation de la Mer) in Nantes, for further analyses. Analytical procedure and instrumental analyses followed the protocol developed by Ifremer. Extraction of the sediment samples was performed using accelerated solvent extraction (ASE), with dichloromethane as the solvent. The sediment extracts were purified and fractionated by column chromatography, using activated SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) as adsorbents. After fractionation, the solvent was reduced by rotary evaporation and further concentrated under gentle nitrogen steam. Activated copper was added to the samples prior to instrumental analysis to remove sulphur traces, which may interfere with the chromatography column. Internal standards (phenanthrene-d\({}_{10}\), benzo\([e]\)pyrene-d\({}_{12}\), fully deuterium-labelled compounds) were added to each sample prior to extraction to control the quality of the analyses. Instrumental analysis of PAHs was performed by high-resolution gas chromatography, using a HP 6890 gas chromatograph equipped with a 5973-mass selective detector (MSD). PAHs were separated on a DB5-MS capillary column made of fused silica (coated with 5% phenyl-methyl-silicone) with a length of 60 m and an inner diameter of 0.25 mm, using helium as the carrier gas. Injections were performed using a Combi-PAL CTC autosampler. Injection volume of 1-2 \(\upmu\)L with an on-column port was used. The mass selective detector was  
Figure 1: Sediment-sampling stations selected for source apportionment of polycyclic aromatic hydrocarbons and PAH-related toxicity evaluation in Adriatic Sea.  
operated in an electron impact mode at 70 eV and for quantitative analysis of individual PAHs in selected ion monitoring mode (SIM) in conjunction with perdeuterated calibration standards added prior to injection with the autosampler (acenaphthene-d10, fluorene-d10, pyrene-d10, benzo[_a_]anthracene-d12 and Indeno [1,2,3-cd]pyrene-d10). The list of analyzed PAH compounds, along with target ions, internal standards used for quantification, and abbreviations used in the text are listed in Table S3 of SI.  
Identification of each compound was based on the single mass fragment ion characteristic for the compound and its retention time. The concentrations of the compounds were determined in the extracts using an eight-point calibration curve (linear regression) prepared for each compound and laboratory-prepared calibration solutions. The calibration curves were in the range of the concentrations of the analytes in the samples. A separate calibration curve was used for very low PAH concentrations in the extracts. Calibration solutions were prepared in iso-octane by appropriate dilutions (by weight). Prior to injection, deuterated surrogates for quantification were automatically added to each sample extract and to external calibration solutions. Example of characteristic chromatogram of PAH mixture in sediment samples, obtained by GC-MS operating under described conditions, is shown in Figure S1 of SI. Sediment samples with recoveries greater than 110% and lower than 70% were reanalyzed until recoveries for both internal standards were within the desirable range. Standard reference materials (SRM 1491 and SRM 2977) from the National Institute of Standards and Technology (NIST) were incorporated into a batch of 10 sediment samples for additional control of the analytical procedure. Internal standard recovery factors were used as an uncertainty matrix for the PMF model.  
A detailed description of PAH analyses in sediment samples from the Adriatic Sea has been described in previous publications [22; 25].