Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants widely abundant in multi-stressed coastal environments worldwide. Herein, seawater (dissolved phase/suspended particles) and sediment samples were collected during a survey on June 2024 across five stations, reflecting multiple anthropogenic stressors, at the heavily impacted Saronikos Gulf, Greece. In the collected samples, 47 PAH homologues were monitored by gas chromatography - mass spectrometry, resolved into source-related profiles by employing the EPA's Positive Matrix Factorization model and examined in relation to bacterial community composition inferred from eDNA metabarcoding sequencing. Our aim was to assess the potential links of PAH sources to microbial diversity and community structure, providing a targeted tool to support coastal monitoring of complex PAHs mixtures in multi-stressed environments. Total PAHs (TPAH₄₇) concentrations ranged between 127 and 462 ng L^-1 in the dissolved phase with alkylated 2- and 3-ring compounds dominating, 5.78-10.4 ng L^-1 in suspended particles and 860-5450 ng g^-1 in sediments, dominated by high-MW 4- to 7-ring compounds. Bacterial community composition based on 16S rRNA gene metabarcoding differed between seawater and sediments. In seawater, community co-varied with physicochemical gradients (temperature, salinity, dissolved oxygen, chlorophyll-a), while PAH source profiles showed weaker associations. In sediments, bacterial assemblages exhibited a stronger statistical association with source-resolved PAH profiles based on the constrained ordination framework. In the dissolved phase the taxa Flavobacterium, Sulfitobacter, and Labedella gwakjiensis, in the suspended particles the genus Algiphilus, and in sediments the species Parahaliea maris were identified as source-associated candidate indicator taxa, highlighting compartment-specific potential bioindicators that require functional validation with -omics tools.

This study investigates the composition, abundance, and vertical export of polycyclic aromatic hydrocarbons (PAHs) across three deep basins of the northeastern Mediterranean Sea (NEMS) over one year. Sinking particles were collected using sediment traps, and PAH analysis was conducted via gas chromatography-mass spectrometry. PAH fluxes varied significantly, peaking in the north Aegean Sea due to mesotrophic conditions, nutrient-rich riverine and Black Sea water inflows, and maritime anthropogenic inputs. The fluxes were highest in winter and lowest in fall. In the Cretan Sea, petrogenic sources (~70%) dominated, driven by currents, with fluxes highest in spring and lowest in winter. The Ionian Sea exhibited lower fluxes, peaking in summer and decreasing in fall. Atmospheric deposition seems to be the main transport pathway of pyrolytic PAHs in this site, while its high-water column depth (4300 m) compared to the other sites presumably enables extended degradation of organic constituents during particle settling. The positive matrix factorization (PMF) and principal component analysis (PCA) results reveal complementary insights into PAH sources and transport mechanisms. PMF analysis identified combustion (61%) and petrogenic (22%) sources, while PCA highlighted biogenic fluxes (57.7%) and atmospheric deposition. Seasonal productivity, riverine inputs, and water circulation shaped PAH variability, linking combustion-related PAHs to atmospheric soot and petrogenic PAHs to organic-rich particles.