Spatial, vertical distribution and budget of polycyclic aromatic hydrocarbons in the western Mediterranean seawater

Polycyclic aromatic hydrocarbons (PAHs) were determined in the suspended particulate matter (SPM) (21 surface and 6 vertical profiles) and in the dissolved phase (DP) (7 sampling sites) of the western Mediterranean seawater. Terrigenous inputs were recognized by the co-occurrence of perylene (SPM) and trimethyl-1,2,3,4-tetrahydrochrysenes (SPM and DP) collected at the major river plumes. The PAH patterns in the SPM (>0.7 mu m) and DP (<0.7 mu m) phases were dominated by the three-ring aromatics (i.e., phenanthrene, dibenzothiophene, and their alkylated derivatives), reflecting a predominant contribution of fossil hydrocarbon inputs. Only the DP collected at the continental shelf and slope (fluoranthene), presumably of pyrolytic origin, predominated. PAHs associated with SPM were evenly distributed in subsurficial waters, and their concentrations ranged from 200 to 750 pg L(-1), respectively, maximizing at the Gibraltar and Sicilian Straits and at a frontal zone located midway between the Iberian Peninsula and the Balearic islands. Vertical PAH profiles associated with the SPM exhibited a surface-enrichment depth-depletion distribution where the concentration maxima were located at the 20-30 m depth concurrently with fluorescence attributable to biomass uptake or adsorption to organic rich detritus. An enrichment in PAHs in the deeper samples of vertical profiles was found in stations collected near submarine canyons and at the sewage disposal zone attributable to advective transport of particles. Concurrently, a higher depletion of the three-ring aromatic PAHs in comparison with the four-five-ring aromatics according to depth was ubiquitously found. Budget of PAHs in the SPM and DP was estimated according to a three-box model to be 335 and 372 t, respectively, and their residence time in the continental shelf and in the open sea were 0.95 and 6.5 yr, respectively.