Fluxes and transport of anthropogenic and natural polycyclic aromatic hydrocarbons in the western Mediterranean Sea

Abstract

Surface sediments were collected in the Gulf of Lions and in the Rhône delta and analyzed for composition of polycyclic aromatic hydrocarbons (PAH). After isolation of lipids, the hydrocarbons were separated into fractions by high-performance liquid chromatography (HPLC) and fractions were analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Annual PAH fluxes were calculated for the northwestern Mediterranean basin. The fluxes of open-sea sediments varied from 164 μg m −2 year −1, for a station located far from the coast and influenced by atmospheric deposition, up to 1420 μg m −2 year −1 for stations directly influenced by the Rhône river inputs, whereas stations located in the Rhône delta were characterized by higher fluxes, up to 12 250 μg m −2 year −1. PAH concentrations decreased significantly with distance from the river mouth. Detailed analysis of PAH revealed the presence of anthropogenic compounds, pyrolytic and petrogenic, and naturally derived compounds. The distribution and ratios of specific compounds of PAH are discussed as a function of morphological and sedimentological features to evaluate and characterize the respective importance of atmospheric and Rhône-derived river inputs. Pyrolytic inputs from anthropogenic combustion processes were predominant at all studied stations. Compounds of natural origin were quantified, such as retene and related abietic acid precursors, and pentacyclic triterpenes derived from α- and β-amyrins. Anthropogenic PAH fluxes, determined for an open-sea sediment corresponding to the end of the nineteenth century (∼ 100 years ago), were three to four times less than the current flux; however, the retene flux was equal to or higher than that of today.