| Abstract |
Surface sediments were collected in the Rhone delta, NW Mediterranean, at two seasons and analyzed for composition of non-aromatic hydrocarbons (NAH), long-chain linear alkylbenzenes (LAB) and polycyclic aromatic hydrocarbons (PAH) by GC and GC/MS following fractionation by normal phase HPLC. Concentrations varied from 21.2 to 166.7 mu/g for NAH, from 2097.9 to 9324.2 ng/g for total PAH and from 342.5 to 2713.0 ng/g for LAB. These levels are comparable to those reported for other coastal areas worldwide in the vicinity of important urban and industrial activities. Detailed analysis permitted identification of several contributions to the bulk sedimentary hydrocarbon mixture from fossil fuel related sources, pyrolytic processes, domestic wastes as well as from natural precursors. The various hydrocarbon inputs showed distinct variations at the two seasons. Thus, pyrolytic inputs were significantly higher in winter, whereas other hydrocarbon inputs (fossil and natural) showed a slight increase in late summer. Distributions in the deltaic area, from the river mouth as far as the limit of the continental shelf, evidenced that hydrocarbons followed dissimilar dispersal modes depending on their origin, which indicated specific, non identical particle associations. Fossil and naturally-derived hydrocarbons displayed a regular decreasing trend seawards which was highly cor-related to the decrease of the organic carbon content of sediments. Compounds derived from domestic wastes (LAB) showed a very sharp decrease offshore, suggesting their association with very rapidly settling particles. Hydrocarbons derived from pyrolytic sources were not significantly correlated with the organic carbon and also showed some accumulation trends in specific areas. Our data indicate that simultaneous analysis of multiple hydrocarbon classes constitutes a powerful and indispensable approach in estuarine and coastal regions for the comprehensive assessment of various inputs, both anthropogenic and natural, as well as for the determination of their environmental behaviour. |
