Search

International audience; Mercury (Hg) is a contaminant of global concern in marine ecosystems, notably due to its ability to accumulate and concentrate in food webs. Concentrations of total mercury (THg), methylmercury (MeHg) and inorganic mercury (IHg) were assessed and compared in different tissues (liver, muscle, and gonads) of three common fish species (hake Merluccius merluccius, red mullet Mullus surmuletus, and sole Solea solea) from the continental shelf from the southern part of the Bay of Biscay. Several studies investigated Hg concentration in fish muscle, but few assessed concentrations in other organs, despite the importance of such data to understand contaminant organotropism and metabolization. Results showed that trophic position and feeding habitat are required to understand the variability of Hg concentration in muscle between fish species. In addition, high MeHg/THg ratio in muscle could be explained by the predatory behavior of the studied fish species and the biomagnification of this Hg species within the food web, MeHg. Despite differences between species, Hg concentration was always higher in muscle (from 118 ± 64 to 338 ± 101 ng g−1 w.w.) and liver (from 122 ± 108 to 271 ± 95 ng g−1 w.w.). These results can be related to physiological processes especially the MeHg detoxification strategies.

International audience; Concentrations of 6 trace metals (Ag, Cd, Cu, Ni, Pb, Zn) in the muscle of 2 sharks (Galeus melastomus and Scyliorhinus canicula), 4 teleosts (Helicolenus dactylopterus, Lepidorhombus boscii, Micromesistius poutassou and Phycis blennoides) and 1 crustacean (Nephrops norvegicus) were compared between the Bay of Biscay (Atlantic Ocean) and the Gulf of Lions (Mediterranean Sea). Although average concentrations and the trace element pollution index were generally higher in the Gulf of Lions, significant differences between the two ecosystems were only found for Zn for Helicolenus dactylopterus, and for Ag and Cu for the crustacean N. norvegicus. Moreover, some relationships between trophic level or size and metal concentrations were found for these two species. The absence of clear pattern may result from the blurring effect of contamination and excretion that may act differentially for all species and all elements.

Sedimentary hydrocarbons have been studied quantitatively and qualitatively in 11 coastal stations located in the Gulf of Fos (French Mediterranean coast). Hydrocarbon levels ranged from 10 to 260 mg kg−1 sed. dry weight. A new parameter “NAR” (Natural n-alkane ratio) is proposed to evaluate the contribution of terrestrial inputs of hydrocarbons in the sediments. The origins of hydrocarbons are multiple: terrestrial inputs, biogenic, pyrolytic (industry emissions mainly steel and iron industries, ship and road traffic). Generally, the main source of contamination is not petroleum. Several ratios between parent polycyclic aromatic hydrocarbons show that the sources of hydrocarbons in the sediments are generally much more pyrolytic than petrogenic.

In March 1986, plots of a peaty mangrove were delimited and polluted by Arabian Light crude oil. Superficial sediments were sampled (0–5; 5–10 and 10–20 cm core section) in 1987, 1990, 1994 and petroleum hydrocarbons were analysed by FID-GC, high resolution GC-MS and MRM GC-MS. One year later, no significant evolution of the petroleum chemical composition was noted. Four years later, n -alkanes had strongly decreased and isoprenoids were predominant. Eight years later, isoprenoids were severely degraded and biomarkers were more or less altered as follows in the declining order of importance: steranes > hopanes > bicyclic terpanes > triand tetracyclic terpanes > diasteranes > norhopanes and triaromatic steroids > C-ring monoaromatic steroids. For steranes, the following order of degradation can be proposed C 26 > C 27 > C 28 > C 29 > C 30 with the stereochemical degradation sequence aaa 20R > αββ 20(R + S) > ααα 20S. Regarding pentacyclic terpanes, a decreasing removal is observed in the order C 35 > C 34 > C 33 > C 32 > C 31 with a preferential degradation of the 22R epimers compared to the 22S epimers. The C 30 -17α(H), 21β(H)-hopane appears more sensitive to weathering than its higher homologues. We also observed that there was selective degradation with drimanes/homodrimanes, diasteranes/steranes and norhopanes/hopanes. A light depletion of the C 20 –C 21 triaromatic steroids can be noted whereas no degradation of C-ring monoaromatic steroids is observed. Biomarkers, widely used in geochemistry, can be also used to follow the weathering of petroleum in natural conditions and can be considered as environmental markers.

Petroleum hydrocarbon pollution in the Gulf of Fos (South France) was studied following the cessation of petroleum waste discharge from an oil refinery in the Lavera area. Sediments were collected in core samples of 30 cm at eight stations along a radial from the refinery to the open sea. Petroleum contamination has been detected up to the beginning of the open sea but decreased gradually (from 40 to 3 g kg−1 sediment dry wt). GC profiles (aliphatics and aromatics) are characteristic of petroleum. They reveal the disappearance of short chain n-alkanes (up to C25) and of one and two aromatic ring compounds, the increase and the modification of the UCM depends on the depth and the situation, resulting from weathering processes. Biomarkers and three to five aromatic ring compounds are unaltered whatever the depth and the location. If some petroleum hydrocarbons are present for the open sea stations (perhaps from other sources), natural and pyrolytic hydrocarbons are also detected. Sediments from the open sea could be considered to be unpolluted (less than 0.1 g kg−1), and unaffected by the refinery wastes two years after the end of overspills.

Biodegradation of oil hydrocarbons trapped in a peaty mangrove substratum is a very slow process. In spite of soil periodical oxygenation, aerobic microorganism activity seems to be limited. This may be accounted for by a nutrient deficiency related to a slow organic matter mineralization. This hypothesis was confirmed by stimulating normal alkanes biodegradation with an oleophilic fertilizer. To resort to such a product may compensate the slowness of oil biodegradation in mangrove soils.

Les analyses sont effectuees, apres extraction des hydrocarbures, par chromatographie en phase gazeuse