Origin and distribution of hydrocarbons and organic matter in the surficial sediments of the Sfax-Kerkennah channel (Tunisia, Southern Mediterranean Sea)

We investigated the origin and distribution of aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs) and organic matter (OM) in surficial sediments of the Sfax-Kerkennah channel in the Gulf of Gabès (Tunisia, Southern Mediterranean Sea). TOC, AH and PAH concentrations ranged 2.3-11.7%, 8-174μgg^-1sed.dw and 175-10,769ngg^-1sed.dw, respectively. The lowest concentrations were recorded in the channel (medium sand sediment) and the highest ones in the Sfax harbor (very fine sand sediment). AHs, PAHs and TOC were not correlated for most of the stations. TOC/N and δ¹³C values revealed a mixed origin of OM with both marine and terrestrial sources. Hydrocarbon molecular composition highlighted the dominance of petrogenic AHs and the presence of both petrogenic and pyrogenic PAHs, associated with petroleum products and combustion processes. This work underscores the complex distribution patterns and the multiple sources of OM and hydrocarbons in this highly anthropogenized coastal environment.

Response of the unicellular diazotrophic cyanobacterium Crocosphaera watsonii to iron limitation

Iron (Fe) is widely suspected as a key controlling factor of N₂ fixation due to the high Fe content of nitrogenase and photosynthetic enzymes complex, and to its low concentrations in oceanic surface seawaters. The influence of Fe limitation on the recently discovered unicellular diazotrophic cyanobacteria (UCYN) is poorly understood despite their biogeochemical importance in the carbon and nitrogen cycles. To address this knowledge gap, we conducted culture experiments on Crocosphaera watsonii WH8501 growing under a range of dissolved Fe concentrations (from 3.3 to 403 nM). Overall, severe Fe limitation led to significant decreases in growth rate (2.6-fold), C, N and chlorophyll a contents per cell (up to 4.1-fold), N₂ and CO₂ fixation rates per cell (17- and 7-fold) as well as biovolume (2.2-fold). We highlighted a two phased response depending on the degree of limitation: (i) under a moderate Fe limitation, the biovolume of C. watsonii was strongly reduced, allowing the cells to keep sufficient energy to maintain an optimal growth, volume-normalized contents and N₂ and CO₂ fixation rates; (ii) with increasing Fe deprivation, biovolume remained unchanged but the entire cell metabolism was affected, as shown by a strong decrease in the growth rate, volume-normalized contents and N₂ and CO₂ fixation rates. The half-saturation constant for growth of C. watsonii with respect to Fe is twice as low as that of the filamentous Trichodesmium indicating a better adaptation of C. watsonii to poor Fe environments than filamentous diazotrophs. The physiological response of C. watsonii to Fe limitation was different from that previously shown on the UCYN Cyanothece sp, suggesting potential differences in Fe requirements and/or Fe acquisition within the UCYN community. These results contribute to a better understanding of how Fe bioavailability can control the activity of UCYN and explain the biogeography of diverse N₂ fixers in ocean.

Role of cyanobacteria in the biodegradation of crude oil by a tropical cyanobacterial mat

Cyanobacterial mats are ubiquitous in tropical petroleum-polluted environments. They form a high biodiversity microbial consortium that contains efficient hydrocarbons degraders. A cyanobacterial mat collected from a petroleum-contaminated environment located in Indonesia was studied for its biodegradation potential. In the field, the natural mat was shown to degrade efficiently the crude oil present in the environment. This natural mat demonstrated also a strong activity of degradation on model crude oil under laboratory conditions. In axenic cultures, the monospecific cyanobacterium Phormidium animale that constitute the bulk of the biomass did not exhibit any degradative capacity on hydrocarbons in the range of C13-C35 carbon atom number either in autotrophic or heterotrophic conditions. It was concluded that this cyanobacterial strain living on a heavily contaminated site had no direct effect on biodegradation of crude oil, the degradation activity being exclusively achieved by the other microorganisms present in the microbial consortium of the mat.

Hydrocarbons in surface sediments from the Sfax coastal zone, (Tunisia) Mediterranean Sea

The Semi-enclosed Mediterranean Sea records various signals of high anthropic pressures from surrounding countries and the industrialized European countries. This is particularly true for oil pollution. Although accounting for 1% of the world's ocean surface, it receives about 25% of the petroleum inputs to the ocean. To achieve a global budget we need to collect information from different parts of the Mediterranean. Particularly, we focus in this paper on the Southern Mediterranean, where data are presently very scarce. In this context, the University of Sfax has undertaken an estimation of hydrocarbon pollution along the coasts of Sfax and Gabès Gulf. Non-aromatic hydrocarbons were analysed in 8 surface sediments by FT/IR and GC/MS. Non-aromatic hydrocarbon concentrations vary in the range 310-1406 microg g(-1) sediments dry weight, which is high, compared to other Mediterranean sites. GC/MS data indicate a large group of unresolved compounds suggesting a petroleum contamination, confirmed by the identification of hopanes with predominant C29 and C30alpha,beta compounds and steranes with predominance of C27 over C28) and C29 compounds.

Identification and biodegradation potential of tropical aerobic hydrocarbon-degrading microorganisms

Screening of aerobic culturable hydrocarbon (HC)-degrading microorganisms isolated from petroleum-polluted soils and cyanobacterial mats from Indonesia resulted in the collection of 33 distinct species. Eight bacteria, 21 fungi and 4 yeasts were identified to the specific level by molecular and phenotypic techniques. Bacterial strains belonged to the genera Gordonia, Brevibacterium, Aeromicrobium, Dietzia, Burkholderia and Mycobacterium. Four species are new and not yet described. Fungi belonged to Aspergillus, Penicillium, Fusarium, Amorphoteca, Neosartorya, Paecilomyces, Talaromyces and Graphium. Yeasts were Candida, Yarrowia and Pichia. All strains were cultivated axenically in synthetic liquid media with crude oil as sole carbon and energy source. After incubation, the detailed chemical composition of the residual oil was studied by gravimetric and gas-chromatographic techniques. Thirteen parameters for assessing the biodegradation potential were defined and computed for each strain. Maximum degradation was observed on the saturated HCs (n- and isoalkanes, isoprenoids), whereas aromatic HC degradation was lower and was related to the structural composition of the molecules. A principal components analysis (PCA) permitted grouping and classifying the strains as a function of their degradative capacities. It was shown that the most active strains produced polar metabolites which accumulated in the resins and asphaltene fractions. These fractions are highly resistant to microbial metabolism. No taxonomic trend could be defined between microbial phyla in terms of HC biodegradation activity.

Sea transport of animal and vegetable oils and its environmental consequences

The increasing production-and therefore sea traffic--of vegetable oils has regularly led to spillages during the past 40 years. The accident of Allegra, on October,lst, 1997, in the English Channel gave rise to a spillage of 900 tonnes of palm nut oil. The drift of this solid vegetable oil was followed by aerial observations. Samples of oil were collected in order to analyse its chemical evolution. This study, associated with several bibliographic cases of pollution by non-petroleum oils, shows that drifting oils can mix with floating material to sink or form a crust. They can also be oxidized or disperse and/or be degraded by bacteria. They may also polymerise. The coating properties of vegetable oils act as crude oils to affect sea life, tourism and yachting. As a result, it is necessary to quickly collect the oil after a spillage, using usual equipment (booms and pumps).

Novel marine flagellate fatty acid: structural elucidation by GC-MS analysis of DMOX derivatives and DMDS adducts

In situ biodegradation experiments of marine particles were performed in deep Atlantic waters. Lipid changes were associated with the colonization of the decaying detritus by marine flagellates smaller than 10 microm in size. Fatty acid methyl esters (FAMEs) of these flagellates showed high proportion of a FAME with a molecular weight (MW) of 320. Its structure could not be unambiguously resolved by retention times on gas chromatography runs using polar and nonpolar columns, nor by routine gas chromatography coupled to mass spectrometry (GC-MS). Complementary GC-MS analysis of two types of derivatives was performed to fully elucidate the structure of this novel acid. GC-MS analysis of 4,4-dimethyloxazoline (DMOX) derivative of the compound enabled localization of a double bond in position Delta17, whereas other double bond locations could not be unambiguously located by spectrum interpretation. DMDS addition on the flagellate biomarker produced monocyclic triadducts. Fragment suites corresponding to gradual losses of thiomethyl substituents indicated the presence of a five-membered thioether cycle, located on the methyl side of the derivative. Fragment suites produced by cleavage of C linked to sulfured substituents revealed various possible structures. However, interpretation of the spectra in relation with the fragmentation of the DMOX derivative yielded a convergent identification of the flagellate biomarker, as a non-methylene-interrupted C20:3Delta7,13,17 FAME.

Hydrocarbons in surface sediments from the Changjiang (Yangtze River) Estuary, East China Sea

Sedimentary aliphatic (AH) and polycyclic aromatic hydrocarbons (PAHs) were studied in the Changjiang Estuary and the adjacent East China Sea. Total AH ranged from 2.20 to 11.82 microg g(-1) and consisted of n-alkanes and a dominant petroleum-related unresolved complex mixture (UCM). Within the n-alkanes, terrestrial plant wax compounds prevailed at nearly all stations. Of the PAHs, biogenic perylene dominated at stations receiving riverine inputs. Anthropogenic PAHs originating from combustion/pyrolysis processes varied from 17 to 157 ng g(-1), while fossil PAH concentrations ranged from 42 to 187 ng g(-1). Both biogenic and anthropogenic hydrocarbons are primarily derived from riverine discharges and accumulate at shallow-water stations. Distinct phase associations lead, nevertheless, to different sedimentation patterns. Fossil PAHs are enhanced at offshore stations where they are introduced directly by shipping activities. Biomarker fingerprints ascribe their source to Chinese crude oils. The overall levels of anthropogenic hydrocarbons are low compared to relevant areas worldwide and reveal a low/moderate level of hydrocarbon pollution.

Hydrocarbon contamination of coastal sediments from the Sfax area (Tunisia), Mediterranean Sea

The coastal area off the city of Sfax (730,000 inhabitants), well-known for fisheries and industrial activities, receives high inputs of organic matter mostly anthropogenic. Eighteen stations were selected in the vicinity of the direct discharge of industrial sewage effluents in the sea in order to study the spatial distribution of the organic contamination. Surface sediments sampled in the shallow shelf were analysed for hydrocarbons by Fourier transform infrared spectroscopy, gas chromatography and gas chromatography/mass spectrometry. Total hydrocarbon distributions revealed high contamination as compared to other coastal Mediterranean sites, with an average concentration of 1865 ppm/dry weight sediment. Gas chromatographic distribution patterns, values of unresolved mixture/n-alkane ratio and distributions of steranes and hopanes confirmed a petroleum contamination of the Arabian light crude oil type. Biogenic compounds were also identified with a series of short-chain carbon-numbered n-alkenes in the carbon range 16-24.

Physicochemical Characterization of Natural and ex-Situ Reconstructed Sea-Surface Microlayers

Chemical composition and physico-chemical characteristics of natural and ex-situ reconstructed sea surface microlayer samples were studied using a complex methodological approach. Surface microlayer samples and the underlying seawater were collected in different seasons and different weather conditions in the northern most part of the Adriatic sea. The techniques used were thin layer chromatography with flame ionization detection for lipid classes analysis, electrochemical characterization of adsorbable organic substances using the ONP probe, and monolayer techniques for surface pressure (pi) and surface potential (DeltaV) measurements, as well as Brewster angle microscopy. Our results indicated higher enrichment of organic matter for the microlayer sample collected in the warm period of the year (summer). This was reflected in the high surface activity of the present organic substances, and formation of a more condensed layer than for the other two samples collected in the spring. Of the two spring samples, the one sampled on a sunny day was reacher in surface active organic material. We concluded that the most important source of surface active substances is the in-situ production of organic susbtances by the present plankton and bacteria, promoted by sunlight, while antrophogenic input comprises a smaller part of the present organic matter, around 10% for all samples. Copyright 1998 Academic Press.

Aliphatic and aromatic hydrocarbons in the mediterranean aerosol

The atmospheric transport of organic pollutants over long distances and their effect on the biological cycles of the sea are two major questions of concern in environmental chemistry. These processes are of particular importance in the Mediterranean Sea because of its semi-enclosed characteristics, which determine the accumulation of the pollutants entering into the system. In order to get some insight into these processes a project (PHYCEMED), was developed for the evaluation of the atmospheric budget of organic and inorganic substances in the Western Mediterranean and for the investigation of the exchange mechanisms of these materials across the air/sea interface. A high volume air sampling system including a cascade impactor was placed on board of the R/V le Suroit for collecting the aerosols along several transects parallel to the French, Spanish and North-African coasts, facing areas of different population densities and industrial activities. The cruise was realised on October 1983 and the particulate material was fractionated into the following sizes: 7.2, 3.0, 1.5, 0.96, and 0.03 micron. Quantitative and qualitative analyses of the aliphatic and the aromatic hydrocarbons present in these fractions were performed by high resolution gas chromatography and gas chromatography-mass spectrometry.

Hydrocarbons in the Western Mediterranean Sea, 1981

Hydrocarbons in the western Mediterranean Sea were analysed for surface microlayer and subsurface waters during April 1981. Three methods were used for determining both concentrations and markers distribution patterns: U.V. spectrofluorimetry, and original HPLC/U.V. spectrophotometry method and capillary gas liquid chromatography. No systematic relationship was found between concentrations determined by U.V. spectrofluorimetry and HPLC/U.V. spectrophotometry. Concentrations variation ranges are: 0.01-0.20 microgram 1(-1) for dissolved aromatic hydrocarbons; 0.02-0.13 microgram 1(-1) for particulate aromatic hydrocarbons; 0.02-20.57 micrograms 1(-1) for dissolved n-alkanes; 0.13-0.83 microgram 1(-1) for particulate n-alkanes. Surficial waters appear as very slightly polluted with an exception the Ligurian Sea for which highest concentrations were encountered. There is a slight enrichment of particulate hydrocarbons in the surface microlayer in the range 1-3. But, dissolved hydrocarbons can be either depleted or enriched up to 270 times in the surface microlayer, indicating the extreme efficiency of sea-air exchange processes. Aromatic fingerprints and n-alkane distribution patterns are discussed both for pollution and fractionation processes indicators at the sea-air interface.

The diversity of marine sterols and the role of algal bio-masses; from facts to hypothesis

Modern analytical methods have revealed the great variety of marine sterols, which possess many different side chains and unsaturation patterns. Such biochemical transformations require well-defined mechanistic pathways, and there must be some 'Raison d'Etre' for a situation which has withstood evolution and adaptive changes. However, in this area, insufficient and sometimes not very substantial experimental work has made it difficult to see correlations, and hence to form a solid hypothesis. A review is now presented in which the molecules dissolved in sea water, or found in marine organisms are considered with particular reference to algal production, and to the bio-ecological significance of the main sterols.