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The fatty acid composition of the marine phototrophic bacterium Erythrobacter sp. strain MG3 was analysed. The involvement of an unusual enzymatic peroxidation of the allylic carbon 10 of cis-vaccenic acid in this strain was confirmed. This process, which seems to be a characteristic of some aerobic and anaerobic phototrophic bacteria, appeared to also act on the allylic carbon 10 of octadeca-5,11-dienoic acid. Enzymatic degradation of 10-hydroperoxyoctadec-11(cis)-enoic acid resulting from the peroxidation of cis-vaccenic acid mainly involves reduction to the corresponding hydroxy acid (probably catalysed by peroxygenases) and cleavage to the corresponding oxoacid, which is then biohydrogenated. Abiotic degradation of this hydroperoxide involves allylic rearrangement to 10-hydroperoxyoctadec-11(trans)-enoic and 12-hydroperoxyoctadec-10(trans)-enoic acids and cyclisation to the very unusual 7,10-epoxyoctadec-11(cis)-enoic acid. Several tests carried out at different periods of growth and under different growth conditions allowed to show that the induction of this enzymatic peroxidation process strongly depends on the physiological state of the cells and is enhanced during C-limitation and at low temperatures.

The electron ionization (EI) mass spectral fragmentation of the bis- and tris-trimethylsilyl derivatives of cholestane-3beta,4alpha,5alpha-triol, cholestane-3beta,5alpha,6beta-triol and cholestane-3beta,5alpha,6alpha-triol was investigated. The EI mass spectrum of the 3beta,4alpha-bis-trimethylsilyl derivative of cholestane-3beta,4alpha,5alpha-triol exhibits interesting fragment ions at m/z 142 and 332 resulting from the initial loss of TMSOH between the carbons 2 and 3 and subsequent retro-Diels-Alder (RDA) cleavage of the ring A. Trimethylsilyl transfer between the 4alpha- and the 5alpha-hydroxy groups acts significantly before RDA cleavage affording an ion at m/z 404. Complete silylation of cholestane-3beta,4alpha,5alpha-triol strongly stabilizes the molecule, affording an abundant molecular ion at m/z 636 and decreasing the abundance of the RDA cleavage. Loss of water (from the non-silylated 5alpha-hydroxy group) plays a very important role during the decomposition of the molecular ion of 3beta,6alpha/beta-bis-trimethylsilyl derivatives of cholestane-3beta,5alpha,6alpha/beta-triols. These derivatives appear to be very useful in assigning the configuration of the carbon 6. This assignment is based on the abundance of the fragment ions at m/z 321, 367 and 403, which are more prominent in the EI mass spectrum of the beta-isomer. In contrast, EI mass spectra of the tris-trimethylsilyl derivatives of cholestane-3beta,5alpha,6beta-triol and cholestane-3beta,5alpha,6alpha-triol differ only slightly and appear to be poorly informative.

The electron ionization (EI) mass spectral fragmentation of ω-hydroxycarboxylic and ω-dicarboxylic acid trimethylsilyl derivatives was investigated. The mass spectra of these compounds exhibited fragment ions resulting from classical fragmentation of the trimethylsilyl ether and ester groups, and others resulting from the interactions between the two functionalities (m/z 147, 204, 217, [M–31]+ and [M–105]+ in the case of ω-hydroxycarboxylic acid derivatives and m/z 147, 204, 217 and [M–131]+ in the case of ω-dicarboxylic acid derivatives). Several fragmentation pathways were proposed to explain the formation of these different fragment ions. It is proposed that the ions at m/z 204 and 217 are formed via an initial trimethylsilyl transfer between the ether and the ester group or between the two ester groups. This transfer appeared to be more favoured in the case of ω-dicarboxylic acid derivatives and to be dependent on the chain length. A more efficient transfer was in fact observed for compounds with a relatively long alkyl chain. In the case of shorter ω-hydroxycarboxylic and ω-dicarboxylic acid trimethylsilyl derivatives the formation of the ions at m/z 204 and 217 suffers strongly from competition from production of the ion at m/z 147. Copyright © 2004 John Wiley & Sons, Ltd.

The electron ionization (EI) mass spectra of saturated and α,β-unsaturated C19 isoprenoid aldehydes and carboxylic acid methyl and trimethylsilyl esters are reported. Different pathways are proposed in order to explain the main fragmentations observed. The conjugated double bond migrates more or less readily before γ-hydrogen rearrangement according to the structure of the considered compound. Configurations of the double bond of α,β-unsaturated C19 isoprenoid aldehydes and fatty acid methyl and trimethylsilyl esters can be easily determined thanks to the peaks at m/z 97, 127 and 185, respectively, which are much more abundant in the mass spectra of the Z isomers owing to the formation of a cyclic ion. In the case of trimethylsilyl esters, subsequent fragmentation of the cyclic ion at m/z 185 affords two other diagnostic ions at m/z 95 and 169. Copyright © 2003 John Wiley & Sons, Ltd.

Analytically useful pentafluoro ketone derivatives of fatty acids are described. The gas chromatographic/mass spectrometric characteristics of these new derivatives are compared with those of methyl, trimethylsilyl and pentafluorobenzyl esters. Pentafluoro ketones exhibit excellent chromatographic properties and significantly shorter chromatographic retention times than these other esters. The electron impact mass spectra of these new compounds show informative acylium ions, whose intensity decreases with the degree of unsaturation of the parent fatty acid. The formation of strong and informative fragment ions in negative chemical ionization (CH(4)) mass spectra of pentafluoro ketone derivatives allows the detection and the characterization (length of the chain and number of double bonds) of fatty acids at trace levels (femtomole), even in the case of polyunsaturated compounds. The scope and limitations of this new derivatization technique are also discussed.

The photodegradation rates of chlorophyll-a and phytol in both its esterified and free forms were followed in killed cells of Phaeodactylum tricornutum Bohlin, a diatom possessing a strong chlorophyllase activity. The Chlorophyll Phytyl side chain Photodegradation Index (CPPI), defined as the molar ratio of phytyldiol (a specific photoproduct of the phytyl chain) versus phytol, was used to estimate the chlorophyll-a photodegradation rate. Despite the strong chlorophyllase activity of this alga and the high photoreactivity of free phytol, the CPPI gave a good estimation of the chlorophyll-a photodegradation state. These estimates were good for the axenic and non-axenic incubations, since aerobic bacterial degradation processes act upon free phytyldiol and phytol without high selectivity.

Various derivatization methods have been tested for their usefulness in determining the position of double bonds in α,β- and β,γ-unsaturated isoprenoid acids by gas chromatography/electron ionization mass spectrometry. Stereospecific oxidation with osmium tetroxide followed by trimethylsilylation gave positive results, while the use of dimethyl disulphide, epoxide and pyrrolidide derivatives must be discarded. Configurations of the double bonds of α,β-unsaturated isoprenoid acids could be easily determined from electron ionization mass spectra of their methyl and trimethylsilyl esters. © 1998 John Wiley & Sons, Ltd.

The light-induced degradation of unsaturated fatty acids in killed phytoplanktonic cells seems to involve mainly singlet oxygen and to a lesser extent radical oxidation. These processes afford isomeric allylic hydroperoxyacids, which are then either reduced to the corresponding hydroxyacids or cleaved to ω-oxocarboxylic acids and aldehydes (Hock cleavage). α,ω-Dicarboxylic acids are also produced by subsequent oxidation of the corresponding ω-oxocarboxylic acids. These different compounds constitute useful markers of photooxidative alterations of phytoplanktonic populations.

Irradiation of killed cells of Skeletonema costation resulted in a quick photodegradation of the sterol components of this algae. Light-dependent degradation rates of these compounds showed a good fit to apparent first-order kinetics. Identification of the main photoproducts using gas chromatography/electron impact mass spectrometry analyses demonstrated that sterol photodegradation in killed cells of phytoplankton involved pure type II (i.e. involving singlet oxygen) photoprocesse 5α- and 6α/6β-hydroperoxides, which constitute the bulk of the sterol photoproducts, appeared to be relatively stable in phytodetritus and are proposed as potential markers of photodegradation processes in the marine environment.

Reactions of singlet oxygen (1O2) with isomeric phytadienes appear strongly regioselective. Rate constants are discussed.

3,7,11,15-Tetramethyl-2-hexadecen-1-yl propionate (a model for the intact phytyl side chain of chlorophyll), 3-hydroxy-3,7,11,15-tetramethyl-1-hexadecen-1-yl propionate and 2-hydroxy-3-methylidene-7,11,15-trimethylhexadecyl propionate (models for a photo-oxidized chlorophyll phytyl chain) were heated in the presence of montmorillonite in order to simulate their abiotic degradation under geological conditions. Thermo-catalytic breakdown of phytyl propionate yielded most of the degradation products previously generated from phytol by heating in the presence of clays. Some interesting mechanisms involving protonation of the phytol double bond are proposed to explain the formation of phytanal and prist-1-ene observed during these manipulations. The abiotic degradation of 3-hydroxy-3,7,11,15-tetramethyl-1-hexadecen-1-yl propionate led to the production of 6,10,14-trimethylpentadecan-2-one, phytenals and phytenic acids as major products, whereas 2-hydroxy-3-methylidene-7,11,15-trimethylhexadecyl propionate afforded 6,10,14-trimethylpentadecan-2-one, 3,7,11,15-tetramethyl-2-oxohexadecanol-1 and 3,7,11,15-tetramethylhexadecan-1,2,3-triol. A kinetic study allowed comparison of the abiotic stability of intact and photooxidized chlorophyll phytyl chains in sediments and suggested potential markers for monitoring chlorophyll photodegradation.

The photodegradation rates of chlorophylls in their entirety and chlorophyll phytyl chains were compared in dead phytoplanktonic cells. The experimentally determined degradation rates were approximately five to eight times higher for the chlorophyll tetrapyrrolic structure than for the phytyl chain. Analysis of the photoproducts clearly established that the photodegradation of this isoprenoid chain involved mainly singlet oxygen. On the basis of the results obtained, it is predicted that a non-negligible part of the phytoplanktonic chlorophyll phytyl chain will be photodegraded during senescence in the upper portion of the euphotic zone of the oceans.

Oxidation of E phytol and chlorophyll a phytyl chain by hydroxyl and peroxy radicals yielded several interesting isoprenoid compounds. Gas chromatography (GC) and GC—mass spectrometry analyses allowed us to identify notably 6,10,14-trimethylpentadecan-2-one, Z and E phytenals, Z and E 3,7,11,15-tetramethyl-2,3-epoxyhexadecanols and 3,7,11,15-tetramethylhexadecan-1,2,3-triol. Different mechanisms were proposed to explain the formation of these degradation products. The detection of Z and E 3,7,11,15-tetramethyl-2,3-epoxyhexadecanols and 3,7,11,15-tetramethylhexadecan-1, 2,3-triol after photodegradation of chlorophyll a in sea water shows that oxy-free radicals act parallel to 1 O 2 on the phytyl chain during the photodestructive oxidation of this pigment.

Solar light irradiation of chloroform solutions or aqueous dispersions of cholesterol in the presence of anthraquinone (a powerful sensitizer of hydrogen-atom abstraction) yielded several photoproducts of which six compounds were identified using gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) analyses. Non-acidic photoproducts (originating essentially from an initial hydrogen-atom abstraction at the carbon 7 position of the cholesterol molecule) included epimeric cholest-5-ene-3β,7-diols, 3β-hydroxy-cholest-5-en-7-one, cholesta-3,5-dien-7-one and2,3,3aα,6,7,7aα-hexahydro-7a-methyl-β-(1,5-dimethylhexyl)-indene. 2,6-Dimethylheptanoic acid, an interesting acidic cholesterol photoproduct derived from an attack of the carbon 17 position, was also detected. Different mechanisms were proposed to explain the formation of these compounds.

A non-negligible production of 6,10,14-trimethylpentadecan-2-one has been often observed during aerobic phytol incubations with bacteria. In this work involving a marine Acinetobacter , a combination of biotic and abiotic processes is proposed in order to explain this phenomenon. In seawater, phytenal produced by bacterial oxidation of phytol can be converted abiotically to this isoprenoid ketone after addition of a water molecule and subsequent retro-aldol reaction. This abiotic process is very sensitive to temperature. It was demonstrated in this study that at 30°C an important part of phytol is metabolized through 6,10,14-trimethylpentadecan-2-one, whereas this pathway practically disappeares at 13°C. Consequently, in studies concerning phytol biodegradation, it will be important to take into account the effect of temperature.

Photodegradation of chlorophyll-a in seawater leads to the formation of some relatively stable photoproducts, acidic or alkaline hydrolysis of which affords 6,10,14-trimethylpentadecan-2-one. Owing to their high polarity, these compounds are not extracted during Soxhlet extraction of sediments with chloroform, but can be recovered in part in the form of 6,10,14-trimethylpentadecan-2-one after acidic and alkaline hydrolysis of the Soxhlet extraction residues. Hence, we suggest the use of this “bound” ketone as a marker for the photodegradation of chlorophylls with a phytol ester group in the marine environment.

Experiments carried out in vitro in the presence of anthraquinone allowed to simulate the photosensitized oxidation of linear and isoprenoid alkanes in the marine environment. The main acidic photoproducts formed after solar irradiation were identified by gas chromatography and gas chromatography/mass spectrometry and different mechanisms were proposed in order to explain their production. The detection of most of these photoproducts among the acidic compounds formed during the photodegradation of a petroleum fraction proved the suitability of anthraquinone as a model sensitizer for studies of the photochemical degradation of petroleum saturated hydrocarbons in water.

A suspension of chlorophyll- a in synthetic seawater was irradiated with solar light until bleaching. After irradiation, methyl ethyl maleimide and several isoprenoid photoproducts were identified by gas chromatography and gas chromatography/mass spectrometry analyses. In order to explain the formation of these isoprenoid compounds, various mechanisms involving the initial addition of singlet oxygen on the double bond of the chlorophyll- a phytyl chain were proposed. The photosensitized oxidation of phytyl propionate in the presence of haematoporphyrin confirmed these mechanisms.

A crude oil hydrocarbon fraction was photooxidized as a surface film on seawater under simulated environmental conditions. After irradiation, gas chromatography and gas chromatography/mass spectrometry analyses allowed to demonstrate the presence of relatively high quantities of compounds deriving from the photosensitized oxidation of n-alkanes, pristane and phytane, being among the non-acidic photoproducts of this fraction. The results suggest that the photochemical degradation of alkanes should be considered in studies of the fate of petroleum crudes in the marine environment.

cis -Decalin and trans -decalin were photooxidized in chloroform by sunlight in the presence of anthraquinone as sensitizer. The main photosensitized oxidation mechanisms, which act on all the carbon atoms of these molecules, were described and it appeared that steric factors strongly influenced their selectivity. An interesting photoisomerization mechanism of cis -1-decalone and trans -1-decalone was also proposed.

The acyclic isoprenoid aldehydes—E and Z 3,7,11,15-tetramethylhexadec-2-enal (phytenals) and 2,6,10,14-tetramethylpentadecanal (pristanal), themselves previously shown to be products of the photosensitized oxidation of phytol in seawater—were stirred in the dark in synthetic seawater. Examination of the products showed that the phytenals were partially transformed to the corresponding unsaturated acids and the ketone 6,10,14-trimethylpentadecan-2-one, whereas pristanal was converted solely to the corresponding acid. A new pathway for abiotic production of acyclic isoprenoids in the water column is postulated. This theory is supported by the identification of several of the compounds in particulate matter and sediments from the Gulf of Lyon (Mediterranean Sea).

The electron ionization (EI) mass spectral fragmentation of the bis- and tris-trimethylsilyl derivatives of cholestane-3beta,4alpha,5alpha-triol, cholestane-3beta,5alpha,6beta-triol and cholestane-3beta,5alpha,6alpha-triol was investigated. The EI mass spectrum of the 3beta,4alpha-bis-trimethylsilyl derivative of cholestane-3beta,4alpha,5alpha-triol exhibits interesting fragment ions at m/z 142 and 332 resulting from the initial loss of TMSOH between the carbons 2 and 3 and subsequent retro-Diels-Alder (RDA) cleavage of the ring A. Trimethylsilyl transfer between the 4alpha- and the 5alpha-hydroxy groups acts significantly before RDA cleavage affording an ion at m/z 404. Complete silylation of cholestane-3beta,4alpha,5alpha-triol strongly stabilizes the molecule, affording an abundant molecular ion at m/z 636 and decreasing the abundance of the RDA cleavage. Loss of water (from the non-silylated 5alpha-hydroxy group) plays a very important role during the decomposition of the molecular ion of 3beta,6alpha/beta-bis-trimethylsilyl derivatives of cholestane-3beta,5alpha,6alpha/beta-triols. These derivatives appear to be very useful in assigning the configuration of the carbon 6. This assignment is based on the abundance of the fragment ions at m/z 321, 367 and 403, which are more prominent in the EI mass spectrum of the beta-isomer. In contrast, EI mass spectra of the tris-trimethylsilyl derivatives of cholestane-3beta,5alpha,6beta-triol and cholestane-3beta,5alpha,6alpha-triol differ only slightly and appear to be poorly informative.

The FA composition of 12 strains of marine aerobic anoxygenic phototrophic bacteria belonging to the genera Erythrobacter, Roseobacter, and Citromicrobium was investigated. GC-MS analyses of different types of derivatives were performed to determine the structures of the main FA present in these organisms. All the analyzed strains contained the relatively rare 11-methyloctadec-12-enoic acid, and three contained 12-methyl-octadec-11-enoic acid, which has apparently never been reported before. High amounts of the very unusual octadeca-5,11-dienoic acid were present in 9 of the 12 strains analyzed. A FA containing a furan ring was detected in three strains. Analytical data indicated that this FA was 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid. A very interesting enzymatic peroxidation of the allylic carbon 10 of cis-vaccenic acid was observed in three strains. Deuterium labeling and GC-MS analyses enabled us to demonstrate that this enzymatic process involves the initial dioxygenase-mediated formation of 10-hydroperoxyoctadec-11(cis)-enoic acid, which is then isomerized to 10-hydroperoxyoctadec-11(trans)-enoic acid and converted to the corresponding hydroxy-acids and oxoacids. Different biosynthetic pathways were proposed for these different compounds.

The electron ionization (EI) mass spectral fragmentation of the trimethylsilyl derivatives of 3-methylidene-7,11,15-trimethylhexadecane-1,2-diol, Z- and E-3,7,11,15-tetramethylhexadec-3-ene-1,2-diols and Z- and E-3,7,11,15-tetramethylhexadec-2-ene-1,4-diols resulting from chlorophyll phytyl side-chain photo- and autoxidation was investigated. Different pathways (substantiated by deuterium labelling) were proposed in order to explain the main fragmentation observed. Then, some sufficiently specific fragment ions were selected and used to characterize these compounds in natural environmental samples.

Recently, there has been a renewal of interest concerning the study of heterogeneous visible light-induced degradative reactions of lipid compounds associated with phytodetritus. The present paper reviews the results obtained in the course of these studies. In a first part, the photo-oxidation of the main lipid cell components (chlorophyll phytyl chain, carotenoids, sterols, unsaturated fatty acids, alkenones and unsaturated alkenes) in senescent phototrophic organisms (phytoplankton, cyanobacteria, higher plants, purple sulfur bacteria and aerobic anoxygenic phototrophic bacteria) is examined. Emphasis is given to the structure and the tracer potentialities of the photoproducts formed. This part also describes the induction of visible light-induced photoprocesses in attached heterotrophic bacteria during the senescence of phytoplankton, which was recently demonstrated. The second part of this review deals with the characterization of these photoproducts in different particulate matter, recent sediment and microbial mat samples collected in the north-western Mediterranean Sea and to the use of some of them as stress indicators.

The electron ionization (EI) mass spectral fragmentation of derivatized 4,5- and 5,6-epoxysterols was investigated. Interesting fragmentation processes involving a transannular cleavage of the epoxide ring after transfer of the trimethylsilyl group are significant in the case of 4,5-epoxysterol trimethylsilyl ethers (affording abundant fragment ions at m/z 403 and 404). Different pathways, which have been substantiated by deuterium labelling, are proposed in order to explain the formation of these ions. In contrast, this transfer is not significant in the case of 5,6-epoxysterol trimethylsilyl ethers. The EI mass spectra of these latter compounds appear to be very complex and to differ slightly according to the stereochemistry of the epoxy group. Acetate and trifluoroacetate derivatives of 4,5-epoxysterols display interesting EI mass spectra dominated by a fragment ion at m/z 332 resulting from cleavage of the steroid ring A. Copyright © 2004 John Wiley & Sons, Ltd.

Positive-ion chemical ionization (CI) mass fragmentations were studied in the case of different 1,3-dioxolanes. The formation in methane CI mass spectra of interesting fragment ions allowing the characterization of their parent carbonyl compounds and diols is discussed and some mechanisms (supported by D2O CI analyses) are proposed in order to explain these fragmentations.

Analytically useful pentafluoro ketone derivatives of fatty acids are described. The gas chromatographic/mass spectrometric characteristics of these new derivatives are compared with those of methyl, trimethylsilyl and pentafluorobenzyl esters. Pentafluoro ketones exhibit excellent chromatographic properties and significantly shorter chromatographic retention times than these other esters. The electron impact mass spectra of these new compounds show informative acylium ions, whose intensity decreases with the degree of unsaturation of the parent fatty acid. The formation of strong and informative fragment ions in negative chemical ionization (CH(4)) mass spectra of pentafluoro ketone derivatives allows the detection and the characterization (length of the chain and number of double bonds) of fatty acids at trace levels (femtomole), even in the case of polyunsaturated compounds. The scope and limitations of this new derivatization technique are also discussed.

This paper reviews the rates, pattern and possible mechanisms of light-induced degradation of lipidic components in detritus derived from phytoplankton. After a brief discussion of the main photooxidation reactions which can occur in the euphotic zone of the oceans, emphasis is given to the photodegradation of lipids during the senescence of phytoplankton. Production and quenching of excited states of chlorophyll and toxic oxygen species (singlet oxygen, Superoxide ion, hydroxyl radical and hydrogen peroxide) in healthy and senescent cells are discussed and the photooxidation of the main lipidic cell components (chlorophylls, carotenoids, fatty acids, sterols, alkenones and hydrocarbons) is examined. Areas requiring further work are indicated.

n-Butylcyclohexane was photo-oxidized by solar light on synthetic seawater containing traces of anthraquinone. After identification of the main photoproducts formed, it appeared that the photochemical processes acted essentially on the carbons of the cycle, leading in the case of the secondary carbons to the formation of different n-butylcyclohexanones and of the corresponding alcohols. The tertiary branched carbon undergoes different reactions which lead to opening of the cycle or to breakdown of the alkyl chain (formation of cyclohexanone).

In the presence of a photosensitizer (anthraquinone) a surface film of pristane on synthetic sea water was photo-oxidized by sunlight. The photochemical processes are affected not only by the secondary carbons (producing different 2,6,10,14-tetramethylpentadecanones), but also, and more strongly, by the tertiary carbons. This photo-oxidation leads on the one hand to the formation of tertiary alcohols and on the other hand, after α-cleavage reactions, to different fragmentations of the pristane molecule into alkanes and ketones. These very important results provide new information that must be taken into account when considering the degradation of branched alkanes in a marine environment.

A mixed bacteria population (EM4) was isolated from foams formed on the surface of a zone chromically polluted by hydrocarbons (Gulf of Fos, French Mediterranean coast, October 1981). The population was able to degrade crude oil very effectively in the presence of sea water supplemented with nitrogen, phosphorus and iron. The percentage of hydrocarbon degradation was 81% at 30°C, pH 8, and partial oxygen pressure of 100%. After 12 d incubation, 92 and 83% of satured and aromatic compounds (mono-, di- and triaromatics) were degraded, respectively, as well as 63% of polar products and 48.5% of asphaltenes. Maximum degradation was attained at a sodium chloride concentration of between 400 and 800 mM with Population EM4, which is constituted of 8 strains, four of which are weak halophiles. Bacterial growth on hydrocarbons induces the production in the culture medium of surface-active agents which are able to emulsify the substrate. There is high specificity between the nature of the growth substrate and such emulsifying activity, particularly as far as petroleum is concerned: only the culture medium from Population EM4 is able to emulsify petroleum. These surface-active agents contain sugars and lipids (fatty acids, mono- and diglycerides). The foams, which always contain a high concentration of both hydrocarbons (100 to 180 mgl-1) and bacteria that are able to grow on these types of substrates, have a strong emulsifying activity. Our results would seem to demonstrate the importance of biosurfactants in the elimination of hydrocarbons from polluted biotopes.

In synthetic seawater containing traces of anthraquinone, phytol is photo-oxidized rapidly by solar radiation. The photochemical processes lead mainly to the formation of 2,6,10-trimethyltridecane, 6,10,14-trimethyl-2-pentadecanone, pristanal and phytenal. In order to explain the formation of these different compounds, mechanisms which first involve abstraction reactions of hydrogen atoms in an allylic position are proposed. These results suggest a non-negligible photodegration of the free phytol in seawater before its incorporation into the marine sediments.

In a general study on the petroleum contamination of the Fos-sur-mer Gulf (Mediterranean Sea), the surface microlayer was sampled. We present here the first results reported up to date in this area, based on a sampling carried out with a rotating PVC drum at 3 stations in May 1985. Very high hydrocarbons concentrations were sometimes observed in the surface film, which appears more heterogeneous than the underlaying water column (0.5-2m). Water samples were filtered through fiberglass filters (0.5-1 μm). Both dissolved and particulate phases were separately extracted and analysed, providing evidence that suspended particles are the major vector for the accumulation and the transport of petroleum pollutants in these neritic waters. The petroleum origin of “total hydrocarbons” fractions is confirmed by GC and HPLC which reveal characteristic features for n-alkanes and polynuclear aromatic hydrocarbons. HPLC analysis of polar (non-hydrocarbons) fractions could indicate their formation from petroleum...

The influence of n-butyl group position upon the fragmentation behavior of the three isomeric n-butylcyclohexanones was studied. The different fragmentation processes are described and have been applied to the differentiation of the positional isomers of long-chain n-alkylcyclohexanones. In the case of the 4-n-alkyl isomers, an interesting mechanism involving a recyclization is proposed and substantiated by deuterium labelling.

The degradation of crude oil in continuous culture of a mixed bacteria population has been studied. The degradation percentage reaches 83 % with a 0.05 h-1 dilution rate and a 6 g 1-1 crude oil concentration. The different crude oil compounds : saturated, aromatic, polar hydrocarbons and asphaltenes are degraded at 97 %, 81 %, 52 % and 74 % respectively.

Very polar oil compounds are predominant in the resulting water soluble fraction (WSF) of crude oil, in agreement with their high solubility in seawater. Non‐volatile hydrocarbons represent only a low proportion of total soluble extracts. The experimental process we have achieved allows us to obtain quantitative and reproducible soluble oil extracts that could be used in ecotoxicological tests and for the study and the characterization of marine oil pollution.