contents determined by mass spectrometry are on the order of 5 3 %. 

 Cyclane contents decrease gradually from 14.2 % for the single- 

 membered cycloparaf fin rings, to 2.3 % for six-membered rings. 



The combination of gas-phase chromatography with mass spectro- 

 metry (GPC/MS) made it possible to distinguish the components of the 

 aromatic fraction : monoaromatic, diaromatic, and triaromatic hydro- 

 carbons . 



Aromatic sulfur compounds of the thiophenic type are the benzo- 

 thiophenes, dibenzothiophenes, and naphthobenzothiophenes. 



Polar compounds (resins) contain oxygenated functions (princi- 

 pally hydroxyls and carboxyls) shown by infra-red spectrometer ana- 

 lysis. Elemental analysis of this resin fraction made it possible to 

 assess contents of the following elements : 



C = 78 % 



H = 8.9 % 



N = 1.5 % 



= 4.5 % 



In this case, the oxygen content is not calculated by subtracting 

 the total of the other contents from 100 %, but is titrated by the 

 Unterzaucher method. 



Asphaltene compounds, separated from the oil by cold-hexane 

 precipitation, are known to have very complex laminated structures. 



Metal (such as nickel and vanadium) and sulfur contents were 

 determined on a dry extract before deasphalting (Fig. 2). Metals are 

 essentially present in heavy fractions of crude (resins and asphal- 

 tenes) as chelate compounds. Their contents range from 14 to 16.5 ppm 

 for nickel and from 45 to 60 ppm for vanadium, with a ratio Ni/V of 

 0.27 to 0.31. Sulfur contents are on the order of 2.35 % by weight. 



These determinations will eventually serve as a point of depar- 

 ture in following the pathways of the pollutant. It is to be noted 

 that this study is not intended to cover the light evaporated and/or 

 dissolved third of the cargo, of which about 25,000 tons is light 

 aromatic hydrocarbons. Benzene, toluene, and xylene are estimated at 

 respectively 3,300, 4,600, and 3,000 tons. 



EVOLUTION OF THE PHYSICO-CHEMICAL PARAMETERS OF THE HYDROCARBONS 



We followed the chemical evolution of the hydrocarbons in three 

 different types of samples taken from three areas of pollution : 



- subtidal sediments (Aber Wrac'h) ; 



- water surface-stable emulsions (hydrocarbons with water, or "choco- 

 late mousse") ; 



- intertidal sediments (beaches) . 



The Subtidal Sediments of the Aber Wrac'h 



A detailed study of these sediments was made by DUCREUX and 

 MARCHAND (1979) (collaboration IFP/COB) . The evolution of the 



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