certain chemical species which are easily degradable and/or soluble, 

 such as n-alkanes, light aromatics, etc... leaving a higher relative 

 concentration of sulfurous species, which are more resistant to degra- 

 dation. Metal concentrations (nickel and vanadium) , and their ratio, 

 did not vary significantly through the one-year pariod of the study 

 (Table 9) . This behavior was noted above in the discussion of the Aber 

 Wrac'h samples. 



TABLE 9. Sulfur, nickel and vanadium contents. 



As we did with the samples of emulsified mousse, as described 

 above (Fig. 24), we recorded the saturated and aromatic hydrocarbons, 

 and the polar compounds (resins and asphaltenes) on the triangular 

 diagram (Table 8) . 



The most notable evolution took place in the latest samplings 

 of polluted sand. But it is difficult to isolate the factors contri- 

 buting to evolution in the beach sands : time, extent of dispersion 

 of' the crude, how long the oil was on the sea, the support material 

 (sand, mud, rocks) . This is all the more true of a sampling taken a 

 year after the catastrophe, which may have undergone a very complex 

 history of burial before being picked up again by the water during a 

 storm or a spring tide. Even with these reservations, however, it 

 seems that the triangular diagram shows that the crude follows several 

 pathways in its evolution : 



- a very short and stable pathway, as we saw above in emulsions on 

 free water ; 



- a pathway in which a relatively slow disappearance of saturated 

 hydrocarbons (n-alkanes) and aromatics (Mono- and diaromatics) 

 results in a moderate increase in polar products, when the crude is 

 trapped in sand ,- 



- an evolving pathway followed by crude which is trapped in more or 

 less muddy subtital sediments of the Aber Wrac'h, as demonstrated 

 above . 



The chromatograms of the saturated hydrocarbons in the polluted 

 samples taken in 1979 all show a general degradation of n-paraffins to 

 n-C30, confirmed by an increase in the ratios of isoprenoids to 

 n-alkanes (n-C17 and n-C18). This degradation seems slower in polluted 

 beach sands than in the sediments of the Aber Wrac'h. 



The mass spectrometry study of the (n+iso) distribution, and 

 that of the 1- to 6-membered rings of cycloparaf f ins confirms this 



138 



