and phytane/n-Cl8 were among the highest and that this degradation was 

 among the most advanced (Table I). In figure 5, a continual decrease 

 in saturated hydrocarbons is noted over time (33 % on March 31, 1978 

 — 22 % on June 24, 1980). In spite of a maximum aromatic hudrocarbons 

 content observed in June 1979, they underwent the same type of evolu- 

 tion (34.3 % on March 31, 1978 -> 24.8 % on June 24, 1980). The result 

 is an increase in the relative contents of resins ; but it should be 

 noted that in March 1978, polar compound contents (24.6 %) were higher 

 at this station, which is located in the outer part of the Aber, than 

 at Station 5 (17.2 %) where the marine character is more pronounced. 

 This level held true until June 1979, when the increase became the 

 same as at Station 5 . 



This phenomenon can be explained by the presence of polar com- 

 pounds of terrestrial origin deposited by the river which flows into 

 the Aber. This contribution of autochthonous organic matter is seen 

 in the presence of n-alkanes of odd carbon numbers (n-C25, 27, 29, 31, 

 33) in the aliphatic fraction, all the more accentuated by the signi- 

 ficant acceleration in the degradation of the normal fossil paraffins 

 (Fig. 12) The result is a relative enrichment in cyclic satured hydro- 

 carbons (cycloparaf fins) — particularly of 3-, 4-, and 5-membered 

 rings around n-C30 — which are less easily degradable . 



Chromatogram profiles of the aromatic hydrocarbons indicate how 

 polluted the station is, principally in the FDP response (Fig. 13), 

 where the persistence of dibenzothiophene and its alkylate derivatives 

 (and also of naphthobenzothiophenes) may be noted. The stability of 

 these compounds made it possible for us to use these chromatograms as 

 the "fingerprints" of the pollution. 



As a matter of fact, according to the DGMK. report, biogenic 

 hydrocarbons of terrestrial origin (recent sediments) are poor in 

 aromatic compounds (< 5 %) , and particularly low in sulfurous com- 

 pounds of the thiophenic type. 



The evolutions observed in the resins are similar to those at 

 Station 5 ; an oxidizing degradation increases the oxygen contents 

 (8.5 % in June 1980), and an upward curve is noted in the infra-red 

 absorption bands of the hydroxyls and carbonyls, the latter of which 

 are predominantly carboxylic acid compounds (Fig. 14). Metal and sul- 

 fur contents remain fairly constant over time. 



Station 8 



This station was distinguished in being the farthest from the 

 sea, in an area of sandy mud. Hydrocarbon contents show that the 

 decontamination process at this station was virtually nil (Fig. 4) . 



An anomaly is noted in January 1980, when the hydrocarbon con- 

 tents went over 5,000 mg-/kg of sediment. As we shall see below, this 

 is due to pollution from petroleum cuts or fuel oil which was later 

 deposited on top of the pollution under study (Fig. 15 and 16). Al- 

 through information is lacking on some samples, which were too small, 

 it can be seen that metal and sulfur contents remained very stable 

 over time. 



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