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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 evolution
(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 compounds
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 significant
acceleration in the degradation of the normal fossil paraffins
(Fig. 12) The result is a relative enrichment in cyclic satured hydrocarbons
(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 compounds
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 sulfur
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 contents
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). Althrough
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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