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affected a very large section of the western English Channel. One month
after the AMOCO CADIZ wreck, the most polluted areas were located in the
coastal zones, such as the Aber zone (38.9 + 6.7 ug/l) , the Bay of
Morlaix (11.5 + 5.1 ug/1), and the Bay of Lannion (10.7 + 3.0 ug/1) .
Analysis of samples from various depths revealed that the contamination
extended throughout the water column. The 49°N parallel roughly constituted
the northern limit of pollution. Beyond this limit, oil in
surface seawater was not observed (1.6 + 0.5 jug/1) . In March 1979, one
year after the AMOCO CADIZ stranding, hydrocarbon concentrations
returned to a normal level (below 2.0 ug/1) ; however, some residual
traces of pollution were still observed near the Abers and at the bottom
of the Bay of Lannion (about 2.0 ug/1).
We also began a chemical follow-up study of oil pollution in marine
sediments. Some data have already been presented during the international
symposium held in Brest (France) in November 1979 (CNEXO, 1981;
Ducreux and Marchand, 1981; Marchand, 1981; Marchand and Caprais, 1981) .
In this document, results of our study are presented in three
parts: (1) oil pollution in sediments collected from the western
English Channel one month after the wreck, (2) specific study in the
Bays of Morlaix and Lannion to determine the distribution of oil
pollution in surface sediments and at various depths, and the evolution
of oil contamination over one year, and (3) specific study of the Aber
Wrac'h to determine oil evolution from 1978 to 1981.
MATERIAL AND METHODS
Surface marine sediments were collected in the western English
Channel with a Shipek grab. In coastal areas, small Ekman and Hamon
grabs were used. The samples, after freezer storage, were dried by
using a Soxhlet apparatus or by stirring with chloroform. The organic
extract was concentrated to dryness, then dissolved with 10 ml of carbon
tetrachloride. A first indication of petroleum pollution in sediment
was obtained through a direct analysis of nonpurified extracts by IR
spectrophotometry (Perkin Elmer 397). Quantitative measurements were
carried out at 2920 cm corresponding to the presence of hydrocarbons
and polar compounds. The data also reflect coextracted
substances (fats, fatty acids, etc.) from sediments.
spectrophotometer was calibrated with a mixture of Arabian and
natural
The IR
Iranian
light crude oils.
Hydrocarbons were analyzed after cleanup of organic extracts on
activated Florisil (200°C) in glass columns (15 cm x 0.6 cm i.d.).
Hydrocarbons were eluted with 15 ml of carbon tetrachloride and measured
by IR spectrophotometry. For some samples, organic carbon was
determined with an auto-analyzer LECO WR-12. In a joint study with the
French Petroleum Institute concerning the Aber Wrac'h sediments (Ducreux
and Marchand, 1981), we compared the gravimetric determinations and the
IR spectrophotometr ic analysis of nonpurified organic extracts. Results
of the two methods are similar (Fig. 2). We also compared the IR
spectrophotometric results obtained on nonpurified and purified organic
extracts from some Aber Wrac'h sediments. In this case, correlation was
significant (Fig. 3) .
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