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 con- 

 stituted 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 interna- 

 tional 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 natural 

 substances (fats, fatty acids, etc.) from sediments. The IR 

 spectrophotometer was calibrated with a mixture of Arabian and 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) . 



144 



