RESULTS AND DISCUSSION 



Petroleum Hydrocar bons 



Concentrations of total aliphatic and aromatic hydrocarbons in 

 tissues of oysters Crassostvea gigas from Aber Benoit and Aber Wrac'h, 

 heavily contaminated with Amoco Cadiz oil, and from supposedly clean 

 reference stations are summarized in Table 4. Reference oys-ters for the 

 first two collections were Rade de Brest oysters which had been held for 

 a -short period of time in concrete holding tanks on the shore of Aber 

 Benoit at St. Pabu. These reference oysters were heavily contaminated 

 with Amoco Cadiz oil as were the authentic Aber Benoit and Aber Wrac'h 

 oysters. "Hydrocarbon status" of samples was determined by comparing 

 GC peak profiles of f\ and t^ hydrocarbon fractions of tissue extracts 

 to GC profiles of authentic weathered Amoco Cadiz oil. Apparently, 

 sufficient oil was still leaching from the sediments of the Aber 13 

 months after the spill to allow rapid and heavy contamination of oysters 

 exposed to waters of the bay. Michel and Grizel (1979) reported similar 

 rapid hydrocarbon contamination of oysters transplanted to stations in 

 Aber Benoit and Aber Wrac'h. Subsequent reference oyster samples were 

 obtained from sites which had not received Amoco Cadiz oil. They con- 

 tained low levels of petroleum hydrocarbons not of Amoco Cadiz origin. 

 Concentrations of total aliphatic and aromatic hydrocarbons in oysters 

 from Aber Benoit and Aber Wrac'h did not vary substantially over the 

 time-course of this investigation (up to 27 months after the spill) . 

 The persistence of petroleum hydrocarbons in tissues of oysters probably 

 represents, in part, a continuous recontamination with hydrocarbons 

 leaching gradually into the water from the heavily contaminated sediments 

 of the Abers. Oysters from the Baie of Morlaix, east of Aber Wrac'h and 

 less heavily contaminated with Amoco Cadiz oil than the Abers, collected 

 17 months after the spill, contained about half the aromatic hydrocarbons 

 of Aber Wrac'h oysters. It is interesting to note that Aber Benoit 

 oysters collected in December 1978 and April 1979 had a distinctly oily 

 taste. Oysters sampled in August 1979 and later did not taste oily. 

 Apparently, 200 ppm aromatics is not readily detected by taste, whereas 

 500 ppm is. 



More detailed analysis of the aliphatic fraction of the oyster 

 samples revealed some interesting trends (Tables 5-7). In all but one 

 case (Aber Wrac'h, April 1979), the aliphatic fraction of Aber Benoit 

 and Aber Wrac'h oysters was dominated by the low boiling aliphatics, 

 C 10 ~ C 20> inciting n-alkanes, branched and isoprenoid compounds. 

 This is quite unlike weathered Amoco Cadiz oil or oil in the Aber 



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