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Petroleum Hydrocarbons
RESULTS AND DISCUSSION
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 contained
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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