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The significant features of the chemical changes that were observed
included a marked decrease in the proportion of n-alkanes relative to
isoprenoid hydrocarbons, the transient occurrence of an increase in
unresolved hydrocarbons within the first year following the AMOCO CADIZ
spillage, and the decreased importance of unsubstituted polynuclear
aromatic hydrocarbons relative to dibenzothiophenes and the comparable
or substituted forms of the polynuclear aromatic hydrocarbons (Figs. 2
and 3).
The In vitro hydrocarbon biodegradation experiments confirmed the
fact that the indigenous microbial populations were capable of rapid and
extensive degradation of Arabian crude oil. Much greater rates of
biodegradation were observed in agitated compared to flow through
experiments (Figs. 4-9). Both the in vitro experiments and the analysis
of field experiments support the hypothesis that mixing energy has a
very significant effect on the rates of hydrocarbon biodegradation.
Rates of biodegradation appear to be environmentally influenced by the
turbulence of mixing which can ensure a continued supply of nutrients
and oxygen as well as dispersing the oil so as to establish a favorable
surface area to volume ratio for rapid microbial hydrocarbon
biodegradation. The similarity of changes, observed in the composition
of the hydrocarbon mixture i_n vitro compared to the analysis of field
samples also suggests that nutrients were not a limiting factor that
determined the rates of hydrocarbon biodegradation.
The analysis of the polar fractions from the iri vitro experiments
showed some surprising results (Table 21). There was a lack of
oxygenated aromatic compounds. It had been predicted that there would
be a greater accumulation of polar products from aromatic biodegradation
since less CO was being produced than from aliphatic biodegradation
where a significant proportion of the hydrocarbon that was biodegraded
was released as CO . There were significant accumulations of polar
compounds that appear to be biodegradation products of aliphatic
hydrocarbons, especially as C.,-C „ acids. Interestingly, the major
polar products included unsaturated acids. As a rule, the predominant
biochemical pathway for the biodegradation of straight chained
hydrocarbons does not involve the formation of unsaturated compounds,
although a biochemical pathway has recently been elucidated for some
bacteria that does introduce a double bond into the hydrocarbon. It
appears that the microbial populations indigenous to the sediment of the
Brittany Coast possess such a biochemical capability.
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