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 favor- 

 able 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. 



18 



