CONCLUSIONS 



Microbial degradation appears to have played a very important role 

 in the weathering of oil spilled from the AMOCO CADIZ. Microbial 

 hydrocarbon degradation potentials are in general agreement with the 

 observed changes in the composition of oil stranded within the littoral 

 zone. The chemical evolution of the hydrocarbon mixture within 

 intertidal sediments led to a relative enrichment in isoprenoid alkanes, 

 a transient complex unresolved mixture, and a relative enrichment of 

 dibenzothiophenes and alkylated phenanthrenes. 



There was a general, but variable decline in concentrations of 

 hydrocarbons over the three year period following the AMOCO CADIZ spill 

 within Aber Wrac'h. The concentrations of hydrocarbons also declined at 

 sites that were regularly covered by tides. At the one site in lie 

 Grande, which is not subject to daily tidal washing, the concentrations 

 of hydrocarbons remained high even three years following the spill. At 

 nearby sites within the lie Grande salt marsh, which were physically 

 cleansed of AMOCO CADIZ oil, there was little chemical or microbial 

 evidence of any impact from the AMOCO CADIZ spill at any of the sampling 

 times. The incurrence of oil from the TANIO wreck was apparent even at 

 sites that had been oiled as a result of the AMOCO CADIZ spill. 



The microbial population levels generally reflected the relative 

 degrees of persistence of petroleum hydrocarbons. The microbial 

 community at all of the sites studied had essentially the same potential 

 capability for degrading hydrocarbons and as such the differences in the 

 hydrocarbon concentrations and composition recovered from the field 

 samples probably reflect the initial rates of oiling and environmental 

 influences. The indigenous microbial community retained the capability 

 of responding to a second incursion of oil resulting from the TANIO 

 spill. 



Both the field experiments and the i_n vitro studies suggest that 

 mixing energy, related to nutrient and oxygen availability, was 

 extremely important in permitting the high rates of observed oil 

 weathering. The occurrence of both saturated and unsaturated acids in 

 the sediments studied in vitro suggest that several biochemical pathways 

 were active in the biodegradation of the aliphatic hydrocarbon fraction. 

 The hydrocarbon biodegradation potential suggested that relatively high 

 concentrations of oxygenated aromatic hydrocarbons should accumulate, 

 but for unexplained reasons the analyses of the polar fraction generally 

 failed to show such accumulations. 



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