A most interesting observation from our investigations is that 

 oysters, which were heavily contamianted by the oil spill and remained 

 so for the duration of the investigation, showed little evidence of 

 histopathological or biochemical damage, whereas plaice from the Abers, 

 although not heavily contaminated with oil, showed evidence of serious 

 and progressive histopathological and biochemical damage. This may 

 be due to differences in the sensitivity of molluscs and fish to petrol- 

 urn. However, an alternative hypothesis is that the metabolites of 

 petroleum hydrocarbons, particularly of the polycyclic aromatic hydro- 

 carbons, are much more toxic than the unmetabolized parent compounds 

 and cause much of the damage in a chronic pollution situation. It is 

 well-established that the phenolic, epoxide and diol metabolites of 

 polycyclic aromatic hydrocarbons are much more elctrophilic and bio- 

 logically reactive than the unoxygenated parent compounds (Neff, 1979). 

 Since oysters have little or no capability to oxygenate polycyclic aro- 

 matic hydrocarbons to reactive metabolites, they are quite tolerant to 

 oil. Fish on the other hand have a highly active mixed-function oxygen- 

 ase system and so rapidly convert polycyclic aromatics to reactive 

 metabolites which cause tissue damage. This hypothesis warrents further 

 investigation. 



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