in living tissue exceed 30 mg/g at the most heavily impacted station C. 

 Animals at the other shoreline stations D and E contain aliphatic hydro- 

 carbon levels of 7.6 mg/g and 4.1 mg/g respectively during the November 

 1977 sampling. These values are 300 to 500 times the background hydro- 

 carbon levels in tissues from these stations. Although depuration of 

 aliphatic hydrocarbons appears to commence very soon after the initial 

 impact in animals surviving the oil's landfall, it is not until 1 year 

 after the event that tissue hydrocarbon levels appear to reapproach the 

 background levels. However, examination of the detailed hydrocarbon 

 composition of the tissues 1 year after the spill still reveals petro- 

 leum hydrocarbon inputs at some stations. This will be discussed. 



High resolution gas chromatograms of the tissue hydrocarbon com- 

 positions reveal a rapidly changing suite of hydrocarbons in the mus- 

 sels. Initially, tissues from the most heavily impacted stations appear 

 to have taken up hydrocarbons very similar in composition to the spilled 

 oil (Fig. 11.2a and 11.2b). However, all samples obtained in December, 

 2 months after the spill, reveal GC patterns indicating substantial 

 alteration of the cargo oil pattern, with n-alkanes being preferentially 

 degraded compared with corresponding branched and isoprenoid compounds 

 (Fig. 11.2c and 11. 2d). At several stations, most notably I, even the 

 November tissue samples already exhibit notable preferential n-alkane 

 degradation throughout the entire boiling range of the oil (approxi- 

 mately n-C,- through n-C„ n ). The GC of Fig. 11.2c illustrates such a 

 case, where the isoprenoid hydrocarbons, having retention indices of 

 1370, 1460 (farnesane), 1560, 1650, 1710 (pristane), and 1812 (phytane), 

 become chromatographically prominent due to their greater resistance to 

 microbial degradative processes (Kator, 1973). 



The rapid alteration in the tissue hydrocarbon composition from an 

 essentially unaltered oil to an n-alkane-depleted, isoprenoid-enriched 

 assemblage is the single most important aspect of the changing hydro- 

 carbon chemistry of Mytilus tissue. This change is expressed in Table 

 11.1 as the ALK/IS0 ratio, which is simply the ratio of n-alkane to 

 isoprenoid hydrocarbons in the n-C 10 to n-C lc , boiling range. In the 



1 J lo 

 spilled cargo oil the n-alkanes predominate (ALK/ISO = 7.0). The most 



230 



