lived in the tissues. The structures of these compounds were examined 

 by GC/MS. A selection search for m/e=133 (Fig. 11.5) shows that the 

 series is present in the Tsesis oil although in relatively small amounts. 

 However, the series emerges rapidly, presumably due to its retention by 

 the organisms or due to difficulty in biotransformation, and persists 

 until 1 year after the spill when analyses fail to reveal significant 

 quantities of TMB compounds. 



11.3.2 Sediment Traps 



The material collected in the sediment traps at Stations II, IV, 

 and V contains large amounts of weathered Tsesis cargo oil. Concentra- 

 tions of Tsesis oil in the traps are presented in Table 11.5 and illu- 

 strate that the rate of deposition of oil through the water column is 

 similar at the upwind station (IV), at the wreck site (II), and downwind 

 in the direction of the movement of the visible slick (V). Thus, it 

 appears that oil is dispersed in the water column, adsorbs to detrital 

 material, is quickly weathered, and is redistributed by subsurface water 

 movement through the study region. The petroleum hydrocarbon deposition 

 rate was high during the second week after the spill (.November 1 to 

 November 9) and presumably was as high or higher during the last week in 

 October. Thereafter the amount of petroleum hydrocarbons in the sedimen- 

 ted material decreased markedly and 1 to 2 months afterward the spill 

 reached very low levels. At these low levels, petrogenic hydrocarbon 

 inputs are non-detectable. 



Very significant in terms of interpreting benthic as well as inter- 

 tidal bivalve uptake patterns, are the detailed gas chromatograms of the 

 hydrocarbon material found in the traps. As illustrated in Fig. 11.6 

 and 11.7, the spilled Tsesis oil that is sedimented has been significant- 

 ly altered as early as 1 week after the spill. In the aliphatic fraction 

 (Fig. 11.6), the n-alkane degradation has altered in oil's composition, 

 presumably by microbial agents, to the point where the ALK/ISO ratio is 

 0.3 to 1.0, down from an initial value of 7.0. In addition, the increased 

 importance of the UCM in these early deposition samples is evident from 

 Fig. 11.6. 



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