394 



R.J. Barsdate et al. 



60- 



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 o 



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 Time 



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13 days 5yrs 



FIGURE 9-4. Composition of Prudhoe Bay crude oil as a 

 percentage of the total. The classes are benzene-soluble as- 

 phaltenes (BSA). benzene-insoluble asphaltenes (BIA), the 

 saturate fraction, the aromatic fraction, and the nitrogen-, 

 sulfur- or oxygen-containing fraction (NSO). (After Miller 

 et al. 1978b.) 



day"' at 25°C in a laboratory hood with moving air. The loss of all 

 fractions of the oil was 18 to 19% in 36 days when the oil was placed in 

 darkened Petri dishes in the field. When clear dishes were placed in the 

 sun, 24% of the oil was lost, so this photo-decomposition could be 

 important in the arctic. The loss was even higher when the oil was placed in 

 plastic tubes containing natural water and sediment and incubated in the 

 pond. After 45 days, 75% of the oil disappeared, which indicates that biotic 

 processing was not too important. Somewhat slower rates were reported 

 by Federle et al. (1979); after 1 year 58% of the oil remained in core tubes. 



Despite the rapid loss of oil, the overall composition of the remaining 

 oil does not change appreciably over time (Figure 9-4). The different 

 classes were separated on solid-liquid chromatographic columns as 

 described by Jobson et al. (1972) after separation from the water and 

 sediment by Freon extraction. Even after 5 years in the pond, the 

 composition of the oil is about the same. However, the saturate fraction 

 (pentane soluble) did show some biological degradation, as Miller et al. 

 (1978b) found that in the saturate fraction all of the hydrocarbons with 

 fewer than 13 carbon atoms were lost within 13 days (measured by gas- 

 liquid chromatography). 



