CHANGES IN MOLECULAR COMPOSITION AND LEVELS OF AEROBIC BIODEGRADATION LEVEL DESCRIPTION 0 paraffinic crude oil not biodegraded 1 [C.sub.1] to [C.sub.15] n-alkanes depleted minor 2 90% of [C.sub.1] to [C.sub.35] n-alkanes light removed 3 alkylcyclohexanes and alkylbenzenes removed, moderate
isoalkanes (including isoprenoids) reduced 4 isoprenoids and methylnaphthalenes removed, moderate aromatics depleted in order of increasing molecular weight and alkyl substitution 5 [C.sub.14]-[C.sub.16] bicyclic alkanes extensive removed 6 smaller steranes removed, larger steranes heavy altered, 25-norhopanes formed 7 all steranes removed, 25-norhopanes more heavy abundant 8 hopanes altered very heavy 9 hopanes removed, disteranes altered, severe