17-ALPHA(H),21-BETA(H)-HOPANE AS A CONSERVED INTERNAL MARKER FOR ESTIMATING THE BIODEGRADATION OF CRUDE-OIL

Hopanes are common constituents of crude oils, and they are very resis tant to biodegradation. They can therefore serve as conserved internal standards for assessing the biodegradation of the more degradable com pounds in the oil. Here we address two important questions that attend such use. The first is whether the ''internal standard'' is being cre ated during the biodegradation process itself, for this could result i n an overestimate of the extent of biodegradation. The second is wheth er the internal standard is indeed relatively resistant to biodegradat ion on time scales of relevance to the biodegradation process under st udy; for if it was not, this could result in an underestimate of the e xtent of biodegradation. We find that 17alpha(H),21beta(H)-hopane is n either generated nor biodegraded during the biodegradation of crude oi l fractions on time scales relevant to estimating the cleansing of oil spills, and so it has the appropriate characteristics to serve as an internal standard for studying the biodegrdation of crude oil in the e nvironment.