Differential biodegradation of polynuclear aromatic hydrocarbons

Polynuclear aromatic hydrocarbons (PAHs) are generally considered to be the most toxic components of crude oil and are moderately resistant to biodegradation. Studies have documented that as crude oil is degraded, the percentage of aromatic hydrocarbons by weight of the residual petroleum compounds increases. However, recent studies have documented the complete biodegradation of some aromatic compounds by microbes. A series of laboratory experiments was conducted to monitor the biodegradation of crude oil, specifically the PAHs. Bioreactors were spiked with artificially-weathered Alaska North Slope crude oil, inorganic nutrients, and commercially-available mixed cultures of bacteria. The experiments were monitored over a 28 day period. It was determined that although the relative percent aromatics increased with time, the concentration of the resolved PAHs peaks were decreasing. The PAHs displayed a resistance towards degradation with increasing molecular weight and alkyl substitution on the ring structure. It was also detected that within an alkylated series specific isomers were preferentially degraded.