Rates of hydrocarbon biodegradation in the field compared to the laboratory

A field study conducted on the shoreline of Delaware in 1994 showed that the first-order rate constants calculated from the field study were nearly identical to rate constants calculated in sealed laboratory flasks, using the same microbial populations from the study site, when the rate data were normalized to the highest alky-substituted homologue in a given polycyclic aromatic hydrocarbon (PAH) series. A laboratory experiment was conducted to determine how widespread this relationship was among a diverse series of microbial consortia. Eight undefined mixed cultures isolated from various U.S. marine shorelines were incubated for a period of one month in quadruplicate shake flasks in the presence of artificial seawater containing weathered crude oil. Flasks were sacrificed at periodic intervals and the contents analyzed for depletion of crude oil constituents by gas chromatography/mass spectrometry (GC/MS). Rates of biodegradation were calculated by nonlinear regression analysis of the analyte depletion data and compared to rates measured in the Delaware field study. Results affirmed the findings from Delaware. Six of the eight mixed cultures isolated from different parts of the U.S, behaved similarly in closed flasks (with respect to the relative rates of biodegradation of crude oil hydrocarbons) to the microbial consortium that degraded the light crude oil in the open field on the beach of Delaware Bay. Results suggested that one can use the relationship between degradation rate and substrate structure or molecular weight as a reliable indicator of biological activity.