Laboratory methods for evaluating migrated high molecular weight hydrocarbons in marine sediments at naturally occurring oil seeps

A laboratory study has been conducted to determine the best methods for the detection of C10-C40 hydrocarbons at naturally occurring oil seeps in marine sediments. The results indicate that a commercially available method using n-C6 to extract sediments and gas chromatography-flame ionization detection (GC-FID) to screen the resulting extract is effective at recognizing the presence of migrated hydrocarbons at concentrations from 50 to 5000 ppm. When non-biodegraded, the amount of oil charge is effectively tracked by the sum of n-alkanes in the gas chromatogram. However, once the charge oil becomes biodegraded, with the loss of n-alkanes and isoprenoids, the amount of oil is tracked by the quantification of the unresolved complex mixture (UCM). Gas chromatography-mass spectrometry (GC-MS) was also found to be very effective for the recognition of petroleum related hydrocarbons and results indicate that GC-MS would be a very effective tool for screening samples at concentrations below 50 ppm oil charge.