POLYCYCLIC HYDROCARBON BIOMARKERS CONFIRM SELECTIVE INCORPORATION OF PETROLEUM IN SOIL AND KANGAROO RAT LIVER SAMPLES NEAR AN OIL WELL BLOWOUT SITE IN THE WESTERN SAN JOAQUIN VALLEY, CALIFORNIA

摘要

Following an accidental oil well blow out at an oil field in the western part of the San Joaquin Valley, Kern County, California, soil samples and specimens of Heermann's kangaroo rats (Dipodomys heermanni) were collected from two oil-impacted areas and one control area. The chemical characteristics of the crude oil, soils, and rat livers were compared. Fingerprinting by gas chromatography-mass spectrometry and quantitative evaluation of metabolized petroleum hydrocarbons was performed on oil, soil extracts, and rat livers. A liver from a domestically raised rabbit was used as an experimental control. The results show that compared to background values for control samples and procedural blanks, there is no significant incorporation of PAHs or low molecular weight n-alkanes (C_(13)-C_(25)) into the liver tissues. The C_(25) to C_(35) n-alkane range for all soil samples, kangaroo rat livers, and rabbit liver, is dominated by a high abundance of C_(27), C_(29), C_(31), and C_(33) hydrocarbons typical of epicuticular plant waxes. In all liver tissue samples, squalene, the cholesterol precursor, is the dominant hydrocarbon. Although evidence is lacking for metabolism of PAHs and paraffinic petroleum hydrocarbons, very strong evidence is available for incorporation of a set of polycyclic hydrocarbons (biomarkers) belonging to the terpane, sterane, and monoaromatic and triaromatic sterane families, identified by ion monitoring at 191, 217, 253, and 231 m/z, respectively. Because these hydrocarbons are not known to exist in the biosphere, but are only synthesized during oil- and coal-forming processes, their presence in the liver samples constitutes proof for crude oil incorporation into tissues. This conclusion is further substantiated by the selective incorporation of only the 205 enantiomer of C_(28) and C_(29) steranes and aromatic steranes into the livers, with the exclusion of the 20R enantiomer. The results from the study conclusively demonstrate that polycyclic hydrocarbon biomarkers provide excellent indices for proof of petroleum exposure and metabolism in some terrestrial herbivores.