Distribution of petroleum hydrocarbons in sediments from Dianchi Lake, China

Thirteen Dianchi Lake sediments were analyzed for parent and alkylated polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes by gas chromatography-mass spectrometry. Total PAH concentrations in the sediment ranged from 590 to 23,250 ng/g. The alkylated phenanthrene/phenanthrene and alkylated pyrene/pyrene ratios displayed a strong correlation with the total PAH concentrations, suggesting that the sediments were heavily impacted by petrogenic PAHs. This finding was consistent with the ratios and compositional features of hopanes and steranes, and confirmed the presence of mature petroleum in the sediments. The sedimentary total organic carbon contents were correlated with the organic pollutant concentrations (R2 = 0.81–0.88), suggesting that the distribution was controlled by an extensive point source and/or transport and sedimentation processes. Principal component analysis results indicated two major sources of inputs to the aquatic environment in the area: (1) discharge from the Daguanhe River, and (2) leakage of oil from motor boats in nearby harbors. A gradient of increasing parent PAH (relative to alkylated PAHs) concentrations toward the lower section of Dianchi Lake, as compared to those in the upper section, reflected the resistance of the parent PAHs to degradation and bioavailability during pollutant diffusion. The uniform composition between sedimentary steranes and hopanes was explained not by one diffuse single source but, rather, by the lack of change in the composition of oil residues after natural transport and sedimentation processes.