A Study On The Distribution And Source Apportionment Of Petroleum Hydrocarbons In Surface Sediments From The Bohai Sea And Adjacent Area

Petroleum hydrocarbons have become one of the main pollutants of China’scoastal seas. Determination of the content, composition and sources of petroleumhydrocarbons in surface sediments from Bohai and adjacent area can provideimportant guidance and reference for assessing oil pollution levels of the study area,and for taking appropriate measures. To select an efficient and stable extractionmethod, we compared the efficiencies of soxhlet, oscillation and ultrasonic extractionfor the total petroleum hydrocarbons in oil spiked sediments. We used orthogonaldesign to optimize the extraction conditions of the selected method for improving theefficiency. The petroleum hydrocarbons of26surface sediment samples in the BohaiSea and adjacent area were then extracted under the optimized conditions and weredetected by GC-FID according to the CEN standards. Various characteristicparameters and ratio of the n-alkanes were used to determine the source of petroleumhydrocarbons. Major conclusions in this dissertation are as following:（1） Our experiments on the extraction efficiencies and standard deviations ofdifferent methods for the total petroleum hydrocarbons （TPHs） in oil spiked sedimentsindicated that: soxhlet extraction has good efficiency but time-consuming and poorreproducibility; Oscillation extraction has poor efficiency and reproducibility;Ultrasonic extraction is an efficient and stable method with simple operation. We thenused orthogonal experiment to optimize ultrasonic extraction condition. Optimizedeffeciency was obtained while extracting5g sediment4times with15mL methylenechloride for15min every time. Under the optimized condition, we obtained asignificantly improved efficiency with a better reproducibility for an oil-spikedsediment sample at a spiking level of1mg/g. （2） The contents of total organic carbon （TOC） in the surface sediments from theBohai Sea and adjacent area are between0.12%and1.13%, with an average value of0.44%. The TOC contents in sediments from Laizhou Bay are generally low, with anaverage value of0.27%. The TOC contents in sediments from Liaodong Bay arerelatively high, with an average value of0.48%. The TOC content increases withdistance offshore from the estuary in Laizhou Bay，while it gradually decreases inLiaodong Bay. In Bohai Bay, the distribution of TOC content is complexed byhydrodynamic factors, presenting higher values in the Gulf center, surrounded bylower values, but no gradual trend was observed. TOC contents are generally higherin the northeastern coast of Shandong Peninsula and northern South Yellow Sea（SYS）, with an average of0.54%; and it was significantly higher in mud area than innon-mud area.（3） The contents of total nitrogen （TN） in the surface sediments from the BohaiSea and adjacent area are between0.01%and0.16%, with an average value of0.06%.TN is significantly correlated with TOC%（R²=0.95）, with a very similar distributionpattern one another, indicating that their sources are similar. C/N ratios in the surfacesediments from the Bohai Sea and adjacent area range from4.67to12.31, with anaverage value of8.02. δ¹³C ranges from-26.0‰to-22.1‰, with an average of-23.1‰. C/N and δ¹³C values are not typical for either marine or land derived source. Therelatively low C/N and positive δ¹³C values indicate that sedimentary organic matterin Bohai Sea and adjacent area is terrestrial and marine mixed sources while marinesource dominates.（4） The contents of total petroleum hydrocarbon （TPH） in surface sedimentsfrom the Bohai Sea and adjacent area are in the range of15.2to65.3μg·g^-1, with anaverage value of30.1μg·g^-1. In general, TPH concentration in the mud area near thenortheast coast of Shandong Peninsula is higher than that in non-mud area stations.The averaged TPH contents of Liaodong Bay, Bohai Bay and Laizhou Bay are29.55、33.65and21.9μg·g^-1, respectively. TPH content decreases with distance offshore fromthe estuary in both Laizhou Bay and Liaodong Bay. In Bohai Bay, except for stationB24which is closer to the coastline, the TPH concentrations of the remaining stations were very close each other. Distribution of petroleum hydrocarbons in the surfacesediments of the Bohai Sea and adjacent area is affected not only by the complexhydrodynamic environment but also by the human activities.（5） The carbon number of n-alkanes in the surface sediments from the Bohai Seaand adjacent area is in the range of C₁₁to C₃₆, with content ranged from0.90to5.1μg·g^-1and averaged at2.25μg·g^-1. A bimodal distribution of carbon chain length ofn-alkanes was observed in most stations, suggesting mixed sources of n-alkanes fromterrestrial and marine origin. The main peaks of shorter chain n-alkanes are C₁₆or C₂₁,and those of longer chain n-alkanes are C₂₉and C₃₁.（6） The results of L/H, TAR and C₃₁/C₁₉ratio indicate that terrigenouscontribution is greater than marine source of n-alkanes in the surface sediments of theBohai Sea and adjacent area. OEP, CPI, Σn-Alk/C₁₆, U/R, Pr/Ph ratio and UCM showthat surface sediments of the Bohai Sea and adjacent area are suffering frompetroleum pollution. C₁₇/Pr and C₁₈/Ph ratios indicate that petroleum hydrocarbons insurface sediments of the Bohai Sea and adjacent area were degraded to a certaindegree.