Sources And Characteristics Of Petroleum Organic Pollutants In Soils Of Gudao Oil Region

With the rapid development of society and economy, the petroleum plays an important role in our daily life. However, numerous of oil pollutants have been brought during the petroleum exploration, transportation, deposit and usage due to natural and man-made reasons. The environment and human health would be affected by these pollutants if they were discharged into the soil, air and water. The Yellow River delta has been given comprehensive attention and support because of its particular ecological environment, and it has been defined as the efficient ecological economic zone. The Gudao oil region, where the oil pollution is serious in some degree during the petroleum exploration, locates in the Yellow River Delta, so it does not correspond to the construction requirements of the Yellow River Delta. Therefore, it is necessary to understand the situation caused by oil pollution and get acknowledge of the distribution, sources and pollution characteristics of the pollutants, in order to provide the technical and theoretical bases for government and environmental management department in formulating relevant standards and norms and strengthening environmental supervision and improving the soil environment quality. The soil pollution in Gudao oil region was invested and characteristic pollutants were chosen. The analytical methods were established and the time and space distribution were analyzed and the sources were studied. The results are as follows:(1)Three aspects, including the components with higher content in the petroleum, with strong poison and persistence to environment and with different contents from petroleum produced elsewhere, were considered together in order to determine the characteristic pollutants. Through the literature and experiments, the characteristic pollutants were chosen as petroleum hydrocarbons, n-alkanes, PAHs, BTEX and total sulfur content.(2) The analytical methods were studied and established for the characteristic pollutants through series of optimization and integration taking the U.S.EPA environmental standards as the reference. The sulfur content was measured by infrared carbon and sulfur analyzer and some parameters were optimized. The method detection for sulfur was0.013g/kg and the relative standard deviations(RSD) was4.9%. The BTEX were measured by ultrasonic extraction and purge and trap-gas chromatography (P&T-GC) detection. The purge time was optimized and the method detection for BTEX were0.132-0.679μg/kg, the RSD were4.6%-14.3%and the method recovery percentage were83.2%-99.7%. The rest of characteristic pollutants were measured by soxhlet extraction, silicone and Al2O3purification and n-alkanes were monitored by GC while the PAHs were analyzed by GC-MS, and the petroleum hydrocarbons were measured using gravimetric method. The volumes of extraction and elution solvent were optimized and the RSD for n-alkanes and PAHs were2.5%-14.1%and1.8%-12.5%, respectively. The method recovery percentages for n-alkanes and PAHs were76.5%-102.3%and75.8%-98.5%. The method detection for n-alkanes and PAHs were3.2-19.5μg/kg and2.3-23.7μg/kg, respectively. All of the recovery and RSD results meet the U.S.EPA standard.(3) The contents of characteristic pollutants in soils of Gudao oil region were measured according to the established methods and the time distribution were analyzed. The results were shown as follows:the petroleum hydrocarbons, n-alkanes, PAHs, BTEX and sulfur content at oil wells which were exploit at different times(1970s,1980s,1990s and2000s) were in the range of0.8-22.1g/kg,9.1-93.7mg/kg,588.5-5234.6μg/kg,428.4-2363.5μg/kg and166.4-1072.9mg/kg, respectively. The longer the oil wells exploited, the higher contents in the soils. Statistical Product and Service Solutions (SPSS) was used to analyze the correlations between petroleum hydrocarbons and the rest of the characteristic pollutants. The results showed that the contents of n-alkanes and sulfur were both significantly correlated with the content of petroleum hydrocarbons (p<0.01), while the contents of PAHs and BTEX were both correlated with the content of petroleum hydrocarbons O<0.05).To study the space distribution of characteristic pollutants, surface soil samples were collected according to the distance between oil wells and sampling points and different function zoned of Gudao town, while profile samples were collected at sites where the surface soils were heavily polluted by the petroleum. The results showed that at different function zones the content of petroleum hydrocarbons were all exceeded the control standard (500mg/kg), and according to the PAHs standard established by the Europe, the farmlands and wastelands were middle-polluted and slighted-polluted by PAHs, respectively, while the oil regions and town around were heavily polluted by PAHs. The farther the points from the oil wells, the lower contents of the characteristic pollutants, but the decay rates of characteristic pollutants were largely different because of their characters and soil physical and chemical properties. With the depth from0-100cm, the characteristic pollutants except BTEX showed a decreased trend while BTEX showed an increased trend before the decreased trend, however, the proportion of PAHs and BTEX in petroleum hydrocarbons were both increased. The correlations between physicochemical properties and characteristic pollutants showed that the particle size and organic matter content were the main factors affected their distributions.(4) The sources of characteristic pollutants were determined through the methods of ratios, correlated analysis and principal component analysis (PCA), et al. The results showed that the petroleum hydrocarbons were mainly from oil wells in heavily polluted areas and from the migration nearby in middle polluted areas, while the pollutants in slightly polluted areas were from irrigation, surface runoff or atmospheric deposition. The sources of PAHs in farmlands were composed of petroleum and incomplete combustion of straw and fuel oil which used during the farming, while the sources of PAHs in town around were from petroleum, exhausted gases emitted from automobile and industries as oil processing plants and the combustion of coal used by local residents.