陆地石油开采区PAHs环境多介质分布及迁移转化模拟

Simulated model of the fate and transfer for PAHs in the multimedia environment for a onshore oilfield

利用Mackay的Ⅲ级逸度模型估算16种优先控制多环芳烃(Polycyclic Aromatic Hydrocarbon,PAHs)在典型陆地石油开采区气、水、土壤及沉积物相间分布及迁移转化规律,根据研究区域年石油开采量估算污染物排放速率,利用实测浓度数据和文献值验证模型的可靠性。大气、水、土壤和沉积物相中的对数单位平均残差分别为1.12、1 35、1.41和1.39,表明模型对气、水、土壤和沉积物中浓度的估算与实测值大体吻合。土壤相是PAHs的主要环境归宿,落地原油是污染物主要输人方式,土壤相降解为主要输出方式,介质间迁移过程主要为沉积物相与水相的质量交换。

The present paper is aimed to introduce a simulated model of the fate and transfer for PAHs in the multimedia environment for an inland oilfield. For this purpose, we have built up a level-III fugacity model so as to determine the fate and the transfer regularity of the 16 kinds of priority-controlled polycyclic aromatic hydrocarbon （PAHs） of the different bulk compartments in an onshore oilfield, China. The above-said fugacity model consists actually of air （pure air and particulates）, water （pure water and suspended solids）, soil （air, water and solids）, and sediment （water and solids） in its four compartments, in which the following processes are supposed to take place, including oil spill on the clean soil, the discharge and volatilization of oil-contained sewage and waste gas, advection inflow and outflow in the air/water bulk from the nearby area and the study area, in addition to the exchanges between the inter-compartment and the degradation. To test the validity and the reliability of the fugacity model, we have applied the method of average residual errors analysis consisting of 1.12, 1.35, 1.41, and 1.39 logarithmic units between the measured and the predicted values for the four bulks, respectively, which reveals that the concentrations estimated of PAHs in the air, water, soil, and sediment compartments are well in accord with the values observed. It can thus be predicted that PAHs with lower molecular weight are easily to get soluble in the water, which is just opposite in sediment. However, the concentrations of the 16 PAHs in the air bulk is lower than the ones in the other three compartments. Thus, it can be predicted that the longest residue time of the 16 PAHs in the multimedia environment were BaP and PYR, which are equal to 2.63 years and 1.89 years, respectively. Whereas the soil compartment is identified as the main sink of PAHs, of all the varieties of pathways, the main silk of 16 PAHs in the study area and the source emission in the soil are the leading inputs of PAHs in the oilfield, the degradation in the soil is but the major output. Thus, the predominant transfer process of all the processes of PAHs in the given study area is that of resuspension from sediment to water, the volatilization and wind resuspension from the soil to air, and then surface runoff from the soil to water.