Multimedia Environmental Ecological Risk Assessment Of Heavy Metals In A Typical Oilfield

With the rapid development of economy in China, it is inevitable to drill for oil on land based on the requirement of petroleum and gas. Increase of crude oil output will lead to more and more persistent contamination and ecological risks. Among hazardous materials from terrestrial petroleum exploit, heavy metal contamination in several environmental media has become one of the most compelling global issues. It is significant to investigate activity routines of heavy metals in various environmental media and to estimate risk assessment on typical terrestrial oil concessions before contamination treatment, environmental plan and protection. However, the investigations focus too much on the oil pollution derived from petroleum exploitation in the individual environmental media such as water, soil, sediment and plants, and lack the multimedia environmental pollutant and risk assessment in the onshore oilfield. In this study, multimedia transport and fate for five kinds of heavy metals (Cd, Cr, Cu, Pb, and Zn) in the onshore oilfield were investigated, and then the present situation of soil pollution and ecological risks in multimedia research area were evaluated.This study selects multimedia aquivalence environmental mathematical model to simulate the transports and fates for Cd, Cr, Cu, Pb, and Zn in the onshore oilfield multimedia environment (air, water, soil, sediment and plants). The validation and verification of model are conducted through comparison between measured and simulated data. Results show that, the mean logarithmic residual phases for air, soil and sediment were0.38,0.67and0.16, lower than these for water (1.67) and plants (1.43). Heavy metal pollutions in all phases of the average logarithmic residuals are an order of magnitude. Therefore, it is a reasonable model which can be used to simulate the behavior of pollutants in multimedia environment. Simulation results show that heavy metals make contamination into multimedia environment by ground crude oil and atmospheric sedimentation. Transportation and migration mainly occur in water and atmosphere, while degradation happens in sediment and soil. Contamination fate for heavy metal is primarily sediments. The trend of contamination transportation from soil to atmosphere is obviously observed. It is crucial to monitor quality of water and atmosphere for prevention of heavy metal contamination. With occurrence of heavy metal contamination, efforts should be made on recovery of sediments and soil.Potential ecological risk index method is introduced to assess ecological risk of heavy metals in water, soil and sediment. Results of assessment show that Cd has the highest level in single ecological risk assessment, especially in water medium. Contamination of Cd possesses high destruction on water, sediments and soil. In the future, focus on Cd should be put at important position for environmental contamination and terrestrial oil concessions planning. Meanwhile, analyses for heavy metal contamination on atmosphere by analytic hierarchy process method show that Pb is the most hazardous material. Other heavy metal contaminations could be not neglected as well. Finally, reeds are regarded as risk representative to estimate ecological risk assessment on plants. Results show that Cr and Cd possess high migration capability from both sediments to seeds and soil to seeds, which could enter circle of biologic chain.Combination of multimedia aquivalence environmental mathematical model and the ecological risk assessment method integrates double functions of model simulation and ecological risk assessment.This research realizes the quantitative characterization in terms of the environmental behaviors and ecological risks of the heavy metal pollutants in the typical onshore oilfield, which can support decision makings for relevant departments.