Migration, speciation and distribution of heavy metals in an oil-polluted soil affected by crude oil extraction processes.

Heavy metals are among the major pollutants in the worldwide soil environment. In oilfields, the crude oil extraction process results in the simultaneous contamination of the soil with petroleum and heavy metals. In this work, we investigated the influence of oil extraction on the migration, speciation, and temporal distribution of heavy metals (Cu, Zn, Pb, Cd, Cr, Mn, Ni, V, and Mn) in soils of an oil region of Shengli Oilfield, China. The results showed that oil-polluted soils were contaminated with Cu, Zn, Cd and Ni, with mean concentrations of 27.63, 67.12, 0.185 and 33.80 mg kg(-1), respectively (greater than the background values of local surface soils). Compared with the control profile, the vertical distributions of Cu, Zn, Pb, Cd, Ni, and V were affected in oil-polluted soils, particularly those of Cd and Ni. The concentrations of Zn, Cd, Ni, V, and Mn in oil-polluted soils increased with the duration of oil well development, which indicated the levels of these metals in the oil field were enhanced by human activities. Fractionation analysis revealed that the mobility potential of heavy metals in oil polluted soil decreased in the sequence Cd > Mn > Zn > Ni > Pb > Cu > Cr > V. The most important proportion of Cd is ion exchangeable and acid soluble, which indicates that Cd is the most labile, available, and harmful heavy metal among the elements that damage the soil environment in oil-polluted soil.