Abstract: Polycyclic aromatic hydrocarbons (PAHs) residue in petroleum contaminated soils around Zhongyuan Oilfield was investigated. Results showed that residue of PAHs in the soils ranged from 70.8 to 5013.2 μg·kg^-1 and was mainly composed of multi-ring(over 3 rings) PAHs,of which high concentration of benzo(a)pyrene (BaP) was detected in all the soil samples with the highest being 996.9 μg·kg^-1,in the surface soils in front of the christmas trees.By referring to the standard Canada uses in controlling PAHs contamination in the soils of its agricultural zones,Nemerow composite index method was appiled to the assessment of ecological risk of the contamination.Results show that the ecological risk of the soils around the wells,either in operation or recently closed,was quite high,and closely related to the working state and downtime of the wells and the distance from the christmas trees.The longer the downtime of a well, the lower the ecological risk of the soil around it,and the further to the well,the lower the risk.

Key words: peroleum, soil, polycyclic aromatic hydrocarbons(PAHs), ecological risk