Objective  The purpose is to find out the distribution and risks of heavy metal pollution in farmland soils around the oil exploitation and petrochemical industrial areas of Songnen Plain.

  Method  Taking the farmland soil in Ranghulu District of Daqing as the research object, 96 soil samples were collected to analyze the contents of heavy metals (Cd, Hg, Ni, Pb, Cu, Zn, Cr and As). The Kriging interpolation was applied to analyze the spatial distribution of heavy metals using geostatistics module software. With adoption of geo-accumulation index method and potential ecological hazard index method, an assessment was carried out to research the pollution of farmland soil in this area.

  Result  The results showed that the contents of Cd and Ni were 1.39 and 1.27 times of the soil background value. The contents of Pb, Zn, Cu and Cr exceeded the soil background value to different extent in some sample points. The mean geo-accumulation index of Cd was 0.11, indicating mild ~ medium pollution. The mean potential ecological risk index (RI) of heavy metals in soil was 84.84 in the researched area, and the RI followed the sequence of Cd > Hg > Ni > As > Pb > Cu > Zn > Cr. The RI value of Cd was the largest at 190.23 among them, indicating the medium ecological hazard. In terms of spatial distribution of heavy metals in farmland soil in the researched area, Cd, Zn and Pb were concentrated in the central area, while the concentration of the rest heavy metals was relatively scattered.

  Conclusion  The mean content of the 8 heavy metals is lower than the risk screening value, while that of both Cd and Ni exceeds the background value. For the geo-accumulation index, Cd pollution reaches Level-I and the rest 7 elements are at non-pollution level. It can be learned from the potential ecological risk analysis that the pollution is in the mild ecological hazard in this area.