Spatial distribution and ecological risk assessment of heavy metal pollution in the soil of Limu Mountain- Wanling Town, Qiongzhong, Hainan Province

In order to understand the spatial distribution and ecological risk assessment of heavy metal pollution in the soil of Limu Mountain-Wanling Town, Qiongzhong, 2682 topsoil samples(0~20 cm) and 304 middle-soil layer samples(80~100 cm) and subsoil samples(180~200 cm) were respectively collected to analyze for 8 heavy metal elements(Cu, Pb, Zn, Cr, Ni, Cd, As and Hg).Based on the metals' distribution, geoaccumulation index and potential ecological hazard index, multivariate statistics was conducted to evaluate the potential ecological risks.Results show that the mean values of 8 heavy metal elements in topsoils are higher than the soil background values of Hainan, showing different degree of accumulation effect.The accumulation of heavy metal in topsoils is associated with different land-use types and various planting patterns.Vertically, the contents of Pb、Zn、Cu、Cr、Ni decrease a little with depth, but contents of Cd, As and Hg are characterized by surface accumulation.Pearson correlation analysis and factor analysis suggest that Cu, Cr and Ni in the topsoils are mainly controlled by geological background, others are controlled by geological background and human activities.The mean geoaccumulation indexes of other heavy metal elements except for Hg(0.08) are less than 0.The ecological risk assessment show that Cd and Hg are the main hazard elements, Cd is mainly of slight to medium hazard, Hg is of medium to strong risk, and the hazard indexes of the other elements are all slight.The overall potential ecological hazard index of 96% of the soil is below medium hazard.