Polluting Characteristics and Ecological Risk Assessment of Heavy Metals in Cultivated Land Around a Mining Area in Northern Hebei Province

To investigate the polluting characteristics and to assess ecological risk of heavy metals in cultivated land around a mining area in northern Hebei Province, the concentrations of Hg, As, Cd, Pb, Cu, Zn, Ni and Cr in the 25 top soil (0-20 cm) samples were determined and the spatial distribution of the heavy metals in the cultivated land was analyzed based on geostatistical analysis. The potential ecological risks were assessed by the single factor (P_i), Nemerow index method (P_N), and potential ecological risk index (I_R) and the main sources of heavy metals were discussed according to the multivariate statistical analysis. The results show that the average concentrations of all heavy metals except As in the soil exceeded the background values of soil, meanwhile the Hg, Pb, Zn and Ni concentrations did not exceed the national agricultural land soil pollution risk screening value, and met the national pollution risk screening standards, meanwhile the over standard rates of Cd, Cu and Cr contents were 33%, 46% and 8%, respectively. The higher concentrations of Zn, Hg, Cd, Pb, Cu and As were mainly concentrated in north and south-central parts of the research area, and the higher concentrations of Cr and Ni were mainly concentrated in north and central parts. The single factor assessment results indicate that the degree of heavy mental pollution was in the order of Cd > Pb > Cu > Hg > Cr > Ni > Zn > As and it had some potential ecological risks in the cultivated land, according to the Nemero comprehensive pollution index and potential ecological risk index. Cd and Hg in the soil were the main sources of pollution. The sources of As, Hg, Cd, Zn, Pb and Cu were mainly affected by anthropogenic pollution factors, whereas Cr and Ni were mainly affected by soil parent material and geological activities.