Assessment of Heavy Metals Pollution Risk in Soils of Central Zanjan Province Based on Pollution Indices

This study was conducted to determine natural concentration of heavy metals and their pollution risk using pollution indices in a 2000 km2 area in central Zanjan. Soil samples (N=241) was takenfrom 0-10 cm depth based on gridding procedurein a completely randomized design. Geometric means of 53 natural soilsamples were used to determine heavy metals background concentrationin the area. Results showed that the background concentration for Fe, Mn, Co, Cr, Ni, Cu, Zn, Pb and Cd were 16509, 628.4, 24.2, 20, 40.7, 27, 91.8, 57.8 and 0.25 mgkg-1, respectively. The means of enrichment factor for Cd, Zn, Pb, Cu, Ni, Cr, Co and Mnwere found 4.20, 2.16, 1.69, 1.64, 1.19, 1.17, 1.04 and 1.02, respectively. In all land uses studied, the geo-accumulation index was negative for the elements Fe, Mn, Co, Cr and Ni, indicating that the study area is categorized in non-polluted soil groups. However, the geo-accumulation index for Pb, Zn, Cd and Cu varied in urban land uses was positive.The pollution index for Cd and Zn under agriculture (3.01 and 1.83), rangeland (3.33 and 1.60) and urban (9.86 and 4.35) land uses were higher than other elements studied. Moreover, the lowest pollution indexes in all land uses were attributed to the metals Fe,Mn,Co and Cr. The mean of potential of ecological risk in agriculture, rangeland and urban land uses were 114.09,122.08 and 339.62, respectively; in which the urban land use showed the highest potential of ecological risk for inhabitants of the area.