Estimation of Background Concentration of Selected Heavy Metals for Pollution Assessment of Surface Soils of Mazandaran Province, Iran

One of the main problems in soil pollution evaluation is the lack of regional standards. The objectives of this study were (i) to estimate the background concentration of some heavy metals for environmental assessment and, (ii) to locate heavy metal polluted soils in part of central Mazandaran Province. The study region with 5500 km¬2¬ area is important in terms of agricultural activities and population density. Using nested-systematic method, 256 composite soil samples were taken from the depth of 0-10 cm, including 148, 60, and 48 soil samples in agricultural land, urban area, and natural lands (forest and rangeland), respectively. After preparation and extraction of soil samples with 5 N nitric acid, the total concentration of Cu, Zn, Ni, Pb, and Cd was measured by an atomic absorption spectrometer. Natural background concentration (NBC) of Cu, Zn, Ni, Pb, and Cd was estimated to be 28.3, 40.2, 45.7, 34.2, and 0.23 mg kg-1, respectively. Interpolated distribution map of contamination factors (CF) and pollution load index (PLI) of heavy metals were prepared using NBC. The overlap of CF and PLI maps with geology and land use maps was indicated that the concentration of Pb, Zn, and Cu has been affected by human activities such as traffic, whereas Cd and Ni contents are controlled by natural factors such as parent material, and agricultural activities, mostly. Based on the classes of CF, most samples are moderately contaminated with heavy metals.