Distribution of Heavy Metals in Soils Around the Lead and Zinc Production Plant in Zanjan

Soil heavy metals pollution is a major and growing problem in our country. Therefore, awareness of the spatial distribution of soils contaminated by heavy metals can play an important role in evaluating the pollution potentials of a region. The present study aimed at analyzing the spatial variability and current spatial pattern of six heavy metals (Co, Ni, Cu, Zn, Cd and Pb) in top soils surrounding the National Iranian Lead and Zinc Company (NILZ) in Bonab Industrial Estate (Zanjan, Iran), by spatial statistics. To this end, 126 soil samples were collected from 0-15 cm depths from the area surrounding NILZ Company within a radius of 5 km. Results showed that the highest and lowest average of heavy metals concentration in surface soils was related to Zn and Co, respectively (Zn > Pb >Ni>Cu > Cd > Co) and, compared with international standards, they are outside the range of measured limits. The Moran’s I, at 0.01 level of significance, showed that all the studied heavy metals had a spatial structure and cluster pattern, indicating that they were not distributed randomly and anthropogenic factors caused such a spatial distribution. Spatial distribution of heavy metals in the study area showed that the observed high concentrations of heavy metals, i.e. hot spots, surrounding the NILZ Company related to Zn, Co, and Pb. Maximum concentration of these metals was 2990, 20, and 30167 mg metal per kg of soil, respectively. It was concluded that the company activities had a big impact on distribution of these heavy metals in the study area. The variogram analysis of heavy metals revealed that soils containing Ni had weak spatial dependency, Cu, Cd, and Pb had strong, and Co and Zn had medium spatial dependencies.