Statistical evaluation of topsoil heavy metal pollution around a lead and zinc production plant in Zanjan province, Iran

Heavy metal contamination was evaluated around the National Iranian Lead and Zinc Company (NILZ) in Zanjan province. Collected data were used to appraise the degree of soil contamination and also the source of pollution in the study area based on geoaccumulation index (Igeo), and enrichment factor (EF). The levels of Fe, Zn, Cd and Pb in the samples exceed those reported in literature. The analyzed soils can be considered unpolluted to moderately polluted by Cd and Pb, and moderately polluted by Zn. Evaluated EF also showed moderate to severe enrichment of the soil samples by Zn and Pb, and very strong enrichment by Cd. These results indicated an anthropogenic contribution mainly for Zn, Cd and Pb elements. Bivariate correlation among the investigated metals showed the contamination of soil around the study area resulted from the NILZ Company activity. Based on the Mann-Whitney assessment, it was found that the presence of Co, Cu, Zn, Cd and Pb was also attributed to the plant. Parametric and non-parametric tests revealed the leaching of metals to deeper soil layers. Hierarchical Clustering Analysis (HCA) allowed categorizing the investigated metals in three groups. These groups were cluster I (Zn, Cd, Co and Ni), cluster II (Pb and Cu) and Fe in an independent cluster III. Principal Component Analysis (PCA) and Factor Analysis (FA) elucidated the anthropogenic source of the pollutants.