Concentrations and chemical speciation of five heavy metals (Zn, Cd, Ni, Cu, and Pb) in selected agricultural calcareous soils of Hamadan Province, western Iran

The content of five heavy metals (Zn, Cd, Ni, Cu and Pb) and their chemical speciation were determined in 21 surface soil samples (0–20 cm) of agricultural topsoil from Hamadan Province, an area with intensive agricultural production. The selected sites represent calcareous soils which have not received any biosolid or industrial-waste applications. Mean concentrations of Pb (67.9 mg kg−1) and Cd (1.67 mg kg−1) were the highest in soils, suggesting anthropogenic inputs, whereas Cu (16.0 mg kg−1), Zn (59.1 mg kg−1) and Ni (32.8 mg kg−1) were lower than regulatory limits (6–60, 17–125 and 2–100 for Cu, Zn and Ni mg kg−1, respectively). The order of abundance in the soils was Pb > Zn > Ni > Cu > Cd. Generally, the topsoil in Hamadan Province showed high Pb and Cd concentrations, suggesting an anthropogenic origin of the pollution in the studied area, arising from the use of mineral fertilizers and atmospheric deposition. Copper and Ni existed in soil mainly in residual (∼56.3 and 54.4%, respectively) and organic forms (∼20.3 and 16.2%, respectively), whereas Pb occurred essentially as residual mineral phase (∼37.1%).