Spatial variability of total Ni and Cu concentration in surface soils surrounding the Hamadan city using geostatistic technique

Due to accumulation of heavy metals in soil, their recognition, origin and distribution have attracted considerable interest. No information is currently available on the distribution pattern of heavy metals concentration in soils of Hamadan province. The purpose of this research was to determine the spatial variability of Ni and Cu in soils of a selected area surrounding the city of Hamadan. A total of 263 composite surface soil samples (0-10 cm) were taken from an area of about 1600 km2 in Hamadan. The location of each sampling site and its land use were recorded using a GPS. Also, parent rock samples were collected to study the effect of parent material on the concentration of these elements. The total Ni and Cu were measured by atomic absorption spectrophotometer. The spatial variability of these variables was examined by variogram models and kriging. Geostatistical analysis of data showed that spherical model is the best model for describing the spatial variability of these elements. The major factor controlling the high concentrations of Ni and Cu in the area appears to be parent materials. Parent material analysis indicated that the concentration of Ni (97.5 mg kg-1) and Cu (75 mg kg-1) in shales was much higher than that in any other parent rocks. Therefore, these elements can enter the soils by weathering of the parent rocks. Also, the Cu concentration in urban soils is higher than that in other land uses. Therefore, the content of Cu in the soils studied seems to be mainly controlled by soil parent material and land use. Distribution of measured metal concentrations showed that the levels often exceed the guidelines established by the England. Ni had the greatest number of sites in excess of the England target value by 63%. Likewise, the concentration of Cu exceeded the England, guidelines in 1.5% of the study sites.