spatial variability of pb and zn concentration and its relationship with land use and parent materials in selected surface soils of hamadan province

abstract accumulation of heavy metals in soils has become a serious environmental problem in many parts of the world. no information is currently available on the distribution pattern of heavy metals concentration in soils of hamadan province. the objective of this research was to determine the spatial distribution of pb and zn and its relationship with land use and parent materials 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. the location of each sampling site was recorded by using a gps and its land use type (residential, uncultivated, agricultural land and dryland wheat) was also determined. in addition from six major types of bedrock in the hamadan province were also sampled with 3 replicates. the total and plant available zn and pb in soil samples and the total concentration of these elements in parent rocks were measured by atomic absorption spectrophotometer after extraction. selected soil properties including ph, electrical conductivity, organic matter, cation exchange capacity and soil texture were also determined. the spatial variability of variables was examined by variography and kriging analysis. the mean concentration of total and available zn were 71.4 and 2.5 mg kg-1 and those for pb were 24 and 2.5 mg kg-1, respectively. the results of geostatistical analysis showed that spherical model was the best model for describing the spatial variability of pb and zn. the range of influence was estimated 9750 m for pb and 11550 m for zn. it seems that the major factor controlling the high concentration of total pb and zn in the area is land use type. analysis of parent rock samples indicated that shale as the major parent rock occurring in the southeast and west part of the study area contains a high quantity of zn (96.2 mg kg-1). therefore, it appears that zn has entered the soils in the study area through the weathering of parent materials. in other words, the content of zn in the soils studied seems to be mainly controlled by soil parent material and land use. a significant correlation was found between organic matter and the concentration of pb.(r2= 0.35) and zn (r2= 0.33).