Variations of Ni, Zn and Pb Affected by Parent Material and Land Use in Mashhad Plain

To evaluate the effect of parent material and land use on the variations of Ni, Zn and Pb,the number of 181 soil samples (0-10 cm) in 12 parent material-land use units were taken from an area of approximately 1500 km2 in Mashhad plain, Norteastern Iran. Aqua-regia extractable of the mentioned elements were measured. The amount of Ni in rangland and urban areas were measured of 205.8 and 68.9 mg/kg, respectively in ultramafic-methamorphic parent material which not significantly different. While in other units the concentration of this element varied from 43.2 to 62.9 mg/kg and was not influenced by land use. In all units, Zn with averages of 48.8 to 84.7 and Pb with average of 25.1 to 36.1 mg/kg showed less variations than Niandwere less affected by parent material. Zn in soils with metamorphic origin was slightly higher than the other parent materials. The amount of Zn and Pb in urban areas (only in ultramafic-methamorphic parent materials) were nearly 40% higher than cultivated and pasture land uses indicating the addition from the external pollutant source. Increase of Pb and Zn in urban lands can be attributed to industrial and urban activities.