Statistical and spatial distribution of some heavy metals in surface soil particle size fractions in South of Isfahan

Metal contents in bulk soil samples are commonly used to evaluate pollution. However, many documents indicated that metal accumulations in soils are increased with decreasing particle size. We investigated the distribution of heavy metal (Zn, Pb and Cd) concentrations in various particle size fractions and assessed spatial variability of their concentrations in soil surface around Sepahan Shahr Town located 25 Km south of Isfahan metropolis. One hundred composite soil samples were taken randomly and after air-drying fractionated in five classes including 250-500, 125-250, 75-125, 50-75 and <50 μm. Results indicated that metal contents increased with decreasing particle size. The mean of Zn concentration increased from 224 mg kg-1 in 250-500 μm size fraction to 401 mg kg-1 for the finest fraction of <50 μm. The same trend was observed for the mean of Pb and Cd concentrations. Kriged maps indicated the same general pattern for all metal concentrations. The amount of metal pollution decreased with increasing distance from sources (mines). The results could provide important information that might be useful in assessing risks associated with urban soils and areas around Isfahan metropolis where under intensive development.