Variability of available cadmium in relation to soil properties and landuse in an arid region in central Iran

Due to potential problems associated with their toxicities, concentration of heavy metals in soils is of great environmental concern. To evaluate Cd content, its spatial pattern, and availability in the surface soils of agricultural, industrial and urban regions of Isfahan, central Iran, we collected 255 topsoil samples (0-20 cm) from the nodes of an irregular grid in a study area of 6800 km(2). In the soil samples we measured total and DTPA-extractable Cd concentrations, soil pH, organic mater (OM), clay content, soil salinity, and chloride concentration. The total Cd concentration in 90% of the samples exceeded the suggested Swiss thresholds of 0.8 mg kg(-1). Landuse had a significant effect on total concentration of Cd in the soil but had no effect on DTPA-extractable Cd. High values of total Cd were found in industrial and urban areas whereas low values occurred in uncultivated lands. The correlation analysis revealed that soil salinity alone explained 36% of the Cd variation in the entire study area. The correlation was particularly strong in uncultivated areas (R-2 = 0.70). Spatial analysis of available Cd using indicator kriging and soil salinity showed a spatial co-occurrence of these two variables.