Cadmium spatial variability of soil and grain wheat farms of Khuzestan province

Heavy metals particularly cadmium (Cd) enter in food chain through soil and plants. Therefore, determining spatial variability of Cd concentration in soil and crops is important to manage adverse effects of Cd on environment. This research was conducted to assess the spatial variability of soil and wheat grain Cd in large farms. A number of 255 farms in Khuzestan province (355000 ha) at wheat maturity stage were sampled, using an irregular weighting sampling scheme. In each region, the density of samples was chosen according to the area and spatial distribution of the wheat farms. Pair compound soil (0-20 cm) and grain samples were taken from each wheat farm. The Cd concentrations in soil (total and DTPA-extractable) and grain samples were then measured. Also, the spatial variability of soil and grain Cd were obtained by normal Kriging method. The results indicated that the total Cd concentrations in 95 percent of samples exceed 0.8 mg kg-1. However, the DTPA-Cd concentrations in 25 percent of soil samples were more than 0.1 mg kg-1. In addition, grain Cd concentrations in 95 percent of the samples were exceeded the threshold of 0.2 mg kg 1 grain. The semivariograms of soil (total and DTPA-extractable) and grain Cd were well fitted with a spherical model. The spatial distribution of total Cd using normal Kriging, revealed two most contaminated zones, one at south and the other at west. Also, for DTPA-Cd, the east and south were the most contaminated regions in the study area. The spatial distribution of grain Cd indicated high Cd concentrations at the east, west and some parts of south area.