IntroductionCadmium is a trace element that has no biological functions but is highly toxic to plants and animals (Jarup et al., 1998). It enters the environment and agricultural soils mainly from industrial processes and application of phosphate fertilizers. Cadmium is a relatively rare element (about 0.2 mg kg -1 in the earth's crust). It occurs mainly in association with the sulfide ores of zinc, lead, and copper. It is a byproduct of the zinc industry and production is determined essentially by that of zinc (Jensen and Bro-Rasmussen, 1992). The major factors governing cadmium speciation, adsorption, and distribution in soils are pH, soluble organic matter, clay type and contents, presence of organic and inorganic ligands, and competition from other metal ions (OECD, 1994).In Japan, Cd has caused itai-itai disease and the death of many people (Kobayashi, 1978). Following this event, the attention of world public opinion has focused on this element (Adriano, 1986;Fergusson, 1990).Irregular and excessive use of agrochemicals with high contents of metals created a very serious problem for agricultural soils (Crocker, 1989). Organic and inorganic fertilizers used in agriculture often contain heavy metals such as Fe, Cu, Zn, Pb, and Cd, and, therefore, the amount and composition of their application need to be carefully examined (Mermut et al., 1996).On average, Cd level in soils is around 0.1 mg kg -1 soil. According to Kabata-Pendias and Pendias (1992), the world average of Cd concentration in agricultural soil is 0.53 mg kg -1 , and it ranges between 0.01 and 2.7 mg kg -1 . According to Dobson (1992), Cd concentrations of uncontaminated areas range between 0.2 and 0.4 mg kg -1 soil. However, Cd concentration in some contaminated areas was found to be 160 mg kg -1 soil. In recent studies, the most striking research findings are the elevated levels of Cd in plants (Kirkham, 2006). Wheat normally accumulates more Cd than other commonly grown cereals with the order: rye < barley < oats < wheat (Jansson, 2002). Durum wheat accumulates more Cd than bread wheat,