Association of cadmium in durum wheat grain with soil chloride and chelate-extractable soil cadmium

Cadmium uptake by food crops needs to be understood in order to limit Cd accumulation in the food chain. Cadmium is a potentially toxic heavy metal with no known benefit to humans, and plant foods are the predominant sources of Cd in human diets. In this study, 124 paired samples of soil and grain were collected from a field of durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.] cultivar Munich in northeastern North Dakota. This field on the Langdon Research Extension Center was selected for study because it provided a range in soil pH and salinity. Cadmium in the durum grain ranged widely from 0.025 to 0.359 mg kg(-1). Accumulation of Cd in grain was strongly and positively associated with soil salinity as represented by soluble chloride, soluble sulfate, or extractable Na, and also with chelate-extractable Cd. Relationships to salinity were curvilinear. Concentrations of Cd in grain were not closely related to soil pH. The relationship of Cd in grain to the logarithm of water-extractable soil Cl- (Cl-w) was especially close. A predictive model based on chelate-extractable Cd and logCl(w)(-) in soil accounted for 66% of the variability of Cd in grain. Based on these results, and published work for other crops, we believe that the accumulation of Cd in durum wheat grain is enhanced by Cl- in the soil. Although the mechanism is not clear, It is likely to involve increased solubility or availability of soil Cd resulting from the formation of chloro-complexes in soil solution.