Salinity increases cadmium uptake by wheat and Swiss chard from soil amended with biosolids

Abstract

Soil salinity has been shown to significantly increase cadmium (Cd) concentrations in crops grown on soils fertilised with phosphatic fertilisers containing Cd. However, the effect of soil salinity on plant availability of Cd derived from biosolids is unknown. This paper reports the influence of increasing chloride (Cl) (NaCl) concentrations in soil solution on the phytoavailability of Cd in soils amended with biosolids (equivalent to 50 t/ha). Wheat (Triticum aestivum cv. Halberd) and Swiss chard (Beta vulgaris cv. Foodhook Giant) were grown in biosolids-amended soil and watered daily with a dilute NaCl solution (0–27.4 mМ). After 30 days, plant shoots were analysed for Cd and soil solution was displaced. Major cations and anions in soil solution were determined and Cd speciation was calculated with the computer program GEOCHEM-PC. Cadmium concentrations in soil solution and shoots of wheat and Swiss chard plants increased linearly with increasing Cl concentration in soil solution of the biosolids-amended soil. The activity of CdCl⁺ species correlated best with the Cd uptake of both plant species. Increases in shoot Cd concentrations were unrelated or only weakly correlated to the activity of the free Cd²⁺ ion in solution. It was concluded that chloro-complexation of Cd increased the phytoavailability of Cd in biosolids-amended soil.