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Keywords:

  • cadmium;
  • chloride ion;
  • kinetic isotherm;
  • salinity;
  • uptake

Abstract

We conducted a pot trial to investigate the effects of soil cadmium (Cd) content, soil pH, soil type and soil chloride (Cl) content on Cd uptake by garland chrysanthemum (Chrysanthemum coronarium cv. Kiwame-Cyuba) to improve predictions of plant Cd uptake. We concluded that predictions of plant Cd uptake should involve the following two procedures: (i) predicting the Cd concentration of the soil solution as a function of the chemical properties of the soil, (ii) predicting plant Cd uptake as a function of the Cd concentration in the soil solution. A unique hyperbolic relationship was observed between plant Cd uptake and total Cd concentration in the soil solution. The relationship was independent of soil type, soil Cd content and salinity treatment, and was explained by: UCd = Vp[CdT] + {Vmax[CdT]/Km + [CdT]}, where UCd represents plant Cd uptake, [CdT] represents the total Cd concentration of the soil solution, and Vp, Vmax and Km are constants. The Cd adsorption kinetics were investigated using the “monodentate coordination model,” which enabled Cd2+ activity in the soil solution to be explained by: log(Cd2+) = log Kmon + log QCd – pH – log CCd, where Kmon represents the equilibrium constant of Cd adsorption, (Cd2+) represents Cd2+ activity, Qcd represents the amount of Cd adsorbed, and CCd represents the Cd adsorption capacity. The total Cd concentration in the soil solution showed a linear correlation with the Cl concentration in the soil solution. The effect of Clsalinity on the total Cd concentration in the soil solution was attributed to the formation of a cadmium–chloride complex (CdCl+). For a more robust prediction of plant Cd uptake, there is a clear need for a simple method that can simultaneously determine the soil Cd concentration, the coefficient constant for Cd adsorption and the Cd adsorption capacity of the soil.