A widely applicable model for predicting the cadmium concentration in soil solution

We developed a method for predicting the total cadmium (Cd) concentration [CdT] in soil solution. Disregarding minor ion pairs, [CdT] was approximated by . We assumed that Cd2+ activity (Cd2+) is dominated by the adsorption–desorption equilibrium, expressed stoichiometrically as . From this, we derived the balance equation We calculated (CdCl+) as the product of (Cd2+), chloride activity (Cl–), and a production constant. Our proposed prediction model was We conducted an experiment using six types of soil and manipulated the Cd content, pH, and chloride concentration [Cl−] to determine the effect on Cd concentration in the soil solution. The soil solution measurements produced rectilinear regression relationships between log(Cd2+) and log Q Cd – 0.6pH with slopes of 1.0 in all soil types, which validated the proposed Cd adsorption–desorption stoichiometry; the y-intercept of the regression lines represented log(K Cd/C Cd) and depended on the soil type. Furthermore, we were able to predict log(K Cd/C Cd) as...