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

Abstract

We developed a method for predicting the total cadmium (Cd) concentration [Cd T . From this, we derived the balance equationWe calculated (CdCl þ ) as the product of (Cd 2þ ), chloride activity (Cl -), and a production constant. Our proposed prediction model wasWe conducted an experiment using six types of soil and manipulated the Cd content, pH, and chloride concentration [Cl À ] to determine the effect on Cd concentration in the soil solution. The soil solution measurements produced rectilinear regression relationships between log(Cd 2þ ) 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 a function of cation exchange capacity (CEC), and the activity coefficient

TRANSPIRATION INFLUENCES CADMIUM UPTAKE BY BABY LEAF SPINACH (<i>SPINACIA OLERACEA</i> L.)

“…(1) The Cl concentration was fixed at 100 mg L −1 ; and (2) that no other ligands of significance were present. For orders of magnitude variations in the concentration of Cd in solution relevant to soil solutions (0.1-100 µg L −1 ), the proportion estimated to be present as chlorocomplexes varied relatively little (40-15%), which is informative if not unexpected (McLaughlin et al, 1997;Kamewada and Nakayama, 2011). That is, these calculations suffice to show that under our conditions, an appreciable proportion of the Cd in the soil solution should have been mobile by mass flow.…”

“…We estimated complexation of Cd by Cl in the soil solution (GEOCHEM-EZ, Shaff et al, 2010), because the chlorocomplexes of Cd are more mobile by mass flow than Cd itself (Boekhold et al, 1993;Kamewada and Nakayama, 2011). There were two assumptions:…”

“…The greater the transpiration rate, the greater the potential delivery of Cd to the roots by mass flow. Chloride (Cl) is predicted to facilitate this process by increasing the concentration and mobility of Cd in the soil solution due to the formation of chlorocomplexes (Boekhold et al, 1993;Kamewada and Nakayama, 2011). Moreover, Cl occurs ubiquitously in soils (Ure and Berrow, 1982) and the predicted enhancement of Cd uptake is well established (Bingham et al, 1983;McLaughlin et al, 1997;Wu et al, 2002).…”