Implications of chloride-enhanced cadmium uptake in saline agriculture: modeling cadmium uptake by maize and tobacco

Chloride salinity has been strongly related to enhanced cadmium (Cd) uptake by plants due to increased solubility in the soil solution, even in agricultural soil with very low levels of cadmium. This finding is relevant because the cadmium content of food crops is an important concern for human health. Therefore, the aim of this study was to predict and discuss the chlorine-enhanced uptake of cadmium by two common crops: maize and tobacco under “non-saline” (1 mM) and “very strongly saline” (200 mM) scenarios using a modified ‘biotic ligand model’ and datasets from a set of soil and hydroponic experiments. Results indicated that predicted cadmium uptake rates (expressed as cadmium in plant μmol m^-2 root) by maize and tobacco plants were consistently higher (54 and 15%, respectively) assuming conditions of ‘very strong salinity’ soil compared to the simulated ‘non-saline’ soil. In the light of the results of the present research, valuable information is given on modeled cadmium phytoavailability as an indication of the potential risk due to increased cadmium uptake by crops under saline conditions, especially as the enhancement of cadmium uptake in the presence of Cl^- salinity may be a general trend that occurs in many edible crops. The biotic ligand model parameterization applied in the present study attempted to simulate conditions commonly found in natural cadmium and salt-affected soils. However, caution is needed to extrapolate results obtained from these models to real soil conditions.

Keywords
Biosolids; Biotic ligand model; Cadmium speciation; Free ion activity model; Irrigation; Soil salinity; Nicotiana tabacum; Zea mays