Modeling the Interaction and Uptake of Cd-As(V) Mixture to Wheat Roots Affected by Humic Acids, in Terms of root cell Membrane Surface Potential (ψ).

The joint toxicological effects of Cd and As(V) mixture on wheat root as affected by environmental factors, such as pH, coexisting cations, and humic acids etc., were investigated using hydroponic experiments. The interaction and toxicological mechanisms of co-existing Cd and As(V) at the interface of solution and roots in presence of humic acid were further explored by incorporating root cell membrane surface potential ψ into a mechanistic model of combined biotic ligand model (BLM)-based Gouy-Chapman-Stern (GCS) model and NICA-DONNAN model. Besides, molecular dynamics (MD) simulations of lipid bilayer equilibrated with solution containing Cd and HAsO further revealed the molecular distribution of heavy metal(loid) ions under different membrane surface potentials. HAsO and Cd can be adsorbed on the surface of the membrane alone or as complexes, which consolidate the limitation of the macroscopic physical models.