ABSTRACT
Roots growing in soil are immersed in the soil solution, a dynamic and complex ionic environment from which they draw water and nutrients but may encounter toxic ions as well. Nonessential ions (e.g., Al, As, Cd, Cr, Hg, and Pb) as well as micronutrients and beneficial elements [cations: Fe, Cu, Zn, Mn, and Ni; anions: B(OH)4
concentrations or activities in the soil solution. The soil-plant system is open to inputs (fertilizers, pollutants, etc.) and losses (erosion,
leaching, etc.). Metal ions are released into soil solution directly through the weathering of soil minerals and the decomposition of organic matter as well as from the ionexchange processes. Concentrations or activities of metal ions in the soil-plant system depend on soil chemical and physical processes, relevant aspects of which are described here.
