Mobilisation and fixation of Zn in polluted soils by variations of pH

Abstract

The concentration of Zn in soil solution (the free cation and its soluble complexes) is largely controlled by the equilibrium that it has with the quantity of metal associated with the soil solid phase (Tiller et al., 1972a). Radioisotope procedures to measure this quantity of solid phase metal, that has been termed 'readily phytoavailable', have proved invaluable in that the L value has often been shown to be statistically equivalent to the isotopically exchangeable metal in the soil - the E value (Tiller et al., 1972b). Therefore, E values provide a direct indication of the quantity of potentially phytoavailable Zn in soils (L value). However, plants have the ability to induce pH changes in the rhizosphere and, therefore, may increase (mobilisation) or decrease (fixation) the quantity of isotopically dilutable Zn in polluted soils. This hypothesis was examined in a polluted acid (pH 6.2) and calcareous soil (pH 7.5) using a batch experimental system.