Effect of Ph on The Bioavailability of Metals in Soils

Abstract

Heavy metals in soils may have a toxic effect on soil biota depending on the bioavailability of these metals. The fraction of a total metal content that is available for uptake by biota depends strongly on the chemical form in which the metals are present and where they are located in the soil system. Thus, the speciation of the metals in soils, that is the distribution of the metals over different ion species and different phases in the soil, has to be known to interpret observed (toxic) effects. In this paper copper is used as an example to illustrate the distribution of a heavy metal over the soil solid phase, the soil solution and the biotic phase. For the latter yeast cells are used as an example. It turns out that the largest part of the total metal content is bound to the soil solid phase and that the solid phase controls the metal ion activity in the soil solution. Both the metal binding to soils and to yeast cells as a function of solution concentration increase with pH. Only when the pH effect on binding to soil and biota are determined independently, it is possible to predict the net pH effect on metal binding to biota in the soil environment.