Medium pH can have dramatically impacts on solution-phase metal concentration. Specifically, in media that contains phosphate as a buffer, a minor change in pH can affect metal solubility, and hence metal bioavailability by several orders of magnitude. In general, at high pHs metals have a tendency to form insoluble metal phosphates and carbonates , whereas
at low pHs the initial leaching of metals from the sludge occurs, and hence their solubility increases . Most of the studies in the literature focus on the effect of pH reduction on metal bioavailability.