Release of trace metals to the soil solution from a phosphate rock containing soil at different acid loads

Abstract

In agricultural practice basic phosphate rocks (PRs) may be efficient P sources if applied on acidic soils. However, due to their potentially toxic elements content environmental hazards may arise. In a laboratory bulk experiment the appearance and accumulation of such elements (As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sr and Zn) in the soil solution of an acidic sandy soil was studied after various PR and acid treatments. The degree of pH elevating effect of PR treatments was also tested. In the liquid phase of the PR-enriched soil, metal concentrations were generally lower than in the control sample because their release to the soil solution was influenced less by the amount of the pollutants carried into the soil with PR doses than by the pH increasing and/or solubility altering effect of PR. Acid loads, as expected, considerably increased the concentrations of cation forming elements in the soil solution, but their concentrations – due to the immobilizing effect of PR – decreased in the acid treated soil, as well. Extreme strong acid treatment was necessary to compensate for this effect and, while Ba, Co, Cu and Mn concentrations practically did not change with the increasing PR doses, Cd, Sr and Zn concentrations were eleveated. In contrast, the immobilizing effect of PR in case of Pb dominated even under the extreme acid treatment, its concentration decreased with increasing PR doses. Concentration of the anion forming elements (As, Mo) in the acidic soil solution was negligible even at the highest P dose.