Leaching of Trace Metals from Soil under Alternating Oxic-anoxic Conditions: a Column Study

Abstract

One of the most important and abundant transition metals in the Earth's crust is iron, which plays a key role in environmental biogeochemistry. A large number of trace metals and other contaminants are associated to Fe(III) minerals; under anoxic conditions, Fe(III) can be reduced and, consequently, potentially dangerous compounds can be released. In this work we present column experiments of metal mobilization from soils sampled from a mining area in Northeastern Romania. A preliminary study was carried out to determine the extractability of metals in CaCl2 0.01 M solution and the influence of adding 1 g L -1 lactose as a carbon source. The results showed that the heavy metals were rapidly brought into solution in the medium supplemented with lactose. Then, the release of metals was studied using columns packed with soil percolated with the CaCl2 solution. It was observed that, while Zn and Pb are released in the solution congruently with the reduction of Fe and Mn, copper is mobilized immediately and can be found in the leachate. This suggests that, under alternating oxic-anoxic conditions, the soil can become a source of contamination.