Assessment of the Critical Load of Trace Elements in Soils Polluted by Pyrite tailings. A Laboratory Experiment

Nineteen soil samples (SE Spain) with very different chemical physical properties and developed over different parent materials were contaminated by adding increments of an acidic solution from oxidised pyrite tailings. The quantities of Cu, Zn, Cd and Pb precipitated by the soil samples were directly and significantly related to the pH-buffering capacity. However, when the contamination caused the pH to fall below 3.0 the soil tended to release a fraction of the element adsorbed, which increased as the pH decreased. The quantity of each precipitated element at which the action value for each element is reached, was also directly related to the pH-buffering capacity. Nevertheless, in carbonate-rich soils, the precipitated Cu and Zn maintained a relatively high level of bioavailability, while Cd reached a critical level with a content exceeding 25 mg kg, regardless of the pHbuffering capacity.