Mercury and other trace elements in soils affected by the mine tailing spill in Aznalcóllar (SW Spain)

7 pages, 9 figures, 2 tables, 31 references. We wish to thank Mr. J.A. Diez de la Cortina for assistance with the maps. The authors thank Prof. N. Lepp for his helpful comments.

The Aznalcóllar accident (28thApril 1998) occurred because the collapse of the tailing-damdike of the Aznalcóllar–Los Frailes mines. Soilswere affected by a slurry of acidic water loadedwith trace elements, finely divided metal sulphides, and materials used in the refining /floating process. Studies carried out before and after the soil restoration activities (sludge removal, amending, tilling, and afforestation) showed severe trace-element contamination (mainly As, Cd, Cu, Pb, Tl and Zn) in the superficial layer of the sludge-affected soils. Despite Hg being an important component of the Los Frailes ore and therefore of the contaminant sludge, data on Hg content of sludge-affected soils are scarce and sometimes controversial. The aim of this study was to determine the effect of the spill and of restoration measures on the Hg content of soils and how this related to other elements. Concentration of Hg immediately after the spill was 8-fold above background (0.061±0.012mgkg−1;mean±SD) at the surface (0–5 cm)and 3–4- fold greater in deeper layers (0–20; 0–50 cm). After the remediation measures, mean values of Hg and other elements (As, Cd, Cu, Pb and Zn) were very variable and remained above background values. These anomalies are due to the sludge left on the soil surface or buried during restoration operations, resulting in an irregular distribution of trace elements. The highest values for the lessmobile elements (up to 176 mg kg−1 As, 2.36 mg kg−1 Hg and 1556 mg kg−1 Pb) were observed in the area 15 km downstream of the tailings dam.

This study was carried out in the framework of the projects REN 2000-1519 TECNO and CTM 2004-01985 TECNO supported by the CICYT of the Ministerio de Ciencia y Tecnología and the Ministerio de Educación y Ciencia of Spain, and of the PICOVER research program of the Consejería de Medio Ambiente of the regional government (Junta de Andalucía).

Peer reviewed