Prediction of the impact of the Aznalcollar toxic spill on the trace element contamination of agricultural soils

The interaction of several trace elements (Cd, Zn, Cu, Pb, As, Bi, and Tl) was studied by leaching experiments in agricultural soils affected by the A znalcollar toxic spill. The spill led to contamination by acid waste waters and sludge deposition. The levels of contamination recorded after the slud ge was removed from soils showed that highly contaminated areas remained. A comparison of soils directly affected by sludge deposition and acid waste waters with soils contaminated only by acid waste waters demonstrated that Zn/As and Cd/As ratios were good indicators of the two contributions to the contamination. Soil samples were characterised and grouped according to th eir texture and carbonate content. The response of elements to single extra ctions with CaCl2 0.01 mol l(-1), CaCl2 1 mol l(-1), CH3COOH 0.43 mol l(-1) , and EDTA 0.05 mol l(-1) enabled us to estimate their mobility in the soil s. Cd and Zn were found to be the most mobile elements. Cu showed an interm ediate mobility, especially in an acidic medium. Pb, As, Bi and Tl were fou nd to be non-mobile elements. A comparison of referent, low and highly cont aminated samples showed that the presence of sludge had an effect on desorp tion yields, in part due to the short-term after the contamination. Calcula tions of a relative scale of long-term mobility, between soils and trace el ements, provided further conclusions derived from the use of single extract ions. (C) 1999 Elsevier Science B.V. All rights reserved.