Arsenic contamination in soils affected by a pyrite-mine spill (Aznalcollar, SW Spain)

On 1998, a settling pond of a pyrite mine in Aznalcollar (SW Spain) broke open, spilling some 3.6 x 10(6) m(3) of water and 0.9 x 10(6) m(3) of toxic tailings into the Agrio and Guadiamar river basin 40 km downstream, nearly to Do ana National Park. The soils throughout the basin were studied for arsenic pollution. Almost all the arsenic penetrated the soils in the solid phase (tailings) in variable amounts, mainly as a result of the different soil structure. The chemical oxidation of the tailings was the main cause of the pollution in these soils. A study of the relationships between the main soil characteristics and arsenic extracted with different reagents (water, CaCl2, acetic acid, oxalic - oxalate and EDTA) indicates a direct relationship with the total arsenic concentration. The highest amount of arsenic was extracted by oxalic - oxalate (24%-36% of the total arsenic), indicating the binding with the iron oxides.