Heavy metals in organisms of the River Guadalquivir estuary: possible incidence of the Aznalcóllar disaster

On the 25 April 1998, the giant holding pool of the Aznalcóllar mine, owned by the Canadian–Swedish Company Boliden Ltd burst its banks; 5 million cubic meters (6.7 million cubic yards) of sludge poured into the nearby River Guadiamar, which is a tributary of the River Guadalquivir (the main river of the south Iberian Peninsula). Within hours of the accident, approximately 2.5 Hm 3 of acidic water with high concentrations of metals, especially Zn, had entered the River Guadalquivir. A biomonitoring program has been carried out to evaluate the incidence of this spill on the fauna of the River Guadalquivir. Six sampling stations within the estuary of were established and six species of molluscs ( Crassostrea angulata, Scrobicularia plana), crustaceans (Palameon l ongirostris, Uca tangeri, Melicertus kerathurus) and fish ( Liza ramada) were chosen for analysis. In the Portuguese oyster, Crassostrea angulata, Cd and Cu concentrations were above the maximum allowed by the Spanish legislation for bivalves for human consumption (60 μg·g −1 wet wt. for Cu and 1.0 μg·g −1 wet wt. for Cd). The crustaceans Palaemon longirostris and Uca tangeri, also showed values above the legal limits for Cu (20 μg·g −1 wet wt.). An increase of the Zn levels was observed, as Zn concentrations in C. angulata were higher than those reported 30 years ago. The heavy metal concentrations in some of the organisms collected in the River Guadalquivir were higher than in the Bay of Cadiz or the Mediterranean Sea (clean sites), showing that this estuary was subjected to a heavy metal load. One month after the accident, concentrations of Zn were higher in C. angulata and in Palaemon longirostris compared with levels recorded on the 25 April. Nevertheless, some organisms did not show a clear tendency during the sampling period, probably due to the fluctuations of environmental (salinity, temperature) and physiological variables that affect bioaccumulation.