Trace elements in grasses affected by the toxic spill of the Aznalcollar mines

摘要

Although the mine sludge that covered in 1998 ca. 4600 ha of the Agrio and Guadiamar valleys was removed immediately, three years after the spill occurred the affected soils are still polluted by metals. We have studied the accumulation of As, Cd, Cu, Pb, Tl and Zn in shoots of two native grasses, bermudagrass (Cynodon dactylon (L.) Pets.) and wild sorghum (Sorghum halepense (L.) Pets.), collected in spill-affected soils, and in an experimental plot from which the sludge was not removed. In the sledge-covered soil, trace element concentrations in grasses reached toxic levels for livestock (up to 157 mg kg~(-1) of As in bermudagrass and 59 mg kg~(-1) in sorghum; around 0.7 mg kg~(-1) of Cd in both grasses; 149 mg kg~(-1) of Pb in bermudagrass and 47 mg kg~(-1) in sorghum, and 36 mg kg~(-1) of Cu in bermudagrass). These concentrations were even higher in unwashed samples, which is the way they would be ingested by livestock. These results support the adequacy of the urgent cleaning-up operations carried out in 1998. Trace element concentrations in grasses from the cleaned-up soils were greater than those from unaffected soils. In some cleaned-up sites, unwashed samples of bermudagrass reached concentrations of Cd (up to 0.8 mg kg~(-l), Cu (more than 25 mg kg~(-1)), and Pb (60 mg kg~(-1)) that were above the tolerance threshold for livestock. All of this suggests that the monitoring of the pollution levels in plants should be continued, and the possible risks for the trophic web must be assessed.