Efectos subletales de la exposición al vertido tóxico de Aznalcóllar en aves de larga vida

Abstract

Sublethal effects of the exposure to the Aznalcóllar toxic spill in long-lived birdsIn 1998, the rupture of the tailings dam at the Aznalcóllar pyrite mine (Sevilla, Southwestern Spain) caused a toxic spill in the surroundings of the Doñana National Park. Here, we review the potential impact of this mining spill on birds using the White Stork Ciconia ciconia and the Black Kite Milvus migrans as sentinel species. We employed a biomarker approach to study the relationships between blood levels of Pb, Cd, Zn, Cu and As (the most abundant metals in the spill), and molecular, biochemical, cellular, and physiological aspects of vital importance -including the immune system, DNA damage, the adrenocortical stress response, and bone development and metabolism -to organism functioning. We found that, although often below threshold toxicity values, levels of some metals (e.g. Cu) could be related to an impaired cellular immune response (PHA-skin-test) and to DNA damage (comet assay) both in White Stork and Black Kite nestlings. The adrenocortical stress response in White Stork nestlings was positively related to low Pb levels. This association was stronger in individuals that had suffered additional stress from other environmental factors. The morphological deformities detected in White Stork nestlings after the spill were related to disrupted bone metabolism (P levels, Ca:P, bone alkaline phosphatase), especially in younger birds. Moreover, female storks developmentally exposed to the spill experienced an altered age-dependent pattern of breeding performance in comparison with their non-developmentally exposed counterparts (hatched before the spill), showing an unusually high productivity in their early reproductive life and premature breeding senescence. We propose that sublethal effects compromising White Storks' health during the nestling period might play an important role in shaping this pattern of reproduction (terminal investment hypothesis). In summary, the biomarker approach used in the short-and medium-terms can serve as an early-warning signal of long-term contaminant effects in wild birds. This review shows that the exposure to pollutants in early life, even at low levels, may affect individual fitness (reproduction) and is evidence of the need for longterm monitoring and evaluation when attempting to correctly assess the impact of pollutants on wildlife populations. We conclude that the Aznalcóllar mine spill is the most likely cause of the effects detected in storks and kites. However, we cannot completely rule out the idea that these effects may be the result of the combined exposure to spill-related metals and other contaminants associated with the industrial and agricultural activities practiced in the surroundings of the Doñana National Park.