Heavy Metals in Native Mediterranean Grassland Species Growing at Abandoned Mine Sites: Ecotoxicological Assessment and Phytoremediation of Polluted Soils

Abstract

The closing of several mines in the central Iberian Peninsula has left behind a bleak scenario of areas of soils highly polluted with heavy metals and trace elements. The plant communities that thrive at these sites are mainly comprised of grassland species, and it is of major concern that these plants are consumed by livestock or wild animals. These grasslands have been the focus of several years of study by our research group, both because of the impacts of their polluted soils on ecosystems and because of their possible remediation role (Pastor and Hernández 2008). Based on the results of numerous plant surveys, the dynamics of these communities exposed to elevated levels of trace elements (Hernández and Pastor 2008a) can be summarised as follows. The most evident impact of pollutants on plant communities is a loss of species diversity. The presence of a pollutant in a habitat affects either the area occupied by each species or the resources they use. These effects depend on the tolerance level of species or their sensitivity to a given pollutant (Pastor and Hernández 2007). As a consequence, effects of pollutants on competition may upset the balance among the community's components, which could wipe out some of the more sensitive populations. This may be observed at the sites examined here; although the dominance of grassland species is evident, legume species are hardly present, probably due to the heavy metals in their soils (Hernández and Pastor 2005). Thus, species frequencies in an ecosystem will vary along a gradient of chronic pollution.