Tolérance et accumulation des métaux lourds par la végétation spontanée des friches métallurgiques : vers de nouvelles méthodes de bio-dépollution

Abstract : Among the main pollutants generated by industrial activities, heavy metals, such as Cu, Pb or Cr, are of major concern. Indeed, these elements, which are nonbiodegradable, are highly ecotoxic and could be implied in different human diseases. Thus, to resume the terms of a recent report of the Parliamentary Office of the Scientific and Technological Choices, "if heavy metals made civilization, they can also dismantle it". It is today essential not only to better know the effects of these pollutants on the living organisms, but also to develop adapted solutions, in order to limit the risks. In this context, plants are really interesting. Indeed, plants, which are directly confronted with the toxic compounds of the medium, could be not only used as biomarkers of toxicity of the medium, but also as a tool for stabilization of the pollutants. However, data concerning influence of heavy metals on vegetation, subjected to a chronic metal exposure, as well as the role of the plants on metal becoming are still insufficient. Consequently, is necessary to carry on research in this field in order to better understand interactions between plants and pollutants and to find new species usable in phytoremediation programs.
This work presents results of the study of the natural vegetations developing on three metallurgical dumps in Rhone Alpes region. Although heavily polluted soils, more than 200 plant species were identified, belonging to 50 botanical families. Thus, using a standardized procedure, metals were highly “phytoavailable”, whereas mean leaf metal contents in native vegetation showed no more accumulation than a reference plant growing in uncontaminated environments. Consequently, metal phytoavailability can be considered as low despite very high total levels. Although poor phytoavailable metals levels were demonstrated, metallurgical waste deposits had clearly an impact on the structure of plants communities. Phytosociological relevés performed on the metallurgical sites evidenced four quite unusual well-marked major vegetation goup whose three of them had never been described. Among these groupments, the abundant species, Plantago arenaria Waldst. & Kit. showed high metal tolerance, especially for Cd. For Cd and Ni tolerance was a constitutive character and an adaptative trait for Cu. This good constitutive tolerance could be a characteristic of pioneer and dryness resistant species. In P. scabra, the mechanisms of Cd resistance to cadmium could imply an activation of the antioxydant root system and a translocation limitation.
To continue this work, it's necessary to get complementary information on resistance mechanisms involved in heavy metal tolerance in P. arenaria and particularly on intracellular chelation. In addition, it would be interesting to carry out the first tests of recolonisation in real conditions.
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Esteban Remon. Tolérance et accumulation des métaux lourds par la végétation spontanée des friches métallurgiques : vers de nouvelles méthodes de bio-dépollution. Biologie végétale. Université Jean Monnet - Saint-Etienne, 2006. Français. ⟨tel-00362527⟩

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