Abstract:
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In Jebel Hamimat, an old operating opencast of ore antimony generated large amounts of debris that led to the contamination of the surrounding area.
It often contains high concentrations not only of exploited metal but also other heavy metals. Because of the high toxicity of the environment, very few plants become established on these spoils mine. The study of the impact of such contamination on vegetation in place, by Rached-Mosbah and Gardou (1988), has shown that there are several species able to grow on the most toxic environments. Among these, Artemisia herba alba Asso. and Thymus algeriensis B.& R. (both medicinal and fodder species) had proven able to take relatively high concentration of antimony (Mosbah-Rached et al., 1992). However, these two plants have not been the subject of any chemical analysis to determine its mode of tolerance for other heavy metals (Cd, Pb, Zn and Cu).
In our study, it appears that the two studied plants can absorb large amounts of trace metals elements (Cd, Pb and Zn) in their leaves and can have a bioaccumulation factor (BAF) very close to or above 1, in particular for Cd and Pb. They suggest that Thymus algeriensis and Artemisia herba alba are resistant to abundant presence of these metal trace elements in their rhizosphere, either by excluding from their leaves (case of zinc) or by accepting it so accumulating them (case of cadmium and lead). As regards the copper, it is found that the two plants are deficient in that metal in their leaves, which would perhaps be the consequence of antagonism with high concentrations of Zn soil (high Cu transfer inhibition by Zn).
Finally, we can learn through this study that the determination of tolerance mode (accumulation or exclusion) of these two species in the presence of heavy metals in excess in metalliferous soils, allows us to envisage their use for the remediation of polluted soils metals in question. However, it appears that Thymus algeriensis, the fact that it is able to grow on soils most highly charged with heavy metals, would be more appropriate for such a purpose. It can also be considered to improve its bioaccumulation factor, in subsequent experiments, by adding fertilizer or chelates. It would also be interesting to study the mode of translocation of these metals trace elements or other metal that adaptive strategies put in place by these species at the cellular and molecular level.
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