Background, Aim and Scope:
The settlement of non-ferrous metal-polluted soil by phytoremediation requires an overall and permanent vegetal cover. To select the most suitable plant species, it is necessary to study over time metal effects on plants, thereby checking that metals remain stored in root systems and not transferred in aerial parts. Seasonal and annual variations of metal bioaccumulation, transfer, and phytotoxicity in two plant species, Trifolium repens and Lolium perenne, grown in a Cd, Pb, and Zn-contaminated soil were also studied.
Materials and Methods:
The experimental site was located near a closed smelter. In spring 2004, two areas were sown with T. repens and L. perenne. Thereafter, samplings of plant roots and shoots, and surrounded soils were realized in autumn 2004, and spring and autumn 2005. Agronomic parameters of soils, Cd, Pb and Zn concentrations in surrounded soils and plant organs, and oxidative alterations (superoxide dismutase, malondialdehyde, and 8-hydroxy-2’-deoxyguanosine) in plant organs were carried out.
Results:
Whatever the sampling period, metal concentrations in soils and plants were higher than background values. Contrary to metal concentrations in soils, they were slight fluctuation of metal concentrations in plant organs over time. Bioaccumulation and transfer factors confirmed that metals were preferentially accumulated in roots, as follow: Cd>Zn>Pb, and their transfer to shoots was limited. There was also foliar metal deposition. The result show that there are seasonal and annual variations of metal accumulation in the two studied plants. These variations differ according to the organs and these variations follow nearly the same pattern for the two species. Oxidative alterations were observed on biomolecules (polyinsatured fatty acids, DNA) in plant organs with regard to antioxidant enzyme activities, MDA and 8-OHdG concentrations. These alterations vary according to temporal variations of metal concentrations.
Discussion:
Metal concentrations in surrounded soils and plant organs showed the effective contamination by dust industrial emissions. Metals absorbed by plant were mainly stored in roots. With regard to this storage these plants seem to limit the metal transfert to aerial parts over time, thereby indicating their availability for metal phytostabilization. Aerial deposition was another source of plant exposure to non-ferrous metals. Despite the occurrence of metal-induced oxidative alterations in plant organs, both the plant models seemed tolerate a high heavy metal concentration in soils.
Conclusions:
Taken together, these results indicated that these two plant species were able to form a vegetal cover on heavily Cd, Pb, and Zn-polluted soils, to limit the metal transfer to aerial parts and to resist to oxidative damages. All these characteristics make them suitable for the phytostabilization on metal contaminated soil. These findings also highlighted the necessity to take into account seasonal and annual variations for a future phytomanagement by phytostabilization.
Recommendations and
Perspectives:
In a phytostabilization way, the technique used for Lolium perenne et Trifolium repens could be mixed with tree species adapted to heavy metal contaminated soils. It could be interesting to evaluate the pertinence of studied stress biomarkers on these specific plants.
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