Biological filtration to reduce trace elements in poplar leaves in a contaminated dredged sediment landfill site

Abstract : Aided phytostabilisation is a management option which aims at reducing environmental risk, by the action of plants and amendments. Reported as a sustainable alternative to conventional techniques of soil management, aided phytostabilisation is an attractive strategy but rarely applied by soil management professionals due to the lack of feedbacks. Demonstrations at a field scale are still needed to evaluate its long term performance. Therefore, a field trial of 1 ha was set up in April 2011, on a contaminated landfill site of dredged sediments in Fresnes-sur-Escaut (Hauts-de-France, France). The site was contaminated with Cd (11 ± 17 mg kg-1), Cu (79 ± 33 mg kg-1), Pb (541 ± 1398 mg kg-1) and Zn (1506 ± 856 mg kg-1) and presented a spatial heterogeneity in TE (trace element) distribution in topsoil. Two poplars clones (I214 and Skado) were planted in Short Rotation Coppice (SRC) then inoculated with mycorrhizal inoculum to reduce TE mobility and translocation to aerial parts of trees. This mycorrhizal association was also expected to improve growth and tolerance of trees with a perspective of biomass valorisation via energy production. We investigated the influence of soil conditions and mycorrhizal inoculum on TE mobility, as well as TE accumulation in leaves, four year after the establishment of the field trial. Ca(NO3)2 extractions (0.01M) were performed on sediment samples collected in the site to assess TE extractability. In parallel, poplar leaves and nettles, which highly colonized the site, were collected to study TE accumulation in plants. In addition, sequential extractions (Quevauviller, 1997) were carried out to study the effects of the inoculation on TE speciation in the rhizosphere. Poplars did not show any toxicity symptoms, and exhibited higher biomass with the inoculation. However, both cultivars accumulated high amounts of Cd and Zn in their leaves (above physiological values), particularly in the plots with higher extractable Cd and Zn contents. Foliar Cd and Zn contents mainly decreased in I214 inoculated clones from the most contaminated plot, suggesting an efficiency of the inoculation, which may depend on the contamination level and cultivar. TE contents found in nettles were higher than physiological values, but rather low compared to physiological values of other plants. Therefore, the suitability of nettle in aided phytostabilisation need to be more investigated, since plant cover is necessary to limit TE exposure and soil erosion. Sequential extractions revealed that Cd and Zn were mostly bound to carbonates and Fe and Mn oxides in all tested plots. Cd and Zn could be dissolved easily under acidic conditions induced by exudates, enhancing TE accumulation in trees. Otherwise Cr, Cu and Pb were mostly bound to the residual fraction and organic matter. The inoculation did not affect TE speciation, since no differences were detected between plots with or without mycorrhizal poplars. Even so, mycorrhizae may play a role in the transfer of Cd and Zn in trees as “biofilters”, since lower Cd and Zn contents were found in leaves of I214 inoculated clones.
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Submitted on : Friday, August 3, 2018 - 2:30:48 PM
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Phonethip Phanthavongsa, M. Chalot, Arnaud Papin, Valérie Bert. Biological filtration to reduce trace elements in poplar leaves in a contaminated dredged sediment landfill site. 14. International Conference on the Biogeochemistry of Trace Elements (ICOBTE 2017), Jul 2017, Zurich, Switzerland. ⟨ineris-01853612⟩

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