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Efficacité du vétiver (Vetiveria zizanioides) pour limiter la dispersion de trois micropolluants dans les sols cotonniers et maraîchers du Burkina Faso : endosulfan, cuivre et cadmium

Abstract : Vetiver was chosen to form hedges around the cotton crops and market gardens in Burkina Faso, in order to limit pollutants dispersal towards plants, surface water and groundwater. The influence of vetiver on the fate of two heavy metals (Cu and Cd) and an insecticide (endosulfan) in the soil-water-vetiver system was studied in two representative soils of Burkina Faso, a vertisol and a lixisol. Batch adsorption coefficient measurements, pot and leaching experiments, under phytotronic and outdoor conditions, respectively, were conducted. For both soils, adsorption coefficient values (Kf) of endosulfan, Cu and Cd were higher on planted soils (Kf = 6.5 - 9.7, 3162.6 - 4445.1 and 76.8 - 280.2 mg1-n Ln kg-1, respectively) than on unplanted soils (Kf = 6.3 - 7.2, 328.1 - 2921.9 and 37.2 - 206.1 mg1-n Ln kg-1, respectively). In addition, vertisol adsorbed larger endosulfan, Cu and Cd amounts than lixisol, probably due to its highest organic carbon and clay contents. In the pot experiments, 6 months after treatment, endosulfan was neither detected in the vetiver shoots and roots, nor in soils. The non-detection of endosulfan could be explained by its degradation, mineralization, volatilization and the non-extractable residue's formation. In our conditions, the estimated endosulfan half-life (DT50) was higher in lixisol (43,1 days) than in vertisol (40,6 days). The endosulfan DT50 in planted soils was 1.1-fold lower compared to unplanted soils, in accordance with the significant increase of the microflora degrading endosulfan in planted soils. Moreover, the Cu and Cd contents in vetiver grass were significantly higher for the lixisol than for the vertisol, 6 months after treatment, related to the CuMgCl2 and CdMgCl2 contents, higher in lixisol than in vertisol. The biological absorption coefficient (BAC) and bioconcentration factor (BCF) of Cu and Cd were greater than 1 in vetiver, but their translocation factor (TF) was less than 1, that showed the efficiency of vetiver to absorb and accumulate Cu and Cd. In outdoor conditions, 6 months after treatment, the leached Cu amounts were very low for all columns (0.001 to 0.010%). For endosulfan and Cd, the leaching losses through the lixisol (0.07% and 1.48%, respectively) are higher than through the vertisol (0.01 and 0.04%, respectively). In the presence of vetiver, the Cd and endosulfan leached amounts were more than 2-fold lower than those of unplanted soils, related to their higher adsorption and the faster degradation of endosulfan in planted soils. The effectiveness of vetiver to limit micropollutants transfer towards surface and groundwaters would need a plot scale validation before encouraging the hedges implementation around the cotton plots and market gardens in Burkina Faso.
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Submitted on : Tuesday, December 4, 2012 - 6:38:32 PM
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Norbert Ondo Zue Abaga. Efficacité du vétiver (Vetiveria zizanioides) pour limiter la dispersion de trois micropolluants dans les sols cotonniers et maraîchers du Burkina Faso : endosulfan, cuivre et cadmium. Sciences de l'environnement. Université de Lorraine, 2012. Français. ⟨NNT : 2012LORR0026⟩. ⟨tel-01749194v2⟩

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