Phytoremediation Potential of Vetiver Grass (Vetiveria Zizanioides) in Two Mixed Heavy Metal Contaminated Soils from the Zoundweogo and Boulkiemde Regions of Burkina Faso (West Africa)

In the agricultural regions of Burkina Faso, urban solid waste fertilizers were usually applied. This activity is likely to contaminate the soils and expose populations to serious diseases. This study aims to assess rate of heavy metal (Cd, Cu, Mn, Pb, Zn, Ni, Cr) contamination in both agricultural lixisol and vertisol and to evaluate the removal efficiency of heavy metals using Vetiver grass on different two mixed heavy metal contaminated soils. A pot experiment was conducted to compare the metal accumulation and overall efficiency of metal uptake by different plant parts (roots and shoots) on both tropical soils. After 3 and 6 months growing on laboratory conditions, Vetiver grass plants were harvested and heavy metal concentrations in shoot and root parts determined by Inductively Coupled Plasma - Atomic Emission Spectroscopy. The results indicate that at 3 and 6 moths, the shoot and root concentrations of heavy metals in Vetiver grass harvested in lixisol were higher than vertisol. For different plant parts, all metal concentrations were higher in root than in shoot, except Cu and Pb. At the 3 and 6 months, the BCF values > 1 for Cd, Cu and Zn in both soils showed Vetiver grass as an effective phyto-stabilizer for these metals. However, the TF values > 1 for Cd (lixisol), Mn, Zn Ni and Cr (vertisol) indicated the efficiency of Vetiver for phytoextraction. The results of this study showed that Vetiver is more effective in lixisol, but it can be used for remediation of both studied tropical soils from agricultural region of Burkina Faso. Nevertheless, considering the special limitations of the experimental conditions, further field monitoring is necessary to demonstrate the phytoremediation efficiency of Vetiver in agricultural soils under the climatic conditions of Burkina Faso.

Compost Effect on Diuron Retention and Transport in Structured Vineyard Soils

Diuron is frequently detected in surface- and groundwater under the vineyards, where organic amendments are often used, in Burgundy of France. Undisturbed column experiments were conducted to study the influence of three composted organic amendments on diuron leaching through columns of two vineyard soils from Vosne-Roman′ee(VR, calcareous Cambisol) and Beaujolais(Bj, sandy Leptosol), France. Bromide(used as non-reactive tracer) and diuron breakthrough curves(BTCs) were analyzed using convectivedispersive equation(CDE), two-region(mobile-immobile, MIM) and two-site models. No influence of the composts was observed on the bromide recovery rates. The CDE model described well the bromide BTCs for all columns of the Bj soil and seven of the VR soil, suggesting a homogeneous water flow. However, for five VR soil columns, the MIM model fitted better, suggesting a partition of the water flow(15%–50% of matrix flow). The texture, the coarse material content and the tillage of the VR soil could explain this heterogeneity. However, for all columns, diuron leaching was greater through the Bj soil(46%–68%) than the VR soil(28%–39%). The compost addition resulted in a contrasting effect on diuron leaching: no difference or a decrease was observed for the VR soil, probably due to an increase of adsorption sites, whereas no difference or an increase was observed for the Bj soil possibly because of interactions and/or competition of diuron with the compost water-extractable organic matter which could facilitate its transport. All the diuron BTCs were best described using the two-site model, suggesting a large proportion of time-dependent sorption sites(30%–50%). The soil type and the nature of the amendments had contrasting influences on diuron transport. Composts with a high water-soluble fraction must be avoided in sandy soils to reduce the risk of groundwater contamination.

Vetiver Grass and Micropollutant Leaching Through Structured Soil Columns Under Outdoor Conditions

In Burkina Faso, significant amounts of endosulfan are applied to cotton fields; in addition, urban vegetable agriculture is often characterised by high fertiliser inputs, such as urban solid wastes containing heavy metals(e.g., Cu and Cd). Thus, the relevance of surrounding cotton and urban vegetable plots with vetiver(Vetiveria zizanioides) hedges to reduce environmental pollution by micropollutants was investigated using a leaching experiment, with outdoor lysimeters filled with two representative agricultural soils of Burkina Faso: Vertisol and Lixisol. After 6 months, little Cu was found in the leachates(< 0.010% of the applied amount) due to its high adsorption coefficient and its tendency to remain at the soil surface. Despite leachate and bromide recoveries being greater in soils planted with vetiver grass than in the bare soils, smaller amounts of endosulfan and Cd were found in the effluents from the planted soils(0.01% to 0.70% of the applied amount) than in those from the bare soils(0.01% to 1.48% of the applied amount), in agreement with their adsorption coefficients. These results may also be explained by a greater degradation of endosulfan in planted soils compared to bare soils and the absorption of Cd by vetiver. Thus, vetiver may decrease the risk of groundwater contamination,especially for Cd and endosulfan, which are more mobile than Cu. In addition, despite the smaller amounts of endosulfan and Cd measured in the Vertisol leachates(0.01% and 0.04% of the applied amount, respectively) compared to the Lixisol leachates, vetiver was more effective in decreasing the leaching of micropollutants if planted on Lixisol rather than on Vertisol. Further field monitoring is necessary to demonstrate the effectiveness of vetiver under the climatic conditions of Burkina Faso.