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.