Acacia trees-legumes potential for phytoremediation of urban landfill soil in Bonoua (Côte d’Ivoire)

Landfills in urban areas contribute to soil and water pollution with heavy metals. In Côte d’Ivoire, urban landfill soil is used to produce food, which presents health risks. This study evaluates the growth capacity of Acacia spp. trees-legumes (Acacia mangium, Acacia auriculiformis, and Acacia crassicarpa) and their potential for landfill soil remediation and restorations. These trees-legumes were grown under controlled conditions for six months in polluted soils sampled from urban landfills located in southeastern Côte d'Ivoire. The study used a simple, completely randomized design with four treatments (Acacia mangium, Acacia auriculiformis, Acacia crassicarpa, and control) and five replicates. Growth parameters, soil pH, metal contents (bulk soil, leachate), and plants were measured during this experiment. The results indicated that Acacia auriculiformis and Acacia mangium displayed better growth indicators (dry biomass, heights, and number of phyllodes) compared to Acacia crassicarpa. The soil pH under the trees-legumes indicated a significant decrease compared to the control (p < 0.05). In addition, heavy metal contents significantly decreased in the leached solutions of the planted soil compared to the control (p < 0.05). In the exchangeable soil fraction, only the Acacia auriculiformis treatment showed a significant decrease in Zn compared to the control. Regarding the plants, Acacia auriculiformis showed the highest amounts of Pb (111 µg plant-1) and Cd (54 µg plant-1) in total biomasses. Acacia crassicarpa had the highest metal extraction capacity from the polluted soil (Pb: 24 µg plant‑1, Cr: 11 µg plant-1, Cd: 14 µg plant-1, and Zn: 83 µg plant-1) compared to the two other species. The Acacia crassicarpa species appears to be the best one for the phytoremediation of landfill soils.