Search Results (2)

The use of trees to revegetate urban areas contaminated by mining activity is a low-cost, low-maintenance technique, of which the success will depend on the plant species, planting methods, and geochemical processes at the soil-plant interface. This study analyzed the evolution of mineral composition in the rooting soil, tree, and herbaceous vegetation on soils contaminated by As, Cd, Cu, Co, Pb, and Zn. An in-situ experiment was carried out in Lubumbashi (South-eastern DR Congo) with six tree species (Acacia auriculiformis, Albizia lebbeck, Delonix regia, Leucaena leucocephala, Mangifera indica, and Syzygium guineense), in 0.187 m³ pits amended with municipal compost and limestone. After planting in the amended and unamended (control) pits, soil samples were taken for chemical analysis. Eighteen months after planting, a floristic inventory was carried out to assess the spontaneous colonization of herbaceous species. The results show an increase in metal concentrations in the rooting soil between 2019 and 2023 (Cu: 725 ± 136 to 6141 ± 1853 mg kg⁻¹; As: 16.2 ± 1.4 to 95 ± 28.5 mg kg⁻¹; Cd: 2.7 ± 1.3 to 8.7 ± 2.0 mg kg⁻¹; Co: 151 ± 36.3 to 182 ± 113 mg kg⁻¹; Zn: 558 ± 418 to 1098 ± 1037 mg kg⁻¹), with a stable pH and a decrease in nutrients (P, K, Ca, and Fe). The trees planted in the amended pits showed better height and diameter growth and greater survival than the controls, reaching average heights of 8 m and a DBH of up to 22 cm four years after planting. A total of 13 spontaneous herbaceous species were recorded, with an increased abundance during the second inventory. These results confirm the effectiveness of pit amendment for the rapid revegetation of urban soils polluted by trace metals. Full article

This study aims to contribute to the characterization of Katangese Copperbelt’s (DR Congo) mining wastes and soils polluted with trace metals, using pollution indices and direct concentration measurements. This study also evaluated the use of these indices in assessing the success of remediation projects. Data from previous studies and samples collected from six types of discharge and one polluted soil were used to address the first objective. Soil and plant samples were collected at Kipushi and Penga Penga for the second objective. The results reveal very high concentrations of As, Cd, Co, Cu, Mn, Pb, and Zn in all mine tailings and polluted soils, compared with local references. The degree of contamination (DC) values (from 72 to 5440) and potential ecological risk (RI) values (from 549 to 162,091) indicate very high-risk situations associated with polluted discharges and soils. Regarding revegetation trials, the results show lower concentrations and RIs in tree rhizospheres compared with unamended areas at both sites. However, trace metal concentrations are higher in tree rhizospheres compared with local references, and RI values are in the considerable risk range for Penga Penga (RI = 533) and in the very high range (>1500) for Kipushi. Bioconcentration factor values are below 1, indicating low accumulation in roots, wood, and leaves, and low risk of contamination of the trophic chain. In this context, it seems that the pollution indices used are suitable for characterizing pollution and prioritization for remediation. However, there seems unsuitable for assessing the effectiveness of phytotechnology processes based on metal stabilization. Direct plant performance measurements combined with direct measurements of metals in substrates and plants to assess transfer and efficiency are more appropriate. Full article