Copper smelting has been the source of soil contamination in trace metals in Penga Penga (Lubumbashi). Residents are exposed to trace metal ingestion and planting trees is challenging in such soil conditions. Nevertheless, planting trees in former household dumps or using various types of amendments allowed the provisioning of fruits in few residences. In the perspective of scaling up the process, a survey has been conducted with the aim of assessing the effectiveness of the planting processes on the trace metal content in fruits and leaves of Mangifera indica L. and Syzygium guineense (Willd) DC. Samples were collected in residential households from Penga Penga and Kalebuka (a non-polluted suburb). The bioconcentration factor (BCF) and the safe weekly consumption (SWC) were calculated for each species. Results showed higher values of total and soluble concentrations of Cu, Pb, and Zn in the rhizosphere of the two species at Penga Penga. Metal concentrations were higher in fruits and leaves from Penga Penga with 47% of samples above FAO and WHO thresholds (vs 18.5% in Kalebuka). The BCF values were below 1 demonstrating the effectiveness of the process to reduce metal translocation to leaves and fruits. Recommendations from the SWC limited by Pb for consumption to 9 kg for mango flesh and by Cd 6.6 kg for S. guineense fruits at Penga Penga (Vs 78 and 68 kg at Kalebuka). Finally, results from this study provide interesting lessons from the scaling up and the technical itinerary of planting tree un Penga Penga.

This study aims to contribute to the characterization of Katangese Copperbelt's mining wastes and soils polluted with trace metals, using pollution indices and direct concentration measurements. The study also evaluated the use of these indices in assessing the success of remediation projects. Analytical 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 revealed 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 very high (>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 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.