Physicochemical qualities and ecological risk assessment of soil and plants heavy metals contamination in a selected areas around Kipushi mining at the Congolese Copperbelt in DR Congo

Abstract

Mining activities in Kipushi, Democratic Republic of Congo, have generated extensive tailings and waste rock, leading to long-term accumulation of trace metals in soils and vegetation. Despite their ecological and public health significance, integrated assessments of contamination levels, metal speciation, and ecological risks remain scarce in this mining-impacted region. Soil (n = 6) and plant (n = 6) samples were collected from six sites during rainy and dry seasons. Total and bioavailable concentrations of Cd, Co, Cr, Cu, Pb, and Zn were determined using ICP-OES after acid digestion. Sequential extraction (BCR protocol) was applied to assess metal speciation. Contamination was quantified using enrichment factor (EF), contamination factor (CF), geo-accumulation index (Igeo), pollution index (PI), and potential ecological risk index (PERI). Statistical analyses included ANOVA and Pearson correlations. Soils displayed high variability in pH (4.4–7.5), organic matter (2.8–8.1 %), and cation exchange capacity (6–10 meq/100 g). Co, Cu, and Zn frequently exceeded FAO limits, with maximum values of 60.1, 424.1, and 560.7 mg/kg, respectively. CF and Igeo indicated considerable to very high contamination for Cu, Zn, and Co at multiple sites. Sequential extraction revealed that Cd, Cr, and Pb were mainly in reducible fractions, suggesting high remobilization potential, while Cu and Cr were largely residual. In plants, Persea americana, Melissa officinalis, and Lanea discolor accumulated Co, Cr, and Cu above WHO thresholds, with bioconcentration factors up to 0.29. PERI highlighted very high ecological risks, particularly for Pb and Zn in P1–P4. These findings confirm severe contamination of Kipushi soils and vegetation by mining residues, with metals present in labile forms prone to environmental transfer. Native species showed contrasting roles in phytoextraction (P. americana) and phytostabilization (Bamboussa vulgaris). The results underline the urgent need for phytoremediation-based strategies, stricter environmental controls, and systematic monitoring to protect ecosystems and human health in the Congolese Copperbelt.