Comparative assessment of the state of growth and bioaccumulation of manganese in Poaceae growing on the Mbembele manganese mine in Gabon

Abstract

The study conducted at the Mbembele manganese mine in Ndjolé, central Gabon, aimed to evaluate the manganese (Mn) levels in soil from the tailings dam and assess the phytoremediation potential of selected Poaceae species. Four species, namely Phacelurus gabonensis, Cenchrus setosus, Panicum sp, and an undetermined gramineae species, were chosen for their rapid growth, high biomass production, and adaptation to the mine's soil conditions. Soil analysis revealed elevated Mn concentrations, surpassing the average composition of the upper continental crust (UCC), indicating significant Mn contamination. The Poaceae species exhibited substantial biomass growth after six months, suggesting their adaptation to high Mn levels in the soil. Mn accumulation was generally higher in the roots than in the leaves, except for Phacelurus gabonensis, which showed higher Mn concentrations in the leaves. Interestingly, Mn concentrations in plant tissues were higher at three months than at six months, implying a limited biological uptake capacity over time for these species. While the bioconcentration factor (BCF) was less than 1 for all plants, only Phacelurus gabonensis demonstrated a translocation factor (TF) greater than 1, indicating its potential for moving Mn from roots to shoots. The findings suggest that, among the studied Poaceae species, Phacelurus gabonensis could be a promising candidate for phytoremediation of Mn-contaminated soils in Gabon. Renewing this species every three months may enhance its effectiveness in rehabilitating mining soils impacted by Mn contamination. The study provides valuable insights into the potential use of indigenous plant species for sustainable environmental remediation efforts in the region.