Assessment of phytoremediation potentials of native economically-valuable tree species in a lead-zinc abandoned mining site in Enyigba, Nigeria

This study investigated heavy metal contamination in soils from an abandoned minefield and assessed the phytoremediation potential of Spondias mombin, Cola gigantea, and Ceiba pentandra tree species . Soils from the minefield exhibited significantly higher concentrations of heavy metals, including Pb (1411 ± 164.1 mg/kg), Ni (194.9 ± 20.5 mg/kg), Cd (22.9 ± 4.4 mg/kg), and Fe (50.3 ± 10.8 mg/kg), compared to the control site. These elevated levels indicate persistent pollution from past mining activities. In plants, heavy metals were mainly concentrated in root tissues. Spondias mombin accumulated the highest levels of As (12.1 mg/kg), Ni (127 mg/kg), and Fe (28.2 mg/kg), while Ceiba pentandra showed maximum Hg (6.9 mg/kg) and Pb (1417 mg/kg) uptake. Bioaccumulation factors (BAFs) for all species were below 1, indicating none are hyperaccumulators. However, Spondias mombin recorded relatively high BAFs (e.g., Pb = 0.97, Hg = 0.97), making it the most effective for phytostabilization. Translocation factors (TFs) were also below 1, signifying metal retention in roots. Ceiba pentandra had the lowest BAF and TF values, limiting its remediation potential. These results underscore Spondias mombin and Cola gigantea as suitable species for phytostabilization of mine-contaminated sites. The study highlights the need for species-specific phytoremediation strategies, including biomass management and soil amendments. Soil analysis showed higher concentrations of Hg, As, Ni, Pb, Cr, Cd, Fe, Cu, and Zn in the minefield, with Pb, Cd, and Fe posing the greatest risks. Plant tissue analysis revealed metal accumulation in roots, with Spondias mombin showing the highest bioaccumulation potential for Hg, As, Pb, and Zn, making it ideal for phytostabilization. Cola gigantea exhibited moderate uptake, while Ceiba pentandra had the lowest bioaccumulation. The study suggests alternative methods like soil amendments and microbial-assisted techniques for better metal stabilization and risk reduction.