Evaluating the phytoremediation potential of native plants for potentially toxic elements removal from contaminated soils around artisanal and small-scale gold minings in Tanzania
Abstract
Although Artisanal and Small-Scale Gold Mining (ASGM) is a vital economic driver in Tanzania, supporting more than 1.5 million livelihoods, it significantly contributes to Potentially Toxic elements (PTEs) contamination, threatening soil health and public safety. This study assessed the phytoremediation potential of indigenous plant species within the Lupa Goldfield (Chunya District, Mbeya). Analysis of 50 soil samples and 19 plant species collected from five mining sites (Chokaa, Makongolosi, Itumbi, Matundasi, and Mbugani) was conducted at distances ranging from the source to 200 meters. Atomic Absorption Spectroscopy (AAS) was used to quantify Pb, Hg, Cd, As, and Zn concentrations in both soil and plant samples and compared to WHO/FAO (2008) benchmarks. Findings revealed significant point-source pollution: mean soil concentrations near tailings were 40.73 ± 0.5 mg kg-1 (Pb), 3.17 ± 0.14 mg kg-1 (Hg), 4.36 ± 0.25 mg kg-1 (Cd), 1.69 ± 0.02 mg kg-1 (As), and 24.9 ± 0.54 mg kg-1 (Zn). These levels declined sharply at the 200 m mark (p < 0.05), with Pb dropping to 17.48 ± 0.64 mg kg-1, Cd to 0.16 ± 0.05 mg kg⁻1 As to 0.27±0.01 mg kg-1 and Zn to 5.99±0.54 mg kg-1 (Zn) at 200 m (p < 0.05). Voucher specimens have been deposited at the NM-AIST Herbarium for reference. On phytoremediation potential, the results recorded Urochloa mutica (BAF=3.0), Bauhinia petersiana (BAF=1.7), Cyperus rotundus (BAF=1.3), and Cariniana estrellensis (BAF=1.1) as good candidates for phytoremediation of As. Furthermore, the study identified Bauhinia petersiana (BAF=1.3) and Terminalia sambesiaca (BAF=1.4) as effective candidates for cadmium (Cd) phytoremediation, while Schoenoplectus corymbosus (BAF=1.3) demonstrated significant potential for mercury (Hg) remediation. These results establish a quantitative framework for using these native species in cost-effective ecological restoration programs in the ASGM-affected regions of the Lupa Goldfield.