Assessing Phytoremediation Potentials of Selected Plant Species in Restoration of Environments Contaminated by Heavy Metals in Gold Mining Areas of Tanzania

Abstract

Phytoremediation uses green plants for in-situ removal, degradation, and containment of contaminants in soils, surface waters and groundwaters. However, little research has been conducted on the phytoremediation potential of plant species in removing heavy metals in the contaminated soils within the gold mining concession areas. Therefore, this study assessed and classified the phytoremediation potentials of selected plant species around gold mining areas in restoring the environments contaminated by heavy metals. The geographic focuses of the study were the Golden Pride Gold Mine (GPGM) and Geita Gold Mine (GGM) in Tanzania. The shoots and roots of plant species surrounding the mining areas and the samples of associated soils were collected and analysed for total concentrations of lead (Pb), chromium (Cr), cadmium (Cd), copper (Cu), arsenic (As), manganese (Mn) and nickel (Ni) using Atomic Absorption Spectrophotometer (AAS) and UV-VIS spectrophotometry. Routine soil analysis was performed to provide an impression of the fertility status of soils in these gold mining areas. Further, the plants were classified based on their ability to accumulate or exclude heavy metals from the soils. Results indicated that the soils from study areas were loamy textured and slightly acid (pH 6.1–6.5), soil organic carbon and organic matter were low (0.6–2.0%), total nitrogen was very low (<0.10%), phosphorous ranged from low (6–12 mg kg-1 soil) to high (13–25 mg kg-1 soil), and cation exchange capacity ranged from low (6.0–12.0 cmol(+) kg-1 soil) to medium (12.1–25.0 cmol(+) kg-1 soil). In assessing heavy metals using plant parts, the roots of giant rats-tail grass (Sporobolus pyramidalis) accumulated highest Pb (757.78 µg g-1), Creeping Blepharis (Blepharis maderaspatensis) Cd (158.11 µg g-1), lantana (Lantana camara) As (68.61 µg g-1), and leuceana (Leucaena leucocephala) accumulated higher Mn (2734.61 µg g-1) and Ni (4464.33 µg g-1). In shoots, L. leucocephala accumulated higher Cr (1276.67 µg g-1) and higher Cu (2744.44 µg g-1) in L. camara. Results indicated that S.pyramidalis and L.camara are hyper-accumulators of Pb and Cu, respectively. No hyper-accumulator of Cr, Cd, As, Mn and Ni in the areas. Results further revealed that S. pyramidalis, Natal grass (Melinis repens), L. camara, L. leucocephala and B. maderaspatensis are potential phytoremediators, as were either accumulators or excluders of Pb, Cr, Cd, Cu, As, Mn and Ni. Although S. pyramidalis, M. repens, L. camara, B. maderaspatensis and L. leucocephala are likely to pose hazards to herbivores (grazing animals) while entering the food chain, they are still the potential phytoremediators in decontaminating of metalliferous affected ecosystems.