The effect of compost and moringa leaf extract biostimulant on the phytoremediation of gold mine tailing in South Africa using Chrysopogon Zizanioides (l.) roberty

This study investigated the efficacy of compost and Moringa oleifera leaf extract (MLE) in enhancing the phytoremediation potential of vetiver grass on the gold mine tailings storage facilities (TSF) in the Witwatersrand goldfields region in South Africa. We hypothesized that: (1) Concentrations of heavy metals are high on the tailings material, (2) The growth and phytoremediation potential of vetiver grass will be enhanced in compost-amended tailings with MLE application, with the greatest improvement observed at the highest compost amendment rate (30 % > 15 % > 0 %). The TSF indeed exhibited elevated levels of heavy metals, with arsenic (As) and chromium (Cr) concentrations surpassing both Soil Screening Values (SSV) 1 and 2, while copper (Cu), lead (Pb), and nickel (Ni) levels exceeded SSV1, indicating potential environmental and health risks. A factorial split-plot design was employed, with three levels of compost treatment (0 %, 15 %, and 30 %) and either 0 % or 3 % MLE application sprayed on vetiver grass weekly for 16 weeks. The results showed that vetiver grass died in unamended tailings regardless of MLE application. However, there was no significant difference in growth parameters between vetiver planted on 15 % and 30 % compost amendment. The concentrations of As, Cr, Ni, and Cu were higher in the roots than in the leaves across all treatments. Application of MLE significantly reduced metal uptake (As, Cu, Cr, Ni) in vetiver roots in both the 15 % and 30 % compost amendments. But MLE did not affect the metal accumulation in the leaves of the vetiver grass except for a significant decrease in the uptake of As in 30 % compost amendment as well as a significant decrease in Ni in 15 % amendment. Pb was undetected in both leaves and roots. Notably, the application of MLE biostimulant significantly enhanced vetiver biomass in both 15 % and 30 % compost amendment treatments. This study highlights the synergistic benefits of combining compost and MLE, which enhanced phytostabilization by reducing metal uptake into roots while promoting vetiver grass growth. The findings have significant implications for tailings management, pollutant mitigation, bioenergy production, and carbon sequestration, offering a game-changing approach for sustainable and circular economy practices in mine tailings management.