Induced accumulation of Au, Ag and Cu in Brassica napus grown in a mine tailings with the inoculation of Aspergillus niger and the application of two chemical compounds

Abstract

This study evaluated the ability of Brassica napus for extracting gold (Au), silver (Ag) and copper (Cu) from a mine tailings, with the inoculation of two Aspergillus niger strains, and the application of ammonium thiocyanate (NH₄SCN) or ammonium thiosulfate [(NH₄)₂S₂O₃]. After seven weeks of growth inoculated or non-inoculated plants were applied with 1 or 2 g kg^-1 of either NH₄SCN or (NH₄)₂S₂O₃, respectively. Eight days after the application of the chemical compounds, plants were harvested for determining the total dry biomass, and the content of Au, Ag, and Cu in plant organs. Application of (NH₄)₂S₂O₃ or NH₄SCN resulted in enhanced Au-accumulation in stems (447% and 507%, respectively), while either (NH₄)₂S₂O₃+Aspergillus, or NH₄SCN increased the Au-accumulation in roots (198.5% and 404%, respectively) when compared to the control. Treatments with (NH₄)₂S₂O₃ or (NH₄)₂S₂O₃+Aspergillus significantly increased (P ≤ 0.001) the accumulation of Ag in leaves (677% and 1376%, respectively), while NH₄SCN + Aspergillus, and (NH₄)₂S₂O₃ enhanced the accumulation in stems (7153% and 6717.5%). The Ag-accumulation in roots was stimulated by NH₄SCN+ Aspergillus, and (NH₄)₂S₂O₃+ Aspergillus (132.5% and 178%, respectively), when compared to the control. The combination of NH₄SCN+Aspergillus significantly enhanced the Cu-accumulation in leaves (228%); whereas NH₄SCN+ Aspergillus, or (NH₄)₂S₂O₃+ Aspergillus resulted in greater accumulation of Cu in stems (1233.5% and 1580%, respectively) than the control. Results suggest that either NH₄SCN or (NH₄)₂S₂O₃ (with or without Aspergillus) improved the accumulation of Au and Ag by B. napus. Accumulation of Au and Ag in plant organs overpassed the hyperaccumulation criterion (> 1 mg kg^-1 of plant biomass); whereas Cu-accumulation in stems and roots also overpassed such criterion (> 1000 mg kg^-1) by applying either NH₄SCN or (NH₄)₂S₂O₃ + A. niger.

Keywords: Chemical lixiviation; Hyperaccumulation; Phytomining; Plant biomass; Precious metals.