Artisanal gold mine spoil types within a common geological area and their variations in contaminant loads and human health risks.

This study answered the question of whether mine spoils occurring in a common geological location had similarities in their contaminant load and associated health risks. Using inductively coupled plasma mass spectrometry, the total contents of Cd, Pb, As, Hg, Zn, Fe, and Al were determined for 110 digested soil samples obtained from underground rock ore (URS), oxide ore (OXS), and alluvial ore (AVS) mine spoils. Independent sample Kruskal-Wallis test and pairwise comparisons of sources were used to ascertain the variation in elemental load between the mine spoil investigated. The results showed that mine spoil contaminations and their ecological and health risk significantly varied (p < 0.01) from each other and fell in the order OXS > URS > AVS > forest soils because of their geochemistry. Determined enrichment and geo-accumulation indices revealed that OXS and URS sites were severely-extremely polluted with Cd, Hg, and As, while AVS mine spoils were only moderately contaminated by Cd and As contents. Children had the highest tendency for developing noncarcinogenic health defects largely due to toxic contents of As, Cd, and Hg in soil materials near them than adult men and women would after obtaining a hazard index of 73.5 and 67.7 (unitless) at both OXS and URS sites. Mine spoils especially where hard rocks and oxide ores were processed are not fit for agricultural use or human habitation. The restriction of human access and sustainable remediation approaches are required to avert health defects. Even so, area-specific potentially toxic elements must be targeted during soil cleaning due to the significant variations in contaminant load between mined sites.

Impact of Soil Inoculation with Bacillus amyloliquefaciens FZB42 on the Phytoaccumulation of Germanium, Rare Earth Elements, and Potentially Toxic Elements.

Bioaugmentation promises benefits for agricultural production as well as for remediation and phytomining approaches. Thus, this study investigated the effect of soil inoculation with the commercially available product RhizoVital®42, which contains Bacillus amyloliquefaciens FZB42, on nutrient uptake and plant biomass production as well as on the phytoaccumulation of potentially toxic elements, germanium, and rare earth elements (REEs). Zea mays and Fagopyrum esculentum were selected as model plants, and after harvest, the element uptake was compared between plants grown on inoculated versus reference soil. The results indicate an enrichment of B. amyloliquefaciens in inoculated soils as well as no significant impact on the inherent bacterial community composition. For F. esculentum, inoculation increased the accumulation of most nutrients and As, Cu, Pb, Co, and REEs (significant for Ca, Cu, and Co with 40%, 2042%, and 383%, respectively), while it slightly decreased the uptake of Ge, Cr, and Fe. For Z. mays, soil inoculation decreased the accumulation of Cr, Pb, Co, Ge, and REEs (significant for Co with 57%) but showed an insignificant increased uptake of Cu, As, and nutrient elements. Summarily, the results suggest that bioaugmentation with B. amyloliquefaciens is safe and has the potential to enhance/reduce the phytoaccumulation of some elements and the effects of inoculation are plant specific.

Phytoaccumulation potential of nine plant species for selected nutrients, rare earth elements (REEs), germanium (Ge), and potentially toxic elements (PTEs) in soil.

Given the possible benefits of phytoextraction, this study evaluated the potential of nine plant species for phytoaccumulation/co-accumulation of selected nutrients, rare earth elements, germanium, and potentially toxic elements. Plants were grown on 2 kg potted soils for 12 weeks in a greenhouse, followed by a measurement of dry shoot biomass. Subsequently, elemental concentrations were determined using inductively coupled mass spectrometry, followed by the determination of amounts of each element accumulated by the plant species. Results show varying accumulation behavior among plants for the different elements. Fagopyrum esculentum and Cannabis sativa were better accumulators of most elements investigated except for chromium, germanium, and silicon that were better accumulated by Zea mays, the only grass species. F. esculentum accumulated 9, 24, and 10% of Copper, Chromium, and Rare Earth Elements in the mobile/exchangeable element fraction of the soils while Z. mays and C. sativa accumulated amounts of Cr and Ge ∼58 and 17% (for Z. mays) and 20 and 9% (for C. sativa) of the mobile/exchangeable element fraction of the soils. Results revealed co-accumulation potential for some elements e.g., (1) Si, Ge, and Cr, (2) Cu and Pb, (3) P, Ca, Co, and REEs based on chemical similarities/sources of origin.

This is a novel study because it focuses on evaluating plant species not only the accumulation behavior but the possibilities of co-accumulation of elements comprising selected nutrients, PTEs and CRMs (Ge and REEs) by plants. It provides new information on the biomass production and accumulation behavior of some plant species for some elements, some of which have not been previously studied. It also provides information on the possibility of predicting species accumulation behavior for some elements based on similarities in the source of origin, chemical similarities, or antagonism.