A long-term study was conducted between 1985 and 2003 on rehabilitation trials at Sishen Iron Ore Mine, South Africa, to identify grass species that would survive in the artificial growth medium applied to the sites, and to determine the most suitable medium for sustainable vegetation growth. Vegetation establishment was tested at slopes of 18o and 34o and with five different cover materials. After 17 years of rehabilitation, investigations showed that weathered limestone sloped at 18o produced the highest percentage of plant cover and least erosion. Sixteen grass species were introduced and identified in the survey, with Eragrostis sp. and Cenchrus ciliaris as the dominant species. In 2004, new trials were initiated at the same mine to evaluate the effectiveness of different seeding methods and supplementation of the growth medium with organic material. After 4 years, hydro seeding was found to be the best method to distribute seeds evenly and to ensure uniform vegetation growth. Different engineering designs, such as changing the contour length and slope, had little influence on the measured parameters. A total of 28 grass species were identified in the sampling plots, with Enneapogon cenchroides and Cenchrus ciliaris as the dominant ones. Dehydrogenase activity was used as a proxy for microbial activity, and a positive association was observed between microbial activity and percentage organic carbon, emphasising the importance of soil organic matter in the soil development process.

Vegetation at mining sites can produce increased heavy metal leaching by the organic acids and protons originating from root secretion and litter degradation. Batch experiments were conducted to investigate the effects of organic acids and pH on the extraction of Pb, Cd, Zn and Cu from an alkaline mine soil and an acid mine soil. The results showed that in the presence of organic acids (acetic, oxalic, malic, fumaric, tartaric and citric acids) at pH 7, the extraction of Pb, Cd, Zn and Cu from the acid mine soil was much higher than that from the alkaline mine soil, in which only citric acid with higher concentration was capable of extracting some heavy metals. Citric acid had the strongest ability in extracting heavy metals, followed by oxalic acid. Heavy metal extraction dramatically decreased with increasing pH. Moreover, at low pH, oxalic acid promoted the risk of Cu leaching; at high pH, the leaching of Pb, Zn, Cd and Cu was enhanced by both oxalic and citric acids. This indicated that those plants which can produce substantial citric acid or oxalic acid by root secretion and litter degradation should not be selected for the REVEGETATION of mining sites.

Sanitary landfills, created for the disposal of solid waste, usually are developed into parks after they are closed. However, soil amelioration with organic matter is usually needed to restore fertility and promote REVEGETATION. Sewage sludge creates a massive waste disposal problem. The use of composted sewage sludge (biosolid) as a soil conditioner might restore the soil fertility at landfill sites and simultaneously alleviate the need for sewage sludge disposal. We applied biosolid to waste landfill soil and evaluated its effects on soil properties and tree growth in a field experiment. Biosolid improved soil characteristics including moisture, organic matter, and nitrogen content and also increased tree height and diameter at breast height.Physiological measures, such as chlorophyll content and photosynthetic rate, showed positive responses in trees grown in biosolid treatments. Heavy metal concentrations in soil and tree leaves after applying compost did not differ from concentrations measured at control sites. Therefore, we conclude that the use of biosolid in waste landfills would be an efficient, environmentally beneficial, and cost-effective method to restore the conditions of landfill soil for plants.

Industrialization advances have led to an increase soil contamination by heavy metals. Among different technologies, in situ stabilization of metals combined with REVEGETATION attracted attention. Therefore, this study aimed at comparing effects of biochars [rice husk biochar (RHB), maple leaves biochar (MLB)] and common inorganic amendments [red mud (RM), and steel slag (SS)] at different rates (0.5, 1, and 2% w/w) on leaching, and phytoavailability of metals (assessed using mustard green ‘‘Brassica juncea"). Soil pH in treated soils significantly (p<0.01) increased, with the optimal pH ranges for plant growth observed in biochar-treated soils. The leaching of Cd, Cu, Pb, and Zn through soil significantly (p<0.05) decreased in treated soils. Plant uptake and accumulation of Cd, Cu, Pb, and Zn decreased by 79–66, 13–19, 87–86, and 37–36% in RHB- and MLB-treated soils, respectively. Sequential extraction analysis pointed out that the major stabilization mechanism for metals using biochars involved the formation of organic and carbonate bonds, while for RM and SS was believed to involve the formation of inner sphere complexes with Fe/Al (hydr) oxides. The plant available fractions for Cd were generally higher than those for others. Overall, high dosage addition (2%) of each amendment offered the best compromise as it successfully reduced both leaching and phytoavailability of metals. Using MLB for the first time, showed promising results to immobilize metals with an increase in plant biomass.

The degree of contamination by heavy metals (arsenic, copper, lead, tin and zinc) in soil and transfer to plants has been studied. Specimens of plant species from five locations in an area of 10 x 10 m were sampled with their corresponding soils. Thirty six plant species including two shallow water aquatic plants were identified. Soil and plant specimens were analyzed by using inductively coupled plasma optical emission spectrometry. It was found that metal concentration in soil was highly variable while concentration of metals in plants directly depends on the concentration of metals it was rooted. Roots showed highest metal concentration followed by leaves, shoots and flowers. Bioconcentraion factor and translocation factor were calculated, representing Cyperus rotundus L. as a potential tin-hyperaccumulator plant, previously not reported in literature. Plant Species Imperata cylindrica, Lycopodium cernuum, Melastoma malabathricum, Mimosa pudica Linn, Nelumbo nucifera, Phragmites australis L., Pteris vittata L. and Salvinia molesta, were metal accumulator while Acacia podalyriaefolia G. Don, Bulb Vanisium, Dillenia reticulate King, Eugenia reinwardtiana, Evodia roxburghiania Hk. f. clarke, Gleichenia linearis, Grewia erythrocarpa Ridl., Manihot esculenta Crantz, Paspalum conjugatum Berguis, Passiflora suberosa, Saccharum officinarum, Stenochlaena palustris (Burm.) Bedd. and Vitis trifolia Linn. were tolerated plant species. All other studied plants were excluders. Identified plant species could be useful for REVEGETATION and erosion control in metals contaminated ex-mining sites. Morphological changes such as reduction in size, change in color and deshaping have also been observed in plant species with high metal values.