PGE Production in Southern Africa, Part II: Environmental Aspects

The importance and status of the micronutrient selenium in South Africa: a review

Selenium (Se) is a vital micronutrient with widespread biological action but leads to toxicity when taken in excessive amounts. The biological benefits of Se are mainly derived from its presence in active sites of selenoproteins such as glutathione peroxidase (GPx). An enzyme whose role is to protect tissues against oxidative stress by catalysing the reduction of peroxidase responsible for various forms of cellular damage. The benefits of Se can be harvested when proper regulations of its intake are used. In South Africa, Se distribution in people's diets and animals are low with socio-economic factors and heterogeneous spread of Se in soil throughout the country playing a significant role. The possible causes of low Se in soils may be influenced by underlying geological material, climatic conditions, and anthropogenic activities. Sedimentary rock formations show higher Se concentrations compared to igneous and metamorphic rock formations. Higher Se concentrations in soils dominates in humid and sub-humid areas of South Africa. Furthermore, atmospheric acid deposition dramatically influences the availability of Se to plants. The studies reviewed in this article have shown that atomic absorption spectroscopy (AAS) is the most utilised analytical technique for total Se concentration determination in environmental samples and there is a lack of speciation data for Se concentrations. Shortcomings in Se studies have been identified, and the future research directions of Se in South Africa have been discussed.

Metal contamination and toxicity of soils and river sediments from the world's largest platinum mining area

Mining activities in the world's largest platinum mining area in South Africa have resulted in environmental contamination with Pt (e.g., the Hex River's vicinity). The present study compared a Pt mining area with a non-mining area along this river in terms of (1) metal concentrations in different grain size fractions from soils and aquatic sediments; (2) the toxicological potential of aquatic sediments based on the Consensus-Based Sediment Quality Guideline (CBSQG); and (3) the chronic toxicity of aqueous eluates from soils and sediments to Caenorhabditis elegans. Platinum concentrations were higher in the mining area than in the non-mining area. For most metals, the sediment silt and clay fraction contained the highest metal concentrations. Based on the CBSQG, most sampling sites exhibited a high toxicological potential, driven by Cr and Ni. Eluate toxicity testing revealed that C. elegans growth, fertility, and reproduction inhibition were not dependent on mining activities or the CBSQG predictions. Toxicity was instead likely due to Cd, Fe, Mn, Ni, Pt, and Pb. In conclusion, the investigated region is loaded with a high geogenic background resulting in high reproduction inhibition. The mining activities lead to additional environmental metal contamination (particularly Pt), contributing to environmental soil and sediment toxicity.