Urban Geochemical Characterisation of Soil from Winnie Mandela Informal Settlement in Gauteng, South Africa: Implications for Environmental Health

Universally, informal settlements form a major parts of the urban landscape due to urbanisation and upsurge in population. The large population in urban informal settlements leads to a huge accumulation of wastes and the release of chemicals such as heavy metals to the surrounding environment. The aim of the study was to give an overview on the current heavy metal content in soil from Winnie Mandela informal settlement in Gauteng, South Africa and evaluate their possible health implications. Methods: Five soil samples were collected from five different functional areas of the settlement during dry season. A random sampling method was used to collect the samples. A 10 g sample was pulverised to a particle size of less than 200 mesh. To determine the concentration of elements, the samples were analysed by the wavelength dispersive XRF method. The level of pollution was assessed by the use of pollution indices, such as geo-accumulation and enrichment factor. Results: The major elements concentrations decreased as SiO2, Al2O3, Fe2O3, MnO, K2O, TiO2, CaO, MgO, P2O5, and Na2O with SiO2, Fe2O3, P2O5, and TiO2 above their average shale values. The concentration of trace elements was descending as Cr > Ba > Zr > V > Zn > Ni > Cu > Rb > Sr > Co > Pb > As > Y > Sc > Nb > Th > U with V, Cr, Co, Ni, Cu, Zn, As, Zr, Nb, and Pb above their average shale values. Moreover, Cr and V were also above the South African soil screening values. All the pollution indices exhibited the highest value of Cr in soil possibly from anthropogenic activities. A strong correlation was witnessed between pairs of Y–Sr (r = 0.94), Zr–As (r = 0.90), Pb–As (r = 0.92), Pb–Zr (r = 0.95), Ni–Cr (r = 0.89), Sr–Rb (r = 0.85), Nb–Co (r = 0.75), Nb–Rb (r = 0.85), Th–Y (r = 0.87), and U–Zn (r = 0.89). The analysis of variance displayed a significant difference (P < 0.05) of trace elements in soil signifying that the trace elements pollutants in this informal settlement originate from different anthropogenic sources. Possibly, traffic, sewage waste, poor waste management, waste burning, and construction materials may be attributed as the sources of these trace elements. The level of trace elements in soil exhibited a possibility of non-cancer risks to children and adult. For carcinogenic risk, the total cancer risk values in children and adults were also above the acceptable limit signifying a likelihood of cancer risk to the local inhabitants. In this informal settlement, children were at higher risk of both non-cancer and cancer risk than adult. Conclusion: Urban informal settlements impact the environment negatively therefore, there is a need to raise awareness on heavy metal pollution and their possible health effects. The study will serve as a basis for future research on geochemistry and health risk assessment of urban informal settlement’s soil. It will also help to develop guidelines for management of informal settlements environment and protection of inhabitants’ health.