Mlalazi, Nkanyiso2018-07-182018-07-182017Mlalazi, Nkanyiso (2017) Metal content on soil and a wild leafy vegetable, Bidens pilosa L. on the Witwatersrand gold fields, University of the Witwatersrand, Johannesburg, https://hdl.handle.net/10539/25031https://hdl.handle.net/10539/25031A research report submitted in partial fulfillment of the requirement for the degree of Master of Environmental Science to the Faculty of Science, School of Animal, Plant and Environmental Sciences (AP&ES) Johannesburg. 31 August 2017.Metal pollution could result in health and economic risks to communities. Plant absorbs both essential and toxic elements from polluted soil and water. Consumption of contaminated vegetables and incidental ingestion of soils have been confirmed to be a pathway of contaminants for humans and livestock. Previous studies have established that some species which are utilized as wild leafy vegetables (WLVs) grow on polluted land in Witwatersrand goldfields, and people harvest these vegetables for consumption. An edible plant that is harvested and consumed is Bidens pilosa (black jack). Samples of soil and corresponding B. pilosa leaves were collected from a mine contaminated site on the Witwatersrand known as the Varkenslaagte, in Gauteng Province which is being monitored since the implementation of phytoremediation about 14 years ago. Metal concentrations were compared with those in soil and leaf material collected from different sites, viz., (i) the nearby Kraalkop nature reserve (n=2); (ii) a commercial/industrial site in Johannesburg’s central business district (n=1) and (iii) a residential site in Johannesburg (n=1). Different soil particle size fractions and leaf material subjected to different treatments were analysed for iron (Fe), zinc (Zn), arsenic (As), and lead (Pb) concentrations. Concentration of As in unfractionated soils were highest in Kraalkop plot 2 (52.6 mg/kg). Johannesburg commercial area had the least As concentration (6.3 mg/kg). Zinc concentrations in soils were highest in Johannesburg commercial area (649.3 mg/kg) and lowest in Varkenslaagte (84.0 mg/kg). Kraalkop plot 1 had the highest Fe concentrations (61000 mg/kg) and Johannesburg residential suburb had the lowest Fe concentrations (31720 mg/kg). Lead concentrations in soils were highest in Johannesburg commercial area (185.9 mg/kg) and lowest in Varkenslaagte (32.6 mg/kg). While the mean concentrations of Pb, As and Zn in soil and B. pilosa in Varkenslaagte (n=8) was in some cases lower than concentrations in some of the comparison sites, the metal concentrations in some plots in Varkenslaagte were above the concentrations of the samples obtained from the comparison sites. This indicates that metal concentrations are still high in some areas of the Varkenslaagte despite remediation. There was no significant difference in distribution of metal concentrations between different soil particle size ranges. Different preparatory and cooking methods resulted in different concentrations of Fe and Pb. However, concentrations of As and Zn were not affected by different categories of B. pilosa treatment and cooking methods. Concentrations of Zn and Pb exceeded minimum allowable limit levels as stipulated in FAO/WHO, European Union (EU) and South African regulations relating to maximum levels of metals in leafy vegetables. A dietary risk index (DRI) indicated that there is no obvious risk to adult populations from B. Pilosa consumption, particularly as this species is not consumed in the same volumes as other, more popular, wild leafy vegetables. However, this preliminary study does not include DRI in children, dietary exposure through consumption of other foods besides B. pilosa and does not encompass dermal and inhalation exposure pathways which are important contributing factors to health risk indices. Key words: Wild leafy vegetables, gold mining, pollution, contaminated land, dietary riskOnline resource (xiv, 95 leaves)enEnvironmental pollutionMetal--Environmental aspectsPollutionThesis