MENVSC / Department of Hydrology and Water Resources / ABSTRACT Siloam and Tshipise Springs are scalding geothermal springs geologically located within the Soutpansberg Group in the Limpopo Province of South Africa. These geothermal springs are associated with faults and impermeable dykes and are assumed to be of meteoric origin. The optimal use of a geothermal spring largely depends upon its physical and chemical properties as well as the geological controls at source and surrounding pathway to the surface. This study aimed at investigating trace element concentrations in these geothermal springs in order to quantify their impacts on neighbouring soil and vegetation. Impact on vegetation was assessed by incorporating seasonal variations of the trace element mobility from the geothermal springs to the vegetation (Mangifera indica at Siloam and Acacia robusta at Tshipise) via soil. The geothermal spring water, soil and vegetation samples at both sites were collected from May – July (winter) and September – November (summer), 2014. The soil samples were collected at 5 m intervals up to 20 m away from the geothermal spring in each of the sites. The bark and leaf parts of the vegetation were sampled. The control samples for water, soil and vegetation were obtained from Riverside residence at University of Venda, Thohoyandou, Limpopo Province, where there is non-geothermal source of water. The temperature, electrical conductivity (EC), pH and total dissolved solid (TDS) of the geothermal spring water and control samples were determined in situ and in the laboratory. The water samples were acidified for major cations and trace elements determination. There were also non-acidified water samples for major anion analyses. The soil and vegetation samples were digested using microwave and hot block methods, respectively. Concentrations of arsenic (As), antimony (Sb), barium (Ba), beryllium (Be), boron (B), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), mercury (Hg), lanthanum (La), lead (Pb), lithium (Li), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se), tin (Sn), strontium (Sr), tellurium (Te), thallium (Tl), titanium (Ti), tungsten (W), vanadium (V), and zinc (Zn) were determined by inductively coupled plasma – mass spectrometry (ICP-MS) (Agilent 7700 series). Concentrations of calcium (Ca), magnesium (Mg), sodium (Na) and potassium (K) were analysed using inductively coupled plasma – optical emission spectrometry (ICP-OES) (X – Series 2) whereas the concentrations of chloride (Cl-), fluoride (F-), nitrate (NO3-), phosphate (PO42-), bicarbonate (HCO3-) and sulphate (SO42-) were determined by ion chromatography (IC) (Dionex Model DX 500). Results from this study revealed that the geothermal springs were rich in trace elements compared to that from non-geothermal source of water. The mineral elements present were vii mainly due to rock-water interaction in the deep aquifer at both sites. The geothermal spring water is not fit for drinking because it is particularly high in fluoride (F) having 6.66 and 5.97 mg/L at Siloam ; 6.72 and 7.28 mg/L at Tshipise for winter and summer, respectively. Also, high Nickel (Ni) with 462 µg/L and 868 µg/L: Lead (Pb) with 652 µg/L and 211 µg/L at Siloam and Tshipise respectively, for summer season. In addition, it is not suitable for irrigation owing to high sodium absorption ratio (SAR) values which were above the standard guidelines (˂1) by South African Bureau of Standards (SABS) and World Health Organization (WHO) at both sites. In summer season, there were higher trace elements concentrations than in the winter season. The higher concentration values could be attributed to rainfall, which aids in the dissociation of rock particles, resulting in higher concentrations of these elements. Siloam spring water was more mineralised than Tshipise spring water, hence its neighbouring soils and vegetation possess more trace elements concentrations than the latter. Owing to their high mineral elements content, the geothermal spring water flows across the soil, making it vulnerable to sorption of the trace elements. The trace elements present in the surrounding soil of the geothermal spring were as a result of geothermal water and soil pedogenesis. The geothermal water contaminates the surrounding soil with substantial quantity of trace elements, which decreases with the distance from the geothermal spring, making far distanced soil less-contaminated. High levels of Cr, Co, Ni, Cu, Zn and Pb at Siloam soil can be attributed to more minerals present in the spring, therefore making absorption by Mangifera indica inevitable. Soils at Tshipise are moderately concentrated owing to moderate trace elements concentrations from the geothermal spring water. Generally, seasonal variations were observed in the parameters analysed in the geothermal spring water, surrounding soil and vegetation to ascertain the most favourable season in terms of the trace elements concentrations. There were higher concentrations of trace elements in the geothermal spring, particularly during the summer season, compared to the winter season; this leads to more contamination of the surrounding soils and vegetation. This study showed that geothermal spring has potential to enrich the neighbouring soils and vegetation with trace elements, which could result in contamination. It can be concluded that geothermal spring, despite its benefits to humans, also contaminates the surrounding surface soils with toxic trace elements. Soils are a platform for vegetation. Therefore, if the soil is contaminated by toxic elements, there are high possibilities that these trace elements are absorbed by the neighbouring vegetation, which is likely to affect human beings adversely.

MSc (Chemistry / Department of Chemistry / In this study, three sampling sites (Tshipise thermal spring, Mphephu thermal spring and Siloam borehole) in Limpopo Province South Africa were considered for an investigation into the mineral composition of their water and soil samples. Tshipise and Mphephu thermal springs are well developed and located within tourist resorts. On the other hand, Siloam is a borehole on the grounds of a private household. The water is used for various domestic purposes such as laundry, general cleaning of the household and bathing. Water and soil samples from the three sites were collected once per week every week in February 2018. The sampling bottles were spiked with 1M HNO3 before sampling to keep any metal ions present in the water samples in solution. The soil and water samples were analysed for their chemical composition using X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) respectively. XRF analysis of the soil samples found many major oxides of which SiO2 made up 63.67%, 85.37% and 46.28% by mass of Tshipise, Mphephu and Siloam soil samples respectively. XRF analysis also showed the presence of dangerous levels of heavy metals such as As, Tl, Pb and V. The analysis of the water samples by ICP-MS found that Tshipise, Mphephu and Siloam mineral water were soft, soft-moderately hard and soft-hard respectively with regards to the water hardness scale according to the United States Geological Survey (USGS) and the Water Quality Association (WQA). Analysis of water samples also found the presence of As, Cd, Cr and V. Arsenic was found to occur at concentrations above the Maximum Allowable Concentration (MAC) set by the World Health Organisation (WHO) (10 μg L-1) for Tshipise, Mphephu and Siloam mineral water (13.63 μg L-1, 15.83 μg L-1 and 20.97 μg L-1 respectively). Water temperatures for the three sites ranged from 38°C (Siloam borehole) to 64°C (Tshipise thermal spring). The pH values were 7.25 (Siloam borehole), 7.40 (Mphephu thermal spring) and 8.67 (Tshipise thermal spring). Due to the presence of As, Tl, Pb, V, Cd and Cr, the mineral water from all three thermal springs is unsafe to consume as it would lead to serious negative health effects some of which are outlined in this study. / NRF

PhDENV / Department of Hydrology and Water Resources / Geothermal springs are natural geological phenomena that occur throughout the world. South Africa is endowed with several springs of this nature. Thirty-one percent of all geothermal springs in the country are found in Limpopo province. The springs are classified according to the residing mountain: Soutpansberg, Waterberg and Drakensberg. This study focused on the geothermal springs within the Soutpansberg region; that is, Mphephu, Siloam, Sagole and Tshipise. The study was aimed at elucidating on the isotopic signatures and trace metals concentrations from the geothermal springs to their environmental media in Soutpansberg region. This study also assessed the interconnectivity of the isotopic signatures within the ecosystem and evaluated the potential human health risks associated with trace metals from geothermal springs and surrounding soils in the study areas. Geothermal springs and boreholes were sampled for a period of twelve months (May 2016 – May, 2017) to accommodate two major seasons in the study areas. The surrounding soils were sampled vertically from a depth of 10 cm to 50 cm for trace metals and isotopic compositions. Three different plants were sampled at each of the study sites, namely, Amarula tree, Guava tree and Mango tree at Siloam; Acacia tree, Fig tree and Amarula tree at Mphephu; Amarula tree, Lowveld mangosteen and Leadwood tree at Sagole; Sausage tree, Amarula tree and Acacia tree at Tshipise. To achieve the objectives, the physicochemical, geochemical and isotopic compositions of the geothermal springs, boreholes, soils and vegetation were analysed using ion chromatography (IC) (Dionex Model DX 500), inductively coupled plasma-mass spectrometer (ICP-MS), HTP-Elemental analyzer, Liquid water isotope analyzer (LWIA-45-EP) and Liquid scintillation analyzer. The temperature, electrical conductivity (EC), pH and total dissolved solid (TDS) of the geothermal springs and boreholes samples were measeured in situ and in the laboratory. Trace metals analysed in geothermal springs, boreholes, soil and vegetation include Beryllium (Be), Chromium (Cr), Manganese (Mn), Cobalt (Co), Nickel (Ni), Copper (Cu), Arsenic (As), Selenium (Se), Cadmium (Cd), Antimony (Sb), Barium (Ba), Vanadium (V), Zinc (Zn), and Mercury (Hg). vii | Isotopic signatures and trace metals in geothermal springs and their environmental media within Soutpansberg Results obtained from this study in the studied geothermal springs and boreholes were classified according to their temperature as hot and scalding; except for tepid boreholes. This study has provided comprehensive physicochemical, geochemical and isotopic compositions of the geothermal springs within the Soutpansberg region (Siloam, Mphephu, Sagole and Tshipise). The local meteoric line (δD = 7.56δ18O + 10.64) was generated from rainwater in Vhembe district. This is a crucial component for depicting the source and flow path of the geothermal springs/boreholes; and could be used for future isotopic hydrological studies within the locality. Rain formation processes within Soutpansberg occurred under isotopic equilibrium conditions with minor evaporation effect during rainfall. The δD and δ18O values of the geothermal spring water/boreholes confirm that the waters are of meteoric origin, which implies that rainfall is the fundamental component of these groundwaters because they were derived from the infiltration of rainwater, with significant contribution of another type of water in the deeper part of the aquifer. Na-Cl and Na-HCO3 were established as the water types, which are typical of marine and deep groundwaters which are influenced by the ion - exchange process. The reservoir/aquifer temperature of these springs ranges between 95 – 185°C (Na-K geothermometer), which implies most of the waters are mature water (not native). Hence, geothermal springs water is a mixture of the rainwater and salt water. Radiocarbon values of the geothermal springs ranged from 2700 to 7350 BP, this implies that they are submodern and a mixture of submodern and modern waters. Tritium relative age also corroborates with radiocarbon age, that is the groundwaters were recharged before and after 1952. This gives an indication that the rainfall contributes to the geothermal springs recharge. Various radiocarbon correction models were employed and constrained by tritium relative age. Ingerson and Pearson, Eichinger and Fontes and Garnier correction models have been shown to be the most appropriate models for radiocarbon correction of groundwater in this semi-arid region. Although, geothermal springs water and boreholes are not fit for drinking due to high fluoride content, they could be used for the following: domestic uses (drinking exclusive) due to its softness, direct heating in refrigeration, green-housing, spa, therapeutic uses, aquaculture, sericulture, concrete curing, coal washing and power generation. In contrast with mentioned uses, viii | Isotopic signatures and trace metals in geothermal springs and their environmental media within Soutpansberg the studied geothermal springs are currently used for domestic purposes (drinking inclusive), limited irrigation and spa (swimming and relaxation). This is an eco-hydrological study that shows the interconnectivity of isotopic signatures among water (rainwater, geothermal springs and boreholes), soils and vegetation. The soil-water reflects the rainwater/geothermal springs water in isotopic composition, which is more depleted as a result of isotopic fractionation in soil. δD values of soil-water increase, whereas δ13C values in soil-water decrease with the soil depth at all sites. Two equations connecting δD and δ13C in soil-water were deduced per season for soil-water; δ13C = 0.0812δD - 10.657 in winter; δ13C = -0.0278δD - 21.945 for summer. δ13C in soil-water is induced by Crassulacean Acid Metabolism (CAM) (mixture of C3 and C4 photosynthetic cycles) with a stronger C4 trend, which corroborates with δ13C of the geothermal springs. From literature, Amarula and Acacia trees have been documented for isotopic compositions, while this study has given additional information on other plants including Lowveld, Leadwood, Sausage, Fig, Guava and Mango trees. These plants are categorised as C3, C4 and CAM plants. C3 plants include Amarula, Lowveld and Leadwood trees; C4 plants include Acacia and Sausage trees; and CAM plants include Fig, Guava and Mango trees. This study shows that with CAM soils, there is a possibility of having either C3, C4 or CAM vegetation. This finding has shown that the δD and δ13C isotopes in water, soil and vegetation are interrelated, which has been statistically justified. This study has shown the potential human health risks associated with trace metals concentrations from geothermal springs and their surrounding soils. From the geothermal spring’s water, it was found that As, Cr and Cd were the highest contributors to the cancer risk with children having a higher risk than adults. Whereas in soils, it was found that Cr, As and Co were the highest contributors to the cancer risk in the studied communities. Therefore, the cancer risk is high in the general population; that is 1 in 72-162 individuals in children and 1 in 7-107 individuals for adults. The ingestion route seems to be the major contributor to excess lifetime cancer risk followed by the dermal pathway. Therefore, proper monitoring and control measures to protect human health, particularly in children, should be implemented for safety. The study also explored the use of surrounding trees ix | Isotopic signatures and trace metals in geothermal springs and their environmental media within Soutpansberg for phytoremediation and found their uptake capacity to be high, thus, they could be used as bio-indicators to assess the level of contamination of trace metals in the soil. In conclusion, this study has eludicated on the isotopic signatures and trace metals concentrations from the geothermal springs and their surrounding soils and vegetation within Soutpansberg. This study has contributed towards the advancement and enhancement of the existing knowledge of the geothermal systems, such that water resource management could be applied successfully in the respective areas with similar characteristics for the benefit of the local communities and society at large. Hence, this study recommends that proper monitoring and control measures need to be put in place to protect human health, especially in children. / NRF