Environmental Impacts of Tin Mine Waste: A Case Study of the Zaaiplaats Tin Mine, Limpopo Province, South Africa

Abstract

This research focused on the potential impacts of the Zaaiplaats tin mine waste on the environment and on human health. It investigated the heavy metals and their distribution pattern at the Zaaiplaats tin mine. Heavy metals were investigated in the tailings, water and plants found at the mine. A radiation survey was also conducted to check for the possibility of potential radionuclides induced by the mine. Fieldwork involved collection of tailings within the old river channel, Heap A, B and C. A total of 65 samples were collected, 15 of them, across the river profile, while 6, 24 and 20 were collected from Heap A, B and C respectively. Samples were prepared and analysed at the Mining and Environmental Geology laboratory at the University of Venda using X-ray Fluorescence Spectrometry. The maximum values were 2842.4 ppm, 885.1 ppm, and 740.7 ppm for lead from Heap B followed by copper, and zinc from the river channel respectively. The distribution pattern of some metals like lead, zinc and copper were increasing with depth. The highest Pi (Environmental quality index of the pollutant) was registered by Pb followed by Cu and As and the values are 47.11, 29.95 and 26.89 respectively. Cu, Zn, As, Pb, Th and U had shown a higher degree of pollution which is presented by Pi values of 3 and above in all the different sampling locations of the tailings. The total water samples collected were depending on the availability. Therefore, only 3 water samples were obtained by use of 250 ml bottles. Water samples were prepared and analysed using Atomic Absorption Spectrometry. There are no values for metals such as Cr, Ni and Co in water samples collected at Zaaiplaats tin mine. However, the maximum values of Pb and Cu metals were 0.67 ppm and 0.59 ppm respectively which is higher as compared to the South African water quality guidelines and it is thus polluted. A plant commonly known as horsetail (Equisetum ramosissimum) was collected during dry and wet season for comparison purposes. A total of 9 plant samples were collected, prepared and analysed using Atomic Absorption Spectrometry. Bioaccumulation factor of these plant samples were higher during the dry season and lower during the wet season. The trend in the BAF for heavy metals during dry season are in the ranking order of Cr > Cu > Pb > Co. The trend in the BAF for heavy metals during wet season are in the ranking order of Co > Cu > Pb > Cr. Cr was transferred effectively in dry season while cobalt was transferred effectively in wet season. Cr and Cu metals were absorbed and accumulated during dry season as opposed to wet season wherein Co was absorbed and accumulated in wet season than in dry season. BAF and TF values were lower in both dry and wet season. The horsetail plant is a hyper-accumulator of these metals and can be used for their clean up as a remediation strategy paired with other remediation measures. Radiation dose rate and dose surveying was also conducted by means of a portable radiation survey meter DP802i-RAYTECH Radiation Detector. Radiation dose is increasing from a higher elevation which is the first surveying point along the river channel to low elevation. Radiation dose rate is inconsistent and does not have a general trend. The radiation dose rate mean, minimum, maximum values in microsievent per year (mSv/y) were 4.03 mSv/y, 0.96 mSv/y, and 11.65 mSv/y respectively. The maximum value of radiation dose rate was slightly higher compared to UNSCEAR background radiation of 2.4 mSv/y to 10 mSv/y. However, Zaaiplaats tin mine tailings are of no immediate concern since there are some areas that have had a radiation dose rate of 10 times higher than that of UNSCEAR and no deleterious health effects were associated with this elevated radiation exposure.