Determination of tritium (3H) and radiocarbon (14C) levels in groundwater using alpha/beta spectrometry

Abstract

With the current state of water scarcity in Mahikeng due to the low water levels, increasing population and increased demand for fresh water supply, it is therefore crucial to ensure the sustainability and availability of the available water resources such as groundwater (borehole) by making sure that these resources are protected and well-managed. Hence it is important to study water quality, contamination and flow dynamics. In this study, the levels of tritium and radiocarbon were determined using the Perkin Elmer Ultra low liquid scintillation counter 2000. The mean activity concentrations for groundwater samples with analysed for tritium in different villages in Mahikeng were as follows; 3.61 ± 0,01 Bq/L for samples from Dibate, 386 ± 0.01 Bq/L for sample from Lokaleng and 1.83 ± 0.02 Bq/L for samples from Moletsamongwe, Lekung, Airport view and Seweding. The mean activity concentrations for groundwater samples with analysed radiocarbon in different villages in Mahikeng were as follows; 0.59 ± 0.01 Bq/L for samples from Dibate, 0.83 ± 0.01 Bq/L for sample from Lokaleng and 1.38 ± 0.02 Bq/L for samples from Moletsamongwe, Lekung, Airport view and Seweding. Out of the 30 samples analysed for radiocarbon, 2 of the samples were below the minimum detectable activity (0.37 Bq/L). For groundwater samples analysed for 3H, samples from Dibate village had a mean annual effective dose average of 0.05 μSv/y, 0.05 μSv/y for samples from Lokaleng village, while samples from Moletsamongwe, Lekung, Airport view and Seweding had an average of 0.02 μSv/y. The annual effective dose for 14C groundwater samples from Dibate village had an average of 0.25 μSv/y, Lokaleng village had an average of 0.37 μSv/y and the average annual effective dose for ground water samples from Moletsamongwe, Lekung, Airport view and Seweding was 0.58 μSv/y. The lifetime cancer risk for mortality and morbidity in adults was also evaluated and the values for this study were lower than the radiological cancer risk limit of 1.63 x 10-3 set by the United Nations Scientific Committee on the Effects of Atomic Radiation.According to the radiological values recommended by the World Health Organization and other international organizations, these results were within the permissible limits and show that consumption of the studied groundwater by humans does not pose any health risks in terms of tritium and radiocarbon. This is the first study of tritium and radiocarbon in groundwater consumed in the studied villages in Mahikeng, therefore this will provide a valuable baseline study for future researchers and water resource management experts in Mahikeng.