Radiological survey and elemental analysis in the gold mining belt, Southern Nyanza, Kenya.

Abstract

A radiological survey and elemental analysis in the gold mining belt was carried out at Osiri, Mikei, Masara and Macalder goldmines in Macalder Division of Migori district, in southern Nyanza, Kenya, where gold has been mined since 1920s. This was after it was realized that none of the previous studies in the region had considered radionuclide activity and elemental flux measured. This study aimed to provide data and information on the radiological as well as elemental impact of gold mining. To achieve this gold ore, water, sediments and dust from the mines were collected and analysed. Elemental analysis of rock, water, sediment and dust samples was done using the ED-XRF technique. Activity concentration of 226Ra in water samples was measured using liquid scintillation counting (LSC) spectrometry and the activity concentrations of 40K and the decay products of 232Th and 226Ra were measured using gamma - ray spectrometry. Relevant exposure scenarios and pathways were identified and the doses received from these pathways were estimated by calculations based on generic dosimetric models. Measurement of dust loading at the various ore crushing sites was carried out by trapping the dust particles on a 0.45 micron cellulose acetate filter paper of 47 mm diameter using a vacuum pump. Absorbed doses in air at the mining sites, crushing sites and panning sites were evaluated from the measured activities of the radionuclides in these samples. The major elements and their concentration in gold ore and sediments are: titanium (711 – 13,000) mg/kg; cobalt (83 - 1,010) mg/kg; zinc (30 – 63,210) mg/kg;; gold (14 - 73) mg/kg; copper (40-118,533) and mercury (16 - 150) mg/kg. Lead and arsenic were also available in high quantities. The major elements and their concentrations in the water samples on the other hand were: copper (29 - 14,976) µg /l; zinc (34 - 683) µg/l, lead and arsenic were also detectable in higher quantities. Iron and magnesium were detected in all the dust levels. The activity concentrations of 40K, 226Ra and 232Th range from (80 - 413) Bq/Kg, (12- 145) Bq/Kg and (21 - 258) Bq/Kg with mean values of 100, 25 and 41 Bq/Kg, respectively. The 226Ra in water samples was found to be below the detection limit (LD= 0.94 kBq m-3). The dust loading at Masara was found to be 3.668 mg/m3 while the dust loading at Mikei was found to vary between (0.843 - 1.650) mg/m3 with a mean of 1.334 mg/m3. The absorbed dose was found to range from 16 - 178 nGy/h with a mean of 42 nGy/h. The total calculated effective dose from the three exposure scenarios considered ranged from 0.7 - 4.2 µSv y-1. The most significant pathway is the inhalation of the auriferous ore dust while the least significant is the external dose due to gamma-rays emitted by the radionuclides contained in the mining environment. The activity concentration of the radionuclides as well as the annual absorbed dose were found to be below the worlds average while presence of toxic elements like arsenic, lead and zinc in high quantities were also noted. Inhalation of the gold ore dust was found to be the worst exposure pathway with crushing being the worst exposure scenario to the artisanal miners.