Contour Maps of Gross Alpha and Beta Radioactivity Distribution in Surface Water Supply Within the Naraguta Sheet 168, Plateau State, Nigeria

Abstract

Formal mining started in Plateau State as far back as 1902 with Tin and Columbite as major targets. The occurrence of these minerals brought about intense mining activities in the state. The early growth and development of the areas covered by the Naraguta Topographical Sheet 168 are closely related to commercial tin mining activities in the area and Plateau State at large. This has left behind a post mining environment scattered by numerous mine ponds and dams surrounded by heaps of mine spoils (dumps/overburden), mine tailings containing radioactive minerals that are washed in the water supply and a devastated landscape. A survey of gross alpha and beta radioactivity in Surface water supply from tin mining areas of Plateau State was carried out. Forty eight (48) Surface water samples (25 mine ponds and 23 streams) were drawn randomly. Each sample was drawn in two litres plastic container and about 10 ml of Nitric acid was immediately added for preservation and to avoid adsorption of radionuclides onto the walls of the containers. The samples were later evaporated to dryness and the residues were transferred into Planchets. They were then counted for gross alpha and beta activity using a Proportional Counter (MPC-2000-DP). The results obtained showed that the range of alpha activity varied from (0.05±0.01– 6.64±0.03)Bq/l with a geometric mean of 0.41Bq/l for mine pond samples and (0.14±0.01– 4.310±0.01)Bq/l with a geometric mean of 0.64Bq/l for stream water samples. While the range of beta activity varied between (0.01±0.001–6.68±0.04)Bq/l with geometric mean of 0.14Bq/l and (0.04±0.01-1.17±0.02)Bq/l with geometric mean of 0.25Bq/l for mine ponds and stream water samples respectively. The experimental results obtained show that gross alpha and gross beta activities in most locations of surface water are above the World Health Organization recommended guideline value of 0.5Bq/L for alpha activity and 1.0Bq/L for beta activity. This may constitute radiological hazards to the consumers of the water over a long period of time. Superimposing the contour maps of activity concentrations over the geology of the area showed higher activities within the Younger Granites areas compared to the Basement rocks and the Newer Basalts.