Analysis And Multivariate Modeling Of Heavy Metals And Associated Radiogenic Impact Of Gold Mining In The Migori-transmara Complex Of Southwestern Kenya

Abstract

Gold mining economically empowers not only the miners but also the entire country. However, it involves massive discharge of wastes like tailings, gangues etc. containing heavy metals and radionuclides that maybe harmful to exposed animals and plants if their concentrations are beyond certain limits. It was necessary analyze and multivariately model heavy metal and associated radiogenic impact of gold mining in The Migori Transamara gold mining complex of Southwestern Kenya in order advice the concerned parties. The aim of this study was to determine elemental concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn and activity concentrations of 40K, 232Th and 238U in lichens, moss, mine tailings, river sediments and soil. This study also computed absorbed dose, annual effective dose and pollution indices from their concentrations and also identified the sources of the heavy metals. To achieve our objectives lichens, mosses, river sediments, soil and tailings were randomly were collected from various sites and analyzed using AAS and HPGe gamma ray spectrometric techniques. Multivariate and Ordinary Kriging analysis were then used to analyze the heavy metals and radionuclide concentrations, their possible sources and spatial distribution. Heavy metal concentration in tailings is the highest compared to the rest of the matrices, the concentration of all the heavy metals apart fron Cr in the tailings are at least 9.5 times higher than their background concentration in soil. The median concetration of all the heavy metals apart from Cr and Cd in lichens and mosses respectively were above their background values. The median concentrations of As and Hg are 6 and 5 times higher than the background values in sediments while the median concentration of Cu, As and Hg in soil are 6, 4 and 3 times respectively above the background concentrations in all the sampling locations and the median of mercury is 272 times above the maximum permissible limit by FAO and WHO in soil. The soils are extremely highly enriched (82 – 3069) by mercury in all the sampling areas, this is supported by mean geo-accumulative index (Igeo=6.95). The mean EF, the river sediments are extremely highly (812) and significantly (13) enriched by Hg and As. The median activity concentration (Bq/kg) of 238U, 232Th and 40K in soil were 33.09 } 10.12, 58.57 } 18.62 and 417.05 } 163.95 respectively while the median absorbed dose and annual effective dose were 70.48 nGy/h and 0.09 } 0.03 mSv/y respectively. Activity concentration of 238U, 232Th and 40K in river sediments were 28.00 } 17.83, 42.32 } 15.32 and 342.00 }200.03 respectively and its absorbed dose (60.63 } 19.80 nGy/h) and AEDE (0.07 } 0.02). Radioactivity in the soil and sediments are within the world’s average according to UNSCEAR. As, Cr and Pb and (Cu, Zn, Ni Cd and Ni) originate from gold mining, natural soil formation and a mixture gold mining and anthropogenic processes. Spatial distribution of As, Hg, Cu, Zn and Pb in lichens, mosses and soil show high concentration around the mines implying negative impact of mining. The miners are encouraged to embrace gold recovery methods that do not require mercury besides wearing protective masks and clothing to shield them dust and hence exposure to heavy metals. Direct disposal of tailings to the environment should be discouraged by building tailing dams. Results from this study will help local and national government formulate policies on artisanal gold mining besides acting as a baseline for future studies.