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.
Publisher
University of Nairobi
Rights
Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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