| dc.description.abstract | The aim of this studywas to evaluate the impact of tungsten mining on degradation of
agricultural soil quality in selected regions of Rwanda. The determination of heavy metals
(As, Pb, Mn, Cu,Zn, Co, Cd, Ni, Cr and Hg) content and radioactivity measurements of
primordial radionuclidese38U, 232Th and theirdaughters and 40K) concentrations was
performed.
Energy Dispersive X-Ray Fluorescence (EDXRF) and HPGe gamma-ray spectroscopy
methods together with multivariate analysis technique were used in this study. Soil samples
of tungsten minerals, tailing and agricultural soils were collected from Nyakabingo, Gifurwe,
Rwinkwavu and Ntunga and analyzed forradioactivity of 226Ra (238U), 232Th and their
daughters and 40K and heavy metal contents respectively. External exposure dose rate was
evaluated from mathematical models and theresults compared to the global averages. Since
run- off was assumed to be the main source of contamination dispersion downstream from
the mines, control samples were collected upstream for analysis and the results compared.
Tile elemental contents in soil samples were classified into two groups; namely major
constituents of soil, such as Fe, Mn, Ti and Zr and heavy toxic metals associated to tungsten
mining, i.e W, As and Pb which were found to be in traces, perhaps is due to the association
of arsenopyrite and tungsten minerals in quartz veins. The presence of Wand tailings is
attributed to poor extraction processing methods used by the artisanal miners. Arsenic (As),
in agricultural soil, was found in the following concentrations; 157 mg/kg, 163 mg/kg, 98
mg/kg and 55 mg/kg in Nyakabingo, Gifurwe, Rwinkwavu and Ntunga respectively. This is
above intervention value (or clean -up criterion) of 50 mg/kg.
The average dose rate for farm land around the mines was found to be 136.7 n Gyfh (2.5
times above the world average). This may be attributed to high activity in mine tailings and in
the soil samples from the adjacent areas of these mines.
Multivariate analysis techniques, such as Principal Components Analysis (PCA) with
VARIMAX rotation and Hierarchical Cluster Analysis (HCA), were used to explore the
general trends and interrelationships in the data sets, from which arsenic and radioactive soil
contamination was found to be strongly associated with tungsten mining activities. | en |
