| dc.description.abstract | Artisan miners are faced with risks of radiation exposures due to the presence of
naturally occurring radioactive materials (NORM) in the earth and in the materials
(products, by-products, and wastes) derived from mining operations. The aim of this
research work was to assess the potential radiation exposure doses to artisan miners in
the Democratic Republic of Congo (DRC) as they mine, mill and handle coltan
(Columbite- Tantalite).
Samples of coltan were collected from various mines in Masisi, a territory noted for
coltan mining in the North Kivu province of the eastern DRC, and analysed in our
laboratories at the Institute of Nuclear Science, University of Nairobi. The analyses
were in three parts, i.e. elemental analysis using Energy Dispersive X-ray
Fluorescence and Neutron Activation Analysis (NAA was Qualitative); measurement
of activity concentrations of the naturally occurring radionuclides using gamma ray
spectroscopy; and dose estimation based on model calculations.
The elements identified, and the range of concentrations encountered were Sn (207 -
464) mg/g, Ta (144.1 - 340) mg/g, Nb (17.2 - 123.7) mg/g, Fe (40.5 - 100.4) mg/g,
Mn (31.9 - 86.2) mg/g, and Ca «0.41 - 72.5) mg/g. Other elements also identified at
relatively low concentrations are
Ti «0.08 - 29) mg/g, Au «0.03 - 11.6) mg/g, Pb (0.2 - 3.6) mg/g, Rb «0.0005 - 0.6)
mg/g, Sr «0.004 - 0.3) mg/g, Y «0.003 - 0.5) mg/g, Zr (1.0 - 2.3 mg/g), Th (0.2 -
1.0) mg/g, and U (0.2 - 0.9) mg/g. The activity concentrations vary from 4.0 Bq/g to
IV
13.45 Bq/g for 238U and from 0.05 Bq/g to 0.9 Bq/g for 232Th. In most cases 40K was
below the minimum detection limit of the gamma-ray detector method used for
analysis.
The working scenarios considered in the dose calculations include digging to expose
the coltan ore, sloshing the ore and soil in washtubs to separate coltan from soil,
drying the coltan in open air, and finally grinding and sieving the dried coltan. The
exposure pathways considered in the dose calculations include: external exposure due
to gamma-rays from bulk materials containing gamma emitting radionuclides and due
to submersions in air containing radioactive dusts and internal exposure due to
ingestion and inhalation of radionuclides.
Among the exposure pathways considered, inhalation resulted in the highest doses.
Also, among the working scenarios, grinding and sieving coltan at the mills
contributed the highest average effective dose to the workers, about 2.1 E-02 Sv per
annum, compared to digging which contributes about 0.5 E-05 Sv per annum. In order
to put the findings of this research into perspective, the dose values were compared
with the exemption levels and dose limits for workers, as specified by international
bodies and national regulatory authorities in other parts of the world. For example, the
exemption levels for workers in mining industries specified in the IAEA Basic Safety
Standards and the European Atomic directive were based on an individual dose
criterion of the order of 10 E-06 Sv per annum. This value is several orders of
magnitude lower than the doses experienced by workers in the mining and milling of
coltan in the DRC. | en |
