Occupational radiation exposures of artisans mining columbite-tantalite in the eastern Democratic Republic of Congo

Artisans in Masisi and other parts of the North Kivu province in the eastern Democratic Republic of Congo (DRC) mine columbite-tantalite mineral ores (also called 'coltan') for the tantalum content. The potential occupational radiation exposures in the course of this operation, due to the presence of naturally occurring radioactive material (NORM), have been investigated in this screening survey. Activity concentrations of the naturally occurring radionuclides in samples of coltan were measured using gamma-ray spectrometry. The average values in Bq g-1 are 10.75 ± 5.11 for 238U, 7.06 ± 3.39 for 226Ra, 1.75 ± 0.85 for 232Th, and 1.63 ± 0.52 for 40K. Based on these values and the working scenarios involved in artisanal coltan mining, the occupational doses that may accrue from a variety of exposure pathways were determined by model calculations. The results, assuming conservative dust load and dilution factors, indicate that grinding and sieving coltan can give rise to high occupational doses, up to 18 mSv per annum on average