Microorganism tolerance to high radioactivity and salinity was discovered in
the soils deposited from the weathered granite in Bahi Swamp of Dodoma Region,
Tanzania, which has an area of 125 – 140 km2 and located approximately 50 km
to the west of Dodoma. This swamp is underlain by layers of black clayey soils
about 110 m thick. Some of the clay layers have been found to be radioactive due
to their content of uranium-bearing minerals such as uranyl vanadates; (Ba,
Pb)(UO2)2V2O8･5(H2O). The β(γ)-ray counts and trace elements were analyzed
respectively by a scintillation counter and X-ray fluorescence (XRF) spectrometer.
Salt and black clayey soils showed theirγ-ray radioactivity ranging from 130 to
200 cpm and contained Sr abundant, and Ga, Rb, Y, and Zr slightly less
abundant, whereas La, Ce, Th and Ni detected slightly. Besides, their
mineralogical characteristics were analyzed by using X-ray powder
diffractometer (XRD), which identified clay minerals such as smectite, mica clay
minerals and kaolin minerals whereas halite and bischofite in salts. The
presence of microorganisms was observed with Scanning Electron Microscopy
(SEM) equipped with Energy Dispersive X-ray Analyzer (EDS), and
Transmission Electron Microscopy (TEM). Filamentous bacteria were fully
covered with flakes of clay minerals, which are recognized as kaolinite from its
hexagonal particles. The clay minerals such as kaolinite, smectite, etc. could
have functions to alleviate or even absorb the effect of the salinity and the
radiation. This is the first report revealing high radioactivity of paddy soils and
salt associated with microorganisms in Dodoma, Tanzania.