Abstract:
In an attempt to assess the radiological impact of phosphate fertilization on
natural radioactivity of arable land, a sizable number of farm soils fertilized
with different rates of super phosphate fertilizers were collected from different
agricultural projects which provide the Khartoum State with vegetables
(Umdoam, Aselait and Genaid) as well as unfertilized soils from areas adjacent
to the Nile. The activity concentration of 226Ra, 232Th and 40K in these
agricultural soils has been measured using a high- resolution gamma
spectrometry equipped with HPGe detector with relative efficiency 50%. Over
all, the activity concentrations encountered in both fertilized and unfertilized
farm soils are characteristic of normal background radiation areas. Upon
comparing the activity levels met in fertilized soils categorically location-wise,
the intensity of fertilization was evident as Umdoam soils which are fertilized
at a rate of 200 kg/feddan displayed higher values relative to those from Aselait
and Genaid where the rate of fertilization amounts to 25 and 75 kg/feddan,
respectively. However, upon comparing the activity levels found in fertilized
soils and unfertilized soils collected from areas prone to annual flood, it was
apparent that unfertilized soils which were rich in silt exhibit higher activity
concentrations for 226Ra, 232Th and 40K. This let us to conclude that the impact
of fertilization rate on enhancing soil radioactivity is negligible for the time
being, however, on the long term it will have impact through accumulation of
radionuclides contained in phosphate fertilizer. The corresponding absorbed
radiation dose in air 1 m height above the ground level as estimated from the
activity concentrations of
226
Ra, 232Th and 40K using DRCF's ranged from
38.52±7.95 to 45.55±5.51 nGy/h for fertilized soils and from 46.01±10.32 to
63.34±10.85 nGy/h for unfertilized soils. These values fall within world-wide
range for normal background areas. The major contribution to the exposure
came from 40K followed by 226Ra. They were converted to annual effective dose
taking into account the environmental occupancy factor.
