ASSESSMENT OF RADIOLOGICAL IMPACT OF PHOSPHATE FERTILIZATION ON ARABLE LAND

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.