Natural radioactivity intake into wheat grown on fertilized farms in two districts of Pakistan

The use of phosphate fertilizers on agricultural farms enhances gamma-ray activity concentration in the farms and therefore absorbed dose rates to the public. The most common natural radionuclides in fertilizer and soil are 40K, 226Ra and 232Th. Agricultural farms at four locations in two districts in Pakistan consisting of saline and normal soils had been under fertilizer treatment for the past 30, 20, 10 and 0 y, therefore, natural radioactivity has been measured in soil samples from these sites to investigate the effect of fertilizers in soil and wheat grown in these sites. Radioactivity measured in soil of the sites under investigation was 550-644, 20-35 and 42-58 Bq kg-1 for 40K, 226Ra and 232Th, respectively. Wheat was grown in the farms and radioactivity transferred from soil to roots, shoots and grains was also measured. Relatively high natural radioactivity has been observed in the fertilized agricultural farms and in the wheat plants grown in these farms. From the total amount of an element up-taken in a plant, distribution of the element in different parts of the plant has been studied. The distribution of potassium was almost uniform in roots, shoots and grains of wheat; that of radium was different in the three parts of wheat; and that of thorium was almost equal in shoots and grains but quite large in the roots. Soils to grain transfer factors of the natural radionuclides have been determined as 3-4 x 10-2 for 226Ra, 2-3 x 10-2 for 232Th and 17-20 x 10-2 for 40K. Annual doses of 40K and 226Ra received by intake of grain products have been estimated to lie within range while the dose received from intake of 232Th is larger than the range specified in UNSCEAR report 2000. (authors)