Determination of Ra-226, Ra-228 and K-40 specific activities in samples of mineral fertilizer marketed in the Rio de Janeiro City

The use a fertilizers ia a common practice in agriculture and several samples have radionuclides in their composition, this content is natural but some samples may have high concentrations of these radionuclides and this represent a potential radiological risk for plants, animals and water. Therefore the radiometric analyses these compounds is important and the main aim of this paper is to determine the specific concentration of K-40, Ra-226 and Ra-228 in fertilizer samples available in market of Rio de Janeiro city and discussing the impacts to agricultural soils caused by this practice. The analyzed fertilizer samples are of four types: nitrogen, potash, phosphate and NPK, they were analyzed using gamma spectroscopy with a Hp-Ge detector and with the LabSOCS software for the calculation of the efficiency curve. The specific activities of Ra-226 ranged from 1.48 Bq/kg to 597 Bq/kg, Ra-228 ranged from 2.66 Bq/kg to 832 Bq/kg and K-40 ranged from 16 Bq/kg to 13941 Bq/kg. All samples, except two nitrogen fertilizer samples, presented the absorbed dose rate in air at 1 m above the ground level higher than the estimated average global terrestrial radiation of 51 n Gy/h and the phosphate fertilizer samples presented the highest average absorbed dose rate of 532.5 n Gy/h, which indicates a greater potential of environmental contamination. But considering a dilution (1:1000) g of fertilizer in soil was found an average increase of 0.36 μSv/y at the annual outdoor effective dose while the annual average for the soil is of 63 μSv/y, so the risk to human health is minimum. (Author)