Radiological risk assessment of use of phosphate fertilizers in soil

ABSTRACT Background: The radiological impact of the use of phosphate fertilizers in soil is due to the internal irradiation of the lung by the alpha particles, short lived radon-thoron progeny and the external irradiation of the body by gamma rays emitted from radionuclides in situ. This paper describes the results of gamma spectrometric measurements of the concentration of the natural radionuclides namely 226Ra, 232Th and 40K in the soil samples collected from the fields where a variety of phosphate fertilizers are being used by the farmers to enhance the crop yield. Materials and Methods: The experimental work utilizes actual measurements of 226Ra, 232Th and 40K using gamma spectrometry and radon concentration and exhalation rates measurements using solid state nuclear track (LR-115, Type- II plastic) detectors to asses a first order exposure risk for the persons working in the fields where lot of fertilizers are being used to enhance crop yield in terms of occupational exposure. Results: The concentration of Radium, Thorium and Potassium in the mixed soil sample from crop fields is 16.2±0.22, 68.1±1.44 and 875.0±9.68 Bq/kg, where as in barren soil sample is 9.1±0.13, 59.4±1.45 and 668.4±8.01 Bq/kg respectively. The radium equivalent activity (Raeq) in the mixed soil sample from crop fields is 225.9 Bq/kg, where as in barren soil sample is 193.1 Bq/kg. The values of absorbed dose and annual effective dose (indoors and outdoors) are found to vary from 90.87 nGyh-1 to 119.71nGyh-1, 0.45mSv/y to 0.59mSv/y and 0.11mSv/y to 0.15mSv/y respectively in soil sample from crop fields, whereas the value of absorbed dose and annual effective dose (indoors and outdoors) is 92.29 nGyh-1, 0.45mSv/y, 0.11 respectively in soil sample collected from barren land. The radon concentration and exhalation rates have also been reported. Conclusion: The activity concentration, exhalation rate and absorbed dose were found to increase substantially with the use of phosphate fertilizers and it varies from sample to sample. The radium equivalent activities in all the soil samples were found to be lower than the limit (370 Bq/kg) set in the Organization for Economic Cooperation and Development (OECD) report and the dose equivalent is within the safe limit of 1mSv/y.