Radiological risk assessment of use of phosphate fertilizers in soil

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 [226]Ra, [232]Th and [40]K 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. The experimental work utilizes actual measurements of [226]Ra, [232]Th and [40]K 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. 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 [Ra[eq]] 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. 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

Alpha activity in Indian thermal springs

Dissolved radon is contained in natural water due to primordial uranium in rocks and soils with which it comes in contact. There is dual exposure from radon in water i.e. due to inhalation of the radon released from the water into the ambient air and through ingestion when water is used for drinking. As radon contaminated water adversely affects the health, it is therefore fundamental from health and hygiene point of view to measure radium concentration and radon exhalation rates in water. LR-115, Type- II plastic track detectors were used to measure the radium concentration and radon exhalation rate in water samples collected from various thermal springs. The alpha tracks registered were counted by optical microscope at suitable magnification and converted into radium concentration and subsequently radon exhalation rates were measured. The radon concentration emanated from water samples [air borne] varied from 84 Bq m[-3] to 827 Bq m[-3] with an average of 429 +/- 12.72 Bqm[-3] and the dissolved radon concentration varied from 5.65 Bq l[-1] to 55.66 Bq l[-1] with an average of 28.88 +/- 0.85 Bq l[-1]. The radon mass exhalation rates varied from 2.37 mBq kg[-1]hr[-1] to 23.39 mBq kg[-1]hr[-1] with an average of 12.14 +/- 0.36 mBq kg[-1]hr[-1] and surface exhalation rates from 52.34 mBq m[-2]hr[-1] to 515.29 mBq m[-2]hr[-1] with an average of 267.36 +/- 7.93 from different thermal spring water samples. The radium concentration varied from 0.30 Bq l[-1] to 2.93 Bq l[-1] with an average of 1.52 +/- 0.045 Bq l[-1]. Results indicate that the thermal spring water, which is also being used for drinking, is safe as far as radium concentration is concerned with the exception of a few isolated thermal spring sources

Measurement of inhalation dose due to radon and its progeny in an oil refinery and its dwellings

Radon, an invisible, odorless, heaviest [nine times heavier than air] and radioactive gas is an aberration [the only gas in the long decay chain of heavy metal elements]. It is ubiquitously present in dwellings and in the environment. Humans receive the greatest radiation dose in their homes. That's where they spend most time - typically 70%, more for small children. Recent worldwide surveys reveal that an average person receives each year more radiation from radon than from all other natural or man-made sources combined. Over the years, the radiation exposure accumulated at home may exceed the exposure of uranium miners and lead to lung disorders. Therefore it is fundamental and justified to make a quantitative assessment of the radon in dwellings and the environment of work place. In this study, measurement of radon and its progeny levels was carried out in the environment of an oil refinery. Besides, radon and its progeny levels were also measured in the dwellings situated on the refinery premises and the dwellings in the city for comparison. Materials and LR-115, Type- II [Kodak Pathe, France], plastic track detectors commonly known as solid state nuclear track detectors [SSNTDs] were used to measure the radon concentration over long integrated times. Alpha particles emitted from radon cause radiation damage tracks, which were subsequently revealed by chemical etching in NaOH. These alpha tracks registered were counted by optical microscope at suitable magnification and converted into radon concentration. The geometric means [GM] of potential alpha energy concentration [PAEC], Equilibrium Equivalent Concentration of radon [EEC value], annual exposure and annual effective dose in the environment of refinery premises was 10.09 mWL, 93.43 Bq m-3, 0.41 WLM and 1.61 mSv, in refinery dwellings 12.21 mWL, 112.96 Bq m-3, 0.50 WLM and 1.94 mSv and in city dwellings 8.24 mWL, 76.23 Bq m-3, 0.34 WLM and 1.31 mSv respectively. The dose levels in the refinery premises were found to be marginally below the ICRP recommendations. The radon and its progeny levels were higher in the dwellings of refinery township as compared to the city dwellings. While studying seasonal variation, it was found that the measured values of radon and its progeny levels were higher in winter [November to February] than in summer [May to August]. This study showed that the presence of fossil fuels like natural gas, LPG etc. in the environment had resulted into higher levels of radon and its progeny in the refinery dwellings