Radiological risk assessment from the Gamma spectrometry of soil samples in the vicinity of a research centre in Nilore, Pakistan

Measurements of radionuclides' activities in air, water, and soil give clues about the anthropogenic activities in the region, and imperative to assess the overall radiological risk for individuals. Such an investigation was carried out to characterize the soil activities in the region hosting a research center, and to calculate the associated elements of radiological risk in terms of radiation doses and hazard indices. The soil samples were collected within the radius of 10 km in local area, Nilore, and analysed for activity using a high-purity germanium (HPGe) gamma spectrometric system. In all samples, only the basic nuclides, contributing to terrestrial activity, i.e., ⁴⁰ K, ²³²Th, ²²⁶Ra, and ¹³⁷Cs, were observed within the detectable limits of activity. The distribution of the data set and the correlation between the measured activities were studied with the use of the principal component analysis (PCA). The measured average specific activities of ²²⁶Ra, ²³²Th, ⁴⁰ K, and ¹³⁷Cs were 40.65 ± 9.84 Bq/kg, 59.31 ± 16.53 Bq/kg, 528.24 ± 131.18 Bq/kg, and 5.16 ± 4.56 Bq/kg respectively. The corresponding dose rate in air was found to be 76.63 ± 18.39 nGy/h, which is slightly higher than the world median value of 51 nGy/h calculated from concentration of terrestrial radionuclides in soil but falls within the world average value range of outdoor external exposure of 18-93 nGy/h obtained through direct measurement, and therefore not harmful for the living species. The standard hazard indices for all soil samples such as radium equivalent activity ([Formula: see text]), external hazard index (H_ex), and internal hazard index (H_in) were also found within safe limits for the soil to be used as construction of building material. This investigation led to conclusion that the soil activities are consistent with the usual background level of terrestrial activities, and their associated dose rates are well within the safe limits for public.

An overview of radioactivity measurement studies in Pakistan

In our environment, various naturally occurring radionuclides are present (both underground and overground) in several places, which results in lifelong human exposure. The radiation dose received by human beings from the radiation emitted by these naturally occurring radionuclides is approximately 87%. Exposure to radiation poses radiological health hazards. To assess the human health hazards from radiation, the concentration of these naturally occurring radionuclides are measured in soil (used for cultivation), building materials (soil, bricks, sand, marble, etc.), water and dietary items, worldwide. The available literature revealed that numerous studies related to the subject have been carried out in Pakistan. Most of these studies measured the radioactivity concentrations of primordial [uranium (238U), thorium (232Th), radium (226Ra) and potassium (40K)] and anthropogenic [cesium (137Cs)] radionuclide in soil samples (used for cultivation), fertilizers, building materials (i.e. bricks, rocks, sand, soil, marble, etc.), as well as water and dietary items, using a sodium iodide detector or high purity germanium. An effort was made in 2008 to compile these studies as a review article. However, since then, considerable studies have been undertaken and reported in the literature. Therefore, the main objective of the present article is to provide a countrywide baseline data on radionuclide levels, by overviewing and compiling the relevant studies carried out in Pakistan.

Enhancement of natural radioactivity in fertilized soil of Faisalabad, Pakistan

BACKGROUND, GOAL, AND SCOPE: Natural radioactivity in phosphate rock (PR) is transferred to phosphate fertilizer (PF) during the manufacturing process of the PF. The continuous addition of the PF to the cultivated soil accumulates the radionuclides in the land and increases the level of radioactivity in the soil. The purpose of the present study was to investigate the enhanced level of accumulated radioactivity due to the continuous addition of the PF in the farmlands of Nuclear Institute of Agriculture and Biology (NIAB) at Faisalabad in Pakistan. The selected study area consisted of the highly fertilized farmlands and an unfertilized barren land of the NIAB.

INTRODUCTION

The understudy area is very fertile for the growth of various types of crops; therefore, four agricultural research institutes have been established at Faisalabad and NIAB is one of those. The NIAB has developed various research farmlands at different places in Pakistan. The crop yield has been increased by adding various fertilizers in the farmlands. The addition of the PF accompanied with the radionuclides enhances radioactivity in the fields. Human being is exposed directly or indirectly to this radiological hazard. A prolong exposure may become a cause of health risk.

MATERIALS AND METHODS

The area of study consisted of three types of lands: the land under cultivation for the last 40 and 30 years called Site 1 and Site 2, respectively, and the barren land was called Site 3. A total of 75 soil samples were collected within the crop rooting zone (up to 25 cm deep) of the soil of the NIAB farms. The samples were dried, pulverized to powder, sealed in plastic containers, and stored to achieve equilibrium between (226)Ra and (222)Rn. Activity concentrations of the radionuclides (238)U ((226)Ra), (232)Th, and (40)K in soil samples were determined by using a high resolution gamma ray spectrometry system, consisting of an high purity germanium detector coupled through a spectroscopy amplifier with a PC based MCA installed with Geni-2000 software.

RESULTS

The measured activity concentration levels of (40)K were 662 ± 15, 615 ± 17, and 458 ± 20 Bq kg(-1), (226)Ra were 48 ± 6, 43 ± 5, and 26 ± 4 Bq kg(-1), and that of (232)Th were 39 ± 5, 37 ± 5, 35 ± 5 Bq kg(-1), respectively, in the soil of the Sites 1, 2, and 3. Gamma dose rate 1 m above the soil surface was 55, 51, and 40 nGy h(-1) from Sites 1, 2, and 3, respectively. External dose rates in the rooms constructed of the bricks made of the soil from Sites 1, 2, and 3 were 161, 149, and 114 nGyh(-1), respectively.

DISCUSSIONS

Activity concentration values of (40)K and (226)Ra in the soil of Sites 1 and 2 were higher than that in the soil of Site 3. The relative rise of (40)K was 43 % and 34 % and that of (226)Ra was 85 % and 65 % respectively in these sites. Activity concentrations of (232)Th in all these sites were in the background range. Gamma dose rate 1 m above soil surface of Sites 1 and 2 was 40 % and 30 % respectively higher than that from the soil of Site 3. The rise in activity of (40)K and (226)Ra and gamma dose from the Site 1 was greater than that from the Site 2. The least activity and dose were observed from the Site 3. Gamma dose in the dwellings made of fertilized soil bricks of Site 1 and Site 2 were respectively calculated to be 41 % and 32 % higher than that in the abodes made of unfertilized soil bricks of Site 3.

CONCLUSIONS

Activity concentrations of (226)Ra and (40)K were observed to be enhanced in the fertilized farmlands of the NIAB. Outdoor and indoor gamma dose as radiological hazard were found to be increasing with the continuous addition of PF in the understudy farmlands.

RECOMMENDATIONS

It is recommended that naturally occurring radioactive metal should be removed during the process of manufacturing of the PF from the PR. PROSPECTIVE: The rise in radioactivity in the farmlands due to the addition of the PF can be a source of direct or indirect exposure to radiation that may enhance cancer risk of the exposed individuals.

Measurement of radionuclides and absorbed dose rates in soil samples of Peshawar, Pakistan, using gamma ray spectrometry

The analysis of gamma-emitting radionuclides in nature, i.e. (226)Ra, (232)Th, (40)K and (137)Cs, has been carried out in soil samples collected from Peshawar University Campus and surrounding areas using a high purity germanium detector coupled with a computer-based high-resolution multichannel analyser. The activity concentrations in soil ranged from 30.20±0.65 to 61.90±0.95, 50.10±0.54 to 102.80±1.04, 373.60±4.56 to 1082±11.38 and 9.50±0.11 to 46.60±0.42 Bq kg(-1) for (226)Ra, (232)Th, (40)K and (137)Cs, with a mean value of 45±7.70, 67±12.50, 878±180 and 19±9.20 Bq kg(-1), respectively. The radium equivalent activity, internal and external hazard indices have mean values of 203.40±29.40 Bq kg(-1), 0.56 and 0.68, respectively. The mean values of outdoor and indoor absorbed dose rates in air and the annual effective dose equivalents were found to be 106.50 and 128 nGy h(-1) and 0.19 and 0.54 mSv y(-1), respectively. In the present study, (40)K was the major radionuclide present in soil samples. The presence of (137)Cs indicates that this area also received some fallout from the nuclear accident of the Chernobyl power plant in 1986. The activity concentrations of radionuclides found in soil samples during the current investigation were nominal. Therefore, they are not associated with any potential source of health hazard to the public.

Natural radioactivity measurements in Pakistan--an overview

Humans have always been exposed throughout their period of existence to naturally occurring ionising radiation. Specifically, naturally occurring radionuclides are present in variable amounts in our environment. To assess radiological health hazards, naturally occurring radionuclides are being measured in soil, sand, marble, bricks etc throughout the world. In this regard, extensive data have been reported for Pakistan, which have been compiled and reviewed in this article. The majority of the reported articles are about monitoring of the radiological health hazards of naturally occurring radionuclides. In a few articles, use of the radionuclides has been reported for the exploration of uranium and thorium deposits. Most of the reported data have been obtained using a high purity germanium detector or a sodium iodide detector.