Abstract
The aims of this study were to investigate the vertical distributions of natural radionuclides 232Th, 226Ra and 40K as well as anthropogenic radionuclide 137Cs in soil samples and to analyze the correlation among the radioactivity of these radionuclides and the physiochemical characteristics of soil samples namely pH, grain size, carbonate content and organic matter. Risk assessment of the radiological hazard has also been estimated. Forty-four soil samples were collected from eleven locations in Qatar at four depth levels from 0 to 16 cm. The average concentrations of 232Th, 226Ra, 40K and 137Cs in the soil depth of 16 cm were 10, 17, 201 and 4 Bq/kg, respectively, which were within the reported world mean. The external absorbed gamma dose rate, the annual effective dose, the mean radium equivalent activity, the external hazard index and the lifetime cancer risk were 22 nGy/h, 0.027 mSv/y, 47 Bq/kg, 0.125 and 0.096 × 10−3, respectively. These values were far below the minimum recommended international values. The level of radioactivity concentrations in the soil was affected by the physiochemical characteristics of the soil. The positive correlation with highest R2 value was found among the radioactivity concentrations of 232Th and 40K and the soil clay content. Total organic carbon was also positively correlated for 226Ra and 137Cs activity concentrations, whereas, carbonate content was negatively correlated with the radioactivity concentrations of 232Th and 40K. As far as soil moisture content is concerned, the positive correlation with highest R2 value was obtained for 226Ra activity concentrations.
Highlights
Radioactivity has become an issue of major concern over the years due to its association with human health[1,2]
TOC gives an indicator about the organic matters in soil samples
Because of the high cationic exchange capacity of the organic matter, the results of low organic matter may lead to assumption that adsorption in soil samples may be controlled mainly by an ion exchange mechanism with the clay minerals[15]
Summary
Radioactivity has become an issue of major concern over the years due to its association with human health[1,2]. Assessment of the diffusion of natural and artificial radionuclides in soil is important to protect human and environment[5]. Terrestrial radionuclides contain nucleogenesis or primordial natural radioactive isotopes This can be classified into: natural radioactive decay series (235U, 238U, and 232Th) and the daughter nuclides with relatively long half-lives and the daughter elements of these daughter nuclides, for example, 226Ra, 210Pb, 210Bi, and 210Po. The second group is the long-life nuclei, which become stable daughter nuclides in one-step; 40K is the most critical radionuclide in this group. Changing in the natural state of NORM causes technologically enhanced naturally occurring radioactive material (TENORM), or enhanced levels of NORM8 The anthropogenic activities such as coal mining, oil and gas extraction, geothermal energy production, water and wastewater treatment, application of phosphate fertilizers, uranium, thorium and copper mining can increase the level of naturally occurring radioactive particles[9]
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