Natural radionuclides content and radiological hazard of commercial ornamental stones: An integrated radiometric and mineralogical-petrographic study

Health Hazards Assessment and Geochemistry of ElSibai-Abu ElTiyur Granites, Central Eastern Desert, Egypt

In this paper, a thorough radio- and chem-ecological evaluation of ElSibai-Abu ElTiyur granites located within Egypt’s crystalline basement rocks was conducted for risk and dose assessments. Twenty granitic samples from the study area’s various lithological units were analyzed using high-resolution γ-ray spectrometry to determine the natural radioisotopes (U-238, Th-232, and K-40) concentrations. The average concentrations of U-238, Th-232, and K-40 were 38.72, 38.23, and 860.71 Bq/kg, respectively, exceeding the GAV (global average value) documented by UNSCEAR (Scientific Committee on the Effects of Atomic Radiation, Vienna, Austria). The radiological parameters and indices judging the usage of ElSibai-Abu ElTiyur granites in homes were computed. The obtained results showed that ElSibai-Abu ElTiyur granites are safe to be used by inhabitants as superficial building materials, as per the globally accepted values and the recommended safety limits approved by UNSEAR, WHO (World Health Organization, Geneva, Switzerland), ICRP (International Commission on Radiological Protection, Ottawa, ON, Canada), and EC (European Commission, Luxembourg). Further, the samples were subjected to ICP-MS (inductively coupled plasma mass spectrometry) analysis for quantifying radionuclide variations with chemical composition. Geochemically based on the ICP-MS results, the studied granites proved to be highly evolved A-type granites. They span the metaluminous to peralkaline fields. The REE patterns are characterized by the enrichment of the light rare earths (LREE) over the heavy ones (HREE) where (La/Yb)n = 5.2, (Gd/Yb)n = 1.63 with pronounced negative Eu-anomalies (Eu/Eu*)n = 0.49. The albite granite exhibits the highest concentrations of Ga, Nb, Ta, U, and Y, and REE (Gd, Dy, Ho, Yb) than the Na-metasomatic granites. Finally, the obtained data serve as a valuable future database for finding out the compatibility of the geochemical data with the natural radioactivity levels of granites.

Considerable radioactivity levels in the granitic rocks of the central areas of the Eastern Desert, Egypt

The distribution of the natural radioisotopes ²³⁸U, ²²⁶Ra, ²³²Th, and ⁴⁰K in addition to their radiological parameters in granitic rock samples from five different localities (Gebel El-Missikat, Gebel El-Gidamy, Gebel Ria El-Garra, Gebel El-Aradiya, and Gebel Kab Amira) in the central area of the Eastern Desert, Egypt, was measured using high purity germanium (HPGe) detector-based γ-spectrometry. The average activity concentrations of ²³⁸U, ²²⁶Ra, ²³²Th, and ⁴⁰K in all five studied areas are higher than the corresponding global average values. The highest average activity concentrations of ²³⁸U and ²²⁶Ra were observed in Gebel El-Missikat, whereas the highest average value of ²³²Th activity concentration was found at Gebel El-Gidamy, and the highest concentration of ⁴⁰K was obtained at Gebel El-Aradiya. The radiological hazard parameters radium equivalent (Ra_eq), external hazard index (H_ex), internal hazard index (H_in), absorbed dose rate (ADR), annual effective dose rate (AEDR) outdoors, annual gonadal dose equivalent (AGDE), and excess lifetime cancer risks (ELCR) were calculated to assess the radiation hazards associated with the rock samples. The average values of these parameters are higher than the recommended reference levels. The obtained data provide a valuable future database for estimating the impact of radioactive contamination in the studied area and in the places where the rocks are used.

Comparative Analysis of Natural Radioactivity Content in Tiles made in Nigeria and Imported Tiles from China

In this investigation, natural radioactive contents in tiles manufactured in Nigeria and tiles imported from China were measured using gamma ray spectroscopy. High Purity Germanium detector was used to estimate the concentrations of some radioisotopes present in 17 samples of various tiles from Nigeria and China. The average activity concentrations of 226Ra, 232Th, and 40K for the tiles were found to be 68.2 ± 0.5; 173.9 ± 9.2 and 490 ± 15 Bq/kg and 58.2 ± 0.5, 161.5 ± 9.4 and 455.7 ± 15.1 Bq/kg for the tiles from Nigeria and China respectively. Radiological hazard indices such as absorbed dose rate, radium equivalent activity, external Hazard Index (Hex), internal Hazard Index (Hin), Annual Effective Dose (mSv/y), Gamma activity Index (Iγ) and Alpha Index (Iα) were determined for both kind of tiles from Nigeria and China. The mean values obtained were: 354.56 and 317.16 Bq/kg; 169.22 nGyh-1 and 153.92 nGyh-1; 0.95 and 0.87; 1.14 and 1.08; 1.59 mSv/y and 1.52 mSv/y; 1 and 1.15 and; 0.34 and 0.29 respectively. The mean value of radium equivalent obtained in this study is less than that of the international reference value of 370 Bq/kg for the both kind of tiles.

Assessment of lithogenic radioactivity in the Euganean Hills magmatic district (NE Italy)

The Euganean Hills of North East Italy have long been recognised as an area characterized by a higher than average natural radiation background. This is due to two main reasons: a) primary lithogenic radiation due to rhyolitic and trachytic outcrops, which are "acidic alkaline" magmatic rocks potentially enriched in uranium and thorium; b) secondary sources related to a geothermal field - widely exploited for spa tourism in the area since the Roman age - producing surface release of radon-enriched fluids. Though radioactivity levels in the Euganean district have been often investigated in the past - including recent works aimed at assessing the radiation doses from radon and/or total gamma radiation - no effort has been put so far into producing a thorough assessment linking radiation protection data to geological-structural features (lithology, faults, water, organic matter content, etc.). This work represents the first part of the interdisciplinary project "Geological and geochemical control on Radon occurrence and natural radioactivity in the Euganean Hills district (North-Eastern Italy)", aimed at producing detailed results of the actual radiation levels in connection mainly with lithological parameters. A detailed sampling strategy, based on lithostratigraphy, petrology and mineralogy, has been adopted. The 151 rock samples collected were analyzed by high resolution γ-ray spectrometry with ex situ HPGe detectors. Statistical and geostatistical analyses were performed, and outlier values of U and Th - possibly associated with anomalies in the geological formation - were identified. U, Th and K concentration maps were developed using both the entire database and then again after expunging the outliers; the two were then compared. In all maps the highest values can be associated to trachyte and rhyolite lithologies, and the lowest ones to sedimentary formations. The external dose due to natural radionuclides in the soil - the so called terrestrial gamma dose rate - has been calculated using the U, Th and K distribution measured in the bedrock samples.

Assessment of gamma radiation exposure of beach sands in highly touristic areas associated with plutonic rocks of the Atticocycladic zone (Greece)

This study aims to evaluate the activity concentrations of ²³⁸U, ²²⁶Ra, ²³²Th, ²²⁸Th and ⁴⁰K along beaches close to the plutonic rocks of the Atticocycladic zone that ranged from 15 to 628, 12-2292, 16-10,143, 14-9953 and 191-1192 Bq/kg respectively. A sample from island of Mykonos contained the highest ²³²Th content measured in sediments of Greece. The heavy magnetic fraction and the heavy non-magnetic fraction as well as the total heavy fraction, were correlated with the concentrations of the measured radionuclides in the bulk samples. The heavy fractions seem to control the activity concentrations of ²³⁸U and ²³²Th of all the samples, showing some local differences in the main ²³⁸U and ²³²Th mineral carrier. Similar correlations have been found between ²³⁸U, ²³²Th content and rare earth elements concentrations. The measured radionuclides in the beach sands were normalized to the respective values measured in the granitic rocks, which at least in most cases are their most probable parental rocks, so as to provide data upon their enrichment or depletion. Since the Greek beaches are among the most popular worldwide the annual effective dose equivalent received due to sand exposure has been estimated and found to vary between 0.002 and 0.379 mSv y^-1 for tourists and from 0.018 to 3.164 mSv y^-1 for local people working on the beach. The values corresponding to ordinary sand samples are orders of magnitude lower than the limit of 1 mSv y^-1, only in the case of heavy minerals-rich sands the dose could reach or exceed the recommended maximum limit.

Variation in the radon concentrations and outdoor gamma radiation levels in relation to different geological formations in the thermal regions of Bursa, Turkey

Spring waters used as spas and their region may contain significant amounts of natural radionuclides. The main sources of exposure are the inhalation of radon and its decay products released from the water and soil and terrestrial gamma-radiation. In order to evaluate the potential risk of thermal regions in Bursa, located in the impact area of the NAF (North Anatolian Fault), radon and thoron concentrations in soil gas, radon concentrations in thermal waters and outdoor gamma radiation levels were measured in thermal regions that have different geological formations. The radon and thoron concentrations in soil-gas were found to vary from 2272  ±  121 to 245196  ±  3455 Bq m^-3 and from 999  ±  218 to 178 848  ±  17 742 Bq m^-3, respectively. The radon concentrations in thermal waters ranged from 0.99  ±  0.21 to 226.74  ±  2.51 Bq l^-1 in the rainy season and from 0.26  ±  0.10 to 178.03  ±  12.86 Bq l^-1 in the dry season. The measured outdoor gamma radiation levels varied from 38 to 180 nGy h^-1. The gamma dose rates were found to be strong positively correlating with the radon and thoron concentrations in soil-gas. The radon and outdoor gamma radiation levels were observed to be a function of the geological formations of the area.

Assessement of doses to members of the public arising from the use of ornamental rocks in residences

The main pathways to human exposure associated with naturally occurring radionuclides in ornamental rocks are external irradiation and the inhalation of radon. Usually, external doses and risks are assessed by using generic approaches in which the specific properties and use of the material are not considered. Moreover, limited information on radon inhalation dose due to the use of rock is available. The radionuclide concentrations in 180 rock samples reached a wide range of values: for ²²⁸Ra from  <2 to 530 Bq kg^-1, for ²²⁶Ra between  <5 and 600 Bq kg^-1and for ⁴⁰K varied between 190 and 2797 Bq kg^-1. Considering the rock properties, mathematical models, a residential scenario and radionuclide concentrations in the rocks, ²²²Rn concentrations and inhalation and external doses were estimated to range from 0.1 to 13 Bq m^-3, from 0.01 and 0.26 mSv yr^-1 and from 0.01 and 0.61 mSv yr^-1, respectively. The ventilation and the emanation rates are key parameters for the Rn dose, whereas the location of the receptor significantly affects the external dose. The overestimations of doses and risks by the generic approaches highlight the necessity of considering the properties and use of the materials for those estimations.

Development of a couple of methods for measuring radon exhalation from building materials commonly used in the Iberian Peninsula

Radon is considered to be the main contributor to the worldwide population exposure to natural sources of radiation and so a lot of efforts have been made in most countries to assess indoor radon concentrations. Radon exhales from the earth's surface and is part of the radioactive decay series of uranium, which is also present in building materials. In this work, measurements of radon exhalation rates in building materials commonly used in the Iberian Peninsula have been carried out by using two different methods: active and passive techniques. In the first technique, the radon exhalation rate was measured following the radon activity growth as a function of time, by using a continuous radon monitor. The second technique is based on integrated measurements by using solid-state nuclear track detectors and a Spark Counter reading equipment. The results obtained by both measuring methods were found to be consistent.

Natural radioactivity and radiation index of the major plutonic bodies in Greece

The natural radioactivity of the major plutonic bodies in Greece, as well as the assessment of any potential health hazard due to their usage as decorative building materials is studied. One hundred and twenty one samples from every major plutonic body in Greece, including various rock-types from gabbro to granite, have been measured for their natural radioactivity using γ-spectrometry methodology. According to the experimental results, the natural radioactivity levels were ranged up to 315 Bq kg(-1) for (226)Ra, up to 376 Bq kg(-1) for (232)Th and up to 1632 Bq kg(-1) for (40)K, with arithmetic mean values and standard deviations of 74 (±51), 85 (±54) and 881 (±331) Bq kg(-1) respectively, which are below the international representative mean values for granite stones. The excess on the effective dose received annually indoors due to granite tiles usage is estimated considering a standard room model where granite tiles with 1.5 cm in thickness cover only the floor of the room. The increment on the external γ-radiation effective dose rate shows a Gaussian distribution well dispersed below 0.3 mSv y(-1), presenting a mean value of 0.14 (±0.06) mSv y(-1). In case of the internal α-radiation a log-normal distribution is appeared scattering below 0.5 mSv y(-1) with a mean value 0.19 (±0.13) mSv y(-1), for a well-ventilated living environment. In case of a poor-ventilated room the increment on internal effective dose rate is estimated with a mean value 0.27 (±0.19) mSv y(-1) scattering below 0.8 mSv y(-1). The majority of the samples increase the external as well as the internal dose less than 30% of the maximum permitted limit of the effective dose rate. Therefore, at least from radiological point of view, the plutonic rocks of Greece could be safely used as decorative building materials.

Correlation between radioactivity levels and heavy metal content in the soils of the North Kosovska Mitrovica environment

This paper reports the results of radioactivity concentrations and heavy metal content in soil samples collected from non-agricultural areas in the municipality and vicinity of North Kosovska Mitrovica, formerly the most important mining area in Europe. The estimated average activity concentrations of (226)Ra, (232)Th, (40)K and (137)Cs are 40.6 ± 19, 48 ± 25.4, 743.2 ± 200.5 and 81 ± 119 Bq kg(-1), respectively. The estimated average absorbed dose rate in the air and the annual effective dose are 78.7 nGy h(-1) and 96.6 μSv, respectively. The radium equivalent activity and external hazard index were also calculated. High contents of Pb, Zn, Cu, Cd, As and Ni were found in the analyzed soil samples, thus indicating pollution of the environment. Most metals have a wide range of values spanning 2 to 3 orders of magnitude, which is particularly evident for Pb and Zn. Correlations between the activity concentrations of the radionuclides, the heavy metal content in soil and the basic soil properties were determined by means of the Pearson linear coefficient. Strong positive correlations between the naturally occurring radionuclides, and also among Pb, Zn, Cu and Cd were found.