Natural Radioactivity and Radiological Hazard Effects from Granite Rocks in the Gabal Qash Amir Area, South Eastern Desert, Egypt

Abstract

The existence of radioactivity linked to the heavy-bearing minerals in building materials—such as granite—has increased attention to the extraction procedure. Granite rocks play an essential economic role in various areas of Egypt. Thus, this study intended to detect the ²³⁸U, ²³²Th, and ⁴⁰K activity concentrations in the examined granite samples and to determine the corresponding radiological risks associated with the granite. The studied rocks were collected in the Gabal Qash Amir area (south Eastern Desert, Egypt). The obtained results of the activity concentrations for ²³⁸U (193 ± 268) Bq/kg, ²³²Th (63 ± 29) Bq/kg, and ⁴⁰K (1034 ± 382) Bq/kg indicated that there were moderate concentrations in the investigated samples, which were greater than the worldwide average. The radioactivity levels in the studied granite samples are due to the secondary alteration of radioactive-bearing minerals associated with cracks of granites (secondary minerals in muscovite granites are wolframite, uraninite, uranophane, beta-uranophane, autunite, xenotime, columbite, zircon, and monazite). The radiological risk assessment for the public from the radionuclides that were associated with the studied granite samples was predicted via estimating the radiological hazard factors, such as the radium equivalent content (362 Bq kg⁻¹), compared with the recommended limit. The dosing rate D_air in the air (169.2 nGy/h), the annual effective dose both outdoors (AED_out ~ 0.21 ± 0.17 mSv) and indoors (AED_in ~ 0.83 ± 0.67 mSv), the annual gonadal dose equivalent (AGDE ~ 1.18 ± 0.92 mSv), as well as the external (H_ex) and internal (H_in) hazard indices (>1), and another factor were associated with excess lifetime cancer risk. According to the statistical investigation, the studied granites were inappropriate for use in construction and infrastructure fields. They may induce health problems due to the radioactivity levels, which exceed the recommended limits.

1. Introduction

Terrestrial radioactivity and cosmic radiation are the origins of natural radioactivity. The two main types of exposure to humans are external exposure, which is related to gamma rays emitted from terrestrial radionuclides, such as ²³⁸U, ²³²Th, and ⁴⁰K, and internal exposure from inhaled radon gas and its decay products [1,2,3].

Numerous analyses have been performed on areas with high natural radioactivity around the world and have come to attention in recent years for risk assessments. The previous studies have illustrated the existence of radionuclides with high concentrations in granite rocks, sediments, and soils, etc. Among various geological items, granite rocks and sediments play a fundamental role in building materials, as well as the accumulation and transportation of radionuclides from one zone to another [4,5,6,7].

Anthropogenic impacts, such as U-mining, have led to the elimination of radionuclides, which then disperse into the environment [8,9,10]. Therefore, the radioactivity levels around mining zones are high compared to other areas and accordingly, the background radiation will increase. Consequently, the long-term exposure to gamma radiation can induce many acute diseases, such as those associated with the kidneys, liver, bones, lungs, and pancreas [11]. Moreover, diseases, such as lung cancer, digestive system cancer, and kidney cancer, can be linked to a variety of pathways, including the inhalation of radon gas and its derivatives, as well as the ingestion of radioactive food [12,13].

Performing a radiological environmental assessment for building components in order to investigate and control the radioactive effects on people and the environment is a large and difficult task that must be caried out in order to fulfill long-term development goals. In order to analyze the radiation consequences, quantifiable factors that may be utilized as input parameters for modeling the environmental dispersion and determining the radiation dosage should be used [14,15].

The investigation area was selected due to the economic value of the heavy radioactive minerals amassed in the granite and sediments rocks, compared to the different areas that have been investigated in Egyptian deserts. The novelty of the current investigation is the detection of the levels of radionuclide concentrations in the investigated granites, which may be involved in infrastructure implementations. In addition, the evaluation of the public exposure to radiation via the assessment of the radiological hazards was detected with different radioactive factors.

2. Geological Description

The Gabal Qash Amir muscovite granite area is found near the Sudan border in Egypt’s Eastern Desert, and it makes up the southern part of the Elba topographical sheet (NF-37 I). It is around 27 km southwest of Abu-Ramad city. It is bound by longitudes of 36°14′24″ E–36°10′59″ E and latitudes of 22°15′21″ N–22°14′7″ N. (Figure 1).

The study location forms an isolated ovoid pluton with intruding schistose metavolcanic rocks. The pluton outcrops along a NW–SE oriented ridge and it is bordered by wadi sediments (Khalaf, 2005).

Khalaf (2005) concluded that the muscovite granites are a highly-fractionated component of the calc-alkaline granite series, which was deposited in a post-orogenic tectonic setting [16]. The muscovite granite of the studied area, and its environs, were subjected to a thorough geological investigation (Figure 2).

2.1. Metavolcanics

The metavolcanic rocks crop out in the western and southern sectors of the investigated area. The low to moderate relief hills of these rocks are dark-green to greyish-green in color, massive, porphyritic, fine-grained, foliated, extensively jointed, and very schistose in certain parts. They are made up of metavolcanics (dacite, andesite, and rhyolite). The metavolcanics show andesite, dacite, and rhyolite compositions. Meta-agglomerates, banded meta-crystal tuffs, and tuffs are most commonly associated with meta-pyroclastics [17].

According to the field surveys, the biotite and muscovite granites show sharp intrusive contacts with the metavolcanics (Figure 3a).

2.2. Biotite Granite

Low to high granite relief landscapes and isolated scattered granitic blocks are found in this granite. It comes in a variety of colors and grain sizes, ranging from medium to coarse, with a coarse-granite domination. Vertical joints, fractures, and exfoliation are common features (Figure 3b). The primary constituents are biotite, K–feldspar, quartz, plagioclase, and rare muscovite. The fractures of granites include manganese oxides and iron. Radioactive mineralization is produced in the granites, due to hydrothermal alteration. The alteration can be seen as albitization, kaolinization, and hematitization. It intrudes the metavolcanics with intrusive sharp contact, and is invaded by numerous types of dykes e.g., microgranite, bostonite, basic dykes, and veins [18,19].

2.3. Muscovite Granite

The muscovite granite is found in the studied area as moderate to high relief hills (Figure 2). Its color varies from pink to red, and its grain size extends from medium to coarse, with coarse-grained granite dominating. This granite has been heavily worn, exfoliated, and jointed (Figure 3c). N–S, E–W, and NE–SW oriented cracks, joints, and fractures affect this rock. Manganese fracture filling characterizes the pluton’s peripheral areas, particularly in the southwestern section.

Various secondary processes (kaolinization, hematization, albitization, and greening tacks) have altered these granites [20,21]. Visible uranophane mineralization can be found along the joint planes. The bostonite dyke cuts through the eastern half of the investigated area of the muscovite granite and is characterized by the crimson to deep-red color; it is heavily jointed and fractured (Figure 3d).

3. Materials and Methods

3.1. Sampling and Sample Preparation

About 136 chosen samples of muscovite granite were collected regularly from the studied area, utilizing a metallic scoop, and were stored in plastic zip bags. The collected samples were transported into the laboratory, were crushed, and the homogenous samples were sieved below 200 meshes. The samples were stored in plastic containers with a known volume of 250 cm³ for twenty-eight days, after which the radon gas and its daughters had reached secular radioactive equilibrium.

3.2. Gamma-Ray Spectroscopic Analysis

The radioactivity in the storage samples was detected via a solid-state detector, namely, a hyper pure germanium (HPGe) detector. The analysis of the samples was conducted regularly, in which each sample was measured for approximately 20 h. The detection of radioactivity in the examined samples relied on the resolution of the HPGe detector. The resolution was detected at 1.85 and 1332.5 for ²²⁶Ra and ⁶⁰Co, respectively. Before the measurement of radioactivity in the granite samples was taken, calibration of the HPGe detector was conducted utilizing various radioactive approved sources, such as ²²⁶Ra, ⁶⁰Co, and ²⁴¹Am (USA, 1994, approved the standard sources), and the efficiency curve was presented with two phases, with an energy range of 186–2450 keV. The ²²⁶Ra point source was applied to determine the relative efficiency curve. At the same time, in the other phase, the normalization of the relative curve of the spectrometer was achieved with potassium chloride. After the calibration, and before the measurements were taken, the background radiation was detected via a blank vessel with an identical volume and was estimated at an identical duration. Finally, after the detection, the activity of the radionuclide was determined by the following Formula (1) [22]:

$$A=\frac{N/t}{\epsilon I_{\gamma }m}$$

(1)

where A refers to the activity of the radionuclide (Bq kg⁻¹), N denotes the full-energy peak’s total net count (by subtracting the background area from the overall area, the peak areas are found), t shows the duration of the count (Sec), ε represents the efficiency of the HPGe detector, I_γ refers to the γ-abundance, and m is the mass of the measured sample (kg). The detection of ²³⁸U in the granite samples was analyzed by determining ²²⁶Ra (186 keV), ²¹⁴Pb (0.352, 0.295 MeV), ²³⁴Pa (1.001 MeV), and ²¹⁴Bi (0.609, 1.120, 1.765 MeV), while the ²³²Th activity concentration was determined from its decay products at energies of 0.911, 0.338 MeV for ²²⁸Ac and 0.583, 2.614 MeV for Tl. Furthermore, the ⁴⁰K activity concentrations were detected at photopeak energy (1.460 MeV) [23]. To eliminate any inaccuracy in the ray intensities, and the influence of coincidence summation, the efficiency calibration of the spectrometry system was performed utilizing the radionuclide-specific efficiency approach. Certified reference materials, such as RGU-1, RGTh-1, and RGK-1, were employed; their densities were equal to that of the building materials after pulverization [24]. The container geometry was selected according to the sample type in order to distribute the samples homogeneously. The ²²⁶Ra, ²³²Th, and ⁴⁰K had MDAs of 2, 4, and 12 Bq kg⁻¹, respectively. Total radiation level uncertainty was estimated using systematic and random detection errors. Random errors of up to 5% were found in radioactivity readings, and regular mistakes of 0.5 to 2% were found in efficiency calibration [25]. After the detection of activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K, the radiological variables were estimated according to

Table 1. Important radiological parameters and indices [26,27].

Parameter	Definition	Formula
Raeq	The radium equivalent content (Raeq) is a radioactive parameter that is widely applied in radiation health hazards. The results of Raeq must be less than 370 Bq kg−1, which keeps the AED for the public lower than one mSv.	Raeq (Bq kg−1)= ARa + 1.43 ATh + 0.077 AK
D (nGy/h)	The radioactive factor known as the absorbed dose rate is used to evaluate the effect of gamma radiation at a distance of 1 m from radiation sources in the air, owing to the concentrations of 238U, 232Th, and 40K.	Dair (nGy h−1) = 0.430 AU + 0.666 ATh + 0.042 AK
AEDout	An element of radioactivity called the yearly effective dose is used to gauge radiation exposure levels over a fixed period of time (1 year).	AEDout (mSv/y) = Dair (nGy/h) × 0.2 × 8760 (h/y) × 0.7 (Sv/Gy) × 10−6 (mSv/nGy)
AEDin		AEDin (mSv/y) = Dair (nGy/h) × 0.8 × 8760 (h/y) × 0.7 (Sv/Gy) × 10−6 (mSv/nGy)
Hex	The radiological parameters used to evaluate the risk of gamma radiation are known as the external hazard index. When radon and its decay products are exposed internally, the internal hazard index is used.	${\mathrm{H}}_{\mathrm{ex}}=\frac{A_U}{370}$$+\frac{A_{Th}}{259}$$+\frac{A_K}{4810}$
Hin		${\mathrm{H}}_{\mathrm{in}}=\frac{A_U}{185}$$+\frac{A_{Th}}{259}$$+\frac{A_K}{4810}$
Iγ	Due to the various combinations of distinct natural activities in the sample, another index was proposed by a group of specialists to determine the amount of radiation hazard linked with the natural radionuclides in the samples.	${\mathrm{I}}_{\mathsf{\gamma }}=\frac{A_{Ra}}{150}$$+\frac{A_{Th}}{100}$$+\frac{A_K}{1500}$
AGDE	The radioactive measure known as the yearly gonadal dose equivalent is used to calculate the doses of gamma radiation that are absorbed by the gonads.	AGDE (mSv y−1) = 3.09ARa + 4.18ATh + 0.314AK
ELCR	The radioactive factor used to determine whether gamma radiation exposure has caused lethal cancer is called excess lifetime cancer.	ELCR = AEDout × DL × RF

.

4. Results and Discussion

4.1. Radioactivity in Granites

Table S1 displays the ²³⁸U, ²³²Th, and ⁴⁰K activity concentrations that were detected in the granite samples.

Table 2. Basic statistical summary of muscovite granite rocks, Gabal Qash Amir, Egypt.

Variables *	U-238	Th-232	K-40	Raeq	Hin	Hex	Iγ	Dair	AEDout	AEDin	AGDE	ELCR
	(Bq/kg)	(Bq/kg)	(Bq/kg)	(Bq/kg)				nGy/h	mSv	mSv	mSv
N	136	136	136	136	136	136	136	136	136	136	136	136
Mean	193	63	1034	362	1.50	0.98	1.30	169.2	0.21	0.83	1.18	0.0007
SD	268	29	382	298.21	1.52	0.81	1.01	137.0	0.17	0.67	0.92	0.0006
Min	22.23	9.74	125.20	65.09	0.24	0.18	0.25	31.56	0.04	0.15	0.23	0.0001
Max	2099.50	182.70	1658.90	2351.01	12.03	6.35	7.89	1078	1.32	5.29	7.24	0.0046
Skew	4.19	0.77	−0.46	3.41	3.82	3.41	3.25	3.37	3.37	3.37	3.27	3.37
Kurtosis	22.15	2.69	−1.04	16.79	19.57	16.80	15.68	16.45	16.45	16.45	15.81	16.45

* N = Number; SD = Standard deviation; Max = Maximum; Min = Minimum; Skew = Skewness.

depicts the activity concentration means of the ²³⁸U, ²³²Th, and ⁴⁰K samples have surpassed the worldwide averages of 35, 45, and 412, respectively [3]. As elucidated in the investigated granite samples, the mean of A_U was 193 ± 268 Bq kg^−1, greater than the mean reported value (33 Bq kg⁻¹), with a factor of approximately six. It ranged from 22 to 2099 Bq kg⁻¹, while the mean of A_Th was 63 ± 29 Bq kg⁻¹, which is higher by a factor of 1.4 compared to the 45 Bq kg⁻¹ worldwide average, and its minimum value was 10 Bq kg⁻¹. The maximum value was 183 Bq kg⁻¹. The values of the A_K were altered from 125 to 1659 Bq kg⁻¹, with a mean value of 1034 ± 382 Bq kg⁻¹, which is greater by a factor of 2.5 compared to the worldwide average (412 Bq kg⁻¹). The skewness values of ²³⁸U and ²³²Th activity concentrations were positive and demonstrate a positive asymmetric nature. In contrast, a negative asymmetric distribution was displayed in the skewness values of the ⁴⁰K activity concentration. Additionally, the kurtosis values reflect the distribution probability’s peak. Table 1 illustrates that the kurtosis values are positive for the ²³⁸U and ²³²Th activity concentrations (the distributions are peaked). The activity concentration distribution of ⁴⁰K is flat, due to the fact that the kurtosis values are negative.

The frequency distribution of A_U, A_Th, and A_K are presented in Figure 4. However, the ²³⁸U, ²³²Th, and ⁴⁰K activity concentrations displayed a multi-modality degree. This illustrates that the granites were enriched with various radioactive-bearing minerals; thus, this study needs to analyze the minerals. The present results of A_U, A_Th, and A_K are compared with other studies in various countries (

Table 3. Comparison of ²³⁸U, ²³²Th, and ⁴⁰K activity concentrations in the Gabal Qash Amir area with other studies of different countries.

Country	238U	232Th	40K	References
Egypt	193	63	1034	Present study
Egypt	137	82	1082	[28]
Saudi Arabia	28.82	34.83	665.08	[29]
Palestine	71	82	780	[30]
Jordan	41.52	58.42	897	[31]
India	25.88	42.82	560.6	[32]
Iran	77.4	44.5	1017.2	[33]
Spain	84	42	1138	[34]
Greece	74	85	881	[25]
Turkey	80	101	974	[35]
Nigeria	63.29	226.67	832.59	[1]
Italy	85.86	24.71	1340.49	[36]

).

Figure 5 exhibits a map for the granite samples with the A_U, A_Th, and A_K. The proportion A_U/A_Th indicates that the granite has been enriched with uranium as a result of rainwater leaching, which has aided in the movement of uranium minerals and precipitation at faults and joints [10].

As shown in Figure 5, the highest uranium activity concentrations were found in the examined samples that were collected from the southeastern region of the studied area. This is linked to the disruption of radioactive materials that have been deposited inside of the granite fissures. Moreover, several of the analyzed areas had high thorium activity concentrations. This is due to the presence of several minerals in the granite samples, such as thorianite, zircon, and monazite.

4.2. Radioactive Assessment

The Ra_eq values in the granite samples are computed and presented in Figure 6. As reported in Figure 6, 34% of the examined samples represent higher values of Ra_eq than 370 Bq kg⁻¹. The Ra_eq mean value was 362 Bq kg⁻¹, which is comparable with the recommended limit, and the Ra_eq values ranged from 65.09 to 2351.01 Bq kg⁻¹ in the examined granite. The highest Ra_eq reveals the presence of U and Th in the examined granite with high activity concentrations.

The results of D_air reveal that the highest D_air values were detected in the granite samples from the southeastern region of the studied area. Statistically, the D_air data changed from 31.56 to 1078 nGy/h, with the mean value being 169.2 ± 137.0 nGy/h above the approved limit (59 nGy/h) [3,37]. This displays that the granites of the Gabal Qash Amir area are inappropriate for various infrastructure fields. This leads to evaluating the public exposure from the investigated granites. Based on the D_air data of the examined granites, the AED values were estimated based on two scenarios and are displayed in Table S1. Table 2 illustrates that the AED_out values varied from 0.04 to 1.32 mSv, with a mean value of 0.21 ± 0.17 mSv, > 0.07 mSv (recommended limit) [3], while 0.15 and 0.67 mSv are the Min and Max values of the AED_in, respectively, with a mean value of 0.83 ± 0.67 mSv, which is two times that of the recommended value of 0.41 mSv. Moreover, long-term exposure to huge dosages might cause tissue degeneration, cancer, coronary heart disease, and may impact deoxyribonucleic acid (DNA) in genes [38].

The significant health risks can be detected with higher radiological hazard indices. In the current study, H_ex data ranged from 0.18 to 6.35, with a mean value of 0.98, which is comparable to the recommended value (H_ex ≤ 1), while the maximum value of H_in in the investigated granites was 12.03 and the minimum was 0.24, with a mean value 1.5, which is higher than the recommended value (H_in ≤ 1). Consequently, a significant risk can be observed due to the internal hazard index. This indicates that health effects, stemming from the inhalation of emitted radon gas and its decay products from the granite rocks, will be observed [39].

The range of I_γ values in the investigated granite samples varied between 0.25 and 7.89 for the minimum and maximum values, respectively. The high I_γ values show that the granite samples in the southeastern half of the study area provide a considerable health risk and, thus, are not compatible for use in construction materials.

The AGDE data were calculated for all of the granite samples and are shown in Table S1 and the consistent descriptive statistics are shown in Table 1. The range of AGDE values altered between 0.23 (Sample number S9 and S14) and 7.24 (Sample number 126) mSv y⁻¹. The mean value was 1.18 ± 0.92 mSv y⁻¹, which is four times higher than the limit of 0.3 mSv y⁻¹ [3]. Thus, the granite rocks in the investigated area are inconvenient for masonry materials.

Moreover, the ELCR values of the granite rocks studied here show a range of 0.0001 to 0.0046, with a mean value of 0.0007, which is two times greater than the maximum limit (0.00029) [40]. This demonstrates that public exposure to the investigated granite causes cancer effects over the course of their lives.

4.3. Statistical Analysis

The study divides the association between natural radioactive indicators into two components. First, the correlation between A_U, A_Th, and A_K with the Ra_eq was studied and is plotted in Figure 7a–c. A strong positive correlation (R² = 0.96) between the Ra_eq and ²³⁸U activity concentrations was found. A good correlation (R² = 0.53) between Ra_eq and ²³²Th activity concentrations was also found, while there was a weak correlation (R² = 0.04) with ⁴⁰K. The correlation of Ra_eq with the natural radionuclide activity concentrations indicates that the granite rock is enriched with uranium, which is the main contribution to Ra_eq. This establishes the geological properties of the granite rocks in the investigated zone, where weathering has caused the occurrence of heavy radioactive minerals, including thorite, uranophane autunite, and uranothorite.

Moreover, rare metals are contained in monazite, zircon, samarskite, xenotime, columbite, rutile, fergusonite, and fluorite [16]. Second, the Pearson correlation was used to look at the links between the natural radioactivity and the radiological risks (

Table 4. Pearson correlation between natural radionuclides and the radiological hazard coefficients of muscovite granite rocks, Gabal Qash Amir, Egypt.

	U-238	Th-232	K-40	Raeq	Hin	Hex	Iγ	Dair	AEDout	AEDin	ELCR	AGDE
U-238	1
Th-232	0.58	1
K-40	0.02	0.67	1
Raeq	0.98	0.73	0.21	1
Hin	0.99	0.66	0.12	0.99	1
Hex	0.98	0.73	0.20	0.99	1.00	1
Iγ	0.97	0.74	0.24	0.99	0.99	0.99	1
Dair	0.98	0.73	0.21	0.99	0.99	0.99	0.99	1
AEDout	0.98	0.73	0.21	0.99	0.99	0.99	0.99	1	1
AEDin	0.98	0.73	0.21	0.99	0.99	0.99	0.99	1	1	1
ELCR	0.98	0.73	0.21	0.99	0.99	0.99	0.99	1	1	1	1
AGDE	0.97	0.74	0.23	0.99	0.99	0.99	0.99	0.99	0.99	0.99	0.99	1

). The Pearson correlation shows a substantial link among all of the radiological hazard indices and ²³⁸U, and a strong correlation with ²³²Th, because the ²³⁸U and ²³²Th series are naturally associated together. Furthermore, a weak correlation was found between the radiological parameters and the ⁴⁰K activity concentration. This emphasizes that the granitic rocks with significant uranium activity are accountable for the radioactive hazards and health risks.

The PCA (principal component analysis) used varimax rotations in order to control the correlation matrix between several items. In Figure 8, the PC1 and PC2 components are provided and plotted. The A_U is highly positive in the PC1 loading, correlating with all of the radioactive variables, and is explained with a variance of 87.83%. This indicates that the A_U is the primary source of the natural radioactivity in the granitic rocks studied here.

The PC2 load, on the other hand, is weakly positive for A_Th and strongly negative for A_K, which is explained with a variance of 10.98%. As can be seen, the loading variance is positive, which is explained by the fact that ²³²Th and ⁴⁰K do not affect the radiation exposure grade. The total explained variance in the PC analysis is 98.81%, indicating that the radioactive data proved to be good [41].

The correlations between the radiological parameters have been studied by applying hierarchical clustering analysis (HCA) and are plotted in Figure 9.

The dendrogram of the results is divided into two clusters. Cluster I contains ²³²Th and ⁴⁰K, whereas cluster II comprises the rest of the radiological variables. The application of HCA indicates that the radioactivity of the granitic rocks is attributed to the activity concentration of ²³⁸U. The HCA agrees with the other statistical investigations, such as the Pearson analysis and the PCA.

5. Conclusions

The goal of this study was to produce a comprehensive assessment of the radioactivity associated with granite rocks that can be applied in building materials and infrastructure fields. A statistical study was carried out in order to show the geological processes that result in a rise in radioactive content in granite rocks. The activity concentrations of 193, 63, and 1034 Bq kg⁻¹ of A_U, A_Th, and A_K, respectively, are moderate concentrations and are greater than the mean worldwide value. Moreover, all of the radiological hazard parameters were detected in the studied samples and displayed greater values than the recommended levels. This is attributed to the existence of radioactive-bearing minerals and rare metals in the investigated granite rocks. The granite in the examined area is not appropriate to consume and should not be employed in construction materials or in infrastructure applications.