Environmental risk assessment of naturally radioactive beryl-bearing rocks, Sinai and Eastern Desert, Egypt

Beryl mineralization represents one of the most significant gemstones. The radioactive concentrations of 238U, 232Th, and 40K in beryl-bearing rocks in South Sinai, Central and South Eastern Desert, Egypt were measured using a portable RS230 gamma spectrometer. 238U (40 ± 14), 232Th (51 ± 19), and 40K (1176 ± 277 Bq/kg) are recorded for Ghazala, 54 ± 16, 36 ± 12, and 921 ± 243 Bq/kg for Sedri, 39 ± 15, 27 ± 12, and 842 ± 356 Bq/kg for Igla, 69 ± 16, 34 ± 3, and 1572 ± 83 Bq/kg for Homrit-Akarem, 89 ± 21, 130 ± 16, and 1439 ± 175 Bq/kg for Homrit-Mikpid, and 35 ± 13, 21 ± 12, and 940 ± 645 Bq/kg for Zabara-Um Addebaa. Radiological risk assessment parameters (e.g., annual effective dose, radium equivalent activity) were estimated to deduce the radiation effects on human organs. The obtained results are within acceptable limits.

The inhalation of radionuclides from a radioactive material, for a long time, certainly produce some negative effect on human health such as anemia, acute leucopoenia as well as lung and bone cancers [18][19][20][21]. 232Th, 238 U and 40 K are the main terrestrial radionuclides of γ-radiation [18,19,22,23], and are variably distributed in the lithosphere.Radioactivity increase with increasing natural radionuclides, with the granitoids and their related evolved rocks such as pegmatites possessing the higher concentration in natural radionuclides [20].
Due to the significant economic importance of beryl/ emerald mineralization [5], the current contribution aims to investigate the natural radionuclides concentration in the beryl/emerald-bearing rocks in Egypt from six representive areas in the Eastern Desert and Sinai (Zabara-Um Addebaa belt, Homrit Akarem, Homrit Mikpid, Igla, Wadi Ghazala, and Wadi Sedri).This is to assess the radiological impacts on human health for Bedouin population, extraction workers and others if the host rocks used in the construction sector as a decorative stones [24][25][26].

Wadi Ghazala
This area lies in Southeastern Sinai, and it is bounded by latitudes (29 • 1′ 0.87′′ and 29 • 0′ 53′′ N) and longitudes (34 • 30′ 30′′ and 34 • 31′ 16′′ E) of about (2 km 2 ) (Fig. 2a).The basement rock units cropped in W. Ghazala area are dominated by older granites, biotite gneissose granites and biotite pink granites.Older granites are well exposed in the southern part of the study area, with moderate relief and are greyish in color.They exhibit highly weathered and fractured outcrops.Biotite gneissose granites are mainly medium-to coarse-grained gneissose textured and pinkish red color.Biotite pink granites are the main rock type exposed in W. Ghazala area that are mostly sheared and intruded by basic dykes.Beryl mineralization in W. Ghazala area hosted in biotite gneissose granites and their crosscutting pegmatites and quartz veins (Fig. 3a-c).

Wadi Sedri area
This area lies in Southwestern Sinai and is delineated by latitudes (28 • 53′ 33′′ and 28 • 55′ 41′′ N) and longitudes (33 • 25′ 50′′ and 33 • 30′ 56′′ E), covering an area of about 40 km 2 (Fig. 2b).The area is covered by orthogneiss, older granites and biotite pink granites.The former is represented by biotite-hornblende gneiss and well exposed along both banks of W. Um Maghar, W. Sedri and W. Seih.It is mediumto course-grained with greyish color and characterized by obvious gneissose structure (Fig. 3d).Older granites are well exposed in the southern part of the study area showing medium-to course-grain size with moderate relief and greyish color.On the other hand, biotite pink granites outcrops show high relief topography and are coarse-grained and red color.Beryl mineralization in W. Sedri area is disseminated within quartz vein cutting across the orthogneiss with NW-SE direction (Fig. 3e, f).

Igla area
Igla area is located in the central Eastern Desert at the intersection of Latitude 25°5′ 26.70′′ N and Longitude 34° 38′ 31.61′′E (Fig. 4a).The exposed rock units in this area are metavolcanics, older granites, biotite pink granites and postgranitic dykes (mafic and felsic) and quartz veins [35,36].The area is dissected by a several quartz veins and interlocking loads that vary from few to several meters in thickness and up to several kilometers in extension with predominant NW-SE trend.This area is rather enriched by various mineralization such as malachite, zinnwaldite and cassiterite.Several ancient mining activities for cassiterite suggest that this area was exploited in the past (Fig. 5a).However, beryl mineralization has not been explored previously in this mapped area.
The ophiolitic metagabbro rocks represent the most predominant rock unit within Z-UD belt.They vary from dark grey to dark green in color and are characterized by well-developed layering owing to variation in composition between mafic-rich and felsic compositions [37,38].The Ophiolitic mélange matrix, hosting the beryl mineralization [39], comprise several varieties of schistose rocks such as graphite-biotite schist, garnet-hornblende-biotite schist, quartzo-feldspathic schist and phlogopite schist.
Biotite gneissose granites are exposed only in Nugrus-Sikait area, forming high lands of the Abu Rusheid pluton [37].Muscovite leucogranite occurs as large white masses in Nugrus-Sikait area where the largest one of them (about 1.5 km in length and 250 m in width) is exposed at W. Um Solimat along NW-SE trend.Biotite pink granites are characterized by pink color and massive appearance.Beryl mineralization in this belt occurs either in phlogopite schist (Fig. 5b) or in pegmatite and quartz veins (Fig. 5c).The good quality beryl with green grass color is mostly found in phlogopite schist.Z-UD belt has the earliest known beryl quarries and excavations (W.Sikait) suggesting that this area was widely exploited in the past.

Homrit Akarem area
Homrit Akarem area lies in the SED and is bounded by latitudes 24° 9′ 17′′ and 24° 12′ 27′′ N and longitudes 34° 1′ 22′′ and 34° 5′ 47′′ E covering an area of about 40 km 2 (Fig. 6a).This area is occupied by metasediments, older granites, muscovite leucogranites and biotite pink granites.Metasediments form low hills, being greyish black colored in outcrop and are intruded by the surrounding granitic rocks.Older granites occur in the northern part forming low relief landscape and expose intensively weathered and fractured outcrops.Biotite pink granites form small intrusion intruding the contiguous metasediments.They are dissected by numerous pegmatite, fluorite, and quartz veins.Some parts of the biotite pink granite intrusion are affected by hydrothermal and metasomatic processes (albitization, greisenization, and silicification [17,40].Green beryl mineralization in Homrit Akarem area occurs within pegmatite veins cutting across the biotite pink granites (Fig. 5d).

Homrit Mikpid area
This area lies in the SED and is bounded by latitudes 24° 8′ 38′′ and 24° 12′ 15′′ N and longitudes 34° 22′ 15′′ and 34° 24′ 54′′ E (Fig. 6b).Homrit Mikpid area comprises metasediments, metagabbros and biotite pink granites as the main rock units exposed in this area.Homrit Mikpid forms a highly topographic terrane (up to 900 AMSL).Metasediments are exposed in the northern part of this area forming low-relief hills.Metagabbros are exposed in the southeastern corner of the mapped area as scattered hills and hummocks of moderate relief [14,40].The outcrops of the biotite pink granites are extensively faulted, dissected by joints, and invaded by E-W-trending, post-granitic dykes of variable composition, quartz veins and pegmatites.Several pods and veins of beryl are intermittently distributed, and beryl mineralization typically occurs as disseminations in pegmatite and granitic bodies (Fig. 5e).
Fig. 4 Geological maps of a Igla area, CED, Egypt [35,36]; and b Zabara-Um Addebaa district (Z-UD), SED, Egypt [17] Material and methods 238 U, 232 Th, and 40 K in the studied beryl-bearing rocks of Ghazala, Sedri, Igla, Homrit Akarem, Homrit Mikpid and Zabara-Um Addebaa belt are detected using a portable handheld RS230 (1024 channels) spectrometer in the contact with rock body.It has a higher bismuth germinate oxide, which can measure U (ppm) and Th (ppm) and K (%) after a 40 s measurement time [41].It is auto-stabilizing when measuring these radionuclides and does not need any test sources.In addition, its performance is similar to a 21 cu in Sodium Iodide detector.It is characterized by 6.3 in 3 (103 cm 3 ) with high sensitivity (3 × greater than Nal crystal of the same volume).Any data about this instrument such as calibration, uncertainty, assay, survey mode and other features are available in this site (http:// www.daxan.co.uk/ radia tion-solut ions-rs-230).
Some radiological hazards were performed in the prospecting stations of the different areas to deduce the radiation impact on human organs.They include absorbed gamma dose rate (D air ), annual effective dose (AED out&in ), radium equivalent activity (Ra eq ), internal (H in ) and external (H ex ) indices, excess lifetime cancer index (ELCR), and effective dose (D organs out&in ) to human organs.

Absorbed γ-dose rate (D air )
D air is the radiological index that is used to assess the released γ-rays at distances > 1 m from radionuclides on the Earth's surface [42,43].It can be obtained using the relation below: where AU, ATh and AK are 238 U, 232 Th and 40 K activities.

Radium equivalent activity (Ra eq )
Ra eq is a proper index that is used to determine the 238 U, 232 Th and 40 K activity levels in the prospecting beryl-bearing rocks.The 238 U, 232 Th and 40 K activities can be used in the following equation [21,44]; The Ra eq is ascribed to an internal and external dose of alpha particles and γ-ray exposure dose, respectively.It should be less than 370 Bq/kg to eliminate the annual effective dose (to be below 1 mSv). (1)

Annual effective dose (AED)
AED can be estimated using the absorbed dose values with the conversion factor of 0.7 Sv/Gy, whereas the outdoor and indoor occupancy factor of 0.2 and 0.8, respectively [21,45];

Internal radiation index (H in )
H in can be determined to deduce the radiation impact on respiratory organs.The H in can be calculated using the following equation [43,44]:

External hazard index (H ex )
H ex can be used in order to assess the radiation dose as below [43,44],

Annual gonadal dose (AGD)
Annual Gonadal index can be estimated by using 238 U, 232 Th and 40 K emitted from γ-rays as below [46]:

Excess lifetime cancer index (ELCR):
It can be estimated using annual effective dose (outdoor) and international commission of radiation protection (ICRP) cancer index (RP = 0.05 Sv) and over a lifetime (DL = 70 years) [43,44]:

Effective Dose (Do) to human organs
The rate of effective dose for several can be obtained using the following equation: (3) AED is the outdoor and indoor annual effective dose and F is the conversion factor to organ dose.F values are 0.58, 0.46, 0.62, 0.64, 0.68, 0.82 and 0.69 for the Ovaries, Liver, Kidneys, Lungs, Whole Body, Testes and Bone Marrow, respectively [47].

Radionuclide distributions
The concentrations of radionuclide of the examined beryl-bearing rocks are listed in Supplementary Table 1.The equivalent uranium (eU, ppm), equivalent thorium (eTh, ppm), and K (%) of beryl-bearing rocks in Ghazala area, (Southeastern Sinai, Egypt) range from 2 to 6 ppm, 5 to 24 ppm, and 1.9 to 5.2%, with their corresponding mean values 3.24 ppm, 12.6 ppm, and 3.75%, respectively.In Sedri area, (Southwestern Sinai, Egypt), the mean values of eU, eTh, and K are 4.36 ppm, 8.8 ppm and 2.94%, respectively.The mean concentrations of eU in Igla, Homrit Akarem and Homrit Mikpid are 3.16, 5.6 and 7.08 ppm, respectively, whereas, the mean values of eTh, and K are 6.74 ppm and 2.69% for Igla area, 8.46 ppm and 5.02% for Homrit Akarem, 32.16 and 4.59 for Homrit Mikpid, SED.
The obtained results show that the radionuclides are highly related to the host rock units/processes.Among the examined areas, Zabara-Um Addebaa belt has the lowest eU (2.8 ppm), eTh (5.12 ppm), and K (3%) concentrations, where the predominant host rock is phlogopite schist (Fig. 7a).On the other hand, Homrit Mikpid has the highest radionuclide concentrations of U, Th, and K compared to those of the studied areas [48].This is ascribed to the highly evolved granitic rocks of Homrit Mikpid are enriched with accessory minerals such as zircon, iron oxides, allanite, fluorite, and sphene) and radioactive minerals (uranophane and allanite).These minerals represent a reservoir of uranium and thorium elements (because the radionuclides incorporate in the crystal structure of these minerals) [20,21,49].Zircon (8) Do (mSv∕y) = AED × F possesses Th and U concentrations varied from 1 to 2% and 0.01% to 0.19%, respectively [50].
The mean values of eTh/eU of Ghazala (4.21) and Homrit Mikpid (4.81) are higher than the recommended Clark value (3.5).eU versus eTh and Th/U diagrams reveal positive and ill-defined relationships reflecting a magmatic role in uranium and thorium mineralization, whereas eTh and Th/U binary variation reveals positive correlation suggesting thorium enrichment (Fig. 7a-c).Wignall and Myers [47] detected the migration (mobilization) of uranium through this equation (eUm = eU − eTh/3.5).The obtained uranium values are negative, reflecting removal and leaching out of uranium (Fig. 7d).Among the measured 238 U and 232 Th activity concentrations, Zabara-Um Addebaa belt have the lowest content relative to other areas and lower than the safety limit (33, 45 Bq/kg, respectively) of [43].On contrary, Homrit Mikpid has the highest 238 U and 232 Th activity concentrations relative to the safety limits of [43,52].This may be related to the nature of their lithological units (granitic rocks) that are enriched with accessory minerals that incorporate U and Th in their crystal structures (Fig. 7a).

U, 232 Th and 40 K activity concentrations
In addition, It is noticeable that the mean values of the estimated 40 K are higher than safety limit (412 Bq/kg) [23,43].Furthermore, in the prospecting beryl-bearing rocks of the examined areas, the mean 232 Th/ 238 U values (1.37, 0.71, 0.73, 0.52, 1.51, and 0.61 for Ghazala, Sedri, Igla, Homrit Akarem, Homrit Mikpid and Zabara-Um Addebaa belt, respectively) are lower than the mean of the worldwide (3.94) [19-21, 23, 53, 54].Descriptive statistics (kurtosis, and skewness) for the examined beryl-bearing rocks in different areas are given in Table 1.Asymmetric distribution can be manifested by using the skewness factor.The positive skewness of 238 U reflects positive symmetric affinity, whereas 232 Th and 40 K negative values suggest flatness of its probability distributions.In addition, kurtosis coefficients are used to manifest the activity concentrations ( 238 U, 232 Th and 40 K) probability distributions.Flat distributions are indicated by negative kurtosis coefficients, while positive kurtosis values reflect the Preakness of a probability distribution.The distributions frequency of activity concentrations was determined for all stations by analyzing all related diagrams (Figs. 8, 9).
Activity concentrations of 238 U, 232 Th, and 40 K in the studied emerald-bearing rocks were compared with others from Egypt and different countries.The estimated results of radionuclide activity concentrations are observed to be higher than those recorded in Seih-Sidri area (Southwestern Sinai, Egypt; [18], commercial granites [21].All the examined area contain low activity concentrations in comparison with those of El-Missikat area [53], Saryu Formation (India, with exception of Homrit Mikpid) [55] and those from different countries [56].
The mean Ra eq values of the prospecting beryl-bearing rocks in the examined areas are lower than the permitted level (370 Bq/kg) except that in Homrit Mikpid (385.54Bq/kg).It is noticeable that the mean AGD for the examined areas ranges from 0.48 (Zabara-Um Addebaa belt) to 1.27 mSv/y, reflecting moderately higher than the agreeable level of 0.3 mSv/y.
The radiation amassed in human organs for a person per year can be detected by D organs .From Table 1, it is noticeable that the indoor D organs values are higher than the outdoor D organs and both are within the permitted level [59].Furthermore, the indoor and outdoor (D organs ) for  testes received dose is higher than others human organs [18,20,59].
In addition, it is noticeable that the Homrit Mikpid measurements (indices) are high relative to other areas, reflecting highly fractionated rocks.Accessory minerals such as xenotime, zircon and allanite that represent uranium and thorium reservoir [21].

Conclusion
This study investigated and assessed the radionuclide distribution in the prospecting emerald-and beryl-bearing rocks in six restricted areas in South Sinai, Central (CED), and South Eastern Desert (SED), Egypt.These areas are Ghazala, and Sedri (South Sinai), Igla (CED), Homrit Akarem, Homrit Mikpid and Zabara-Um Addebaa belt (SED).In the prospecting beryl-bearing rocks of the examined areas, the mean 232 Th/ 238 U values (1.37, 0.71, 0.73, 0.52, 1.51, and 0.61 for Ghazala, Sedri, Igla, Homrit Akarem, Homrit Mikpid, and Zabara-Um Addebaa belt, respectively) are lower than the mean of the worldwide standards.Radiological risk assessment parameters (e.g., radium equivalent index, external and internal hazard, excess lifetime cancer index (ELCR), effective dose (D organs ), and other indices were estimated in the examined beryl-bearing rocks and assessed in this study to deduce the radiation effects on human organs.The results of most of the estimated indices are lower than the permissible worldwide levels.Overall, Homrit Mikpid, (SED) has the highest values of the radiological indices, which may be ascribed to the enrichment of accessory minerals related to other areas.otherwise in a credit line to the material.If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.To view a copy of this licence, visit http:// creat iveco mmons.org/ licen ses/ by/4.0/.

Fig. 3
Fig. 3 Field photographs showing beryl mineralization hosted in a Pegmatite vein at Wadi Ghazala area, Southeastern Sinai, Egypt; b Quartz vein at Wadi Ghazala area, Southeastern Sinai, Egypt; c Biotite gneissose granites at Wadi Ghazala area, Southeastern Sinai, Egypt; d Gneissose structure in orthogneisses unit at Wadi Sedri area,

Fig. 7
Fig. 7 Binary variation diagrams a eU vs. eTh, b eU vs. Th/U; c eTh vs Th/U; and d eU vs eUm (eU-eTh/3.5)for the studied beryl-bearing rocks in different areas

Table 1
Radionuclide activity concentrations and the esimated radiological hazard indices for different areas