Vol 5, Issue 3, 2016 Toward Assessment the High ...

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Human Health Impacts from Precambrian Granites, Na'wah Area,. Yemen ... Yemen Republic is mostly covered by Precambrian rocks, up to 25% of the total.
Toward Assessment the High Gamma Dose Levels and Relevant Human Health Impacts from Precambrian Granites, Na'wah Area, Yemen Republic Mohamed Th. S. Heikal1*Kamal R.Mahmoud2, Tamer. I. Elsobky3, Gulcan Top4

1Geology

Department, Faculty of Science, Tanta University, Tanta 31527, Egypt Physics Department, Faculty of Science, Kafr El Sheikh University, Egypt 3Geochemistry Department, Nuclear Material Authority (NMA), Egypt 4Istanbul Technical University, Eurasia Institute of Earth Sciences, İstanbul, Turkey 2

Abstract The natural radioactivity concentrations (Bq/Kg) of 226Ra, 232Th, 238U and 40K of Precambrian rocks (gneissic granites, alkali feldspar granites and pegmatite-aplites) as well as Cretaceous sandstones around Na'wah town that is located at SW Sana'a, Yemen Republic. The Present paper aims to determine the assessment of radiation hazards and human health impacts around this area due to external irradiation from gneiss-granites and associated dikes. The radiological and health risk assessments were investigated by calculating the different main parameters, based on the activity concentration of 238U, 232Th, 226Ra and 40K in basement exposures as determined by gamma-ray spectrometry. Concentrations of radioactivity in the studied rocks are detected using specially shielded low level gamma-ray spectroscopy. The radiological doses are calculated for evaluation of the health effects by using measured activity concentrations of the elements. Increase in gamma dose values were observed at almost every Precambrian rocks, while the measured Cretaceous sandstone values were normal and safe. At limited areas, the obtained results show that the dose values of uraniferous granites and gneissic granites associated with pegmatites and aplites are higher than radiation-risk limits; which most probably causes a significant radiation hazards especially on the settlements of Na'wah and Guban towns as well. . In addition, the present data were discussed and compared with those given in the literatures. Keywords: Gamma dose levels; Radiation hazards; Radiological dose assessment, Precambrian Granites, Na'wah, Yemen. *Corresponding author:Mohamed Th. S. Heikal Email:[email protected] 1. Introduction The sources of the radionuclides are natural as well as man-made. The natural radioactivity background originates from 238U and 232Th series, from 40K and from the interaction of cosmic radiation with matter (UNSCEAR, 2000; IAEA 1999). In general, approximately 85% of the annual total radiation dose of any person comes from natural radionuclides of both terrestrial and cosmogenic origin (e.g., Belivermis et al. 2010; UNSCEAR, 2000). Gamma radiation emitted from primordial radionuclides and their progenies is one of the main external and internal ionizing source of radiation exposure to humans (UNSCEAR 2000). The terrestrial gamma dose rates (TGDRs) depends mainly on local geological and geographical conditions, and is related especially to the rock types (eg., Ramli, 1997; El-Sharkawi et al. 2012; Heikal et al. 2007, 2013; Saleh et al. 2013). ___________________________________________________________________________ Page1 Vol 5, Issue 3, 2016

Variations in TGDR due to the geological formations and soil types can be classified and used for the radioactivity predictions of terrains. Since to measure TGDR is expensive and time consuming, such a form can be used to predict terrestrial gamma dose, in particular for larger or poorly accessible areas ( Saleh et al., 2015). Yemen Republic is mostly covered by Precambrian rocks, up to 25% of the total mountainous area (Heikal et al. 2014). The southern parts of Yemen are occupied by vast areas of gneisses and granites (Fig.1). Therefore, the present study is concentrated on southern terrains of Yemen Precambrian rocks due to its target-pathfinder lithology (Heikal, et al. 2014). The collected rocks from the present area (Fig.2), in particular, gneisses and granites can be used as a pathfinder for determining of high radioactive backgrounds due to their radioactivity potential The main target of the present comprehensive work is calculating all relevant parameters of the potential health risk related with environmental irradiation by using spectroscopic radioactivity measurements of the samples collected around and within Na'wah town (Figs. 1-2).Where, risk potential is determined by before depending on high amount of uranium and thorium concentrations in the surrounding rocks (Heikal et al. 2007). This study was based on 25 samples; gamma measurements taken along shear zones cross cutting almost rock unites exposed around Na'wah area (Fig.2). The obtained data are relevant to the main rock units, Precambrian rock units and Cretaceous sandstone rock unit, according to gamma dose rate variations. The radioactive equilibrium, radioactive element mobilization, weathering and magma processes are also discussed in terms of radionuclide concentrations. All results were evaluated and compared to the mean values proposed by UNSCEAR, 2000 and data of rocks from different parts of the world (eg. Avwiri et al. 2012; Tanic et al. 2014). 2. Literature Review Very limited publications concern with radioactivity and/or radiation hazards of large rock exposures of gneisses and granites that cover 25% of the total mountain area of Yemen (Heikal et al. 2014). Some recent literatures highlighted radioactivity perspectives, dealing with assessment of radiation hazards in few regions of Yemen (ElMageed et al. 2010) and studying the natural and anthropogenic radioactivity levels in rocks and soils in the environs of Juban town, nearby the present area. Their results show that the highest concentration values of 226Ra, 232Th and 40K were found in granite and gneissic granites, while the lowest values were found in sandstone outcrops. They added that, the 226Ra and 232Th activity concentrations of the soil samples consistent with the worldwide average activity concentrations of these radionuclides in soils except 40K, which was higher than the values reported by UNSCEAR, 2000. On the other hand, Saleh et al. (2015) studied that the natural radioactivity on farm surface soil at Abyan Delta, located at the southwestern part of the present area. They determined that 226Ra and 40K activity concentrations were in average, 34.9±2.9, 84.5±7.8, 1232.7±40 Bq.kg–1 respectively for far surface soil irrigated by flood water. 3. Geology and Petrochemical Characteristics The Na'wah area (~ 24 km2, Figs. 1 & 2) is located nearby the south of Juban town pertaining to the southern terrain of Yemen Precambrian belt (Windley et al. 1996). This area is occurred among the suture zones and associated mylonite ones along and close ___________________________________________________________________________ Page2 Vol 5, Issue 3, 2016

to the boundaries of the Precambrian terranes (Windley et al. 1996; Whitehouse et al. 2001) (Fig.1).The present area includes two major lithologic units (Heikal et al. 2007): Cretaceous sandstone Younger (Aplite& pegmatite dikes) (Gneisses, granites) Precambrian basement Older Field data reveal unconformable and fault contacts (in part) between Cretaceous sandstone and Precambrian gneissic granite (Heikal et al. 2007). Cretaceous sandstone (~ 6 km2) rested as an unconformable contact on the Precambrian granites and gneissicgranites (Fig. 2).The faults occurring in Cretaceous sandstone (E-W and NW-SE trends) may be reactivated basement structures. Preccambrian basement (~18km2) includes granites and gneissic granite giving rise to discordant intrusive sharp contact. Almost Precambrian rocks are invaded by numerous pegmatitic bodies and aplite dikes trending E-W and ENE-WSW. A most promising mineralized area (along shear zones) trending NEN and EW (Fig. 2) cover about 10 km2. Intensive alterations like kaolinitization, hematitization, albitization (wall-rock alteration) occur within the contact zones of Cretaceous sandstone-Precambrian alkali feldspar granite and gneissic granite. Furthermore, silica injection in the form of smoky quartz veins is well developed nearby shear zone trending E-W and ENE. This zone is the most richest in uranium and thorium mineralization as indicated by field measurements (up to 159 ppm of U & 48 ppm of 232Th (Heikal et al. 2007).The pegmatite dikes under consideration are small, varying from a few meters to ten meters. They are simple form consisting of giant crystal of alkali feldspar, plagioclase and quartz with variable components of mica and uranophane patches. On the basis of petrographic characteristics (Heikal et al. 2007), the dominant mineral assemblages in the studied granitic rocks are microperthite of different types; braid and vein ones, the next most abundant mineral is quartz which occurs either as long drops or as anhedral crystals. Sodic plagioclase (An10-12) represents minor components. Zircon, apatite, allanite and radioactive minerals represent the main accessories. Radioactive minerals are mostly enriched found in almost present gneissic granites as well as pegmatites-aplites (eg. Uraninite, uranophanen, uranosilite, uvanite, curite, davidite, thorite). 4. Research Methodology The total of 25 samples collected along shear zones cross cutting Precambrian rocks and Cretaceous sandstones, exposed on Na'wah area (Fig.2) They were crushed into small pieces and ground to powder. Each sample was dried in an oven at 105 0C and sieved through a 100 mesh which is the optimum size enriched in heavy mineral. The samples were packed in plastic containers, cylindrical 75 × 90mm. The samples were weighed, stored approximately 4 weeks to reach secular equilibrium between thorium and radium and their decay products and then were counted for 480-720 min depending on the concentration of the radionuclides. 4-1. Experimental setup The specific activities were measured using p-type HPGe gamma-ray spectrometer (ORTEC AMETEK) with a high-resolution 8192 channel multichannel analyzer. A coaxial closed end, and a closed facing window geometry with vertical dipstick (500-800 μm) detector is used. The detector has the following specifications: resolution (FWHM) at 57Co is 1100 eV at 122 KeV, 60Co is 2.00 KeV at 1.33 MeV - relative efficiency at 1.33 MeV ___________________________________________________________________________ Page3 Vol 5, Issue 3, 2016

60Co

is 30%. The detector is shielded in a chamber of four layers to reduce different background radioactivity, starting with plexiglass (10 mm thick), continue with copper (30 mm thick), lead (100 mm thick) and finally cadmium (3 mm thick).The emitted Xrays from lead, which contains radioactive impurities due to antimony impurities, can be absorbed by lining shield from inside with a graded layer of 0.05 inch cadmium and 0.25 inch Perspex. 4.2 Determination of terrestrial radionuclide activities and terrestrial gamma dose rates 4-2.1Radium equivalent activity

The radium equivalent activity (Raeq) is a weighted sum of activities of the 226Ra, 232Th and 40K radionuclides based on the assumption that 370 Bq.kg-1 of 226Ra, 259 Bq.kg-1 of 232Th and 4810 Bq.kg-1 of 40K produce the same gamma ray dose rate (Krisiuk et al. 1971). The exposure to radiation (Beretka and Mathew, 1985; Tufail et al. 1992) can be defined in terms of the radium equivalent activity (Raeq), which can be expressed by the following equation: Raeq = ARa + 10/7ATh + 10/130AK ≤ 370 (1) Where ARa, ATh and AK are the specific activities of 226Ra, 232Th and 40K, respectively, in Bq.kg-1. The permissible value of Raeq is ≤ 370 Bq.kg-1 (Tufail et al. 1992; OECD, 1979; UNSCEAR, 1982). Calculated radium equivalent activity (Table1). 4-3-2. External and Internal Hazard Indices Another criterion, known as the external hazard index, has been defined as (OECD, 1979; Beretka and Mathew, 1985): A( Ra ) A(Th) A( K ) (2)    1, 370 259 4810 Where A(Ra), A(Th) and A(K) are the activity concentrations of 226Ra, 232Th and 40K in Bq/kg respectively. This index is used to estimate the level of γ-radiation hazard associated with the natural radionuclides in the studied samples. We can also calculate the internal hazard index Hin due to radon and its daughters using equation:

(Hex) I ex 

(3) Where ARa, ATh and AK are the activity concentrations of 226Ra, 232Th and 40K, respectively. This is based on the fact that, radon and its short-lived products are also hazardous to the respiratory organs. For construction materials of dwellings to be considered safe for dwellers, the values of the indices (Hex, Hin) must be less than unity (>1) for the radiation hazard to be negligible (Diab et al. 2008; Agbalagba et al. 2012). 4-2-3. Absorbed Gamma Dose Rate The gamma dose rate in the air is measured at one meter above ground level and the conversion factors used to calculate the absorbed dose rate are given in equation: The terms ATh, ARa and AK are the average activity concentration of 232Th, 226Ra and 40K in Bq.kg-1 respectively, and D is the dose rate in nGy/h. 4-2-4. Annual Outdoor Effective Dose The measurement of the concentrations of radionuclides in the environment due to terrestrial gamma radiation from 40K, 238U and 232Th, can estimate by the average outdoor conversion coefficient from absorbed dose rate in the air and the average ___________________________________________________________________________ Page4 Vol 5, Issue 3, 2016

annual effective dose equivalent (AEDE). The conversion factor values were established by UNSCEAR, 2000; and UNSCEAR, 1993, and its estimated value is 0.7 Sv.Gy-1 for gamma ray exposure in the environment and the occupancy factor outdoor to be about 0.2. The AEDE can be calculated as follows: AEDE (µSv/y) = D (nGy/h ×8760 (h/y) × 0.2 × 0.7(Sv/Gy) × 10-3 (4) For in indoor measurements (as the case in building materials) the occupancy factor is approximately 0.8 UNSCEAR (2000) and the equation (4) becomes: AEDE (µSv/y) = D (nGy/h ×8760 (h/y) × 0.8 × 0.7(Sv/Gy) × 10-3 (5) The world average annual effective dose equivalent (AEDE) from outdoor or indoor terrestrial gamma radiation is 0.460 mSv/year (Mantazul et al. 1979). 4-2-5. Representative Gamma Index (Iγ): This is used to estimate the γ- radiation hazard associated with the natural radionuclide in specific investigated samples. The representative gamma index as (OECD, 1979) Iγ = CRa/150 + CTh/100 + Ck/1500 (6) This gamma index is also used to correlate the annual dose rate due to the excess external gamma radiation caused by superficial materials. It is a screening tool for identifying materials that might become of health concern when used for construction (Tufail et al. 2007). Values of Iγ ≤ 1 corresponds to an annual effective dose of less than or equal to 1mSv, while Iγ ≤ 0.5 corresponds to annual effective dose less or equal to 0.3mSv (Avwiri et al. 2012). 4-2-6. Excess Lifetime Cancer Risk Outdoors (ELCR) This deals with the probability of developing over a lifetime at a given exposure level. It is presented as a value representing the number of extra cancers expected in a given number of people on exposure to a carcinogen at a given dose. Excess lifetime cancer risk (ELCR) is given as (Taskin et al. 2009) ELCR=AEDE×DL×RF 8 (7) Where, AEDR is the Annual Equivalent Dose Equivalent, DL is average Duration of Life (estimated to be 70years), and RF is the Risk Factor (S/v), i.e. fatal cancer risk per Sievert. For stochastic effects, ICRP uses RF as 0.05 for the public (Taskin et al. 2009). 5. Results and Discussion Based on the results obtained in this study, there are specific locations toward south of Na'wah town. The results show that the mean activity of 226Ra and232Th is higher than the world average of 25 Bqkg-1 for both of them, whereas the mean value for 40K is about five times of the world average of 370 Bqkg-1 (Khatiret al. 1998a,b). The averages of 226Ra,232Th, and 40K are 78.20, 83.64,and 2296.87 Bqkg-1 for Precambrian gneissic granites, while alkali feldspar granites show 60.18, 48.46, and 1957.27Bqkg-1 whereas sandstones reveals 34.69, 21.5,and 22.78 reflecting normal levels except 226Ra is slightly over the world average. Aplite and pegmatite dikes show average values 34.69, 358.11 and 2424.994 Bqkg-1. The huge increase in 40K must be taken into account due to relevant alkali feldspar enriched with 40K content that encountered as the main component of the studied Precambrian rocks. The measured and calculated parameters significantly exceed the expected values, marked as Precambrian rocks, including gneissic granites, alkali feldspar granites, aplites and pegmatites (Fig.3a,b,d), that located within a shear zone, trending E-W (Fig.2, Heikal et al. 2007). The average calculated values of Raeq are 374.36, 279.96, 933.64, ___________________________________________________________________________ Page5 Vol 5, Issue 3, 2016

67.16 Bqkg-1 for Precambrian gneissic granites, alkali feldspar granites, aplite-pegmatite dikes and Cretaceous sandstone, respectively. In addition, Precambrian gneissic granites, and aplite-pegmatite show values more than worldwide average, 370 Bqkg-1 ( UNSCEAR, 1982 ; Tufail et al. 1992). . On the other hand, the calculated results of sandstone (Table 1) (Fig.3c) are usual, safe and insignificant environmental impacts. The results indicate high average values of Hex and Hin (>1nGyy-1) for aplite and pegmatite dikes 2.52, and 3.16 nGyy-1 respectively. Whereas, the rest of the rock types, especially aplite and pegmatite dikes, are less or equal to unity (