Inter-Comparison Study of the Population Dose Due to Gamma-Radiation in the Coast of North Sinai Between Rafah and Sir El-Abd Areas

EG0700180 5th Conference on Nuclear and Particle Phyilcs 19 - 23 Nov. 2005 Cairo, Egypt

INTER-COMPARISON STUDY OF THE POPULATION DOSE DUE TO GAMMA-RADIATION IN THE COAST OF NORTH SINAI BETWEEN RAFAH AND SIR EL-ABD AREAS

M.K. Seddeek1, T. Sharshai* H.M. Badran3'4

'Department of Physics, Faculty of Education, Suez Canal University, Al-Arish, Egypt 2Department of Physics and Chemistry, Faculty of Education, Tanta University, Kqfr El-Shaikh, Egypt 3Department of Physics, Faculty of Science, Tanta University, Tanta, Egypt 4 Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, P.O. Box 97, Amado, AZ 85645, USA

ABSTRACT

This study compares the external dose due to the y-ray emitting radionuclides in various areas in north Sinai, Egypt. The whole area was divided into 10 regions. The average absorbed dose rates were evaluated for each region. It was found that Zaranik protected area and Al-Massaid have the highest values of 69.0 and S4.7 nGy h"1, respectively. The corresponding values of the remaining regions were below 21 nGy h"1. The mean annual effective dose equivalent for the four largest cities Rafah, El-Sheikh Zuwaied, Al-Arish and Bir El-Abd were 20.7,16.1,53.4 and 13.9 jiSv. That is one individual at risk due to the radiation exposure of naturally occurring radionuclides in 50.8, 84.7, 8.7 and 85.3 years -for these cities, respectively. The results are compared with those from different areas in Egypt and in various countries.

Keywords: Naturally occurring radionuclides, Dose rate, Radiation hazard indices, Coastal environment, Black sand, Sinai, Egypt.

1. INTRODUCTION

Natural radiation is the largest contributor to the external dose of the world's population [1]. Terrestrial radiation arising fromth e Earth's crust and building materials gives rise to the external exposure and inhalation or ingestion of natural radionuclides. The most important source of external radiation exposure is due to y-rays emitted from

-481 - *

the ,XU and 232Th decay chains and The radiological implication of these radionuclides is due to the y-ray exposure of the body and irradiation of lung tissue from inhalation of radon and its daughters.

Knowledge of the distribution of radionuclides is an essential prerequisite for : evaluation and control of public exposure. It enables one to assess any possible radiological risks to human health. The assessment of the y-radiation dose from natural sources is of particular importance for public health. To evaluate the terrestrial y-dose rate for outdoor occupation, it is very important to estimate the natural radioactivity level.

The hazard due to y-rays was assessed by calculating radium equivalent, Raeq, according to [2],

Raeq = Cru + 1 -43 Cjh + 0.077 CK (1)

226 232 40 where Cr8, On, and Ck are the activity concentrations of Ra, Th and K, respectively. This index is defined for comparison of the activities of the materials containing different concentrations of radionuclides. The assumed criteria are that 1 Bq kg1 of 226Ra, 0.7 Bq kg1 of 232Th or 13 Bq kg1 of'"'K produces the same y-ray dose rate and that the Ra^ should not exceed a maximum of 370 Bq kg'1 [3]. The absorbed dose rate D (nGy h'1) in outdoor air is calculated at a height of 1 meter above the ground surface for different sites. The formula used [4] is given by, 1 D = 0.462 Cu+ 0.604 C77, + 0.0417 CK (nGy h" ) (2)

MA 1 where Cu is the activity concentration of U. By assuming a ratio of 0.72 Sv Gy" for absorbed dose in air to effective dose in the human body [1] and outdoor occupancy factors of 0.2, the effective dose equivalent was also calculated [1].

In order to evaluate the population dose due to outdoor y-radiation, the annual collective effective dose equivalents, Se, in the study area were assessed according to [5],

,Se=HXN (3)

where H is the mean annual effective dose equivalent and N is the estimated population of the studied area. Considering Rk, the risk factor, 1.65 *10"2 Sv*1 [6], the collective health detriment G is given by

G = RKXSE (4)

The objective of the present study is to estimate and compare the radiological hazards due to radioactivity contents of sand samples from various locations in north Sinai and to assess any health risks.

-482- 2. STUDY AREA AND EXPERIMENTAL PROCEDURES

Sinai Peninsula lies in the northeast of Egypt The area under study is located in the north of Sinai along the Mediterranean coast (Fig. 1). The first study [7] covered a region (referred to as region 1) which extends for about 40 km along the coast line. The eastern and western limits of region I were 8 km east and 32 km west (the Zaranlk protected area) of Al-Arish city. Region I encompassed a total area of about 150 km2. Hie second study [8] covered, two regions; the eastern region (region II) extends from the eastern limit of region I west (8 km east Al-Arish city) to Rafah city east and the western region (region III) extends from the Zaranik protected area east (western limit of region I) to Bir El-Abd city west The whole area included in both studies (—650 km2) is situated between East longitudes 33° 00' and 34° 17' and North latitudes 31° 00" and 31° 20'. 100 sample locations were included in both studies. For the purpose of comparing the general public's external exposure dose, the whole area was divided into 10 local regions (R1,R2 ... and R1Q in Fig. 1). The division is based on geographic conditions and political divisions.

A description of the sampling methods and sample preparations can be found elsewhere [7]. The activity concentrations of the samples were tneasured using a 204 cm3 p-type HPGe detector (Tennelec) with a relative efficiency of 50%. The details of the calibrations of the detecting system and the activity concentration measurements are found in Refs. 7-10.

3. RESULTS AND DISCUSSION

3.1 Sand characteristics and activity concentrations

Sand samples in the 10 regions are weak base with the same mean pH value of ~8.0. The total organic matter (TOM) content was found to be less than 1% for all samples. No significant correlation between ibe sand characteristics and any of the sample activity concentrations was found. The results of the activity concentration measurements [7,8] indicate that the activity concentrations of 7,26Ra and mTh in some locations in Al- Massaid (R4) and the Zaranik priftected areas (R3) were high compared with those in other locations. The rest of the 8 areas have little variations and low concentrations (<20 Bq kg1) for their ~r'Ra and 232Xh activities with Only one exception (beach site) with activities 46.5±0.6 and 68.1±1.3 Bq kg"1, respectively [8].

3.2 Dosimetry

The calculated radium equivalent, absorbed dose rate in outdoor air at a height of 1 meter above the ground surface and effective dose rate 'due to the presence of the natural radionuclides in the sand are given for the 10 local regions in Table 1. The highest 1 average values of Raoq were 170.8 and 138.0 Bq kg" in the Zaranik protected area (R3) and Al-Massaid (R4), respectively. Also, both areas showed a wide range of Ra^, values

483 - 31° 10'

00' 09 4*

Fig. 1. The map of the study areas, showing the 100 sampling locations, North Sinai. The locations included in region I [7] are marked with a closed box, while those represented by open triangles are corresponding to the two others II and III [8]. The 10 local regions are; RI Bir El-Abd, R2 EI-Mazar, Et-Telol and Misfaq, R3 Zaranik, R4 Al-Massaid, R5 Al- Arish, R6 Al-Arish valley, R7 El-Kharruba and As-Sakaska, R8 El-Sheikh Zuwaied and Esh-Shalak, R9 Al-Ahrash and Saladin and R10 Twyiel AI-Amir and El-Masora. compared with the ranges of others. The high Ra^ values are due mainly to the high concentrations of 226Ra and 232Th in the sand samples of both areas because of the existence of black sand. The calculated values of Ra«, for all 10 regions were cleanly lower than the recommended limit of 370 Bq kg"1 [3]. Three local regions, Al-Arish (R5), Twyiel Al-Amir and EI-Masora (RIO), and El-Kharruba and As-Sakaska (R7), have nearly the same value of —45 Bq kg"1. The remaining 5 regions have nearly the same Ra^ values (<28.5 Bq kg"1).

Table 1. The average and range of the radium equivalent, absorbed dose rate and effective dose equivalent for the 10 local regions. The total number of beach sand (bs) or dune sand (ds) locations included in the calculations in each regions are given. No. of Region Raeq Dose rate Eff. D. eq. Region locations No. Bqkg"1 nGy h"1 HSv a"1 (bs,ds) R1 Bir El-Abd (1,8) 26.9±4.5 12.5±4.2 15.7±4.8 (15.6-47.3) (7.7-20.8) (9.7-26.3) R2 El-Mazar, Et-Telol (0,6) 19.7±3.5 8.8±3.0 11.2±3.4 & Misfaq (14.2-23.7) (5.9-10.4) (7.4-13.2) R3 Zaranik (5,9) 170.8±11.4 69.0±13.6 87.1±17.0 (12.0-990.2) (5.3-387.9) (6.7-489.7) R4 Al-Massaid (8,2) 138.0±8.3 54.7±10.3 69.0±12.9 (17.6-428.7) (8.9-165.5) (11.2-208.9) R5 Al-Arish (9,5) 50.3±6.4 20.8±7.3 26.3±9.0 (14.1-154.4) (7.7-68.5) (9.7-86.4) R6 Al-Arish valley (0,4) 28.4±3.2 17.1±2.9 21.6±3.2 (26.9-31.3) (11.4-21.6) (14.3-27.2) R7 El-Kharruba & (5,5) 41.7±5.8 18.2±6.2 22.9±7.6 As-Sakaska (15.3-148.8) (7.3-61.4) (9.2-77.5) R8 El-Sheikh Zuwaied (4,9) 27.7±5.5 12.5±5.5 15.8±6.5 & Esh-Shalak (10.4-44.8) (4.6-20.2) (5.8-25.5) R9 Al-Ahrash & (1,9) 25.1±4.2 12.9±4.3 16.2±4.9 Saladin (17.9-49.3) (7.9-21.2) (9.9-26.7) R10 Twyiel Al-Amir ~(0,10) 45.2±5.2 19.9±4.4 25.1±5.0 &El-Masora (35.9-50.3) (15.8-22.3) (20.0-28.2)

The highest average absorbed dose rates were 69.0 and 54.7 nGy h"1 for the Zaranik protected area and Al-Massaid, respectively. Except for the results of the Zaranik protected area, all values are below that of the world average value of 59 (18-93 nGy h"1) [4]. The absorbed dose rates in these two areas correspond to an annual effective dose of 87.1 and 69.0 jxSv. These values are also below that of the world average value 410 |j,Sv a"1 [1]. The results show that the radiation hazard indices of the two regions (R1 and R2) west of Zaranik area and R6, R8 and R9 are the lowest Tegions. The three local regions (R6, R8 and R9) have nearly the same values of the radiation hazard indices. The number of beach and dune sand samples may have slightly affected the obtained results.

-485- Table 2 gives the radium equivalent, absorbed dose rate and effective dose equivalent for sand in different Egyptian regions. The maximum values of Ra«q in all cases are below 180 Bq kg'1 except in three cases; namely R3 and R4 in the present study, beach sand from Rosetta [11] and the shore sediment from the red sea [12]. The range of Ra«„ absorbed dose rate and effective dose equivalent of sand in Egypt excluding these three results are 8-180 Bq kg"1,5-90 nGy h"1 and 6-114 nSv a"1, respectively.

Table 2. The radium equivalent, absorbed dose rate and effective dose equivalent for sand samples in various regions in Egypt. No. of Dose rate Eff. D. eq. Region ' Reference samples Bq kg1 nGy h"1 jiSva"1 North Sinai 24 157.1±14.1 63.1±17.0 79.6±21.3 R3&R4 (12.0-990.2) (5.3-387.9) (6.7-489.7) North Sinai 76 3S.5±13.9 15.7±13.9 19.9±16.6 R1.R2& (10.4-154.4) (4.6-68.5) (5.8-86.4) R5-R10 90 km southwest of b b b - 58.7±2.1 28.4±0.9 35.9±l.l [16] Al-Arish city € Sinai, Suez gulf 21 80.6±22.31 39.6±10.7* 50.5±13.6S [17] (34.4-179.7) (15.7-86.8) (19.8-109.6) Sinai, Aqaba gulf 20 72.9±25.5a 36.2±12.5* 45.7±15.7* [17] (13.8-174.1) (6.7-90.0) (8.4-113.7) Sinai, St. Catherine 9 53.6±8.5a 26.0±4.1" 32.8±5.2a [17] (18.8-134.5) (8.6-67.4) (10.9-85.1) Red sea, shore 36 101.2±18.0 41.6±6.2 62.1±19.2" [12] sediment (16.4-442.7) (8.4-156.0) (10.5-259.6) Red sea, Wadi Wizr 1 69.4' 30.0 43.3* [18] Red sea, Safaga 26 103.0±61.0 50.9±28.3 65.4±35.7" [19] (63.1-176.9) (32.1-86.6) (41.3-109.8) Red sea, Hurghada 26 94.0±45.4 26.5±21.1 59.9±26.7* [19] (74.0-106.8) (21.3-36.7) (47.2-67.6) Rosetta 2 155.5±13.7* 71.1±6.1b 89.7±7.7 * [11] (beach sand) (103.3-207.7) (47.0-93.2) (59.9-119.5) b Nile delta and middle 12 35.4±16.5* 17.3±7.5 21.9±9.4* [11] Egypt (dune sand) (16.0-80.4) (7.6-37.0) (9.8-52.0) Not defined, RBM* 32.5 b 15.9b 20.1b [15] (31.7-33.2) (15.6-16.3) (19.7-20.5) b b b Not defined, RBM* - 55.2 - 25.0 31.6 [20] Not defined, RBM* 10 16.6±5.1 8.2±2.31 10.3±2.9" [13] Not defined, RBM* 25 18.5 8.9 b 11.3b [14] (7.7-3 6.6) * calculated from the concentrations of the given number of samples. b calculated from the mean concentrations of the given number of samples. c The surrounding areas around EI-Maghara coal mine. * RBM is raw building materials.

Generally, the calculated mean values for R3 and R4 are very comparable with those for beach sand in Rosetta [11]. The mean Raeq in both cases is between 1.5 and 10 times higher than that obtained for sand samples collected from other Egyptian regions. The mean values of the calculated radiation hazard indices for the rest of the regions (RI, R2 and R5-R10) are less than that obtained from other studies expect in two case of raw building material (RBM) sand [13,14]. On the other hand, these values are comparable with that for dune sand from Nile Delta and middle Egypt [11] and RBM sand [15].

Table 3 gives the radiation hazard indices for sand samples collected from different countries. All the listed results are within the reported range for Egypt except that for RBM and beach sand collected from Brazil [21-23]. From Tables 2 and 3, the results of R3 and R4, and shore sediment from Red Sea are lower than that obtained for Brazil [21- 23]. On the other hand, there are other regions all over the world with elevated natural radioactivity. The radiation hazard indices of these regions are between ~6 and ~28 times higher than that obtained for R3, R4, and shore sediment from Red Sea [24-27].

The annual collective effective dose equivalents, SE, in the study area were assessed. In this particular case four cities were considered; namely Rafah, El-Sheikh Zuwaied, Al- Arish and Bir El-Abd cities. The estimated populations are 57,799, 44,351, 130,035 and 51,065 (Information Centre of North Sinai Governorate), respectively. The respective calculated Se values for the 4 cities were 1.19, 0.72, 6.94 and 0.71 man-Sv a"1. Therefore, the numbers of individuals at risk in these cities are 0.020, 0.012, 0.115 and 0.012 man a"1. This indicates that one person may be at risk due to radiation exposure of naturally occurring radionuclides in 50.8, 84.7, 8.7 and 85.3 years for these four cities.

4. CONCLUSION

The results indicate that the radiation hazard indices in the Zaranik protected area and Al-Massaid area are high compared with those of the remaining regions in North Sinai. Only in the Zaranik protected area was the calculated absorbed dose rate higher than the world average value of 59 nGy h'1. However, the calculated values of Ra«q and effective dose equivalent received by the people living in all areas are below the world average of 370 Bq kg-1 and 410 jiSv a , respectively. No high risk exists for people living in these areas. The results of different radiation hazard indices from the present study indicates that almost all locations (except R3 and R4) are comparable with that for other regions in Egypt and from other countries. The collective health risk was determined for Rafah, El- Sheikh Zuwaied, Al-Arish and Bir El-Abd cities. The highest risk is that for Al-Arish city.

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-487- Table 3. The radium equivalent, absorbed dose rate and effective dose equivalent for sand in different countries. No. of Dose rate Eff. D. eq. Region Ra«q Sand type References samples Bqk*1 nGy h"1 ItSva'1 Middle East Algeria 12 28±7.1 13.0±1.4B 16.4±1.8" RBM [28] Egypt' >182 (7.7-207.7) (4.6-93.2) (5.8-119.5) Beach & Present study dune Jordan - 73 60.4*15.8 28.5±8.8b 36.0±11.2b Dune [29] (24.8-104.2) (19.0-41.3) (23.9-52.2) Kuwait 45.4±2.1 26.2±1.1 29.6±1.3 b RBM [30] 20 29.3±20.9" 13.8±9.6" 17.4±12.2* Beach [31] (18.3-46.1) (8.6-21.3) (10.9-26.9) Libya 60 44.8±4.4b 23±2.1 28.3±2.6b Dune [32] Africa 0 Zambia - 135.5±9.5 86.2±5.7 RBM [33] (117.0-154.0) (58.7-77.9) (74.1-98.3) Asia Bangladesh 38 83.2 * 37.7 47.5 RBM, river, [34,35] (42.7-156.3) sea & beach b b b China - 92.0±6.8 45.5±3.1 57.4±3.9 River [36] Hong Kong 3 100.4 49.3 b 62.3 b Sea & river [37] (38.7-162.0) (19.5-79.1) (24.7-99.8) India 2 170.8 81.0 b 102.2 b RBM [38] (163.3-178.8) Malaysia 136±33 66.6 b 84.1 b RBM [39] 5 150.6 b 70.5 b 89.0 b RBM [40] Pakistan 31 122.2 b 59.7 Kb 75.3 * RBM& [41-43] River Europe Greece 15 70.5° 34.8" 43.9" RBM [44] Ireland 3 54.7±2.3 4 27.4±1.1 • 34.6±1.3 1 RBM [45] (11.2-96.1) (5.0-48.0) (6.3-60.5) Italy . 63.3±2.8b 30.9±1.4 39.0±1.7 RBM [46] Netherlands 4 38.6 b 19.1b 24.1b RBM [47] Americas Australia 3 70.3 30.4° 38.4° RBM [2] (66.6-74.0) Brazil 31 252.6" » 82.1 M 100.8 "-b RBM& [21-23] beach USA 5 63.2 *•" 31.6 Kb 39.9 *'b RBM [48] " calculated from the concentrations of the given number of samples. b calculated from the mean concentrations of the given number of samples. c R3 & R4 and shore sediment from Red sea are not included (see Table 2).

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