Research Article

Radiological Hazards Assessment of Radium in Beach Sand from selected Public Beaches in Egypt

Wafaa F. Bakr, A. El-Sharkawy*
Nuclear and Radiological Regulatory Authority, Egypt
*Corresponding author:

A. El-Sharkawy, Nuclear and Radiological Regulatory Authority, Cairo, 11762, P. O. Box 7551, Egypt, Email: ahmedtharwat741@gmail.com

Keywords:

Radium isotopes, Beach sand, Mediterranean coast, Gamma spectrometry, Quality assurance, Radiological hazards

Radiological hazards assessment in some public beaches along the Mediterranean coast in Egypt has been carried out to ensure that the radiation dose from the combined radium isotopes (226Ra and 228Ra) in beach sand received to the public are insignificant, as well as updating the radiological data base map in these regions. Beach sand samples were collected from Rashid to Port Said beaches along the Mediterranean coast and were analyzed for 226Ra and 228Ra by gamma spectrometry using high purity germanium detector. The activity concentrations of 226Ra and 228Ra showed relatively higher values in Rashid and Burullus beaches due to the presence of black sand. Quality assurance and methods validation were established through the efficiency calibration of the detector, the estimation of uncertainties, the use of blanks, the analysis of standard reference materials and proficiency tests. Radiation hazards were estimated through the assessment of the absorbed dose rate and the annual effective dose. Also, the external hazard index values for the selected beaches were estimated.

The Egyptian Mediterranean coast contains a wide variety of sediments, which are mainly composed of two principal types; carbonate sands and quartz-dominant sands. The area of study, which extends from Rashid to Port Said, consists of deltaic sandy beaches of medium to very fine sand. It hosts the majority of the country’s population and is flanked by limestone ridges and coastal sand dunes (200 km long) [1].

Beach sand from Alexandria to Rashid primarily consists of quartz grains with common shell fragments [2]. In addition, the black sand deposits are located along the beaches of Rashid and Burullus on the Egyptian Mediterranean coast; these black sands contain some important minerals such as zircon and monazite [3], both of which contain uranium and thorium in their chemical structures. High background radioactivity values at Rashid have been detected as a result of these black sands [4]. The knowledge of the activity concentrations and distribution of these radionuclides is the main tool to assess any radiological hazards to the public. The main feature of this northern coast is the presence of a large number of beaches and resorts. Considering the popularity of these beaches and the habits of the population to spend long hours on the beach, it was a useful approach to determine the radioactivity levels of the radium isotopes (226Ra and 228Ra) in the beach sand of these areas, and to estimate the radiological hazards to the public.

Sample preparation


The collection of samples was performed at selected sampling points along the Mediterranean coastal beaches. The selection of sampling sites was based primarily on the population existence at these beaches and the presence of nearby industrial activities.Seven shore sediment samples were collected from Rashid to Port Said, as shown in fig. (1). The samples were collected using a template for guidance to 25 cm2 area and a depth of 10 cm. For quality assurance purpose and the limited number of samples, four sub-samples were collected at each sampling point and mixed thoroughly to produce a homogeneous representative sample for each public beach, packed in plastic bags and transferred to laboratory. The beach sand samples were oven-dried at 100ºC to a constant weight, homogenized, sieved through 2 mm mesh, packed into 100 mL standard plastic containers and hermetically sealed for four weeks to allow secular equilibrium between 226Ra and its decay products.


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Figure 1.Location Map of beach sand samples sites.

Experimental Techniques


The gamma measuring system consists of a Canberra p-type coaxial HPGe with an efficiency of 40% and a resolution of 1.95 keV at the 1.33 MeV energy of the 60Co. The gamma spectrum was recorded by using an 8192 multi-channel analyzer and the PC software Genie-2000. The detector was energy calibrated using a set of certified gamma radiation standard point sources (137Cs, 57Co and 60Co). The absolute detection efficiencies were calibrated by using the IAEA certified reference material RGU-1. The absolute efficiency at each gamma energy line of the 226Ra spectrum was determined, an absolute efficiency curve was fitted and the fitting equation was exploited to calculate the target photo-peak efficiencies.


Radioactivity Counting


The counting time for each sample was nearly 24 h. The net area count after background corrections in each photo peak was used in the computation of the activity concentration A (Bq/kg) at each photo peak was determined using the following equation [5]:
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Where, F is the intensity per hundred decays for each gamma energy line, Net CR is the net count rate, ηx is the photo peak efficiency and M is the mass of sample (kg). The gamma energy lines of 214Pb and 214Bi (352, 609.3, 1120.2 and 1764.5 keV) were used for the determination of the activity concentrations of 226Ra while for 228Ra, the 911.2 keV gamma line was used.


Quality Assurance


For quality assurance and validation purpose, the sampling was performed according to the ISO 18689-2 [6], replicate samples were measured for precision determination. Reference sediment samples were determined using the same measurement protocol, and were compared against their certified values to test the closeness of the measured samples to its reference values. Also, method validation through inter- comparison and proficiency tests was carried out using IAEA-368, IAEA-384, IAEA-TEL- 2014-03, IAEA- TEL-2016- 04. Errors were propagated due to nuclear counting statistics (ranged from 5 to 8%), reference standards and volume. The minimum detectable activity (MDA) was calculated according to the equation:

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Presented by Currie, 1968 [7], where BG is the background counts, t is the counting time, Eff is the efficiency of the gamma energy line and V is the sample volume. The MDAs were found to be 0.8 and 0.7 Bq/kg for 226 Ra and 228 Ra respectively.

Radioactivity concentrations in shore sediment samples

The activity concentrations of 226Ra and 228Ra in the beach sand samples are presented in fig. (2). The values are given in Bq/kg on a dry weight basis.

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Figure 2.Activity concentrations of 226Ra and 228Ra in beach sand samples.

The combined radium isotopes (226Ra and 228Ra) showed relatively higher values in S1, S2 and S7 (Rashid, Burullus and Port Said) beaches, which could be explained by the presence of black sand in these beaches. High 238U and 232Th series activities have been reported in the black sand at Rashid beach compared with other beaches along the Egyptian Mediterranean coast [8, 9]. Other study of natural radioactivity levels in coastal waters and sediments in Rashid showed that the activity concentrations of 238U and 232Th in Rashid shore sediments had an average of 199.3 and 147.8 Bq/kg respectively [10]. The values obtained for 226Ra and 228Ra in sites S3, S4, S5 and S6 are well comparable to those in coastal marine sediments in Egypt (10.7 and 13.7 Bq/kg respectively [11], 24.7 and 31.4 Bq/kg respectively [12]), and the limited variations in the combined radium activities in these beaches appear to be influenced by some sediment properties such as carbonates and particle size that differently affect the mobilization of natural radionuclides [13]. The 226Ra/228Ra activity ratio in the analyzed sand samples had values less than unity in Rashid and Burullus beaches, as shown in table (1), which may be explained by the higher monazite content in these regions. It has been discussed by many authors that the thorium is higher than uranium in monazite [14]. So, we may conclude that the major contributor to the relatively higher 228Ra activities in Rashid and Burullus beaches is monazite rather than zircon [15, 16].


Location

Ra-226

 (Bq/kg)

±

Ra-228

 (Bq/kg)

±

226Ra/228Ra

Rasheed

131.60

7.00

266.00

12.30

0.49

Burullus

245.10

16.90

253.80

11.80

0.96

Baltim

20.10

1.50

17.30

1.00

1.16

Gamasa

9.70

0.40

8.10

0.60

1.20

Damietta

10.80

0.80

8.60

0.80

1.25

Ras El-Bar

11.20

1.00

10.40

0.80

1.08

 Port said

46.60

2.40

52.00

3.10

0.90

 

Table 1. Activities of radium isotopes in beach sand sample ± 1σ uncertainties and the 226Ra/228Ra activity ratio.


Radiological hazards indices

The assessment of the potential exposure of the public to the combined radium isotopes (226Ra and 228Ra) present in the investigated beaches along the Egyptian Mediterranean coast has been carried out utilizing different indices.


Absorbed dose rate

The gamma radiation field was approximately calculated for a height of 1 meter above the ground surface in each site using the following equation [17]: D = Ru Cu + RTh CTh (2) Where: D is the absorbed dose in nGy/hr., Ru, RTh are the conversion factors (0.467 and 0.661 nGy/hr.per Bq/kg for 226Ra and 228Ra respectively) [18, 19] and Cu, CTh are the activity concentrations of uranium and thorium in soil samples. As shown in table (2), the absorbed dose rate from the combined radium isotopes had relatively higher values in Rashid and Burullus than the other beaches. For the other beaches, the absorbed dose rate estimated values were below the world average value of 57.0 nGy/h as reported in the UNSCEAR [17].


The annual effective dose


Based on the absorbed dose rate, a conversion coefficient from absorbed dose to effective dose of 0.7 and an outdoor occupancy factor of 0.20 proposed by the UNSCEAR, the annual effective dose was calculated using the formula [17]: AED (mSv/yr) = D (nGy/h) × 8760 (h/yr) × 0.20 × 0.70 (Sv/Gy) × 10-6 (3) The annual effective dose ranged from 0.01to 0.35 mSv/yr, with an average of 0.11 mSv/yr, as shown in table (2). These values are well below the world average value of 0.46 mSv/y [17].


Code

Location

Absorbed dose rate nGy/h

Annual Effective Dose

 mSv/y

External Hazad Index

S1

Rasheed

237.30

0.29

1.38

S2

Burullus

282.20

0.35

1.64

S3

Baltim

20.80

0.03

0.12

S4

Gamasa

9.90

0.01

0.06

S5

Damietta

10.70

0.01

0.06

S6

Ras El-Bar

12.10

0.01

0.07

S7

 Port said

56.10

0.07

0.33

 

Table 2. The absorbed dose rate, the annual effective dose and the external hazard index values in the investigated beaches.

 


The annual effective dose

The external hazard index (Hex) that quantifies the exposure factor and evaluates the hazard of the natural gamma radiation was calculated from the equation [20, 21]: (4) Where ARa, ATh, and AK are the mean activities of 226Ra, 232Th, and 40K in Bq/kg. Table (2) presents the external hazard index values from the radium isotopes (226Ra and 228Ra) in the beach sand samples. It is noticed that for Rashid and Burullus beaches, the values of the external hazard index are above unity. The value of this index must be less than unity in order to keep the radiation hazard insignificant [22].

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Where ARa, ATh, and AK are the mean activities of 226Ra, 232Th, and 40K in Bq/kg. Table (2) presents the external hazard index values from the radium isotopes (226Ra and 228Ra) in the beach sand samples. It is noticed that for Rashid and Burullus beaches, the values of the external hazard index are above unity. The value of this index must be less than unity in order to keep the radiation hazard insignificant [22].

A study of the activity levels of radium isotopes (226Ra and 228Ra) along the Mediterranean coastal beaches has been carried out. The combined radium isotopes were analyzed in the beach sand samples using high purity germanium detector. The coastal shore sediments in Rashid and Burullus beaches showed that there were relatively higher values for 226Ra and 228Ra than the other regions, which may be explained by the presence of black sands. Radiation hazards were estimated through the assessment of the absorbed dose rate and the annual effective dose. Both Rashid and Burullus sites showed absorbed dose rate values little above the world average value of 57 nGy/h, which may be explained by the presence of black sand. Also, the external hazard index for the studied beaches was estimated.

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Citation: Wafaa F. Bakr, A. El-Sharkawy (2017) Radiological Hazards Assessment of Radium in Beach Sand from selected Public Beaches in Egypt. J Mar Sci Res Technol 1:004.

Published: 27 November 2017

Reviewed By : Prof.Dr. Mohamed Amin Mahmoud Uosif, Dr. Muhammet Turkoglu,

Copyright:

© 2017 Bakr et al. . This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.