Assessment of Natural Radionuclides and Heavy Metal Concentrations in Marine Sediments in View of Tourism Activities in Hurghada City, Northern Red Sea, Egypt

The specific activity of 40K, 232Th and 226Ra in marine sediment samples collected from National Institute of Oceanography and Fisheries (NIOF) and Safier Hotel area in Hurghada city (the most important regions in Egypt), were measured by gamma ray spectrometry using NaI(Tl) detector. The values of specific activity varied from 7 ± 1 Bq kg–1 to 53 ± 4 Bq kg–1, 6 ± 1 Bq kg–1 to 32 ± 6 Bq kg–1, and from 167 ± 11 Bq kg–1 to 1120 ± 63 Bq kg–1 for 226Ra, 232Th and 40K, respectively. The heavy metals have been measured and analysed by atomic absorption spectrometer. The major range values of heavy metals concentrations in marine sediment samples were: Cu (10.5–78.0 μg g–1), Zn (21–150 μg g–1), Pb (30–53 μg g–1), Cd (2.50–4.00 μg g–1), Fe (5100–13150 μg g–1), Mn (118–298 μg g–1), Ni (17–36 μg g–1) and Co (16–18 μg g–1). The total organic matter (TOC) and carbonates (CaCo3) distribution have been measured at some locations. Also, the frequency distribution and the value of ( 232Th/226Ra), ( 232Th/40K) Assessment of Natural Radionuclides 22 and ( 226Ra/40K) ratio for all measured samples were determined. Additionally, evaluations have been made of the radiological hazards and the results are diagrammed by Surfer program in maps.


INTRODUCTION
The main environmental problems and threats to the Red Sea coasts and aquatic environment locations include oil pollution, water pollution, solid waste disposal, navigation activities, phosphate ship pollution and fishing activities. 1 As a result of human activities, pollution extends along the shore, and waste is discharged to the nearby shore waters. 2 Mining, phosphate fertilisers manufacture, agricultural applications, coal combustion, cement production, street construction and other human activities are non-nuclear industries which have produced and redistributed increasing amounts of radioactive matters, leading to a considerable contribution radio-ecological pollution for these beaches. 3 Some of these pollutants may directly or indirectly be captured by bottom sediments. 4 Sediment acts as a medium of migration for transfer of radionuclides to the biological systems and hence, it is the basic indicator of radiological contamination of the environment. 5 Beach sediments are mineral deposits formed through weathering and erosion of either igneous or metamorphic rocks. Among the rock constituent minerals, there are natural radionuclides that contribute to the ionising radiation exposure on earth. 6 The natural radionuclides of the uranium and thorium series and 40 K as well as the artificial radionuclides of 137 Cs, 90 Sr and 239+240 Pu are the major longlived radionuclides already present or introduced into seas. 7 Biological effects of radionuclides in humans are due to physical and chemical processes that occur immediately after the passage of radiation through living matter. 8,9 Therefore, the knowledge of concentration and distribution of natural radionuclide in the sediments along Red Sea coasts and aquatic environmental locations are of great interest since it provides useful information in monitoring the environmental contamination and associated human health by natural radioactivity. Heavy metal pollution of the aquatic environment has become a worldwide problem. Metals like arsenic, cadmium, chromium, mercury, nickel and lead are often considered indicators of anthropogenic influence in marine environment and are of potential risk to the natural environment. 10,11 A number of researchers have demonstrated that the evaluation of metal distribution in marine shore is of great importance as a result of high pollution of heavy metals. 12 Hence, assessing and tracking the abundance of these heavy metals in coastal ecosystem are an important task.
The aim of this study is to compare the concentrations of natural radionuclides at two different stations. The first is National Institute of Oceanography and Fisheries (NIOF) and the second is Safier Hotel area, which was nurture station as well as a centre for research activities and at second was adding external sediments from the red mounts to expand the beaches of the Hotel Safire. Measurement of radiological hazard of populations is done to provide a background data on natural radioactive isotopes for the studied region.

Study Area
NIOF is located about 5 km north of Hurghada city, between 27° 17' 07" N and 33° 46' 30" E ( Figure 1). The location does not affect the activities of anthropogenic; it is distinguished by high sedimentation rate. This site is characterised by a long patchy reef, representing the front edge of a wide and shallow reef flat with many depressions and lagoons. Seaward of the reef edge is mostly a shallow sandy bottom area extending a long distance with few coral patches. The depth ranges from 3 m at the reef front with gentle slope towards depth water. The area is generally exposed to strong waves and the currents follow the prevailing current direction in the Red Sea from north to south. Fishing is considered a major activity in this area, mainly net fishing on the reef flat and the lagoons. A medium development does undergo along the coast of this area. The source rock at NIOF is composed of limestone and raised reefs; the back-shore area is occupied by buildings of El-Aheaa. The bottom topography of this area is characterised by sea grasses and algae in intertidal and subtidal area in addition to coral. An extended reef flat with seagrass and seaweed beds suitable for fish and shellfish breeding characterises this site. 13 Safier Hotel area is one of Hurghada resorts which is located 8 km south of Hurghada at 27° 12' 14" N, and 33° 51' 07" E, seen in Figure 1. Most of the activities taking place in the area are landfilling, dredging and reclamation of the intertidal zone. The filling operations have been carried out above the setback line area and around the dredged lagoon in the intertidal zone and violated two small channels have been dredged in the intertidal zone for water circulation inside lagoon. Nets are mounted at the entrances of the channels to prevent the marine litters from entering the lagoon. Currently, the original coastline of this area has been completely altered by dredging and land filling operations. Landfilling results in burying and obliteration of a number of biologically productive intertidal and subtidal habitats. The seabed in the area is covered by patches of seagrasses and algae with coral fragments. The bottom facies are characterised by many patches of seagrasses, algae and coral reefs.

Samples Collection and Preparation
The sediment samples have been collected from Hurghada City (nine samples from NIOF area, coded with I1 to I9, and six samples from North Safier Hotel, coded with H1 to H6) as shown in Figure 1. Sediment samples were collected by hand, grab sampler and scuba diving. The physical criteria of water, i.e., temperature, salinity, pH, depth, specific conductivity (SPC) and total dissolved salts (TDS), were measured directly in the field using Hydrolab Instrument (HANNA HI 9828) during samples collection at the studied localities, shown in Table   To determine the carbonate content, 1 g of each prepared sample was treated by 1N HCL acid, filtered and washed away several times by distilled water, dried and reweighed in order to calculate the percentage of carbonate content of the sediments. For organic carbon and total organic matter, 1 g of each crude sample was burned to 550°C for about 2 h. The organic matter content of the sediments was determined by sequential weight loss at 550°C. In case of heavy metals, about 0.5 g of homogenised ground sediment samples were accurately weighed on an analytical balance and then transferred into a Teflon beaker and were completely digested by using a mixture of concentration. 5 Nitric, per chloric and hydrofluoric acids were mixed with the ratio 3:2:1, respectively. 14 For gamma spectroscopic analysis, each sample was dried in an oven at 110°C for 48 h to ensure that moisture is completely removed. The samples were crushed, homogenised and sieved through a 200 μm. Weighted samples were placed in polyethylene beaker, of 350 cm 3 volume each and weighted. The beakers were completely sealed for 4 weeks to reach secular equilibrium radium and thorium, and their progenies. 15

Gamma Spectrometric Analysis
Activity measurements have been performed by gamma-ray spectrometer, employing a scintillation detector (7.62 × 7.62 cm). It had a hermetically sealed assembly, which included a NaI(Tl) crystal, coupled with a PC-MCA Canberra Accuspec. To reduce the gamma-ray background, a cylindrical lead shield (100 mm thick) with a fixed bottom and movable cover shielded the detector. The lead shield contained an inner concentric cylinder of copper (0.3 mm thick) in order to absorb X-rays generated in the lead. In order to determine the background distribution in the environment around the detector, an empty sealed beaker was counted in the same manner and in the same geometry as the samples. 16 The measurement period of the activity or background was 43,200 s. The background spectra were used to correct the net peak area of the gamma rays of the measured isotopes. A dedicated software program was used. 17 The calculations were done using the MS Excel program.
The 226 Ra radionuclide was estimated from the 351.9 keV γ-peak of 214 Pb, and 609.3 keV, 1120.3 keV, 1728.6 keV and 1764 keV γ-peak of 214 Bi. The 232 Th radionuclide was estimated from the 911.2 keV γ-peak of 228 Ac and the 238.6 keV γ-peak of 212 Pb. The 40 K radionuclide was estimated using the 1461 keV γ-peak from 40 K itself. 18-20

Concentration and uncertainty of activity
The specific activity in Bq kg −1 (A) in the sediment samples was obtained as follows: where N p is the count per second of sample (cps), e is the abundance of the γ-peak in radionuclide, η is the measured efficiency for each gamma line observed for the same number of channels either for the sample, and m is sample mass in kg.

Radium equivalent activities
The radium equivalent activities (Ra eq ) have been calculated on the estimation that 370 Bq kg -1 of 226 Ra, 259 Bq kg -1 of 232 Th and 4810 Bq kg -1 of 40 K produce the same gamma ray dose rate. 21 Therefore, the Ra eq was estimated by Equation 2: 22 Ra eq = A Ra + 1.43A Th + 0.077A k (2) where A Ra , A Th and A K are the activities of 226 Ra, 232 Th and 40 K (Bq kg -1 ), respectively.

Absorbed gamma dose rate
The absorbed dose rates (D) due to gamma radiations in air at 1 m above the ground surface for the uniform distribution of the naturally occurring radionuclides ( 226 Ra, 232 Th and 40 K) were calculated. 14 The D value can be calculated from Equation 3: where A Ra , A Th and A K are the same as in Equation 2.

Internal hazard index
On the other hand, the internal hazard index (H in ) gives the internal exposure to carcinogenic radon and its short-lived progeny and it is given by the following formula: [24][25][26] H in = (A Ra /185 + A Th /259 + A K /4810) ≤ 1 (5) where A Ra , A Th and A K are the same as in Equation 2.

Gamma radiation hazard index
In order to examine whether the samples meet the limit of dose criteria, another radiation hazard index, the representative level index Iγ is used to estimate the level of gamma-radiation hazard associated with the natural radionuclides in the investigated samples and is defined from the following formula. 27 I γ = 0.0067 A Ra + 0.01 A Th + 0.00067 A K (6) where A Ra , A Th and A K are the same as in Equation 2.

Annual effective dose
Annual estimated average effective dose equivalent (AED) received by an individual was calculated using a conversion factor of 0.7 SvG y -1 , which was used to convert the absorbed rate to the human effective dose equivalent. 14 The annual effective dose was evaluated using Equation 7: where T is the occupancy time and F is the conversion factor (0.7 SvG y -1 ).

Excess Lifetime Cancer Risk
Excess lifetime cancer risk (ELCR) can be defined as the excess probability of developing cancer at a lifetime due to exposure level of human to radiation. ELCR was calculated by using the following equation: 28 where EDR is the annual effective dose equivalent, DL is the duration of life  year) and RF is a risk factor (Sv -1 ) fatal cancer risk per Sievert. For stochastic effects, International Commission on Radiological Protection (ICRP) 60 uses values of RF = 0.05 for public. 14 The worldwide recommended value is 0.29 × 10 -3 .

Sediment Types, Calcium Carbonates and Total Organic Matter
The values of sediment types, carbonates (CaCo 3 ) and total organic matter (TOM) are presented in Table 2. From Table 2, we can observe that the values of sediment types in samples from Safier Hotel are between 1.27% and 10.31% with an average of 4.7%, between 89.69% and 98.61% with an average of 94.8%, and between 0.00% and 2.37% with an average of 0.5% for gravel, sand and mud, respectively.
In samples from NIOF, the values of gravel, sand and mud fluctuate from 0.41% to 19.75% with an average of 13.09%, ranged from 78.08% to 98.52% with an average of 85.57%, and from 0% to 3.21% with an average of 1.34%, respectively. The purpose of such mechanical analysis of the sediment is not only for the nature of the sediment but also to understand the physical properties of the sediments, and reveal the relationship and effect of the grain size, source materials and depositional environment. Figure 2 shows the distributions of gravel, sand and mud in sediment samples from the studied regions.
The average values of carbonates content in the investigated sediments fluctuate from 40.08% (Safier Hotel) to 48.87% (NIOF). As shown in Table 2, NIOF areas recorded the highest mean value of carbonate contents. This may be due to inorganic chemical precipitation, limestone rock on the sea floor residual from weathering and accumulation of skeletal grains. 29 Organic matter affects the aquatic ecosystem by interacting with organic matter to form complex compounds, which in its structure contain several other elements. 30 The content of organic matter in sediment samples vary from 6.90% to14.40% (Safier Hotel) and from 3.10% to 42.35% (NIOF) as shown in Table 3 and Figure 3.    Figure 3: The distribution of CaCO 3 content and TOC in sediment samples from Safier Hotel and NIOF (full-coloured illustration are available in the digital version).

Heavy Metals Concentrations
The concentrations of heavy metals (Cu, Zn, Pb, Cd, Fe, Mn, Ni and Co) were analysed to understand the effect of human action and natural inputs on the quality of marine sediments and to examine the pollution situation. The obtained results are listed in Table 4 and diagrammed in Figures 4 and 5. As shown in Table 4

Activity Concentrations
The results of measured specific activity as well as the uncertainty of 226 Ra, 232 Th and 40 K of sediment samples were listed in Table 5. From the table, it can be seen that the values of specific activity varied from 7 ± 1 Bq kg -1 to 53 ± 4 Bq kg -1 , 6 ± 1 Bq kg -1 to 32 ± 6 Bq kg -1 and from 167 ± 11 Bq kg -1 to 1120 ± 63 Bq kg -1 for 226 Ra, 232 Th and 40 K, respectively. The variation of radionuclides concentration in studying sediment samples may be due to their presence in the marine environment and their physical, chemical and geo chemical properties. 31,32 The highest mean value of 226 Ra, 232 Th and 40 K specific activity are found in samples from NIOF area as shown in Figure 6. This may be due to the terrestrial deposits transported from the fringing mountains to the beaches of the Red Sea, where uranium concentration in the shore sediment depends on the uranium concentration in the fringing mountains. 33 The mean concentrations of 226 Ra and 232 Th were lower than the permissible activity levels which are 35 Bq kg -1 , 35 Bq kg -1 and 400 Bq kg -1 respectively for 226 Ra, 232 Th and 40 K, while the mean concentrations of 40 K were higher than the permissible activity levels in samples from NIOF area and lower than in samples from Safier Hotel. 3 Figure 7 shows good correlation (R 2 = 0.62) between activity concentration of 40 K and 226 Ra. The correlation indicates that the 40 K and 226 Ra is representative of a common geological origin. Figure 7 also shows a weak correlation between 226 Ra and 232 Th (R 2 = 0.31) and a poor correlation between 232 Th and 40 K (R 2 = 0.06), which indicates that 40 K concentrations are not related to the presence of 232 Th in samples.
Also, the value of 232 Th/ 226 Ra, 232 Th/ 40 K and 226 Ra/ 40 K ratios in all measured samples were listed in Table 6.

Histograms
The frequency distributions of the radionuclides in sediment samples from Safier Hotel and NIOF area were analysed by SPSS19 and histograms are given in Figures  8 to 10. A histogram is a graphical representation of the distribution of data. It is an estimate of the probability distribution of continuous variables. The graph of 232 Th for sediment samples from Safier Hotel and NIOF area shows that these radionuclides demonstrate a normal (bell-shape) distribution as shown in Figure 9. But the graphs of 226 Ra and 40 K show that the radionuclides exhibited some degree of multi-modality. This multi-modal feature of the radio-elements demonstrates the complexity of sediments samples as shown in Figures 8 and 10.

Comparison of Specific Activity Studied in Other Countries
The specific activity of 226 Ra, 232 Th and 40 K in sediment samples from the studied areas were compared with those from similar investigations in other countries and presented in Table 7. It can be seen from Table 7 that the mean values of 226 Ra, 232 Th and 40 K in sediment samples were in the range or less than the corresponding values in the listed countries.

Radiological Hazards Indices of Investigated Samples
Ra eq , D, H ex , H in , I γ , AED and ELCR were estimated using Equations 3 to 9 and their results are presented in Tables 8 and 9. From Table 8, it is observed that the values of radium equivalent in sediment samples are lower than the allowed maximum value of 370 Bq kg -1 , and fluctuate from 29 Bq kg -1 to 159 Bq kg -1 . Figure 11 shows the distribution of Ra eq in samples from NIOF area and Safier Hotel. 22 As listed in Table 8, the mean value of dose rates in sediment samples is lower than the international limit 59 nGyh -1 . The average annual effective dose rates vary from 35.2 µSvy -1 (Safier Hotel) to 51.0 µSvy -1 (NIOF), which are lower than the world average values at 70.0 µSv year -1 . Figure 12 shows the distribution of AED in samples from NIOF area and Safier Hotel. 26  38 29 ± 0.4 8 ± 0.1 282 ± 7 Egypt El-Hamraween BS) 38 238 ±4 11 ± 0.3 195 ± 7 Egypt (Ras El Behar SS) 38 14 ± 0.3 13 ± 0.3 396 ± 12 Egypt (Ras El Behar BS) 38 16 ± 0.4 19 ± 0.4 266 ± 10 Egypt (Safaga sand) 39 25.3 ± 13.7 21.4 ± 10 618 ± 122 Sudan Red Sea Coastal) 40 11.6 6.02 158.4 Egypt (Red Sea shore sediment) 33 24.7 ± 4.3 31.4 ± 9.6 427.5 ± 35 Egypt (Nasser Lake) 40 222-326 222-326 222-326 Egypt (Suez Canal) 41 4.9-20.2 3.3-35.4 59-368 Saudi Arabia (Ras Tanura) 11 11.68 ± 1.22 6.21 ± 0.58 169.40 ± 7 Denmark (Beach sediment) 14 17 19 460 Spain ((Beach sediment)) 14 32 33 470 Hong Kong (Beach sediment) 14 59 95 530  Table 9 shows that the H ex and H in values resulting from all samples are lower than the unity, which do not cause any harm to the populations in all regions under investigation. 14 The calculated I γ values for the samples under investigation are given in Table 9. It is clear that the sediment samples are lower than unity. 14  Finally, Table 9 gives the results for ELCR for samples, the highest average value is 339 × 10 -6 for marine sediment samples from NIOF, while the lowest average value is 60 × 10 -6 for samples from Safire Hotel. These values are lower than the worldwide recommended value of 0.29 × 10 -3 . Figure 13 shows the distribution of ELCR in samples from NIOF area and Safier Hotel.

CONCLUSION
The specific activity of 40 K, 232 Th and 226 Ra in marine sediment samples collected from NIOF and Safier Hotel area in Hurghada city, Egypt were measured. The concentrations of 226 Ra and 232 Th were lower than the permissible activity levels which are 35 Bq kg -1 and 35 Bq kg -1 , respectively, whereas concentration of 40 K at 400 Bq kg -1 was higher than the permissible activity levels in samples from NIOF area and lower than samples from Safier Hotel. The highest concentrations of Cu, Zn, Cd and Co were found in sediment samples from NIOF area. As expected, the highest concentration of Pb, Fe, Mn and Ni are obtained in samples from Safier Hotel area. All measured radiological hazards are less than permissible limit. Hence harmful radiation effects are not posed to the public going to NIOF, tourists going to Safier Hotel for recreation, or to the sailors and fishermen involved in their activities in the area as a result of the natural radioactivity of beach sediments.
The data obtained in this study may be useful for natural radioactivity mapping and also used as a reference data for monitoring possible radioactivity pollution in future.