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

Abstract

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 variedfrom 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 yg g-1), Zn (21-150 yg g-1), Pb (30-53 yg g-1), Cd (2.50-4.00 yg g-1), Fe (5100-13150 yg g-1), Mn (118-298 yg g-1), Ni (17-36 yg g-1) and Co (16-18 yg 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) 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.

Headnote

Abstract: 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 + 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 ug g-1), Zn (21-150 ug g-1), Pb (30-53 ug g-1), Cd (2.50-4.00 ug g-1), Fe (5100-13150 ug g-1), Mn (118-298 ug g-1), Ni (17-36 ug g-1) and Co (16-18 ug 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) 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.

Keywords: Marine sediments, natural radioactivity, heavy metals, Red Sea, Egypt

(ProQuest: ... denotes formulae omitted.)

1. 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 ofthese 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 40K as well as the artificial radionuclides of 137Cs, 90Sr and 239+240Pu are the major long-lived 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.

2. EXPERIMENTAL

2.1 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 ofthe 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.

2.2 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 Safter 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 1. The salinity of seawater ranged from 42.3% to 42.47% at depth 0.5 m and 0.8 m, respectively. On the other hand, the water temperature ranges between 22.1 C at depth 25 cm and 22.13 C at depth 30 cm, as shown in Table 1.

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 pm. Weighted samples were placed in polyethylene beaker, of 350 cm3 volume each and weighted. The beakers were completely sealed for 4 weeks to reach secular equilibrium radium and thorium, and their progenies.15

2.3 Gamma Spectrometric Analysis

Activity measurements have been performed by gamma-ray spectrometer, employing a scintillation detector (7.62 x 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 226Ra radionuclide was estimated from the 351.9 keV ?-peak of 214Pb, and 609.3 keV, 1120.3 keV, 1728.6 keV and 1764 keV ?-peak of 214Bi. The 232Th radionuclide was estimated from the 911.2 keV ?-peak of 228Ac and the 238.6 keV ?-peak of 212Pb. The 40K radionuclide was estimated using the 1461 keV y-peak from 40K itself.18-20

2.4 Analytical Method

2.4.1 Concentration and uncertainty of activity

The specific activity in Bq kg-1 (A) in the sediment samples was obtained as follows:

... (1)

where Np is the count per second of sample (cps), e is the abundance of the y-peak in radionuclide, n 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.

2.4.2 Radium equivalent activities

The radium equivalent activities (Raeq) have been calculated on the estimation 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.21 Therefore, the Raeq was estimated by Equation 2:22

... (2)

where ARa, ATh and AK are the activities of226Ra, 232Th and 40K (Bq kg 1), respectively.

2.4.3 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 (226Ra, 232Th and 40K) were calculated.14 The D value can be calculated from Equation 3:

... (3)

where ARa, ATh and AK are the same as in Equation 2.

2.4.4 Internal hazard index

On the other hand, the internal hazard index (Hin) gives the internal exposure to carcinogenic radon and its short-lived progeny and it is given by the following formula:24-26

... (5)

where ARa, ATh and AK are the same as in Equation 2.

2.4.5 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 Iy 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

... (6)

where ARa, ATh and AK are the same as in Equation 2.

2.4.6 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:

... (7)

where T is the occupancy time and F is the conversion factor (0.7 SvG y 1).

2.4.7 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

... (8)

where EDR is the annual effective dose equivalent, DL is the duration of life (30-70 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 x 10-3.

3. RESULTS AND DISCUSSION

3.1 Sediment Types, Calcium Carbonates and Total Organic Matter

The values of sediment types, carbonates (CaCo3) 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 of1.34%, 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.

3.2 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, the major range values of heavy metals concentrations in marine sediment samples were: Cu (10.5-78.0 fig g-1), Zn (21.0-150.0 fig g-1), Pb (30.0-53.0 fig g-1), Cd (2.5-4.0 fig g-1), Fe (5100.0-13150.0 fig g-1), Mn (118.0-298.0 fig g-1), Ni (17.0-36.0 fig g-1) and Co (16.0-18.0 fig g-1) . 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 in samples from Safier Hotel as shown in Figures 4 and 5. The high concentration of iron (Fe) and manganese (Mn) in sediment samples may be due to human activation like sewage, shipment and navigation.30

3.3 Activity Concentrations

The results of measured specific activity as well as the uncertainty of 226Ra, 232Th and 40K 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 226Ra, 232Th and 40K, 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 226Ra, 232Th and 40K 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 226Ra and 232Th were lower than the permissible activity levels which are 35 Bq kg-1, 35 Bq kg-1 and 400 Bq kg-1 respectively for 226Ra, 232Th and 40K, while the mean concentrations of 40K 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 (R2 = 0.62) between activity concentration of 40K and 226Ra. The correlation indicates that the 40K and 226Ra is representative of a common geological origin. Figure 7 also shows a weak correlation between 226Ra and 232Th (R2 = 0.31) and a poor correlation between 232Th and 40K (R2 = 0.06), which indicates that 40K concentrations are not related to the presence of 232Th in samples.

Also, the value of 232Th/226Ra, 232Th/40K and 226Ra/40K ratios in all measured samples were listed in Table 6. From the obtained results, it is evident that the average values of 232Th/226Ra, 232Th/40K and 226Ra/40K ratios are 1.078, 0.041 and 0.040 in samples from Safier Hotel, while the average ratios in samples from NIOF area are 0.745, 0.044 and 0.060, respectively.

3.4 Statistical Analysis

3.4.1 Histograms

The frequency distributions of the radionuclides in sediment samples from Safter 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 232Th for sediment samples from Safter Hotel and NIOF area shows that these radionuclides demonstrate a normal (bell-shape) distribution as shown in Figure 9. But the graphs of 226Ra and 40K 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.

3.5 Comparison of Specific Activity Studied in Other Countries

The specific activity of 226Ra, 232Th and 40K 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 226Ra, 232Th and 40K in sediment samples were in the range or less than the corresponding values in the listed countries.

3.6 Radiological Hazards Indices of Investigated Samples

Raeq, D, Hex, Hin, Iy, 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 Raeq 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 pSvy-1 (Safier Hotel) to 51.0 pSvy-1 (NIOF), which are lower than the world average values at 70.0 pSv year-1. Figure 12 shows the distribution of AED in samples from NIOF area and Safier Hotel.26

Table 9 shows that the Hex and Hm 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 Iy 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 x 10-6 for marine sediment samples from NIOF, while the lowest average value is 60 x 10-6 for samples from Safire Hotel. These values are lower than the worldwide recommended value of 0.29 x 10-3. Figure 13 shows the distribution of ELCR in samples from NIOF area and Safier Hotel.

4. CONCLUSION

The specific activity of 40K, 232Th and 226Ra in marine sediment samples collected from NIOF and Safier Hotel area in Hurghada city, Egypt were measured. The concentrations of 226Ra and 232Th were lower than the permissible activity levels which are 35 Bq kg-1 and 35 Bq kg-1, respectively, whereas concentration of 40K 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.

Sidebar

Published online: 25 November 2019

To cite this article: Zakaly, H. M. et al. (2019). Assessment of natural radionuclides and heavy metal concentrations in marine sediments in view of tourism activities in Hurghada city, northern Red Sea, Egypt. J. Phys. Sci., 30(3), 21-47, https://doi.org/10.21315/ jps2019.30.3.3

Footnote

*Corresponding author: [email protected]

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