THE CONCENTRATION LEVELS OF SOME ISOTOPIC RADIONUCLIDES IN THE COASTAL SEDIMENTS OF THE RED SEA,...

ISOTOPE & RAD. RES., 42(1), 11-27 (2010). ISSN 0021-1907 INIS ISRRAC EG

THE CONCENTRATION LEVELS OF SOME ISOTOPIC RADIONUCLIDES IN THE COASTAL SEDIMENTS

OF THE RED SEA, EGYPT ∗

EL SAHARTY, A.A.(1) and DAR, M.A.(2)

(1) National Institute of Oceanography and Fisheries, Alexandria, Egypt and (2) National Institute of Oceanography and Fisheries, Hurghada, Egypt.

Key words: Radionuclides, Red Sea, Sediments, Uranium, Thorium, Cesium, Potassium.

رواسب شاطئ البحر األحمر، مصر ىدراسة ترآيزات بعض النظائر المشعة فدار ىعبير عباس السحرتى و محمود عبد الراض

ةـخالصباإلضافة إلى 40- ، البوتاسيوم232- ، الثوريوم238- تم قياس األنشطة اإلشعاعية لنظائر اليورانيوم

آما تم قياس ترآيز المواد العضوية ،حباستخدام جهاز قياس أشعة جاما عالية الوضو 137- السيزيوموالكربونات فى نفس عينات الرواسب السطحية المجمعة من مصبات ثالث وديان بجنوب مصر على ساحل البحر األحمر حيث تتميز هذه المناطق بتواجد مستنقعات أشجار المانجروف مع آثافة عالية

.دئة لترسيب الرواسب الدقيقة والمواد العالقةللجذور الهوائية ألشجار المانجروف والتى توفر ظروف هامستويات متقاربة من النشاط اإلشعاعى فى مناطق 232- والثوريوم 238- سجلت نظائر اليورانيوم

ن تواجدها بتلك المستويات من األنشطة يدل على أن تجمع هذه النظائر ربما تم نتيجة أالدراسة آما روف الترسيب فى بيئات المانجروف وهذه العمليات تشمل لعمليات متعددة ومرآبة وهى التى تميز ظ

التجمع من الرواسب الناعمة والعالقة التى يحملها تيار الماء من البحر، االدمصاص فوق أسطح حبيبات اآاسيد وهيدروآسيدات الحديد والمنجنيز من مياه البحر، االرتباط الترآيبى داخل النسيج الهيكلى

الحبيبات التى تحملها الرياح واألمطار من المناطق الجبلية المحيطة آما سجل للكربونات باإلضافة إلى ت مشعة قادمة من نشاط إشعاعى ملحوظ فى مناطق الدراسة مما يدل على تواجد نويا 40- البوتاسيوم

لم تكن ذات قيمة ملحوظة مما يؤآد عدم وجود مصادر 137- لكن ترآيزات السيزيوم المناطق األرضية .لصناعى ذات تأثير على الرواسب الساحلية بمناطق الدراسةلإلشعاع ا

ABSTRACT The radionuclide activities of 238U, 232Th, 40K and 137Cs were measured using

high resolution gamma spectrometry system. The total organic matter (TOM) and carbonate contents were also measured in the surface sediments of three valleys downstream at the southern Egyptian Red Sea coast. These localities are characterized by the presence of mangrove swamps with dense aerobic roots that provide calm conditions for particulate and fine sediments settlement. 238U and 232Th recorded almost equal activity values in the studied localities and their

Accepted January 2010.

EL SAHARTY, A.A. and DAR, M.A. 12

occurrence in the localities indicated that the metal accumulation are due to the complex and multiple processes that characterize the mangrove environments including accumulation in particulate form with the fine sediments, absorption on iron and manganese oxides and hydroxides from the sea water, incorporation inside the carbonate frameworks and as detrital phase. 40K showed obvious radioactivity in the three localities indicating the presence of terrestrial radionuclide. 137Cs concentrations were not evident in the studied localities which may indicate non-significant artificial source of radionuclide activity.

INTRODUCTION Radionuclides are powerful tracers providing basic insights into varieties of

marine processes. Because of the relatively well defined temporal and spatial aspects of the introduction of radionuclides into the ocean, their movement within the ocean provides many insights into a large number of processes in the water column, biological and sedimentary systems (Livingston and Povinec, 2000). Marine sediments are the essential reservoir for natural and artificial radionuclides retention due to their diverse composition. The uptake of radionuclides by marine sediments depends on their physical and chemical properties (Noureddine and Baggoura, 1997). The radionuclides distributions in the marine sediments (natural and artificial) provide essential information about sediment movement and accumulation that provide a strong signal about the sediment origin (Noureddine and Baggoura, 1997). It is also considered the basic information about any future abnormality in the artificial radionuclide concentrations in the marine environment.

The Red Sea is considered one of the most important navigation paths in the world. Its importance was increased throughout the last three decades of the twentieth century after Suez Canal opening for navigation especially for oil tankers between the Middle East and Europe. A considerable amount of international trade is transported in Egypt through the Suez Canal including radioactive materials (Abril and Abdel-Aal, 2000). The Red Sea importance was appeared vigorously in the last 15 years during the first and second Gulf wars, when it was used to transfer the military ships, weapons and submarines from the Mediterranean Sea to the Arabian Gulf.

In the last few years, the Red Sea was seriously threatened. Many ships charged with nuclear wastes from Europe were cruising around the world as well as the Red Sea to dump their charges into the sea bottom or in any country that accept these wastes to be dumped in its land. Increasing numbers and quantities of radioactive materials in many different forms are being transported throughout the world resulting in increased public concern about radiation safety transport. Some studies were devoted to investigate the artificial radionuclide occurrence in the Red Sea (Sam et al., 1998b and 2000).

The present study aims to determine the actual concentrations of some natural (238U, 232Th and 40K) and artificial (137Cs) radionuclides along the coastal areas of

THE CONCENTRATION LEVELS … 13

Red Sea. These radionuclides will be identified in order to have baseline information for any future changes along the Egyptian Red Sea coast.

MATERIALS AND METHODS Throughout three periodical trips between January 2004 and May 2005, the total

of thirty sediment samples were collected from three valleys downstream located along the southern Red Sea coasts of Egypt. These localities are Al-Sharm Al-Bahari, Wadi Al-Gemal and Gola’an (fig. 1). The areas under study cover a distance of 300 km along the Red Sea coast. These valleys downstream are distinguished by dense mangrove vegetations of Avicennia marina characterized by the presence of Pneumatophores lattice (aerobic roots). This situation minimizes the erosional wave actions and preserves the accumulated fine and particulate sediments in site.

The sediment samples were air dried and about 50 g of each sample were powdered and sieved to a grain size less than 100 μm. The powdered samples were bottled in 40 ml containers and stored for about four weeks to reach the equilibrium state (El-Arabi, 2005). These samples were analyzed at the Atomic Energy Authority, Second Research Reactor ETRR2, Abu Zaabal, Egypt. The samples were measured using low level gamma ray spectrometer connected with high purity germanium detector. This detector has relative efficiency of about 30% with resolution energy of 1.95 keV FWHM for the 1332 keV gamma transition of 60Co (El-Arabi, 2005). The estimated data were corrected by background subtraction.

The grain sizes of the disaggregated raw sediments were measured using sieve analysis. The estimated fractions were grouped to three groups; coarse group (Ø-1+ Ø0), medium group (Ø1+ Ø2) and fine group (Ø3+ Ø4+ Ø5). The total organic matter (TOM) contents in the sediments were determined as the ignition weight loss at 550°C (Brenner and Binford, 1988). The carbonate content (expressed as CaCO3%) was determined by dissolution of 1g of each powdered sample with diluted glacial acetic acid (12%) for 4h hence, the remaining weight represented the non-carbonate residues.


Ras Gharieb

Hurghada

Safaga

Al-Qusier

Red

Sea0 150 300 Km

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32 34 36

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Mersa Alam

Hamata

Sinai

Suez

Gola'an

Wadi Al Gemal

Al Sharm Al Bahari

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Al Sharm Al Bahari

Red Sea

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25 51 47

25 52 33

25 52 02

25 52 17

34 24 35 34 25 2734 24 55 34 25 12

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Wadi Al-G

emal

Downstream

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areaMangrove Forest

Wadi Al-G

emal

Island

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RED SEA

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24 38

24 39

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34 36 40 36 50 36 60 36 70 36 80 36 90

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Gola'an Village

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Tidal Flat

StudyArea

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24 21 20

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35 17 50 35 18 00 35 18 10 35 18 20 35 18 30

N

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D

Fig. (1): Location map shows the different valleys downstream;

A- General map. C- Wadi Al-Gemal. B- Al-Sharm Al-Bahari. D- Gola'an.

RESULTS AND DISCUSSION Thorium and uranium in beach sand contained mainly resistant heavy minerals

such as monazite, zircon and xenotime (Mahdavi, 1964) and potassium is present in the light mineral fractions as potash-feldspars mica and glauconite where it is slowly converted into soluble forms by weathering (El-Araby, 2005). Noureddine et al. (1998) reported that the major source of natural radionuclides results from the weathering and recycling of terrestrial minerals and rocks that give rise to 40K, 232Th


and 238U. They added that sediments are known to be good receptacles of radioactivity compared with other marine materials. The uptakes by marine sediments depend on the physical and chemical properties of radionuclides and on the grain size of the sediments (NAS, 1971). The present sources of anthropogenic radionuclides in the marine environment are consisting of global fallout, nuclear weapons testing, releases from nuclear facilities, radioactive waste dumping, the Chernobyl accident and nuclear submarine and aircraft accidents (Livingston and Povinec, 2000).

The fate of the released radionuclides will be strongly dependent on the chemical affinity to particulate matter in suspended loads and bottom sediments (Abril and Abdel-Aal, 2000). Sam et al. (1998a) documented that the different natural radionuclides concentrations measured in the marine environment depends on the physical, chemical and geochemical properties and the pertinent environment in the biological process. Noureddine et al. (1998) reported that the uptake of radioactivity is seen to be dependant on the nature of sediments and ranged from very fine grain to larger pore size particles. In sediments, the concentration varies from class to another and the highest value is seen in the fraction less than 100μm and the level of radioactivity is correlated with the variations of the finest particles. Particle characteristics reflect the properties of the material from which the particle originated and they can be used for estimating the location of the release site, time of release and possible formation and transport mechanisms of the particles (Pollanen et al., 1999). Nicholson and Hunt (1995) attributed the observed radionuclides concentration in the marine environment to complex processes depending upon present and past discharges, the rates of decay, dispersion, uptake and elimination.

Kim et al. (2004) hypothesized two reasons for uranium accumulation in the salt marshes and tidal area; 1) uranium scavenging occurs during the process of tidal mixing and attendant flocculation of humic acids and iron oxides during its extensive redox cycling or 2) uranium extraction occurs at the marsh surface during extensive flooding of the surface sediments due to higher organic content and subsequent decomposition.

The average recorded values of uranium concentrations in the studied localities (Al-Sharm Al-Bahari, Wadi Al-Gemal and Gola’an) are nearly equal. They were 16.76±7.94 Bq kg-1, 16.83±1.32 Bq kg-1 and 15.79±4.63 Bq kg-1, respectively (tables 1, 3, 5). These values are much lower than the average recorded values for the coastal sediments of Sudanese Red Sea at the fringing reefs of Port Sudan and Sanganeb Atoll (Sam et al., 1998a). On the other hand, they are higher than the values recorded for the shallow water sediments of Port Sudan (Sam, 2003). Sam et al. (1998a) pointed out that uranium is higher in the shallow water sediments of the Sudanese Red Sea and the authigenic fraction constituent was 12% on the average. El-Araby (2005) documented that the uranium concentrations in Safaga and Hurghada along the Red Sea coast are more dependant upon the climate,


seasonal variability, the effects of evapotranspiration and the concentration of suitable complexing agents which can increase the solubility of uranium such as the seasonal variations of rainfall and run-off whereas increasing the rainfall may result in more effective leaching and/or transport of uranium and lead to an increase in uranium concentration.

Anderson (1982) suggested that particulate authigenic uranium is primarily formed in surface water but it is rapidly re-mineralized in deep water, therefore, the 238U: 232Th ratios in surface marine sediments should be representative of that in detrital phases. Lomitschka and Mangini (1999) indicated that the marine carbonates are frequently coated with iron and manganese oxides/hydroxides which absorb additional thorium and uranium out of sea water.

The behavior of uranium depends on redox conditions. Under anoxic conditions, uranium is immobile and it diffuses from seawater into reducing sediments then enriched there. The depth of reducing layers and the sediments accumulation rate determine the enrichment of authigenic uranium (Mangini et al., 2001). Its dominant forms are U(VI) under oxidizing conditions and U(IV) under reducing conditions. In contrast, U(VI) may be present in high concentrations under low pH conditions and becomes increasingly adsorbed when the pH increased (Lauria et al., 2004). Uranium appears to be largely associated with organic matter entrained in the sediment and is commonly so recently accumulated that radioactivity, which is produced mostly by the daughter isotopes of uranium decay, is very low (Otton et al., 1989).

The uranium concentrations recorded in the different sites may by affected by the anoxic conditions of the mangrove swamps in the localities and may be subjected to complex and multiple processes including absorption on the iron and manganese oxides and hydroxides from the sea water, re-mineralization under the highly reducing conditions of the localities, incorporation inside the carbonates frameworks and scavenging during tidal mixing as detrital phase from the downstream floods but with different intensities. This is supported by the uranium tendency to accumulate in the finest fraction sediments much more than the medium and coarse sediments (Noureddine et al., 1998). They found that the sediments of less than 100 μm grain size have the highest level of radioactivity uptake. Sam (1998b) observed non-significant relationship between the activity concentrations of all the radionuclides and the content of organic matter in the sediments.

The average 232Th concentrations as recorded in the studied localities were 10.15±2.29 Bq kg-1, 10.26±6.00 Bq kg-1 and 8.67±4.08 Bq kg-1 at Al-Sharm Al-Bahari, Wadi Al-Gemal and Gola’an, respectively (tables 1, 3, 5). Gola'an locality recorded low 232Th concentration relative to Al-Sharm Al-Bahari and Wadi Al-Gemal, which may indicate that Al-Sharm Al-Bahari and Wadi Al-Gemal receive fresh sediments slightly more than Gola'an locality. The concentrations recorded in all localities were significantly higher than the average contents recorded by Sam et al. (1998a) in the Sudanese Red Sea (6.02 Bq kg-1) but much


lower than that recorded by El-Arabi (21.4-22.4 Bq kg-1) in the beach sands of Safaga in the northern Red Sea, which may indicate that the areas under investigation received fresh sediments much more than the coastal areas of Sudan. This illustration had been supported by Sam et al. (1998a) who documented that 232Th activity ratio has been used as geochronometer in dating coastal marine sediment deposited during the last decade or so, providing that the sedimentation rate is rapid enough to allow the delineation of decreasing excess 232Th with depth.

232Th is essentially tended to accumulate in the coarsest and medium fraction sediments at Al-Sharm Al-Bahari as demonstrated from the correlation coefficients which are 0.22 and 0.56, respectively (fig. 3). 232Th was positively correlated with 238U at Wadi Al-Gemal and Gola'an localities (tables 4, 6) but it shows inverse relationship with 238U at Al-Sharm Al-Bahari (table 2, fig. 4). This may indicate the local variations in the accumulation conditions between the three localities of the oxidation state (variation in oxic and anoxioc conditions), the letter production and decomposition, the tidal range that affects the phase change of metals from sulfides to oxides or the reverse, the aerobic lattice (Pneamatophores) density that help in fine and particulate sediment accumulation and the continuity of sediment feeding source from terrestrial or from the sea. 232Th also shows positive correlation with carbonates (fig. 5) which may indicate that 232Th tends to accumulate with carbonates and fine fraction sediments. These relations may infer that 232Th radionuclides in the different locations accumulated from more than one source. At Al-Sharm Al-Bahari, the main source of 232Th is the incorporation with the carbonate frameworks (fig. 5B) throughout the biogenic processes and the second source is the absorption over the sediment surfaces in the presence of high organic matter content. At Wadi Al-Gemal, non-significant source can be identified, however, the absorption accumulation over the coarse particles may be the main source. At the third locality, the incorporation with the carbonate frameworks of the coral reefs was the dominant 232Th source followed by the detrital origin.

40K is dominantly having terrestrial origin and it can be considered as the essential constituent of the lightest minerals in the earth’s crust and resulted from weathering and recycling of terrestrial minerals and rocks (Noureddine et al., 1998). Al-Sharm Al-Bahari locality recorded the highest 40K concentration followed by Gola’an locality then Wadi Al-Gemal; 593.01±339.67 Bq kg-1, 373.62±205.90 Bq kg-1 and 350.54±334.15 Bq kg-1, respectively (tables 1, 3, 5). The values recorded at Al-Sharm Al-Bahari locality were in the range of the values recorded at Hurghada and Safaga in the northern Red Sea (618-548 Bq kg-1) by El-Arabi (2005). 40K concentrations in three localities were significantly higher than the average concentration recorded by Sam et al. (1998a) in the Sudanese Red Sea coast (158.4 Bq kg-1) and with the average range recorded in the sands and fine sediments by Noreddine et al. (1998) in the Mediterranean coast of Algeria (205-475 Bq kg-1). These high 40K concentrations indicating that the Egyptian Red Sea coastal areas may receive very high amounts of light minerals (e.g. potash-feldspars, micas, chlorites and plagioclases).


Table (1): The concentration levels of the natural and artificial radionuclides, carbonate %, TOM% and sediment fractions at Al-Sharm Al-Bahari.

Sample no.

238U 232Th 40K 137Cs CO3% TOM% Coarse Medium Fine

Sh 1 16.40 10.20 210.00 0.00 17.10 1.95 10.02 38.80 51.18

Sh 2 10.90 9.80 911.00 2.60 20.10 4.05 0.42 35.63 63.95

Sh 3 17.30 11.30 570.30 0.00 22.05 2.80 1.55 65.94 32.53

Sh 4 12.80 12.40 600.00 0.00 12.40 2.00 2.87 72.67 24.46

Sh 5 8.90 12.30 990.00 0.00 72.90 5.80 35.21 41.89 22.92

Sh 6 15.20 11.60 583.00 0.00 72.71 4.20 14.93 25.81 59.25

Sh 7 17.80 6.10 18.80 0.00 34.85 2.80 9.20 28.06 62.74

Sh 8 34.80 7.50 861.00 0.00 35.95 3.53 11.32 33.33 55.35

Maximum 34.80 12.40 990.00 2.60 72.90 5.80 35.21 72.67 63.95

Minimum 8.90 6.10 18.80 0.00 12.40 1.95 0.42 25.81 22.92

Average 16.76 10.15 593.01 0.33 36.01 3.39 10.69 42.77 46.55

SD 7.94 2.29 339.67 0.92 24.12 1.29 11.16 17.29 17.19

Table (2): Correlation coefficients illustrate the relation between the radioactive

metal isotopes with the carbonate %, TOM % and the sediment fractions at Al-Sharm Al-Bahari:

238U 232Th 40K 137Cs CO3% TOM% Coarse Medium Fine238U 1.00

232Th -0.61 1.00 40K -0.03 0.43 1.00

137Cs -0.30 -0.06 0.38 1.00

CO3% -0.12 0.19 0.30 -0.27 1.00

TOM% -0.23 0.21 0.68 0.21 0.81 1.00

Coarse -0.17 0.22 0.30 -0.37 0.82 0.73 1.00

Medium -0.22 0.56 0.11 -0.17 -0.51 -0.40 -0.33 1.00

Fine 0.33 -0.70 -0.31 0.41 -0.02 -0.07 -0.32 -0.79 1.00Significant correlation coefficient (r) values are more than ± 0.25.


Table (3): The concentration levels of the natural and artificial radionuclides,

carbonate %, TOM % and sediment fractions at Wadi Al-Gemal: Sample

no. 238U 232Th 40K 137Cs CO3% TOM% Coarse Medium Fine

WG 1 18.60 19.60 303.00 0.00 17.99 3.25 5.47 17.27 45.82

WG 2 17.60 16.90 305.80 0.00 13.07 3.75 0.65 7.50 63.84

WG 3 16.90 5.80 304.50 0.00 68.58 5.15 6.57 44.73 16.28

WG 4 17.90 4.90 306.00 0.00 8.19 2.50 0.28 4.04 92.26

WG 5 15.80 12.10 1070.00 0.00 70.00 8.30 12.59 37.21 19.49

WG 7 14.80 5.90 83.00 2.00 22.83 4.50 5.54 8.48 69.81

WG 8 16.20 6.60 81.50 2.06 35.78 2.65 3.16 23.13 60.48

Maximum 18.60 19.60 1070.00 2.06 70.00 8.30 12.59 44.73 92.26

Minimum 14.80 4.90 81.50 0.00 8.19 2.50 0.28 4.04 16.28

Average 16.83 10.26 350.54 0.58 33.78 4.30 4.89 20.34 52.57

SD 1.32 6.00 334.15 0.99 25.75 2.01 4.19 15.64 27.44

Table (4): Correlation coefficients illustrate the relation between the radioactive

metal isotopes with the carbonate %, TOM % and the sediment fractions at Wadi Al-Gemal:

238U 232Th 40K 137Cs CO3% TOM% Coarse Medium Fine 238U 1.00

232Th 0.52 1.00 40K -0.07 0.26 1.00

137Cs -0.68 -0.46 -0.55 1.00

CO3% -0.42 -0.21 0.57 -0.12 1.00

TOM% -0.48 0.07 0.84 -0.25 0.78 1.00

Coarse -0.46 0.08 0.73 -0.09 0.81 0.90 1.00

Medium -0.21 -0.11 0.47 -0.19 0.96 0.64 0.73 1.00

Fine 0.14 -0.21 -0.56 0.31 -0.89 -0.74 -0.80 -0.93 1.00 Significant correlation coefficient (r) values are more than ± 0.25.


Table (5): The concentration levels of the natural and artificial radionuclides, carbonate %, TOM % and sediment fractions at Gola’an.

Sample no.

238U 232Th 40K 137Cs CO3% TOM% Coarse Medium Fine

G 1 15.80 8.40 593.00 0.00 64.40 3.75 9.75 26.49 63.76

G 2 12.20 9.00 592.00 0.00 49.05 9.50 6.72 35.92 35.28

G 3 9.50 10.70 586.00 0.00 75.75 5.10 2.97 45.46 23.09

G 4 12.80 3.90 440.00 0.00 82.35 12.10 7.18 55.55 18.01

G 5 13.20 3.60 460.00 0.00 8.25 1.75 27.21 64.30 4.90

G 6 17.90 4.30 38.60 0.00 45.12 2.01 17.65 55.28 16.52

G 7 16.60 10.30 230.00 0.00 56.17 2.31 13.65 59.20 17.04

G 8 18.90 12.50 233.00 0.00 71.30 2.14 6.79 28.07 36.22

G 9 25.20 15.30 190.00 3.70 65.41 2.45 18.15 44.37 29.06

Maximum 25.20 15.30 593.00 3.70 82.35 12.10 27.21 64.30 63.76

Minimum 9.50 3.60 38.60 0.00 8.25 1.75 2.97 26.49 4.90

Average 15.79 8.67 373.62 0.41 57.53 4.57 12.23 46.07 27.10

SD 4.63 4.08 205.90 1.23 22.09 3.74 7.65 13.66 16.97

Table (6): Correlation coefficients illustrate the relation between the radioactive metal isotopes with the carbonate %, TOM % and the sediment fractions at Gola’an.

238U 232Th 40K 137Cs CO3% TOM% Coarse Medium Fine238U 1.00

232Th 0.53 1.00 40K -0.73 -0.12 1.00

137Cs 0.76 0.61 -0.33 1.00

CO3% 0.07 0.44 0.05 0.13 1.00

TOM% -0.51 -0.28 0.52 -0.21 0.41 1.00

Coarse 0.37 -0.30 -0.40 0.29 -0.81 -0.55 1.00

Medium -0.15 -0.53 -0.29 -0.05 -0.46 -0.05 0.59 1.00

Fine 0.15 0.39 0.35 0.04 0.42 0.05 -0.48 -0.91 1.00Significant correlation coefficient (r) values are more than ± 0.25.


Fig. (2): The behaviour of 238U against TOM% at:

(B) Wadi Al-Gemal. (C) Gola'an.

y = 1.0533x

y = 4.1604x + 0.56

0

10

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5 6 7 8 9 10 11 12 13232Th

Frac

tion%

Coarse Medium Linear (Coarse) Linear (Medium) Fig. (3): The behaviour of 232Th towards coarse and medium

sediment fractions at Al-Sharm Al-Bahari.


r= 0.52

0.0

5.0

10.0

15.0

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25.0

15.00 16.00 17.00 18.00 19.00238U

232T

h

Fig. (4): The behaviour of 232Th towards 238U at:

(A) Al-Sharm Al-Bahari. (B) Wadi Al-Gemal. (C) Gola'an.

B


A

r = 0.19

0

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0 5 10 15232Th

CO

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0.00 5.00 10.00 15.00 20.00 25.00232Th

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Fig. (5): The relation between 232Th and CO3% at:



Fig. (6): The relation between 40K and TOM% at:



Significant positive relationships were recorded between 40K and TOM% at the different localities which may indicate that this isotope tends to accumulate in the highly reducing conditions (fig. 6).

137Cs is the radionuclide was the most intensely used in studies of marine processes and radiological assessment on both regional and worldwide scales (Livingston and Povinec, 2000). The mobility of 137Cs ions leached from the waste will depend on the interactions with sediment particles. Whether sediments will act as a continuous permanent sink for released 137Cs or contaminated sediments will serve as a diffuse source of 137Cs in the future depends on the interaction kinetics and binding mechanisms involved (Borretzen and Salbu, 2002).

The anthropogenic radionuclide 137Cs content in the studied locations is considered in order to ascertain if there is any fallout in the Red Sea coastal zones as mentioned by Sam et al. (1998a). In the studied localities, 137Cs concentrations were not evident and its average activities at Al-Sharm Al-Bahari, Wadi Al-Gemal and Gola’an were 0.33±0.92 Bq kg-1, 0.58±0.99 Bq kg-1 and 0.41±1.23 Bq kg-1, respectively (tables 1, 3, 5). Standard deviation is indicating that 137Cs recorded high variation in Gola’an locality. The recorded 137Cs values were much lower than those recorded by Sam et al. (1998a) in Sudanese Red Sea (average 4.1 Bq kg-1), Noureddine and Baggoura (1997) in the western coast of Algeria in the Mediterranean Sea (from 6.9 Bq kg-1 to 8.5 Bq kg-1), Sanchez and Molero (2000) close to the coast of Vandellos, Spain (5.46±0.17 Bq kg-1) and Heldal et al. (2002) in Spitsbergen, Bear Island, Norway (from 0.5 Bq kg-1 to 9.3 Bq kg-1).

These results indicating that there are no artificial 137Cs radionuclides threatening in the southern Egyptian Red Sea coasts. Sam et al. (1998a) attributed the small amounts of the anthropogenic radionuclides 137Cs measured in the Sudanese Red Sea coasts to the long lived radionuclides from the previous atmospheric nuclear explosions remain in sediments.

CONCLUSION The natural (238U, 232Th and 40K) and the artificial (137Cs) radionuclides were

studied in the sediments at three valleys downstream along the southern Egyptian Red Sea coast characterized by sediment accumulation from both land and sea. The recorded data demonstrated that uranium is tending to accumulate in the finest fraction sediments much more than the medium and coarse sediments. It is concentrated from complex and multiple processes including absorption on the iron and manganese oxides and hydroxides from the sea water and re-mineralization under the highly reducing conditions of the localities, incorporation inside the carbonates frameworks, scavenging during tidal mixing and as detrital phase from the downstream floods.

232Th was essentially tended to accumulate with the coarsest and medium fraction sediments more than the fine sediments. It has more than one effective source of accumulation; incorporation in the carbonate frameworks throughout the


biogenic processes of the marine benthos, the absorption over the sediment surfaces in the presence of high organic matter content and from detrital origin. The relatively high 232Th in the localities indicated that they still receiving fresh sediments from land and sea.

The high 40K concentrations indicating that the Egyptian Red Sea coastal areas may receive very high amounts of light minerals (such as potash-feldspars, micas, chlorites and plagioclases).

137Cs concentrations in the studied locations were non-significant and can't ascertain if there has been any anthropogenic fallout in the Red Sea coastal zones. These results indicating to that there are no artificial radionuclides threatening in the southern Egyptian Red Sea coasts.

Continuous monitoring program for the Egyptian Red Sea coasts as well as Aqaba and Suez gulf is important in order to protect the living and non-living resources. The data recorded in this study seem to be not enough to judge on the coastal safeness against the artificial radionuclides threatening.

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THE CONCENTRATION LEVELS OF SOME ISOTOPIC RADIONUCLIDES IN THE COASTAL SEDIMENTS OF THE RED SEA,...

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