third international conference on radiation sciences and

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RRaaddiiaattiioonn SScciieenncceess aanndd AApppplliiccaattiioonnss 12 – 16 November 2012/ Hurghada, Egypt

The radiological hazards of some radionuclides in Mariout and Brullus Lakes, Egypt Mahmoud A. Dar* and Abeer A. El Saharty** * National Institute of Oceanography and Fisheries, Red Sea Branch, Hurghada, Egypt ** National Institute of Oceanography and Fisheries, Alexandria Branch, Alexandria, Egypt. E-mail: [email protected]

ABSTRACT

Mariout and Brullus were considered two of the highly fish productive lakes in Egypt as well as they widely used to drain huge quantities of industrial wastewater, sewage and agriculture drainage. Thousands of peoples inhabited the areas around the lakes and depend on them completely in their lives. The activities of 238U, 232Th and 40K were measured in the upper most part of the surface sediments of the two lakes using gamma ray spectrophotometery. Brullus Lake recorded significantly higher 238U and 232Th and lower 40K (17.22±2.49 Bq/kg, 10.03±0.56 Bq/kg and 299.70±17.78 Bq/kg) than Mariout Lake (12.65±1.53 Bq/kg, 7.24±0.76 Bq/kg and 518.75±46.24 Bq/kg respectively). Inversely, the mean average of absorbed dose rate (D), annual effective dose rate (mSvy-1), radium equivalent (Raeq), external hazard index (Hex) and the representative level index (Ir) were; 32.01nGy/h, 0.04mSv/y, 62.95Bq/kg, 0.17 and 0.50 at Mariout Lake higher than those in Brullus lake (26.42 nGy/h, 0.03 mSv/y, 54.25 Bq/kg, 0.15 and 0.41) respectively. The recorded and calculated values were lower than the acceptable limits published in the different localities around the world. The activity distributions of the radiological hazards show the highest intensities in the western part of Mariout Lake and decreasing gradually eastward and northeastward affecting by the drainage agriculture water from Kabary Drain, Umum Drain, S.W. Basin and Nubaria Canal. At Brullus Lake, the radiological hazard intensities were concentrated in the west and southwest influenced by Zaglul Drain, Rosetta Drain, Brembal canal, Drain 11, Drain 9, Drain 8 and partially by Drain 1 while the lowest intensities were in the north and northeast affecting by the interaction with the Mediterranean Sea. K-40 recorded positive correlations and significant linear regression relationships with radiological hazard parameters at Mariout Like meaning that 40K is the main gamma emitter in the lake, while the different radioelements are participating gamma emitters at Brullus Lake.

Abeer A. El Saharty. et al., J. Rad. Res. Appl. Sci., Vol. 5, No. 2(2012) 561

Keywords: Mariout and Brullus lakes, radionuclides, radiological hazards, activity distributions, linear regressions, anthropogenic sources.

INTRODUCTION

Mariout and Brullus lakes are of the most important shallow coastal lakes northern of the Nile Delta of Egypt. They provide a multitude of uses and are prime regions for human settlement and habitation. Economically, Mariout Lake fisheries were representing the most important source of fish production in Egypt. The lake production represents between 50% and 70% of the total fish production of the coastal lakes [1-2]. Brullus Lake produced only about 21% of the landed fish tonnage in all the delta lakes. The lake production accounted for 40.6%, 13.5% of the northern Lakes and national fish production respectively [3, 1]. The uses of lakes include municipal water supply; industrial; commercial and recreational fisheries; fishing, agricultural irrigation and drainage, canalisation and for waste disposal and other aesthetic recreational uses. The lakes are subjected to active process of contamination with different kinds of pollutants. Consequently, they act as recipients of domestic sewage, industrial wastes, and agricultural wastewater [4].

The sources of the anthropogenic radionuclides in the marine environment are divided into nuclear and non- nuclear activities. Phosphate fertilizers 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 matter leading to a considerable contribution to the radio-ecological pollution [5-6]. Most radionuclides are absorbed directly to sediments or to sinking particles within 1-2 years [7], however, some of these radionuclides may later be remobilized from the sediments to the water column and subsequently be taken up by biota or exported hydrologically from the system [8-9]. In the natural environments, living organisms are chronically exposed to low doses and dose rates of ionizing radiation [10]. Human beings are exposed to background radiation that stems both from natural and man-made sources. Natural background radiation, which is equivalent to 2.4 mSv per person, makes up approximately 80% of the total radiation dose a person is exposed in a year [11]. In order to evaluate risks to human and environmental health, it is important to monitor the export of radionuclides from the contaminated lakes.

The objective of this study is to determine the radiological hazards due


to the different anthropogenic stress by calculating the absorbed dose rate, annual effective dose rate and the external hazard index.

MATERIALS AND METHODS

I- Geomorphic and environmental settings

A- Mariout Lake

Lake Mariout is a small shallow basin which lies at the southwestern part of Alexandria, it has 25km long and about 10km width. It is the smallest and the most polluted among then northern lakes of Egypt and it is the only one that doesn’t have a natural connection to the Mediterranean Sea. The maximum water depth is about 120cm and the excess water is constantly discharged into the sea through El-Max Pumping Station [12]. The lake serves as a drainage basin for adjacent cultivated lands [13]. Subsequently, the main basin of the lake has been suffering from high levels of pollution. Water quality was not suitable for aquaculture activities because of the basin receives daily about 200,000–300,000 m3 of sewage and 400,000 m3 of agricultural waste water mixed with sewage in addition discharging about 25,000 – 35,000 m3/day of raw sewage and some industrial wastewater into the lake [14- 15]. Throughout the last forty years, the lake has been subjected to man made changes in its morphometrical features as its area has been reduced from 66,000 acres to 17,000 acres due to reclamation projects to agriculture lands.

B- Brullus Lake

Brullus Lake is considered the second largest lake of the Nile Delta with a surface area of about 500 km2. It is about 65km long, 6km to 16km width and from 0.5 to 2.5m water depth [16] that increases from the east to the west and from the south to the north. Subsequently it was considered one of the important fishery lagoons. It is connected to the sea at its north-eastern edge through the Brullus inlet, which is about 250m wide and 5m deep [17]. Therefore the level of the lake is affected by both the amount of drainage water and the water exchange with the Mediterranean Sea which depends of the wind direction [18]. The environment of Brullus Lagoon has witnessed the significant change during the last three decades as many drains were constructed to convey agricultural wastes into the lagoon. The lake receives drainage water which fluctuated between 78×106 and 272×106 m3/month during January and July 2002, respectively [19]. The amount of the drainage water discharged annually into the lake fluctuates from one year to the other, with the average of about 2.5 billion m3/year [20].


II- Experimental Techniques:

Fifteen surface samples were collected from the upper most part of the seabed sediments (0-20cm) at each of Mariout and Brullus lakes using small fishing boat and grab sampler (Fig. 1). The samples selected to cover the different geomorphic and other observed features in the lakes.

Fig. (1) Mariout and Brullus lakes location maps.

The collected samples were prepared and sealed in polyethelene containers to reach secular equilibrium between radium and thorium and their progenies [21]. Measurements of the activity concentrations of 238U, 232Th and 40K in Bq/kg dry wt. of the collected samples were carried out using gamma-ray spectrometry based on a highly pure germanium coaxial detector (HPGe) of 40% relative efficiency [22-23]. The resolving power of the spectrometer was found to be 1.92keV for 1332keV gamma-ray line of 60Co. Cesium-137 content


in sediment samples was measured by gamma spectrometry method using an HPGe detector with a relative efficiency of 18% and a resolution of 1.8 keV for peak of 1332 keV of 60Co. The gamma-ray spectrometer was calibrated for energy using point source of 60Co (1172and1332.3keV). The detector was coupled with an 8192-channel computer analyser and GENIE 2000 software. The measurement time for gamma spectrometry was 80,000s [24]. The IAEA standard gamma-ray spectrometry reference materials RGU-1, IAEA-375, IAEA-312 and IAEA-314 were used for the spectrometer efficiency calibration in the geometry of the sample measurements. The gamma transitions used for activity calculations of 40K were 1460.7 [6].

III- Calculation of radiological effects:

1- Dose rate calculation:

The absorbed dose rate was calculated from the measured activities of 238U, 232Th and 40K in the surface sediment samples using the formula of [25]:

D (nGy h-1) = 0.462 CU +0.604CTh +0.042CK (1)

Where D is the absorbed dose rate (nGy h-1). CU, CTh and CK are the activity concentrations (Bqkg-1) of 238U, 232Th and 40K respectively.

To estimate the annual effective dose rates, the conversion coefficient from absorbed dose to effective dose, 0.7 SvGy-1 and outdoor occupancy factor of 0.2 proposed by UNSCEAR, (2000) were used. The effective dose rate (m Sv y-1) was calculated by the formula of Ramasamy et al. [26]:

(m Sv y-1) = D (nGy h-1) × 8760 h × 0.2 × 0.7 SvGy-1 × 10-6 (2)

Where, 0.2 is the occupancy factor for outdoor, 8760 is the total time of the year in hours and 0.7 SvGy-1 is the conversion factor for external gamma irradiation.

2. Calculation of hazard indexes: 1-External hazard index (Hex)

The external hazard index (Hex) represents the external radiation exposure associated with gamma irradiation from radionuclides of concern. The value of Hex should not exceed the maximum acceptable value of one in order to keep the hazard insignificant.

The external hazard index (Hex) is defined by Jankovic et al., [27]:

Hex = (CU/370 + CTh/259 + CK/4810) ≤ 1 (3)


II. Representative level index (Ir):

An additional hazard index so called representative level index is calculated by using the formula of Harb, [28]:

Ir = (CU/150 + CTh/100 + CK/1500) (4)

Where CU, CTh and CK are the specific activities (Bqkg-1) of 238U, 232Th and 40K, respectively. The value of these indexes must be less than unity in order to keep the radiation hazard insignificant.

II. Radium equivalent activity (Raeq):

The distribution of 238U, 232Th and 40K in sediments is not uniform. Uniformity with respect to exposure to radiation has been defined in terms of radium equivalent activity (Raeq) in Bq/Kg to compare the specific activity of material containing different amounts of 238U, 232Th and 40K. It is calculated from the following relation [29]:

Raeq =CU + 1.43CTh + 0.077CK (5)

RESULTS AND DISCUSSION The activity concentrations of 238U, 232Th and 40K as well as the

calculated radiological hazard parameters the mean average of absorbed dose rate (D), annual effective dose rate (mSvy-1), radium equivalent (Raeq), external hazard index (Hex) and the representative level index (Ir) the in the sediments of Mariout and Brullus lakes were presented in tables (1 and 2). At Mariout Lake, the activity levels of 238U were varied between 10.52 and 15.91 Bq/Kg with average of 12.65±1.53 Bq/Kg, 238Th changed from 5.44 to 8.33 Bq/Kg averaging of 7.24±0.76 Bq/Kg, 40K from 441.64 to 582.31 Bq/Kg and the average was 518.75±46.24 Bq/Kg. Uranium-238 at Brullus Lake was varied between 12.60 and 19.90 Bq/Kg with average of 17.09±2.49 Bq/Kg, 232Th between 8.5 and 10.52 Bq/Kg averaging of 9.93±0.56 Bq/Kg, 40K from 258.87 Bq/Kg to 316.8 Bq/Kg with average of 296.95±17.87 Bq/Kg. Uranium-238 and 232Th activities at Brullus Lake were significantly higher than those at Mariout Lake while 40K at Mariout Lake reaching about two folds its average activity at Brullus Lake.


Table (1): Concentration activities of 238U, 232Th, 40k, D (nGy/h), (m Sv/y), Raeq, Hex and Ir at Mariout Lake:

Table (2): Concentration activities of 238U, 232Th, 40k, D (nGy/h), (m Sv/y), Raeq, Hex

and Ir at Brullus Lake:

The majority of radionuclides in soil are attached or captured by fractions of soil with diameters less than 0.02mm, larger fractions contain only traces of these radionuclides [30]. Noureddine et al. [31] reported that uranium have the tendency to accumulate in the finest fraction sediments much more than the medium and coarse sediments. Bell et al., [32] documented that the radionuclides are absorbed onto Suspended Particulate Matter (SPM) in the water column and then settling out in the seabed sediment. Therefore, Mariout and Brullus lake sediments provide the suitable conditions for the radionuclide accumulations. The bottom sediments of Mariout Lake were soft and rich in


water content due to the continuous supply of sewage and industrial wastes into the lake [33]. These sediments consist of sandy nature near the periphery changed to clay and silty clay mixed with shell fragments and organic remains inside the lake basin. The nature of bottom sediments of Brullus Lake differs within the different zone, thus, the sediments at the eastern and western sectors of the lake as well as the southern margins are usually of silty clay mixed with shell fragments while in the middle lake, it is either clayey sand or sandy silty clay [20]. These sediments were characterized by high organic matter contents mainly due to the increase in the amount of allochthonous and autochthonous organic matter with slow rates of decomposition [33]. Soil radionuclide activity concentration is one of the main determinants of the natural background radiation [34]. Radioisotopes that are present in soil significantly affect terrestrial gamma radiation levels. It is critical to evaluate soil radioactivity in order to understand background radiation concentrations.

Dar and El Saharty [35] indicated that the natural radionuclides at the coastal stations near the industrial zones of Alexandria may accumulate mostly in the ionic and particulate forms from many natural and anthropogenic sources as; accretion processes, the drainage systems of the fertilizer factories, petrochemical and paper industries, agriculture drainages in addition to the particulate radionuclides that come from the neighbor localities with the marine currents and through the subsurface drainage waters. Fahmi et al., [29] attributed the maximum levels of radionuclides 238U, 232Th and 40K in the east of Idku Lake to the high density of human activities. Jacobi [36] and Al-Trabulsy et al., [6] concluded that phosphate industry has been considered a major source polluting the marine environment and the high levels of natural radionuclides attributed to the industrial operations involve phosphate ores, whereas phosphate fertilizers are speed over agricultural areas with radioactive contaminations. Most of these industrial pollutants and the untreated sewage were drainage directly into the studied lakes. Mariout Lake was heavily contaminated with pollutants such as anthropogenic organic matter and nutrients received from the domestic sewage and industrial effluents [37]. Saad, [33] recorded that Maruoit Lake receives large amounts of allochthonous organic matter in sewage and industrial wastes, which continuously enter into the lake as a result of severe pollution. The lake receives agriculture drainage water mixed with industrial and municipal wastes in particular forms [13]. Fathi and Abdel Zaher [38] subjected Brullus Lake to huge inputs of terrigenous materials and anthropogenic nutrient from drains discharge sewage and


agriculture runoff as well as reclamation programs. The continuous release of wastewater from the southern drains is much greater than seawater discharge into the lake [39].

Because of Mariout and Brullus lakes are highly exploited by fishermen and other workers in fish farms. Those peoples were exposed to additional radiations from the anthropogenic accumulated radionuclides in the underlying sediments. Therefore, the radiation hazards to these people are of interests in order to ensure that no additional doses are imposed on to them. As shown in table (3), the calculated means of absorbed dose rate (D), annual effective dose rate (mSvy-1), external hazard index (Hx), radium equivalent (Raeq) and the representative level index (Ir) at Mariout Lake (32.01 nGy/h, 0.04 mSvy-1, 0.17 and 62.95 Bq/Kg, 0.50) were higher than those in Brullus Lake (26.62 nGy/h, 0.03 mSvy-1, 0.157 and 54.67 Bq/Kg, 0.42) respectively. These values were lower than Idku Lake. Fahmi et al., [29] concluded that, the values of absorbed dose rates at Idku Lake fluctuate from 16.97 to 66.35 nGy/h, with a mean value of 36.06 nGy/h, and the average of the annual effective dose rate was 0.05mSvy-1 and the average radiation hazard parameters were lower than the recommended limit value of 370 Bq/kg (for Raeq) and unity (for Hex). It the calculated values of Raeq, Ir and Hex from the lake sediments were lower than the than the comparable values reported elsewhere (Table 4).

Table (3): The radiological hazard parameters calculated in the sediment samples of Mariout and Brullus lakes compared with some other localities around the world:


Table (4): The results of correlation coefficients and the linear regression significance (*) at 95% confidence between calculated radiological hazard parameters:

Mariout Lake Brullus lake

238U 232Th 40K

238U 232Th 40K D (nGy/h) 0.20 0.17 (0.83)* D (nGy/h) (0.91)* (0.80)* (0.78)*

(m Sv/y) 0.20 0.17 (0.83)* (m Sv/y) (0.91)* (0.80)* (0.78)*

Raeq 0.32 0.29 (0.74)* Raeq (0.92)* (0.81)* (0.76)*

Hex 0.32 0.29 (0.74)* Hex (0.92)* (0.81)* (0.76)*

Ir 0.17 0.15 (0.84)* Ir (0.90)* (0.80)* (0.78)*

As shown in fig., (2) The activity distributions of the different radiological hazard parameters at Mariout Lake where decreased in their intensities from west and southwest gradually to the eastward and northeastward affecting intensively by the drainage agriculture waters from Kabary Drain, Umum Drain, S.W. Basin and Nubaria Canal much more than the industrial zone and Gaisa Drain to the east. At Brullus Lake, the radiological hazard intensities were concentrated in the west and southwest influenced by Zaglul Drain, Rosetta Drain, Brembal canal, Drain 11, Drain 9, Drain 8 and partially by Drain 1 (Fig., 3) then decreased to the north and northeastwards near Brullus opening with the Mediterranean Sea, Brullus Drain and Gharabia Drain may be due to the interaction with the Mediterranean Sea that may dilute the radiological effects.


Fig., (2): Activity distribution trends of the different radiological parameters at

Mariout Lake.

Correlation analyses

The results of correlation coefficients and the linear regression relationships between the natural radionuclides and the calculated radiological


hazard parameters; absorbed dose rate (D), annual effective dose rate (mSvy-1), external hazard index (Hx), radium equivalent (Raeq) and the representative level index (Ir) at Mariout and Brullus lakes were in table (4). At Mariout Lake, 238U and 232Th recorded weak and insignificant correlations with the different radiological parameters. Only 40K recorded positive correlation and significant linear regression at 95% confidence with the different of radiological hazard parameters (Fig., 3. These correlations indicate that 40K is the main gamma emitter radioelement in Mariout Lake. At Brullus Lake, the different radionuclides recorded positive correlations and positive linear regression but with different degrees significances with the radiological hazard parameters (Figs., 5-7) indicating to all the radioelements are the gamma emitters participating at Brullus Lake.

Fig., (3): Activity distribution trends of the different radiological parameters at

Brullus Lake.


Fig. (4): The linear regression relations of 40K with the different radiological

hazard parameters at 95% confidence at Mariout Lake.


Fig. (5): The linear regression relations of 238U with the different radiological

hazard parameters at 95% confidence at Brullus Lake.


Fig. (6): The linear regression relations of 232Th with the different radiological



Fig. (7): The linear regression relations of 40K with the different radiological



CONCLUSIONS

Mariout and Brullus lakes are of the most important lakes in the Nile Delta. They were exploited for fishing and fish farms as well as most of their lands were reclaimed for tourist and agriculture purposes. Thousands of peoples inhabited around the lakes and work as fishermen and in fish farms, farmers and many others.

The lakes receive huge amounts of water mixed with industrial wastes, untreated sewage and the agriculture drainages. The bottom sediments of these lakes were mainly silty sand to silt and mud mixed high percentages of organic matter.

Brullus Lake recorded 238U and 232Th activities significantly higher than those in Mariout Lake while 40K at Mariout Lake reaches about two folds its average activity at Brullus Lake.

The calculated absorbed dose rate (D), annual effective dose rate (mSvy-1), external hazard index (Hx), radium equivalent (Raeq) and the representative level index (Ir) at Mariout Lake were higher than those in Brullus lake.

In general, the value of Raeq, Ir and Hex calculated at the lake sediments are less than the comparable values reported elsewhere.

K-40 is the main gamma emitter at Mariout Lake, while the different natural radioactive elements are participating gamma emitters at Brullus Lake.

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المؤتمر الدولي الثالثالمؤتمر الدولي الثالث

للعلوم الإشعاعیة وتطبیقاتھاللعلوم الإشعاعیة وتطبیقاتھا مصر- الغردقة – ٢٠١٢ نوفمبر ١٦ – ١٢

التأثیرات الاشعاعیة الضارة لبعض النویات المشعة فى بحیرتى ماریوت والبرلس

مصر– تعتبر بحیرتى ماریوت والبرلس من اكبر البحیرات المنتجة للاسماك فى مصر بالاضافة الى

الاف البشر یقیمون حول . انھما تستقبلان كمیات مھولة من میاه الصرف الصناعى والصحى والزراعىتم قیاس الانشطة الاشعاعیة . لبحیرتین ویعتمدون علیھما بصفة كلیة كمصدر للمعیشة والرزقھاتین ا

فى طبقة الرواسب السطحیة ) ٤٠(والبوتاسیوم ) ٢٣٢(والثوریوم ) ٢٣٨(لنویات عناصر الیورانیوم زات الاعلى سجلت بحیرة البرلس التركی. العلیا فى ھاتین البحیرتین باستخدام التحلیل الطیفى باشعة جاما

١٧٫٧٨±٢٩٩٫٧٠ ، ٠٫٥٦±١٠٫٠٣ ، ٢٫٤٩±١٧٫٢٢(یوم للیورانیوم والثوریوم والاقل للبوتاس ٤٦٫٢٤±٥١٨٫٧٥ ، ٠٫٧٦±٧٫٢٤ ، ٠٫٦٥±١٢٫٥٦(عنھا فى بحیرة ماریوت ) كیلوجرام/بكریكعلى العكس من ذلك فقد كان المعدل المتوسط لجرعة الاشعاع ). كیلوجرام وزن جاف على التوالى/بكریك

ومعامل الضرر الخارجى ) Raeq(كافئ الرادیوم وم) mSvy-1(والمعدل السنوى المؤثر ) D(الممتصھ )Hex ( ومعامل المستوى النموذجى للاشعاع)Ir (٦٢٫٩٥ ، ٠٫٠٤ ، ٣٢٫٠١: فى بحیرة ماریوت ھو ،

. على التوالى٠٫٤١ ، ٠٫١٥ ، ٥٤٫٢٥ ، ٠٫٠٣ ، ٢٦٫٤٢: اعلى منھا فى بحیرة البرلس٠٫٥٠ ، ٠٫١٧كما . ن القم المقبولة والمنشورة فى مناطق مختلفة حول العالموھذه القیم المقاسة والمحسوبة تعتبر اقل م

لوحظ ان التأثیرات الضارة لھذه الانشطة الاشعاعیة سجل اعلى نشاط فى الجزء الغربى من بحیرة ماریوت ویقل فى اتجاه الشرق والشمال الشرقى ولك نتجة لوجود مصبات الصرف الزراعى المتمثل فى

فى بحیرة البرلس فقد تركزت مستویات . الجنوبى الغربى وقناة النوباریةالقبارى والعموم والحوض ١١الاشعاعا الاعلى فى الغرب والجنوب الغربى متأثرة بمصارف زغلول ورشید والبربال والمصارف

فى حین ان الانشطة الاقل فقد كانت فى الشمال والشمال الشرقى نتیجة للاتصال بالبحر ١ ،٨ ،٩،ظیر البوتاسیوم المشع علاقات موجبة مع كل معاملات التأثیر الاشعاعى فى بحیرة سجل ن. المتوسط

ماریوت بما یعنى انھ المصدر الاساسى للاشعاع فى البحیرة فى حین ان كل العناصر المشعة سجلت علاقات موجبة مع معاملات التأثیر الاشعاعى ببحیرة البرلس بما یعنى ان كل العناصر المشعة ساھمت

.یم تلك المعاملات بالبحیرةفى ق

third international conference on radiation sciences and

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