INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 4, No 4, Copyright by the authors - Licensee IPA- Under Creative Commons license 3.

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1 INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 4, No 4, 2013 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN Evaluation of radon gas concentration in the drinking water and dwellings of south-west Libya, using CR-39 Physics Department, Faculty of Science, Beni Suef University, Beni Suef, Egypt. rafatamin@yahoo.com doi: /ijes ABSTRACT In the present study radon ( 222 Rn) concentrations in drinking water and dwellings at south of Libya was performed by using CR-39. The were chemically etched and the alpha track density was measured using an optical microscope. The average indoor radon concentration for the whole survey was 29.7±3.8 Bq/m 3 corresponds to an average effective dose rate of 0.67 msv yr -1. Variation of radon concentrations were found for different types of rooms: 17±1.9, 29±2.7, 35.5±3.1 and 37.3±3.4 Bq/m 3 for living rooms, bedrooms, guest rooms and kitchens, respectively. In addition, the average radon level in drinking water samples from different water wells was 3.46 ±1.76 Bq/L which corresponds to an average effective dose rate of 25.3μSv/y. Results reveal that there is no significant public health risk from radon ingested with drinking water and indoor radon concentration in the study region. Keywords: indoor radon, drinking water, effective dose, Libya 1. Introduction Radiation is a natural part of the environment in which we live. All people receive exposure from naturally occurring radioactivity in soil, water, air and food. Radon-222 is a noble gas with a half-life of 3.82 d. It is formed from radium-226, which is the fifth decay product of uranium-238 and is the heaviest gaseous element in the natural sequential decay series of uranium, thorium and actinium. The largest fraction of the natural radiation exposure we receive comes from a radioactive gas, radon and its daughter. Researches carried out in recent decades show that; under normal conditions, more than 70% of a total annual radioactive dose received by people originates from natural sources of ionizing radiation, whereby 54% is due to the inhalation and the ingestion of natural radioactive gas radon 222 Rn and its decay products. When inhaled into the lung, densely ionizing alpha particles emitted by deposited Po-218 and Po-214, short-lived decay products of radon, can interact with biological tissue leading to DNA damage and houses are an important exposure location due to the large proportion of time spent at home. Also, radon from water contributes to the total inhalation risk associated with radon in indoor air. The International Commission on Radiological Protection (ICRP) suggests that radionuclides in water are absorbed more easily than radio nuclides incorporated in food (ICRP, 1999). In groundwater, 222 Rn occurs in a dissolved form and its activity concentration may vary from a few Bq/L to thousands of Bq/L. The highest activity concentrations are found from bedrock water. In surface water 222 Rn is generally found at very low levels (Aeita et al, 1987; Salonen, 1994). So, drinking water contains dissolved radon and the radiation emitted by radon and its radioactive decay products exposes sensitive cells in the stomach as well as other organs once it is absorbed into the bloodstream. The present study focused on the Sabha and Murzuq regions located in south-west of Libya and preliminary evaluation of radon concentration obtained from long term measurements of radon in water and indoor air by using a passive integrated radon dosimeter. Received on November 2013 Published on January

2 2. Methodology 2.1 General features of the studied area The Libyan climate can be generally classified as a dry desert climate particularly in the central and southern regions. It is characterized by the wide variations in temperature between summer and winter seasons along with scarcity and irregularity of rainfall, with yearly average rainfall ranging from just ten millimeters to 500 mm. So, Groundwater represents the main source of water supply in Libya. It is extracted through wells ranging from few meters to more than 1000 m in depth. The majority of the system s water comes from Libya s two largest groundwater resources-the Murzuq and Kufra groundwater basins located in Libya s southern desert. They hold over two thirds of Libya s groundwater reserves (Alghariani, 2007). Most of the houses (namely HAUSH) in the study region are the same height, and few have more than one storey. The main building materials used in these houses, are steel, cement, aggregate, hollow cement blocks, wood, mosaic and marble. Table 1: The 222 Rn activity concentrations and annual effective doses of the south-west of Libya water samples. No. Location Rn Concentration Effective dose per Annual effective (Bq/L) liter (nsv/l) dose (μsv/y) 1 Alsobitat 6.42± Traghen 5.17± Sabha 2.14± Umm AlAranib 1.02± Zawilah 1.41± Sabha ± Ghoddua 4.46± Umm AlAranib1 2.29± Tasawa 7.26± Sabha ± Average 3.46 ± Experimental technique Indoor radon was measured by using the passive closed-can technique (Amin and Eissa, 2008). About 56 were distributed in the houses of Traghen city in Murzuq District in southwest of Libya. The CR-39 were cut into Square pieces (2 2 cm, 500 μm thick) and placed in diffusion chamber. The were hanged in the various rooms of the houses in Traghen city at a height of 2 m from the ground level from January 2008 to June The sensitive lower surface of the detector was freely exposed to the emergent radon so that it was capable of recording the alpha-particles resulting from the decay of radon in the room. After the 6 months exposure, the were subjected to chemical etching in a 6 M potassium hydroxide solution at (70±1)ºC, for 6 h in a constant temperature water bath to enlarge the latent tracks produced by alpha particles from the decay of radon. After the etching, the were washed with running cold water, then with distilled water. After a 485

3 few minutes of drying in air, the were ready for track counting by an optical microscope at a magnification of 400. Water samples were collected directly from 10 wells in the Sabha and Murzug districts. The wells were pumped for several minutes before collecting samples in clean plastic bottles. Water samples were collected from different sites in the study area, as shown in Figure 1. The sampled sites comprise boreholes of depths ranging from 100 to 400 m, wells. Each sample was placed in plastic bottles chamber with radius 5 cm and height 15 cm (Figure 2). Square pieces of CR-39 plastic foil were mounted on the bottom of the cylindrical cans cup and covered by a fiberglass filter. As the half-life of 222 Rn is 3.82 days, the chosen exposure period was 30 days, during which 99.5% of radon nuclei contained in the water samples decayed. Since then the exposed (CR-39) were collected and chemically etched as explained previously. 3. Results and discussion 3.1 Radon in drinking water The recorded values of radon concentration (Bq/L) in drinking water are given in table (1). The average radon concentration in drinking water in Sabha and Murzuq districts was 3.46 ±1.76 Bq/L. Therefore, the radon levels in Libyan wells are comparatively low since the recommended maximum level (MCL) of U.S. Environmental Protection Agency is 300pCi/L, which is equivalent to 11.1 Bq/L. On the other hand, radon concentration was varying from region to another due to many reasons, including the nature of the rocks of the study area, population of the study area, depth of wells and time of storage water in wells and it has a maximum of 7.26 Bq/L in Tasawa village in West zone and minimum of 1.02 Bq/L in Umm Al Aranib village in East zone. Studies conducted all over the world to measure the level of radon in the water and the values of 222 Rn activity in drinking waters were compared with the results obtained by other workers elsewhere (Table 2). Figure 1: Map of Libya showing the investigated area. 486

4 3.2 Annual effective doses from 222 Rn ingested with water The annual effective dose (msv/y) was calculated by taking in account the activity concentration of radon (Bq/L), the dose coefficient (Sv/Bq) and the annual water consumption (L/y) according to equation Ding = CR.IF.ED (1) Where Ding is the committed effective dose from ingestion (Sv), CR is the concentration of 222 Rn (Bq/L), IF is the ingesting dose conversion factor of 222 Rn (10-8 Sv/Bq for adults, and Sv/Bq for children (UNSCEAR, 1993), ED is the water consumption (2 L/day) (WHO, 2004). For the dose calculations, a conservative consumption of 2 L/day per year for standard adult drinking the same water and directly from the source point was assumed (UNSCEAR, 1993; Galan Lopez et al, 2004). The effective dose due to intake of 222 Rn from drinking water varied from 7.5 to 53.0 μsv/y with an average value of 25.3 μsv/y. In the present study, the effective dose from 222 Rn due to intake of drinking water is less than the recommended value of 0.1 msv/y (Somlai et al, 2007), therefore, the contribution to the dose can be neglected. 3.3 Radon in dwellings The results of the Rn concentrations in the dwellings are summarized in Table 3. We found that radon concentrations in Traghen city ranged from 17.1 to 37.3 Bq/m 3 with an average of 29.7±3.8 Bq/m 3. This value is lower than the world-wide average of 46 Bq/m 3 with GSD 2.2 (UNSCEAR, 2000). Equilibrium Factors (EF, defined as the ratio of the radon progeny equilibrium equivalent concentration (EEC) to the radon gas concentration) were estimated using the bare detector exposure mode along with the cup with membrane mode in these locations for 222 Rn progeny. For the measurement of the equilibrium factor in a dwelling, measurements for both Rn concentration (Bq/m 3 ) and the Rn daughter concentration were carried out in 20 dwellings. For this purpose, CR-39 film was used in `cup with membrane' mode to get the Rn gas concentration while films in bare mode for EEC Rn measurements. Measured mean EFs range between 0.14 and 0.85 with a median of 0.36 ± 0.20 and most of the values are found to be within 30% of the typical value of 0.4 used by the UNSCEAR (1993) for inhalation dose calculations. Figure 2: Schematic diagram for measuring radon concentration in the water samples 487

5 Living rooms, bedrooms, guest rooms and kitchens in Traghen city give an average radon concentration of 17.1±1.9, 29.0±2.7, 35.5±3.1 and 37.3±3.4 Bq/m 3, respectively. It seems that the living rooms are characterized by the lowest concentration because the living rooms are open most of the time and ventilation is much better than bedrooms while guest rooms are ventilated occasionally because they are closed most of the time to keep its expensive furniture away from dust. However, bedrooms are less used than living rooms but more used than guest rooms. The higher kitchen levels in all dwellings may be due to the use of either cooking gas, i.e. liquid petroleum gas (Wojcik, 1989) or other fuel and use of water (Nazaroff et al., 1988) which enhances the Rn concentration. Table 2: Comparison of mean concentrations of radon concentration in drinking water with previous measurements from different countries Country Radon activity (Bq/L) Water type Reference Saudi Arabia Groundwater Alabdula aly, (1999) USA Groundwater Hopke et al, (2000) Jordan Spring water Al-Bataina et al, (1997) Venezuela Spring water Horvath et al, (2000) Brazil Groundwater Lima and Bonotto, (1996) Brazil Groundwater Marques et al, 2004 Libya Groundwater Present work 4. Dose due to 222 Rn in dwellings According to the UNSCEAR (2000) report, annual mean effective dose H (msv/y) to the public from 222 Rn and its progeny is estimated using the following equation: H = C E F T D (2) where C is the 222 Rn concentration (Bq/m 3 ), E is the measured equilibrium factor (0.36), F is the occupancy factor (0.8), T is hours in a year (8760 h/y) and D is the dose conversion factor (9 nsv/bq/m 3 /h). Table 3: Minimum, Maximum and average radon concentration in various types of rooms of Traghen houses. Type of rooms 222 Rn concentration No. of (Bq/m 3 Arithmetic ) Mean (Bq/m samples Effective ) Minimu dose (msv/y) Maximum m Bed rooms ± ±7 35.5± Living rooms ± ±5 17± Kitchens ± ±8 37.3± Guest rooms (marboa) ± ±4.5 29± Average 29.7± The effective dose varied from 0.39 to 0.85 msv/y with a mean value of 0.67 msv/y, based on the estimated annual radon activity concentration level (29.7 Bq/m 3 ) for the dwellings. This value is lower than the world average annual effective dose of 1.15 msv, presented in 488

6 the UNSCEAR 2000 report and is lower than the upper value (300Bq/m 3 ) of radon in dwellings (ICRP, 2009). 5. Conclusions Radon concentration in drinking water and dwellings of Murzuq and Sabha districts of Libya has been measured. From the measured radon concentration annual effective doses received by the inhabitants of the surveyed area have been estimated. Concentration of 222 Rn in drinking water varies from 1.02 Bq/L to 7.26 Bq/L with a mean value of 3.46 ± 1.76 Bq/L. From these results it can be concluded that the majority of drinking water is safe to use from the stand point of concentration of radon in them. Mean values of effective dose per liter and annual effective dose from radon ingested with drinking water for an individual consumer are 34.6 nsv/l and 25.3μSv/y, respectively. The highest average radon concentration in dwellings has been observed in kitchens followed by guest rooms while minimum average concentration was noticed in bed rooms followed by living rooms. The obtained results are in the range from 17.1 Bq/m 3 to 37.3 Bq/m 3 with an average of 29.7±3.8 Bq/m 3 which is less than the less than UNSCEAR limits. The experimental equilibrium factor ranged from 0.14 and 0.85 with a median of 0.36 ± 0.2. The average annual effective dose from indoor air is 0.67 msv/y. So it is concluded that radon level in the dwellings as well as in water wells of the Murzuq and Sabha districts in Libya are within the safe limits as proposed by ICRP, UNSCEAR and WHO etc. 6. References 1. Aieta M., Singley, J. E., Trussell, A. R., Thorbjarnarson, K. W. and McGuire, M. J., 1987, Radionuclides in Drinking Water: An Overview, Journal American Water Works Association, 79 (4), pp Alabdula aly A. I., (1999), Occurrence of radon in the central region groundwater of Saudi Arabia, Journal of Environmental Radioactivity, 44, pp Al-Bataina B. A., Ismail A. M., Kullab M. K., Abmurad K. M. and Mustafa H., (1997), Radon measurements in different types of natural waters in Jordan, Radiation Measurements, 28(1-6), pp Alghariani S., (2007), Reducing Agricultural Water Demand in Libya through Improving Water Use Efficiency and Crop Water Productivity, Proceedings of water resources management, Honolulu Hawaii. 5. Amin Rafat M., and Eissa M. F., (2008), Radon level and radon effective dose rate determination using SSNTDs In Sannur cave, Eastern desert of Egypt, Environmental Monitoring Assessment, 143, pp Galán López M., Martín Sánchez, A. and Gómez Escobar V., (2004), Estimates of the dose due to 222 Rn concentrations in water, Radiation Protection Dosimetry, 111(1), pp Hopke P. K., Borak T. B., Doull J., Cleaver J. E., Eckerman K. F., Gundersen L. C. S., Harley N. H., Hess C. T., Kinner N. E., Kopecky K. J., Mckone T. E., Sextro R. G. 489

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