Abstract: Radioactive element radium produces radon gas with the alpha decay. Radon is a colorless gas without smell, weak, ineffective and over 50% radiation of the annual dose human body is involved. The two heavy radioactive elements in the natural decay chain from uranium and thorium is produced. Radon through breathing, eating and drinking enters the body. Alpha emission from gas and other radiations emitted from daughter nuclei of its short life makes serious damage to the respiratory system and into the human digestive, therefore after smoking this radiation is the second risk factor of lung cancer. In this study, the concentration of radium and radon in water sources, springs and rivers of Shandiz, Zoshk and Abrdeh regions (Mashhad-Iran) and using light and portable PRASSI system is measured. Total 120 samples including 38 samples of drinking water, 56 river water samples and 26 samples of spring water has been tested. A total of 19 samples had concentrations >11 (Bq L-1), the reference level set by the U.S. Environmental Protection Agency. Radium concentration of all samples was <1, only sample No. 21 related to drinking water of Shandiz city is about 2.2 (Bq L-1).
INTRODUCTION
222Rn radioisotope with half-life 3.8 days from the 238U decay series and 220Rn with half-life 55 sec from 232Th decay series are produced. Radon gas is alpha emitter and enters the body with breathing, eating and drinking. In addition to radon exposure, its daughter nuclei which are very short lived as sediment in the inner membrane respiratory or digestive body remain and increase the body absorption dose (United States Environmental Protection Agency, 1991; UNSCEAR, 1998; ICRP, 1993; IARC, 1988; Mowlavi et al., 2009; Baykara and Dogru, 2006). Natural exposure of people is about 50% of radon gas that many people in the annual risk of cancers of the respiratory and gastrointestinal die. Thus, measurement of radon in water and air is very important and many studies have been done in this area (IARC, 1988; Mowlavi et al., 2009; Baykara and Dogru, 2006; Vogiannis et al., 2004; Field et al., 2001; Tayyeb et al., 1998; Yu et al., 1994; Mancini and Giannelli, 1995; Alabdulaaly, 1999; Schmitz and Nickels, 2001; Mortazavi, 2000). This study is the first report measuring radon and radium in drinking water and springs in the region.
MATERIALS AND METHODS
In this study, to measure radon in water samples PRASSI system has been used. This system is lightweight and portable device that has the ability to measure radon concentration in water, soil and air.
Figure 1 shows the system set up of measurement including bubbler and drier column. PRASSI pumping circuit operates with constant fallow rate at 3 L min-1 in order to degassing the water sample properly.
Its detector is a scintillation cell coated with ZnS (Ag) 1830 cm3 volume. The sensitivity of this system in continuous mode is 4 Bq m-3 during the integration time 1 h.
Numbers shown by the device is based on Bq m-2. Using relationship Eq. 1, radon gas density is calculated based on (Bq L-1).
| (1) |
Where:
| QPRASSI | = | The value recorded by the device |
| Vtot | = | The total volume of air connections |
| V | = | The volume sample and within the brackets is a correction factor in the delay measurement |
| Fig. 1: | View from the device to measure radon in water |
RESULTS AND DISCUSSION
Measuring radon in water samples: In this study, 120 samples of radon concentration of water including drinking water, rivers and springs of Shandiz, Zoshk and Abrdeh regions and adjacent villages (Mashhad-Iran) have been measured. The third column in Table 1, radon concentration samples that have been ordered from low to high. Also, the radon gas density results are shown in histogram of Fig. 2 and 3. Seen that only 83/15% of the samples, the last 19 samples in Table 1 have concentrations >11 (Bq L-1) particularly the sample number 120 that related to the spring in the village of Zoshk has concentration about 32 (Bq L-1).
Measuring radium in water samples: For measuring radium in water samples, the water samples have kept in the bottles for 35 days to let radon reach the equilibrium with radium. So, by measuring, we obtain radium concentration in the samples. Figure 4 shows the histogram of radium concentration in different water samples as well as the data are listed in fourth column of Table 1.
| Table 1: | Radon and radium concentration data of different water samples |
| Fig. 2: | The histogram of radon gas concentration in 120 water samples of Shandiz, Zoshk and Abrdeh regions |
| Fig. 3: | Locations of sampling in Shandiz, Zoshk and Abrdeh regions |
| Fig. 4: | The histogram of radium concentration in different water samples |
It is notice that all the radium concentration of samples was <1 (Bq L-1), except sample number 21, drinking water of Shandiz region is about 2.2 (Bq L-1).
CONCLUSION
Measurement results of radon concentration in the water samples shows that only 15.83% sample concentrations are higher than the normal 11 (Bq L-1). This limit by United States Environmental Protection Agency (EPA) as normal is defined and 148 (Bq L-1) is limit the amount of action or reaction that radon should be reduced (Mowlavi et al., 2009). Any sample has not this amount of concentration but most amount of radon concentration with 32 (Bq L-1) is related to spring in Zoshk that is almost one-fifth of the reaction too. Radium concentration of all samples, except sample number 21, drinking water of Shandiz is small and <1 (Bq L-1). Therefore, radon and radium concentration in the water of the regions is not high and this is appropriate.