Evaluation of Toyserkan City’s Water Contamination, due to the existence of Radon, and Estimation of the annual effective dose

The gas of 222 Rn is one of the natural radioactivesources which is the decay product of 226 Ra from 238 U decay chain. Based on the latest information presented bythe United Nations Scientific committee in the field of the effects of atomic radiations, the respiration of Radon and its daughters (Plutonium, Bismuth and Lead), are one of the most important factors in human radiation inhalation, since Radon and its daughters account for approximately 1.2 msv of the total of 2.4 msv (mili Sievert) annual effective dose of natural radioactive sources produced. The fluctuation in the levels of Radon resolved in water, due to the hazards caused by the emitted radiations, is considerable; because studies show that long-term exposure to Radon increases the chances of lung cancer. The amount of radon in underground waters is more than that of surface waters. If water is exposed to free air, especially when it’s mixed as well, a considerable amount of its radon content is released. In this paper, Radon concentration (Bq/L) in waters of the wells and springs located in Toyserkan, is measured using Lucas chamber technique by means of a light weighted and transportable machine namely PRASSI (SFLENAmod5s). The results showed that the radon density in four measured samples in the waters of this region exceed 10 Bq/L, the allowable amount determined by the US Environmental Protection Agency (USEPA). For the cases where the concentration is high, is it proposed that drinkable water be preserved in open pools or at least waterfalls be used in order to agitate the water to release itsradon content. It is better to install a system for settling and exposing the water to air so that Radon and its decay products are dispersed and the contamination problem is solved.


INTRODUCTION
Radon with the chemical sign of Rn, is a colorless, odorless, neutral and heavy gas; which is hazardous to the human health. 222 Rn is the decay product of 226 Ra from decay chain for 238 U and the natural decay series of 238 Th [16]. According to figure 1, in which the natural isotopes of Radon are introduced, it should be stated that on average, in every 10 21 molecules of air, there is one molecule of Radon; and in each square miles of soil with the depth of 6inches, one gram of Radium exists that is also degraded to Radon (Ferri ,2002). The regions where the Radon comes to the surface by the upstream current, it is expected that the diffusion of Radon from underground waters and soil, represent the soil structure of that region. (Adilson 2007, Vasarheli 1997. Furthermore, the measurement of the concentration of Radon in the air available in soil is of great importance in the construction of new buildings that are resistant against Radon and prevent the increase in the internal Radon level (Jonsson 1995, Theodorsson 1996. This element has 20 isotopes, the most stable of which is 222 Rn with the half-life of 3.8 days and it is used in radiotherapy (Field 2001). When this gas is cooled down below its freezing point, it exhibits a brilliant phosphoric color that is changed to yellow for lower temperatures and has an orange-red color in normal temperatures [7]. This element was discovered by Ernest Radford and Fredrich Eren in 1900. Almost 50 percent of the human radiation inhalation is due to Radon, lots of people suffering from digestive and respiratory diseases lose their lives each year. This number is 21000 people only in the United States.
The main purpose of this research is to evaluate the Radon and Radium concentration in the drinking waters of Toyserkan city and other regional water resources using PRASSI system.

.RADON IN WATER AND ITS HAZARDS
A part from respiration, Radon can enter the human body by digesting, drinking and showering which is illustrated in figure  2. The amount of Radon existing in underground and static waters, especially deep wells, is more. In the United States of America, deaths due to cancers caused by Radon in drinking waters are estimated about 180 persons per year [9].
. It should be noted that if only 40-50 percent of the Radon in water is decreased prior to entering households, the number of people suffering from respiratory and digestive diseases is decreased by 30-35 percent which is very effective in the long-term reduction in the medical costs. Since one of the major water pollutants that plays an important role in the drinking water health is Radon, and according to recent reports regarding the pollution of the waters in the city of Toyserkan leading to the increase in the lung cancer, therefore in this research, the authors have the intention to measure the concentration of Radon gas in water resources by means of the PRASSI device.

.RADON MEASURMENT IN WATER SAMPLES
The amount of Radon in springwaters, deep wells and especially in underground waters is more. Also, the more the water is agitated, the more the amount of Radon is decreased. Therefore, the water samples were collected from the entrance of the springs, in the lowest depth in a 25cm distance from the free water surface and reverse pressure conditions. The samples were then transferred to the measuring site while kept cool and in the least time possible (Figure 3).
In this research, the PRASSI system, model 5S, was utilized for the purpose of measuring the Radon gas concentration. This system has special features for measuring the concentration of Radon in water and air such as high sensibility, high memory capacity, short response time and large LCD screen which has the capability of monitoring the Radon density diagrams.

Figure3:How the sampling was done
In figure 4, the design and the measurement method of Radon in water samples using the PRASSI device is illustrated.The device's built-in detector is made of a 1830 cm 3 chamber whose internal walls are coated with ZnS(Ag). This device is suitable for closed-cycle measurements. The pumping cycle of PRASSI functions with the constant speed of 2 Liter per second in this research [11].  Furthermore, figure 6 shows the histogram graph of the radon gas density in the evaluated samples. The results determine that the amount of radon in 4 samples is more than 10 Bq/L. S e p t 1 5 , 2 0 1 3

A Comparison between the Current Sampling and a Sampling Done in Covalency City Campus, Swaziland
The results from the measured radon concentration in Covalency city are shown in table 2 and the related diagram and histogram graphs are illustrated in figures 7 and 8, respectively.  According to the results, for both case studies (Toyserkan and Covalency Campus), radon gas concentration in the water samples is less than the proposed amount by USEPA which is 10 Bq/L. Therefore the radon concentration in the regional waters of Toyserkan and Covalency Campus is not hazardous to the human health

. Calculation of the Annual Effective Adsorbed Dose of Radon in the Region
The effectivedose in every material includes the direct and indirect ionizing radiations which can be easily measured and is defined by the following equation In order tocalculate the annual effective dose, it is assumed that each inhabitant of the Toyserkan region daily consumes 2.5 liters of water. Based on the results found in table 1 and the calculations regarding the effective dose of stomach and lung, the correction factor for the stomach and lung were found as follows, respectively: 2.628 and 2.79 dm dE D  S e p t 1 5 , 2 0 1 3 [EPA, 1998]. Using these factors, the effective dose for the regional water samples of Toyserkan were determined and are presented in table 3 [2]. . Since almost 50 percent of the human radiation inhalation is due to Radon gas, which is one of the main causes of the annual death due to respiratory and digestive cancers, and according to the fact that the most Radon intake is from drinking water and respiration while showering and etc., the measurement of the Radon gas concentration in the regional underground waters of Toyserkan was carried out [10]. The results found in this research show that the radon concentration in 4 samples of the consumed water by the inhabitants exceeds the allowable limit proposed by USEPA which is 10 Bq/L. (Samples numbers 4, 5 11 and 13) However, currently, no serious hazard threatens the consuming water of Toyserkan regarding its Radon content [12]. Therefore, in order to improve the water health and to decrease the potential hazards due to Radon, it is proposed that the drinking waters settle in open pools for a while, before distribution or at least waterfalls for agitation and removal of the gas, be used [5].